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CLASSIFICATION, DIAGNOSTIC IMAGING, AND IMAGING CHARACTERIZATION OF A LUMBAR HERNIATED DISK Radiologic Clinics of North America - Volume 38, Issue 6 (November 2000) - Copyright © 2000 W. B. Saunders Company IMAGING OF LOW BACK PAIN I CLASSIFICATION, DIAGNOSTIC IMAGING, AND IMAGING CHARACTERIZATION OF A LUMBAR HERNIATED DISK Pierre C. Milette MD, FRCPC Department of Radiology, Hopital Saint-Luc, Centre Hospitalier de l'Universite de Montreal, Montreal, Quebec, Canada Address reprint requests to Pierre C. Milette, MD, FRCPC Department of Radiology Hopital Saint-Luc Centre Hospitalier de l'Universite de Montreal 1058 Saint-Denis Street Montreal, Quebec, Canada H2X 3J4 To communicate their findings, scientists must assign names to the object of their study and then arrange them in some order. This process of naming and arranging is called classification. Classification is a descriptive arrangement that allows one not only to communicate about included objects, but also to identify these objects consistently for archiving and retrieval. [ ] 25 Uniformity of classification is essential to compare research results regarding diagnosis and treatment of disk disorders. Spine surgeons resort to an impressive number of different terms to describe the same operating room findings. [ ] 19 Any discussion of lumbar disk herniations, whether related to diagnosis or management, must define clearly its terminology regarding the pathologic condition of a disk. [ ] 30 The absence or disparity of morphologic or pathologic term definitions in the scientific literature is such that comparing published results or meta-analysis is very often impossible. [ ] 35 During the last decade, several articles have dealt with the nomenclature and classification of disk

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Page 1: CLASSIFICATION, DIAGNOSTIC IMAGING, AND IMAGING ... · PDF fileclassification, diagnostic imaging, and imaging characterization of a lumbar herniated disk ... classification, diagnostic

CLASSIFICATION DIAGNOSTIC IMAGING AND IMAGING CHARACTERIZATION OF A LUMBAR HERNIATED DISK Radiologic Clinics of North America - Volume 38 Issue 6 (November 2000) - Copyright copy 2000 W B Saunders Company

IMAGING OF LOW BACK PAIN I

CLASSIFICATION DIAGNOSTIC IMAGING AND IMAGING CHARACTERIZATION OF A LUMBAR HERNIATED DISK

Pierre C Milette MD FRCPC

Department of Radiology Hopital Saint-Luc Centre Hospitalier de lUniversite de Montreal Montreal Quebec Canada

Address reprint requests to Pierre C Milette MD FRCPC Department of Radiology Hopital Saint-Luc Centre Hospitalier de lUniversite de Montreal 1058 Saint-Denis Street Montreal Quebec Canada H2X 3J4

To communicate their findings scientists must assign names to the object of their study and then arrange them in some order This process of naming and arranging is called classification Classification is a descriptive arrangement that allows one not only to communicate about included objects but also to identify these objects consistently for archiving and retrieval[ ]25 Uniformity of classification is essential to compare research results regarding diagnosis and treatment of disk disorders Spine surgeons resort to an impressive number of different terms to describe the same operating room findings[ ]19 Any discussion of lumbar disk herniations whether related to diagnosis or management must define clearly its terminology regarding the pathologic condition of a disk[ ]30 The absence or disparity of morphologic or pathologic term definitions in the scientific literature is such that comparing published results or meta-analysis is very often impossible[ ]35 During the last decade several articles have dealt with the nomenclature and classification of disk

abnormalities in relation to the interpretation of imaging studies[ ]9 [ ]10 [ ]11 [ ]12 [ ]13 [ ]35 [ ]38 [ ]46 [ ]51 [ ]79 [ ]81 [ ]93 Classifications and glossaries have also been proposed by the American Academy of Orthopedic Surgeons[ ]2 and the North American Spine Society[ ]21 None of the proposed schemes has succeeded in generating a universal consensus however and the usage of language still varies greatly causing confusion and controversy[ ]3 The historical lack of interest of traditional physicians fundamental anatomists and imaging specialists for the deemed trivial and vulgar issue of low back pain is probably responsible to some extent for this situation[ ]47 We are still unclear about spinal anatomy especially in reference to spinal ligaments and membranes[ ]73 [ ]89 Controversies regarding surgical indications have created undeniable biases To reassure patients about the good prognosis of an acute back pain episode certain terms (eg ruptured disks) have been considered too alarming by some nonoperative care physicians[ ]16 Socioeconomic and legal considerations have unfortunately colored many scientific debates and in many parts of the world the presence or absence of the term disk herniation in an imaging report has a very significant impact in a litigation context Some authors have suggested abandoning the term herniation because of its legal implications but this word has been used in so many scientific clinical and lay discussions of the past seven decades and is so firmly established in various lexicons as to make proscription impossible[ ]53

DEFINITION OF A DISK HERNIATION

In Dorlands Medical Dictionary [ ]18 herniation is defined as an abnormal protrusion of an organ or other body structure through a defect or natural opening in a covering membrane muscle or bone This definition has been generally accepted over centuries The definition of the term disk herniation used by radiologists has evolved over the years particularly during the last decade This term initially meant a focal extension of nucleus pulposus beyond the margin of the disk[ ]43 The term herniation of the intervertebral disk was synonymous with herniation of the nucleus pulposus This restrictive definition has been found impractical because it is generally impossible for observers of imaging studies to determine the exact nature of the material coming out of a disk space Even surgeons in the operating room find it difficult to distinguish torn anulus fragments from nuclear material especially in situations where a herniation has generated an important inflammatory reaction The definition proposed by Herzog[ ]30 is more realistic focal displacement of nuclear anular or end plate material beyond the normal peripheral margins of the disk delimited by the margins of the vertebral body end plates The term end plates refers to the entire surface of the vertebral body and includes both the central cartilaginous plate and the peripheral ring epiphysis The qualifier normal in reference to the peripheral margin of the disk is important and is meant to refer to the initial or original limits of the adult intervertebral space exclusive of any osteophytes that may have developed This initial boundary may have been modified by the presence of vertebral body osteophytes A chronic localized displacement of disk material accompanied by marginal localized vertebral body osteophytes still qualifies as a disk herniation The bony end plates also delineate the upper and lower boundaries of the

normal intervertebral disk and displacement of disk material inside a vertebral body through a break in the end plate may be properly named an intravertebral disk herniation

Despite the controversies associated with disk nomenclature the general modern definition of disk herniation just discussed has gained general acceptance by imaging specialists Debates most often arise as to whether or not a particular image in a given individual qualifies for this theoretical definition because of the impact on management or compensation previously discussed Using CT or even MR imaging some herniations can mimic symmetric or asymmetric disk bulging because the disk material coming out of the disk space at the disk level is confined by the anterior or posterior longitudinal ligament and often generates the illusion of a process that is not focal Because of this the definition of the disk herniation should probably be broadened to localized displacement of nuclear anular or end plate material beyond the normal limits of the disk space The term localized is meant in opposition to generalized the latter term being reasonably applied to displacement of disk material involving more than 50 (180 degrees) of the disk periphery Localized displacement in the axial (horizontal) plane can be further described as focal signifying that less than 25 of the disk circumference is involved or broad-based meaning between 25 and 50 of the disk circumference As was emphasized by Mink et al[ ]53 the term disk herniation like all anatomic descriptive terms of disk abnormalities should not by itself imply disability cause relation to injury relation to pain or the need for treatment or reimbursement On the other hand a bulging disk may be defined as a disk in which the contour of the outer anulus extends or appears to extend in the horizontal (axial) plane beyond the edges of the disk space usually over greater than 50 (180 degrees) of the disk circumference

Even though the modern definition of disk herniation can apply to all intervertebral disks this article deals exclusively with lumbar disk herniations Some aspects that are discussed can apply to thoracic and cervical disks but because of the important anatomic differences between the different spinal segments all extrapolations must be conducted very cautiously Even in the lumbar area there are significant anatomic differences between upper and lower vertebrae and certain concepts like the lateral recess syndrome are really meaningful only in relation to the L4 L5 and S1 vertebrae[ ]58

CLASSIFICATION OF A HERNIATED LUMBAR DISK

Some classifications of disk herniations that have been proposed to imaging specialists have not met with success essentially because categories were defined in terms of microscopic anatomy and pathology[ ]2 [ ]66 Such models were actually suitable for pathologists performing cryotome sections on postmortem specimens and to some degree for surgeons reporting operating room observations but were not really useful for radiologists describing abnormal findings on myelograms diskograms CT or MR images Conceivably a classification of lumbar disk herniations could be based on the clinical staging of the disease Stage 1 low back pain plusmn radiating pain no objective sign Stage 2 low back pain plusmn radiating pain segmental pain muscle spasm Stage 3 low back pain plusmn radiating pain signs of dural or radicular irritation Stage 4 low back pain plusmn

radiating pain neurologic deficit[ ]47 Although useful for patient management this model is not adequate for imaging study interpretation A useful nomenclature needs to propose categories based on observable distinctions that take into consideration the limitations of present-day imaging techniques

Main Categories of Noninfectious Disk Abnormalities

Ideally a valid and useful system for classifying noninfectious disk abnormalities should provide categories that correspond to real anatomic and pathologic entities and if possible correspond to specific clinical situations The system should be applicable to all currently used imaging modalities It should be simple to understand to memorize and to teach It should also be reliable and generate substantial intraobserver and interobserver agreement in terms of Kappa statistics[ ]41 The nomenclature to describe disk lesions demonstrated by imaging studies has been greatly influenced by our concepts of disk degeneration throughout life (ie what is normal aging) and our understanding of what constitutes a disk lesion likely to generate clinical signs and symptoms The nomenclature we favor is directly related to our physiopathologic model The clinical concept that followed the description by Mixter and Barr[ ]54 of herniation of the nucleus pulposus through a ruptured anulus fibrosus was that should this occur in a posterior or posterolateral direction and encroach on the neural canal cord or nerve root compression may result with consequent segmental root pain and muscle spasm[ ]59 Because compression of neural structures was believed to be the only logical explanation for pain associated or not with a neurologic deficit imaging strategies have been developed over the last 20 years with a clear focus on identifying displacement of disk material associated with compression of neural structures[ ]28 [ ]31 [ ]32 [ ]36 [ ]74 [ ]82 [ ]86 [ ]87 Classifications of disk abnormalities that were associated with this concept have obviously been influenced by this bias In the early 1980s for the interpretation of myelograms and the first generation of high-resolution CT of the spine a very simple terminology was proposed that had essentially three categories (1) the normal disk (2) the bulging disk without nerve root compression and (3) the herniated disk with nerve root compression[ ]36 [ ]85 The definition of disk herniation was very restrictive because nerve root compression was considered by some investigators a sine qua non condition to make the diagnosis This requirement appeared acceptable however because it was estimated that only 10 of herniations occurred in a posterior central direction[ ]42 [ ]87

The validity of this model has been questioned in recent years and nerve root compression has been found less important than inflammation in the genesis of painful symptoms[ ]78 This relatively new concept has led to the development of two nomenclature models based on very different perspectives

The Morphologic Model

This model is essentially based on one parameter the assessment of the disk contour to determine the degree of disk extension beyond the interspace (DEBIT) [ ]13 The categories are normal disk bulging disk protrusion and extrusion (Fig 1) (Figure Not Available) Normal indicates no disk extension beyond the interspace Bulge refers to circumferential symmetric DEBIT (around the end plates) Protrusion indicates focal or

asymmetric DEBIT into the canal the base against the parent disk broader than any other diameter of the protrusion Extrusion means focal obvious DEBIT the base against the parent disk narrower than any diameter of the extruding material itself or no connection between displaced disk material and parent disk The use of the term herniation to designate collectively protrusions and extrusions has been suggested[ ]15 but maintaining the distinction may have some clinical relevance because extrusions are rarely found in asymptomatic individuals as opposed to protrusions and bulges[ ]34 It has also been argued that the term extruded disk is less frightening and emotionally laden than disk herniation or ruptured disk[ ]17 This classification is based on very simple geometric concepts and the categories are mutually exclusive but the line drawings in Figure 1 (Figure Not Available) are misleading because they represent the disk as a two-dimensional structure Disk extrusions such as the one depicted are practically never seen at the disk level on CT or MR imaging axial sections large posterior displacement of disk material beyond the margins of the intervertebral space still generally creates images corresponding to the definition of a protrusion because they are outlined by the posterior longitudinal ligament (Fig 2) Significant migration of disk material is usually necessary to generate a typical extrusion image Distinction between protrusions and extrusions at the disk level is very often only possible on sagittal sections (Fig 3) and this distinction is not very practical for the interpretation of CT because sagittal reconstructions are usually not part of the routine imaging protocol On CT or MR imaging this distinction is difficult in the presence of a narrow central spinal canal and very often impossible for foraminal herniations (Fig 4)

Figure 1 (Figure Not Available) Morphologic nomenclature based on the assessment of the disk contour (From Milette PC The proper terminology for reporting lumbar intervertebral disk disorders AJNR Am J Neuroradiol 181859-1866 1997 with permission)

Figure 2 Axial CT scan section through the L4-L5 disk space showing a relatively large posterior right central displacement of disk material with dural sac compression and probable right L5 nerve root compression Although the overlying posterior longitudinal ligament complex (PLLC) is not seen it constrains the displaced disk material and is responsible for maintaining a protrusion shape

Figure 3 When a relatively large amount of disk material is displaced distinction between protrusion (A) and extrusion (B or C) will generally only be possible on sagittal MR sections or sagittal CT scan reconstructions In C although the shape of the displaced material is similar to that of a protrusion the greatest cranio-caudal diameter of the fragment is greater than the craniocaudal diameter of its base at the level of the parent disk and the lesion therefore qualifies as an extrusion

Figure 4 Axial CT scan section through the upper portion of the L4-L5 foramina in a 45-year-old man Abnormal soft tissues likely representing displaced disk material are seen in the right foramen The material cannot be precisely delineated and the distinction between protrusion and extrusion is difficult A typical extrusion shape is practically never seen with foraminal herniations

Despite its apparent simplicity only moderate interobserver agreement has been reported using this nomenclature in three independent studies[ ]13 [ ]33 [ ]48 It is also incomplete because it considers exclusively the contour of the disk and the shape of the displaced disk material Disks demonstrating normal contour but abnormal central or peripheral signal patterns have no place in this system and associated vertebral body bone marrow changes are completely ignored even though the clinical relevancy of those changes has been well demonstrated[ ]4 [ ]48 [ ]55 [ ]57 [ ]72 This nomenclature is unfortunately misleading because it creates artificial pathologic entities The bulging disk category is the most problematic[ ]60 Obviously a severely dessicated and atrophic disk may bulge diffusely as the intervertebral space narrows with buckling of the anterior and posterior longitudinal

ligaments But an impression has been unjustifiably derived from early postmortem studies[ ]86 that even in young individuals a disk with an intact anulus may be responsible for a detectable bulge on axial CT sections It has also been hypothesized that bulging disks are caused by diffuse anular hyperlaxity which occurs as a result of tears in collagen bridges between the concentric anular fibers while these concentric fibers remain intact[ ]15 This theory has never been proved because such collagen bridges between the concentric fibers of the anulus have never been found[ ]45 It is important to realize that a bulging disk is not an anatomic or pathologic entity it is an image that requires a differential diagnosis It sometimes represents a normal anatomic variant this is often the case with the L5-S1 disk On CT images it is often an illusion caused by a volume-averaging effect (Fig 5) It may be associated with remodeling of adjacent vertebral bodies because of osteoporosis (Fig 6) It may of course result from chronic disk deterioration and collapse A bulging disk illusion is often created on CT by a posterior anular disk rupture with displaced disk material peeling off the posterior longitudinal ligament and displacing it backward creating a posterior wide base protrusion that mimics diffuse symmetric disk bulging on both axial CT and MR imaging sections and is not differentiated from a bulging disk on sagittal MR images unless close attention is paid to the anterior aspect of the disk (Fig 7) Except for the fact that extrusions are rarely found in asymptomatic individuals[ ]34 this system does not really provide categories that correspond to clinical entities

Figure 5 A Bulging disk appearance of the L4-L5 disk shown on a 5-mm-thickness axial CT scan section in a 57-year-old woman The height of the intervertebral space was preserved and there was no reactive vertebral body end-plate modifications This aspect is probably partly due to vertebral body remodeling caused by osteoporosis but is mostly created by volume averaging (From Milette PC Fontaine S Daniels C et al Imaging of Low Back Pain CD-ROM SSB Multimedia Medical Series Montreal 1997 with permission) B Using 4- or 5-mm-thickness CT sections an intermediate gray shade halo is often computer generated by volume averaging of tissues with different attenuation coefficients in voxels represented by two-dimensional pixels located at the disk space periphery This creates the illusion of a three-dimensional image demonstrating diffuse disk bulging ST = slice thickness

Figure 6 Axial CT scan section of a L4-L5 disk in a 78-year-old man demonstrating diffuse disk bulging caused by remodeling of the adjacent vertebral bodies due to osteoporosis The intervertebral space was normal in height and there were no reactive adjacent bony endplate modifications

Figure 7 A T2-weighted axial section of a L5-S1 disk showing a left posterolateral wide base protrusion that can be easily confused with diffuse circumferential bulging B Corresponding T2-weighted left paracentral and central sagittal sections demonstrating loss of the L5-S1 disk signal intensity with posterior small left-central protrusion the anterior aspect of the disk does not extend beyond the endplates and therefore such a disk should not be labeled bulging disk

The Pathoanatomic Model

As opposed to the previous model that can be applied only to the interpretation of CT and MR imaging studies this model can be used for the interpretation of all imaging modalities including plain films and diskograms[ ]47 [ ]51 It consists of five categories that are not mutually exclusive so that different combinations are possible (Fig 8) (Figure Not Available) The first three refer to the general state of the disk (1) normal young disk (2) normal aging disk and (3) deteriorated disk (formerly called the scarred disk) The last two refer to localized lesions anular tear and herniated disk In this model the previously discussed definition of disk herniation proposed by Herzog[ ]30 is applicable The use of this system requires an effort to distinguish the normal aging changes from those of pathologic degeneration Resnick and Niwayama[ ]66 have emphasized the differentiating features of two degenerative processes involving the intervertebral disk which had been previously described by Schmorl and Junghanns[ ]75 (1) spondylosis deformans which affects primarily the anulus fibrosus and bony ring epiphysis and (2) intervertebral osteochondrosis which affects essentially the nucleus pulposus and the vertebral body end plates

Figure 8 (Figure Not Available) Schematic representation of a nomenclature based on a three-dimensional assessment of the anatomic and pathologic characteristics of both disk and adjacent vertebral bodies The categories are not mutually exclusive and some combinations are possible A Categories related to the general aspect of the disk normal young disk (a) normal aging disk (b) deteriorated disk (c) B Categories related to local lesions normal young disk (a) anular tear (b) herniated disk (c) (Adapted from Milette PC The proper terminology for reporting lumbar intervertebral disk disorders AJNR Am J Neuroradiol 181859-1866 1997 with permission)

There is convincing evidence in the scientific literature that the features of spondylosis deformans represent the normal aging process whereas intervertebral osteochondrosis denotes true pathologic disk degeneration[ ]61 [ ]71 [ ]75 [ ]83 [ ]84 Schmorl and Junghanns[ ]75 found spondylotic changes in 60 of women and almost 80 of men over the age of 50 In a series of 400 dried skeletons Nathan[ ]61 found anterior vertebral body osteophytes which constitute the main feature of spondylosis deformans in 100 of individuals over age 40 whereas posterior osteophytes were found in only 39 of individuals even after the age of 80 Twomey and Taylor[ ]83 [ ]84 have found that loss of disk height is unusual in a normal aging population and that loss of stature in the elderly is attributable to loss of intervertebral body height rather than loss in disk height During the normal aging process the mucoid matrix of the nucleus pulposus is progressively replaced by fibrous tissue[ ]37 but the intervertebral height is preserved and the disk margins remain regular Dessication and thining of disks or disks that bulge like an underinflated automobile tire are not typical of elderly spines Slight symmetric bulging may occur if there has been vertebral body remodeling resulting from osteoporosis Small amounts of gas can be detected on plain films or CT images near the insertion of the anulus on the ring epiphysis and this gas is probably located in transverse anular tears adjacent to the ring epiphysis During the fourth decade anterior and lateral marginal vertebral body osteophytes constitute normal findings comparable with having gray hair but end plate erosions with osteosclerosis or chronic reactive bone marrow changes type 2 or 3 as described by Modic et al[ ]57 should not be seen Slight to moderate decrease in central signal intensity can be detected on T2-weighted MR images as part of the normal aging process but the changes should involve uniformly all lumbar disks

Deteriorated disks represent real pathologic degeneration which is sometimes referred to as chronic diskopathy On microscopic examination they show total structural disorganization and general replacement of normal disk material by scar tissue For this reason they were initially labeled scarred disks by the members of a joint committee on spinal nomenclature created by the Quebec Association of Radiologists[ ]14 Because of possible confusion with postoperative changes the term deteriorated disk has been proposed as an acceptable substitute Strictly speaking the term degeneration could be used to designate this entity but this latter term has such a broad nonspecific meaning that it is best avoided The deteriorated disk is characterized by narrowing of the intervertebral space irregular disk contour generally associated with symmetric or asymmetric bulging abundant presence of gas in the central portion of the intervertebral disk space multidirectional osteophytes that do not respect the central spinal canal or the foramina end plate erosions with reactive osteosclerosis and chronic bone marrow changes On T2-weighted MR images the central disk signal intensity is usually markedly decreased and the number of affected lumbar disks is variable Even though transverse concentric and radial anular tears have been identified on postmortem specimens[ ]92 the anular tear category in this model refers essentially to the radial tears that are generally demonstrated by diskography in symptomatic patients For a more precise description of those tears this model may be supplemented by the Dallas Discogram Description system[ ]70 with or without its recently proposed updates[ ]4 [ ]72 [ ]80

It should be emphasized that the pathoanatomic model is not based on direct identification of a particular geometric pattern but on the anatomy and pathology that are expected as a result of the analysis of specific criteria Using this model the conclusion of any imaging report does not consist of terms related to the shape of the disk contour or the displaced disk material but on a pathologic diagnosis that should be presented with an appropriate confidence level (possible probable or definite) The diagnosis of a probable major radial anular tear may be inferred from the presence of a definite central signal intensity loss because as a result of diskographic MR imaging correlations the positive predictive value of this sign has been estimated at 96[ ]48 The use of this model requires an effort to understand the criteria allowing differentiation of normal aging from true pathologic degeneration so this system is slightly more complicated than the morphologic model Its reliability has never been tested Some intraobserver or interobserver disagreement would probably occur trying to distinguish anular tears without herniation from anular tears with small herniations With respect to correspondance to clinical situations this scheme like the morphologic model has limited interest it has been shown that disks demonstrating the features of the deteriorated disk are likely to be responsible for symptoms but this relationship has been statistically established to be significant only for the L4-L5 disk[ ]24

Which Model Should Be Used

In other areas of diagnostic radiology the aim of image analysis is always to predict what the pathologist would find if he or she could be provided with an adequate specimen immediately following the imaging study radiologic diagnoses are presented with a pathologic perspective There is no reason why the reporting of disk disorders should be

any different Terms like bulging disk are meaningless to a pathologist and I personally favor the pathoanatomic model Nomenclature standardization however is not a task that can be achieved by an individual or even a single group of authors[ ]12 To have any impact recommendations have to emanate from well established national or international societies The multiplicity of scientific societies with an interest in the spine all over the world creates a special problem but new joint committees have recently been set up combining efforts to come up with a practical unified system that it is hoped could be proposed jointly by the North American Spine Society the American Academy of Orthopedic Surgeons the American Academy of Neurological Surgeons the American Society of Spine Radiology and the American Society of Neuroradiology Agreeing in North America on a classification of disk disorders that could gain universal acceptance like the TNM classification of neoplastic diseases would be a major achievement Meanwhile the choice of the nomenclature is up to the best judgement of each practicing radiologist and the essential issue in a given hospital or community practice remains clear communication between radiologists and referring physicians by way of a local agreement as to the meaning of words

A major problem frequently occurs because observers of imaging studies try to combine elements of the morphologic classification with those of the pathoanatomic classification Trying to differentiate a bulging disk (morphologic qualifier) from a disk herniation (pathologic diagnosis) cannot work because a bulging disk aspect is a common feature of the aging disk the deteriorated disk and some posterior central disk herniations (Fig 9) Trying to make the distinction is doomed to failure because it defies formal logic On the other hand it is theoretically possible to differentiate a radial anular tear (without herniation) from a disk herniation because these are two different pathologic entities although one may be the continuum of the other It is best to adopt either one of the two systems and avoid trying to straddle the two A general classification of disk disorders attempting to conciliate the morphologic and the pathoanatomic model is proposed in Table 1

Figure 9 A bulging disk aspect often conceals a posterior central herniation A Complete rupture of the outer anular fibers allowing nuclear material to escape and peel off the posterior longitudinal ligament (and sometimes a few intact peripheral anular fibers) from the torn disk creating a detectable focal or asymmetric extension of the disk margin beyond the interspace which qualifies as a protrusion B With more gelatinous nuclear material escaping underneath the rigid posterior longitudinal ligament the focal bulge is no longer detectable as its radius increases and if the tear occurs in the posterior midline or para-medial direction the aspect mimics symmetric disk extension beyond the interspace C Since in most cases only the outline of a diffusely hypointense disk is perceived on MR images this creates the illusion of circumferential disk bulging on axial sections D The real nature of a bulging disk of this type may be suspected by scrutinizing the sagittal sections and appreciating that unless one is dealing with a chronically degenerated scarred disk the bulge is not symmetric but limited to the posterior aspect of the disk

TABLE 1 -- GENERAL

CLASSIFICATION OF DISK LESIONS Normal (excluding aging changes)

Congenitaldevelopmental variants

Inflammationinfection

Neoplasia

Degenerativetraumatic

Degeneration

Anular tear

Herniation Protrusion

Extrusion

Degeneration Spondylosis deformans

Intervertebral osteochondrosis

Further Qualifying the Displaced Disk Material Beyond the Disk Space

Regardless of the basic system that is used the type of herniation should be assessed The volume and location of the displaced disk material beyond the normal peripheral margin of the intervertebral space also need to be specified In certain cases it is also possible to determine the composition of this material For the sake of simplicity the term herniation is used consistently in the remainder of this article to refer to all displaced disk material but what is discussed can also be applied to protrusions and extrusions if one wants to use the morphologic nomenclature

Type of Herniation

Upward or downward migration of nuclear material may occur through a break in a vertebral body end plate creating an intravertebral herniation sometimes referred to as an intraspongy herniation or a Schmorls node[ ]67 (Fig 10) Although a herniation occurring in any horizontal direction is likely to cause symptoms because of the presence of pain-sensitive nerve endings in the outer anulus[ ]7 [ ]8 [ ]65 herniations occurring in a posterior or posterolateral direction deserve special consideration because of the added possibility of dural sac or individual nerve root compression

Figure 10 Various types of intravertebral herniations (Schmorls nodes) A Intravertebral herniation through the inferior end plate of the L3 vertebral body demonstrated by diskography in a 35-year-old man suffering from chronic low back pain The patients typical pain was reproduced during injection and the lesion was considered responsible for the patients symptoms B T2-weighted sagittal section demonstrating an intravertebral herniation through the inferior end plate of the L4 vertebral body in a 24-year-old woman presenting with chronic low back pain The high signal intensity of the lesion associated with the loss of normal central signal intensity of the parent disk suggests that the lesion is a bona fide acquired intraspongy herniation and not just a developmental defect C T2-weighted sagittal section demonstrating an intravertebral herniation through the inferior end plate of the L3 vertebral body (arrow) Because both the herniation and the parent disk show normal signal intensity the abnormality was

considered a probably asymptomatic developmental defect

Other characteristics of disk herniations have become relevant with the development of new therapeutic possibilities (eg chemonucleolysis and percutaneous diskectomy) The term sequestration is confusing and has often been used to indicate displacement of disk material away from the parent disk The term sequestered disk should be used restrictedly to designate a fragment of diskal tissue that has migrated from the disk space and has no connection by diskal tissue to the disk of origin[ ]20 [ ]21 [ ]42 Sequestration refers to loss of continuity with disk tissue still present in the intervertebral disk space The term migration has a broader meaning indicating displacement of disk material away from the edge of the rent in the outer anulus either in the central spinal canal at the disk level or above or below the disk level This difference is illustrated in Figure 11 The terms communicating and noncommunicating derive from a different perspective and are mostly used in the context of intradiskal therapeutic injections They refer to the interruption of the periphery of the disk allowing fluid injected into the disk to leak into the spinal canal and reach displaced disk material[ ]20 [ ]51 The terms contained and uncontained are unfamiliar to most radiologists in a contained herniation the displaced disk material is still covered by a few intact but distended outer anular fibers or by a capsule formed by outer anular fibers and the adherent posterior longitudinal ligament

Figure 11 Various types of posterior central herniations A Small subligamentous herniation (protrusion) without significant disk material migration B Subligamentous herniation with downward migration of disk material under the PLLC C Sub-ligamentous herniation with downward migration of disk material and sequestered fragment (arrow)

The terms subligamentous and extraligamentous (or transligamentous) refer to the position of the displaced disk material with respect to the posterior longitudinal ligament The anatomy of the posterior longitudinal ligament has been recently revised[ ]73 [ ]89 It is a membranous structure that has multiple components a deep layer attached to disks and vertebral bodies a superficial layer attached to the dura by fibrous tissue (Hoffmanns

ligament) and lateral extensions known as the lateral membranes or peridural membranes (Fig 12) (Figure Not Available) It should probably be referred to as the posterior longitudinal ligament complex (PLLC) It actually divides the epidural space into the perithecal space and the anterior epidural space where displaced disk material can be entrapped (Fig 13) A potential space allowing accumulation of displaced disk material has also been detected between the outer anular fibers and the deep fibers of the PLLC on the posterior central aspect of the disk[ ]63 Posterior midline herniations seldom rupture the PLLC and are generally subligamentous The lateral membranes are less resistant and transligamentous herniations are usually the result of posterior off-center herniations or posterolateral herniations

Figure 12 (Figure Not Available) The PLLC is portrayed here in relation to various types of subligamentous disk displacement At the disk level posteriorly displaced disk material frequently occupies the midline Below and above the disk an anterior epidural space (AES) exists between the PLLC and the posterior aspect of the vertebral bodies In this space disk fragment motion across the midline is curtailed by a sagittal midline septum (dashed line) A delicate translucent membrane (shown only on left side of drawing) is stretched between the free edge of the deep layer of the posterior longitudinal ligament and the lateral spinal canal (From Schellinger D Manz HJ Vidic B et al Disk fragment migration Radiology 175831-836 1990 with permission)

Figure 13 Relationship of typical posterior disk herniations with the PLLC A Midline sagittal section unless very large a posterior midline herniation usually remains entrapped underneath the deep layer of the PLL C and sometimes a few intact outer anulus fibers joining with the PLL C to form a capsule The deep layer of the PLL C (arrow) also attaches to the posterior aspect of the vertebral body so that no potential space is present underneath B Sagittal para-central section the PLL C extends laterally at the disk level (arrowhead) but above and below the disk an anterior epidural space (as) where disk fragments are frequently entrapped is present between the lateral (peridural) membranes and the posterior aspect of the vertebral bodies

Volume of Herniated Material

Quantifying the herniated disk material by measuring in millimeters its greatest diameter or by evaluating its cross-sectional area in square millimeters is rarely done The resulting figures could be misleading without relating this measurement to the size of the spinal canal and the exact location of the lesion[ ]88 A purely qualitative and subjective statement that a mild moderate or severe herniation is present however does not give the person reading the imaging report any indication as to the potential of the lesion to cause significant compression of the dural sac or individual exiting nerve roots A reasonably precise scheme has been proposed in 1995 by the Nomenclature Committee of the North American Spine Society[ ]20 Measurements are taken from an axial CT or MR imaging section at the site of most severe compromise canal compromise of less than 25 at that section is qualified as mild 25 to 75 is moderate 76 to 90 is moderately severe and greater than 90 is severe It is understood that such characterizations describe only the cross-sectional area at one level and do not account for the total volume of displaced material displacement of neural tissue or clinical significance The usefulness of having four categories is questionable and can likely generate poor interobserver or intraobserver agreement especially in situations where the central spinal canal is relatively narrow Bonnevilles scheme[ ]9 [ ]10 [ ]11 should generate greater reliability (Fig 14) (Figure Not Available) Separation of the cross-sectional area in three thirds can be applied to both the central spinal canal and the foramina It can be agreed by way of convention that the terms mild moderate and severe lumen compromise by a disk herniation designate extension of the displaced disk material in the anterior middle or posterior third of the central canal or foramen depending on the specified location of the herniation

Figure 14 (Figure Not Available) The size of the herniation in the horizontal plane is assessed and designated by the numbers 1 2 or 3 by establishing its extension in the anterior middle or posterior third of the spinal canal (From Bonneville JF Plaidoyer pour une classification par limage des hernies discales lombaires la carte-image Rev Imag Med 2557-560 1990 with permission)

Location of Herniated Material

Bonneville[ ]9 [ ]10 [ ]11 has also proposed an interesting and simple alpha-numerical system to classify according to their location the position of disk fragments that have migrated in the horizontal or sagittal plane (Figs 15 (Figure Not Available) and 16) (Figure Not Available) Using more precise anatomic boundaries unfortunately more familiar to surgeons than radiologists Wiltse et al[ ]88 have proposed another system which has been supported by the North American Spine Society[ ]20 [ ]21 Anatomic zones and levels are defined using the following anatomic landmarks medial edge of the articular facets medial lateral upper and lower border of the pedicles and coronal plane at the disk center On the horizontal plane (Fig 17) (Figure Not Available) these landmarks determine the bounderies of the central zone the subarticular zone the foraminal zone the extraforaminal zone and the anterior zone (anterior to the coronal plane at the center of the disk) In the sagittal plane they determine the boundaries of the diskal level the infrapedicular level the pedicular level and the suprapedicular level (Figs 18 (Figure

Not Available) and 19) (Figure Not Available) Radiologists interpreting axial CT or MR images may find it difficult to use the medial edge of the facets as the landmark that separates the central zone from the subarticular zone because the superior articular facets are generally not included in axial sections at the disk level The alternative is to use the expression posterolateral to designate collectively all posterior herniations that are not midline but do not extend into a foramen as was proposed by Bonneville[ ]9 [ ]10 [ ]11

Figure 15 (Figure Not Available) In the horizontal plane herniations are labeled midline (a) posterolateral (b) foraminal (c) and extra-foraminal (d) (From Bonneville JF Plaidoyer pour une classification par limage des hernies discales lombaires la carte-image Rev Imag Med 2557-560 1990 with permission)

Figure 16 (Figure Not Available) In the craniocaudal direction disk migration is labeled +1 +2 +3 or -1 -2 -3 by referring to the height of a vertebral body divided in thirds (From Bonneville JF Plaidoyer pour une classification par limage des hernies discales lombaires la carte-image Rev Imag Med 2557-560 1990 with permission)

Figure 17 (Figure Not Available) The anatomic zones identified on axial images The anterior zone (not shown) is delineated from the extraforaminal zone by an imaginary coronal line in the center of the vertebral body (From Wiltse LL Berger PE McCulloch JA A system for reporting the size and location of lesions in the spine Spine 221534-1537 1997 with permission)

Figure 18 (Figure Not Available) The anatomical levels identified on craniocaudal images (From Wiltse LL Berger PE McCulloch AJ A system for reporting the size and location of lesions in the spine Spine 221534-1537 1997 with permission)

Figure 19 (Figure Not Available) Coronal view of the main zones and levels (From Wiltse LL Berger PE McCulloch JA A system for reporting the size and location of lesions in the spine Spine 221534-1537 1997 with permission)

Composition of Herniated Material

Displaced disk material may consist of glycosaminoglycans type 1 or 2 collagen end plate cartilage and bone fragments avulsed from the ring epiphysis A reactive inflammatory reaction usually results in edematous tissue followed by granulation tissue which may undergo calcification (Fig 20) Necrotic and partially resorbed displaced disk material sometimes produces a large fluid-filled pouch distinguishable from the common high-intensity zone because of its size (Fig 21) or a gas-filled cavity generally in continuity with gas in the intervertebral space (Fig 22) [ ]42 These characteristics may be meaningful if intradiskal injection therapy is considered In imaging reports herniations exhibiting calcium deposits and those exhibiting replacement of disk material by gas or a relatively large fluid collection can be qualified as chronic herniations

Figure 20 A CT scan demonstration of a small posterior central L4-L5 calcified subligamentous herniation The resistant deep layer of the PLLC restrains displacement of the disk material in the posterior central direction and does not allow a detectable distortion of the disk contour In this particular case the presence of the calcification is actually the only evidence that a posterior midline anular tear and a small subligamentous herniation are present B Posterior right central and sub-articular L5-S1 calcified disk herniation in same patient Posterolateral herniations are generally more conspicuous than posterior midline herniations because the deep layer of the PLLC gets thinner away from the midline

Figure 21 Posterior central midline L4-L5 herniation in a 52-year-old man demonstrated on a T2-weighted midline MR sagittal section There is intervertebral space narrowing with loss of normal central disk signal

intensity while the herniated disk material demonstrates high signal intensity consistent with a predominantly fluid consistency

Figure 22 CT scan demonstration in a 51-year-old woman of a left posterolateral L5-S1 disk hernation consisting essentially in a gas-filled pouch (white arrow) Gas is also present in the central portion of the intervertebral disk space (black arrow)

DIAGNOSTIC IMAGING AND CHARACTERIZATION OF A HERNIATED LUMBAR DISK

Assessing the validity of the currently used imaging procedures to diagnose a herniated lumbar disk is not an easy endeavor The validity of a measurement is the extent to which it corresponds to the true biologic value or some accepted gold standard[ ]40 With the exception of postmortem studies evaluation of the pathoanatomy by the surgeon in the operating room has always been considered the gold standard but this does not constitute an ideal situation Inspection of the disk through a small laminectomy incision to determine for instance if nuclear fragments lie within or outside the anular fibers may not be very reliable Also unbiased intraoperative determination of a normal degenerated or herniated disk in a patient with sciatica may also be difficult[ ]86 Because the validity of diskography has been previously established by postmortem studies and surgical correlations[ ]48 it is sometimes used as a gold standard in situations where no surgery has been performed

Conventional Radiographs

Lumbar disk herniations can exceptionally be diagnosed directly on good quality lateral projections because the x-ray attenuation is slightly greater in displaced disk material than in epidural fat Occasionally a calcified rim outlines the displaced disk fragment

(Fig 23) In most situations however narrowing of an intervertebral disk space in the absence of other evidence of chronic diskopathy is the only detectable sign suggesting the presence of a disk herniation To my knowledge the sensitivity and specificity of this sign has never been assessed The accepted rule of thumb is that the height of a given lumbar intervertebral disk space should always be slightly greater than the height of the above located interspace This rule does not apply to the transition disk immediately above the sacrum (usually L5-S1) The specificity of this sign is probably quite high but a few false-positives are seen especially at the L4-L5 level because of minor congenital hypoplasia The presence of posterior or foraminal vertebral body osteophytes associated or not with disk space narrowing is a definite sign of a chronic disk herniation

Figure 23 A Chronic left L3-L4 extraforaminal disk hernation in a 54-year-old man suspected on an AP radiograph demonstrating a calcified shell on the left side of the intervertebral disk space (white arrow) B Axial CT scan section confirming the diagnosis of a chronic extraforaminal L3-L4 herniation

Myelography

Myelography is essentially an exploration of the subarachnoid space Disk herniations are demonstrated only indirectly because they can cause thecal sac deformity and individual nerve root sleeve filling defects (Fig 24) Of all the special imaging procedures

myelography is the only one that allows upright projections with full weight bearing It is not unusual to demonstrate in this way small posterior central or posterolateral herniations that are undetectable on CT sections Interestingly the overall sensitivity of myelography to detect disk herniations has been found to be higher than that of CT whereas its specificity has been found to be lower[ ]74 In comparison with standard CT examination which usually includes only the three or four lower lumbar disks myelography easily allows coverage of the entire lumbar area and assessment of the intrathecal structures (cauda equina and conus medullaris) Far lateral foraminal herniations extraforaminal herniations and anterior herniations however are not detected The sensitivity for detection of posterior central L5-S1 herniations is also relatively poor because of the greater distance between the thecal sac and the posterior aspect of this particular disk

Figure 24 L5-S1 disk herniation in a 25-year-old man detected by indirect signs using lumbosacral myelography A Upright oblique projections showing a filling defect of the left S1 root sleeve (white arrow) suggesting significant nerve root compression by a left posterolateral disk hernation The right S1 root sleeve fills normally with contrast (black arrow) B Subtle compression of the anterior wall of the dural sac by displaced disk material (small arrows) demonstrated on upright lateral projection This sign is usually absent in the presence of a large amount of fat and venous structures in the anterior epidural compartment

CT

The sensitivity of CT to diagnose a herniation of the nucleus pulposus at the L5-S1 interspace is greater than that of myelography if images in the exact plane of the disk can be obtained[ ]23 [ ]39 Otherwise the superiority of plain CT over myelography to demonstrate disk herniations has not been established but CT has the distinct advantage of being

noninvasive and provides direct anatomic information[ ]23 Large herniations are easily detected but as explained previously the distinction between protrusions and extrusions is often difficult without sagittal reconstructions CT essentially allows an assessment of the contour of the disk The diagnosis of very small herniations in the absence of direct or indirect evidence of a radial tear is hazardous and associated with a high percentage of false-positives and false-negatives[ ]52 The diagnosis of moderate and large size herniations in different directions is usually possible but anterior herniations are rarely diagnosed not because they are not detectable but because observers pay little attention to the anterior contour of the disk (Fig 25) Because the PLLC cannot usually be identified the distinction of subligamentous from transligamentous herniation can only be suggested in most cases by the size of the herniated material A definite diagnosis of sequestration is rarely possible Calcifications within the displaced material are readily seen but may be difficult at times to differentiate from an accompanying osteophyte or an avulsed bone fragment from the vertebral body ring epiphysis (Fig 26) The presence of gas in the herniated material is easily detected

Figure 25 Anterior L4-L5 herniation demonstrated by CT scan in a 51-year-old woman with chronic low back pain Although sometimes quite conspicuous such herniations are rarely reported because observers pay little attention to the anterior contour of the disk

Figure 26 CT scan demonstration of a posterior right central L4-L5 disk herniation in a 38-year-old woman with avulsion of a bone fragment from the ring epiphysis and adjacent part of the superior L5 end plate Reactive osteosclerosis is seen around the vertebral body defect (arrows) suggesting a chronic lesion

CT Myelography

This association combines the advantages of both imaging modalities The fact that its accuracy has been reported as being less[ ]22 [ ]32 higher[ ]1 [ ]6 or equivalent[ ]82 to MR imaging is a reflection of the differences in technologic advancement and pathologic nomenclature that hamper valid comparisons between different studies

MR Imaging

Most reported studies establish MR imaging as the first choice modality to diagnose a herniated lumbar disk[ ]5 [ ]22 [ ]32 [ ]46 The associated intravenous injection of a paramagnetic agent has been found useful to demonstrate some anatomic features of disk disease in patients with no previous lumbar disk surgery[ ]56 [ ]68 [ ]90 MR imaging provides a better assessment of disk morphology than CT or CT myelography because sagittal sections are routinely obtained Assessment of foraminal involvement by displaced disk material is more accurate (Fig 27) and anterior disk herniations can be detected more easily than with CT or CT myelography If one is looking specifically for herniated lumbar disks associated with nerve root compression however it has been demonstrated that CT is equally accurate[ ]82 Alterations of the central or peripheral disk signal intensity on T2-weighted images are seen in most disks afflicted with an anular tear[ ]48 and alert the observer to scrutinize the disk contour in search for local modifications indicative of a herniation Because the signal of the displaced disk material is usually very similar to that of the outer anulus PLLC and vertebral body cortical bone small herniations are generally more conspicuous on axial CT sections than on corresponding axial MR imaging sections Gas and calcium deposits within the displaced fragment cannot usually

be detected but associated vertebral body bone marrow changes are typically seen and are helpful in differentiating acute from chronic processes[ ]57 The occasional presence of a high-intensity zone in the herniated material with an occasionally enhancing border after contrast injection is probably caused by a mixture of displaced nuclear material acute and subacute inflammatory tissue and neovascularized reactive tissue[ ]4 [ ]48 [ ]72 Contradictory reports have been published regarding the accuracy of MR imaging to differentiate subligamentous from transligamentous herniations[ ]26 [ ]38 [ ]73 [ ]76 Understanding the anatomy of the PLLC is helpful to make the distinction (Fig 28) (Figure Not Available) Masaryk et al[ ]46 have suggested that MR imaging is accurate to distinguish sequestered disks from other forms of lumbar disk herniations but most observers find this distinction difficult to establish[ ]42

Figure 27 A Left L4-L5 foraminal herniation well seen on an intermediate-weighted left parasagittal MR section (arrow) in a 47-year-old man B The lesion is much less obvious on intermediate-weighted (left) and T2-weighted (right) axial sections and was in fact more conspicuous on the corresponding CT scan section

Figure 28 (Figure Not Available) A Subligamentous disk herniation Left T1-weighted image demonstrating displaced disk material with a smooth outline imposed by the demarcation of the anterior epidural space (AES) by the lateral membrane of the PLLC Right Correlative drawing B Transligamentous disk herniation Left T1-weighted image of a large disk herniation (cervical in this case) which has ruptured through the posterior confines of the AES Penetration of the right lateral membrane can be observed (arrow) and the disk fragment contour is serrated Right Correlative drawing (From Schellinger D Manz HJ Vidic B et al Disk fragment migration Radiology 175831-836 1990 with permission)

Diskography and CT Diskography

During 30 years (1950 to 1980) when myelography was the only available imaging technique to demonstrate lumbar disk herniations diskography was an invasive but efficient way to demonstrate posterior central L5-S1 herniations and other large herniations (other than posterior central and paramedial) that could not be detected by myelography[ ]50 These herniations are now usually well demonstrated by CT and MR imaging Comparing the accuracy of five imaging modalities (excluding MR imaging) for the diagnosis of lumbar disk herniation Jackson et al[ ]31 found that CT diskography (Fig 29) was the most accurate test (87) compared with 77 for CT myelography 74 for CT 70 for myelography 64 for pain reproduction during diskography and 58 for diskography without CT Disk injection reproduced the patients clinical pain pattern in only 36 of herniated disks This clinical test isolated from the images had high specificity (89) but low sensitivity (43) for the diagnosis of disk herniation The reported low sensitivity of diskography images (unassociated with CT) to diagnose disk herniation is to be expected the purpose of the intradiskal injection being primarily the demonstration of an anular tear the contrast leaking through the tear only occasionally delineates an extruded fragment When a disk herniation has been diagnosed by other imaging modalities diskography allows to determine if the herniation is contained or noncontained (Figs 30 and 31) this information may have clinical relevance[ ]62 It also allows to establish if the displaced disk material is communicating or not with the parent disk and establishes the likelihood that it is sequestered or not There always remains a possibility that the contrast injected under pressure may reach a disk fragment that is nevertheless sequestered by leaking through the associated anular tear CT diskography also allows assessment in most cases of the integrity of the PLLC[ ]89 The superior sensitivity of diskography over MR imaging to demonstrate anular tears has been well established[ ]27 [ ]44 [ ]48 [ ]64 [ ]77 [ ]91 [ ]94 The presence of a radial tear and the inflammatory reaction it creates may be symptomatic despite the absence of true disk herniation[ ]29 [ ]48 [ ]49 [ ]69

Figure 29 L4-L5 CT diskogram demonstrating a large left posterolateral radial anular tear associated with

a left foraminal and extraforaminal herniaton (same patient as in Figure 28) (Figure Not Available)

Figure 30 Contained posterior L4-L5 and L5-S1 disk herniations in a 57-year-old man demonstrated by diskography The L3-L4 disk is normal

Figure 31 Noncontained L4-L5 disk herniation in a 23-year-old woman Reflux of injected contrast is seen in the anterior epidural space above and below the disk space The L5-S1 disk also demonstrates incomplete anterior and posterior radial anular tears

SUMMARY

The absence of universal nomenclature standardization with respect to the definition of a disk herniation and its different categories especially regarding type and location is still a major problem that will only be overcome when major national or international scientific societies join efforts to support a particular scheme Meanwhile it is important to realize that the two models that are currently most used are based on a different perspective Trying to straddle the two by opposing for instance bulging disk and herniation is doomed to failure because this exercise defies formal logic MR imaging is currently the most accurate noninvasive imaging modality to diagnose a disk herniation and to determine its exact location The determination of some pathoanatomic characteristics of herniated disks (type and composition) may require the use of CT diskography or CT diskography

References

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  • CLASSIFICATION DIAGNOSTIC IMAGING AND IMAGING CHARACTERIZATION OF A LUMBAR HERNIATED DISK
    • IMAGING OF LOW BACK PAIN I
      • CLASSIFICATION DIAGNOSTIC IMAGING AND IMAGING CHARACTERIZATION OF A LUMBAR HERNIATED DISK
        • DEFINITION OF A DISK HERNIATION
        • CLASSIFICATION OF A HERNIATED LUMBAR DISK
          • Main Categories of Noninfectious Disk Abnormalities
          • Further Qualifying the Displaced Disk Material Beyond the Disk Space
            • DIAGNOSTIC IMAGING AND CHARACTERIZATION OF A HERNIATED LUMBAR DISK
              • Conventional Radiographs
              • Myelography
              • CT
              • CT Myelography
              • MR Imaging
              • Diskography and CT Diskography
                • SUMMARY
                  • References
Page 2: CLASSIFICATION, DIAGNOSTIC IMAGING, AND IMAGING ... · PDF fileclassification, diagnostic imaging, and imaging characterization of a lumbar herniated disk ... classification, diagnostic

abnormalities in relation to the interpretation of imaging studies[ ]9 [ ]10 [ ]11 [ ]12 [ ]13 [ ]35 [ ]38 [ ]46 [ ]51 [ ]79 [ ]81 [ ]93 Classifications and glossaries have also been proposed by the American Academy of Orthopedic Surgeons[ ]2 and the North American Spine Society[ ]21 None of the proposed schemes has succeeded in generating a universal consensus however and the usage of language still varies greatly causing confusion and controversy[ ]3 The historical lack of interest of traditional physicians fundamental anatomists and imaging specialists for the deemed trivial and vulgar issue of low back pain is probably responsible to some extent for this situation[ ]47 We are still unclear about spinal anatomy especially in reference to spinal ligaments and membranes[ ]73 [ ]89 Controversies regarding surgical indications have created undeniable biases To reassure patients about the good prognosis of an acute back pain episode certain terms (eg ruptured disks) have been considered too alarming by some nonoperative care physicians[ ]16 Socioeconomic and legal considerations have unfortunately colored many scientific debates and in many parts of the world the presence or absence of the term disk herniation in an imaging report has a very significant impact in a litigation context Some authors have suggested abandoning the term herniation because of its legal implications but this word has been used in so many scientific clinical and lay discussions of the past seven decades and is so firmly established in various lexicons as to make proscription impossible[ ]53

DEFINITION OF A DISK HERNIATION

In Dorlands Medical Dictionary [ ]18 herniation is defined as an abnormal protrusion of an organ or other body structure through a defect or natural opening in a covering membrane muscle or bone This definition has been generally accepted over centuries The definition of the term disk herniation used by radiologists has evolved over the years particularly during the last decade This term initially meant a focal extension of nucleus pulposus beyond the margin of the disk[ ]43 The term herniation of the intervertebral disk was synonymous with herniation of the nucleus pulposus This restrictive definition has been found impractical because it is generally impossible for observers of imaging studies to determine the exact nature of the material coming out of a disk space Even surgeons in the operating room find it difficult to distinguish torn anulus fragments from nuclear material especially in situations where a herniation has generated an important inflammatory reaction The definition proposed by Herzog[ ]30 is more realistic focal displacement of nuclear anular or end plate material beyond the normal peripheral margins of the disk delimited by the margins of the vertebral body end plates The term end plates refers to the entire surface of the vertebral body and includes both the central cartilaginous plate and the peripheral ring epiphysis The qualifier normal in reference to the peripheral margin of the disk is important and is meant to refer to the initial or original limits of the adult intervertebral space exclusive of any osteophytes that may have developed This initial boundary may have been modified by the presence of vertebral body osteophytes A chronic localized displacement of disk material accompanied by marginal localized vertebral body osteophytes still qualifies as a disk herniation The bony end plates also delineate the upper and lower boundaries of the

normal intervertebral disk and displacement of disk material inside a vertebral body through a break in the end plate may be properly named an intravertebral disk herniation

Despite the controversies associated with disk nomenclature the general modern definition of disk herniation just discussed has gained general acceptance by imaging specialists Debates most often arise as to whether or not a particular image in a given individual qualifies for this theoretical definition because of the impact on management or compensation previously discussed Using CT or even MR imaging some herniations can mimic symmetric or asymmetric disk bulging because the disk material coming out of the disk space at the disk level is confined by the anterior or posterior longitudinal ligament and often generates the illusion of a process that is not focal Because of this the definition of the disk herniation should probably be broadened to localized displacement of nuclear anular or end plate material beyond the normal limits of the disk space The term localized is meant in opposition to generalized the latter term being reasonably applied to displacement of disk material involving more than 50 (180 degrees) of the disk periphery Localized displacement in the axial (horizontal) plane can be further described as focal signifying that less than 25 of the disk circumference is involved or broad-based meaning between 25 and 50 of the disk circumference As was emphasized by Mink et al[ ]53 the term disk herniation like all anatomic descriptive terms of disk abnormalities should not by itself imply disability cause relation to injury relation to pain or the need for treatment or reimbursement On the other hand a bulging disk may be defined as a disk in which the contour of the outer anulus extends or appears to extend in the horizontal (axial) plane beyond the edges of the disk space usually over greater than 50 (180 degrees) of the disk circumference

Even though the modern definition of disk herniation can apply to all intervertebral disks this article deals exclusively with lumbar disk herniations Some aspects that are discussed can apply to thoracic and cervical disks but because of the important anatomic differences between the different spinal segments all extrapolations must be conducted very cautiously Even in the lumbar area there are significant anatomic differences between upper and lower vertebrae and certain concepts like the lateral recess syndrome are really meaningful only in relation to the L4 L5 and S1 vertebrae[ ]58

CLASSIFICATION OF A HERNIATED LUMBAR DISK

Some classifications of disk herniations that have been proposed to imaging specialists have not met with success essentially because categories were defined in terms of microscopic anatomy and pathology[ ]2 [ ]66 Such models were actually suitable for pathologists performing cryotome sections on postmortem specimens and to some degree for surgeons reporting operating room observations but were not really useful for radiologists describing abnormal findings on myelograms diskograms CT or MR images Conceivably a classification of lumbar disk herniations could be based on the clinical staging of the disease Stage 1 low back pain plusmn radiating pain no objective sign Stage 2 low back pain plusmn radiating pain segmental pain muscle spasm Stage 3 low back pain plusmn radiating pain signs of dural or radicular irritation Stage 4 low back pain plusmn

radiating pain neurologic deficit[ ]47 Although useful for patient management this model is not adequate for imaging study interpretation A useful nomenclature needs to propose categories based on observable distinctions that take into consideration the limitations of present-day imaging techniques

Main Categories of Noninfectious Disk Abnormalities

Ideally a valid and useful system for classifying noninfectious disk abnormalities should provide categories that correspond to real anatomic and pathologic entities and if possible correspond to specific clinical situations The system should be applicable to all currently used imaging modalities It should be simple to understand to memorize and to teach It should also be reliable and generate substantial intraobserver and interobserver agreement in terms of Kappa statistics[ ]41 The nomenclature to describe disk lesions demonstrated by imaging studies has been greatly influenced by our concepts of disk degeneration throughout life (ie what is normal aging) and our understanding of what constitutes a disk lesion likely to generate clinical signs and symptoms The nomenclature we favor is directly related to our physiopathologic model The clinical concept that followed the description by Mixter and Barr[ ]54 of herniation of the nucleus pulposus through a ruptured anulus fibrosus was that should this occur in a posterior or posterolateral direction and encroach on the neural canal cord or nerve root compression may result with consequent segmental root pain and muscle spasm[ ]59 Because compression of neural structures was believed to be the only logical explanation for pain associated or not with a neurologic deficit imaging strategies have been developed over the last 20 years with a clear focus on identifying displacement of disk material associated with compression of neural structures[ ]28 [ ]31 [ ]32 [ ]36 [ ]74 [ ]82 [ ]86 [ ]87 Classifications of disk abnormalities that were associated with this concept have obviously been influenced by this bias In the early 1980s for the interpretation of myelograms and the first generation of high-resolution CT of the spine a very simple terminology was proposed that had essentially three categories (1) the normal disk (2) the bulging disk without nerve root compression and (3) the herniated disk with nerve root compression[ ]36 [ ]85 The definition of disk herniation was very restrictive because nerve root compression was considered by some investigators a sine qua non condition to make the diagnosis This requirement appeared acceptable however because it was estimated that only 10 of herniations occurred in a posterior central direction[ ]42 [ ]87

The validity of this model has been questioned in recent years and nerve root compression has been found less important than inflammation in the genesis of painful symptoms[ ]78 This relatively new concept has led to the development of two nomenclature models based on very different perspectives

The Morphologic Model

This model is essentially based on one parameter the assessment of the disk contour to determine the degree of disk extension beyond the interspace (DEBIT) [ ]13 The categories are normal disk bulging disk protrusion and extrusion (Fig 1) (Figure Not Available) Normal indicates no disk extension beyond the interspace Bulge refers to circumferential symmetric DEBIT (around the end plates) Protrusion indicates focal or

asymmetric DEBIT into the canal the base against the parent disk broader than any other diameter of the protrusion Extrusion means focal obvious DEBIT the base against the parent disk narrower than any diameter of the extruding material itself or no connection between displaced disk material and parent disk The use of the term herniation to designate collectively protrusions and extrusions has been suggested[ ]15 but maintaining the distinction may have some clinical relevance because extrusions are rarely found in asymptomatic individuals as opposed to protrusions and bulges[ ]34 It has also been argued that the term extruded disk is less frightening and emotionally laden than disk herniation or ruptured disk[ ]17 This classification is based on very simple geometric concepts and the categories are mutually exclusive but the line drawings in Figure 1 (Figure Not Available) are misleading because they represent the disk as a two-dimensional structure Disk extrusions such as the one depicted are practically never seen at the disk level on CT or MR imaging axial sections large posterior displacement of disk material beyond the margins of the intervertebral space still generally creates images corresponding to the definition of a protrusion because they are outlined by the posterior longitudinal ligament (Fig 2) Significant migration of disk material is usually necessary to generate a typical extrusion image Distinction between protrusions and extrusions at the disk level is very often only possible on sagittal sections (Fig 3) and this distinction is not very practical for the interpretation of CT because sagittal reconstructions are usually not part of the routine imaging protocol On CT or MR imaging this distinction is difficult in the presence of a narrow central spinal canal and very often impossible for foraminal herniations (Fig 4)

Figure 1 (Figure Not Available) Morphologic nomenclature based on the assessment of the disk contour (From Milette PC The proper terminology for reporting lumbar intervertebral disk disorders AJNR Am J Neuroradiol 181859-1866 1997 with permission)

Figure 2 Axial CT scan section through the L4-L5 disk space showing a relatively large posterior right central displacement of disk material with dural sac compression and probable right L5 nerve root compression Although the overlying posterior longitudinal ligament complex (PLLC) is not seen it constrains the displaced disk material and is responsible for maintaining a protrusion shape

Figure 3 When a relatively large amount of disk material is displaced distinction between protrusion (A) and extrusion (B or C) will generally only be possible on sagittal MR sections or sagittal CT scan reconstructions In C although the shape of the displaced material is similar to that of a protrusion the greatest cranio-caudal diameter of the fragment is greater than the craniocaudal diameter of its base at the level of the parent disk and the lesion therefore qualifies as an extrusion

Figure 4 Axial CT scan section through the upper portion of the L4-L5 foramina in a 45-year-old man Abnormal soft tissues likely representing displaced disk material are seen in the right foramen The material cannot be precisely delineated and the distinction between protrusion and extrusion is difficult A typical extrusion shape is practically never seen with foraminal herniations

Despite its apparent simplicity only moderate interobserver agreement has been reported using this nomenclature in three independent studies[ ]13 [ ]33 [ ]48 It is also incomplete because it considers exclusively the contour of the disk and the shape of the displaced disk material Disks demonstrating normal contour but abnormal central or peripheral signal patterns have no place in this system and associated vertebral body bone marrow changes are completely ignored even though the clinical relevancy of those changes has been well demonstrated[ ]4 [ ]48 [ ]55 [ ]57 [ ]72 This nomenclature is unfortunately misleading because it creates artificial pathologic entities The bulging disk category is the most problematic[ ]60 Obviously a severely dessicated and atrophic disk may bulge diffusely as the intervertebral space narrows with buckling of the anterior and posterior longitudinal

ligaments But an impression has been unjustifiably derived from early postmortem studies[ ]86 that even in young individuals a disk with an intact anulus may be responsible for a detectable bulge on axial CT sections It has also been hypothesized that bulging disks are caused by diffuse anular hyperlaxity which occurs as a result of tears in collagen bridges between the concentric anular fibers while these concentric fibers remain intact[ ]15 This theory has never been proved because such collagen bridges between the concentric fibers of the anulus have never been found[ ]45 It is important to realize that a bulging disk is not an anatomic or pathologic entity it is an image that requires a differential diagnosis It sometimes represents a normal anatomic variant this is often the case with the L5-S1 disk On CT images it is often an illusion caused by a volume-averaging effect (Fig 5) It may be associated with remodeling of adjacent vertebral bodies because of osteoporosis (Fig 6) It may of course result from chronic disk deterioration and collapse A bulging disk illusion is often created on CT by a posterior anular disk rupture with displaced disk material peeling off the posterior longitudinal ligament and displacing it backward creating a posterior wide base protrusion that mimics diffuse symmetric disk bulging on both axial CT and MR imaging sections and is not differentiated from a bulging disk on sagittal MR images unless close attention is paid to the anterior aspect of the disk (Fig 7) Except for the fact that extrusions are rarely found in asymptomatic individuals[ ]34 this system does not really provide categories that correspond to clinical entities

Figure 5 A Bulging disk appearance of the L4-L5 disk shown on a 5-mm-thickness axial CT scan section in a 57-year-old woman The height of the intervertebral space was preserved and there was no reactive vertebral body end-plate modifications This aspect is probably partly due to vertebral body remodeling caused by osteoporosis but is mostly created by volume averaging (From Milette PC Fontaine S Daniels C et al Imaging of Low Back Pain CD-ROM SSB Multimedia Medical Series Montreal 1997 with permission) B Using 4- or 5-mm-thickness CT sections an intermediate gray shade halo is often computer generated by volume averaging of tissues with different attenuation coefficients in voxels represented by two-dimensional pixels located at the disk space periphery This creates the illusion of a three-dimensional image demonstrating diffuse disk bulging ST = slice thickness

Figure 6 Axial CT scan section of a L4-L5 disk in a 78-year-old man demonstrating diffuse disk bulging caused by remodeling of the adjacent vertebral bodies due to osteoporosis The intervertebral space was normal in height and there were no reactive adjacent bony endplate modifications

Figure 7 A T2-weighted axial section of a L5-S1 disk showing a left posterolateral wide base protrusion that can be easily confused with diffuse circumferential bulging B Corresponding T2-weighted left paracentral and central sagittal sections demonstrating loss of the L5-S1 disk signal intensity with posterior small left-central protrusion the anterior aspect of the disk does not extend beyond the endplates and therefore such a disk should not be labeled bulging disk

The Pathoanatomic Model

As opposed to the previous model that can be applied only to the interpretation of CT and MR imaging studies this model can be used for the interpretation of all imaging modalities including plain films and diskograms[ ]47 [ ]51 It consists of five categories that are not mutually exclusive so that different combinations are possible (Fig 8) (Figure Not Available) The first three refer to the general state of the disk (1) normal young disk (2) normal aging disk and (3) deteriorated disk (formerly called the scarred disk) The last two refer to localized lesions anular tear and herniated disk In this model the previously discussed definition of disk herniation proposed by Herzog[ ]30 is applicable The use of this system requires an effort to distinguish the normal aging changes from those of pathologic degeneration Resnick and Niwayama[ ]66 have emphasized the differentiating features of two degenerative processes involving the intervertebral disk which had been previously described by Schmorl and Junghanns[ ]75 (1) spondylosis deformans which affects primarily the anulus fibrosus and bony ring epiphysis and (2) intervertebral osteochondrosis which affects essentially the nucleus pulposus and the vertebral body end plates

Figure 8 (Figure Not Available) Schematic representation of a nomenclature based on a three-dimensional assessment of the anatomic and pathologic characteristics of both disk and adjacent vertebral bodies The categories are not mutually exclusive and some combinations are possible A Categories related to the general aspect of the disk normal young disk (a) normal aging disk (b) deteriorated disk (c) B Categories related to local lesions normal young disk (a) anular tear (b) herniated disk (c) (Adapted from Milette PC The proper terminology for reporting lumbar intervertebral disk disorders AJNR Am J Neuroradiol 181859-1866 1997 with permission)

There is convincing evidence in the scientific literature that the features of spondylosis deformans represent the normal aging process whereas intervertebral osteochondrosis denotes true pathologic disk degeneration[ ]61 [ ]71 [ ]75 [ ]83 [ ]84 Schmorl and Junghanns[ ]75 found spondylotic changes in 60 of women and almost 80 of men over the age of 50 In a series of 400 dried skeletons Nathan[ ]61 found anterior vertebral body osteophytes which constitute the main feature of spondylosis deformans in 100 of individuals over age 40 whereas posterior osteophytes were found in only 39 of individuals even after the age of 80 Twomey and Taylor[ ]83 [ ]84 have found that loss of disk height is unusual in a normal aging population and that loss of stature in the elderly is attributable to loss of intervertebral body height rather than loss in disk height During the normal aging process the mucoid matrix of the nucleus pulposus is progressively replaced by fibrous tissue[ ]37 but the intervertebral height is preserved and the disk margins remain regular Dessication and thining of disks or disks that bulge like an underinflated automobile tire are not typical of elderly spines Slight symmetric bulging may occur if there has been vertebral body remodeling resulting from osteoporosis Small amounts of gas can be detected on plain films or CT images near the insertion of the anulus on the ring epiphysis and this gas is probably located in transverse anular tears adjacent to the ring epiphysis During the fourth decade anterior and lateral marginal vertebral body osteophytes constitute normal findings comparable with having gray hair but end plate erosions with osteosclerosis or chronic reactive bone marrow changes type 2 or 3 as described by Modic et al[ ]57 should not be seen Slight to moderate decrease in central signal intensity can be detected on T2-weighted MR images as part of the normal aging process but the changes should involve uniformly all lumbar disks

Deteriorated disks represent real pathologic degeneration which is sometimes referred to as chronic diskopathy On microscopic examination they show total structural disorganization and general replacement of normal disk material by scar tissue For this reason they were initially labeled scarred disks by the members of a joint committee on spinal nomenclature created by the Quebec Association of Radiologists[ ]14 Because of possible confusion with postoperative changes the term deteriorated disk has been proposed as an acceptable substitute Strictly speaking the term degeneration could be used to designate this entity but this latter term has such a broad nonspecific meaning that it is best avoided The deteriorated disk is characterized by narrowing of the intervertebral space irregular disk contour generally associated with symmetric or asymmetric bulging abundant presence of gas in the central portion of the intervertebral disk space multidirectional osteophytes that do not respect the central spinal canal or the foramina end plate erosions with reactive osteosclerosis and chronic bone marrow changes On T2-weighted MR images the central disk signal intensity is usually markedly decreased and the number of affected lumbar disks is variable Even though transverse concentric and radial anular tears have been identified on postmortem specimens[ ]92 the anular tear category in this model refers essentially to the radial tears that are generally demonstrated by diskography in symptomatic patients For a more precise description of those tears this model may be supplemented by the Dallas Discogram Description system[ ]70 with or without its recently proposed updates[ ]4 [ ]72 [ ]80

It should be emphasized that the pathoanatomic model is not based on direct identification of a particular geometric pattern but on the anatomy and pathology that are expected as a result of the analysis of specific criteria Using this model the conclusion of any imaging report does not consist of terms related to the shape of the disk contour or the displaced disk material but on a pathologic diagnosis that should be presented with an appropriate confidence level (possible probable or definite) The diagnosis of a probable major radial anular tear may be inferred from the presence of a definite central signal intensity loss because as a result of diskographic MR imaging correlations the positive predictive value of this sign has been estimated at 96[ ]48 The use of this model requires an effort to understand the criteria allowing differentiation of normal aging from true pathologic degeneration so this system is slightly more complicated than the morphologic model Its reliability has never been tested Some intraobserver or interobserver disagreement would probably occur trying to distinguish anular tears without herniation from anular tears with small herniations With respect to correspondance to clinical situations this scheme like the morphologic model has limited interest it has been shown that disks demonstrating the features of the deteriorated disk are likely to be responsible for symptoms but this relationship has been statistically established to be significant only for the L4-L5 disk[ ]24

Which Model Should Be Used

In other areas of diagnostic radiology the aim of image analysis is always to predict what the pathologist would find if he or she could be provided with an adequate specimen immediately following the imaging study radiologic diagnoses are presented with a pathologic perspective There is no reason why the reporting of disk disorders should be

any different Terms like bulging disk are meaningless to a pathologist and I personally favor the pathoanatomic model Nomenclature standardization however is not a task that can be achieved by an individual or even a single group of authors[ ]12 To have any impact recommendations have to emanate from well established national or international societies The multiplicity of scientific societies with an interest in the spine all over the world creates a special problem but new joint committees have recently been set up combining efforts to come up with a practical unified system that it is hoped could be proposed jointly by the North American Spine Society the American Academy of Orthopedic Surgeons the American Academy of Neurological Surgeons the American Society of Spine Radiology and the American Society of Neuroradiology Agreeing in North America on a classification of disk disorders that could gain universal acceptance like the TNM classification of neoplastic diseases would be a major achievement Meanwhile the choice of the nomenclature is up to the best judgement of each practicing radiologist and the essential issue in a given hospital or community practice remains clear communication between radiologists and referring physicians by way of a local agreement as to the meaning of words

A major problem frequently occurs because observers of imaging studies try to combine elements of the morphologic classification with those of the pathoanatomic classification Trying to differentiate a bulging disk (morphologic qualifier) from a disk herniation (pathologic diagnosis) cannot work because a bulging disk aspect is a common feature of the aging disk the deteriorated disk and some posterior central disk herniations (Fig 9) Trying to make the distinction is doomed to failure because it defies formal logic On the other hand it is theoretically possible to differentiate a radial anular tear (without herniation) from a disk herniation because these are two different pathologic entities although one may be the continuum of the other It is best to adopt either one of the two systems and avoid trying to straddle the two A general classification of disk disorders attempting to conciliate the morphologic and the pathoanatomic model is proposed in Table 1

Figure 9 A bulging disk aspect often conceals a posterior central herniation A Complete rupture of the outer anular fibers allowing nuclear material to escape and peel off the posterior longitudinal ligament (and sometimes a few intact peripheral anular fibers) from the torn disk creating a detectable focal or asymmetric extension of the disk margin beyond the interspace which qualifies as a protrusion B With more gelatinous nuclear material escaping underneath the rigid posterior longitudinal ligament the focal bulge is no longer detectable as its radius increases and if the tear occurs in the posterior midline or para-medial direction the aspect mimics symmetric disk extension beyond the interspace C Since in most cases only the outline of a diffusely hypointense disk is perceived on MR images this creates the illusion of circumferential disk bulging on axial sections D The real nature of a bulging disk of this type may be suspected by scrutinizing the sagittal sections and appreciating that unless one is dealing with a chronically degenerated scarred disk the bulge is not symmetric but limited to the posterior aspect of the disk

TABLE 1 -- GENERAL

CLASSIFICATION OF DISK LESIONS Normal (excluding aging changes)

Congenitaldevelopmental variants

Inflammationinfection

Neoplasia

Degenerativetraumatic

Degeneration

Anular tear

Herniation Protrusion

Extrusion

Degeneration Spondylosis deformans

Intervertebral osteochondrosis

Further Qualifying the Displaced Disk Material Beyond the Disk Space

Regardless of the basic system that is used the type of herniation should be assessed The volume and location of the displaced disk material beyond the normal peripheral margin of the intervertebral space also need to be specified In certain cases it is also possible to determine the composition of this material For the sake of simplicity the term herniation is used consistently in the remainder of this article to refer to all displaced disk material but what is discussed can also be applied to protrusions and extrusions if one wants to use the morphologic nomenclature

Type of Herniation

Upward or downward migration of nuclear material may occur through a break in a vertebral body end plate creating an intravertebral herniation sometimes referred to as an intraspongy herniation or a Schmorls node[ ]67 (Fig 10) Although a herniation occurring in any horizontal direction is likely to cause symptoms because of the presence of pain-sensitive nerve endings in the outer anulus[ ]7 [ ]8 [ ]65 herniations occurring in a posterior or posterolateral direction deserve special consideration because of the added possibility of dural sac or individual nerve root compression

Figure 10 Various types of intravertebral herniations (Schmorls nodes) A Intravertebral herniation through the inferior end plate of the L3 vertebral body demonstrated by diskography in a 35-year-old man suffering from chronic low back pain The patients typical pain was reproduced during injection and the lesion was considered responsible for the patients symptoms B T2-weighted sagittal section demonstrating an intravertebral herniation through the inferior end plate of the L4 vertebral body in a 24-year-old woman presenting with chronic low back pain The high signal intensity of the lesion associated with the loss of normal central signal intensity of the parent disk suggests that the lesion is a bona fide acquired intraspongy herniation and not just a developmental defect C T2-weighted sagittal section demonstrating an intravertebral herniation through the inferior end plate of the L3 vertebral body (arrow) Because both the herniation and the parent disk show normal signal intensity the abnormality was

considered a probably asymptomatic developmental defect

Other characteristics of disk herniations have become relevant with the development of new therapeutic possibilities (eg chemonucleolysis and percutaneous diskectomy) The term sequestration is confusing and has often been used to indicate displacement of disk material away from the parent disk The term sequestered disk should be used restrictedly to designate a fragment of diskal tissue that has migrated from the disk space and has no connection by diskal tissue to the disk of origin[ ]20 [ ]21 [ ]42 Sequestration refers to loss of continuity with disk tissue still present in the intervertebral disk space The term migration has a broader meaning indicating displacement of disk material away from the edge of the rent in the outer anulus either in the central spinal canal at the disk level or above or below the disk level This difference is illustrated in Figure 11 The terms communicating and noncommunicating derive from a different perspective and are mostly used in the context of intradiskal therapeutic injections They refer to the interruption of the periphery of the disk allowing fluid injected into the disk to leak into the spinal canal and reach displaced disk material[ ]20 [ ]51 The terms contained and uncontained are unfamiliar to most radiologists in a contained herniation the displaced disk material is still covered by a few intact but distended outer anular fibers or by a capsule formed by outer anular fibers and the adherent posterior longitudinal ligament

Figure 11 Various types of posterior central herniations A Small subligamentous herniation (protrusion) without significant disk material migration B Subligamentous herniation with downward migration of disk material under the PLLC C Sub-ligamentous herniation with downward migration of disk material and sequestered fragment (arrow)

The terms subligamentous and extraligamentous (or transligamentous) refer to the position of the displaced disk material with respect to the posterior longitudinal ligament The anatomy of the posterior longitudinal ligament has been recently revised[ ]73 [ ]89 It is a membranous structure that has multiple components a deep layer attached to disks and vertebral bodies a superficial layer attached to the dura by fibrous tissue (Hoffmanns

ligament) and lateral extensions known as the lateral membranes or peridural membranes (Fig 12) (Figure Not Available) It should probably be referred to as the posterior longitudinal ligament complex (PLLC) It actually divides the epidural space into the perithecal space and the anterior epidural space where displaced disk material can be entrapped (Fig 13) A potential space allowing accumulation of displaced disk material has also been detected between the outer anular fibers and the deep fibers of the PLLC on the posterior central aspect of the disk[ ]63 Posterior midline herniations seldom rupture the PLLC and are generally subligamentous The lateral membranes are less resistant and transligamentous herniations are usually the result of posterior off-center herniations or posterolateral herniations

Figure 12 (Figure Not Available) The PLLC is portrayed here in relation to various types of subligamentous disk displacement At the disk level posteriorly displaced disk material frequently occupies the midline Below and above the disk an anterior epidural space (AES) exists between the PLLC and the posterior aspect of the vertebral bodies In this space disk fragment motion across the midline is curtailed by a sagittal midline septum (dashed line) A delicate translucent membrane (shown only on left side of drawing) is stretched between the free edge of the deep layer of the posterior longitudinal ligament and the lateral spinal canal (From Schellinger D Manz HJ Vidic B et al Disk fragment migration Radiology 175831-836 1990 with permission)

Figure 13 Relationship of typical posterior disk herniations with the PLLC A Midline sagittal section unless very large a posterior midline herniation usually remains entrapped underneath the deep layer of the PLL C and sometimes a few intact outer anulus fibers joining with the PLL C to form a capsule The deep layer of the PLL C (arrow) also attaches to the posterior aspect of the vertebral body so that no potential space is present underneath B Sagittal para-central section the PLL C extends laterally at the disk level (arrowhead) but above and below the disk an anterior epidural space (as) where disk fragments are frequently entrapped is present between the lateral (peridural) membranes and the posterior aspect of the vertebral bodies

Volume of Herniated Material

Quantifying the herniated disk material by measuring in millimeters its greatest diameter or by evaluating its cross-sectional area in square millimeters is rarely done The resulting figures could be misleading without relating this measurement to the size of the spinal canal and the exact location of the lesion[ ]88 A purely qualitative and subjective statement that a mild moderate or severe herniation is present however does not give the person reading the imaging report any indication as to the potential of the lesion to cause significant compression of the dural sac or individual exiting nerve roots A reasonably precise scheme has been proposed in 1995 by the Nomenclature Committee of the North American Spine Society[ ]20 Measurements are taken from an axial CT or MR imaging section at the site of most severe compromise canal compromise of less than 25 at that section is qualified as mild 25 to 75 is moderate 76 to 90 is moderately severe and greater than 90 is severe It is understood that such characterizations describe only the cross-sectional area at one level and do not account for the total volume of displaced material displacement of neural tissue or clinical significance The usefulness of having four categories is questionable and can likely generate poor interobserver or intraobserver agreement especially in situations where the central spinal canal is relatively narrow Bonnevilles scheme[ ]9 [ ]10 [ ]11 should generate greater reliability (Fig 14) (Figure Not Available) Separation of the cross-sectional area in three thirds can be applied to both the central spinal canal and the foramina It can be agreed by way of convention that the terms mild moderate and severe lumen compromise by a disk herniation designate extension of the displaced disk material in the anterior middle or posterior third of the central canal or foramen depending on the specified location of the herniation

Figure 14 (Figure Not Available) The size of the herniation in the horizontal plane is assessed and designated by the numbers 1 2 or 3 by establishing its extension in the anterior middle or posterior third of the spinal canal (From Bonneville JF Plaidoyer pour une classification par limage des hernies discales lombaires la carte-image Rev Imag Med 2557-560 1990 with permission)

Location of Herniated Material

Bonneville[ ]9 [ ]10 [ ]11 has also proposed an interesting and simple alpha-numerical system to classify according to their location the position of disk fragments that have migrated in the horizontal or sagittal plane (Figs 15 (Figure Not Available) and 16) (Figure Not Available) Using more precise anatomic boundaries unfortunately more familiar to surgeons than radiologists Wiltse et al[ ]88 have proposed another system which has been supported by the North American Spine Society[ ]20 [ ]21 Anatomic zones and levels are defined using the following anatomic landmarks medial edge of the articular facets medial lateral upper and lower border of the pedicles and coronal plane at the disk center On the horizontal plane (Fig 17) (Figure Not Available) these landmarks determine the bounderies of the central zone the subarticular zone the foraminal zone the extraforaminal zone and the anterior zone (anterior to the coronal plane at the center of the disk) In the sagittal plane they determine the boundaries of the diskal level the infrapedicular level the pedicular level and the suprapedicular level (Figs 18 (Figure

Not Available) and 19) (Figure Not Available) Radiologists interpreting axial CT or MR images may find it difficult to use the medial edge of the facets as the landmark that separates the central zone from the subarticular zone because the superior articular facets are generally not included in axial sections at the disk level The alternative is to use the expression posterolateral to designate collectively all posterior herniations that are not midline but do not extend into a foramen as was proposed by Bonneville[ ]9 [ ]10 [ ]11

Figure 15 (Figure Not Available) In the horizontal plane herniations are labeled midline (a) posterolateral (b) foraminal (c) and extra-foraminal (d) (From Bonneville JF Plaidoyer pour une classification par limage des hernies discales lombaires la carte-image Rev Imag Med 2557-560 1990 with permission)

Figure 16 (Figure Not Available) In the craniocaudal direction disk migration is labeled +1 +2 +3 or -1 -2 -3 by referring to the height of a vertebral body divided in thirds (From Bonneville JF Plaidoyer pour une classification par limage des hernies discales lombaires la carte-image Rev Imag Med 2557-560 1990 with permission)

Figure 17 (Figure Not Available) The anatomic zones identified on axial images The anterior zone (not shown) is delineated from the extraforaminal zone by an imaginary coronal line in the center of the vertebral body (From Wiltse LL Berger PE McCulloch JA A system for reporting the size and location of lesions in the spine Spine 221534-1537 1997 with permission)

Figure 18 (Figure Not Available) The anatomical levels identified on craniocaudal images (From Wiltse LL Berger PE McCulloch AJ A system for reporting the size and location of lesions in the spine Spine 221534-1537 1997 with permission)

Figure 19 (Figure Not Available) Coronal view of the main zones and levels (From Wiltse LL Berger PE McCulloch JA A system for reporting the size and location of lesions in the spine Spine 221534-1537 1997 with permission)

Composition of Herniated Material

Displaced disk material may consist of glycosaminoglycans type 1 or 2 collagen end plate cartilage and bone fragments avulsed from the ring epiphysis A reactive inflammatory reaction usually results in edematous tissue followed by granulation tissue which may undergo calcification (Fig 20) Necrotic and partially resorbed displaced disk material sometimes produces a large fluid-filled pouch distinguishable from the common high-intensity zone because of its size (Fig 21) or a gas-filled cavity generally in continuity with gas in the intervertebral space (Fig 22) [ ]42 These characteristics may be meaningful if intradiskal injection therapy is considered In imaging reports herniations exhibiting calcium deposits and those exhibiting replacement of disk material by gas or a relatively large fluid collection can be qualified as chronic herniations

Figure 20 A CT scan demonstration of a small posterior central L4-L5 calcified subligamentous herniation The resistant deep layer of the PLLC restrains displacement of the disk material in the posterior central direction and does not allow a detectable distortion of the disk contour In this particular case the presence of the calcification is actually the only evidence that a posterior midline anular tear and a small subligamentous herniation are present B Posterior right central and sub-articular L5-S1 calcified disk herniation in same patient Posterolateral herniations are generally more conspicuous than posterior midline herniations because the deep layer of the PLLC gets thinner away from the midline

Figure 21 Posterior central midline L4-L5 herniation in a 52-year-old man demonstrated on a T2-weighted midline MR sagittal section There is intervertebral space narrowing with loss of normal central disk signal

intensity while the herniated disk material demonstrates high signal intensity consistent with a predominantly fluid consistency

Figure 22 CT scan demonstration in a 51-year-old woman of a left posterolateral L5-S1 disk hernation consisting essentially in a gas-filled pouch (white arrow) Gas is also present in the central portion of the intervertebral disk space (black arrow)

DIAGNOSTIC IMAGING AND CHARACTERIZATION OF A HERNIATED LUMBAR DISK

Assessing the validity of the currently used imaging procedures to diagnose a herniated lumbar disk is not an easy endeavor The validity of a measurement is the extent to which it corresponds to the true biologic value or some accepted gold standard[ ]40 With the exception of postmortem studies evaluation of the pathoanatomy by the surgeon in the operating room has always been considered the gold standard but this does not constitute an ideal situation Inspection of the disk through a small laminectomy incision to determine for instance if nuclear fragments lie within or outside the anular fibers may not be very reliable Also unbiased intraoperative determination of a normal degenerated or herniated disk in a patient with sciatica may also be difficult[ ]86 Because the validity of diskography has been previously established by postmortem studies and surgical correlations[ ]48 it is sometimes used as a gold standard in situations where no surgery has been performed

Conventional Radiographs

Lumbar disk herniations can exceptionally be diagnosed directly on good quality lateral projections because the x-ray attenuation is slightly greater in displaced disk material than in epidural fat Occasionally a calcified rim outlines the displaced disk fragment

(Fig 23) In most situations however narrowing of an intervertebral disk space in the absence of other evidence of chronic diskopathy is the only detectable sign suggesting the presence of a disk herniation To my knowledge the sensitivity and specificity of this sign has never been assessed The accepted rule of thumb is that the height of a given lumbar intervertebral disk space should always be slightly greater than the height of the above located interspace This rule does not apply to the transition disk immediately above the sacrum (usually L5-S1) The specificity of this sign is probably quite high but a few false-positives are seen especially at the L4-L5 level because of minor congenital hypoplasia The presence of posterior or foraminal vertebral body osteophytes associated or not with disk space narrowing is a definite sign of a chronic disk herniation

Figure 23 A Chronic left L3-L4 extraforaminal disk hernation in a 54-year-old man suspected on an AP radiograph demonstrating a calcified shell on the left side of the intervertebral disk space (white arrow) B Axial CT scan section confirming the diagnosis of a chronic extraforaminal L3-L4 herniation

Myelography

Myelography is essentially an exploration of the subarachnoid space Disk herniations are demonstrated only indirectly because they can cause thecal sac deformity and individual nerve root sleeve filling defects (Fig 24) Of all the special imaging procedures

myelography is the only one that allows upright projections with full weight bearing It is not unusual to demonstrate in this way small posterior central or posterolateral herniations that are undetectable on CT sections Interestingly the overall sensitivity of myelography to detect disk herniations has been found to be higher than that of CT whereas its specificity has been found to be lower[ ]74 In comparison with standard CT examination which usually includes only the three or four lower lumbar disks myelography easily allows coverage of the entire lumbar area and assessment of the intrathecal structures (cauda equina and conus medullaris) Far lateral foraminal herniations extraforaminal herniations and anterior herniations however are not detected The sensitivity for detection of posterior central L5-S1 herniations is also relatively poor because of the greater distance between the thecal sac and the posterior aspect of this particular disk

Figure 24 L5-S1 disk herniation in a 25-year-old man detected by indirect signs using lumbosacral myelography A Upright oblique projections showing a filling defect of the left S1 root sleeve (white arrow) suggesting significant nerve root compression by a left posterolateral disk hernation The right S1 root sleeve fills normally with contrast (black arrow) B Subtle compression of the anterior wall of the dural sac by displaced disk material (small arrows) demonstrated on upright lateral projection This sign is usually absent in the presence of a large amount of fat and venous structures in the anterior epidural compartment

CT

The sensitivity of CT to diagnose a herniation of the nucleus pulposus at the L5-S1 interspace is greater than that of myelography if images in the exact plane of the disk can be obtained[ ]23 [ ]39 Otherwise the superiority of plain CT over myelography to demonstrate disk herniations has not been established but CT has the distinct advantage of being

noninvasive and provides direct anatomic information[ ]23 Large herniations are easily detected but as explained previously the distinction between protrusions and extrusions is often difficult without sagittal reconstructions CT essentially allows an assessment of the contour of the disk The diagnosis of very small herniations in the absence of direct or indirect evidence of a radial tear is hazardous and associated with a high percentage of false-positives and false-negatives[ ]52 The diagnosis of moderate and large size herniations in different directions is usually possible but anterior herniations are rarely diagnosed not because they are not detectable but because observers pay little attention to the anterior contour of the disk (Fig 25) Because the PLLC cannot usually be identified the distinction of subligamentous from transligamentous herniation can only be suggested in most cases by the size of the herniated material A definite diagnosis of sequestration is rarely possible Calcifications within the displaced material are readily seen but may be difficult at times to differentiate from an accompanying osteophyte or an avulsed bone fragment from the vertebral body ring epiphysis (Fig 26) The presence of gas in the herniated material is easily detected

Figure 25 Anterior L4-L5 herniation demonstrated by CT scan in a 51-year-old woman with chronic low back pain Although sometimes quite conspicuous such herniations are rarely reported because observers pay little attention to the anterior contour of the disk

Figure 26 CT scan demonstration of a posterior right central L4-L5 disk herniation in a 38-year-old woman with avulsion of a bone fragment from the ring epiphysis and adjacent part of the superior L5 end plate Reactive osteosclerosis is seen around the vertebral body defect (arrows) suggesting a chronic lesion

CT Myelography

This association combines the advantages of both imaging modalities The fact that its accuracy has been reported as being less[ ]22 [ ]32 higher[ ]1 [ ]6 or equivalent[ ]82 to MR imaging is a reflection of the differences in technologic advancement and pathologic nomenclature that hamper valid comparisons between different studies

MR Imaging

Most reported studies establish MR imaging as the first choice modality to diagnose a herniated lumbar disk[ ]5 [ ]22 [ ]32 [ ]46 The associated intravenous injection of a paramagnetic agent has been found useful to demonstrate some anatomic features of disk disease in patients with no previous lumbar disk surgery[ ]56 [ ]68 [ ]90 MR imaging provides a better assessment of disk morphology than CT or CT myelography because sagittal sections are routinely obtained Assessment of foraminal involvement by displaced disk material is more accurate (Fig 27) and anterior disk herniations can be detected more easily than with CT or CT myelography If one is looking specifically for herniated lumbar disks associated with nerve root compression however it has been demonstrated that CT is equally accurate[ ]82 Alterations of the central or peripheral disk signal intensity on T2-weighted images are seen in most disks afflicted with an anular tear[ ]48 and alert the observer to scrutinize the disk contour in search for local modifications indicative of a herniation Because the signal of the displaced disk material is usually very similar to that of the outer anulus PLLC and vertebral body cortical bone small herniations are generally more conspicuous on axial CT sections than on corresponding axial MR imaging sections Gas and calcium deposits within the displaced fragment cannot usually

be detected but associated vertebral body bone marrow changes are typically seen and are helpful in differentiating acute from chronic processes[ ]57 The occasional presence of a high-intensity zone in the herniated material with an occasionally enhancing border after contrast injection is probably caused by a mixture of displaced nuclear material acute and subacute inflammatory tissue and neovascularized reactive tissue[ ]4 [ ]48 [ ]72 Contradictory reports have been published regarding the accuracy of MR imaging to differentiate subligamentous from transligamentous herniations[ ]26 [ ]38 [ ]73 [ ]76 Understanding the anatomy of the PLLC is helpful to make the distinction (Fig 28) (Figure Not Available) Masaryk et al[ ]46 have suggested that MR imaging is accurate to distinguish sequestered disks from other forms of lumbar disk herniations but most observers find this distinction difficult to establish[ ]42

Figure 27 A Left L4-L5 foraminal herniation well seen on an intermediate-weighted left parasagittal MR section (arrow) in a 47-year-old man B The lesion is much less obvious on intermediate-weighted (left) and T2-weighted (right) axial sections and was in fact more conspicuous on the corresponding CT scan section

Figure 28 (Figure Not Available) A Subligamentous disk herniation Left T1-weighted image demonstrating displaced disk material with a smooth outline imposed by the demarcation of the anterior epidural space (AES) by the lateral membrane of the PLLC Right Correlative drawing B Transligamentous disk herniation Left T1-weighted image of a large disk herniation (cervical in this case) which has ruptured through the posterior confines of the AES Penetration of the right lateral membrane can be observed (arrow) and the disk fragment contour is serrated Right Correlative drawing (From Schellinger D Manz HJ Vidic B et al Disk fragment migration Radiology 175831-836 1990 with permission)

Diskography and CT Diskography

During 30 years (1950 to 1980) when myelography was the only available imaging technique to demonstrate lumbar disk herniations diskography was an invasive but efficient way to demonstrate posterior central L5-S1 herniations and other large herniations (other than posterior central and paramedial) that could not be detected by myelography[ ]50 These herniations are now usually well demonstrated by CT and MR imaging Comparing the accuracy of five imaging modalities (excluding MR imaging) for the diagnosis of lumbar disk herniation Jackson et al[ ]31 found that CT diskography (Fig 29) was the most accurate test (87) compared with 77 for CT myelography 74 for CT 70 for myelography 64 for pain reproduction during diskography and 58 for diskography without CT Disk injection reproduced the patients clinical pain pattern in only 36 of herniated disks This clinical test isolated from the images had high specificity (89) but low sensitivity (43) for the diagnosis of disk herniation The reported low sensitivity of diskography images (unassociated with CT) to diagnose disk herniation is to be expected the purpose of the intradiskal injection being primarily the demonstration of an anular tear the contrast leaking through the tear only occasionally delineates an extruded fragment When a disk herniation has been diagnosed by other imaging modalities diskography allows to determine if the herniation is contained or noncontained (Figs 30 and 31) this information may have clinical relevance[ ]62 It also allows to establish if the displaced disk material is communicating or not with the parent disk and establishes the likelihood that it is sequestered or not There always remains a possibility that the contrast injected under pressure may reach a disk fragment that is nevertheless sequestered by leaking through the associated anular tear CT diskography also allows assessment in most cases of the integrity of the PLLC[ ]89 The superior sensitivity of diskography over MR imaging to demonstrate anular tears has been well established[ ]27 [ ]44 [ ]48 [ ]64 [ ]77 [ ]91 [ ]94 The presence of a radial tear and the inflammatory reaction it creates may be symptomatic despite the absence of true disk herniation[ ]29 [ ]48 [ ]49 [ ]69

Figure 29 L4-L5 CT diskogram demonstrating a large left posterolateral radial anular tear associated with

a left foraminal and extraforaminal herniaton (same patient as in Figure 28) (Figure Not Available)

Figure 30 Contained posterior L4-L5 and L5-S1 disk herniations in a 57-year-old man demonstrated by diskography The L3-L4 disk is normal

Figure 31 Noncontained L4-L5 disk herniation in a 23-year-old woman Reflux of injected contrast is seen in the anterior epidural space above and below the disk space The L5-S1 disk also demonstrates incomplete anterior and posterior radial anular tears

SUMMARY

The absence of universal nomenclature standardization with respect to the definition of a disk herniation and its different categories especially regarding type and location is still a major problem that will only be overcome when major national or international scientific societies join efforts to support a particular scheme Meanwhile it is important to realize that the two models that are currently most used are based on a different perspective Trying to straddle the two by opposing for instance bulging disk and herniation is doomed to failure because this exercise defies formal logic MR imaging is currently the most accurate noninvasive imaging modality to diagnose a disk herniation and to determine its exact location The determination of some pathoanatomic characteristics of herniated disks (type and composition) may require the use of CT diskography or CT diskography

References

1 Albeck MJ Hilden J Kjaer L et al A controlled comparison of myelography computed tomography and magnetic resonance imaging in clinically suspected lumbar disc herniation Spine 20443-448 1995 Abstract 2 American Academy of Orthopedic Surgeons Glossary on Spinal Terminology Chicago American Academy of Orthopedic Surgeons 1981 3 Andersson GB Weinstein JN Disc herniation [editorial] Spine 211S 1996 Citation 4 Aprill C Bogduk N High-intensity zone A diagnostic sign of painful lumbar disc on magnetic resonance imaging Br J Radiol 65361-369 1992 Abstract 5 Birney TJ White JJ Jr Berens D et al Comparison of MRI and discography in the diagnosis of lumbar degenerative disc disease J Spinal Disord 5417-423 1992 Abstract 6 Bischoff RJ Rodriguez RP Gupta K et al A comparison of computed tomography-myelography magnetic resonance imaging and myelography in the diagnosis of herniated nucleus pulposus and spinal stenosis J Spinal Disord 6289-295 1993 Abstract 7 Bogduk N The innervation of the lumbar spine Spine 8286-293 1983 Abstract 8 Bogduk N Tynan W Wilson AS The nerve supply to the human lumbar intervertebral discs J Anat 13239-56 1981 Abstract 9 Bonneville JF La carte-image des hernies discales lombaires Rachis 2255-257 1990 10 Bonneville JF La topografia simbolica delle ernie discali lombari Riv Neuroradiol 5427-431 1992 11 Bonneville JF Plaidoyer pour une classification par limage des hernies discales lombaires La carte-image Rev Imag Med 2557-560 1990 12 Brant-Zawadzki M Jensen M Spinal nomenclature Spine 20388-390 1995 Abstract

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29 Haughton VM Lim TH An H Intervertebral disk appearance correlated with stiffness of lumbar spinal motion segments AJNR Am J Neuroradiol 201161-1165 1999 Abstract 30 Herzog RJ The radiologic assessment for a lumbar disc herniation Spine 2119S-38S 1996 Abstract 31 Jackson RP Becker GJ Jacobs RR et al The neuroradiographic diagnosis of lumbar herniated nucleus pulposus I A comparison of computed tomography (CT) myelography CT-myelography discography and CT-discography Spine 141356-1361 1989 Abstract 32 Jackson RP Cain JE Jr Jacobs RR et al The neuroradiographic diagnosis of lumbar herniated nucleus pulposus II A comparison of computed tomography (CT) myelography CT-myelography and magnetic resonance imaging Spine 141362-1367 1989 Abstract 33 Jarvik JG Haynor DR Koepsell TD et al Interreader reliability for a new classification of lumbar disk disease Acad Radiol 3537-544 1996 Abstract 34 Jensen MC Brant-Zawadzki MN Obuchowski N et al Magnetic resonance imaging of the lumbar spine in people without back pain N Engl J Med 33169-73 1994 Abstract 35 Kent DL Haynor DR Larson EB et al Diagnosis of lumbar spinal stenosis in adults A meta-analysis of the accuracy of CT MR and myelography AJR Am J Roentgenol 1581135-1144 1992 Abstract 36 Kieffer SA Sherry RG Wellenstein DE et al Bulging lumbar intervertebral disk Myelographic differentiation from herniated disk with nerve root compression AJR Am J Roentgenol 138709-716 1982 Abstract 37 Kieffer SA Stadlan EM Mohandas A et al Discographic-anatomical correlation of developmental changes with age in the intervertebral disc Acta Radiol 9733-739 1969 38 Kim KY Kim YT Lee CS et al MRI classification of lumbar herniated intervertebral disc Orthopedics 15493-497 1992 Abstract 39 Kornberg M Rechtine GR Dupuy TE Computed tomography in the diagnosis of a herniated disk at the L5-S1 level Spine 9433-436 1984 Abstract 40 Kramer MS Clinical Epidemiology and Biostatistics New York Springer-Verlag 1988 41 Landis JR Koch GG The measurement of observer agreement agreement for categorical data Biometrics 33159-174 1977 Abstract 42 Laredo JD Bossard P Vuillemin-Bodaghi Formes anatomo-radiologiques des hernies discales In Morvan G Deburge A Bard H et al (eds) Le Rachis Lombaire Degeneratif Montpellier Sauramps Medical 1998 pp 37-49 43 Lee SH Coleman PE Hahn FJ Magnetic resonance imaging of degenerative disk disease of the spine Radiol Clin North Am 26949-964 1988 Abstract 44 Linson MA Crowe CH Comparison of magnetic resonance imaging and lumbar discography in the diagnosis of disc degeneration Clin Orthop 160-163 1990

45 Marchand F Ahmed AM Investigation of the laminate structure of lumbar disc anulus fibrosus Spine 15402-410 1990 Abstract 46 Masaryk TJ Ross JS Modic MT et al High-resolution MR imaging of sequestered lumbar intervertebral disks AJR Am J Roentgenol 1501155-1162 1988 Abstract 47 Milette PC The proper terminology for reporting lumbar intervertebral disk disorders AJNR Am J Neuroradiol 181859-1866 1997 Citation 48 Milette PC Fontaine S Lepanto L et al Differentiating lumbar disc protrusions disk bulges and discs with normal contour but abnormal signal intensity Magnetic resonance imaging with discographic correlations Spine 2444-53 1999 Abstract 49 Milette PC Fontaine S Lepanto L et al Radiating pain to the lower extremities caused by lumbar disk rupture without spinal nerve root involvement AJNR Am J Neuroradiol 161605-1613 1995 Abstract 50 Milette PC Melancon D A reappraisal of lumbar discography Can Assoc Radiol J 33176-182 1982 51 Milette PC Melancon D Dupuis PR et al A simplified terminology for abnormalities of the lumbar disk Can Assoc Radiol J 42319-325 1991 Abstract 52 Milette PC Raymond J Fontaine S Comparison of high-resolution computed tomography with discography in the evaluation of lumbar disc herniations Spine 15525-533 1990 Abstract 53 Mink JH Deutsch AL Goldstein TB et al Spinal imaging and intervention 1998 Phys Med Rehabil Clin North Am 9343-380 1998 54 Mixter WJ Barr JS Rupture of the intervertebral disc with involvement of the spinal canal N Engl J Med 211210-234 1934 55 Modic MT Masaryk TJ Ross JS et al Imaging of degenerative disk disease Radiology 168177-186 1988 Citation 56 Modic MT Ross JS Obuchowski NA et al Contrast-enhanced MR imaging in acute lumbar radiculopathy A pilot study of the natural history Radiology 195429-435 1995 Abstract 57 Modic MT Steinberg PM Ross JS et al Degenerative disk disease Assessment of changes in vertebral body marrow with MR imaging Radiology 166193-199 1988 58 Morvan G Mathieu P Les stenoses laterales In Morvan G Deburge A Bard H et al (eds) Le Rachis Lombaire Degeneratif Montpellier Sauramps Medical 1998 pp 315-324 59 Murray RO Skeletal trauma Regional In Sutton D (ed) Textbook of Radiology and Imaging ed 3 New York Churchill Livingstone 1980 pp 210-231 60 Nachemson A Lumbar disc herniation Conclusions Acta Orthop Scand 64(suppl 251)49 1993 Citation

61 Nathan H Osteophytes of the vertebral column An anatomical study of their development according to age race and sex with consideration as to their etiology and significance J Bone Joint Surg Am 44243-268 1962 62 Nygaard OP Mellgren SI Osterud B The inflammatory properties of contained and noncontained lumbar disc herniations Spine 222584-2488 1997 Abstract 63 Ohshima H Hirano N Osada R et al Morphologic variation of lumbar posterior longitudinal ligament and the modality of disc herniation Spine 182408-2411 1993 Abstract 64 Osti OL Fraser RD MRI and discography of annular tears and intervertebral disc degeneration A prospective clinical comparison J Bone Joint Surg Br 74431-435 1992 Abstract 65 Palmgren T Gronblad M Virri J et al Immunohistochemical demonstration of sensory and autonomic nerve terminals in herniated lumbar disc tissue Spine 211301-1306 1996 Abstract 66 Resnick D Niwayama G Degenerative disease of the spine In Resnick D (ed) Diagnosis of Bone and Joint Disorders ed 3 Philadelphia WB Saunders 1995 pp 1372-1462 67 Resnick D Niwayama G Intravertebral disk herniations Cartilaginous (Schmorls) nodes Radiology 12657-65 1978 Abstract 68 Ross JS Modic MT Masaryk TJ Tears of the anulus fibrosus Assessment with Gd-DTPA-enhanced MR imaging AJR Am J Roentgenol 154159-162 1990 Abstract 69 Saal JS The role of inflammation in lumbar pain Spine 201821-1827 1995 Abstract 70 Sachs BL Vanharanta H Spivey MA et al Dallas discogram description A new classification of CTdiscography in low-back disorders Spine 12287-294 1987 Abstract 71 Sauser DD Goldman AB Kaye JJ Discogenic vertebral sclerosis J Can Assoc Radiol 2944-50 1978 Abstract 72 Schellhas KP Pollei SR Gundry CR et al Lumbar disc high-intensity zone Correlation of magnetic resonance imaging and discography Spine 2179-86 1996 Abstract 73 Schellinger D Manz HJ Vidic B et al Disk fragment migration Radiology 175831-836 1990 Abstract 74 Schipper J Kardaun JW Braakman R et al Lumbar disk herniation Diagnosis with CT or myelography Radiology 165227-231 1987 Abstract 75 Schmorl G Junghanns H The Human Spine in Health and Disease ed 2 New York Grune and Stratton 1971 76 Silverman CS Lenchik L Shimkin PM et al The value of MR in differentiating subligamentous from supraligamentous lumbar disk herniations AJNR Am J Neuroradiol 16571-579 1995 Abstract 77 Simmons JW Emery SF McMillin JN et al Awake discography A comparison study with magnetic

resonance imaging Spine 16S216-221 1991 Abstract 78 Smyth MJ Wright V Sciatica and the intervertebral disc J Bone Joint Surg Am 401401-1418 1958 79 Taveras JM Radiologic aspects of low back pain and sciatic syndromes [editorial] AJNR Am J Neuroradiol 9351-358 1989 80 Tehranzadeh J Discography 2000 Radiol Clin North Am 36463-495 1998 Full Text 81 Thelander U Fagerlund M Friberg S et al Describing the size of lumbar disc herniations using computed tomography A comparison of different size index calculations and their relation to sciatica Spine 191979-1984 1994 Abstract 82 Thornbury JR Fryback DG Turski PA et al Disk-caused nerve compression in patients with acute low-back pain Diagnosis with MR CT myelography and plain CT Radiology 186731-738 1993 Abstract 83 Twomey L Taylor J Age changes in lumbar intervertebral discs Acta Orthop Scand 56496-499 1985 Abstract 84 Twomey LT Taylor JR Age changes in lumbar vertebrae and intervertebral discs Clin Orthop 22497-104 1987 85 Williams AL CT diagnosis of degenerative disc disease The bulging annulus Radiol Clin North Am 21289-300 1983 Abstract 86 Williams AL Haughton VM Meyer GA et al Computed tomographic appearance of the bulging annulus Radiology 142403-408 1982 Abstract 87 Williams AL Haughton VM Syvertsen A Computed tomography in the diagnosis of herniated nucleus pulposus Radiology 13595-99 1980 Abstract 88 Wiltse LL Berger PE McCulloch JA A system for reporting the size and location of lesions in the spine Spine 221534-1537 1997 Abstract 89 Wiltse LL Fonseca AS Amster J et al Relationship of the dura Hofmanns ligaments Batsons plexus and a fibrovascular membrane lying on the posterior surface of the vertebral bodies and attaching to the deep layer of the posterior longitudinal ligament An anatomical radiologic and clinical study Spine 181030-1043 1993 Abstract 90 Yamashita K Hiroshima K Kurata A Gadolinium-DTPA-enhanced magnetic resonance imaging of a sequestered lumbar intervertebral disc and its correlation with pathologic findings Spine 19479-482 1994 Abstract 91 Yu SW Haughton VM Sether LA et al Comparison of MR and diskography in detecting radial tears of the anulus A postmortem study AJNR Am J Neuroradiol 101077-1081 1989 Abstract 92 Yu SW Sether LA Ho PS et al Tears of the anulus fibrosus Correlation between MR and pathologic findings in cadavers AJNR Am J Neuroradiol 9367-370 1988 Abstract

93 Yussen PS Swartz JD The acute lumbar disc herniation Imaging diagnosis Semin Ultrasound CT MR 14389-398 1993 Abstract 94 Zucherman J Derby R Hsu K et al Normal magnetic resonance imaging with abnormal discography Spine 131355-1359 1988 Abstract

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  • CLASSIFICATION DIAGNOSTIC IMAGING AND IMAGING CHARACTERIZATION OF A LUMBAR HERNIATED DISK
    • IMAGING OF LOW BACK PAIN I
      • CLASSIFICATION DIAGNOSTIC IMAGING AND IMAGING CHARACTERIZATION OF A LUMBAR HERNIATED DISK
        • DEFINITION OF A DISK HERNIATION
        • CLASSIFICATION OF A HERNIATED LUMBAR DISK
          • Main Categories of Noninfectious Disk Abnormalities
          • Further Qualifying the Displaced Disk Material Beyond the Disk Space
            • DIAGNOSTIC IMAGING AND CHARACTERIZATION OF A HERNIATED LUMBAR DISK
              • Conventional Radiographs
              • Myelography
              • CT
              • CT Myelography
              • MR Imaging
              • Diskography and CT Diskography
                • SUMMARY
                  • References
Page 3: CLASSIFICATION, DIAGNOSTIC IMAGING, AND IMAGING ... · PDF fileclassification, diagnostic imaging, and imaging characterization of a lumbar herniated disk ... classification, diagnostic

normal intervertebral disk and displacement of disk material inside a vertebral body through a break in the end plate may be properly named an intravertebral disk herniation

Despite the controversies associated with disk nomenclature the general modern definition of disk herniation just discussed has gained general acceptance by imaging specialists Debates most often arise as to whether or not a particular image in a given individual qualifies for this theoretical definition because of the impact on management or compensation previously discussed Using CT or even MR imaging some herniations can mimic symmetric or asymmetric disk bulging because the disk material coming out of the disk space at the disk level is confined by the anterior or posterior longitudinal ligament and often generates the illusion of a process that is not focal Because of this the definition of the disk herniation should probably be broadened to localized displacement of nuclear anular or end plate material beyond the normal limits of the disk space The term localized is meant in opposition to generalized the latter term being reasonably applied to displacement of disk material involving more than 50 (180 degrees) of the disk periphery Localized displacement in the axial (horizontal) plane can be further described as focal signifying that less than 25 of the disk circumference is involved or broad-based meaning between 25 and 50 of the disk circumference As was emphasized by Mink et al[ ]53 the term disk herniation like all anatomic descriptive terms of disk abnormalities should not by itself imply disability cause relation to injury relation to pain or the need for treatment or reimbursement On the other hand a bulging disk may be defined as a disk in which the contour of the outer anulus extends or appears to extend in the horizontal (axial) plane beyond the edges of the disk space usually over greater than 50 (180 degrees) of the disk circumference

Even though the modern definition of disk herniation can apply to all intervertebral disks this article deals exclusively with lumbar disk herniations Some aspects that are discussed can apply to thoracic and cervical disks but because of the important anatomic differences between the different spinal segments all extrapolations must be conducted very cautiously Even in the lumbar area there are significant anatomic differences between upper and lower vertebrae and certain concepts like the lateral recess syndrome are really meaningful only in relation to the L4 L5 and S1 vertebrae[ ]58

CLASSIFICATION OF A HERNIATED LUMBAR DISK

Some classifications of disk herniations that have been proposed to imaging specialists have not met with success essentially because categories were defined in terms of microscopic anatomy and pathology[ ]2 [ ]66 Such models were actually suitable for pathologists performing cryotome sections on postmortem specimens and to some degree for surgeons reporting operating room observations but were not really useful for radiologists describing abnormal findings on myelograms diskograms CT or MR images Conceivably a classification of lumbar disk herniations could be based on the clinical staging of the disease Stage 1 low back pain plusmn radiating pain no objective sign Stage 2 low back pain plusmn radiating pain segmental pain muscle spasm Stage 3 low back pain plusmn radiating pain signs of dural or radicular irritation Stage 4 low back pain plusmn

radiating pain neurologic deficit[ ]47 Although useful for patient management this model is not adequate for imaging study interpretation A useful nomenclature needs to propose categories based on observable distinctions that take into consideration the limitations of present-day imaging techniques

Main Categories of Noninfectious Disk Abnormalities

Ideally a valid and useful system for classifying noninfectious disk abnormalities should provide categories that correspond to real anatomic and pathologic entities and if possible correspond to specific clinical situations The system should be applicable to all currently used imaging modalities It should be simple to understand to memorize and to teach It should also be reliable and generate substantial intraobserver and interobserver agreement in terms of Kappa statistics[ ]41 The nomenclature to describe disk lesions demonstrated by imaging studies has been greatly influenced by our concepts of disk degeneration throughout life (ie what is normal aging) and our understanding of what constitutes a disk lesion likely to generate clinical signs and symptoms The nomenclature we favor is directly related to our physiopathologic model The clinical concept that followed the description by Mixter and Barr[ ]54 of herniation of the nucleus pulposus through a ruptured anulus fibrosus was that should this occur in a posterior or posterolateral direction and encroach on the neural canal cord or nerve root compression may result with consequent segmental root pain and muscle spasm[ ]59 Because compression of neural structures was believed to be the only logical explanation for pain associated or not with a neurologic deficit imaging strategies have been developed over the last 20 years with a clear focus on identifying displacement of disk material associated with compression of neural structures[ ]28 [ ]31 [ ]32 [ ]36 [ ]74 [ ]82 [ ]86 [ ]87 Classifications of disk abnormalities that were associated with this concept have obviously been influenced by this bias In the early 1980s for the interpretation of myelograms and the first generation of high-resolution CT of the spine a very simple terminology was proposed that had essentially three categories (1) the normal disk (2) the bulging disk without nerve root compression and (3) the herniated disk with nerve root compression[ ]36 [ ]85 The definition of disk herniation was very restrictive because nerve root compression was considered by some investigators a sine qua non condition to make the diagnosis This requirement appeared acceptable however because it was estimated that only 10 of herniations occurred in a posterior central direction[ ]42 [ ]87

The validity of this model has been questioned in recent years and nerve root compression has been found less important than inflammation in the genesis of painful symptoms[ ]78 This relatively new concept has led to the development of two nomenclature models based on very different perspectives

The Morphologic Model

This model is essentially based on one parameter the assessment of the disk contour to determine the degree of disk extension beyond the interspace (DEBIT) [ ]13 The categories are normal disk bulging disk protrusion and extrusion (Fig 1) (Figure Not Available) Normal indicates no disk extension beyond the interspace Bulge refers to circumferential symmetric DEBIT (around the end plates) Protrusion indicates focal or

asymmetric DEBIT into the canal the base against the parent disk broader than any other diameter of the protrusion Extrusion means focal obvious DEBIT the base against the parent disk narrower than any diameter of the extruding material itself or no connection between displaced disk material and parent disk The use of the term herniation to designate collectively protrusions and extrusions has been suggested[ ]15 but maintaining the distinction may have some clinical relevance because extrusions are rarely found in asymptomatic individuals as opposed to protrusions and bulges[ ]34 It has also been argued that the term extruded disk is less frightening and emotionally laden than disk herniation or ruptured disk[ ]17 This classification is based on very simple geometric concepts and the categories are mutually exclusive but the line drawings in Figure 1 (Figure Not Available) are misleading because they represent the disk as a two-dimensional structure Disk extrusions such as the one depicted are practically never seen at the disk level on CT or MR imaging axial sections large posterior displacement of disk material beyond the margins of the intervertebral space still generally creates images corresponding to the definition of a protrusion because they are outlined by the posterior longitudinal ligament (Fig 2) Significant migration of disk material is usually necessary to generate a typical extrusion image Distinction between protrusions and extrusions at the disk level is very often only possible on sagittal sections (Fig 3) and this distinction is not very practical for the interpretation of CT because sagittal reconstructions are usually not part of the routine imaging protocol On CT or MR imaging this distinction is difficult in the presence of a narrow central spinal canal and very often impossible for foraminal herniations (Fig 4)

Figure 1 (Figure Not Available) Morphologic nomenclature based on the assessment of the disk contour (From Milette PC The proper terminology for reporting lumbar intervertebral disk disorders AJNR Am J Neuroradiol 181859-1866 1997 with permission)

Figure 2 Axial CT scan section through the L4-L5 disk space showing a relatively large posterior right central displacement of disk material with dural sac compression and probable right L5 nerve root compression Although the overlying posterior longitudinal ligament complex (PLLC) is not seen it constrains the displaced disk material and is responsible for maintaining a protrusion shape

Figure 3 When a relatively large amount of disk material is displaced distinction between protrusion (A) and extrusion (B or C) will generally only be possible on sagittal MR sections or sagittal CT scan reconstructions In C although the shape of the displaced material is similar to that of a protrusion the greatest cranio-caudal diameter of the fragment is greater than the craniocaudal diameter of its base at the level of the parent disk and the lesion therefore qualifies as an extrusion

Figure 4 Axial CT scan section through the upper portion of the L4-L5 foramina in a 45-year-old man Abnormal soft tissues likely representing displaced disk material are seen in the right foramen The material cannot be precisely delineated and the distinction between protrusion and extrusion is difficult A typical extrusion shape is practically never seen with foraminal herniations

Despite its apparent simplicity only moderate interobserver agreement has been reported using this nomenclature in three independent studies[ ]13 [ ]33 [ ]48 It is also incomplete because it considers exclusively the contour of the disk and the shape of the displaced disk material Disks demonstrating normal contour but abnormal central or peripheral signal patterns have no place in this system and associated vertebral body bone marrow changes are completely ignored even though the clinical relevancy of those changes has been well demonstrated[ ]4 [ ]48 [ ]55 [ ]57 [ ]72 This nomenclature is unfortunately misleading because it creates artificial pathologic entities The bulging disk category is the most problematic[ ]60 Obviously a severely dessicated and atrophic disk may bulge diffusely as the intervertebral space narrows with buckling of the anterior and posterior longitudinal

ligaments But an impression has been unjustifiably derived from early postmortem studies[ ]86 that even in young individuals a disk with an intact anulus may be responsible for a detectable bulge on axial CT sections It has also been hypothesized that bulging disks are caused by diffuse anular hyperlaxity which occurs as a result of tears in collagen bridges between the concentric anular fibers while these concentric fibers remain intact[ ]15 This theory has never been proved because such collagen bridges between the concentric fibers of the anulus have never been found[ ]45 It is important to realize that a bulging disk is not an anatomic or pathologic entity it is an image that requires a differential diagnosis It sometimes represents a normal anatomic variant this is often the case with the L5-S1 disk On CT images it is often an illusion caused by a volume-averaging effect (Fig 5) It may be associated with remodeling of adjacent vertebral bodies because of osteoporosis (Fig 6) It may of course result from chronic disk deterioration and collapse A bulging disk illusion is often created on CT by a posterior anular disk rupture with displaced disk material peeling off the posterior longitudinal ligament and displacing it backward creating a posterior wide base protrusion that mimics diffuse symmetric disk bulging on both axial CT and MR imaging sections and is not differentiated from a bulging disk on sagittal MR images unless close attention is paid to the anterior aspect of the disk (Fig 7) Except for the fact that extrusions are rarely found in asymptomatic individuals[ ]34 this system does not really provide categories that correspond to clinical entities

Figure 5 A Bulging disk appearance of the L4-L5 disk shown on a 5-mm-thickness axial CT scan section in a 57-year-old woman The height of the intervertebral space was preserved and there was no reactive vertebral body end-plate modifications This aspect is probably partly due to vertebral body remodeling caused by osteoporosis but is mostly created by volume averaging (From Milette PC Fontaine S Daniels C et al Imaging of Low Back Pain CD-ROM SSB Multimedia Medical Series Montreal 1997 with permission) B Using 4- or 5-mm-thickness CT sections an intermediate gray shade halo is often computer generated by volume averaging of tissues with different attenuation coefficients in voxels represented by two-dimensional pixels located at the disk space periphery This creates the illusion of a three-dimensional image demonstrating diffuse disk bulging ST = slice thickness

Figure 6 Axial CT scan section of a L4-L5 disk in a 78-year-old man demonstrating diffuse disk bulging caused by remodeling of the adjacent vertebral bodies due to osteoporosis The intervertebral space was normal in height and there were no reactive adjacent bony endplate modifications

Figure 7 A T2-weighted axial section of a L5-S1 disk showing a left posterolateral wide base protrusion that can be easily confused with diffuse circumferential bulging B Corresponding T2-weighted left paracentral and central sagittal sections demonstrating loss of the L5-S1 disk signal intensity with posterior small left-central protrusion the anterior aspect of the disk does not extend beyond the endplates and therefore such a disk should not be labeled bulging disk

The Pathoanatomic Model

As opposed to the previous model that can be applied only to the interpretation of CT and MR imaging studies this model can be used for the interpretation of all imaging modalities including plain films and diskograms[ ]47 [ ]51 It consists of five categories that are not mutually exclusive so that different combinations are possible (Fig 8) (Figure Not Available) The first three refer to the general state of the disk (1) normal young disk (2) normal aging disk and (3) deteriorated disk (formerly called the scarred disk) The last two refer to localized lesions anular tear and herniated disk In this model the previously discussed definition of disk herniation proposed by Herzog[ ]30 is applicable The use of this system requires an effort to distinguish the normal aging changes from those of pathologic degeneration Resnick and Niwayama[ ]66 have emphasized the differentiating features of two degenerative processes involving the intervertebral disk which had been previously described by Schmorl and Junghanns[ ]75 (1) spondylosis deformans which affects primarily the anulus fibrosus and bony ring epiphysis and (2) intervertebral osteochondrosis which affects essentially the nucleus pulposus and the vertebral body end plates

Figure 8 (Figure Not Available) Schematic representation of a nomenclature based on a three-dimensional assessment of the anatomic and pathologic characteristics of both disk and adjacent vertebral bodies The categories are not mutually exclusive and some combinations are possible A Categories related to the general aspect of the disk normal young disk (a) normal aging disk (b) deteriorated disk (c) B Categories related to local lesions normal young disk (a) anular tear (b) herniated disk (c) (Adapted from Milette PC The proper terminology for reporting lumbar intervertebral disk disorders AJNR Am J Neuroradiol 181859-1866 1997 with permission)

There is convincing evidence in the scientific literature that the features of spondylosis deformans represent the normal aging process whereas intervertebral osteochondrosis denotes true pathologic disk degeneration[ ]61 [ ]71 [ ]75 [ ]83 [ ]84 Schmorl and Junghanns[ ]75 found spondylotic changes in 60 of women and almost 80 of men over the age of 50 In a series of 400 dried skeletons Nathan[ ]61 found anterior vertebral body osteophytes which constitute the main feature of spondylosis deformans in 100 of individuals over age 40 whereas posterior osteophytes were found in only 39 of individuals even after the age of 80 Twomey and Taylor[ ]83 [ ]84 have found that loss of disk height is unusual in a normal aging population and that loss of stature in the elderly is attributable to loss of intervertebral body height rather than loss in disk height During the normal aging process the mucoid matrix of the nucleus pulposus is progressively replaced by fibrous tissue[ ]37 but the intervertebral height is preserved and the disk margins remain regular Dessication and thining of disks or disks that bulge like an underinflated automobile tire are not typical of elderly spines Slight symmetric bulging may occur if there has been vertebral body remodeling resulting from osteoporosis Small amounts of gas can be detected on plain films or CT images near the insertion of the anulus on the ring epiphysis and this gas is probably located in transverse anular tears adjacent to the ring epiphysis During the fourth decade anterior and lateral marginal vertebral body osteophytes constitute normal findings comparable with having gray hair but end plate erosions with osteosclerosis or chronic reactive bone marrow changes type 2 or 3 as described by Modic et al[ ]57 should not be seen Slight to moderate decrease in central signal intensity can be detected on T2-weighted MR images as part of the normal aging process but the changes should involve uniformly all lumbar disks

Deteriorated disks represent real pathologic degeneration which is sometimes referred to as chronic diskopathy On microscopic examination they show total structural disorganization and general replacement of normal disk material by scar tissue For this reason they were initially labeled scarred disks by the members of a joint committee on spinal nomenclature created by the Quebec Association of Radiologists[ ]14 Because of possible confusion with postoperative changes the term deteriorated disk has been proposed as an acceptable substitute Strictly speaking the term degeneration could be used to designate this entity but this latter term has such a broad nonspecific meaning that it is best avoided The deteriorated disk is characterized by narrowing of the intervertebral space irregular disk contour generally associated with symmetric or asymmetric bulging abundant presence of gas in the central portion of the intervertebral disk space multidirectional osteophytes that do not respect the central spinal canal or the foramina end plate erosions with reactive osteosclerosis and chronic bone marrow changes On T2-weighted MR images the central disk signal intensity is usually markedly decreased and the number of affected lumbar disks is variable Even though transverse concentric and radial anular tears have been identified on postmortem specimens[ ]92 the anular tear category in this model refers essentially to the radial tears that are generally demonstrated by diskography in symptomatic patients For a more precise description of those tears this model may be supplemented by the Dallas Discogram Description system[ ]70 with or without its recently proposed updates[ ]4 [ ]72 [ ]80

It should be emphasized that the pathoanatomic model is not based on direct identification of a particular geometric pattern but on the anatomy and pathology that are expected as a result of the analysis of specific criteria Using this model the conclusion of any imaging report does not consist of terms related to the shape of the disk contour or the displaced disk material but on a pathologic diagnosis that should be presented with an appropriate confidence level (possible probable or definite) The diagnosis of a probable major radial anular tear may be inferred from the presence of a definite central signal intensity loss because as a result of diskographic MR imaging correlations the positive predictive value of this sign has been estimated at 96[ ]48 The use of this model requires an effort to understand the criteria allowing differentiation of normal aging from true pathologic degeneration so this system is slightly more complicated than the morphologic model Its reliability has never been tested Some intraobserver or interobserver disagreement would probably occur trying to distinguish anular tears without herniation from anular tears with small herniations With respect to correspondance to clinical situations this scheme like the morphologic model has limited interest it has been shown that disks demonstrating the features of the deteriorated disk are likely to be responsible for symptoms but this relationship has been statistically established to be significant only for the L4-L5 disk[ ]24

Which Model Should Be Used

In other areas of diagnostic radiology the aim of image analysis is always to predict what the pathologist would find if he or she could be provided with an adequate specimen immediately following the imaging study radiologic diagnoses are presented with a pathologic perspective There is no reason why the reporting of disk disorders should be

any different Terms like bulging disk are meaningless to a pathologist and I personally favor the pathoanatomic model Nomenclature standardization however is not a task that can be achieved by an individual or even a single group of authors[ ]12 To have any impact recommendations have to emanate from well established national or international societies The multiplicity of scientific societies with an interest in the spine all over the world creates a special problem but new joint committees have recently been set up combining efforts to come up with a practical unified system that it is hoped could be proposed jointly by the North American Spine Society the American Academy of Orthopedic Surgeons the American Academy of Neurological Surgeons the American Society of Spine Radiology and the American Society of Neuroradiology Agreeing in North America on a classification of disk disorders that could gain universal acceptance like the TNM classification of neoplastic diseases would be a major achievement Meanwhile the choice of the nomenclature is up to the best judgement of each practicing radiologist and the essential issue in a given hospital or community practice remains clear communication between radiologists and referring physicians by way of a local agreement as to the meaning of words

A major problem frequently occurs because observers of imaging studies try to combine elements of the morphologic classification with those of the pathoanatomic classification Trying to differentiate a bulging disk (morphologic qualifier) from a disk herniation (pathologic diagnosis) cannot work because a bulging disk aspect is a common feature of the aging disk the deteriorated disk and some posterior central disk herniations (Fig 9) Trying to make the distinction is doomed to failure because it defies formal logic On the other hand it is theoretically possible to differentiate a radial anular tear (without herniation) from a disk herniation because these are two different pathologic entities although one may be the continuum of the other It is best to adopt either one of the two systems and avoid trying to straddle the two A general classification of disk disorders attempting to conciliate the morphologic and the pathoanatomic model is proposed in Table 1

Figure 9 A bulging disk aspect often conceals a posterior central herniation A Complete rupture of the outer anular fibers allowing nuclear material to escape and peel off the posterior longitudinal ligament (and sometimes a few intact peripheral anular fibers) from the torn disk creating a detectable focal or asymmetric extension of the disk margin beyond the interspace which qualifies as a protrusion B With more gelatinous nuclear material escaping underneath the rigid posterior longitudinal ligament the focal bulge is no longer detectable as its radius increases and if the tear occurs in the posterior midline or para-medial direction the aspect mimics symmetric disk extension beyond the interspace C Since in most cases only the outline of a diffusely hypointense disk is perceived on MR images this creates the illusion of circumferential disk bulging on axial sections D The real nature of a bulging disk of this type may be suspected by scrutinizing the sagittal sections and appreciating that unless one is dealing with a chronically degenerated scarred disk the bulge is not symmetric but limited to the posterior aspect of the disk

TABLE 1 -- GENERAL

CLASSIFICATION OF DISK LESIONS Normal (excluding aging changes)

Congenitaldevelopmental variants

Inflammationinfection

Neoplasia

Degenerativetraumatic

Degeneration

Anular tear

Herniation Protrusion

Extrusion

Degeneration Spondylosis deformans

Intervertebral osteochondrosis

Further Qualifying the Displaced Disk Material Beyond the Disk Space

Regardless of the basic system that is used the type of herniation should be assessed The volume and location of the displaced disk material beyond the normal peripheral margin of the intervertebral space also need to be specified In certain cases it is also possible to determine the composition of this material For the sake of simplicity the term herniation is used consistently in the remainder of this article to refer to all displaced disk material but what is discussed can also be applied to protrusions and extrusions if one wants to use the morphologic nomenclature

Type of Herniation

Upward or downward migration of nuclear material may occur through a break in a vertebral body end plate creating an intravertebral herniation sometimes referred to as an intraspongy herniation or a Schmorls node[ ]67 (Fig 10) Although a herniation occurring in any horizontal direction is likely to cause symptoms because of the presence of pain-sensitive nerve endings in the outer anulus[ ]7 [ ]8 [ ]65 herniations occurring in a posterior or posterolateral direction deserve special consideration because of the added possibility of dural sac or individual nerve root compression

Figure 10 Various types of intravertebral herniations (Schmorls nodes) A Intravertebral herniation through the inferior end plate of the L3 vertebral body demonstrated by diskography in a 35-year-old man suffering from chronic low back pain The patients typical pain was reproduced during injection and the lesion was considered responsible for the patients symptoms B T2-weighted sagittal section demonstrating an intravertebral herniation through the inferior end plate of the L4 vertebral body in a 24-year-old woman presenting with chronic low back pain The high signal intensity of the lesion associated with the loss of normal central signal intensity of the parent disk suggests that the lesion is a bona fide acquired intraspongy herniation and not just a developmental defect C T2-weighted sagittal section demonstrating an intravertebral herniation through the inferior end plate of the L3 vertebral body (arrow) Because both the herniation and the parent disk show normal signal intensity the abnormality was

considered a probably asymptomatic developmental defect

Other characteristics of disk herniations have become relevant with the development of new therapeutic possibilities (eg chemonucleolysis and percutaneous diskectomy) The term sequestration is confusing and has often been used to indicate displacement of disk material away from the parent disk The term sequestered disk should be used restrictedly to designate a fragment of diskal tissue that has migrated from the disk space and has no connection by diskal tissue to the disk of origin[ ]20 [ ]21 [ ]42 Sequestration refers to loss of continuity with disk tissue still present in the intervertebral disk space The term migration has a broader meaning indicating displacement of disk material away from the edge of the rent in the outer anulus either in the central spinal canal at the disk level or above or below the disk level This difference is illustrated in Figure 11 The terms communicating and noncommunicating derive from a different perspective and are mostly used in the context of intradiskal therapeutic injections They refer to the interruption of the periphery of the disk allowing fluid injected into the disk to leak into the spinal canal and reach displaced disk material[ ]20 [ ]51 The terms contained and uncontained are unfamiliar to most radiologists in a contained herniation the displaced disk material is still covered by a few intact but distended outer anular fibers or by a capsule formed by outer anular fibers and the adherent posterior longitudinal ligament

Figure 11 Various types of posterior central herniations A Small subligamentous herniation (protrusion) without significant disk material migration B Subligamentous herniation with downward migration of disk material under the PLLC C Sub-ligamentous herniation with downward migration of disk material and sequestered fragment (arrow)

The terms subligamentous and extraligamentous (or transligamentous) refer to the position of the displaced disk material with respect to the posterior longitudinal ligament The anatomy of the posterior longitudinal ligament has been recently revised[ ]73 [ ]89 It is a membranous structure that has multiple components a deep layer attached to disks and vertebral bodies a superficial layer attached to the dura by fibrous tissue (Hoffmanns

ligament) and lateral extensions known as the lateral membranes or peridural membranes (Fig 12) (Figure Not Available) It should probably be referred to as the posterior longitudinal ligament complex (PLLC) It actually divides the epidural space into the perithecal space and the anterior epidural space where displaced disk material can be entrapped (Fig 13) A potential space allowing accumulation of displaced disk material has also been detected between the outer anular fibers and the deep fibers of the PLLC on the posterior central aspect of the disk[ ]63 Posterior midline herniations seldom rupture the PLLC and are generally subligamentous The lateral membranes are less resistant and transligamentous herniations are usually the result of posterior off-center herniations or posterolateral herniations

Figure 12 (Figure Not Available) The PLLC is portrayed here in relation to various types of subligamentous disk displacement At the disk level posteriorly displaced disk material frequently occupies the midline Below and above the disk an anterior epidural space (AES) exists between the PLLC and the posterior aspect of the vertebral bodies In this space disk fragment motion across the midline is curtailed by a sagittal midline septum (dashed line) A delicate translucent membrane (shown only on left side of drawing) is stretched between the free edge of the deep layer of the posterior longitudinal ligament and the lateral spinal canal (From Schellinger D Manz HJ Vidic B et al Disk fragment migration Radiology 175831-836 1990 with permission)

Figure 13 Relationship of typical posterior disk herniations with the PLLC A Midline sagittal section unless very large a posterior midline herniation usually remains entrapped underneath the deep layer of the PLL C and sometimes a few intact outer anulus fibers joining with the PLL C to form a capsule The deep layer of the PLL C (arrow) also attaches to the posterior aspect of the vertebral body so that no potential space is present underneath B Sagittal para-central section the PLL C extends laterally at the disk level (arrowhead) but above and below the disk an anterior epidural space (as) where disk fragments are frequently entrapped is present between the lateral (peridural) membranes and the posterior aspect of the vertebral bodies

Volume of Herniated Material

Quantifying the herniated disk material by measuring in millimeters its greatest diameter or by evaluating its cross-sectional area in square millimeters is rarely done The resulting figures could be misleading without relating this measurement to the size of the spinal canal and the exact location of the lesion[ ]88 A purely qualitative and subjective statement that a mild moderate or severe herniation is present however does not give the person reading the imaging report any indication as to the potential of the lesion to cause significant compression of the dural sac or individual exiting nerve roots A reasonably precise scheme has been proposed in 1995 by the Nomenclature Committee of the North American Spine Society[ ]20 Measurements are taken from an axial CT or MR imaging section at the site of most severe compromise canal compromise of less than 25 at that section is qualified as mild 25 to 75 is moderate 76 to 90 is moderately severe and greater than 90 is severe It is understood that such characterizations describe only the cross-sectional area at one level and do not account for the total volume of displaced material displacement of neural tissue or clinical significance The usefulness of having four categories is questionable and can likely generate poor interobserver or intraobserver agreement especially in situations where the central spinal canal is relatively narrow Bonnevilles scheme[ ]9 [ ]10 [ ]11 should generate greater reliability (Fig 14) (Figure Not Available) Separation of the cross-sectional area in three thirds can be applied to both the central spinal canal and the foramina It can be agreed by way of convention that the terms mild moderate and severe lumen compromise by a disk herniation designate extension of the displaced disk material in the anterior middle or posterior third of the central canal or foramen depending on the specified location of the herniation

Figure 14 (Figure Not Available) The size of the herniation in the horizontal plane is assessed and designated by the numbers 1 2 or 3 by establishing its extension in the anterior middle or posterior third of the spinal canal (From Bonneville JF Plaidoyer pour une classification par limage des hernies discales lombaires la carte-image Rev Imag Med 2557-560 1990 with permission)

Location of Herniated Material

Bonneville[ ]9 [ ]10 [ ]11 has also proposed an interesting and simple alpha-numerical system to classify according to their location the position of disk fragments that have migrated in the horizontal or sagittal plane (Figs 15 (Figure Not Available) and 16) (Figure Not Available) Using more precise anatomic boundaries unfortunately more familiar to surgeons than radiologists Wiltse et al[ ]88 have proposed another system which has been supported by the North American Spine Society[ ]20 [ ]21 Anatomic zones and levels are defined using the following anatomic landmarks medial edge of the articular facets medial lateral upper and lower border of the pedicles and coronal plane at the disk center On the horizontal plane (Fig 17) (Figure Not Available) these landmarks determine the bounderies of the central zone the subarticular zone the foraminal zone the extraforaminal zone and the anterior zone (anterior to the coronal plane at the center of the disk) In the sagittal plane they determine the boundaries of the diskal level the infrapedicular level the pedicular level and the suprapedicular level (Figs 18 (Figure

Not Available) and 19) (Figure Not Available) Radiologists interpreting axial CT or MR images may find it difficult to use the medial edge of the facets as the landmark that separates the central zone from the subarticular zone because the superior articular facets are generally not included in axial sections at the disk level The alternative is to use the expression posterolateral to designate collectively all posterior herniations that are not midline but do not extend into a foramen as was proposed by Bonneville[ ]9 [ ]10 [ ]11

Figure 15 (Figure Not Available) In the horizontal plane herniations are labeled midline (a) posterolateral (b) foraminal (c) and extra-foraminal (d) (From Bonneville JF Plaidoyer pour une classification par limage des hernies discales lombaires la carte-image Rev Imag Med 2557-560 1990 with permission)

Figure 16 (Figure Not Available) In the craniocaudal direction disk migration is labeled +1 +2 +3 or -1 -2 -3 by referring to the height of a vertebral body divided in thirds (From Bonneville JF Plaidoyer pour une classification par limage des hernies discales lombaires la carte-image Rev Imag Med 2557-560 1990 with permission)

Figure 17 (Figure Not Available) The anatomic zones identified on axial images The anterior zone (not shown) is delineated from the extraforaminal zone by an imaginary coronal line in the center of the vertebral body (From Wiltse LL Berger PE McCulloch JA A system for reporting the size and location of lesions in the spine Spine 221534-1537 1997 with permission)

Figure 18 (Figure Not Available) The anatomical levels identified on craniocaudal images (From Wiltse LL Berger PE McCulloch AJ A system for reporting the size and location of lesions in the spine Spine 221534-1537 1997 with permission)

Figure 19 (Figure Not Available) Coronal view of the main zones and levels (From Wiltse LL Berger PE McCulloch JA A system for reporting the size and location of lesions in the spine Spine 221534-1537 1997 with permission)

Composition of Herniated Material

Displaced disk material may consist of glycosaminoglycans type 1 or 2 collagen end plate cartilage and bone fragments avulsed from the ring epiphysis A reactive inflammatory reaction usually results in edematous tissue followed by granulation tissue which may undergo calcification (Fig 20) Necrotic and partially resorbed displaced disk material sometimes produces a large fluid-filled pouch distinguishable from the common high-intensity zone because of its size (Fig 21) or a gas-filled cavity generally in continuity with gas in the intervertebral space (Fig 22) [ ]42 These characteristics may be meaningful if intradiskal injection therapy is considered In imaging reports herniations exhibiting calcium deposits and those exhibiting replacement of disk material by gas or a relatively large fluid collection can be qualified as chronic herniations

Figure 20 A CT scan demonstration of a small posterior central L4-L5 calcified subligamentous herniation The resistant deep layer of the PLLC restrains displacement of the disk material in the posterior central direction and does not allow a detectable distortion of the disk contour In this particular case the presence of the calcification is actually the only evidence that a posterior midline anular tear and a small subligamentous herniation are present B Posterior right central and sub-articular L5-S1 calcified disk herniation in same patient Posterolateral herniations are generally more conspicuous than posterior midline herniations because the deep layer of the PLLC gets thinner away from the midline

Figure 21 Posterior central midline L4-L5 herniation in a 52-year-old man demonstrated on a T2-weighted midline MR sagittal section There is intervertebral space narrowing with loss of normal central disk signal

intensity while the herniated disk material demonstrates high signal intensity consistent with a predominantly fluid consistency

Figure 22 CT scan demonstration in a 51-year-old woman of a left posterolateral L5-S1 disk hernation consisting essentially in a gas-filled pouch (white arrow) Gas is also present in the central portion of the intervertebral disk space (black arrow)

DIAGNOSTIC IMAGING AND CHARACTERIZATION OF A HERNIATED LUMBAR DISK

Assessing the validity of the currently used imaging procedures to diagnose a herniated lumbar disk is not an easy endeavor The validity of a measurement is the extent to which it corresponds to the true biologic value or some accepted gold standard[ ]40 With the exception of postmortem studies evaluation of the pathoanatomy by the surgeon in the operating room has always been considered the gold standard but this does not constitute an ideal situation Inspection of the disk through a small laminectomy incision to determine for instance if nuclear fragments lie within or outside the anular fibers may not be very reliable Also unbiased intraoperative determination of a normal degenerated or herniated disk in a patient with sciatica may also be difficult[ ]86 Because the validity of diskography has been previously established by postmortem studies and surgical correlations[ ]48 it is sometimes used as a gold standard in situations where no surgery has been performed

Conventional Radiographs

Lumbar disk herniations can exceptionally be diagnosed directly on good quality lateral projections because the x-ray attenuation is slightly greater in displaced disk material than in epidural fat Occasionally a calcified rim outlines the displaced disk fragment

(Fig 23) In most situations however narrowing of an intervertebral disk space in the absence of other evidence of chronic diskopathy is the only detectable sign suggesting the presence of a disk herniation To my knowledge the sensitivity and specificity of this sign has never been assessed The accepted rule of thumb is that the height of a given lumbar intervertebral disk space should always be slightly greater than the height of the above located interspace This rule does not apply to the transition disk immediately above the sacrum (usually L5-S1) The specificity of this sign is probably quite high but a few false-positives are seen especially at the L4-L5 level because of minor congenital hypoplasia The presence of posterior or foraminal vertebral body osteophytes associated or not with disk space narrowing is a definite sign of a chronic disk herniation

Figure 23 A Chronic left L3-L4 extraforaminal disk hernation in a 54-year-old man suspected on an AP radiograph demonstrating a calcified shell on the left side of the intervertebral disk space (white arrow) B Axial CT scan section confirming the diagnosis of a chronic extraforaminal L3-L4 herniation

Myelography

Myelography is essentially an exploration of the subarachnoid space Disk herniations are demonstrated only indirectly because they can cause thecal sac deformity and individual nerve root sleeve filling defects (Fig 24) Of all the special imaging procedures

myelography is the only one that allows upright projections with full weight bearing It is not unusual to demonstrate in this way small posterior central or posterolateral herniations that are undetectable on CT sections Interestingly the overall sensitivity of myelography to detect disk herniations has been found to be higher than that of CT whereas its specificity has been found to be lower[ ]74 In comparison with standard CT examination which usually includes only the three or four lower lumbar disks myelography easily allows coverage of the entire lumbar area and assessment of the intrathecal structures (cauda equina and conus medullaris) Far lateral foraminal herniations extraforaminal herniations and anterior herniations however are not detected The sensitivity for detection of posterior central L5-S1 herniations is also relatively poor because of the greater distance between the thecal sac and the posterior aspect of this particular disk

Figure 24 L5-S1 disk herniation in a 25-year-old man detected by indirect signs using lumbosacral myelography A Upright oblique projections showing a filling defect of the left S1 root sleeve (white arrow) suggesting significant nerve root compression by a left posterolateral disk hernation The right S1 root sleeve fills normally with contrast (black arrow) B Subtle compression of the anterior wall of the dural sac by displaced disk material (small arrows) demonstrated on upright lateral projection This sign is usually absent in the presence of a large amount of fat and venous structures in the anterior epidural compartment

CT

The sensitivity of CT to diagnose a herniation of the nucleus pulposus at the L5-S1 interspace is greater than that of myelography if images in the exact plane of the disk can be obtained[ ]23 [ ]39 Otherwise the superiority of plain CT over myelography to demonstrate disk herniations has not been established but CT has the distinct advantage of being

noninvasive and provides direct anatomic information[ ]23 Large herniations are easily detected but as explained previously the distinction between protrusions and extrusions is often difficult without sagittal reconstructions CT essentially allows an assessment of the contour of the disk The diagnosis of very small herniations in the absence of direct or indirect evidence of a radial tear is hazardous and associated with a high percentage of false-positives and false-negatives[ ]52 The diagnosis of moderate and large size herniations in different directions is usually possible but anterior herniations are rarely diagnosed not because they are not detectable but because observers pay little attention to the anterior contour of the disk (Fig 25) Because the PLLC cannot usually be identified the distinction of subligamentous from transligamentous herniation can only be suggested in most cases by the size of the herniated material A definite diagnosis of sequestration is rarely possible Calcifications within the displaced material are readily seen but may be difficult at times to differentiate from an accompanying osteophyte or an avulsed bone fragment from the vertebral body ring epiphysis (Fig 26) The presence of gas in the herniated material is easily detected

Figure 25 Anterior L4-L5 herniation demonstrated by CT scan in a 51-year-old woman with chronic low back pain Although sometimes quite conspicuous such herniations are rarely reported because observers pay little attention to the anterior contour of the disk

Figure 26 CT scan demonstration of a posterior right central L4-L5 disk herniation in a 38-year-old woman with avulsion of a bone fragment from the ring epiphysis and adjacent part of the superior L5 end plate Reactive osteosclerosis is seen around the vertebral body defect (arrows) suggesting a chronic lesion

CT Myelography

This association combines the advantages of both imaging modalities The fact that its accuracy has been reported as being less[ ]22 [ ]32 higher[ ]1 [ ]6 or equivalent[ ]82 to MR imaging is a reflection of the differences in technologic advancement and pathologic nomenclature that hamper valid comparisons between different studies

MR Imaging

Most reported studies establish MR imaging as the first choice modality to diagnose a herniated lumbar disk[ ]5 [ ]22 [ ]32 [ ]46 The associated intravenous injection of a paramagnetic agent has been found useful to demonstrate some anatomic features of disk disease in patients with no previous lumbar disk surgery[ ]56 [ ]68 [ ]90 MR imaging provides a better assessment of disk morphology than CT or CT myelography because sagittal sections are routinely obtained Assessment of foraminal involvement by displaced disk material is more accurate (Fig 27) and anterior disk herniations can be detected more easily than with CT or CT myelography If one is looking specifically for herniated lumbar disks associated with nerve root compression however it has been demonstrated that CT is equally accurate[ ]82 Alterations of the central or peripheral disk signal intensity on T2-weighted images are seen in most disks afflicted with an anular tear[ ]48 and alert the observer to scrutinize the disk contour in search for local modifications indicative of a herniation Because the signal of the displaced disk material is usually very similar to that of the outer anulus PLLC and vertebral body cortical bone small herniations are generally more conspicuous on axial CT sections than on corresponding axial MR imaging sections Gas and calcium deposits within the displaced fragment cannot usually

be detected but associated vertebral body bone marrow changes are typically seen and are helpful in differentiating acute from chronic processes[ ]57 The occasional presence of a high-intensity zone in the herniated material with an occasionally enhancing border after contrast injection is probably caused by a mixture of displaced nuclear material acute and subacute inflammatory tissue and neovascularized reactive tissue[ ]4 [ ]48 [ ]72 Contradictory reports have been published regarding the accuracy of MR imaging to differentiate subligamentous from transligamentous herniations[ ]26 [ ]38 [ ]73 [ ]76 Understanding the anatomy of the PLLC is helpful to make the distinction (Fig 28) (Figure Not Available) Masaryk et al[ ]46 have suggested that MR imaging is accurate to distinguish sequestered disks from other forms of lumbar disk herniations but most observers find this distinction difficult to establish[ ]42

Figure 27 A Left L4-L5 foraminal herniation well seen on an intermediate-weighted left parasagittal MR section (arrow) in a 47-year-old man B The lesion is much less obvious on intermediate-weighted (left) and T2-weighted (right) axial sections and was in fact more conspicuous on the corresponding CT scan section

Figure 28 (Figure Not Available) A Subligamentous disk herniation Left T1-weighted image demonstrating displaced disk material with a smooth outline imposed by the demarcation of the anterior epidural space (AES) by the lateral membrane of the PLLC Right Correlative drawing B Transligamentous disk herniation Left T1-weighted image of a large disk herniation (cervical in this case) which has ruptured through the posterior confines of the AES Penetration of the right lateral membrane can be observed (arrow) and the disk fragment contour is serrated Right Correlative drawing (From Schellinger D Manz HJ Vidic B et al Disk fragment migration Radiology 175831-836 1990 with permission)

Diskography and CT Diskography

During 30 years (1950 to 1980) when myelography was the only available imaging technique to demonstrate lumbar disk herniations diskography was an invasive but efficient way to demonstrate posterior central L5-S1 herniations and other large herniations (other than posterior central and paramedial) that could not be detected by myelography[ ]50 These herniations are now usually well demonstrated by CT and MR imaging Comparing the accuracy of five imaging modalities (excluding MR imaging) for the diagnosis of lumbar disk herniation Jackson et al[ ]31 found that CT diskography (Fig 29) was the most accurate test (87) compared with 77 for CT myelography 74 for CT 70 for myelography 64 for pain reproduction during diskography and 58 for diskography without CT Disk injection reproduced the patients clinical pain pattern in only 36 of herniated disks This clinical test isolated from the images had high specificity (89) but low sensitivity (43) for the diagnosis of disk herniation The reported low sensitivity of diskography images (unassociated with CT) to diagnose disk herniation is to be expected the purpose of the intradiskal injection being primarily the demonstration of an anular tear the contrast leaking through the tear only occasionally delineates an extruded fragment When a disk herniation has been diagnosed by other imaging modalities diskography allows to determine if the herniation is contained or noncontained (Figs 30 and 31) this information may have clinical relevance[ ]62 It also allows to establish if the displaced disk material is communicating or not with the parent disk and establishes the likelihood that it is sequestered or not There always remains a possibility that the contrast injected under pressure may reach a disk fragment that is nevertheless sequestered by leaking through the associated anular tear CT diskography also allows assessment in most cases of the integrity of the PLLC[ ]89 The superior sensitivity of diskography over MR imaging to demonstrate anular tears has been well established[ ]27 [ ]44 [ ]48 [ ]64 [ ]77 [ ]91 [ ]94 The presence of a radial tear and the inflammatory reaction it creates may be symptomatic despite the absence of true disk herniation[ ]29 [ ]48 [ ]49 [ ]69

Figure 29 L4-L5 CT diskogram demonstrating a large left posterolateral radial anular tear associated with

a left foraminal and extraforaminal herniaton (same patient as in Figure 28) (Figure Not Available)

Figure 30 Contained posterior L4-L5 and L5-S1 disk herniations in a 57-year-old man demonstrated by diskography The L3-L4 disk is normal

Figure 31 Noncontained L4-L5 disk herniation in a 23-year-old woman Reflux of injected contrast is seen in the anterior epidural space above and below the disk space The L5-S1 disk also demonstrates incomplete anterior and posterior radial anular tears

SUMMARY

The absence of universal nomenclature standardization with respect to the definition of a disk herniation and its different categories especially regarding type and location is still a major problem that will only be overcome when major national or international scientific societies join efforts to support a particular scheme Meanwhile it is important to realize that the two models that are currently most used are based on a different perspective Trying to straddle the two by opposing for instance bulging disk and herniation is doomed to failure because this exercise defies formal logic MR imaging is currently the most accurate noninvasive imaging modality to diagnose a disk herniation and to determine its exact location The determination of some pathoanatomic characteristics of herniated disks (type and composition) may require the use of CT diskography or CT diskography

References

1 Albeck MJ Hilden J Kjaer L et al A controlled comparison of myelography computed tomography and magnetic resonance imaging in clinically suspected lumbar disc herniation Spine 20443-448 1995 Abstract 2 American Academy of Orthopedic Surgeons Glossary on Spinal Terminology Chicago American Academy of Orthopedic Surgeons 1981 3 Andersson GB Weinstein JN Disc herniation [editorial] Spine 211S 1996 Citation 4 Aprill C Bogduk N High-intensity zone A diagnostic sign of painful lumbar disc on magnetic resonance imaging Br J Radiol 65361-369 1992 Abstract 5 Birney TJ White JJ Jr Berens D et al Comparison of MRI and discography in the diagnosis of lumbar degenerative disc disease J Spinal Disord 5417-423 1992 Abstract 6 Bischoff RJ Rodriguez RP Gupta K et al A comparison of computed tomography-myelography magnetic resonance imaging and myelography in the diagnosis of herniated nucleus pulposus and spinal stenosis J Spinal Disord 6289-295 1993 Abstract 7 Bogduk N The innervation of the lumbar spine Spine 8286-293 1983 Abstract 8 Bogduk N Tynan W Wilson AS The nerve supply to the human lumbar intervertebral discs J Anat 13239-56 1981 Abstract 9 Bonneville JF La carte-image des hernies discales lombaires Rachis 2255-257 1990 10 Bonneville JF La topografia simbolica delle ernie discali lombari Riv Neuroradiol 5427-431 1992 11 Bonneville JF Plaidoyer pour une classification par limage des hernies discales lombaires La carte-image Rev Imag Med 2557-560 1990 12 Brant-Zawadzki M Jensen M Spinal nomenclature Spine 20388-390 1995 Abstract

13 Brant-Zawadzki MN Jensen MC Obuchowski N et al Interobserver and intraobserver variability in interpretation of lumbar disc abnormalities A comparison of two nomenclatures Spine 201257-1263 1995 Abstract 14 Breton G Is that a bulging disk a small herniation or a moderate protrusion [editorial] Can Assoc Radiol J 42318 1991 Citation 15 Czervionke LF Lumbar intervertebral disc disease Neuroimaging Clin North Am 3465-485 1993 16 Deyo RA Nonsurgical care of low back pain Neurosurg Clin North Am 2851-862 1991 17 Deyo RA Loeser JD Bigos SJ Herniated lumbar intervertebral disk Ann Intern Med 112598-603 1990 Abstract 18 Dorlands Illustrated Medical Dictionary ed 28 Philadelphia WB Saunders 1994 19 Fardon D Pinkerton S Balderston R et al Terms used for diagnosis by English speaking spine surgeons Spine 18274-277 1993 Citation 20 Fardon DF Herzog RJ Mink JH et al Nomenclature of Lumbar Disc Disorders Contemporary Concepts in Spine Care Rosemont IL North American Spine Society 1995 21 Fardon DF Herzog RJ Mink JH et al Nomenclature of lumbar disc disorders In Garfin S Vaccaro A (eds) Orthopedic Knowledge Update Spine Rosemont IL American Academy of Orthopedic Surgeons 1997 pp A3-A14 22 Forristall RM Marsh HO Pay NT Magnetic resonance imaging and contrast CT of the lumbar spine Comparison of diagnostic methods and correlation with surgical findings Spine 131049-1054 1988 Abstract 23 Fries JW Abodeely DA Vijungco JG et al Computed tomography of herniated and extruded nucleus pulposus J Comput Assist Tomogr 6874-887 1982 Abstract 24 Frymoyer JW Newberg A Pope MH et al Spine radiographs in patients with low-back pain An epidemiological study in men J Bone Joint Surg Am 661048-1055 1984 Abstract 25 Gospodarowicz M Benedet L Hutter RV et al History and international developments in cancer staging Cancer Prev Control 2262-268 1998 Abstract 26 Grenier N Greselle JF Vital JM et al Normal and disrupted lumbar longitudinal ligaments Correlative MR and anatomic study Radiology 171197-205 1989 Abstract 27 Gunzburg R Parkinson R Moore R et al A cadaveric study comparing discography magnetic resonance imaging histology and mechanical behavior of the human lumbar disc Spine 17417-426 1992 Abstract 28 Haughton VM Eldevik OP Magnaes B et al A prospective comparison of computed tomography and myelography in the diagnosis of herniated lumbar disks Radiology 142103-110 1982 Abstract

29 Haughton VM Lim TH An H Intervertebral disk appearance correlated with stiffness of lumbar spinal motion segments AJNR Am J Neuroradiol 201161-1165 1999 Abstract 30 Herzog RJ The radiologic assessment for a lumbar disc herniation Spine 2119S-38S 1996 Abstract 31 Jackson RP Becker GJ Jacobs RR et al The neuroradiographic diagnosis of lumbar herniated nucleus pulposus I A comparison of computed tomography (CT) myelography CT-myelography discography and CT-discography Spine 141356-1361 1989 Abstract 32 Jackson RP Cain JE Jr Jacobs RR et al The neuroradiographic diagnosis of lumbar herniated nucleus pulposus II A comparison of computed tomography (CT) myelography CT-myelography and magnetic resonance imaging Spine 141362-1367 1989 Abstract 33 Jarvik JG Haynor DR Koepsell TD et al Interreader reliability for a new classification of lumbar disk disease Acad Radiol 3537-544 1996 Abstract 34 Jensen MC Brant-Zawadzki MN Obuchowski N et al Magnetic resonance imaging of the lumbar spine in people without back pain N Engl J Med 33169-73 1994 Abstract 35 Kent DL Haynor DR Larson EB et al Diagnosis of lumbar spinal stenosis in adults A meta-analysis of the accuracy of CT MR and myelography AJR Am J Roentgenol 1581135-1144 1992 Abstract 36 Kieffer SA Sherry RG Wellenstein DE et al Bulging lumbar intervertebral disk Myelographic differentiation from herniated disk with nerve root compression AJR Am J Roentgenol 138709-716 1982 Abstract 37 Kieffer SA Stadlan EM Mohandas A et al Discographic-anatomical correlation of developmental changes with age in the intervertebral disc Acta Radiol 9733-739 1969 38 Kim KY Kim YT Lee CS et al MRI classification of lumbar herniated intervertebral disc Orthopedics 15493-497 1992 Abstract 39 Kornberg M Rechtine GR Dupuy TE Computed tomography in the diagnosis of a herniated disk at the L5-S1 level Spine 9433-436 1984 Abstract 40 Kramer MS Clinical Epidemiology and Biostatistics New York Springer-Verlag 1988 41 Landis JR Koch GG The measurement of observer agreement agreement for categorical data Biometrics 33159-174 1977 Abstract 42 Laredo JD Bossard P Vuillemin-Bodaghi Formes anatomo-radiologiques des hernies discales In Morvan G Deburge A Bard H et al (eds) Le Rachis Lombaire Degeneratif Montpellier Sauramps Medical 1998 pp 37-49 43 Lee SH Coleman PE Hahn FJ Magnetic resonance imaging of degenerative disk disease of the spine Radiol Clin North Am 26949-964 1988 Abstract 44 Linson MA Crowe CH Comparison of magnetic resonance imaging and lumbar discography in the diagnosis of disc degeneration Clin Orthop 160-163 1990

45 Marchand F Ahmed AM Investigation of the laminate structure of lumbar disc anulus fibrosus Spine 15402-410 1990 Abstract 46 Masaryk TJ Ross JS Modic MT et al High-resolution MR imaging of sequestered lumbar intervertebral disks AJR Am J Roentgenol 1501155-1162 1988 Abstract 47 Milette PC The proper terminology for reporting lumbar intervertebral disk disorders AJNR Am J Neuroradiol 181859-1866 1997 Citation 48 Milette PC Fontaine S Lepanto L et al Differentiating lumbar disc protrusions disk bulges and discs with normal contour but abnormal signal intensity Magnetic resonance imaging with discographic correlations Spine 2444-53 1999 Abstract 49 Milette PC Fontaine S Lepanto L et al Radiating pain to the lower extremities caused by lumbar disk rupture without spinal nerve root involvement AJNR Am J Neuroradiol 161605-1613 1995 Abstract 50 Milette PC Melancon D A reappraisal of lumbar discography Can Assoc Radiol J 33176-182 1982 51 Milette PC Melancon D Dupuis PR et al A simplified terminology for abnormalities of the lumbar disk Can Assoc Radiol J 42319-325 1991 Abstract 52 Milette PC Raymond J Fontaine S Comparison of high-resolution computed tomography with discography in the evaluation of lumbar disc herniations Spine 15525-533 1990 Abstract 53 Mink JH Deutsch AL Goldstein TB et al Spinal imaging and intervention 1998 Phys Med Rehabil Clin North Am 9343-380 1998 54 Mixter WJ Barr JS Rupture of the intervertebral disc with involvement of the spinal canal N Engl J Med 211210-234 1934 55 Modic MT Masaryk TJ Ross JS et al Imaging of degenerative disk disease Radiology 168177-186 1988 Citation 56 Modic MT Ross JS Obuchowski NA et al Contrast-enhanced MR imaging in acute lumbar radiculopathy A pilot study of the natural history Radiology 195429-435 1995 Abstract 57 Modic MT Steinberg PM Ross JS et al Degenerative disk disease Assessment of changes in vertebral body marrow with MR imaging Radiology 166193-199 1988 58 Morvan G Mathieu P Les stenoses laterales In Morvan G Deburge A Bard H et al (eds) Le Rachis Lombaire Degeneratif Montpellier Sauramps Medical 1998 pp 315-324 59 Murray RO Skeletal trauma Regional In Sutton D (ed) Textbook of Radiology and Imaging ed 3 New York Churchill Livingstone 1980 pp 210-231 60 Nachemson A Lumbar disc herniation Conclusions Acta Orthop Scand 64(suppl 251)49 1993 Citation

61 Nathan H Osteophytes of the vertebral column An anatomical study of their development according to age race and sex with consideration as to their etiology and significance J Bone Joint Surg Am 44243-268 1962 62 Nygaard OP Mellgren SI Osterud B The inflammatory properties of contained and noncontained lumbar disc herniations Spine 222584-2488 1997 Abstract 63 Ohshima H Hirano N Osada R et al Morphologic variation of lumbar posterior longitudinal ligament and the modality of disc herniation Spine 182408-2411 1993 Abstract 64 Osti OL Fraser RD MRI and discography of annular tears and intervertebral disc degeneration A prospective clinical comparison J Bone Joint Surg Br 74431-435 1992 Abstract 65 Palmgren T Gronblad M Virri J et al Immunohistochemical demonstration of sensory and autonomic nerve terminals in herniated lumbar disc tissue Spine 211301-1306 1996 Abstract 66 Resnick D Niwayama G Degenerative disease of the spine In Resnick D (ed) Diagnosis of Bone and Joint Disorders ed 3 Philadelphia WB Saunders 1995 pp 1372-1462 67 Resnick D Niwayama G Intravertebral disk herniations Cartilaginous (Schmorls) nodes Radiology 12657-65 1978 Abstract 68 Ross JS Modic MT Masaryk TJ Tears of the anulus fibrosus Assessment with Gd-DTPA-enhanced MR imaging AJR Am J Roentgenol 154159-162 1990 Abstract 69 Saal JS The role of inflammation in lumbar pain Spine 201821-1827 1995 Abstract 70 Sachs BL Vanharanta H Spivey MA et al Dallas discogram description A new classification of CTdiscography in low-back disorders Spine 12287-294 1987 Abstract 71 Sauser DD Goldman AB Kaye JJ Discogenic vertebral sclerosis J Can Assoc Radiol 2944-50 1978 Abstract 72 Schellhas KP Pollei SR Gundry CR et al Lumbar disc high-intensity zone Correlation of magnetic resonance imaging and discography Spine 2179-86 1996 Abstract 73 Schellinger D Manz HJ Vidic B et al Disk fragment migration Radiology 175831-836 1990 Abstract 74 Schipper J Kardaun JW Braakman R et al Lumbar disk herniation Diagnosis with CT or myelography Radiology 165227-231 1987 Abstract 75 Schmorl G Junghanns H The Human Spine in Health and Disease ed 2 New York Grune and Stratton 1971 76 Silverman CS Lenchik L Shimkin PM et al The value of MR in differentiating subligamentous from supraligamentous lumbar disk herniations AJNR Am J Neuroradiol 16571-579 1995 Abstract 77 Simmons JW Emery SF McMillin JN et al Awake discography A comparison study with magnetic

resonance imaging Spine 16S216-221 1991 Abstract 78 Smyth MJ Wright V Sciatica and the intervertebral disc J Bone Joint Surg Am 401401-1418 1958 79 Taveras JM Radiologic aspects of low back pain and sciatic syndromes [editorial] AJNR Am J Neuroradiol 9351-358 1989 80 Tehranzadeh J Discography 2000 Radiol Clin North Am 36463-495 1998 Full Text 81 Thelander U Fagerlund M Friberg S et al Describing the size of lumbar disc herniations using computed tomography A comparison of different size index calculations and their relation to sciatica Spine 191979-1984 1994 Abstract 82 Thornbury JR Fryback DG Turski PA et al Disk-caused nerve compression in patients with acute low-back pain Diagnosis with MR CT myelography and plain CT Radiology 186731-738 1993 Abstract 83 Twomey L Taylor J Age changes in lumbar intervertebral discs Acta Orthop Scand 56496-499 1985 Abstract 84 Twomey LT Taylor JR Age changes in lumbar vertebrae and intervertebral discs Clin Orthop 22497-104 1987 85 Williams AL CT diagnosis of degenerative disc disease The bulging annulus Radiol Clin North Am 21289-300 1983 Abstract 86 Williams AL Haughton VM Meyer GA et al Computed tomographic appearance of the bulging annulus Radiology 142403-408 1982 Abstract 87 Williams AL Haughton VM Syvertsen A Computed tomography in the diagnosis of herniated nucleus pulposus Radiology 13595-99 1980 Abstract 88 Wiltse LL Berger PE McCulloch JA A system for reporting the size and location of lesions in the spine Spine 221534-1537 1997 Abstract 89 Wiltse LL Fonseca AS Amster J et al Relationship of the dura Hofmanns ligaments Batsons plexus and a fibrovascular membrane lying on the posterior surface of the vertebral bodies and attaching to the deep layer of the posterior longitudinal ligament An anatomical radiologic and clinical study Spine 181030-1043 1993 Abstract 90 Yamashita K Hiroshima K Kurata A Gadolinium-DTPA-enhanced magnetic resonance imaging of a sequestered lumbar intervertebral disc and its correlation with pathologic findings Spine 19479-482 1994 Abstract 91 Yu SW Haughton VM Sether LA et al Comparison of MR and diskography in detecting radial tears of the anulus A postmortem study AJNR Am J Neuroradiol 101077-1081 1989 Abstract 92 Yu SW Sether LA Ho PS et al Tears of the anulus fibrosus Correlation between MR and pathologic findings in cadavers AJNR Am J Neuroradiol 9367-370 1988 Abstract

93 Yussen PS Swartz JD The acute lumbar disc herniation Imaging diagnosis Semin Ultrasound CT MR 14389-398 1993 Abstract 94 Zucherman J Derby R Hsu K et al Normal magnetic resonance imaging with abnormal discography Spine 131355-1359 1988 Abstract

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  • CLASSIFICATION DIAGNOSTIC IMAGING AND IMAGING CHARACTERIZATION OF A LUMBAR HERNIATED DISK
    • IMAGING OF LOW BACK PAIN I
      • CLASSIFICATION DIAGNOSTIC IMAGING AND IMAGING CHARACTERIZATION OF A LUMBAR HERNIATED DISK
        • DEFINITION OF A DISK HERNIATION
        • CLASSIFICATION OF A HERNIATED LUMBAR DISK
          • Main Categories of Noninfectious Disk Abnormalities
          • Further Qualifying the Displaced Disk Material Beyond the Disk Space
            • DIAGNOSTIC IMAGING AND CHARACTERIZATION OF A HERNIATED LUMBAR DISK
              • Conventional Radiographs
              • Myelography
              • CT
              • CT Myelography
              • MR Imaging
              • Diskography and CT Diskography
                • SUMMARY
                  • References
Page 4: CLASSIFICATION, DIAGNOSTIC IMAGING, AND IMAGING ... · PDF fileclassification, diagnostic imaging, and imaging characterization of a lumbar herniated disk ... classification, diagnostic

radiating pain neurologic deficit[ ]47 Although useful for patient management this model is not adequate for imaging study interpretation A useful nomenclature needs to propose categories based on observable distinctions that take into consideration the limitations of present-day imaging techniques

Main Categories of Noninfectious Disk Abnormalities

Ideally a valid and useful system for classifying noninfectious disk abnormalities should provide categories that correspond to real anatomic and pathologic entities and if possible correspond to specific clinical situations The system should be applicable to all currently used imaging modalities It should be simple to understand to memorize and to teach It should also be reliable and generate substantial intraobserver and interobserver agreement in terms of Kappa statistics[ ]41 The nomenclature to describe disk lesions demonstrated by imaging studies has been greatly influenced by our concepts of disk degeneration throughout life (ie what is normal aging) and our understanding of what constitutes a disk lesion likely to generate clinical signs and symptoms The nomenclature we favor is directly related to our physiopathologic model The clinical concept that followed the description by Mixter and Barr[ ]54 of herniation of the nucleus pulposus through a ruptured anulus fibrosus was that should this occur in a posterior or posterolateral direction and encroach on the neural canal cord or nerve root compression may result with consequent segmental root pain and muscle spasm[ ]59 Because compression of neural structures was believed to be the only logical explanation for pain associated or not with a neurologic deficit imaging strategies have been developed over the last 20 years with a clear focus on identifying displacement of disk material associated with compression of neural structures[ ]28 [ ]31 [ ]32 [ ]36 [ ]74 [ ]82 [ ]86 [ ]87 Classifications of disk abnormalities that were associated with this concept have obviously been influenced by this bias In the early 1980s for the interpretation of myelograms and the first generation of high-resolution CT of the spine a very simple terminology was proposed that had essentially three categories (1) the normal disk (2) the bulging disk without nerve root compression and (3) the herniated disk with nerve root compression[ ]36 [ ]85 The definition of disk herniation was very restrictive because nerve root compression was considered by some investigators a sine qua non condition to make the diagnosis This requirement appeared acceptable however because it was estimated that only 10 of herniations occurred in a posterior central direction[ ]42 [ ]87

The validity of this model has been questioned in recent years and nerve root compression has been found less important than inflammation in the genesis of painful symptoms[ ]78 This relatively new concept has led to the development of two nomenclature models based on very different perspectives

The Morphologic Model

This model is essentially based on one parameter the assessment of the disk contour to determine the degree of disk extension beyond the interspace (DEBIT) [ ]13 The categories are normal disk bulging disk protrusion and extrusion (Fig 1) (Figure Not Available) Normal indicates no disk extension beyond the interspace Bulge refers to circumferential symmetric DEBIT (around the end plates) Protrusion indicates focal or

asymmetric DEBIT into the canal the base against the parent disk broader than any other diameter of the protrusion Extrusion means focal obvious DEBIT the base against the parent disk narrower than any diameter of the extruding material itself or no connection between displaced disk material and parent disk The use of the term herniation to designate collectively protrusions and extrusions has been suggested[ ]15 but maintaining the distinction may have some clinical relevance because extrusions are rarely found in asymptomatic individuals as opposed to protrusions and bulges[ ]34 It has also been argued that the term extruded disk is less frightening and emotionally laden than disk herniation or ruptured disk[ ]17 This classification is based on very simple geometric concepts and the categories are mutually exclusive but the line drawings in Figure 1 (Figure Not Available) are misleading because they represent the disk as a two-dimensional structure Disk extrusions such as the one depicted are practically never seen at the disk level on CT or MR imaging axial sections large posterior displacement of disk material beyond the margins of the intervertebral space still generally creates images corresponding to the definition of a protrusion because they are outlined by the posterior longitudinal ligament (Fig 2) Significant migration of disk material is usually necessary to generate a typical extrusion image Distinction between protrusions and extrusions at the disk level is very often only possible on sagittal sections (Fig 3) and this distinction is not very practical for the interpretation of CT because sagittal reconstructions are usually not part of the routine imaging protocol On CT or MR imaging this distinction is difficult in the presence of a narrow central spinal canal and very often impossible for foraminal herniations (Fig 4)

Figure 1 (Figure Not Available) Morphologic nomenclature based on the assessment of the disk contour (From Milette PC The proper terminology for reporting lumbar intervertebral disk disorders AJNR Am J Neuroradiol 181859-1866 1997 with permission)

Figure 2 Axial CT scan section through the L4-L5 disk space showing a relatively large posterior right central displacement of disk material with dural sac compression and probable right L5 nerve root compression Although the overlying posterior longitudinal ligament complex (PLLC) is not seen it constrains the displaced disk material and is responsible for maintaining a protrusion shape

Figure 3 When a relatively large amount of disk material is displaced distinction between protrusion (A) and extrusion (B or C) will generally only be possible on sagittal MR sections or sagittal CT scan reconstructions In C although the shape of the displaced material is similar to that of a protrusion the greatest cranio-caudal diameter of the fragment is greater than the craniocaudal diameter of its base at the level of the parent disk and the lesion therefore qualifies as an extrusion

Figure 4 Axial CT scan section through the upper portion of the L4-L5 foramina in a 45-year-old man Abnormal soft tissues likely representing displaced disk material are seen in the right foramen The material cannot be precisely delineated and the distinction between protrusion and extrusion is difficult A typical extrusion shape is practically never seen with foraminal herniations

Despite its apparent simplicity only moderate interobserver agreement has been reported using this nomenclature in three independent studies[ ]13 [ ]33 [ ]48 It is also incomplete because it considers exclusively the contour of the disk and the shape of the displaced disk material Disks demonstrating normal contour but abnormal central or peripheral signal patterns have no place in this system and associated vertebral body bone marrow changes are completely ignored even though the clinical relevancy of those changes has been well demonstrated[ ]4 [ ]48 [ ]55 [ ]57 [ ]72 This nomenclature is unfortunately misleading because it creates artificial pathologic entities The bulging disk category is the most problematic[ ]60 Obviously a severely dessicated and atrophic disk may bulge diffusely as the intervertebral space narrows with buckling of the anterior and posterior longitudinal

ligaments But an impression has been unjustifiably derived from early postmortem studies[ ]86 that even in young individuals a disk with an intact anulus may be responsible for a detectable bulge on axial CT sections It has also been hypothesized that bulging disks are caused by diffuse anular hyperlaxity which occurs as a result of tears in collagen bridges between the concentric anular fibers while these concentric fibers remain intact[ ]15 This theory has never been proved because such collagen bridges between the concentric fibers of the anulus have never been found[ ]45 It is important to realize that a bulging disk is not an anatomic or pathologic entity it is an image that requires a differential diagnosis It sometimes represents a normal anatomic variant this is often the case with the L5-S1 disk On CT images it is often an illusion caused by a volume-averaging effect (Fig 5) It may be associated with remodeling of adjacent vertebral bodies because of osteoporosis (Fig 6) It may of course result from chronic disk deterioration and collapse A bulging disk illusion is often created on CT by a posterior anular disk rupture with displaced disk material peeling off the posterior longitudinal ligament and displacing it backward creating a posterior wide base protrusion that mimics diffuse symmetric disk bulging on both axial CT and MR imaging sections and is not differentiated from a bulging disk on sagittal MR images unless close attention is paid to the anterior aspect of the disk (Fig 7) Except for the fact that extrusions are rarely found in asymptomatic individuals[ ]34 this system does not really provide categories that correspond to clinical entities

Figure 5 A Bulging disk appearance of the L4-L5 disk shown on a 5-mm-thickness axial CT scan section in a 57-year-old woman The height of the intervertebral space was preserved and there was no reactive vertebral body end-plate modifications This aspect is probably partly due to vertebral body remodeling caused by osteoporosis but is mostly created by volume averaging (From Milette PC Fontaine S Daniels C et al Imaging of Low Back Pain CD-ROM SSB Multimedia Medical Series Montreal 1997 with permission) B Using 4- or 5-mm-thickness CT sections an intermediate gray shade halo is often computer generated by volume averaging of tissues with different attenuation coefficients in voxels represented by two-dimensional pixels located at the disk space periphery This creates the illusion of a three-dimensional image demonstrating diffuse disk bulging ST = slice thickness

Figure 6 Axial CT scan section of a L4-L5 disk in a 78-year-old man demonstrating diffuse disk bulging caused by remodeling of the adjacent vertebral bodies due to osteoporosis The intervertebral space was normal in height and there were no reactive adjacent bony endplate modifications

Figure 7 A T2-weighted axial section of a L5-S1 disk showing a left posterolateral wide base protrusion that can be easily confused with diffuse circumferential bulging B Corresponding T2-weighted left paracentral and central sagittal sections demonstrating loss of the L5-S1 disk signal intensity with posterior small left-central protrusion the anterior aspect of the disk does not extend beyond the endplates and therefore such a disk should not be labeled bulging disk

The Pathoanatomic Model

As opposed to the previous model that can be applied only to the interpretation of CT and MR imaging studies this model can be used for the interpretation of all imaging modalities including plain films and diskograms[ ]47 [ ]51 It consists of five categories that are not mutually exclusive so that different combinations are possible (Fig 8) (Figure Not Available) The first three refer to the general state of the disk (1) normal young disk (2) normal aging disk and (3) deteriorated disk (formerly called the scarred disk) The last two refer to localized lesions anular tear and herniated disk In this model the previously discussed definition of disk herniation proposed by Herzog[ ]30 is applicable The use of this system requires an effort to distinguish the normal aging changes from those of pathologic degeneration Resnick and Niwayama[ ]66 have emphasized the differentiating features of two degenerative processes involving the intervertebral disk which had been previously described by Schmorl and Junghanns[ ]75 (1) spondylosis deformans which affects primarily the anulus fibrosus and bony ring epiphysis and (2) intervertebral osteochondrosis which affects essentially the nucleus pulposus and the vertebral body end plates

Figure 8 (Figure Not Available) Schematic representation of a nomenclature based on a three-dimensional assessment of the anatomic and pathologic characteristics of both disk and adjacent vertebral bodies The categories are not mutually exclusive and some combinations are possible A Categories related to the general aspect of the disk normal young disk (a) normal aging disk (b) deteriorated disk (c) B Categories related to local lesions normal young disk (a) anular tear (b) herniated disk (c) (Adapted from Milette PC The proper terminology for reporting lumbar intervertebral disk disorders AJNR Am J Neuroradiol 181859-1866 1997 with permission)

There is convincing evidence in the scientific literature that the features of spondylosis deformans represent the normal aging process whereas intervertebral osteochondrosis denotes true pathologic disk degeneration[ ]61 [ ]71 [ ]75 [ ]83 [ ]84 Schmorl and Junghanns[ ]75 found spondylotic changes in 60 of women and almost 80 of men over the age of 50 In a series of 400 dried skeletons Nathan[ ]61 found anterior vertebral body osteophytes which constitute the main feature of spondylosis deformans in 100 of individuals over age 40 whereas posterior osteophytes were found in only 39 of individuals even after the age of 80 Twomey and Taylor[ ]83 [ ]84 have found that loss of disk height is unusual in a normal aging population and that loss of stature in the elderly is attributable to loss of intervertebral body height rather than loss in disk height During the normal aging process the mucoid matrix of the nucleus pulposus is progressively replaced by fibrous tissue[ ]37 but the intervertebral height is preserved and the disk margins remain regular Dessication and thining of disks or disks that bulge like an underinflated automobile tire are not typical of elderly spines Slight symmetric bulging may occur if there has been vertebral body remodeling resulting from osteoporosis Small amounts of gas can be detected on plain films or CT images near the insertion of the anulus on the ring epiphysis and this gas is probably located in transverse anular tears adjacent to the ring epiphysis During the fourth decade anterior and lateral marginal vertebral body osteophytes constitute normal findings comparable with having gray hair but end plate erosions with osteosclerosis or chronic reactive bone marrow changes type 2 or 3 as described by Modic et al[ ]57 should not be seen Slight to moderate decrease in central signal intensity can be detected on T2-weighted MR images as part of the normal aging process but the changes should involve uniformly all lumbar disks

Deteriorated disks represent real pathologic degeneration which is sometimes referred to as chronic diskopathy On microscopic examination they show total structural disorganization and general replacement of normal disk material by scar tissue For this reason they were initially labeled scarred disks by the members of a joint committee on spinal nomenclature created by the Quebec Association of Radiologists[ ]14 Because of possible confusion with postoperative changes the term deteriorated disk has been proposed as an acceptable substitute Strictly speaking the term degeneration could be used to designate this entity but this latter term has such a broad nonspecific meaning that it is best avoided The deteriorated disk is characterized by narrowing of the intervertebral space irregular disk contour generally associated with symmetric or asymmetric bulging abundant presence of gas in the central portion of the intervertebral disk space multidirectional osteophytes that do not respect the central spinal canal or the foramina end plate erosions with reactive osteosclerosis and chronic bone marrow changes On T2-weighted MR images the central disk signal intensity is usually markedly decreased and the number of affected lumbar disks is variable Even though transverse concentric and radial anular tears have been identified on postmortem specimens[ ]92 the anular tear category in this model refers essentially to the radial tears that are generally demonstrated by diskography in symptomatic patients For a more precise description of those tears this model may be supplemented by the Dallas Discogram Description system[ ]70 with or without its recently proposed updates[ ]4 [ ]72 [ ]80

It should be emphasized that the pathoanatomic model is not based on direct identification of a particular geometric pattern but on the anatomy and pathology that are expected as a result of the analysis of specific criteria Using this model the conclusion of any imaging report does not consist of terms related to the shape of the disk contour or the displaced disk material but on a pathologic diagnosis that should be presented with an appropriate confidence level (possible probable or definite) The diagnosis of a probable major radial anular tear may be inferred from the presence of a definite central signal intensity loss because as a result of diskographic MR imaging correlations the positive predictive value of this sign has been estimated at 96[ ]48 The use of this model requires an effort to understand the criteria allowing differentiation of normal aging from true pathologic degeneration so this system is slightly more complicated than the morphologic model Its reliability has never been tested Some intraobserver or interobserver disagreement would probably occur trying to distinguish anular tears without herniation from anular tears with small herniations With respect to correspondance to clinical situations this scheme like the morphologic model has limited interest it has been shown that disks demonstrating the features of the deteriorated disk are likely to be responsible for symptoms but this relationship has been statistically established to be significant only for the L4-L5 disk[ ]24

Which Model Should Be Used

In other areas of diagnostic radiology the aim of image analysis is always to predict what the pathologist would find if he or she could be provided with an adequate specimen immediately following the imaging study radiologic diagnoses are presented with a pathologic perspective There is no reason why the reporting of disk disorders should be

any different Terms like bulging disk are meaningless to a pathologist and I personally favor the pathoanatomic model Nomenclature standardization however is not a task that can be achieved by an individual or even a single group of authors[ ]12 To have any impact recommendations have to emanate from well established national or international societies The multiplicity of scientific societies with an interest in the spine all over the world creates a special problem but new joint committees have recently been set up combining efforts to come up with a practical unified system that it is hoped could be proposed jointly by the North American Spine Society the American Academy of Orthopedic Surgeons the American Academy of Neurological Surgeons the American Society of Spine Radiology and the American Society of Neuroradiology Agreeing in North America on a classification of disk disorders that could gain universal acceptance like the TNM classification of neoplastic diseases would be a major achievement Meanwhile the choice of the nomenclature is up to the best judgement of each practicing radiologist and the essential issue in a given hospital or community practice remains clear communication between radiologists and referring physicians by way of a local agreement as to the meaning of words

A major problem frequently occurs because observers of imaging studies try to combine elements of the morphologic classification with those of the pathoanatomic classification Trying to differentiate a bulging disk (morphologic qualifier) from a disk herniation (pathologic diagnosis) cannot work because a bulging disk aspect is a common feature of the aging disk the deteriorated disk and some posterior central disk herniations (Fig 9) Trying to make the distinction is doomed to failure because it defies formal logic On the other hand it is theoretically possible to differentiate a radial anular tear (without herniation) from a disk herniation because these are two different pathologic entities although one may be the continuum of the other It is best to adopt either one of the two systems and avoid trying to straddle the two A general classification of disk disorders attempting to conciliate the morphologic and the pathoanatomic model is proposed in Table 1

Figure 9 A bulging disk aspect often conceals a posterior central herniation A Complete rupture of the outer anular fibers allowing nuclear material to escape and peel off the posterior longitudinal ligament (and sometimes a few intact peripheral anular fibers) from the torn disk creating a detectable focal or asymmetric extension of the disk margin beyond the interspace which qualifies as a protrusion B With more gelatinous nuclear material escaping underneath the rigid posterior longitudinal ligament the focal bulge is no longer detectable as its radius increases and if the tear occurs in the posterior midline or para-medial direction the aspect mimics symmetric disk extension beyond the interspace C Since in most cases only the outline of a diffusely hypointense disk is perceived on MR images this creates the illusion of circumferential disk bulging on axial sections D The real nature of a bulging disk of this type may be suspected by scrutinizing the sagittal sections and appreciating that unless one is dealing with a chronically degenerated scarred disk the bulge is not symmetric but limited to the posterior aspect of the disk

TABLE 1 -- GENERAL

CLASSIFICATION OF DISK LESIONS Normal (excluding aging changes)

Congenitaldevelopmental variants

Inflammationinfection

Neoplasia

Degenerativetraumatic

Degeneration

Anular tear

Herniation Protrusion

Extrusion

Degeneration Spondylosis deformans

Intervertebral osteochondrosis

Further Qualifying the Displaced Disk Material Beyond the Disk Space

Regardless of the basic system that is used the type of herniation should be assessed The volume and location of the displaced disk material beyond the normal peripheral margin of the intervertebral space also need to be specified In certain cases it is also possible to determine the composition of this material For the sake of simplicity the term herniation is used consistently in the remainder of this article to refer to all displaced disk material but what is discussed can also be applied to protrusions and extrusions if one wants to use the morphologic nomenclature

Type of Herniation

Upward or downward migration of nuclear material may occur through a break in a vertebral body end plate creating an intravertebral herniation sometimes referred to as an intraspongy herniation or a Schmorls node[ ]67 (Fig 10) Although a herniation occurring in any horizontal direction is likely to cause symptoms because of the presence of pain-sensitive nerve endings in the outer anulus[ ]7 [ ]8 [ ]65 herniations occurring in a posterior or posterolateral direction deserve special consideration because of the added possibility of dural sac or individual nerve root compression

Figure 10 Various types of intravertebral herniations (Schmorls nodes) A Intravertebral herniation through the inferior end plate of the L3 vertebral body demonstrated by diskography in a 35-year-old man suffering from chronic low back pain The patients typical pain was reproduced during injection and the lesion was considered responsible for the patients symptoms B T2-weighted sagittal section demonstrating an intravertebral herniation through the inferior end plate of the L4 vertebral body in a 24-year-old woman presenting with chronic low back pain The high signal intensity of the lesion associated with the loss of normal central signal intensity of the parent disk suggests that the lesion is a bona fide acquired intraspongy herniation and not just a developmental defect C T2-weighted sagittal section demonstrating an intravertebral herniation through the inferior end plate of the L3 vertebral body (arrow) Because both the herniation and the parent disk show normal signal intensity the abnormality was

considered a probably asymptomatic developmental defect

Other characteristics of disk herniations have become relevant with the development of new therapeutic possibilities (eg chemonucleolysis and percutaneous diskectomy) The term sequestration is confusing and has often been used to indicate displacement of disk material away from the parent disk The term sequestered disk should be used restrictedly to designate a fragment of diskal tissue that has migrated from the disk space and has no connection by diskal tissue to the disk of origin[ ]20 [ ]21 [ ]42 Sequestration refers to loss of continuity with disk tissue still present in the intervertebral disk space The term migration has a broader meaning indicating displacement of disk material away from the edge of the rent in the outer anulus either in the central spinal canal at the disk level or above or below the disk level This difference is illustrated in Figure 11 The terms communicating and noncommunicating derive from a different perspective and are mostly used in the context of intradiskal therapeutic injections They refer to the interruption of the periphery of the disk allowing fluid injected into the disk to leak into the spinal canal and reach displaced disk material[ ]20 [ ]51 The terms contained and uncontained are unfamiliar to most radiologists in a contained herniation the displaced disk material is still covered by a few intact but distended outer anular fibers or by a capsule formed by outer anular fibers and the adherent posterior longitudinal ligament

Figure 11 Various types of posterior central herniations A Small subligamentous herniation (protrusion) without significant disk material migration B Subligamentous herniation with downward migration of disk material under the PLLC C Sub-ligamentous herniation with downward migration of disk material and sequestered fragment (arrow)

The terms subligamentous and extraligamentous (or transligamentous) refer to the position of the displaced disk material with respect to the posterior longitudinal ligament The anatomy of the posterior longitudinal ligament has been recently revised[ ]73 [ ]89 It is a membranous structure that has multiple components a deep layer attached to disks and vertebral bodies a superficial layer attached to the dura by fibrous tissue (Hoffmanns

ligament) and lateral extensions known as the lateral membranes or peridural membranes (Fig 12) (Figure Not Available) It should probably be referred to as the posterior longitudinal ligament complex (PLLC) It actually divides the epidural space into the perithecal space and the anterior epidural space where displaced disk material can be entrapped (Fig 13) A potential space allowing accumulation of displaced disk material has also been detected between the outer anular fibers and the deep fibers of the PLLC on the posterior central aspect of the disk[ ]63 Posterior midline herniations seldom rupture the PLLC and are generally subligamentous The lateral membranes are less resistant and transligamentous herniations are usually the result of posterior off-center herniations or posterolateral herniations

Figure 12 (Figure Not Available) The PLLC is portrayed here in relation to various types of subligamentous disk displacement At the disk level posteriorly displaced disk material frequently occupies the midline Below and above the disk an anterior epidural space (AES) exists between the PLLC and the posterior aspect of the vertebral bodies In this space disk fragment motion across the midline is curtailed by a sagittal midline septum (dashed line) A delicate translucent membrane (shown only on left side of drawing) is stretched between the free edge of the deep layer of the posterior longitudinal ligament and the lateral spinal canal (From Schellinger D Manz HJ Vidic B et al Disk fragment migration Radiology 175831-836 1990 with permission)

Figure 13 Relationship of typical posterior disk herniations with the PLLC A Midline sagittal section unless very large a posterior midline herniation usually remains entrapped underneath the deep layer of the PLL C and sometimes a few intact outer anulus fibers joining with the PLL C to form a capsule The deep layer of the PLL C (arrow) also attaches to the posterior aspect of the vertebral body so that no potential space is present underneath B Sagittal para-central section the PLL C extends laterally at the disk level (arrowhead) but above and below the disk an anterior epidural space (as) where disk fragments are frequently entrapped is present between the lateral (peridural) membranes and the posterior aspect of the vertebral bodies

Volume of Herniated Material

Quantifying the herniated disk material by measuring in millimeters its greatest diameter or by evaluating its cross-sectional area in square millimeters is rarely done The resulting figures could be misleading without relating this measurement to the size of the spinal canal and the exact location of the lesion[ ]88 A purely qualitative and subjective statement that a mild moderate or severe herniation is present however does not give the person reading the imaging report any indication as to the potential of the lesion to cause significant compression of the dural sac or individual exiting nerve roots A reasonably precise scheme has been proposed in 1995 by the Nomenclature Committee of the North American Spine Society[ ]20 Measurements are taken from an axial CT or MR imaging section at the site of most severe compromise canal compromise of less than 25 at that section is qualified as mild 25 to 75 is moderate 76 to 90 is moderately severe and greater than 90 is severe It is understood that such characterizations describe only the cross-sectional area at one level and do not account for the total volume of displaced material displacement of neural tissue or clinical significance The usefulness of having four categories is questionable and can likely generate poor interobserver or intraobserver agreement especially in situations where the central spinal canal is relatively narrow Bonnevilles scheme[ ]9 [ ]10 [ ]11 should generate greater reliability (Fig 14) (Figure Not Available) Separation of the cross-sectional area in three thirds can be applied to both the central spinal canal and the foramina It can be agreed by way of convention that the terms mild moderate and severe lumen compromise by a disk herniation designate extension of the displaced disk material in the anterior middle or posterior third of the central canal or foramen depending on the specified location of the herniation

Figure 14 (Figure Not Available) The size of the herniation in the horizontal plane is assessed and designated by the numbers 1 2 or 3 by establishing its extension in the anterior middle or posterior third of the spinal canal (From Bonneville JF Plaidoyer pour une classification par limage des hernies discales lombaires la carte-image Rev Imag Med 2557-560 1990 with permission)

Location of Herniated Material

Bonneville[ ]9 [ ]10 [ ]11 has also proposed an interesting and simple alpha-numerical system to classify according to their location the position of disk fragments that have migrated in the horizontal or sagittal plane (Figs 15 (Figure Not Available) and 16) (Figure Not Available) Using more precise anatomic boundaries unfortunately more familiar to surgeons than radiologists Wiltse et al[ ]88 have proposed another system which has been supported by the North American Spine Society[ ]20 [ ]21 Anatomic zones and levels are defined using the following anatomic landmarks medial edge of the articular facets medial lateral upper and lower border of the pedicles and coronal plane at the disk center On the horizontal plane (Fig 17) (Figure Not Available) these landmarks determine the bounderies of the central zone the subarticular zone the foraminal zone the extraforaminal zone and the anterior zone (anterior to the coronal plane at the center of the disk) In the sagittal plane they determine the boundaries of the diskal level the infrapedicular level the pedicular level and the suprapedicular level (Figs 18 (Figure

Not Available) and 19) (Figure Not Available) Radiologists interpreting axial CT or MR images may find it difficult to use the medial edge of the facets as the landmark that separates the central zone from the subarticular zone because the superior articular facets are generally not included in axial sections at the disk level The alternative is to use the expression posterolateral to designate collectively all posterior herniations that are not midline but do not extend into a foramen as was proposed by Bonneville[ ]9 [ ]10 [ ]11

Figure 15 (Figure Not Available) In the horizontal plane herniations are labeled midline (a) posterolateral (b) foraminal (c) and extra-foraminal (d) (From Bonneville JF Plaidoyer pour une classification par limage des hernies discales lombaires la carte-image Rev Imag Med 2557-560 1990 with permission)

Figure 16 (Figure Not Available) In the craniocaudal direction disk migration is labeled +1 +2 +3 or -1 -2 -3 by referring to the height of a vertebral body divided in thirds (From Bonneville JF Plaidoyer pour une classification par limage des hernies discales lombaires la carte-image Rev Imag Med 2557-560 1990 with permission)

Figure 17 (Figure Not Available) The anatomic zones identified on axial images The anterior zone (not shown) is delineated from the extraforaminal zone by an imaginary coronal line in the center of the vertebral body (From Wiltse LL Berger PE McCulloch JA A system for reporting the size and location of lesions in the spine Spine 221534-1537 1997 with permission)

Figure 18 (Figure Not Available) The anatomical levels identified on craniocaudal images (From Wiltse LL Berger PE McCulloch AJ A system for reporting the size and location of lesions in the spine Spine 221534-1537 1997 with permission)

Figure 19 (Figure Not Available) Coronal view of the main zones and levels (From Wiltse LL Berger PE McCulloch JA A system for reporting the size and location of lesions in the spine Spine 221534-1537 1997 with permission)

Composition of Herniated Material

Displaced disk material may consist of glycosaminoglycans type 1 or 2 collagen end plate cartilage and bone fragments avulsed from the ring epiphysis A reactive inflammatory reaction usually results in edematous tissue followed by granulation tissue which may undergo calcification (Fig 20) Necrotic and partially resorbed displaced disk material sometimes produces a large fluid-filled pouch distinguishable from the common high-intensity zone because of its size (Fig 21) or a gas-filled cavity generally in continuity with gas in the intervertebral space (Fig 22) [ ]42 These characteristics may be meaningful if intradiskal injection therapy is considered In imaging reports herniations exhibiting calcium deposits and those exhibiting replacement of disk material by gas or a relatively large fluid collection can be qualified as chronic herniations

Figure 20 A CT scan demonstration of a small posterior central L4-L5 calcified subligamentous herniation The resistant deep layer of the PLLC restrains displacement of the disk material in the posterior central direction and does not allow a detectable distortion of the disk contour In this particular case the presence of the calcification is actually the only evidence that a posterior midline anular tear and a small subligamentous herniation are present B Posterior right central and sub-articular L5-S1 calcified disk herniation in same patient Posterolateral herniations are generally more conspicuous than posterior midline herniations because the deep layer of the PLLC gets thinner away from the midline

Figure 21 Posterior central midline L4-L5 herniation in a 52-year-old man demonstrated on a T2-weighted midline MR sagittal section There is intervertebral space narrowing with loss of normal central disk signal

intensity while the herniated disk material demonstrates high signal intensity consistent with a predominantly fluid consistency

Figure 22 CT scan demonstration in a 51-year-old woman of a left posterolateral L5-S1 disk hernation consisting essentially in a gas-filled pouch (white arrow) Gas is also present in the central portion of the intervertebral disk space (black arrow)

DIAGNOSTIC IMAGING AND CHARACTERIZATION OF A HERNIATED LUMBAR DISK

Assessing the validity of the currently used imaging procedures to diagnose a herniated lumbar disk is not an easy endeavor The validity of a measurement is the extent to which it corresponds to the true biologic value or some accepted gold standard[ ]40 With the exception of postmortem studies evaluation of the pathoanatomy by the surgeon in the operating room has always been considered the gold standard but this does not constitute an ideal situation Inspection of the disk through a small laminectomy incision to determine for instance if nuclear fragments lie within or outside the anular fibers may not be very reliable Also unbiased intraoperative determination of a normal degenerated or herniated disk in a patient with sciatica may also be difficult[ ]86 Because the validity of diskography has been previously established by postmortem studies and surgical correlations[ ]48 it is sometimes used as a gold standard in situations where no surgery has been performed

Conventional Radiographs

Lumbar disk herniations can exceptionally be diagnosed directly on good quality lateral projections because the x-ray attenuation is slightly greater in displaced disk material than in epidural fat Occasionally a calcified rim outlines the displaced disk fragment

(Fig 23) In most situations however narrowing of an intervertebral disk space in the absence of other evidence of chronic diskopathy is the only detectable sign suggesting the presence of a disk herniation To my knowledge the sensitivity and specificity of this sign has never been assessed The accepted rule of thumb is that the height of a given lumbar intervertebral disk space should always be slightly greater than the height of the above located interspace This rule does not apply to the transition disk immediately above the sacrum (usually L5-S1) The specificity of this sign is probably quite high but a few false-positives are seen especially at the L4-L5 level because of minor congenital hypoplasia The presence of posterior or foraminal vertebral body osteophytes associated or not with disk space narrowing is a definite sign of a chronic disk herniation

Figure 23 A Chronic left L3-L4 extraforaminal disk hernation in a 54-year-old man suspected on an AP radiograph demonstrating a calcified shell on the left side of the intervertebral disk space (white arrow) B Axial CT scan section confirming the diagnosis of a chronic extraforaminal L3-L4 herniation

Myelography

Myelography is essentially an exploration of the subarachnoid space Disk herniations are demonstrated only indirectly because they can cause thecal sac deformity and individual nerve root sleeve filling defects (Fig 24) Of all the special imaging procedures

myelography is the only one that allows upright projections with full weight bearing It is not unusual to demonstrate in this way small posterior central or posterolateral herniations that are undetectable on CT sections Interestingly the overall sensitivity of myelography to detect disk herniations has been found to be higher than that of CT whereas its specificity has been found to be lower[ ]74 In comparison with standard CT examination which usually includes only the three or four lower lumbar disks myelography easily allows coverage of the entire lumbar area and assessment of the intrathecal structures (cauda equina and conus medullaris) Far lateral foraminal herniations extraforaminal herniations and anterior herniations however are not detected The sensitivity for detection of posterior central L5-S1 herniations is also relatively poor because of the greater distance between the thecal sac and the posterior aspect of this particular disk

Figure 24 L5-S1 disk herniation in a 25-year-old man detected by indirect signs using lumbosacral myelography A Upright oblique projections showing a filling defect of the left S1 root sleeve (white arrow) suggesting significant nerve root compression by a left posterolateral disk hernation The right S1 root sleeve fills normally with contrast (black arrow) B Subtle compression of the anterior wall of the dural sac by displaced disk material (small arrows) demonstrated on upright lateral projection This sign is usually absent in the presence of a large amount of fat and venous structures in the anterior epidural compartment

CT

The sensitivity of CT to diagnose a herniation of the nucleus pulposus at the L5-S1 interspace is greater than that of myelography if images in the exact plane of the disk can be obtained[ ]23 [ ]39 Otherwise the superiority of plain CT over myelography to demonstrate disk herniations has not been established but CT has the distinct advantage of being

noninvasive and provides direct anatomic information[ ]23 Large herniations are easily detected but as explained previously the distinction between protrusions and extrusions is often difficult without sagittal reconstructions CT essentially allows an assessment of the contour of the disk The diagnosis of very small herniations in the absence of direct or indirect evidence of a radial tear is hazardous and associated with a high percentage of false-positives and false-negatives[ ]52 The diagnosis of moderate and large size herniations in different directions is usually possible but anterior herniations are rarely diagnosed not because they are not detectable but because observers pay little attention to the anterior contour of the disk (Fig 25) Because the PLLC cannot usually be identified the distinction of subligamentous from transligamentous herniation can only be suggested in most cases by the size of the herniated material A definite diagnosis of sequestration is rarely possible Calcifications within the displaced material are readily seen but may be difficult at times to differentiate from an accompanying osteophyte or an avulsed bone fragment from the vertebral body ring epiphysis (Fig 26) The presence of gas in the herniated material is easily detected

Figure 25 Anterior L4-L5 herniation demonstrated by CT scan in a 51-year-old woman with chronic low back pain Although sometimes quite conspicuous such herniations are rarely reported because observers pay little attention to the anterior contour of the disk

Figure 26 CT scan demonstration of a posterior right central L4-L5 disk herniation in a 38-year-old woman with avulsion of a bone fragment from the ring epiphysis and adjacent part of the superior L5 end plate Reactive osteosclerosis is seen around the vertebral body defect (arrows) suggesting a chronic lesion

CT Myelography

This association combines the advantages of both imaging modalities The fact that its accuracy has been reported as being less[ ]22 [ ]32 higher[ ]1 [ ]6 or equivalent[ ]82 to MR imaging is a reflection of the differences in technologic advancement and pathologic nomenclature that hamper valid comparisons between different studies

MR Imaging

Most reported studies establish MR imaging as the first choice modality to diagnose a herniated lumbar disk[ ]5 [ ]22 [ ]32 [ ]46 The associated intravenous injection of a paramagnetic agent has been found useful to demonstrate some anatomic features of disk disease in patients with no previous lumbar disk surgery[ ]56 [ ]68 [ ]90 MR imaging provides a better assessment of disk morphology than CT or CT myelography because sagittal sections are routinely obtained Assessment of foraminal involvement by displaced disk material is more accurate (Fig 27) and anterior disk herniations can be detected more easily than with CT or CT myelography If one is looking specifically for herniated lumbar disks associated with nerve root compression however it has been demonstrated that CT is equally accurate[ ]82 Alterations of the central or peripheral disk signal intensity on T2-weighted images are seen in most disks afflicted with an anular tear[ ]48 and alert the observer to scrutinize the disk contour in search for local modifications indicative of a herniation Because the signal of the displaced disk material is usually very similar to that of the outer anulus PLLC and vertebral body cortical bone small herniations are generally more conspicuous on axial CT sections than on corresponding axial MR imaging sections Gas and calcium deposits within the displaced fragment cannot usually

be detected but associated vertebral body bone marrow changes are typically seen and are helpful in differentiating acute from chronic processes[ ]57 The occasional presence of a high-intensity zone in the herniated material with an occasionally enhancing border after contrast injection is probably caused by a mixture of displaced nuclear material acute and subacute inflammatory tissue and neovascularized reactive tissue[ ]4 [ ]48 [ ]72 Contradictory reports have been published regarding the accuracy of MR imaging to differentiate subligamentous from transligamentous herniations[ ]26 [ ]38 [ ]73 [ ]76 Understanding the anatomy of the PLLC is helpful to make the distinction (Fig 28) (Figure Not Available) Masaryk et al[ ]46 have suggested that MR imaging is accurate to distinguish sequestered disks from other forms of lumbar disk herniations but most observers find this distinction difficult to establish[ ]42

Figure 27 A Left L4-L5 foraminal herniation well seen on an intermediate-weighted left parasagittal MR section (arrow) in a 47-year-old man B The lesion is much less obvious on intermediate-weighted (left) and T2-weighted (right) axial sections and was in fact more conspicuous on the corresponding CT scan section

Figure 28 (Figure Not Available) A Subligamentous disk herniation Left T1-weighted image demonstrating displaced disk material with a smooth outline imposed by the demarcation of the anterior epidural space (AES) by the lateral membrane of the PLLC Right Correlative drawing B Transligamentous disk herniation Left T1-weighted image of a large disk herniation (cervical in this case) which has ruptured through the posterior confines of the AES Penetration of the right lateral membrane can be observed (arrow) and the disk fragment contour is serrated Right Correlative drawing (From Schellinger D Manz HJ Vidic B et al Disk fragment migration Radiology 175831-836 1990 with permission)

Diskography and CT Diskography

During 30 years (1950 to 1980) when myelography was the only available imaging technique to demonstrate lumbar disk herniations diskography was an invasive but efficient way to demonstrate posterior central L5-S1 herniations and other large herniations (other than posterior central and paramedial) that could not be detected by myelography[ ]50 These herniations are now usually well demonstrated by CT and MR imaging Comparing the accuracy of five imaging modalities (excluding MR imaging) for the diagnosis of lumbar disk herniation Jackson et al[ ]31 found that CT diskography (Fig 29) was the most accurate test (87) compared with 77 for CT myelography 74 for CT 70 for myelography 64 for pain reproduction during diskography and 58 for diskography without CT Disk injection reproduced the patients clinical pain pattern in only 36 of herniated disks This clinical test isolated from the images had high specificity (89) but low sensitivity (43) for the diagnosis of disk herniation The reported low sensitivity of diskography images (unassociated with CT) to diagnose disk herniation is to be expected the purpose of the intradiskal injection being primarily the demonstration of an anular tear the contrast leaking through the tear only occasionally delineates an extruded fragment When a disk herniation has been diagnosed by other imaging modalities diskography allows to determine if the herniation is contained or noncontained (Figs 30 and 31) this information may have clinical relevance[ ]62 It also allows to establish if the displaced disk material is communicating or not with the parent disk and establishes the likelihood that it is sequestered or not There always remains a possibility that the contrast injected under pressure may reach a disk fragment that is nevertheless sequestered by leaking through the associated anular tear CT diskography also allows assessment in most cases of the integrity of the PLLC[ ]89 The superior sensitivity of diskography over MR imaging to demonstrate anular tears has been well established[ ]27 [ ]44 [ ]48 [ ]64 [ ]77 [ ]91 [ ]94 The presence of a radial tear and the inflammatory reaction it creates may be symptomatic despite the absence of true disk herniation[ ]29 [ ]48 [ ]49 [ ]69

Figure 29 L4-L5 CT diskogram demonstrating a large left posterolateral radial anular tear associated with

a left foraminal and extraforaminal herniaton (same patient as in Figure 28) (Figure Not Available)

Figure 30 Contained posterior L4-L5 and L5-S1 disk herniations in a 57-year-old man demonstrated by diskography The L3-L4 disk is normal

Figure 31 Noncontained L4-L5 disk herniation in a 23-year-old woman Reflux of injected contrast is seen in the anterior epidural space above and below the disk space The L5-S1 disk also demonstrates incomplete anterior and posterior radial anular tears

SUMMARY

The absence of universal nomenclature standardization with respect to the definition of a disk herniation and its different categories especially regarding type and location is still a major problem that will only be overcome when major national or international scientific societies join efforts to support a particular scheme Meanwhile it is important to realize that the two models that are currently most used are based on a different perspective Trying to straddle the two by opposing for instance bulging disk and herniation is doomed to failure because this exercise defies formal logic MR imaging is currently the most accurate noninvasive imaging modality to diagnose a disk herniation and to determine its exact location The determination of some pathoanatomic characteristics of herniated disks (type and composition) may require the use of CT diskography or CT diskography

References

1 Albeck MJ Hilden J Kjaer L et al A controlled comparison of myelography computed tomography and magnetic resonance imaging in clinically suspected lumbar disc herniation Spine 20443-448 1995 Abstract 2 American Academy of Orthopedic Surgeons Glossary on Spinal Terminology Chicago American Academy of Orthopedic Surgeons 1981 3 Andersson GB Weinstein JN Disc herniation [editorial] Spine 211S 1996 Citation 4 Aprill C Bogduk N High-intensity zone A diagnostic sign of painful lumbar disc on magnetic resonance imaging Br J Radiol 65361-369 1992 Abstract 5 Birney TJ White JJ Jr Berens D et al Comparison of MRI and discography in the diagnosis of lumbar degenerative disc disease J Spinal Disord 5417-423 1992 Abstract 6 Bischoff RJ Rodriguez RP Gupta K et al A comparison of computed tomography-myelography magnetic resonance imaging and myelography in the diagnosis of herniated nucleus pulposus and spinal stenosis J Spinal Disord 6289-295 1993 Abstract 7 Bogduk N The innervation of the lumbar spine Spine 8286-293 1983 Abstract 8 Bogduk N Tynan W Wilson AS The nerve supply to the human lumbar intervertebral discs J Anat 13239-56 1981 Abstract 9 Bonneville JF La carte-image des hernies discales lombaires Rachis 2255-257 1990 10 Bonneville JF La topografia simbolica delle ernie discali lombari Riv Neuroradiol 5427-431 1992 11 Bonneville JF Plaidoyer pour une classification par limage des hernies discales lombaires La carte-image Rev Imag Med 2557-560 1990 12 Brant-Zawadzki M Jensen M Spinal nomenclature Spine 20388-390 1995 Abstract

13 Brant-Zawadzki MN Jensen MC Obuchowski N et al Interobserver and intraobserver variability in interpretation of lumbar disc abnormalities A comparison of two nomenclatures Spine 201257-1263 1995 Abstract 14 Breton G Is that a bulging disk a small herniation or a moderate protrusion [editorial] Can Assoc Radiol J 42318 1991 Citation 15 Czervionke LF Lumbar intervertebral disc disease Neuroimaging Clin North Am 3465-485 1993 16 Deyo RA Nonsurgical care of low back pain Neurosurg Clin North Am 2851-862 1991 17 Deyo RA Loeser JD Bigos SJ Herniated lumbar intervertebral disk Ann Intern Med 112598-603 1990 Abstract 18 Dorlands Illustrated Medical Dictionary ed 28 Philadelphia WB Saunders 1994 19 Fardon D Pinkerton S Balderston R et al Terms used for diagnosis by English speaking spine surgeons Spine 18274-277 1993 Citation 20 Fardon DF Herzog RJ Mink JH et al Nomenclature of Lumbar Disc Disorders Contemporary Concepts in Spine Care Rosemont IL North American Spine Society 1995 21 Fardon DF Herzog RJ Mink JH et al Nomenclature of lumbar disc disorders In Garfin S Vaccaro A (eds) Orthopedic Knowledge Update Spine Rosemont IL American Academy of Orthopedic Surgeons 1997 pp A3-A14 22 Forristall RM Marsh HO Pay NT Magnetic resonance imaging and contrast CT of the lumbar spine Comparison of diagnostic methods and correlation with surgical findings Spine 131049-1054 1988 Abstract 23 Fries JW Abodeely DA Vijungco JG et al Computed tomography of herniated and extruded nucleus pulposus J Comput Assist Tomogr 6874-887 1982 Abstract 24 Frymoyer JW Newberg A Pope MH et al Spine radiographs in patients with low-back pain An epidemiological study in men J Bone Joint Surg Am 661048-1055 1984 Abstract 25 Gospodarowicz M Benedet L Hutter RV et al History and international developments in cancer staging Cancer Prev Control 2262-268 1998 Abstract 26 Grenier N Greselle JF Vital JM et al Normal and disrupted lumbar longitudinal ligaments Correlative MR and anatomic study Radiology 171197-205 1989 Abstract 27 Gunzburg R Parkinson R Moore R et al A cadaveric study comparing discography magnetic resonance imaging histology and mechanical behavior of the human lumbar disc Spine 17417-426 1992 Abstract 28 Haughton VM Eldevik OP Magnaes B et al A prospective comparison of computed tomography and myelography in the diagnosis of herniated lumbar disks Radiology 142103-110 1982 Abstract

29 Haughton VM Lim TH An H Intervertebral disk appearance correlated with stiffness of lumbar spinal motion segments AJNR Am J Neuroradiol 201161-1165 1999 Abstract 30 Herzog RJ The radiologic assessment for a lumbar disc herniation Spine 2119S-38S 1996 Abstract 31 Jackson RP Becker GJ Jacobs RR et al The neuroradiographic diagnosis of lumbar herniated nucleus pulposus I A comparison of computed tomography (CT) myelography CT-myelography discography and CT-discography Spine 141356-1361 1989 Abstract 32 Jackson RP Cain JE Jr Jacobs RR et al The neuroradiographic diagnosis of lumbar herniated nucleus pulposus II A comparison of computed tomography (CT) myelography CT-myelography and magnetic resonance imaging Spine 141362-1367 1989 Abstract 33 Jarvik JG Haynor DR Koepsell TD et al Interreader reliability for a new classification of lumbar disk disease Acad Radiol 3537-544 1996 Abstract 34 Jensen MC Brant-Zawadzki MN Obuchowski N et al Magnetic resonance imaging of the lumbar spine in people without back pain N Engl J Med 33169-73 1994 Abstract 35 Kent DL Haynor DR Larson EB et al Diagnosis of lumbar spinal stenosis in adults A meta-analysis of the accuracy of CT MR and myelography AJR Am J Roentgenol 1581135-1144 1992 Abstract 36 Kieffer SA Sherry RG Wellenstein DE et al Bulging lumbar intervertebral disk Myelographic differentiation from herniated disk with nerve root compression AJR Am J Roentgenol 138709-716 1982 Abstract 37 Kieffer SA Stadlan EM Mohandas A et al Discographic-anatomical correlation of developmental changes with age in the intervertebral disc Acta Radiol 9733-739 1969 38 Kim KY Kim YT Lee CS et al MRI classification of lumbar herniated intervertebral disc Orthopedics 15493-497 1992 Abstract 39 Kornberg M Rechtine GR Dupuy TE Computed tomography in the diagnosis of a herniated disk at the L5-S1 level Spine 9433-436 1984 Abstract 40 Kramer MS Clinical Epidemiology and Biostatistics New York Springer-Verlag 1988 41 Landis JR Koch GG The measurement of observer agreement agreement for categorical data Biometrics 33159-174 1977 Abstract 42 Laredo JD Bossard P Vuillemin-Bodaghi Formes anatomo-radiologiques des hernies discales In Morvan G Deburge A Bard H et al (eds) Le Rachis Lombaire Degeneratif Montpellier Sauramps Medical 1998 pp 37-49 43 Lee SH Coleman PE Hahn FJ Magnetic resonance imaging of degenerative disk disease of the spine Radiol Clin North Am 26949-964 1988 Abstract 44 Linson MA Crowe CH Comparison of magnetic resonance imaging and lumbar discography in the diagnosis of disc degeneration Clin Orthop 160-163 1990

45 Marchand F Ahmed AM Investigation of the laminate structure of lumbar disc anulus fibrosus Spine 15402-410 1990 Abstract 46 Masaryk TJ Ross JS Modic MT et al High-resolution MR imaging of sequestered lumbar intervertebral disks AJR Am J Roentgenol 1501155-1162 1988 Abstract 47 Milette PC The proper terminology for reporting lumbar intervertebral disk disorders AJNR Am J Neuroradiol 181859-1866 1997 Citation 48 Milette PC Fontaine S Lepanto L et al Differentiating lumbar disc protrusions disk bulges and discs with normal contour but abnormal signal intensity Magnetic resonance imaging with discographic correlations Spine 2444-53 1999 Abstract 49 Milette PC Fontaine S Lepanto L et al Radiating pain to the lower extremities caused by lumbar disk rupture without spinal nerve root involvement AJNR Am J Neuroradiol 161605-1613 1995 Abstract 50 Milette PC Melancon D A reappraisal of lumbar discography Can Assoc Radiol J 33176-182 1982 51 Milette PC Melancon D Dupuis PR et al A simplified terminology for abnormalities of the lumbar disk Can Assoc Radiol J 42319-325 1991 Abstract 52 Milette PC Raymond J Fontaine S Comparison of high-resolution computed tomography with discography in the evaluation of lumbar disc herniations Spine 15525-533 1990 Abstract 53 Mink JH Deutsch AL Goldstein TB et al Spinal imaging and intervention 1998 Phys Med Rehabil Clin North Am 9343-380 1998 54 Mixter WJ Barr JS Rupture of the intervertebral disc with involvement of the spinal canal N Engl J Med 211210-234 1934 55 Modic MT Masaryk TJ Ross JS et al Imaging of degenerative disk disease Radiology 168177-186 1988 Citation 56 Modic MT Ross JS Obuchowski NA et al Contrast-enhanced MR imaging in acute lumbar radiculopathy A pilot study of the natural history Radiology 195429-435 1995 Abstract 57 Modic MT Steinberg PM Ross JS et al Degenerative disk disease Assessment of changes in vertebral body marrow with MR imaging Radiology 166193-199 1988 58 Morvan G Mathieu P Les stenoses laterales In Morvan G Deburge A Bard H et al (eds) Le Rachis Lombaire Degeneratif Montpellier Sauramps Medical 1998 pp 315-324 59 Murray RO Skeletal trauma Regional In Sutton D (ed) Textbook of Radiology and Imaging ed 3 New York Churchill Livingstone 1980 pp 210-231 60 Nachemson A Lumbar disc herniation Conclusions Acta Orthop Scand 64(suppl 251)49 1993 Citation

61 Nathan H Osteophytes of the vertebral column An anatomical study of their development according to age race and sex with consideration as to their etiology and significance J Bone Joint Surg Am 44243-268 1962 62 Nygaard OP Mellgren SI Osterud B The inflammatory properties of contained and noncontained lumbar disc herniations Spine 222584-2488 1997 Abstract 63 Ohshima H Hirano N Osada R et al Morphologic variation of lumbar posterior longitudinal ligament and the modality of disc herniation Spine 182408-2411 1993 Abstract 64 Osti OL Fraser RD MRI and discography of annular tears and intervertebral disc degeneration A prospective clinical comparison J Bone Joint Surg Br 74431-435 1992 Abstract 65 Palmgren T Gronblad M Virri J et al Immunohistochemical demonstration of sensory and autonomic nerve terminals in herniated lumbar disc tissue Spine 211301-1306 1996 Abstract 66 Resnick D Niwayama G Degenerative disease of the spine In Resnick D (ed) Diagnosis of Bone and Joint Disorders ed 3 Philadelphia WB Saunders 1995 pp 1372-1462 67 Resnick D Niwayama G Intravertebral disk herniations Cartilaginous (Schmorls) nodes Radiology 12657-65 1978 Abstract 68 Ross JS Modic MT Masaryk TJ Tears of the anulus fibrosus Assessment with Gd-DTPA-enhanced MR imaging AJR Am J Roentgenol 154159-162 1990 Abstract 69 Saal JS The role of inflammation in lumbar pain Spine 201821-1827 1995 Abstract 70 Sachs BL Vanharanta H Spivey MA et al Dallas discogram description A new classification of CTdiscography in low-back disorders Spine 12287-294 1987 Abstract 71 Sauser DD Goldman AB Kaye JJ Discogenic vertebral sclerosis J Can Assoc Radiol 2944-50 1978 Abstract 72 Schellhas KP Pollei SR Gundry CR et al Lumbar disc high-intensity zone Correlation of magnetic resonance imaging and discography Spine 2179-86 1996 Abstract 73 Schellinger D Manz HJ Vidic B et al Disk fragment migration Radiology 175831-836 1990 Abstract 74 Schipper J Kardaun JW Braakman R et al Lumbar disk herniation Diagnosis with CT or myelography Radiology 165227-231 1987 Abstract 75 Schmorl G Junghanns H The Human Spine in Health and Disease ed 2 New York Grune and Stratton 1971 76 Silverman CS Lenchik L Shimkin PM et al The value of MR in differentiating subligamentous from supraligamentous lumbar disk herniations AJNR Am J Neuroradiol 16571-579 1995 Abstract 77 Simmons JW Emery SF McMillin JN et al Awake discography A comparison study with magnetic

resonance imaging Spine 16S216-221 1991 Abstract 78 Smyth MJ Wright V Sciatica and the intervertebral disc J Bone Joint Surg Am 401401-1418 1958 79 Taveras JM Radiologic aspects of low back pain and sciatic syndromes [editorial] AJNR Am J Neuroradiol 9351-358 1989 80 Tehranzadeh J Discography 2000 Radiol Clin North Am 36463-495 1998 Full Text 81 Thelander U Fagerlund M Friberg S et al Describing the size of lumbar disc herniations using computed tomography A comparison of different size index calculations and their relation to sciatica Spine 191979-1984 1994 Abstract 82 Thornbury JR Fryback DG Turski PA et al Disk-caused nerve compression in patients with acute low-back pain Diagnosis with MR CT myelography and plain CT Radiology 186731-738 1993 Abstract 83 Twomey L Taylor J Age changes in lumbar intervertebral discs Acta Orthop Scand 56496-499 1985 Abstract 84 Twomey LT Taylor JR Age changes in lumbar vertebrae and intervertebral discs Clin Orthop 22497-104 1987 85 Williams AL CT diagnosis of degenerative disc disease The bulging annulus Radiol Clin North Am 21289-300 1983 Abstract 86 Williams AL Haughton VM Meyer GA et al Computed tomographic appearance of the bulging annulus Radiology 142403-408 1982 Abstract 87 Williams AL Haughton VM Syvertsen A Computed tomography in the diagnosis of herniated nucleus pulposus Radiology 13595-99 1980 Abstract 88 Wiltse LL Berger PE McCulloch JA A system for reporting the size and location of lesions in the spine Spine 221534-1537 1997 Abstract 89 Wiltse LL Fonseca AS Amster J et al Relationship of the dura Hofmanns ligaments Batsons plexus and a fibrovascular membrane lying on the posterior surface of the vertebral bodies and attaching to the deep layer of the posterior longitudinal ligament An anatomical radiologic and clinical study Spine 181030-1043 1993 Abstract 90 Yamashita K Hiroshima K Kurata A Gadolinium-DTPA-enhanced magnetic resonance imaging of a sequestered lumbar intervertebral disc and its correlation with pathologic findings Spine 19479-482 1994 Abstract 91 Yu SW Haughton VM Sether LA et al Comparison of MR and diskography in detecting radial tears of the anulus A postmortem study AJNR Am J Neuroradiol 101077-1081 1989 Abstract 92 Yu SW Sether LA Ho PS et al Tears of the anulus fibrosus Correlation between MR and pathologic findings in cadavers AJNR Am J Neuroradiol 9367-370 1988 Abstract

93 Yussen PS Swartz JD The acute lumbar disc herniation Imaging diagnosis Semin Ultrasound CT MR 14389-398 1993 Abstract 94 Zucherman J Derby R Hsu K et al Normal magnetic resonance imaging with abnormal discography Spine 131355-1359 1988 Abstract

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  • CLASSIFICATION DIAGNOSTIC IMAGING AND IMAGING CHARACTERIZATION OF A LUMBAR HERNIATED DISK
    • IMAGING OF LOW BACK PAIN I
      • CLASSIFICATION DIAGNOSTIC IMAGING AND IMAGING CHARACTERIZATION OF A LUMBAR HERNIATED DISK
        • DEFINITION OF A DISK HERNIATION
        • CLASSIFICATION OF A HERNIATED LUMBAR DISK
          • Main Categories of Noninfectious Disk Abnormalities
          • Further Qualifying the Displaced Disk Material Beyond the Disk Space
            • DIAGNOSTIC IMAGING AND CHARACTERIZATION OF A HERNIATED LUMBAR DISK
              • Conventional Radiographs
              • Myelography
              • CT
              • CT Myelography
              • MR Imaging
              • Diskography and CT Diskography
                • SUMMARY
                  • References
Page 5: CLASSIFICATION, DIAGNOSTIC IMAGING, AND IMAGING ... · PDF fileclassification, diagnostic imaging, and imaging characterization of a lumbar herniated disk ... classification, diagnostic

asymmetric DEBIT into the canal the base against the parent disk broader than any other diameter of the protrusion Extrusion means focal obvious DEBIT the base against the parent disk narrower than any diameter of the extruding material itself or no connection between displaced disk material and parent disk The use of the term herniation to designate collectively protrusions and extrusions has been suggested[ ]15 but maintaining the distinction may have some clinical relevance because extrusions are rarely found in asymptomatic individuals as opposed to protrusions and bulges[ ]34 It has also been argued that the term extruded disk is less frightening and emotionally laden than disk herniation or ruptured disk[ ]17 This classification is based on very simple geometric concepts and the categories are mutually exclusive but the line drawings in Figure 1 (Figure Not Available) are misleading because they represent the disk as a two-dimensional structure Disk extrusions such as the one depicted are practically never seen at the disk level on CT or MR imaging axial sections large posterior displacement of disk material beyond the margins of the intervertebral space still generally creates images corresponding to the definition of a protrusion because they are outlined by the posterior longitudinal ligament (Fig 2) Significant migration of disk material is usually necessary to generate a typical extrusion image Distinction between protrusions and extrusions at the disk level is very often only possible on sagittal sections (Fig 3) and this distinction is not very practical for the interpretation of CT because sagittal reconstructions are usually not part of the routine imaging protocol On CT or MR imaging this distinction is difficult in the presence of a narrow central spinal canal and very often impossible for foraminal herniations (Fig 4)

Figure 1 (Figure Not Available) Morphologic nomenclature based on the assessment of the disk contour (From Milette PC The proper terminology for reporting lumbar intervertebral disk disorders AJNR Am J Neuroradiol 181859-1866 1997 with permission)

Figure 2 Axial CT scan section through the L4-L5 disk space showing a relatively large posterior right central displacement of disk material with dural sac compression and probable right L5 nerve root compression Although the overlying posterior longitudinal ligament complex (PLLC) is not seen it constrains the displaced disk material and is responsible for maintaining a protrusion shape

Figure 3 When a relatively large amount of disk material is displaced distinction between protrusion (A) and extrusion (B or C) will generally only be possible on sagittal MR sections or sagittal CT scan reconstructions In C although the shape of the displaced material is similar to that of a protrusion the greatest cranio-caudal diameter of the fragment is greater than the craniocaudal diameter of its base at the level of the parent disk and the lesion therefore qualifies as an extrusion

Figure 4 Axial CT scan section through the upper portion of the L4-L5 foramina in a 45-year-old man Abnormal soft tissues likely representing displaced disk material are seen in the right foramen The material cannot be precisely delineated and the distinction between protrusion and extrusion is difficult A typical extrusion shape is practically never seen with foraminal herniations

Despite its apparent simplicity only moderate interobserver agreement has been reported using this nomenclature in three independent studies[ ]13 [ ]33 [ ]48 It is also incomplete because it considers exclusively the contour of the disk and the shape of the displaced disk material Disks demonstrating normal contour but abnormal central or peripheral signal patterns have no place in this system and associated vertebral body bone marrow changes are completely ignored even though the clinical relevancy of those changes has been well demonstrated[ ]4 [ ]48 [ ]55 [ ]57 [ ]72 This nomenclature is unfortunately misleading because it creates artificial pathologic entities The bulging disk category is the most problematic[ ]60 Obviously a severely dessicated and atrophic disk may bulge diffusely as the intervertebral space narrows with buckling of the anterior and posterior longitudinal

ligaments But an impression has been unjustifiably derived from early postmortem studies[ ]86 that even in young individuals a disk with an intact anulus may be responsible for a detectable bulge on axial CT sections It has also been hypothesized that bulging disks are caused by diffuse anular hyperlaxity which occurs as a result of tears in collagen bridges between the concentric anular fibers while these concentric fibers remain intact[ ]15 This theory has never been proved because such collagen bridges between the concentric fibers of the anulus have never been found[ ]45 It is important to realize that a bulging disk is not an anatomic or pathologic entity it is an image that requires a differential diagnosis It sometimes represents a normal anatomic variant this is often the case with the L5-S1 disk On CT images it is often an illusion caused by a volume-averaging effect (Fig 5) It may be associated with remodeling of adjacent vertebral bodies because of osteoporosis (Fig 6) It may of course result from chronic disk deterioration and collapse A bulging disk illusion is often created on CT by a posterior anular disk rupture with displaced disk material peeling off the posterior longitudinal ligament and displacing it backward creating a posterior wide base protrusion that mimics diffuse symmetric disk bulging on both axial CT and MR imaging sections and is not differentiated from a bulging disk on sagittal MR images unless close attention is paid to the anterior aspect of the disk (Fig 7) Except for the fact that extrusions are rarely found in asymptomatic individuals[ ]34 this system does not really provide categories that correspond to clinical entities

Figure 5 A Bulging disk appearance of the L4-L5 disk shown on a 5-mm-thickness axial CT scan section in a 57-year-old woman The height of the intervertebral space was preserved and there was no reactive vertebral body end-plate modifications This aspect is probably partly due to vertebral body remodeling caused by osteoporosis but is mostly created by volume averaging (From Milette PC Fontaine S Daniels C et al Imaging of Low Back Pain CD-ROM SSB Multimedia Medical Series Montreal 1997 with permission) B Using 4- or 5-mm-thickness CT sections an intermediate gray shade halo is often computer generated by volume averaging of tissues with different attenuation coefficients in voxels represented by two-dimensional pixels located at the disk space periphery This creates the illusion of a three-dimensional image demonstrating diffuse disk bulging ST = slice thickness

Figure 6 Axial CT scan section of a L4-L5 disk in a 78-year-old man demonstrating diffuse disk bulging caused by remodeling of the adjacent vertebral bodies due to osteoporosis The intervertebral space was normal in height and there were no reactive adjacent bony endplate modifications

Figure 7 A T2-weighted axial section of a L5-S1 disk showing a left posterolateral wide base protrusion that can be easily confused with diffuse circumferential bulging B Corresponding T2-weighted left paracentral and central sagittal sections demonstrating loss of the L5-S1 disk signal intensity with posterior small left-central protrusion the anterior aspect of the disk does not extend beyond the endplates and therefore such a disk should not be labeled bulging disk

The Pathoanatomic Model

As opposed to the previous model that can be applied only to the interpretation of CT and MR imaging studies this model can be used for the interpretation of all imaging modalities including plain films and diskograms[ ]47 [ ]51 It consists of five categories that are not mutually exclusive so that different combinations are possible (Fig 8) (Figure Not Available) The first three refer to the general state of the disk (1) normal young disk (2) normal aging disk and (3) deteriorated disk (formerly called the scarred disk) The last two refer to localized lesions anular tear and herniated disk In this model the previously discussed definition of disk herniation proposed by Herzog[ ]30 is applicable The use of this system requires an effort to distinguish the normal aging changes from those of pathologic degeneration Resnick and Niwayama[ ]66 have emphasized the differentiating features of two degenerative processes involving the intervertebral disk which had been previously described by Schmorl and Junghanns[ ]75 (1) spondylosis deformans which affects primarily the anulus fibrosus and bony ring epiphysis and (2) intervertebral osteochondrosis which affects essentially the nucleus pulposus and the vertebral body end plates

Figure 8 (Figure Not Available) Schematic representation of a nomenclature based on a three-dimensional assessment of the anatomic and pathologic characteristics of both disk and adjacent vertebral bodies The categories are not mutually exclusive and some combinations are possible A Categories related to the general aspect of the disk normal young disk (a) normal aging disk (b) deteriorated disk (c) B Categories related to local lesions normal young disk (a) anular tear (b) herniated disk (c) (Adapted from Milette PC The proper terminology for reporting lumbar intervertebral disk disorders AJNR Am J Neuroradiol 181859-1866 1997 with permission)

There is convincing evidence in the scientific literature that the features of spondylosis deformans represent the normal aging process whereas intervertebral osteochondrosis denotes true pathologic disk degeneration[ ]61 [ ]71 [ ]75 [ ]83 [ ]84 Schmorl and Junghanns[ ]75 found spondylotic changes in 60 of women and almost 80 of men over the age of 50 In a series of 400 dried skeletons Nathan[ ]61 found anterior vertebral body osteophytes which constitute the main feature of spondylosis deformans in 100 of individuals over age 40 whereas posterior osteophytes were found in only 39 of individuals even after the age of 80 Twomey and Taylor[ ]83 [ ]84 have found that loss of disk height is unusual in a normal aging population and that loss of stature in the elderly is attributable to loss of intervertebral body height rather than loss in disk height During the normal aging process the mucoid matrix of the nucleus pulposus is progressively replaced by fibrous tissue[ ]37 but the intervertebral height is preserved and the disk margins remain regular Dessication and thining of disks or disks that bulge like an underinflated automobile tire are not typical of elderly spines Slight symmetric bulging may occur if there has been vertebral body remodeling resulting from osteoporosis Small amounts of gas can be detected on plain films or CT images near the insertion of the anulus on the ring epiphysis and this gas is probably located in transverse anular tears adjacent to the ring epiphysis During the fourth decade anterior and lateral marginal vertebral body osteophytes constitute normal findings comparable with having gray hair but end plate erosions with osteosclerosis or chronic reactive bone marrow changes type 2 or 3 as described by Modic et al[ ]57 should not be seen Slight to moderate decrease in central signal intensity can be detected on T2-weighted MR images as part of the normal aging process but the changes should involve uniformly all lumbar disks

Deteriorated disks represent real pathologic degeneration which is sometimes referred to as chronic diskopathy On microscopic examination they show total structural disorganization and general replacement of normal disk material by scar tissue For this reason they were initially labeled scarred disks by the members of a joint committee on spinal nomenclature created by the Quebec Association of Radiologists[ ]14 Because of possible confusion with postoperative changes the term deteriorated disk has been proposed as an acceptable substitute Strictly speaking the term degeneration could be used to designate this entity but this latter term has such a broad nonspecific meaning that it is best avoided The deteriorated disk is characterized by narrowing of the intervertebral space irregular disk contour generally associated with symmetric or asymmetric bulging abundant presence of gas in the central portion of the intervertebral disk space multidirectional osteophytes that do not respect the central spinal canal or the foramina end plate erosions with reactive osteosclerosis and chronic bone marrow changes On T2-weighted MR images the central disk signal intensity is usually markedly decreased and the number of affected lumbar disks is variable Even though transverse concentric and radial anular tears have been identified on postmortem specimens[ ]92 the anular tear category in this model refers essentially to the radial tears that are generally demonstrated by diskography in symptomatic patients For a more precise description of those tears this model may be supplemented by the Dallas Discogram Description system[ ]70 with or without its recently proposed updates[ ]4 [ ]72 [ ]80

It should be emphasized that the pathoanatomic model is not based on direct identification of a particular geometric pattern but on the anatomy and pathology that are expected as a result of the analysis of specific criteria Using this model the conclusion of any imaging report does not consist of terms related to the shape of the disk contour or the displaced disk material but on a pathologic diagnosis that should be presented with an appropriate confidence level (possible probable or definite) The diagnosis of a probable major radial anular tear may be inferred from the presence of a definite central signal intensity loss because as a result of diskographic MR imaging correlations the positive predictive value of this sign has been estimated at 96[ ]48 The use of this model requires an effort to understand the criteria allowing differentiation of normal aging from true pathologic degeneration so this system is slightly more complicated than the morphologic model Its reliability has never been tested Some intraobserver or interobserver disagreement would probably occur trying to distinguish anular tears without herniation from anular tears with small herniations With respect to correspondance to clinical situations this scheme like the morphologic model has limited interest it has been shown that disks demonstrating the features of the deteriorated disk are likely to be responsible for symptoms but this relationship has been statistically established to be significant only for the L4-L5 disk[ ]24

Which Model Should Be Used

In other areas of diagnostic radiology the aim of image analysis is always to predict what the pathologist would find if he or she could be provided with an adequate specimen immediately following the imaging study radiologic diagnoses are presented with a pathologic perspective There is no reason why the reporting of disk disorders should be

any different Terms like bulging disk are meaningless to a pathologist and I personally favor the pathoanatomic model Nomenclature standardization however is not a task that can be achieved by an individual or even a single group of authors[ ]12 To have any impact recommendations have to emanate from well established national or international societies The multiplicity of scientific societies with an interest in the spine all over the world creates a special problem but new joint committees have recently been set up combining efforts to come up with a practical unified system that it is hoped could be proposed jointly by the North American Spine Society the American Academy of Orthopedic Surgeons the American Academy of Neurological Surgeons the American Society of Spine Radiology and the American Society of Neuroradiology Agreeing in North America on a classification of disk disorders that could gain universal acceptance like the TNM classification of neoplastic diseases would be a major achievement Meanwhile the choice of the nomenclature is up to the best judgement of each practicing radiologist and the essential issue in a given hospital or community practice remains clear communication between radiologists and referring physicians by way of a local agreement as to the meaning of words

A major problem frequently occurs because observers of imaging studies try to combine elements of the morphologic classification with those of the pathoanatomic classification Trying to differentiate a bulging disk (morphologic qualifier) from a disk herniation (pathologic diagnosis) cannot work because a bulging disk aspect is a common feature of the aging disk the deteriorated disk and some posterior central disk herniations (Fig 9) Trying to make the distinction is doomed to failure because it defies formal logic On the other hand it is theoretically possible to differentiate a radial anular tear (without herniation) from a disk herniation because these are two different pathologic entities although one may be the continuum of the other It is best to adopt either one of the two systems and avoid trying to straddle the two A general classification of disk disorders attempting to conciliate the morphologic and the pathoanatomic model is proposed in Table 1

Figure 9 A bulging disk aspect often conceals a posterior central herniation A Complete rupture of the outer anular fibers allowing nuclear material to escape and peel off the posterior longitudinal ligament (and sometimes a few intact peripheral anular fibers) from the torn disk creating a detectable focal or asymmetric extension of the disk margin beyond the interspace which qualifies as a protrusion B With more gelatinous nuclear material escaping underneath the rigid posterior longitudinal ligament the focal bulge is no longer detectable as its radius increases and if the tear occurs in the posterior midline or para-medial direction the aspect mimics symmetric disk extension beyond the interspace C Since in most cases only the outline of a diffusely hypointense disk is perceived on MR images this creates the illusion of circumferential disk bulging on axial sections D The real nature of a bulging disk of this type may be suspected by scrutinizing the sagittal sections and appreciating that unless one is dealing with a chronically degenerated scarred disk the bulge is not symmetric but limited to the posterior aspect of the disk

TABLE 1 -- GENERAL

CLASSIFICATION OF DISK LESIONS Normal (excluding aging changes)

Congenitaldevelopmental variants

Inflammationinfection

Neoplasia

Degenerativetraumatic

Degeneration

Anular tear

Herniation Protrusion

Extrusion

Degeneration Spondylosis deformans

Intervertebral osteochondrosis

Further Qualifying the Displaced Disk Material Beyond the Disk Space

Regardless of the basic system that is used the type of herniation should be assessed The volume and location of the displaced disk material beyond the normal peripheral margin of the intervertebral space also need to be specified In certain cases it is also possible to determine the composition of this material For the sake of simplicity the term herniation is used consistently in the remainder of this article to refer to all displaced disk material but what is discussed can also be applied to protrusions and extrusions if one wants to use the morphologic nomenclature

Type of Herniation

Upward or downward migration of nuclear material may occur through a break in a vertebral body end plate creating an intravertebral herniation sometimes referred to as an intraspongy herniation or a Schmorls node[ ]67 (Fig 10) Although a herniation occurring in any horizontal direction is likely to cause symptoms because of the presence of pain-sensitive nerve endings in the outer anulus[ ]7 [ ]8 [ ]65 herniations occurring in a posterior or posterolateral direction deserve special consideration because of the added possibility of dural sac or individual nerve root compression

Figure 10 Various types of intravertebral herniations (Schmorls nodes) A Intravertebral herniation through the inferior end plate of the L3 vertebral body demonstrated by diskography in a 35-year-old man suffering from chronic low back pain The patients typical pain was reproduced during injection and the lesion was considered responsible for the patients symptoms B T2-weighted sagittal section demonstrating an intravertebral herniation through the inferior end plate of the L4 vertebral body in a 24-year-old woman presenting with chronic low back pain The high signal intensity of the lesion associated with the loss of normal central signal intensity of the parent disk suggests that the lesion is a bona fide acquired intraspongy herniation and not just a developmental defect C T2-weighted sagittal section demonstrating an intravertebral herniation through the inferior end plate of the L3 vertebral body (arrow) Because both the herniation and the parent disk show normal signal intensity the abnormality was

considered a probably asymptomatic developmental defect

Other characteristics of disk herniations have become relevant with the development of new therapeutic possibilities (eg chemonucleolysis and percutaneous diskectomy) The term sequestration is confusing and has often been used to indicate displacement of disk material away from the parent disk The term sequestered disk should be used restrictedly to designate a fragment of diskal tissue that has migrated from the disk space and has no connection by diskal tissue to the disk of origin[ ]20 [ ]21 [ ]42 Sequestration refers to loss of continuity with disk tissue still present in the intervertebral disk space The term migration has a broader meaning indicating displacement of disk material away from the edge of the rent in the outer anulus either in the central spinal canal at the disk level or above or below the disk level This difference is illustrated in Figure 11 The terms communicating and noncommunicating derive from a different perspective and are mostly used in the context of intradiskal therapeutic injections They refer to the interruption of the periphery of the disk allowing fluid injected into the disk to leak into the spinal canal and reach displaced disk material[ ]20 [ ]51 The terms contained and uncontained are unfamiliar to most radiologists in a contained herniation the displaced disk material is still covered by a few intact but distended outer anular fibers or by a capsule formed by outer anular fibers and the adherent posterior longitudinal ligament

Figure 11 Various types of posterior central herniations A Small subligamentous herniation (protrusion) without significant disk material migration B Subligamentous herniation with downward migration of disk material under the PLLC C Sub-ligamentous herniation with downward migration of disk material and sequestered fragment (arrow)

The terms subligamentous and extraligamentous (or transligamentous) refer to the position of the displaced disk material with respect to the posterior longitudinal ligament The anatomy of the posterior longitudinal ligament has been recently revised[ ]73 [ ]89 It is a membranous structure that has multiple components a deep layer attached to disks and vertebral bodies a superficial layer attached to the dura by fibrous tissue (Hoffmanns

ligament) and lateral extensions known as the lateral membranes or peridural membranes (Fig 12) (Figure Not Available) It should probably be referred to as the posterior longitudinal ligament complex (PLLC) It actually divides the epidural space into the perithecal space and the anterior epidural space where displaced disk material can be entrapped (Fig 13) A potential space allowing accumulation of displaced disk material has also been detected between the outer anular fibers and the deep fibers of the PLLC on the posterior central aspect of the disk[ ]63 Posterior midline herniations seldom rupture the PLLC and are generally subligamentous The lateral membranes are less resistant and transligamentous herniations are usually the result of posterior off-center herniations or posterolateral herniations

Figure 12 (Figure Not Available) The PLLC is portrayed here in relation to various types of subligamentous disk displacement At the disk level posteriorly displaced disk material frequently occupies the midline Below and above the disk an anterior epidural space (AES) exists between the PLLC and the posterior aspect of the vertebral bodies In this space disk fragment motion across the midline is curtailed by a sagittal midline septum (dashed line) A delicate translucent membrane (shown only on left side of drawing) is stretched between the free edge of the deep layer of the posterior longitudinal ligament and the lateral spinal canal (From Schellinger D Manz HJ Vidic B et al Disk fragment migration Radiology 175831-836 1990 with permission)

Figure 13 Relationship of typical posterior disk herniations with the PLLC A Midline sagittal section unless very large a posterior midline herniation usually remains entrapped underneath the deep layer of the PLL C and sometimes a few intact outer anulus fibers joining with the PLL C to form a capsule The deep layer of the PLL C (arrow) also attaches to the posterior aspect of the vertebral body so that no potential space is present underneath B Sagittal para-central section the PLL C extends laterally at the disk level (arrowhead) but above and below the disk an anterior epidural space (as) where disk fragments are frequently entrapped is present between the lateral (peridural) membranes and the posterior aspect of the vertebral bodies

Volume of Herniated Material

Quantifying the herniated disk material by measuring in millimeters its greatest diameter or by evaluating its cross-sectional area in square millimeters is rarely done The resulting figures could be misleading without relating this measurement to the size of the spinal canal and the exact location of the lesion[ ]88 A purely qualitative and subjective statement that a mild moderate or severe herniation is present however does not give the person reading the imaging report any indication as to the potential of the lesion to cause significant compression of the dural sac or individual exiting nerve roots A reasonably precise scheme has been proposed in 1995 by the Nomenclature Committee of the North American Spine Society[ ]20 Measurements are taken from an axial CT or MR imaging section at the site of most severe compromise canal compromise of less than 25 at that section is qualified as mild 25 to 75 is moderate 76 to 90 is moderately severe and greater than 90 is severe It is understood that such characterizations describe only the cross-sectional area at one level and do not account for the total volume of displaced material displacement of neural tissue or clinical significance The usefulness of having four categories is questionable and can likely generate poor interobserver or intraobserver agreement especially in situations where the central spinal canal is relatively narrow Bonnevilles scheme[ ]9 [ ]10 [ ]11 should generate greater reliability (Fig 14) (Figure Not Available) Separation of the cross-sectional area in three thirds can be applied to both the central spinal canal and the foramina It can be agreed by way of convention that the terms mild moderate and severe lumen compromise by a disk herniation designate extension of the displaced disk material in the anterior middle or posterior third of the central canal or foramen depending on the specified location of the herniation

Figure 14 (Figure Not Available) The size of the herniation in the horizontal plane is assessed and designated by the numbers 1 2 or 3 by establishing its extension in the anterior middle or posterior third of the spinal canal (From Bonneville JF Plaidoyer pour une classification par limage des hernies discales lombaires la carte-image Rev Imag Med 2557-560 1990 with permission)

Location of Herniated Material

Bonneville[ ]9 [ ]10 [ ]11 has also proposed an interesting and simple alpha-numerical system to classify according to their location the position of disk fragments that have migrated in the horizontal or sagittal plane (Figs 15 (Figure Not Available) and 16) (Figure Not Available) Using more precise anatomic boundaries unfortunately more familiar to surgeons than radiologists Wiltse et al[ ]88 have proposed another system which has been supported by the North American Spine Society[ ]20 [ ]21 Anatomic zones and levels are defined using the following anatomic landmarks medial edge of the articular facets medial lateral upper and lower border of the pedicles and coronal plane at the disk center On the horizontal plane (Fig 17) (Figure Not Available) these landmarks determine the bounderies of the central zone the subarticular zone the foraminal zone the extraforaminal zone and the anterior zone (anterior to the coronal plane at the center of the disk) In the sagittal plane they determine the boundaries of the diskal level the infrapedicular level the pedicular level and the suprapedicular level (Figs 18 (Figure

Not Available) and 19) (Figure Not Available) Radiologists interpreting axial CT or MR images may find it difficult to use the medial edge of the facets as the landmark that separates the central zone from the subarticular zone because the superior articular facets are generally not included in axial sections at the disk level The alternative is to use the expression posterolateral to designate collectively all posterior herniations that are not midline but do not extend into a foramen as was proposed by Bonneville[ ]9 [ ]10 [ ]11

Figure 15 (Figure Not Available) In the horizontal plane herniations are labeled midline (a) posterolateral (b) foraminal (c) and extra-foraminal (d) (From Bonneville JF Plaidoyer pour une classification par limage des hernies discales lombaires la carte-image Rev Imag Med 2557-560 1990 with permission)

Figure 16 (Figure Not Available) In the craniocaudal direction disk migration is labeled +1 +2 +3 or -1 -2 -3 by referring to the height of a vertebral body divided in thirds (From Bonneville JF Plaidoyer pour une classification par limage des hernies discales lombaires la carte-image Rev Imag Med 2557-560 1990 with permission)

Figure 17 (Figure Not Available) The anatomic zones identified on axial images The anterior zone (not shown) is delineated from the extraforaminal zone by an imaginary coronal line in the center of the vertebral body (From Wiltse LL Berger PE McCulloch JA A system for reporting the size and location of lesions in the spine Spine 221534-1537 1997 with permission)

Figure 18 (Figure Not Available) The anatomical levels identified on craniocaudal images (From Wiltse LL Berger PE McCulloch AJ A system for reporting the size and location of lesions in the spine Spine 221534-1537 1997 with permission)

Figure 19 (Figure Not Available) Coronal view of the main zones and levels (From Wiltse LL Berger PE McCulloch JA A system for reporting the size and location of lesions in the spine Spine 221534-1537 1997 with permission)

Composition of Herniated Material

Displaced disk material may consist of glycosaminoglycans type 1 or 2 collagen end plate cartilage and bone fragments avulsed from the ring epiphysis A reactive inflammatory reaction usually results in edematous tissue followed by granulation tissue which may undergo calcification (Fig 20) Necrotic and partially resorbed displaced disk material sometimes produces a large fluid-filled pouch distinguishable from the common high-intensity zone because of its size (Fig 21) or a gas-filled cavity generally in continuity with gas in the intervertebral space (Fig 22) [ ]42 These characteristics may be meaningful if intradiskal injection therapy is considered In imaging reports herniations exhibiting calcium deposits and those exhibiting replacement of disk material by gas or a relatively large fluid collection can be qualified as chronic herniations

Figure 20 A CT scan demonstration of a small posterior central L4-L5 calcified subligamentous herniation The resistant deep layer of the PLLC restrains displacement of the disk material in the posterior central direction and does not allow a detectable distortion of the disk contour In this particular case the presence of the calcification is actually the only evidence that a posterior midline anular tear and a small subligamentous herniation are present B Posterior right central and sub-articular L5-S1 calcified disk herniation in same patient Posterolateral herniations are generally more conspicuous than posterior midline herniations because the deep layer of the PLLC gets thinner away from the midline

Figure 21 Posterior central midline L4-L5 herniation in a 52-year-old man demonstrated on a T2-weighted midline MR sagittal section There is intervertebral space narrowing with loss of normal central disk signal

intensity while the herniated disk material demonstrates high signal intensity consistent with a predominantly fluid consistency

Figure 22 CT scan demonstration in a 51-year-old woman of a left posterolateral L5-S1 disk hernation consisting essentially in a gas-filled pouch (white arrow) Gas is also present in the central portion of the intervertebral disk space (black arrow)

DIAGNOSTIC IMAGING AND CHARACTERIZATION OF A HERNIATED LUMBAR DISK

Assessing the validity of the currently used imaging procedures to diagnose a herniated lumbar disk is not an easy endeavor The validity of a measurement is the extent to which it corresponds to the true biologic value or some accepted gold standard[ ]40 With the exception of postmortem studies evaluation of the pathoanatomy by the surgeon in the operating room has always been considered the gold standard but this does not constitute an ideal situation Inspection of the disk through a small laminectomy incision to determine for instance if nuclear fragments lie within or outside the anular fibers may not be very reliable Also unbiased intraoperative determination of a normal degenerated or herniated disk in a patient with sciatica may also be difficult[ ]86 Because the validity of diskography has been previously established by postmortem studies and surgical correlations[ ]48 it is sometimes used as a gold standard in situations where no surgery has been performed

Conventional Radiographs

Lumbar disk herniations can exceptionally be diagnosed directly on good quality lateral projections because the x-ray attenuation is slightly greater in displaced disk material than in epidural fat Occasionally a calcified rim outlines the displaced disk fragment

(Fig 23) In most situations however narrowing of an intervertebral disk space in the absence of other evidence of chronic diskopathy is the only detectable sign suggesting the presence of a disk herniation To my knowledge the sensitivity and specificity of this sign has never been assessed The accepted rule of thumb is that the height of a given lumbar intervertebral disk space should always be slightly greater than the height of the above located interspace This rule does not apply to the transition disk immediately above the sacrum (usually L5-S1) The specificity of this sign is probably quite high but a few false-positives are seen especially at the L4-L5 level because of minor congenital hypoplasia The presence of posterior or foraminal vertebral body osteophytes associated or not with disk space narrowing is a definite sign of a chronic disk herniation

Figure 23 A Chronic left L3-L4 extraforaminal disk hernation in a 54-year-old man suspected on an AP radiograph demonstrating a calcified shell on the left side of the intervertebral disk space (white arrow) B Axial CT scan section confirming the diagnosis of a chronic extraforaminal L3-L4 herniation

Myelography

Myelography is essentially an exploration of the subarachnoid space Disk herniations are demonstrated only indirectly because they can cause thecal sac deformity and individual nerve root sleeve filling defects (Fig 24) Of all the special imaging procedures

myelography is the only one that allows upright projections with full weight bearing It is not unusual to demonstrate in this way small posterior central or posterolateral herniations that are undetectable on CT sections Interestingly the overall sensitivity of myelography to detect disk herniations has been found to be higher than that of CT whereas its specificity has been found to be lower[ ]74 In comparison with standard CT examination which usually includes only the three or four lower lumbar disks myelography easily allows coverage of the entire lumbar area and assessment of the intrathecal structures (cauda equina and conus medullaris) Far lateral foraminal herniations extraforaminal herniations and anterior herniations however are not detected The sensitivity for detection of posterior central L5-S1 herniations is also relatively poor because of the greater distance between the thecal sac and the posterior aspect of this particular disk

Figure 24 L5-S1 disk herniation in a 25-year-old man detected by indirect signs using lumbosacral myelography A Upright oblique projections showing a filling defect of the left S1 root sleeve (white arrow) suggesting significant nerve root compression by a left posterolateral disk hernation The right S1 root sleeve fills normally with contrast (black arrow) B Subtle compression of the anterior wall of the dural sac by displaced disk material (small arrows) demonstrated on upright lateral projection This sign is usually absent in the presence of a large amount of fat and venous structures in the anterior epidural compartment

CT

The sensitivity of CT to diagnose a herniation of the nucleus pulposus at the L5-S1 interspace is greater than that of myelography if images in the exact plane of the disk can be obtained[ ]23 [ ]39 Otherwise the superiority of plain CT over myelography to demonstrate disk herniations has not been established but CT has the distinct advantage of being

noninvasive and provides direct anatomic information[ ]23 Large herniations are easily detected but as explained previously the distinction between protrusions and extrusions is often difficult without sagittal reconstructions CT essentially allows an assessment of the contour of the disk The diagnosis of very small herniations in the absence of direct or indirect evidence of a radial tear is hazardous and associated with a high percentage of false-positives and false-negatives[ ]52 The diagnosis of moderate and large size herniations in different directions is usually possible but anterior herniations are rarely diagnosed not because they are not detectable but because observers pay little attention to the anterior contour of the disk (Fig 25) Because the PLLC cannot usually be identified the distinction of subligamentous from transligamentous herniation can only be suggested in most cases by the size of the herniated material A definite diagnosis of sequestration is rarely possible Calcifications within the displaced material are readily seen but may be difficult at times to differentiate from an accompanying osteophyte or an avulsed bone fragment from the vertebral body ring epiphysis (Fig 26) The presence of gas in the herniated material is easily detected

Figure 25 Anterior L4-L5 herniation demonstrated by CT scan in a 51-year-old woman with chronic low back pain Although sometimes quite conspicuous such herniations are rarely reported because observers pay little attention to the anterior contour of the disk

Figure 26 CT scan demonstration of a posterior right central L4-L5 disk herniation in a 38-year-old woman with avulsion of a bone fragment from the ring epiphysis and adjacent part of the superior L5 end plate Reactive osteosclerosis is seen around the vertebral body defect (arrows) suggesting a chronic lesion

CT Myelography

This association combines the advantages of both imaging modalities The fact that its accuracy has been reported as being less[ ]22 [ ]32 higher[ ]1 [ ]6 or equivalent[ ]82 to MR imaging is a reflection of the differences in technologic advancement and pathologic nomenclature that hamper valid comparisons between different studies

MR Imaging

Most reported studies establish MR imaging as the first choice modality to diagnose a herniated lumbar disk[ ]5 [ ]22 [ ]32 [ ]46 The associated intravenous injection of a paramagnetic agent has been found useful to demonstrate some anatomic features of disk disease in patients with no previous lumbar disk surgery[ ]56 [ ]68 [ ]90 MR imaging provides a better assessment of disk morphology than CT or CT myelography because sagittal sections are routinely obtained Assessment of foraminal involvement by displaced disk material is more accurate (Fig 27) and anterior disk herniations can be detected more easily than with CT or CT myelography If one is looking specifically for herniated lumbar disks associated with nerve root compression however it has been demonstrated that CT is equally accurate[ ]82 Alterations of the central or peripheral disk signal intensity on T2-weighted images are seen in most disks afflicted with an anular tear[ ]48 and alert the observer to scrutinize the disk contour in search for local modifications indicative of a herniation Because the signal of the displaced disk material is usually very similar to that of the outer anulus PLLC and vertebral body cortical bone small herniations are generally more conspicuous on axial CT sections than on corresponding axial MR imaging sections Gas and calcium deposits within the displaced fragment cannot usually

be detected but associated vertebral body bone marrow changes are typically seen and are helpful in differentiating acute from chronic processes[ ]57 The occasional presence of a high-intensity zone in the herniated material with an occasionally enhancing border after contrast injection is probably caused by a mixture of displaced nuclear material acute and subacute inflammatory tissue and neovascularized reactive tissue[ ]4 [ ]48 [ ]72 Contradictory reports have been published regarding the accuracy of MR imaging to differentiate subligamentous from transligamentous herniations[ ]26 [ ]38 [ ]73 [ ]76 Understanding the anatomy of the PLLC is helpful to make the distinction (Fig 28) (Figure Not Available) Masaryk et al[ ]46 have suggested that MR imaging is accurate to distinguish sequestered disks from other forms of lumbar disk herniations but most observers find this distinction difficult to establish[ ]42

Figure 27 A Left L4-L5 foraminal herniation well seen on an intermediate-weighted left parasagittal MR section (arrow) in a 47-year-old man B The lesion is much less obvious on intermediate-weighted (left) and T2-weighted (right) axial sections and was in fact more conspicuous on the corresponding CT scan section

Figure 28 (Figure Not Available) A Subligamentous disk herniation Left T1-weighted image demonstrating displaced disk material with a smooth outline imposed by the demarcation of the anterior epidural space (AES) by the lateral membrane of the PLLC Right Correlative drawing B Transligamentous disk herniation Left T1-weighted image of a large disk herniation (cervical in this case) which has ruptured through the posterior confines of the AES Penetration of the right lateral membrane can be observed (arrow) and the disk fragment contour is serrated Right Correlative drawing (From Schellinger D Manz HJ Vidic B et al Disk fragment migration Radiology 175831-836 1990 with permission)

Diskography and CT Diskography

During 30 years (1950 to 1980) when myelography was the only available imaging technique to demonstrate lumbar disk herniations diskography was an invasive but efficient way to demonstrate posterior central L5-S1 herniations and other large herniations (other than posterior central and paramedial) that could not be detected by myelography[ ]50 These herniations are now usually well demonstrated by CT and MR imaging Comparing the accuracy of five imaging modalities (excluding MR imaging) for the diagnosis of lumbar disk herniation Jackson et al[ ]31 found that CT diskography (Fig 29) was the most accurate test (87) compared with 77 for CT myelography 74 for CT 70 for myelography 64 for pain reproduction during diskography and 58 for diskography without CT Disk injection reproduced the patients clinical pain pattern in only 36 of herniated disks This clinical test isolated from the images had high specificity (89) but low sensitivity (43) for the diagnosis of disk herniation The reported low sensitivity of diskography images (unassociated with CT) to diagnose disk herniation is to be expected the purpose of the intradiskal injection being primarily the demonstration of an anular tear the contrast leaking through the tear only occasionally delineates an extruded fragment When a disk herniation has been diagnosed by other imaging modalities diskography allows to determine if the herniation is contained or noncontained (Figs 30 and 31) this information may have clinical relevance[ ]62 It also allows to establish if the displaced disk material is communicating or not with the parent disk and establishes the likelihood that it is sequestered or not There always remains a possibility that the contrast injected under pressure may reach a disk fragment that is nevertheless sequestered by leaking through the associated anular tear CT diskography also allows assessment in most cases of the integrity of the PLLC[ ]89 The superior sensitivity of diskography over MR imaging to demonstrate anular tears has been well established[ ]27 [ ]44 [ ]48 [ ]64 [ ]77 [ ]91 [ ]94 The presence of a radial tear and the inflammatory reaction it creates may be symptomatic despite the absence of true disk herniation[ ]29 [ ]48 [ ]49 [ ]69

Figure 29 L4-L5 CT diskogram demonstrating a large left posterolateral radial anular tear associated with

a left foraminal and extraforaminal herniaton (same patient as in Figure 28) (Figure Not Available)

Figure 30 Contained posterior L4-L5 and L5-S1 disk herniations in a 57-year-old man demonstrated by diskography The L3-L4 disk is normal

Figure 31 Noncontained L4-L5 disk herniation in a 23-year-old woman Reflux of injected contrast is seen in the anterior epidural space above and below the disk space The L5-S1 disk also demonstrates incomplete anterior and posterior radial anular tears

SUMMARY

The absence of universal nomenclature standardization with respect to the definition of a disk herniation and its different categories especially regarding type and location is still a major problem that will only be overcome when major national or international scientific societies join efforts to support a particular scheme Meanwhile it is important to realize that the two models that are currently most used are based on a different perspective Trying to straddle the two by opposing for instance bulging disk and herniation is doomed to failure because this exercise defies formal logic MR imaging is currently the most accurate noninvasive imaging modality to diagnose a disk herniation and to determine its exact location The determination of some pathoanatomic characteristics of herniated disks (type and composition) may require the use of CT diskography or CT diskography

References

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29 Haughton VM Lim TH An H Intervertebral disk appearance correlated with stiffness of lumbar spinal motion segments AJNR Am J Neuroradiol 201161-1165 1999 Abstract 30 Herzog RJ The radiologic assessment for a lumbar disc herniation Spine 2119S-38S 1996 Abstract 31 Jackson RP Becker GJ Jacobs RR et al The neuroradiographic diagnosis of lumbar herniated nucleus pulposus I A comparison of computed tomography (CT) myelography CT-myelography discography and CT-discography Spine 141356-1361 1989 Abstract 32 Jackson RP Cain JE Jr Jacobs RR et al The neuroradiographic diagnosis of lumbar herniated nucleus pulposus II A comparison of computed tomography (CT) myelography CT-myelography and magnetic resonance imaging Spine 141362-1367 1989 Abstract 33 Jarvik JG Haynor DR Koepsell TD et al Interreader reliability for a new classification of lumbar disk disease Acad Radiol 3537-544 1996 Abstract 34 Jensen MC Brant-Zawadzki MN Obuchowski N et al Magnetic resonance imaging of the lumbar spine in people without back pain N Engl J Med 33169-73 1994 Abstract 35 Kent DL Haynor DR Larson EB et al Diagnosis of lumbar spinal stenosis in adults A meta-analysis of the accuracy of CT MR and myelography AJR Am J Roentgenol 1581135-1144 1992 Abstract 36 Kieffer SA Sherry RG Wellenstein DE et al Bulging lumbar intervertebral disk Myelographic differentiation from herniated disk with nerve root compression AJR Am J Roentgenol 138709-716 1982 Abstract 37 Kieffer SA Stadlan EM Mohandas A et al Discographic-anatomical correlation of developmental changes with age in the intervertebral disc Acta Radiol 9733-739 1969 38 Kim KY Kim YT Lee CS et al MRI classification of lumbar herniated intervertebral disc Orthopedics 15493-497 1992 Abstract 39 Kornberg M Rechtine GR Dupuy TE Computed tomography in the diagnosis of a herniated disk at the L5-S1 level Spine 9433-436 1984 Abstract 40 Kramer MS Clinical Epidemiology and Biostatistics New York Springer-Verlag 1988 41 Landis JR Koch GG The measurement of observer agreement agreement for categorical data Biometrics 33159-174 1977 Abstract 42 Laredo JD Bossard P Vuillemin-Bodaghi Formes anatomo-radiologiques des hernies discales In Morvan G Deburge A Bard H et al (eds) Le Rachis Lombaire Degeneratif Montpellier Sauramps Medical 1998 pp 37-49 43 Lee SH Coleman PE Hahn FJ Magnetic resonance imaging of degenerative disk disease of the spine Radiol Clin North Am 26949-964 1988 Abstract 44 Linson MA Crowe CH Comparison of magnetic resonance imaging and lumbar discography in the diagnosis of disc degeneration Clin Orthop 160-163 1990

45 Marchand F Ahmed AM Investigation of the laminate structure of lumbar disc anulus fibrosus Spine 15402-410 1990 Abstract 46 Masaryk TJ Ross JS Modic MT et al High-resolution MR imaging of sequestered lumbar intervertebral disks AJR Am J Roentgenol 1501155-1162 1988 Abstract 47 Milette PC The proper terminology for reporting lumbar intervertebral disk disorders AJNR Am J Neuroradiol 181859-1866 1997 Citation 48 Milette PC Fontaine S Lepanto L et al Differentiating lumbar disc protrusions disk bulges and discs with normal contour but abnormal signal intensity Magnetic resonance imaging with discographic correlations Spine 2444-53 1999 Abstract 49 Milette PC Fontaine S Lepanto L et al Radiating pain to the lower extremities caused by lumbar disk rupture without spinal nerve root involvement AJNR Am J Neuroradiol 161605-1613 1995 Abstract 50 Milette PC Melancon D A reappraisal of lumbar discography Can Assoc Radiol J 33176-182 1982 51 Milette PC Melancon D Dupuis PR et al A simplified terminology for abnormalities of the lumbar disk Can Assoc Radiol J 42319-325 1991 Abstract 52 Milette PC Raymond J Fontaine S Comparison of high-resolution computed tomography with discography in the evaluation of lumbar disc herniations Spine 15525-533 1990 Abstract 53 Mink JH Deutsch AL Goldstein TB et al Spinal imaging and intervention 1998 Phys Med Rehabil Clin North Am 9343-380 1998 54 Mixter WJ Barr JS Rupture of the intervertebral disc with involvement of the spinal canal N Engl J Med 211210-234 1934 55 Modic MT Masaryk TJ Ross JS et al Imaging of degenerative disk disease Radiology 168177-186 1988 Citation 56 Modic MT Ross JS Obuchowski NA et al Contrast-enhanced MR imaging in acute lumbar radiculopathy A pilot study of the natural history Radiology 195429-435 1995 Abstract 57 Modic MT Steinberg PM Ross JS et al Degenerative disk disease Assessment of changes in vertebral body marrow with MR imaging Radiology 166193-199 1988 58 Morvan G Mathieu P Les stenoses laterales In Morvan G Deburge A Bard H et al (eds) Le Rachis Lombaire Degeneratif Montpellier Sauramps Medical 1998 pp 315-324 59 Murray RO Skeletal trauma Regional In Sutton D (ed) Textbook of Radiology and Imaging ed 3 New York Churchill Livingstone 1980 pp 210-231 60 Nachemson A Lumbar disc herniation Conclusions Acta Orthop Scand 64(suppl 251)49 1993 Citation

61 Nathan H Osteophytes of the vertebral column An anatomical study of their development according to age race and sex with consideration as to their etiology and significance J Bone Joint Surg Am 44243-268 1962 62 Nygaard OP Mellgren SI Osterud B The inflammatory properties of contained and noncontained lumbar disc herniations Spine 222584-2488 1997 Abstract 63 Ohshima H Hirano N Osada R et al Morphologic variation of lumbar posterior longitudinal ligament and the modality of disc herniation Spine 182408-2411 1993 Abstract 64 Osti OL Fraser RD MRI and discography of annular tears and intervertebral disc degeneration A prospective clinical comparison J Bone Joint Surg Br 74431-435 1992 Abstract 65 Palmgren T Gronblad M Virri J et al Immunohistochemical demonstration of sensory and autonomic nerve terminals in herniated lumbar disc tissue Spine 211301-1306 1996 Abstract 66 Resnick D Niwayama G Degenerative disease of the spine In Resnick D (ed) Diagnosis of Bone and Joint Disorders ed 3 Philadelphia WB Saunders 1995 pp 1372-1462 67 Resnick D Niwayama G Intravertebral disk herniations Cartilaginous (Schmorls) nodes Radiology 12657-65 1978 Abstract 68 Ross JS Modic MT Masaryk TJ Tears of the anulus fibrosus Assessment with Gd-DTPA-enhanced MR imaging AJR Am J Roentgenol 154159-162 1990 Abstract 69 Saal JS The role of inflammation in lumbar pain Spine 201821-1827 1995 Abstract 70 Sachs BL Vanharanta H Spivey MA et al Dallas discogram description A new classification of CTdiscography in low-back disorders Spine 12287-294 1987 Abstract 71 Sauser DD Goldman AB Kaye JJ Discogenic vertebral sclerosis J Can Assoc Radiol 2944-50 1978 Abstract 72 Schellhas KP Pollei SR Gundry CR et al Lumbar disc high-intensity zone Correlation of magnetic resonance imaging and discography Spine 2179-86 1996 Abstract 73 Schellinger D Manz HJ Vidic B et al Disk fragment migration Radiology 175831-836 1990 Abstract 74 Schipper J Kardaun JW Braakman R et al Lumbar disk herniation Diagnosis with CT or myelography Radiology 165227-231 1987 Abstract 75 Schmorl G Junghanns H The Human Spine in Health and Disease ed 2 New York Grune and Stratton 1971 76 Silverman CS Lenchik L Shimkin PM et al The value of MR in differentiating subligamentous from supraligamentous lumbar disk herniations AJNR Am J Neuroradiol 16571-579 1995 Abstract 77 Simmons JW Emery SF McMillin JN et al Awake discography A comparison study with magnetic

resonance imaging Spine 16S216-221 1991 Abstract 78 Smyth MJ Wright V Sciatica and the intervertebral disc J Bone Joint Surg Am 401401-1418 1958 79 Taveras JM Radiologic aspects of low back pain and sciatic syndromes [editorial] AJNR Am J Neuroradiol 9351-358 1989 80 Tehranzadeh J Discography 2000 Radiol Clin North Am 36463-495 1998 Full Text 81 Thelander U Fagerlund M Friberg S et al Describing the size of lumbar disc herniations using computed tomography A comparison of different size index calculations and their relation to sciatica Spine 191979-1984 1994 Abstract 82 Thornbury JR Fryback DG Turski PA et al Disk-caused nerve compression in patients with acute low-back pain Diagnosis with MR CT myelography and plain CT Radiology 186731-738 1993 Abstract 83 Twomey L Taylor J Age changes in lumbar intervertebral discs Acta Orthop Scand 56496-499 1985 Abstract 84 Twomey LT Taylor JR Age changes in lumbar vertebrae and intervertebral discs Clin Orthop 22497-104 1987 85 Williams AL CT diagnosis of degenerative disc disease The bulging annulus Radiol Clin North Am 21289-300 1983 Abstract 86 Williams AL Haughton VM Meyer GA et al Computed tomographic appearance of the bulging annulus Radiology 142403-408 1982 Abstract 87 Williams AL Haughton VM Syvertsen A Computed tomography in the diagnosis of herniated nucleus pulposus Radiology 13595-99 1980 Abstract 88 Wiltse LL Berger PE McCulloch JA A system for reporting the size and location of lesions in the spine Spine 221534-1537 1997 Abstract 89 Wiltse LL Fonseca AS Amster J et al Relationship of the dura Hofmanns ligaments Batsons plexus and a fibrovascular membrane lying on the posterior surface of the vertebral bodies and attaching to the deep layer of the posterior longitudinal ligament An anatomical radiologic and clinical study Spine 181030-1043 1993 Abstract 90 Yamashita K Hiroshima K Kurata A Gadolinium-DTPA-enhanced magnetic resonance imaging of a sequestered lumbar intervertebral disc and its correlation with pathologic findings Spine 19479-482 1994 Abstract 91 Yu SW Haughton VM Sether LA et al Comparison of MR and diskography in detecting radial tears of the anulus A postmortem study AJNR Am J Neuroradiol 101077-1081 1989 Abstract 92 Yu SW Sether LA Ho PS et al Tears of the anulus fibrosus Correlation between MR and pathologic findings in cadavers AJNR Am J Neuroradiol 9367-370 1988 Abstract

93 Yussen PS Swartz JD The acute lumbar disc herniation Imaging diagnosis Semin Ultrasound CT MR 14389-398 1993 Abstract 94 Zucherman J Derby R Hsu K et al Normal magnetic resonance imaging with abnormal discography Spine 131355-1359 1988 Abstract

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  • CLASSIFICATION DIAGNOSTIC IMAGING AND IMAGING CHARACTERIZATION OF A LUMBAR HERNIATED DISK
    • IMAGING OF LOW BACK PAIN I
      • CLASSIFICATION DIAGNOSTIC IMAGING AND IMAGING CHARACTERIZATION OF A LUMBAR HERNIATED DISK
        • DEFINITION OF A DISK HERNIATION
        • CLASSIFICATION OF A HERNIATED LUMBAR DISK
          • Main Categories of Noninfectious Disk Abnormalities
          • Further Qualifying the Displaced Disk Material Beyond the Disk Space
            • DIAGNOSTIC IMAGING AND CHARACTERIZATION OF A HERNIATED LUMBAR DISK
              • Conventional Radiographs
              • Myelography
              • CT
              • CT Myelography
              • MR Imaging
              • Diskography and CT Diskography
                • SUMMARY
                  • References
Page 6: CLASSIFICATION, DIAGNOSTIC IMAGING, AND IMAGING ... · PDF fileclassification, diagnostic imaging, and imaging characterization of a lumbar herniated disk ... classification, diagnostic

Figure 3 When a relatively large amount of disk material is displaced distinction between protrusion (A) and extrusion (B or C) will generally only be possible on sagittal MR sections or sagittal CT scan reconstructions In C although the shape of the displaced material is similar to that of a protrusion the greatest cranio-caudal diameter of the fragment is greater than the craniocaudal diameter of its base at the level of the parent disk and the lesion therefore qualifies as an extrusion

Figure 4 Axial CT scan section through the upper portion of the L4-L5 foramina in a 45-year-old man Abnormal soft tissues likely representing displaced disk material are seen in the right foramen The material cannot be precisely delineated and the distinction between protrusion and extrusion is difficult A typical extrusion shape is practically never seen with foraminal herniations

Despite its apparent simplicity only moderate interobserver agreement has been reported using this nomenclature in three independent studies[ ]13 [ ]33 [ ]48 It is also incomplete because it considers exclusively the contour of the disk and the shape of the displaced disk material Disks demonstrating normal contour but abnormal central or peripheral signal patterns have no place in this system and associated vertebral body bone marrow changes are completely ignored even though the clinical relevancy of those changes has been well demonstrated[ ]4 [ ]48 [ ]55 [ ]57 [ ]72 This nomenclature is unfortunately misleading because it creates artificial pathologic entities The bulging disk category is the most problematic[ ]60 Obviously a severely dessicated and atrophic disk may bulge diffusely as the intervertebral space narrows with buckling of the anterior and posterior longitudinal

ligaments But an impression has been unjustifiably derived from early postmortem studies[ ]86 that even in young individuals a disk with an intact anulus may be responsible for a detectable bulge on axial CT sections It has also been hypothesized that bulging disks are caused by diffuse anular hyperlaxity which occurs as a result of tears in collagen bridges between the concentric anular fibers while these concentric fibers remain intact[ ]15 This theory has never been proved because such collagen bridges between the concentric fibers of the anulus have never been found[ ]45 It is important to realize that a bulging disk is not an anatomic or pathologic entity it is an image that requires a differential diagnosis It sometimes represents a normal anatomic variant this is often the case with the L5-S1 disk On CT images it is often an illusion caused by a volume-averaging effect (Fig 5) It may be associated with remodeling of adjacent vertebral bodies because of osteoporosis (Fig 6) It may of course result from chronic disk deterioration and collapse A bulging disk illusion is often created on CT by a posterior anular disk rupture with displaced disk material peeling off the posterior longitudinal ligament and displacing it backward creating a posterior wide base protrusion that mimics diffuse symmetric disk bulging on both axial CT and MR imaging sections and is not differentiated from a bulging disk on sagittal MR images unless close attention is paid to the anterior aspect of the disk (Fig 7) Except for the fact that extrusions are rarely found in asymptomatic individuals[ ]34 this system does not really provide categories that correspond to clinical entities

Figure 5 A Bulging disk appearance of the L4-L5 disk shown on a 5-mm-thickness axial CT scan section in a 57-year-old woman The height of the intervertebral space was preserved and there was no reactive vertebral body end-plate modifications This aspect is probably partly due to vertebral body remodeling caused by osteoporosis but is mostly created by volume averaging (From Milette PC Fontaine S Daniels C et al Imaging of Low Back Pain CD-ROM SSB Multimedia Medical Series Montreal 1997 with permission) B Using 4- or 5-mm-thickness CT sections an intermediate gray shade halo is often computer generated by volume averaging of tissues with different attenuation coefficients in voxels represented by two-dimensional pixels located at the disk space periphery This creates the illusion of a three-dimensional image demonstrating diffuse disk bulging ST = slice thickness

Figure 6 Axial CT scan section of a L4-L5 disk in a 78-year-old man demonstrating diffuse disk bulging caused by remodeling of the adjacent vertebral bodies due to osteoporosis The intervertebral space was normal in height and there were no reactive adjacent bony endplate modifications

Figure 7 A T2-weighted axial section of a L5-S1 disk showing a left posterolateral wide base protrusion that can be easily confused with diffuse circumferential bulging B Corresponding T2-weighted left paracentral and central sagittal sections demonstrating loss of the L5-S1 disk signal intensity with posterior small left-central protrusion the anterior aspect of the disk does not extend beyond the endplates and therefore such a disk should not be labeled bulging disk

The Pathoanatomic Model

As opposed to the previous model that can be applied only to the interpretation of CT and MR imaging studies this model can be used for the interpretation of all imaging modalities including plain films and diskograms[ ]47 [ ]51 It consists of five categories that are not mutually exclusive so that different combinations are possible (Fig 8) (Figure Not Available) The first three refer to the general state of the disk (1) normal young disk (2) normal aging disk and (3) deteriorated disk (formerly called the scarred disk) The last two refer to localized lesions anular tear and herniated disk In this model the previously discussed definition of disk herniation proposed by Herzog[ ]30 is applicable The use of this system requires an effort to distinguish the normal aging changes from those of pathologic degeneration Resnick and Niwayama[ ]66 have emphasized the differentiating features of two degenerative processes involving the intervertebral disk which had been previously described by Schmorl and Junghanns[ ]75 (1) spondylosis deformans which affects primarily the anulus fibrosus and bony ring epiphysis and (2) intervertebral osteochondrosis which affects essentially the nucleus pulposus and the vertebral body end plates

Figure 8 (Figure Not Available) Schematic representation of a nomenclature based on a three-dimensional assessment of the anatomic and pathologic characteristics of both disk and adjacent vertebral bodies The categories are not mutually exclusive and some combinations are possible A Categories related to the general aspect of the disk normal young disk (a) normal aging disk (b) deteriorated disk (c) B Categories related to local lesions normal young disk (a) anular tear (b) herniated disk (c) (Adapted from Milette PC The proper terminology for reporting lumbar intervertebral disk disorders AJNR Am J Neuroradiol 181859-1866 1997 with permission)

There is convincing evidence in the scientific literature that the features of spondylosis deformans represent the normal aging process whereas intervertebral osteochondrosis denotes true pathologic disk degeneration[ ]61 [ ]71 [ ]75 [ ]83 [ ]84 Schmorl and Junghanns[ ]75 found spondylotic changes in 60 of women and almost 80 of men over the age of 50 In a series of 400 dried skeletons Nathan[ ]61 found anterior vertebral body osteophytes which constitute the main feature of spondylosis deformans in 100 of individuals over age 40 whereas posterior osteophytes were found in only 39 of individuals even after the age of 80 Twomey and Taylor[ ]83 [ ]84 have found that loss of disk height is unusual in a normal aging population and that loss of stature in the elderly is attributable to loss of intervertebral body height rather than loss in disk height During the normal aging process the mucoid matrix of the nucleus pulposus is progressively replaced by fibrous tissue[ ]37 but the intervertebral height is preserved and the disk margins remain regular Dessication and thining of disks or disks that bulge like an underinflated automobile tire are not typical of elderly spines Slight symmetric bulging may occur if there has been vertebral body remodeling resulting from osteoporosis Small amounts of gas can be detected on plain films or CT images near the insertion of the anulus on the ring epiphysis and this gas is probably located in transverse anular tears adjacent to the ring epiphysis During the fourth decade anterior and lateral marginal vertebral body osteophytes constitute normal findings comparable with having gray hair but end plate erosions with osteosclerosis or chronic reactive bone marrow changes type 2 or 3 as described by Modic et al[ ]57 should not be seen Slight to moderate decrease in central signal intensity can be detected on T2-weighted MR images as part of the normal aging process but the changes should involve uniformly all lumbar disks

Deteriorated disks represent real pathologic degeneration which is sometimes referred to as chronic diskopathy On microscopic examination they show total structural disorganization and general replacement of normal disk material by scar tissue For this reason they were initially labeled scarred disks by the members of a joint committee on spinal nomenclature created by the Quebec Association of Radiologists[ ]14 Because of possible confusion with postoperative changes the term deteriorated disk has been proposed as an acceptable substitute Strictly speaking the term degeneration could be used to designate this entity but this latter term has such a broad nonspecific meaning that it is best avoided The deteriorated disk is characterized by narrowing of the intervertebral space irregular disk contour generally associated with symmetric or asymmetric bulging abundant presence of gas in the central portion of the intervertebral disk space multidirectional osteophytes that do not respect the central spinal canal or the foramina end plate erosions with reactive osteosclerosis and chronic bone marrow changes On T2-weighted MR images the central disk signal intensity is usually markedly decreased and the number of affected lumbar disks is variable Even though transverse concentric and radial anular tears have been identified on postmortem specimens[ ]92 the anular tear category in this model refers essentially to the radial tears that are generally demonstrated by diskography in symptomatic patients For a more precise description of those tears this model may be supplemented by the Dallas Discogram Description system[ ]70 with or without its recently proposed updates[ ]4 [ ]72 [ ]80

It should be emphasized that the pathoanatomic model is not based on direct identification of a particular geometric pattern but on the anatomy and pathology that are expected as a result of the analysis of specific criteria Using this model the conclusion of any imaging report does not consist of terms related to the shape of the disk contour or the displaced disk material but on a pathologic diagnosis that should be presented with an appropriate confidence level (possible probable or definite) The diagnosis of a probable major radial anular tear may be inferred from the presence of a definite central signal intensity loss because as a result of diskographic MR imaging correlations the positive predictive value of this sign has been estimated at 96[ ]48 The use of this model requires an effort to understand the criteria allowing differentiation of normal aging from true pathologic degeneration so this system is slightly more complicated than the morphologic model Its reliability has never been tested Some intraobserver or interobserver disagreement would probably occur trying to distinguish anular tears without herniation from anular tears with small herniations With respect to correspondance to clinical situations this scheme like the morphologic model has limited interest it has been shown that disks demonstrating the features of the deteriorated disk are likely to be responsible for symptoms but this relationship has been statistically established to be significant only for the L4-L5 disk[ ]24

Which Model Should Be Used

In other areas of diagnostic radiology the aim of image analysis is always to predict what the pathologist would find if he or she could be provided with an adequate specimen immediately following the imaging study radiologic diagnoses are presented with a pathologic perspective There is no reason why the reporting of disk disorders should be

any different Terms like bulging disk are meaningless to a pathologist and I personally favor the pathoanatomic model Nomenclature standardization however is not a task that can be achieved by an individual or even a single group of authors[ ]12 To have any impact recommendations have to emanate from well established national or international societies The multiplicity of scientific societies with an interest in the spine all over the world creates a special problem but new joint committees have recently been set up combining efforts to come up with a practical unified system that it is hoped could be proposed jointly by the North American Spine Society the American Academy of Orthopedic Surgeons the American Academy of Neurological Surgeons the American Society of Spine Radiology and the American Society of Neuroradiology Agreeing in North America on a classification of disk disorders that could gain universal acceptance like the TNM classification of neoplastic diseases would be a major achievement Meanwhile the choice of the nomenclature is up to the best judgement of each practicing radiologist and the essential issue in a given hospital or community practice remains clear communication between radiologists and referring physicians by way of a local agreement as to the meaning of words

A major problem frequently occurs because observers of imaging studies try to combine elements of the morphologic classification with those of the pathoanatomic classification Trying to differentiate a bulging disk (morphologic qualifier) from a disk herniation (pathologic diagnosis) cannot work because a bulging disk aspect is a common feature of the aging disk the deteriorated disk and some posterior central disk herniations (Fig 9) Trying to make the distinction is doomed to failure because it defies formal logic On the other hand it is theoretically possible to differentiate a radial anular tear (without herniation) from a disk herniation because these are two different pathologic entities although one may be the continuum of the other It is best to adopt either one of the two systems and avoid trying to straddle the two A general classification of disk disorders attempting to conciliate the morphologic and the pathoanatomic model is proposed in Table 1

Figure 9 A bulging disk aspect often conceals a posterior central herniation A Complete rupture of the outer anular fibers allowing nuclear material to escape and peel off the posterior longitudinal ligament (and sometimes a few intact peripheral anular fibers) from the torn disk creating a detectable focal or asymmetric extension of the disk margin beyond the interspace which qualifies as a protrusion B With more gelatinous nuclear material escaping underneath the rigid posterior longitudinal ligament the focal bulge is no longer detectable as its radius increases and if the tear occurs in the posterior midline or para-medial direction the aspect mimics symmetric disk extension beyond the interspace C Since in most cases only the outline of a diffusely hypointense disk is perceived on MR images this creates the illusion of circumferential disk bulging on axial sections D The real nature of a bulging disk of this type may be suspected by scrutinizing the sagittal sections and appreciating that unless one is dealing with a chronically degenerated scarred disk the bulge is not symmetric but limited to the posterior aspect of the disk

TABLE 1 -- GENERAL

CLASSIFICATION OF DISK LESIONS Normal (excluding aging changes)

Congenitaldevelopmental variants

Inflammationinfection

Neoplasia

Degenerativetraumatic

Degeneration

Anular tear

Herniation Protrusion

Extrusion

Degeneration Spondylosis deformans

Intervertebral osteochondrosis

Further Qualifying the Displaced Disk Material Beyond the Disk Space

Regardless of the basic system that is used the type of herniation should be assessed The volume and location of the displaced disk material beyond the normal peripheral margin of the intervertebral space also need to be specified In certain cases it is also possible to determine the composition of this material For the sake of simplicity the term herniation is used consistently in the remainder of this article to refer to all displaced disk material but what is discussed can also be applied to protrusions and extrusions if one wants to use the morphologic nomenclature

Type of Herniation

Upward or downward migration of nuclear material may occur through a break in a vertebral body end plate creating an intravertebral herniation sometimes referred to as an intraspongy herniation or a Schmorls node[ ]67 (Fig 10) Although a herniation occurring in any horizontal direction is likely to cause symptoms because of the presence of pain-sensitive nerve endings in the outer anulus[ ]7 [ ]8 [ ]65 herniations occurring in a posterior or posterolateral direction deserve special consideration because of the added possibility of dural sac or individual nerve root compression

Figure 10 Various types of intravertebral herniations (Schmorls nodes) A Intravertebral herniation through the inferior end plate of the L3 vertebral body demonstrated by diskography in a 35-year-old man suffering from chronic low back pain The patients typical pain was reproduced during injection and the lesion was considered responsible for the patients symptoms B T2-weighted sagittal section demonstrating an intravertebral herniation through the inferior end plate of the L4 vertebral body in a 24-year-old woman presenting with chronic low back pain The high signal intensity of the lesion associated with the loss of normal central signal intensity of the parent disk suggests that the lesion is a bona fide acquired intraspongy herniation and not just a developmental defect C T2-weighted sagittal section demonstrating an intravertebral herniation through the inferior end plate of the L3 vertebral body (arrow) Because both the herniation and the parent disk show normal signal intensity the abnormality was

considered a probably asymptomatic developmental defect

Other characteristics of disk herniations have become relevant with the development of new therapeutic possibilities (eg chemonucleolysis and percutaneous diskectomy) The term sequestration is confusing and has often been used to indicate displacement of disk material away from the parent disk The term sequestered disk should be used restrictedly to designate a fragment of diskal tissue that has migrated from the disk space and has no connection by diskal tissue to the disk of origin[ ]20 [ ]21 [ ]42 Sequestration refers to loss of continuity with disk tissue still present in the intervertebral disk space The term migration has a broader meaning indicating displacement of disk material away from the edge of the rent in the outer anulus either in the central spinal canal at the disk level or above or below the disk level This difference is illustrated in Figure 11 The terms communicating and noncommunicating derive from a different perspective and are mostly used in the context of intradiskal therapeutic injections They refer to the interruption of the periphery of the disk allowing fluid injected into the disk to leak into the spinal canal and reach displaced disk material[ ]20 [ ]51 The terms contained and uncontained are unfamiliar to most radiologists in a contained herniation the displaced disk material is still covered by a few intact but distended outer anular fibers or by a capsule formed by outer anular fibers and the adherent posterior longitudinal ligament

Figure 11 Various types of posterior central herniations A Small subligamentous herniation (protrusion) without significant disk material migration B Subligamentous herniation with downward migration of disk material under the PLLC C Sub-ligamentous herniation with downward migration of disk material and sequestered fragment (arrow)

The terms subligamentous and extraligamentous (or transligamentous) refer to the position of the displaced disk material with respect to the posterior longitudinal ligament The anatomy of the posterior longitudinal ligament has been recently revised[ ]73 [ ]89 It is a membranous structure that has multiple components a deep layer attached to disks and vertebral bodies a superficial layer attached to the dura by fibrous tissue (Hoffmanns

ligament) and lateral extensions known as the lateral membranes or peridural membranes (Fig 12) (Figure Not Available) It should probably be referred to as the posterior longitudinal ligament complex (PLLC) It actually divides the epidural space into the perithecal space and the anterior epidural space where displaced disk material can be entrapped (Fig 13) A potential space allowing accumulation of displaced disk material has also been detected between the outer anular fibers and the deep fibers of the PLLC on the posterior central aspect of the disk[ ]63 Posterior midline herniations seldom rupture the PLLC and are generally subligamentous The lateral membranes are less resistant and transligamentous herniations are usually the result of posterior off-center herniations or posterolateral herniations

Figure 12 (Figure Not Available) The PLLC is portrayed here in relation to various types of subligamentous disk displacement At the disk level posteriorly displaced disk material frequently occupies the midline Below and above the disk an anterior epidural space (AES) exists between the PLLC and the posterior aspect of the vertebral bodies In this space disk fragment motion across the midline is curtailed by a sagittal midline septum (dashed line) A delicate translucent membrane (shown only on left side of drawing) is stretched between the free edge of the deep layer of the posterior longitudinal ligament and the lateral spinal canal (From Schellinger D Manz HJ Vidic B et al Disk fragment migration Radiology 175831-836 1990 with permission)

Figure 13 Relationship of typical posterior disk herniations with the PLLC A Midline sagittal section unless very large a posterior midline herniation usually remains entrapped underneath the deep layer of the PLL C and sometimes a few intact outer anulus fibers joining with the PLL C to form a capsule The deep layer of the PLL C (arrow) also attaches to the posterior aspect of the vertebral body so that no potential space is present underneath B Sagittal para-central section the PLL C extends laterally at the disk level (arrowhead) but above and below the disk an anterior epidural space (as) where disk fragments are frequently entrapped is present between the lateral (peridural) membranes and the posterior aspect of the vertebral bodies

Volume of Herniated Material

Quantifying the herniated disk material by measuring in millimeters its greatest diameter or by evaluating its cross-sectional area in square millimeters is rarely done The resulting figures could be misleading without relating this measurement to the size of the spinal canal and the exact location of the lesion[ ]88 A purely qualitative and subjective statement that a mild moderate or severe herniation is present however does not give the person reading the imaging report any indication as to the potential of the lesion to cause significant compression of the dural sac or individual exiting nerve roots A reasonably precise scheme has been proposed in 1995 by the Nomenclature Committee of the North American Spine Society[ ]20 Measurements are taken from an axial CT or MR imaging section at the site of most severe compromise canal compromise of less than 25 at that section is qualified as mild 25 to 75 is moderate 76 to 90 is moderately severe and greater than 90 is severe It is understood that such characterizations describe only the cross-sectional area at one level and do not account for the total volume of displaced material displacement of neural tissue or clinical significance The usefulness of having four categories is questionable and can likely generate poor interobserver or intraobserver agreement especially in situations where the central spinal canal is relatively narrow Bonnevilles scheme[ ]9 [ ]10 [ ]11 should generate greater reliability (Fig 14) (Figure Not Available) Separation of the cross-sectional area in three thirds can be applied to both the central spinal canal and the foramina It can be agreed by way of convention that the terms mild moderate and severe lumen compromise by a disk herniation designate extension of the displaced disk material in the anterior middle or posterior third of the central canal or foramen depending on the specified location of the herniation

Figure 14 (Figure Not Available) The size of the herniation in the horizontal plane is assessed and designated by the numbers 1 2 or 3 by establishing its extension in the anterior middle or posterior third of the spinal canal (From Bonneville JF Plaidoyer pour une classification par limage des hernies discales lombaires la carte-image Rev Imag Med 2557-560 1990 with permission)

Location of Herniated Material

Bonneville[ ]9 [ ]10 [ ]11 has also proposed an interesting and simple alpha-numerical system to classify according to their location the position of disk fragments that have migrated in the horizontal or sagittal plane (Figs 15 (Figure Not Available) and 16) (Figure Not Available) Using more precise anatomic boundaries unfortunately more familiar to surgeons than radiologists Wiltse et al[ ]88 have proposed another system which has been supported by the North American Spine Society[ ]20 [ ]21 Anatomic zones and levels are defined using the following anatomic landmarks medial edge of the articular facets medial lateral upper and lower border of the pedicles and coronal plane at the disk center On the horizontal plane (Fig 17) (Figure Not Available) these landmarks determine the bounderies of the central zone the subarticular zone the foraminal zone the extraforaminal zone and the anterior zone (anterior to the coronal plane at the center of the disk) In the sagittal plane they determine the boundaries of the diskal level the infrapedicular level the pedicular level and the suprapedicular level (Figs 18 (Figure

Not Available) and 19) (Figure Not Available) Radiologists interpreting axial CT or MR images may find it difficult to use the medial edge of the facets as the landmark that separates the central zone from the subarticular zone because the superior articular facets are generally not included in axial sections at the disk level The alternative is to use the expression posterolateral to designate collectively all posterior herniations that are not midline but do not extend into a foramen as was proposed by Bonneville[ ]9 [ ]10 [ ]11

Figure 15 (Figure Not Available) In the horizontal plane herniations are labeled midline (a) posterolateral (b) foraminal (c) and extra-foraminal (d) (From Bonneville JF Plaidoyer pour une classification par limage des hernies discales lombaires la carte-image Rev Imag Med 2557-560 1990 with permission)

Figure 16 (Figure Not Available) In the craniocaudal direction disk migration is labeled +1 +2 +3 or -1 -2 -3 by referring to the height of a vertebral body divided in thirds (From Bonneville JF Plaidoyer pour une classification par limage des hernies discales lombaires la carte-image Rev Imag Med 2557-560 1990 with permission)

Figure 17 (Figure Not Available) The anatomic zones identified on axial images The anterior zone (not shown) is delineated from the extraforaminal zone by an imaginary coronal line in the center of the vertebral body (From Wiltse LL Berger PE McCulloch JA A system for reporting the size and location of lesions in the spine Spine 221534-1537 1997 with permission)

Figure 18 (Figure Not Available) The anatomical levels identified on craniocaudal images (From Wiltse LL Berger PE McCulloch AJ A system for reporting the size and location of lesions in the spine Spine 221534-1537 1997 with permission)

Figure 19 (Figure Not Available) Coronal view of the main zones and levels (From Wiltse LL Berger PE McCulloch JA A system for reporting the size and location of lesions in the spine Spine 221534-1537 1997 with permission)

Composition of Herniated Material

Displaced disk material may consist of glycosaminoglycans type 1 or 2 collagen end plate cartilage and bone fragments avulsed from the ring epiphysis A reactive inflammatory reaction usually results in edematous tissue followed by granulation tissue which may undergo calcification (Fig 20) Necrotic and partially resorbed displaced disk material sometimes produces a large fluid-filled pouch distinguishable from the common high-intensity zone because of its size (Fig 21) or a gas-filled cavity generally in continuity with gas in the intervertebral space (Fig 22) [ ]42 These characteristics may be meaningful if intradiskal injection therapy is considered In imaging reports herniations exhibiting calcium deposits and those exhibiting replacement of disk material by gas or a relatively large fluid collection can be qualified as chronic herniations

Figure 20 A CT scan demonstration of a small posterior central L4-L5 calcified subligamentous herniation The resistant deep layer of the PLLC restrains displacement of the disk material in the posterior central direction and does not allow a detectable distortion of the disk contour In this particular case the presence of the calcification is actually the only evidence that a posterior midline anular tear and a small subligamentous herniation are present B Posterior right central and sub-articular L5-S1 calcified disk herniation in same patient Posterolateral herniations are generally more conspicuous than posterior midline herniations because the deep layer of the PLLC gets thinner away from the midline

Figure 21 Posterior central midline L4-L5 herniation in a 52-year-old man demonstrated on a T2-weighted midline MR sagittal section There is intervertebral space narrowing with loss of normal central disk signal

intensity while the herniated disk material demonstrates high signal intensity consistent with a predominantly fluid consistency

Figure 22 CT scan demonstration in a 51-year-old woman of a left posterolateral L5-S1 disk hernation consisting essentially in a gas-filled pouch (white arrow) Gas is also present in the central portion of the intervertebral disk space (black arrow)

DIAGNOSTIC IMAGING AND CHARACTERIZATION OF A HERNIATED LUMBAR DISK

Assessing the validity of the currently used imaging procedures to diagnose a herniated lumbar disk is not an easy endeavor The validity of a measurement is the extent to which it corresponds to the true biologic value or some accepted gold standard[ ]40 With the exception of postmortem studies evaluation of the pathoanatomy by the surgeon in the operating room has always been considered the gold standard but this does not constitute an ideal situation Inspection of the disk through a small laminectomy incision to determine for instance if nuclear fragments lie within or outside the anular fibers may not be very reliable Also unbiased intraoperative determination of a normal degenerated or herniated disk in a patient with sciatica may also be difficult[ ]86 Because the validity of diskography has been previously established by postmortem studies and surgical correlations[ ]48 it is sometimes used as a gold standard in situations where no surgery has been performed

Conventional Radiographs

Lumbar disk herniations can exceptionally be diagnosed directly on good quality lateral projections because the x-ray attenuation is slightly greater in displaced disk material than in epidural fat Occasionally a calcified rim outlines the displaced disk fragment

(Fig 23) In most situations however narrowing of an intervertebral disk space in the absence of other evidence of chronic diskopathy is the only detectable sign suggesting the presence of a disk herniation To my knowledge the sensitivity and specificity of this sign has never been assessed The accepted rule of thumb is that the height of a given lumbar intervertebral disk space should always be slightly greater than the height of the above located interspace This rule does not apply to the transition disk immediately above the sacrum (usually L5-S1) The specificity of this sign is probably quite high but a few false-positives are seen especially at the L4-L5 level because of minor congenital hypoplasia The presence of posterior or foraminal vertebral body osteophytes associated or not with disk space narrowing is a definite sign of a chronic disk herniation

Figure 23 A Chronic left L3-L4 extraforaminal disk hernation in a 54-year-old man suspected on an AP radiograph demonstrating a calcified shell on the left side of the intervertebral disk space (white arrow) B Axial CT scan section confirming the diagnosis of a chronic extraforaminal L3-L4 herniation

Myelography

Myelography is essentially an exploration of the subarachnoid space Disk herniations are demonstrated only indirectly because they can cause thecal sac deformity and individual nerve root sleeve filling defects (Fig 24) Of all the special imaging procedures

myelography is the only one that allows upright projections with full weight bearing It is not unusual to demonstrate in this way small posterior central or posterolateral herniations that are undetectable on CT sections Interestingly the overall sensitivity of myelography to detect disk herniations has been found to be higher than that of CT whereas its specificity has been found to be lower[ ]74 In comparison with standard CT examination which usually includes only the three or four lower lumbar disks myelography easily allows coverage of the entire lumbar area and assessment of the intrathecal structures (cauda equina and conus medullaris) Far lateral foraminal herniations extraforaminal herniations and anterior herniations however are not detected The sensitivity for detection of posterior central L5-S1 herniations is also relatively poor because of the greater distance between the thecal sac and the posterior aspect of this particular disk

Figure 24 L5-S1 disk herniation in a 25-year-old man detected by indirect signs using lumbosacral myelography A Upright oblique projections showing a filling defect of the left S1 root sleeve (white arrow) suggesting significant nerve root compression by a left posterolateral disk hernation The right S1 root sleeve fills normally with contrast (black arrow) B Subtle compression of the anterior wall of the dural sac by displaced disk material (small arrows) demonstrated on upright lateral projection This sign is usually absent in the presence of a large amount of fat and venous structures in the anterior epidural compartment

CT

The sensitivity of CT to diagnose a herniation of the nucleus pulposus at the L5-S1 interspace is greater than that of myelography if images in the exact plane of the disk can be obtained[ ]23 [ ]39 Otherwise the superiority of plain CT over myelography to demonstrate disk herniations has not been established but CT has the distinct advantage of being

noninvasive and provides direct anatomic information[ ]23 Large herniations are easily detected but as explained previously the distinction between protrusions and extrusions is often difficult without sagittal reconstructions CT essentially allows an assessment of the contour of the disk The diagnosis of very small herniations in the absence of direct or indirect evidence of a radial tear is hazardous and associated with a high percentage of false-positives and false-negatives[ ]52 The diagnosis of moderate and large size herniations in different directions is usually possible but anterior herniations are rarely diagnosed not because they are not detectable but because observers pay little attention to the anterior contour of the disk (Fig 25) Because the PLLC cannot usually be identified the distinction of subligamentous from transligamentous herniation can only be suggested in most cases by the size of the herniated material A definite diagnosis of sequestration is rarely possible Calcifications within the displaced material are readily seen but may be difficult at times to differentiate from an accompanying osteophyte or an avulsed bone fragment from the vertebral body ring epiphysis (Fig 26) The presence of gas in the herniated material is easily detected

Figure 25 Anterior L4-L5 herniation demonstrated by CT scan in a 51-year-old woman with chronic low back pain Although sometimes quite conspicuous such herniations are rarely reported because observers pay little attention to the anterior contour of the disk

Figure 26 CT scan demonstration of a posterior right central L4-L5 disk herniation in a 38-year-old woman with avulsion of a bone fragment from the ring epiphysis and adjacent part of the superior L5 end plate Reactive osteosclerosis is seen around the vertebral body defect (arrows) suggesting a chronic lesion

CT Myelography

This association combines the advantages of both imaging modalities The fact that its accuracy has been reported as being less[ ]22 [ ]32 higher[ ]1 [ ]6 or equivalent[ ]82 to MR imaging is a reflection of the differences in technologic advancement and pathologic nomenclature that hamper valid comparisons between different studies

MR Imaging

Most reported studies establish MR imaging as the first choice modality to diagnose a herniated lumbar disk[ ]5 [ ]22 [ ]32 [ ]46 The associated intravenous injection of a paramagnetic agent has been found useful to demonstrate some anatomic features of disk disease in patients with no previous lumbar disk surgery[ ]56 [ ]68 [ ]90 MR imaging provides a better assessment of disk morphology than CT or CT myelography because sagittal sections are routinely obtained Assessment of foraminal involvement by displaced disk material is more accurate (Fig 27) and anterior disk herniations can be detected more easily than with CT or CT myelography If one is looking specifically for herniated lumbar disks associated with nerve root compression however it has been demonstrated that CT is equally accurate[ ]82 Alterations of the central or peripheral disk signal intensity on T2-weighted images are seen in most disks afflicted with an anular tear[ ]48 and alert the observer to scrutinize the disk contour in search for local modifications indicative of a herniation Because the signal of the displaced disk material is usually very similar to that of the outer anulus PLLC and vertebral body cortical bone small herniations are generally more conspicuous on axial CT sections than on corresponding axial MR imaging sections Gas and calcium deposits within the displaced fragment cannot usually

be detected but associated vertebral body bone marrow changes are typically seen and are helpful in differentiating acute from chronic processes[ ]57 The occasional presence of a high-intensity zone in the herniated material with an occasionally enhancing border after contrast injection is probably caused by a mixture of displaced nuclear material acute and subacute inflammatory tissue and neovascularized reactive tissue[ ]4 [ ]48 [ ]72 Contradictory reports have been published regarding the accuracy of MR imaging to differentiate subligamentous from transligamentous herniations[ ]26 [ ]38 [ ]73 [ ]76 Understanding the anatomy of the PLLC is helpful to make the distinction (Fig 28) (Figure Not Available) Masaryk et al[ ]46 have suggested that MR imaging is accurate to distinguish sequestered disks from other forms of lumbar disk herniations but most observers find this distinction difficult to establish[ ]42

Figure 27 A Left L4-L5 foraminal herniation well seen on an intermediate-weighted left parasagittal MR section (arrow) in a 47-year-old man B The lesion is much less obvious on intermediate-weighted (left) and T2-weighted (right) axial sections and was in fact more conspicuous on the corresponding CT scan section

Figure 28 (Figure Not Available) A Subligamentous disk herniation Left T1-weighted image demonstrating displaced disk material with a smooth outline imposed by the demarcation of the anterior epidural space (AES) by the lateral membrane of the PLLC Right Correlative drawing B Transligamentous disk herniation Left T1-weighted image of a large disk herniation (cervical in this case) which has ruptured through the posterior confines of the AES Penetration of the right lateral membrane can be observed (arrow) and the disk fragment contour is serrated Right Correlative drawing (From Schellinger D Manz HJ Vidic B et al Disk fragment migration Radiology 175831-836 1990 with permission)

Diskography and CT Diskography

During 30 years (1950 to 1980) when myelography was the only available imaging technique to demonstrate lumbar disk herniations diskography was an invasive but efficient way to demonstrate posterior central L5-S1 herniations and other large herniations (other than posterior central and paramedial) that could not be detected by myelography[ ]50 These herniations are now usually well demonstrated by CT and MR imaging Comparing the accuracy of five imaging modalities (excluding MR imaging) for the diagnosis of lumbar disk herniation Jackson et al[ ]31 found that CT diskography (Fig 29) was the most accurate test (87) compared with 77 for CT myelography 74 for CT 70 for myelography 64 for pain reproduction during diskography and 58 for diskography without CT Disk injection reproduced the patients clinical pain pattern in only 36 of herniated disks This clinical test isolated from the images had high specificity (89) but low sensitivity (43) for the diagnosis of disk herniation The reported low sensitivity of diskography images (unassociated with CT) to diagnose disk herniation is to be expected the purpose of the intradiskal injection being primarily the demonstration of an anular tear the contrast leaking through the tear only occasionally delineates an extruded fragment When a disk herniation has been diagnosed by other imaging modalities diskography allows to determine if the herniation is contained or noncontained (Figs 30 and 31) this information may have clinical relevance[ ]62 It also allows to establish if the displaced disk material is communicating or not with the parent disk and establishes the likelihood that it is sequestered or not There always remains a possibility that the contrast injected under pressure may reach a disk fragment that is nevertheless sequestered by leaking through the associated anular tear CT diskography also allows assessment in most cases of the integrity of the PLLC[ ]89 The superior sensitivity of diskography over MR imaging to demonstrate anular tears has been well established[ ]27 [ ]44 [ ]48 [ ]64 [ ]77 [ ]91 [ ]94 The presence of a radial tear and the inflammatory reaction it creates may be symptomatic despite the absence of true disk herniation[ ]29 [ ]48 [ ]49 [ ]69

Figure 29 L4-L5 CT diskogram demonstrating a large left posterolateral radial anular tear associated with

a left foraminal and extraforaminal herniaton (same patient as in Figure 28) (Figure Not Available)

Figure 30 Contained posterior L4-L5 and L5-S1 disk herniations in a 57-year-old man demonstrated by diskography The L3-L4 disk is normal

Figure 31 Noncontained L4-L5 disk herniation in a 23-year-old woman Reflux of injected contrast is seen in the anterior epidural space above and below the disk space The L5-S1 disk also demonstrates incomplete anterior and posterior radial anular tears

SUMMARY

The absence of universal nomenclature standardization with respect to the definition of a disk herniation and its different categories especially regarding type and location is still a major problem that will only be overcome when major national or international scientific societies join efforts to support a particular scheme Meanwhile it is important to realize that the two models that are currently most used are based on a different perspective Trying to straddle the two by opposing for instance bulging disk and herniation is doomed to failure because this exercise defies formal logic MR imaging is currently the most accurate noninvasive imaging modality to diagnose a disk herniation and to determine its exact location The determination of some pathoanatomic characteristics of herniated disks (type and composition) may require the use of CT diskography or CT diskography

References

1 Albeck MJ Hilden J Kjaer L et al A controlled comparison of myelography computed tomography and magnetic resonance imaging in clinically suspected lumbar disc herniation Spine 20443-448 1995 Abstract 2 American Academy of Orthopedic Surgeons Glossary on Spinal Terminology Chicago American Academy of Orthopedic Surgeons 1981 3 Andersson GB Weinstein JN Disc herniation [editorial] Spine 211S 1996 Citation 4 Aprill C Bogduk N High-intensity zone A diagnostic sign of painful lumbar disc on magnetic resonance imaging Br J Radiol 65361-369 1992 Abstract 5 Birney TJ White JJ Jr Berens D et al Comparison of MRI and discography in the diagnosis of lumbar degenerative disc disease J Spinal Disord 5417-423 1992 Abstract 6 Bischoff RJ Rodriguez RP Gupta K et al A comparison of computed tomography-myelography magnetic resonance imaging and myelography in the diagnosis of herniated nucleus pulposus and spinal stenosis J Spinal Disord 6289-295 1993 Abstract 7 Bogduk N The innervation of the lumbar spine Spine 8286-293 1983 Abstract 8 Bogduk N Tynan W Wilson AS The nerve supply to the human lumbar intervertebral discs J Anat 13239-56 1981 Abstract 9 Bonneville JF La carte-image des hernies discales lombaires Rachis 2255-257 1990 10 Bonneville JF La topografia simbolica delle ernie discali lombari Riv Neuroradiol 5427-431 1992 11 Bonneville JF Plaidoyer pour une classification par limage des hernies discales lombaires La carte-image Rev Imag Med 2557-560 1990 12 Brant-Zawadzki M Jensen M Spinal nomenclature Spine 20388-390 1995 Abstract

13 Brant-Zawadzki MN Jensen MC Obuchowski N et al Interobserver and intraobserver variability in interpretation of lumbar disc abnormalities A comparison of two nomenclatures Spine 201257-1263 1995 Abstract 14 Breton G Is that a bulging disk a small herniation or a moderate protrusion [editorial] Can Assoc Radiol J 42318 1991 Citation 15 Czervionke LF Lumbar intervertebral disc disease Neuroimaging Clin North Am 3465-485 1993 16 Deyo RA Nonsurgical care of low back pain Neurosurg Clin North Am 2851-862 1991 17 Deyo RA Loeser JD Bigos SJ Herniated lumbar intervertebral disk Ann Intern Med 112598-603 1990 Abstract 18 Dorlands Illustrated Medical Dictionary ed 28 Philadelphia WB Saunders 1994 19 Fardon D Pinkerton S Balderston R et al Terms used for diagnosis by English speaking spine surgeons Spine 18274-277 1993 Citation 20 Fardon DF Herzog RJ Mink JH et al Nomenclature of Lumbar Disc Disorders Contemporary Concepts in Spine Care Rosemont IL North American Spine Society 1995 21 Fardon DF Herzog RJ Mink JH et al Nomenclature of lumbar disc disorders In Garfin S Vaccaro A (eds) Orthopedic Knowledge Update Spine Rosemont IL American Academy of Orthopedic Surgeons 1997 pp A3-A14 22 Forristall RM Marsh HO Pay NT Magnetic resonance imaging and contrast CT of the lumbar spine Comparison of diagnostic methods and correlation with surgical findings Spine 131049-1054 1988 Abstract 23 Fries JW Abodeely DA Vijungco JG et al Computed tomography of herniated and extruded nucleus pulposus J Comput Assist Tomogr 6874-887 1982 Abstract 24 Frymoyer JW Newberg A Pope MH et al Spine radiographs in patients with low-back pain An epidemiological study in men J Bone Joint Surg Am 661048-1055 1984 Abstract 25 Gospodarowicz M Benedet L Hutter RV et al History and international developments in cancer staging Cancer Prev Control 2262-268 1998 Abstract 26 Grenier N Greselle JF Vital JM et al Normal and disrupted lumbar longitudinal ligaments Correlative MR and anatomic study Radiology 171197-205 1989 Abstract 27 Gunzburg R Parkinson R Moore R et al A cadaveric study comparing discography magnetic resonance imaging histology and mechanical behavior of the human lumbar disc Spine 17417-426 1992 Abstract 28 Haughton VM Eldevik OP Magnaes B et al A prospective comparison of computed tomography and myelography in the diagnosis of herniated lumbar disks Radiology 142103-110 1982 Abstract

29 Haughton VM Lim TH An H Intervertebral disk appearance correlated with stiffness of lumbar spinal motion segments AJNR Am J Neuroradiol 201161-1165 1999 Abstract 30 Herzog RJ The radiologic assessment for a lumbar disc herniation Spine 2119S-38S 1996 Abstract 31 Jackson RP Becker GJ Jacobs RR et al The neuroradiographic diagnosis of lumbar herniated nucleus pulposus I A comparison of computed tomography (CT) myelography CT-myelography discography and CT-discography Spine 141356-1361 1989 Abstract 32 Jackson RP Cain JE Jr Jacobs RR et al The neuroradiographic diagnosis of lumbar herniated nucleus pulposus II A comparison of computed tomography (CT) myelography CT-myelography and magnetic resonance imaging Spine 141362-1367 1989 Abstract 33 Jarvik JG Haynor DR Koepsell TD et al Interreader reliability for a new classification of lumbar disk disease Acad Radiol 3537-544 1996 Abstract 34 Jensen MC Brant-Zawadzki MN Obuchowski N et al Magnetic resonance imaging of the lumbar spine in people without back pain N Engl J Med 33169-73 1994 Abstract 35 Kent DL Haynor DR Larson EB et al Diagnosis of lumbar spinal stenosis in adults A meta-analysis of the accuracy of CT MR and myelography AJR Am J Roentgenol 1581135-1144 1992 Abstract 36 Kieffer SA Sherry RG Wellenstein DE et al Bulging lumbar intervertebral disk Myelographic differentiation from herniated disk with nerve root compression AJR Am J Roentgenol 138709-716 1982 Abstract 37 Kieffer SA Stadlan EM Mohandas A et al Discographic-anatomical correlation of developmental changes with age in the intervertebral disc Acta Radiol 9733-739 1969 38 Kim KY Kim YT Lee CS et al MRI classification of lumbar herniated intervertebral disc Orthopedics 15493-497 1992 Abstract 39 Kornberg M Rechtine GR Dupuy TE Computed tomography in the diagnosis of a herniated disk at the L5-S1 level Spine 9433-436 1984 Abstract 40 Kramer MS Clinical Epidemiology and Biostatistics New York Springer-Verlag 1988 41 Landis JR Koch GG The measurement of observer agreement agreement for categorical data Biometrics 33159-174 1977 Abstract 42 Laredo JD Bossard P Vuillemin-Bodaghi Formes anatomo-radiologiques des hernies discales In Morvan G Deburge A Bard H et al (eds) Le Rachis Lombaire Degeneratif Montpellier Sauramps Medical 1998 pp 37-49 43 Lee SH Coleman PE Hahn FJ Magnetic resonance imaging of degenerative disk disease of the spine Radiol Clin North Am 26949-964 1988 Abstract 44 Linson MA Crowe CH Comparison of magnetic resonance imaging and lumbar discography in the diagnosis of disc degeneration Clin Orthop 160-163 1990

45 Marchand F Ahmed AM Investigation of the laminate structure of lumbar disc anulus fibrosus Spine 15402-410 1990 Abstract 46 Masaryk TJ Ross JS Modic MT et al High-resolution MR imaging of sequestered lumbar intervertebral disks AJR Am J Roentgenol 1501155-1162 1988 Abstract 47 Milette PC The proper terminology for reporting lumbar intervertebral disk disorders AJNR Am J Neuroradiol 181859-1866 1997 Citation 48 Milette PC Fontaine S Lepanto L et al Differentiating lumbar disc protrusions disk bulges and discs with normal contour but abnormal signal intensity Magnetic resonance imaging with discographic correlations Spine 2444-53 1999 Abstract 49 Milette PC Fontaine S Lepanto L et al Radiating pain to the lower extremities caused by lumbar disk rupture without spinal nerve root involvement AJNR Am J Neuroradiol 161605-1613 1995 Abstract 50 Milette PC Melancon D A reappraisal of lumbar discography Can Assoc Radiol J 33176-182 1982 51 Milette PC Melancon D Dupuis PR et al A simplified terminology for abnormalities of the lumbar disk Can Assoc Radiol J 42319-325 1991 Abstract 52 Milette PC Raymond J Fontaine S Comparison of high-resolution computed tomography with discography in the evaluation of lumbar disc herniations Spine 15525-533 1990 Abstract 53 Mink JH Deutsch AL Goldstein TB et al Spinal imaging and intervention 1998 Phys Med Rehabil Clin North Am 9343-380 1998 54 Mixter WJ Barr JS Rupture of the intervertebral disc with involvement of the spinal canal N Engl J Med 211210-234 1934 55 Modic MT Masaryk TJ Ross JS et al Imaging of degenerative disk disease Radiology 168177-186 1988 Citation 56 Modic MT Ross JS Obuchowski NA et al Contrast-enhanced MR imaging in acute lumbar radiculopathy A pilot study of the natural history Radiology 195429-435 1995 Abstract 57 Modic MT Steinberg PM Ross JS et al Degenerative disk disease Assessment of changes in vertebral body marrow with MR imaging Radiology 166193-199 1988 58 Morvan G Mathieu P Les stenoses laterales In Morvan G Deburge A Bard H et al (eds) Le Rachis Lombaire Degeneratif Montpellier Sauramps Medical 1998 pp 315-324 59 Murray RO Skeletal trauma Regional In Sutton D (ed) Textbook of Radiology and Imaging ed 3 New York Churchill Livingstone 1980 pp 210-231 60 Nachemson A Lumbar disc herniation Conclusions Acta Orthop Scand 64(suppl 251)49 1993 Citation

61 Nathan H Osteophytes of the vertebral column An anatomical study of their development according to age race and sex with consideration as to their etiology and significance J Bone Joint Surg Am 44243-268 1962 62 Nygaard OP Mellgren SI Osterud B The inflammatory properties of contained and noncontained lumbar disc herniations Spine 222584-2488 1997 Abstract 63 Ohshima H Hirano N Osada R et al Morphologic variation of lumbar posterior longitudinal ligament and the modality of disc herniation Spine 182408-2411 1993 Abstract 64 Osti OL Fraser RD MRI and discography of annular tears and intervertebral disc degeneration A prospective clinical comparison J Bone Joint Surg Br 74431-435 1992 Abstract 65 Palmgren T Gronblad M Virri J et al Immunohistochemical demonstration of sensory and autonomic nerve terminals in herniated lumbar disc tissue Spine 211301-1306 1996 Abstract 66 Resnick D Niwayama G Degenerative disease of the spine In Resnick D (ed) Diagnosis of Bone and Joint Disorders ed 3 Philadelphia WB Saunders 1995 pp 1372-1462 67 Resnick D Niwayama G Intravertebral disk herniations Cartilaginous (Schmorls) nodes Radiology 12657-65 1978 Abstract 68 Ross JS Modic MT Masaryk TJ Tears of the anulus fibrosus Assessment with Gd-DTPA-enhanced MR imaging AJR Am J Roentgenol 154159-162 1990 Abstract 69 Saal JS The role of inflammation in lumbar pain Spine 201821-1827 1995 Abstract 70 Sachs BL Vanharanta H Spivey MA et al Dallas discogram description A new classification of CTdiscography in low-back disorders Spine 12287-294 1987 Abstract 71 Sauser DD Goldman AB Kaye JJ Discogenic vertebral sclerosis J Can Assoc Radiol 2944-50 1978 Abstract 72 Schellhas KP Pollei SR Gundry CR et al Lumbar disc high-intensity zone Correlation of magnetic resonance imaging and discography Spine 2179-86 1996 Abstract 73 Schellinger D Manz HJ Vidic B et al Disk fragment migration Radiology 175831-836 1990 Abstract 74 Schipper J Kardaun JW Braakman R et al Lumbar disk herniation Diagnosis with CT or myelography Radiology 165227-231 1987 Abstract 75 Schmorl G Junghanns H The Human Spine in Health and Disease ed 2 New York Grune and Stratton 1971 76 Silverman CS Lenchik L Shimkin PM et al The value of MR in differentiating subligamentous from supraligamentous lumbar disk herniations AJNR Am J Neuroradiol 16571-579 1995 Abstract 77 Simmons JW Emery SF McMillin JN et al Awake discography A comparison study with magnetic

resonance imaging Spine 16S216-221 1991 Abstract 78 Smyth MJ Wright V Sciatica and the intervertebral disc J Bone Joint Surg Am 401401-1418 1958 79 Taveras JM Radiologic aspects of low back pain and sciatic syndromes [editorial] AJNR Am J Neuroradiol 9351-358 1989 80 Tehranzadeh J Discography 2000 Radiol Clin North Am 36463-495 1998 Full Text 81 Thelander U Fagerlund M Friberg S et al Describing the size of lumbar disc herniations using computed tomography A comparison of different size index calculations and their relation to sciatica Spine 191979-1984 1994 Abstract 82 Thornbury JR Fryback DG Turski PA et al Disk-caused nerve compression in patients with acute low-back pain Diagnosis with MR CT myelography and plain CT Radiology 186731-738 1993 Abstract 83 Twomey L Taylor J Age changes in lumbar intervertebral discs Acta Orthop Scand 56496-499 1985 Abstract 84 Twomey LT Taylor JR Age changes in lumbar vertebrae and intervertebral discs Clin Orthop 22497-104 1987 85 Williams AL CT diagnosis of degenerative disc disease The bulging annulus Radiol Clin North Am 21289-300 1983 Abstract 86 Williams AL Haughton VM Meyer GA et al Computed tomographic appearance of the bulging annulus Radiology 142403-408 1982 Abstract 87 Williams AL Haughton VM Syvertsen A Computed tomography in the diagnosis of herniated nucleus pulposus Radiology 13595-99 1980 Abstract 88 Wiltse LL Berger PE McCulloch JA A system for reporting the size and location of lesions in the spine Spine 221534-1537 1997 Abstract 89 Wiltse LL Fonseca AS Amster J et al Relationship of the dura Hofmanns ligaments Batsons plexus and a fibrovascular membrane lying on the posterior surface of the vertebral bodies and attaching to the deep layer of the posterior longitudinal ligament An anatomical radiologic and clinical study Spine 181030-1043 1993 Abstract 90 Yamashita K Hiroshima K Kurata A Gadolinium-DTPA-enhanced magnetic resonance imaging of a sequestered lumbar intervertebral disc and its correlation with pathologic findings Spine 19479-482 1994 Abstract 91 Yu SW Haughton VM Sether LA et al Comparison of MR and diskography in detecting radial tears of the anulus A postmortem study AJNR Am J Neuroradiol 101077-1081 1989 Abstract 92 Yu SW Sether LA Ho PS et al Tears of the anulus fibrosus Correlation between MR and pathologic findings in cadavers AJNR Am J Neuroradiol 9367-370 1988 Abstract

93 Yussen PS Swartz JD The acute lumbar disc herniation Imaging diagnosis Semin Ultrasound CT MR 14389-398 1993 Abstract 94 Zucherman J Derby R Hsu K et al Normal magnetic resonance imaging with abnormal discography Spine 131355-1359 1988 Abstract

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  • CLASSIFICATION DIAGNOSTIC IMAGING AND IMAGING CHARACTERIZATION OF A LUMBAR HERNIATED DISK
    • IMAGING OF LOW BACK PAIN I
      • CLASSIFICATION DIAGNOSTIC IMAGING AND IMAGING CHARACTERIZATION OF A LUMBAR HERNIATED DISK
        • DEFINITION OF A DISK HERNIATION
        • CLASSIFICATION OF A HERNIATED LUMBAR DISK
          • Main Categories of Noninfectious Disk Abnormalities
          • Further Qualifying the Displaced Disk Material Beyond the Disk Space
            • DIAGNOSTIC IMAGING AND CHARACTERIZATION OF A HERNIATED LUMBAR DISK
              • Conventional Radiographs
              • Myelography
              • CT
              • CT Myelography
              • MR Imaging
              • Diskography and CT Diskography
                • SUMMARY
                  • References
Page 7: CLASSIFICATION, DIAGNOSTIC IMAGING, AND IMAGING ... · PDF fileclassification, diagnostic imaging, and imaging characterization of a lumbar herniated disk ... classification, diagnostic

ligaments But an impression has been unjustifiably derived from early postmortem studies[ ]86 that even in young individuals a disk with an intact anulus may be responsible for a detectable bulge on axial CT sections It has also been hypothesized that bulging disks are caused by diffuse anular hyperlaxity which occurs as a result of tears in collagen bridges between the concentric anular fibers while these concentric fibers remain intact[ ]15 This theory has never been proved because such collagen bridges between the concentric fibers of the anulus have never been found[ ]45 It is important to realize that a bulging disk is not an anatomic or pathologic entity it is an image that requires a differential diagnosis It sometimes represents a normal anatomic variant this is often the case with the L5-S1 disk On CT images it is often an illusion caused by a volume-averaging effect (Fig 5) It may be associated with remodeling of adjacent vertebral bodies because of osteoporosis (Fig 6) It may of course result from chronic disk deterioration and collapse A bulging disk illusion is often created on CT by a posterior anular disk rupture with displaced disk material peeling off the posterior longitudinal ligament and displacing it backward creating a posterior wide base protrusion that mimics diffuse symmetric disk bulging on both axial CT and MR imaging sections and is not differentiated from a bulging disk on sagittal MR images unless close attention is paid to the anterior aspect of the disk (Fig 7) Except for the fact that extrusions are rarely found in asymptomatic individuals[ ]34 this system does not really provide categories that correspond to clinical entities

Figure 5 A Bulging disk appearance of the L4-L5 disk shown on a 5-mm-thickness axial CT scan section in a 57-year-old woman The height of the intervertebral space was preserved and there was no reactive vertebral body end-plate modifications This aspect is probably partly due to vertebral body remodeling caused by osteoporosis but is mostly created by volume averaging (From Milette PC Fontaine S Daniels C et al Imaging of Low Back Pain CD-ROM SSB Multimedia Medical Series Montreal 1997 with permission) B Using 4- or 5-mm-thickness CT sections an intermediate gray shade halo is often computer generated by volume averaging of tissues with different attenuation coefficients in voxels represented by two-dimensional pixels located at the disk space periphery This creates the illusion of a three-dimensional image demonstrating diffuse disk bulging ST = slice thickness

Figure 6 Axial CT scan section of a L4-L5 disk in a 78-year-old man demonstrating diffuse disk bulging caused by remodeling of the adjacent vertebral bodies due to osteoporosis The intervertebral space was normal in height and there were no reactive adjacent bony endplate modifications

Figure 7 A T2-weighted axial section of a L5-S1 disk showing a left posterolateral wide base protrusion that can be easily confused with diffuse circumferential bulging B Corresponding T2-weighted left paracentral and central sagittal sections demonstrating loss of the L5-S1 disk signal intensity with posterior small left-central protrusion the anterior aspect of the disk does not extend beyond the endplates and therefore such a disk should not be labeled bulging disk

The Pathoanatomic Model

As opposed to the previous model that can be applied only to the interpretation of CT and MR imaging studies this model can be used for the interpretation of all imaging modalities including plain films and diskograms[ ]47 [ ]51 It consists of five categories that are not mutually exclusive so that different combinations are possible (Fig 8) (Figure Not Available) The first three refer to the general state of the disk (1) normal young disk (2) normal aging disk and (3) deteriorated disk (formerly called the scarred disk) The last two refer to localized lesions anular tear and herniated disk In this model the previously discussed definition of disk herniation proposed by Herzog[ ]30 is applicable The use of this system requires an effort to distinguish the normal aging changes from those of pathologic degeneration Resnick and Niwayama[ ]66 have emphasized the differentiating features of two degenerative processes involving the intervertebral disk which had been previously described by Schmorl and Junghanns[ ]75 (1) spondylosis deformans which affects primarily the anulus fibrosus and bony ring epiphysis and (2) intervertebral osteochondrosis which affects essentially the nucleus pulposus and the vertebral body end plates

Figure 8 (Figure Not Available) Schematic representation of a nomenclature based on a three-dimensional assessment of the anatomic and pathologic characteristics of both disk and adjacent vertebral bodies The categories are not mutually exclusive and some combinations are possible A Categories related to the general aspect of the disk normal young disk (a) normal aging disk (b) deteriorated disk (c) B Categories related to local lesions normal young disk (a) anular tear (b) herniated disk (c) (Adapted from Milette PC The proper terminology for reporting lumbar intervertebral disk disorders AJNR Am J Neuroradiol 181859-1866 1997 with permission)

There is convincing evidence in the scientific literature that the features of spondylosis deformans represent the normal aging process whereas intervertebral osteochondrosis denotes true pathologic disk degeneration[ ]61 [ ]71 [ ]75 [ ]83 [ ]84 Schmorl and Junghanns[ ]75 found spondylotic changes in 60 of women and almost 80 of men over the age of 50 In a series of 400 dried skeletons Nathan[ ]61 found anterior vertebral body osteophytes which constitute the main feature of spondylosis deformans in 100 of individuals over age 40 whereas posterior osteophytes were found in only 39 of individuals even after the age of 80 Twomey and Taylor[ ]83 [ ]84 have found that loss of disk height is unusual in a normal aging population and that loss of stature in the elderly is attributable to loss of intervertebral body height rather than loss in disk height During the normal aging process the mucoid matrix of the nucleus pulposus is progressively replaced by fibrous tissue[ ]37 but the intervertebral height is preserved and the disk margins remain regular Dessication and thining of disks or disks that bulge like an underinflated automobile tire are not typical of elderly spines Slight symmetric bulging may occur if there has been vertebral body remodeling resulting from osteoporosis Small amounts of gas can be detected on plain films or CT images near the insertion of the anulus on the ring epiphysis and this gas is probably located in transverse anular tears adjacent to the ring epiphysis During the fourth decade anterior and lateral marginal vertebral body osteophytes constitute normal findings comparable with having gray hair but end plate erosions with osteosclerosis or chronic reactive bone marrow changes type 2 or 3 as described by Modic et al[ ]57 should not be seen Slight to moderate decrease in central signal intensity can be detected on T2-weighted MR images as part of the normal aging process but the changes should involve uniformly all lumbar disks

Deteriorated disks represent real pathologic degeneration which is sometimes referred to as chronic diskopathy On microscopic examination they show total structural disorganization and general replacement of normal disk material by scar tissue For this reason they were initially labeled scarred disks by the members of a joint committee on spinal nomenclature created by the Quebec Association of Radiologists[ ]14 Because of possible confusion with postoperative changes the term deteriorated disk has been proposed as an acceptable substitute Strictly speaking the term degeneration could be used to designate this entity but this latter term has such a broad nonspecific meaning that it is best avoided The deteriorated disk is characterized by narrowing of the intervertebral space irregular disk contour generally associated with symmetric or asymmetric bulging abundant presence of gas in the central portion of the intervertebral disk space multidirectional osteophytes that do not respect the central spinal canal or the foramina end plate erosions with reactive osteosclerosis and chronic bone marrow changes On T2-weighted MR images the central disk signal intensity is usually markedly decreased and the number of affected lumbar disks is variable Even though transverse concentric and radial anular tears have been identified on postmortem specimens[ ]92 the anular tear category in this model refers essentially to the radial tears that are generally demonstrated by diskography in symptomatic patients For a more precise description of those tears this model may be supplemented by the Dallas Discogram Description system[ ]70 with or without its recently proposed updates[ ]4 [ ]72 [ ]80

It should be emphasized that the pathoanatomic model is not based on direct identification of a particular geometric pattern but on the anatomy and pathology that are expected as a result of the analysis of specific criteria Using this model the conclusion of any imaging report does not consist of terms related to the shape of the disk contour or the displaced disk material but on a pathologic diagnosis that should be presented with an appropriate confidence level (possible probable or definite) The diagnosis of a probable major radial anular tear may be inferred from the presence of a definite central signal intensity loss because as a result of diskographic MR imaging correlations the positive predictive value of this sign has been estimated at 96[ ]48 The use of this model requires an effort to understand the criteria allowing differentiation of normal aging from true pathologic degeneration so this system is slightly more complicated than the morphologic model Its reliability has never been tested Some intraobserver or interobserver disagreement would probably occur trying to distinguish anular tears without herniation from anular tears with small herniations With respect to correspondance to clinical situations this scheme like the morphologic model has limited interest it has been shown that disks demonstrating the features of the deteriorated disk are likely to be responsible for symptoms but this relationship has been statistically established to be significant only for the L4-L5 disk[ ]24

Which Model Should Be Used

In other areas of diagnostic radiology the aim of image analysis is always to predict what the pathologist would find if he or she could be provided with an adequate specimen immediately following the imaging study radiologic diagnoses are presented with a pathologic perspective There is no reason why the reporting of disk disorders should be

any different Terms like bulging disk are meaningless to a pathologist and I personally favor the pathoanatomic model Nomenclature standardization however is not a task that can be achieved by an individual or even a single group of authors[ ]12 To have any impact recommendations have to emanate from well established national or international societies The multiplicity of scientific societies with an interest in the spine all over the world creates a special problem but new joint committees have recently been set up combining efforts to come up with a practical unified system that it is hoped could be proposed jointly by the North American Spine Society the American Academy of Orthopedic Surgeons the American Academy of Neurological Surgeons the American Society of Spine Radiology and the American Society of Neuroradiology Agreeing in North America on a classification of disk disorders that could gain universal acceptance like the TNM classification of neoplastic diseases would be a major achievement Meanwhile the choice of the nomenclature is up to the best judgement of each practicing radiologist and the essential issue in a given hospital or community practice remains clear communication between radiologists and referring physicians by way of a local agreement as to the meaning of words

A major problem frequently occurs because observers of imaging studies try to combine elements of the morphologic classification with those of the pathoanatomic classification Trying to differentiate a bulging disk (morphologic qualifier) from a disk herniation (pathologic diagnosis) cannot work because a bulging disk aspect is a common feature of the aging disk the deteriorated disk and some posterior central disk herniations (Fig 9) Trying to make the distinction is doomed to failure because it defies formal logic On the other hand it is theoretically possible to differentiate a radial anular tear (without herniation) from a disk herniation because these are two different pathologic entities although one may be the continuum of the other It is best to adopt either one of the two systems and avoid trying to straddle the two A general classification of disk disorders attempting to conciliate the morphologic and the pathoanatomic model is proposed in Table 1

Figure 9 A bulging disk aspect often conceals a posterior central herniation A Complete rupture of the outer anular fibers allowing nuclear material to escape and peel off the posterior longitudinal ligament (and sometimes a few intact peripheral anular fibers) from the torn disk creating a detectable focal or asymmetric extension of the disk margin beyond the interspace which qualifies as a protrusion B With more gelatinous nuclear material escaping underneath the rigid posterior longitudinal ligament the focal bulge is no longer detectable as its radius increases and if the tear occurs in the posterior midline or para-medial direction the aspect mimics symmetric disk extension beyond the interspace C Since in most cases only the outline of a diffusely hypointense disk is perceived on MR images this creates the illusion of circumferential disk bulging on axial sections D The real nature of a bulging disk of this type may be suspected by scrutinizing the sagittal sections and appreciating that unless one is dealing with a chronically degenerated scarred disk the bulge is not symmetric but limited to the posterior aspect of the disk

TABLE 1 -- GENERAL

CLASSIFICATION OF DISK LESIONS Normal (excluding aging changes)

Congenitaldevelopmental variants

Inflammationinfection

Neoplasia

Degenerativetraumatic

Degeneration

Anular tear

Herniation Protrusion

Extrusion

Degeneration Spondylosis deformans

Intervertebral osteochondrosis

Further Qualifying the Displaced Disk Material Beyond the Disk Space

Regardless of the basic system that is used the type of herniation should be assessed The volume and location of the displaced disk material beyond the normal peripheral margin of the intervertebral space also need to be specified In certain cases it is also possible to determine the composition of this material For the sake of simplicity the term herniation is used consistently in the remainder of this article to refer to all displaced disk material but what is discussed can also be applied to protrusions and extrusions if one wants to use the morphologic nomenclature

Type of Herniation

Upward or downward migration of nuclear material may occur through a break in a vertebral body end plate creating an intravertebral herniation sometimes referred to as an intraspongy herniation or a Schmorls node[ ]67 (Fig 10) Although a herniation occurring in any horizontal direction is likely to cause symptoms because of the presence of pain-sensitive nerve endings in the outer anulus[ ]7 [ ]8 [ ]65 herniations occurring in a posterior or posterolateral direction deserve special consideration because of the added possibility of dural sac or individual nerve root compression

Figure 10 Various types of intravertebral herniations (Schmorls nodes) A Intravertebral herniation through the inferior end plate of the L3 vertebral body demonstrated by diskography in a 35-year-old man suffering from chronic low back pain The patients typical pain was reproduced during injection and the lesion was considered responsible for the patients symptoms B T2-weighted sagittal section demonstrating an intravertebral herniation through the inferior end plate of the L4 vertebral body in a 24-year-old woman presenting with chronic low back pain The high signal intensity of the lesion associated with the loss of normal central signal intensity of the parent disk suggests that the lesion is a bona fide acquired intraspongy herniation and not just a developmental defect C T2-weighted sagittal section demonstrating an intravertebral herniation through the inferior end plate of the L3 vertebral body (arrow) Because both the herniation and the parent disk show normal signal intensity the abnormality was

considered a probably asymptomatic developmental defect

Other characteristics of disk herniations have become relevant with the development of new therapeutic possibilities (eg chemonucleolysis and percutaneous diskectomy) The term sequestration is confusing and has often been used to indicate displacement of disk material away from the parent disk The term sequestered disk should be used restrictedly to designate a fragment of diskal tissue that has migrated from the disk space and has no connection by diskal tissue to the disk of origin[ ]20 [ ]21 [ ]42 Sequestration refers to loss of continuity with disk tissue still present in the intervertebral disk space The term migration has a broader meaning indicating displacement of disk material away from the edge of the rent in the outer anulus either in the central spinal canal at the disk level or above or below the disk level This difference is illustrated in Figure 11 The terms communicating and noncommunicating derive from a different perspective and are mostly used in the context of intradiskal therapeutic injections They refer to the interruption of the periphery of the disk allowing fluid injected into the disk to leak into the spinal canal and reach displaced disk material[ ]20 [ ]51 The terms contained and uncontained are unfamiliar to most radiologists in a contained herniation the displaced disk material is still covered by a few intact but distended outer anular fibers or by a capsule formed by outer anular fibers and the adherent posterior longitudinal ligament

Figure 11 Various types of posterior central herniations A Small subligamentous herniation (protrusion) without significant disk material migration B Subligamentous herniation with downward migration of disk material under the PLLC C Sub-ligamentous herniation with downward migration of disk material and sequestered fragment (arrow)

The terms subligamentous and extraligamentous (or transligamentous) refer to the position of the displaced disk material with respect to the posterior longitudinal ligament The anatomy of the posterior longitudinal ligament has been recently revised[ ]73 [ ]89 It is a membranous structure that has multiple components a deep layer attached to disks and vertebral bodies a superficial layer attached to the dura by fibrous tissue (Hoffmanns

ligament) and lateral extensions known as the lateral membranes or peridural membranes (Fig 12) (Figure Not Available) It should probably be referred to as the posterior longitudinal ligament complex (PLLC) It actually divides the epidural space into the perithecal space and the anterior epidural space where displaced disk material can be entrapped (Fig 13) A potential space allowing accumulation of displaced disk material has also been detected between the outer anular fibers and the deep fibers of the PLLC on the posterior central aspect of the disk[ ]63 Posterior midline herniations seldom rupture the PLLC and are generally subligamentous The lateral membranes are less resistant and transligamentous herniations are usually the result of posterior off-center herniations or posterolateral herniations

Figure 12 (Figure Not Available) The PLLC is portrayed here in relation to various types of subligamentous disk displacement At the disk level posteriorly displaced disk material frequently occupies the midline Below and above the disk an anterior epidural space (AES) exists between the PLLC and the posterior aspect of the vertebral bodies In this space disk fragment motion across the midline is curtailed by a sagittal midline septum (dashed line) A delicate translucent membrane (shown only on left side of drawing) is stretched between the free edge of the deep layer of the posterior longitudinal ligament and the lateral spinal canal (From Schellinger D Manz HJ Vidic B et al Disk fragment migration Radiology 175831-836 1990 with permission)

Figure 13 Relationship of typical posterior disk herniations with the PLLC A Midline sagittal section unless very large a posterior midline herniation usually remains entrapped underneath the deep layer of the PLL C and sometimes a few intact outer anulus fibers joining with the PLL C to form a capsule The deep layer of the PLL C (arrow) also attaches to the posterior aspect of the vertebral body so that no potential space is present underneath B Sagittal para-central section the PLL C extends laterally at the disk level (arrowhead) but above and below the disk an anterior epidural space (as) where disk fragments are frequently entrapped is present between the lateral (peridural) membranes and the posterior aspect of the vertebral bodies

Volume of Herniated Material

Quantifying the herniated disk material by measuring in millimeters its greatest diameter or by evaluating its cross-sectional area in square millimeters is rarely done The resulting figures could be misleading without relating this measurement to the size of the spinal canal and the exact location of the lesion[ ]88 A purely qualitative and subjective statement that a mild moderate or severe herniation is present however does not give the person reading the imaging report any indication as to the potential of the lesion to cause significant compression of the dural sac or individual exiting nerve roots A reasonably precise scheme has been proposed in 1995 by the Nomenclature Committee of the North American Spine Society[ ]20 Measurements are taken from an axial CT or MR imaging section at the site of most severe compromise canal compromise of less than 25 at that section is qualified as mild 25 to 75 is moderate 76 to 90 is moderately severe and greater than 90 is severe It is understood that such characterizations describe only the cross-sectional area at one level and do not account for the total volume of displaced material displacement of neural tissue or clinical significance The usefulness of having four categories is questionable and can likely generate poor interobserver or intraobserver agreement especially in situations where the central spinal canal is relatively narrow Bonnevilles scheme[ ]9 [ ]10 [ ]11 should generate greater reliability (Fig 14) (Figure Not Available) Separation of the cross-sectional area in three thirds can be applied to both the central spinal canal and the foramina It can be agreed by way of convention that the terms mild moderate and severe lumen compromise by a disk herniation designate extension of the displaced disk material in the anterior middle or posterior third of the central canal or foramen depending on the specified location of the herniation

Figure 14 (Figure Not Available) The size of the herniation in the horizontal plane is assessed and designated by the numbers 1 2 or 3 by establishing its extension in the anterior middle or posterior third of the spinal canal (From Bonneville JF Plaidoyer pour une classification par limage des hernies discales lombaires la carte-image Rev Imag Med 2557-560 1990 with permission)

Location of Herniated Material

Bonneville[ ]9 [ ]10 [ ]11 has also proposed an interesting and simple alpha-numerical system to classify according to their location the position of disk fragments that have migrated in the horizontal or sagittal plane (Figs 15 (Figure Not Available) and 16) (Figure Not Available) Using more precise anatomic boundaries unfortunately more familiar to surgeons than radiologists Wiltse et al[ ]88 have proposed another system which has been supported by the North American Spine Society[ ]20 [ ]21 Anatomic zones and levels are defined using the following anatomic landmarks medial edge of the articular facets medial lateral upper and lower border of the pedicles and coronal plane at the disk center On the horizontal plane (Fig 17) (Figure Not Available) these landmarks determine the bounderies of the central zone the subarticular zone the foraminal zone the extraforaminal zone and the anterior zone (anterior to the coronal plane at the center of the disk) In the sagittal plane they determine the boundaries of the diskal level the infrapedicular level the pedicular level and the suprapedicular level (Figs 18 (Figure

Not Available) and 19) (Figure Not Available) Radiologists interpreting axial CT or MR images may find it difficult to use the medial edge of the facets as the landmark that separates the central zone from the subarticular zone because the superior articular facets are generally not included in axial sections at the disk level The alternative is to use the expression posterolateral to designate collectively all posterior herniations that are not midline but do not extend into a foramen as was proposed by Bonneville[ ]9 [ ]10 [ ]11

Figure 15 (Figure Not Available) In the horizontal plane herniations are labeled midline (a) posterolateral (b) foraminal (c) and extra-foraminal (d) (From Bonneville JF Plaidoyer pour une classification par limage des hernies discales lombaires la carte-image Rev Imag Med 2557-560 1990 with permission)

Figure 16 (Figure Not Available) In the craniocaudal direction disk migration is labeled +1 +2 +3 or -1 -2 -3 by referring to the height of a vertebral body divided in thirds (From Bonneville JF Plaidoyer pour une classification par limage des hernies discales lombaires la carte-image Rev Imag Med 2557-560 1990 with permission)

Figure 17 (Figure Not Available) The anatomic zones identified on axial images The anterior zone (not shown) is delineated from the extraforaminal zone by an imaginary coronal line in the center of the vertebral body (From Wiltse LL Berger PE McCulloch JA A system for reporting the size and location of lesions in the spine Spine 221534-1537 1997 with permission)

Figure 18 (Figure Not Available) The anatomical levels identified on craniocaudal images (From Wiltse LL Berger PE McCulloch AJ A system for reporting the size and location of lesions in the spine Spine 221534-1537 1997 with permission)

Figure 19 (Figure Not Available) Coronal view of the main zones and levels (From Wiltse LL Berger PE McCulloch JA A system for reporting the size and location of lesions in the spine Spine 221534-1537 1997 with permission)

Composition of Herniated Material

Displaced disk material may consist of glycosaminoglycans type 1 or 2 collagen end plate cartilage and bone fragments avulsed from the ring epiphysis A reactive inflammatory reaction usually results in edematous tissue followed by granulation tissue which may undergo calcification (Fig 20) Necrotic and partially resorbed displaced disk material sometimes produces a large fluid-filled pouch distinguishable from the common high-intensity zone because of its size (Fig 21) or a gas-filled cavity generally in continuity with gas in the intervertebral space (Fig 22) [ ]42 These characteristics may be meaningful if intradiskal injection therapy is considered In imaging reports herniations exhibiting calcium deposits and those exhibiting replacement of disk material by gas or a relatively large fluid collection can be qualified as chronic herniations

Figure 20 A CT scan demonstration of a small posterior central L4-L5 calcified subligamentous herniation The resistant deep layer of the PLLC restrains displacement of the disk material in the posterior central direction and does not allow a detectable distortion of the disk contour In this particular case the presence of the calcification is actually the only evidence that a posterior midline anular tear and a small subligamentous herniation are present B Posterior right central and sub-articular L5-S1 calcified disk herniation in same patient Posterolateral herniations are generally more conspicuous than posterior midline herniations because the deep layer of the PLLC gets thinner away from the midline

Figure 21 Posterior central midline L4-L5 herniation in a 52-year-old man demonstrated on a T2-weighted midline MR sagittal section There is intervertebral space narrowing with loss of normal central disk signal

intensity while the herniated disk material demonstrates high signal intensity consistent with a predominantly fluid consistency

Figure 22 CT scan demonstration in a 51-year-old woman of a left posterolateral L5-S1 disk hernation consisting essentially in a gas-filled pouch (white arrow) Gas is also present in the central portion of the intervertebral disk space (black arrow)

DIAGNOSTIC IMAGING AND CHARACTERIZATION OF A HERNIATED LUMBAR DISK

Assessing the validity of the currently used imaging procedures to diagnose a herniated lumbar disk is not an easy endeavor The validity of a measurement is the extent to which it corresponds to the true biologic value or some accepted gold standard[ ]40 With the exception of postmortem studies evaluation of the pathoanatomy by the surgeon in the operating room has always been considered the gold standard but this does not constitute an ideal situation Inspection of the disk through a small laminectomy incision to determine for instance if nuclear fragments lie within or outside the anular fibers may not be very reliable Also unbiased intraoperative determination of a normal degenerated or herniated disk in a patient with sciatica may also be difficult[ ]86 Because the validity of diskography has been previously established by postmortem studies and surgical correlations[ ]48 it is sometimes used as a gold standard in situations where no surgery has been performed

Conventional Radiographs

Lumbar disk herniations can exceptionally be diagnosed directly on good quality lateral projections because the x-ray attenuation is slightly greater in displaced disk material than in epidural fat Occasionally a calcified rim outlines the displaced disk fragment

(Fig 23) In most situations however narrowing of an intervertebral disk space in the absence of other evidence of chronic diskopathy is the only detectable sign suggesting the presence of a disk herniation To my knowledge the sensitivity and specificity of this sign has never been assessed The accepted rule of thumb is that the height of a given lumbar intervertebral disk space should always be slightly greater than the height of the above located interspace This rule does not apply to the transition disk immediately above the sacrum (usually L5-S1) The specificity of this sign is probably quite high but a few false-positives are seen especially at the L4-L5 level because of minor congenital hypoplasia The presence of posterior or foraminal vertebral body osteophytes associated or not with disk space narrowing is a definite sign of a chronic disk herniation

Figure 23 A Chronic left L3-L4 extraforaminal disk hernation in a 54-year-old man suspected on an AP radiograph demonstrating a calcified shell on the left side of the intervertebral disk space (white arrow) B Axial CT scan section confirming the diagnosis of a chronic extraforaminal L3-L4 herniation

Myelography

Myelography is essentially an exploration of the subarachnoid space Disk herniations are demonstrated only indirectly because they can cause thecal sac deformity and individual nerve root sleeve filling defects (Fig 24) Of all the special imaging procedures

myelography is the only one that allows upright projections with full weight bearing It is not unusual to demonstrate in this way small posterior central or posterolateral herniations that are undetectable on CT sections Interestingly the overall sensitivity of myelography to detect disk herniations has been found to be higher than that of CT whereas its specificity has been found to be lower[ ]74 In comparison with standard CT examination which usually includes only the three or four lower lumbar disks myelography easily allows coverage of the entire lumbar area and assessment of the intrathecal structures (cauda equina and conus medullaris) Far lateral foraminal herniations extraforaminal herniations and anterior herniations however are not detected The sensitivity for detection of posterior central L5-S1 herniations is also relatively poor because of the greater distance between the thecal sac and the posterior aspect of this particular disk

Figure 24 L5-S1 disk herniation in a 25-year-old man detected by indirect signs using lumbosacral myelography A Upright oblique projections showing a filling defect of the left S1 root sleeve (white arrow) suggesting significant nerve root compression by a left posterolateral disk hernation The right S1 root sleeve fills normally with contrast (black arrow) B Subtle compression of the anterior wall of the dural sac by displaced disk material (small arrows) demonstrated on upright lateral projection This sign is usually absent in the presence of a large amount of fat and venous structures in the anterior epidural compartment

CT

The sensitivity of CT to diagnose a herniation of the nucleus pulposus at the L5-S1 interspace is greater than that of myelography if images in the exact plane of the disk can be obtained[ ]23 [ ]39 Otherwise the superiority of plain CT over myelography to demonstrate disk herniations has not been established but CT has the distinct advantage of being

noninvasive and provides direct anatomic information[ ]23 Large herniations are easily detected but as explained previously the distinction between protrusions and extrusions is often difficult without sagittal reconstructions CT essentially allows an assessment of the contour of the disk The diagnosis of very small herniations in the absence of direct or indirect evidence of a radial tear is hazardous and associated with a high percentage of false-positives and false-negatives[ ]52 The diagnosis of moderate and large size herniations in different directions is usually possible but anterior herniations are rarely diagnosed not because they are not detectable but because observers pay little attention to the anterior contour of the disk (Fig 25) Because the PLLC cannot usually be identified the distinction of subligamentous from transligamentous herniation can only be suggested in most cases by the size of the herniated material A definite diagnosis of sequestration is rarely possible Calcifications within the displaced material are readily seen but may be difficult at times to differentiate from an accompanying osteophyte or an avulsed bone fragment from the vertebral body ring epiphysis (Fig 26) The presence of gas in the herniated material is easily detected

Figure 25 Anterior L4-L5 herniation demonstrated by CT scan in a 51-year-old woman with chronic low back pain Although sometimes quite conspicuous such herniations are rarely reported because observers pay little attention to the anterior contour of the disk

Figure 26 CT scan demonstration of a posterior right central L4-L5 disk herniation in a 38-year-old woman with avulsion of a bone fragment from the ring epiphysis and adjacent part of the superior L5 end plate Reactive osteosclerosis is seen around the vertebral body defect (arrows) suggesting a chronic lesion

CT Myelography

This association combines the advantages of both imaging modalities The fact that its accuracy has been reported as being less[ ]22 [ ]32 higher[ ]1 [ ]6 or equivalent[ ]82 to MR imaging is a reflection of the differences in technologic advancement and pathologic nomenclature that hamper valid comparisons between different studies

MR Imaging

Most reported studies establish MR imaging as the first choice modality to diagnose a herniated lumbar disk[ ]5 [ ]22 [ ]32 [ ]46 The associated intravenous injection of a paramagnetic agent has been found useful to demonstrate some anatomic features of disk disease in patients with no previous lumbar disk surgery[ ]56 [ ]68 [ ]90 MR imaging provides a better assessment of disk morphology than CT or CT myelography because sagittal sections are routinely obtained Assessment of foraminal involvement by displaced disk material is more accurate (Fig 27) and anterior disk herniations can be detected more easily than with CT or CT myelography If one is looking specifically for herniated lumbar disks associated with nerve root compression however it has been demonstrated that CT is equally accurate[ ]82 Alterations of the central or peripheral disk signal intensity on T2-weighted images are seen in most disks afflicted with an anular tear[ ]48 and alert the observer to scrutinize the disk contour in search for local modifications indicative of a herniation Because the signal of the displaced disk material is usually very similar to that of the outer anulus PLLC and vertebral body cortical bone small herniations are generally more conspicuous on axial CT sections than on corresponding axial MR imaging sections Gas and calcium deposits within the displaced fragment cannot usually

be detected but associated vertebral body bone marrow changes are typically seen and are helpful in differentiating acute from chronic processes[ ]57 The occasional presence of a high-intensity zone in the herniated material with an occasionally enhancing border after contrast injection is probably caused by a mixture of displaced nuclear material acute and subacute inflammatory tissue and neovascularized reactive tissue[ ]4 [ ]48 [ ]72 Contradictory reports have been published regarding the accuracy of MR imaging to differentiate subligamentous from transligamentous herniations[ ]26 [ ]38 [ ]73 [ ]76 Understanding the anatomy of the PLLC is helpful to make the distinction (Fig 28) (Figure Not Available) Masaryk et al[ ]46 have suggested that MR imaging is accurate to distinguish sequestered disks from other forms of lumbar disk herniations but most observers find this distinction difficult to establish[ ]42

Figure 27 A Left L4-L5 foraminal herniation well seen on an intermediate-weighted left parasagittal MR section (arrow) in a 47-year-old man B The lesion is much less obvious on intermediate-weighted (left) and T2-weighted (right) axial sections and was in fact more conspicuous on the corresponding CT scan section

Figure 28 (Figure Not Available) A Subligamentous disk herniation Left T1-weighted image demonstrating displaced disk material with a smooth outline imposed by the demarcation of the anterior epidural space (AES) by the lateral membrane of the PLLC Right Correlative drawing B Transligamentous disk herniation Left T1-weighted image of a large disk herniation (cervical in this case) which has ruptured through the posterior confines of the AES Penetration of the right lateral membrane can be observed (arrow) and the disk fragment contour is serrated Right Correlative drawing (From Schellinger D Manz HJ Vidic B et al Disk fragment migration Radiology 175831-836 1990 with permission)

Diskography and CT Diskography

During 30 years (1950 to 1980) when myelography was the only available imaging technique to demonstrate lumbar disk herniations diskography was an invasive but efficient way to demonstrate posterior central L5-S1 herniations and other large herniations (other than posterior central and paramedial) that could not be detected by myelography[ ]50 These herniations are now usually well demonstrated by CT and MR imaging Comparing the accuracy of five imaging modalities (excluding MR imaging) for the diagnosis of lumbar disk herniation Jackson et al[ ]31 found that CT diskography (Fig 29) was the most accurate test (87) compared with 77 for CT myelography 74 for CT 70 for myelography 64 for pain reproduction during diskography and 58 for diskography without CT Disk injection reproduced the patients clinical pain pattern in only 36 of herniated disks This clinical test isolated from the images had high specificity (89) but low sensitivity (43) for the diagnosis of disk herniation The reported low sensitivity of diskography images (unassociated with CT) to diagnose disk herniation is to be expected the purpose of the intradiskal injection being primarily the demonstration of an anular tear the contrast leaking through the tear only occasionally delineates an extruded fragment When a disk herniation has been diagnosed by other imaging modalities diskography allows to determine if the herniation is contained or noncontained (Figs 30 and 31) this information may have clinical relevance[ ]62 It also allows to establish if the displaced disk material is communicating or not with the parent disk and establishes the likelihood that it is sequestered or not There always remains a possibility that the contrast injected under pressure may reach a disk fragment that is nevertheless sequestered by leaking through the associated anular tear CT diskography also allows assessment in most cases of the integrity of the PLLC[ ]89 The superior sensitivity of diskography over MR imaging to demonstrate anular tears has been well established[ ]27 [ ]44 [ ]48 [ ]64 [ ]77 [ ]91 [ ]94 The presence of a radial tear and the inflammatory reaction it creates may be symptomatic despite the absence of true disk herniation[ ]29 [ ]48 [ ]49 [ ]69

Figure 29 L4-L5 CT diskogram demonstrating a large left posterolateral radial anular tear associated with

a left foraminal and extraforaminal herniaton (same patient as in Figure 28) (Figure Not Available)

Figure 30 Contained posterior L4-L5 and L5-S1 disk herniations in a 57-year-old man demonstrated by diskography The L3-L4 disk is normal

Figure 31 Noncontained L4-L5 disk herniation in a 23-year-old woman Reflux of injected contrast is seen in the anterior epidural space above and below the disk space The L5-S1 disk also demonstrates incomplete anterior and posterior radial anular tears

SUMMARY

The absence of universal nomenclature standardization with respect to the definition of a disk herniation and its different categories especially regarding type and location is still a major problem that will only be overcome when major national or international scientific societies join efforts to support a particular scheme Meanwhile it is important to realize that the two models that are currently most used are based on a different perspective Trying to straddle the two by opposing for instance bulging disk and herniation is doomed to failure because this exercise defies formal logic MR imaging is currently the most accurate noninvasive imaging modality to diagnose a disk herniation and to determine its exact location The determination of some pathoanatomic characteristics of herniated disks (type and composition) may require the use of CT diskography or CT diskography

References

1 Albeck MJ Hilden J Kjaer L et al A controlled comparison of myelography computed tomography and magnetic resonance imaging in clinically suspected lumbar disc herniation Spine 20443-448 1995 Abstract 2 American Academy of Orthopedic Surgeons Glossary on Spinal Terminology Chicago American Academy of Orthopedic Surgeons 1981 3 Andersson GB Weinstein JN Disc herniation [editorial] Spine 211S 1996 Citation 4 Aprill C Bogduk N High-intensity zone A diagnostic sign of painful lumbar disc on magnetic resonance imaging Br J Radiol 65361-369 1992 Abstract 5 Birney TJ White JJ Jr Berens D et al Comparison of MRI and discography in the diagnosis of lumbar degenerative disc disease J Spinal Disord 5417-423 1992 Abstract 6 Bischoff RJ Rodriguez RP Gupta K et al A comparison of computed tomography-myelography magnetic resonance imaging and myelography in the diagnosis of herniated nucleus pulposus and spinal stenosis J Spinal Disord 6289-295 1993 Abstract 7 Bogduk N The innervation of the lumbar spine Spine 8286-293 1983 Abstract 8 Bogduk N Tynan W Wilson AS The nerve supply to the human lumbar intervertebral discs J Anat 13239-56 1981 Abstract 9 Bonneville JF La carte-image des hernies discales lombaires Rachis 2255-257 1990 10 Bonneville JF La topografia simbolica delle ernie discali lombari Riv Neuroradiol 5427-431 1992 11 Bonneville JF Plaidoyer pour une classification par limage des hernies discales lombaires La carte-image Rev Imag Med 2557-560 1990 12 Brant-Zawadzki M Jensen M Spinal nomenclature Spine 20388-390 1995 Abstract

13 Brant-Zawadzki MN Jensen MC Obuchowski N et al Interobserver and intraobserver variability in interpretation of lumbar disc abnormalities A comparison of two nomenclatures Spine 201257-1263 1995 Abstract 14 Breton G Is that a bulging disk a small herniation or a moderate protrusion [editorial] Can Assoc Radiol J 42318 1991 Citation 15 Czervionke LF Lumbar intervertebral disc disease Neuroimaging Clin North Am 3465-485 1993 16 Deyo RA Nonsurgical care of low back pain Neurosurg Clin North Am 2851-862 1991 17 Deyo RA Loeser JD Bigos SJ Herniated lumbar intervertebral disk Ann Intern Med 112598-603 1990 Abstract 18 Dorlands Illustrated Medical Dictionary ed 28 Philadelphia WB Saunders 1994 19 Fardon D Pinkerton S Balderston R et al Terms used for diagnosis by English speaking spine surgeons Spine 18274-277 1993 Citation 20 Fardon DF Herzog RJ Mink JH et al Nomenclature of Lumbar Disc Disorders Contemporary Concepts in Spine Care Rosemont IL North American Spine Society 1995 21 Fardon DF Herzog RJ Mink JH et al Nomenclature of lumbar disc disorders In Garfin S Vaccaro A (eds) Orthopedic Knowledge Update Spine Rosemont IL American Academy of Orthopedic Surgeons 1997 pp A3-A14 22 Forristall RM Marsh HO Pay NT Magnetic resonance imaging and contrast CT of the lumbar spine Comparison of diagnostic methods and correlation with surgical findings Spine 131049-1054 1988 Abstract 23 Fries JW Abodeely DA Vijungco JG et al Computed tomography of herniated and extruded nucleus pulposus J Comput Assist Tomogr 6874-887 1982 Abstract 24 Frymoyer JW Newberg A Pope MH et al Spine radiographs in patients with low-back pain An epidemiological study in men J Bone Joint Surg Am 661048-1055 1984 Abstract 25 Gospodarowicz M Benedet L Hutter RV et al History and international developments in cancer staging Cancer Prev Control 2262-268 1998 Abstract 26 Grenier N Greselle JF Vital JM et al Normal and disrupted lumbar longitudinal ligaments Correlative MR and anatomic study Radiology 171197-205 1989 Abstract 27 Gunzburg R Parkinson R Moore R et al A cadaveric study comparing discography magnetic resonance imaging histology and mechanical behavior of the human lumbar disc Spine 17417-426 1992 Abstract 28 Haughton VM Eldevik OP Magnaes B et al A prospective comparison of computed tomography and myelography in the diagnosis of herniated lumbar disks Radiology 142103-110 1982 Abstract

29 Haughton VM Lim TH An H Intervertebral disk appearance correlated with stiffness of lumbar spinal motion segments AJNR Am J Neuroradiol 201161-1165 1999 Abstract 30 Herzog RJ The radiologic assessment for a lumbar disc herniation Spine 2119S-38S 1996 Abstract 31 Jackson RP Becker GJ Jacobs RR et al The neuroradiographic diagnosis of lumbar herniated nucleus pulposus I A comparison of computed tomography (CT) myelography CT-myelography discography and CT-discography Spine 141356-1361 1989 Abstract 32 Jackson RP Cain JE Jr Jacobs RR et al The neuroradiographic diagnosis of lumbar herniated nucleus pulposus II A comparison of computed tomography (CT) myelography CT-myelography and magnetic resonance imaging Spine 141362-1367 1989 Abstract 33 Jarvik JG Haynor DR Koepsell TD et al Interreader reliability for a new classification of lumbar disk disease Acad Radiol 3537-544 1996 Abstract 34 Jensen MC Brant-Zawadzki MN Obuchowski N et al Magnetic resonance imaging of the lumbar spine in people without back pain N Engl J Med 33169-73 1994 Abstract 35 Kent DL Haynor DR Larson EB et al Diagnosis of lumbar spinal stenosis in adults A meta-analysis of the accuracy of CT MR and myelography AJR Am J Roentgenol 1581135-1144 1992 Abstract 36 Kieffer SA Sherry RG Wellenstein DE et al Bulging lumbar intervertebral disk Myelographic differentiation from herniated disk with nerve root compression AJR Am J Roentgenol 138709-716 1982 Abstract 37 Kieffer SA Stadlan EM Mohandas A et al Discographic-anatomical correlation of developmental changes with age in the intervertebral disc Acta Radiol 9733-739 1969 38 Kim KY Kim YT Lee CS et al MRI classification of lumbar herniated intervertebral disc Orthopedics 15493-497 1992 Abstract 39 Kornberg M Rechtine GR Dupuy TE Computed tomography in the diagnosis of a herniated disk at the L5-S1 level Spine 9433-436 1984 Abstract 40 Kramer MS Clinical Epidemiology and Biostatistics New York Springer-Verlag 1988 41 Landis JR Koch GG The measurement of observer agreement agreement for categorical data Biometrics 33159-174 1977 Abstract 42 Laredo JD Bossard P Vuillemin-Bodaghi Formes anatomo-radiologiques des hernies discales In Morvan G Deburge A Bard H et al (eds) Le Rachis Lombaire Degeneratif Montpellier Sauramps Medical 1998 pp 37-49 43 Lee SH Coleman PE Hahn FJ Magnetic resonance imaging of degenerative disk disease of the spine Radiol Clin North Am 26949-964 1988 Abstract 44 Linson MA Crowe CH Comparison of magnetic resonance imaging and lumbar discography in the diagnosis of disc degeneration Clin Orthop 160-163 1990

45 Marchand F Ahmed AM Investigation of the laminate structure of lumbar disc anulus fibrosus Spine 15402-410 1990 Abstract 46 Masaryk TJ Ross JS Modic MT et al High-resolution MR imaging of sequestered lumbar intervertebral disks AJR Am J Roentgenol 1501155-1162 1988 Abstract 47 Milette PC The proper terminology for reporting lumbar intervertebral disk disorders AJNR Am J Neuroradiol 181859-1866 1997 Citation 48 Milette PC Fontaine S Lepanto L et al Differentiating lumbar disc protrusions disk bulges and discs with normal contour but abnormal signal intensity Magnetic resonance imaging with discographic correlations Spine 2444-53 1999 Abstract 49 Milette PC Fontaine S Lepanto L et al Radiating pain to the lower extremities caused by lumbar disk rupture without spinal nerve root involvement AJNR Am J Neuroradiol 161605-1613 1995 Abstract 50 Milette PC Melancon D A reappraisal of lumbar discography Can Assoc Radiol J 33176-182 1982 51 Milette PC Melancon D Dupuis PR et al A simplified terminology for abnormalities of the lumbar disk Can Assoc Radiol J 42319-325 1991 Abstract 52 Milette PC Raymond J Fontaine S Comparison of high-resolution computed tomography with discography in the evaluation of lumbar disc herniations Spine 15525-533 1990 Abstract 53 Mink JH Deutsch AL Goldstein TB et al Spinal imaging and intervention 1998 Phys Med Rehabil Clin North Am 9343-380 1998 54 Mixter WJ Barr JS Rupture of the intervertebral disc with involvement of the spinal canal N Engl J Med 211210-234 1934 55 Modic MT Masaryk TJ Ross JS et al Imaging of degenerative disk disease Radiology 168177-186 1988 Citation 56 Modic MT Ross JS Obuchowski NA et al Contrast-enhanced MR imaging in acute lumbar radiculopathy A pilot study of the natural history Radiology 195429-435 1995 Abstract 57 Modic MT Steinberg PM Ross JS et al Degenerative disk disease Assessment of changes in vertebral body marrow with MR imaging Radiology 166193-199 1988 58 Morvan G Mathieu P Les stenoses laterales In Morvan G Deburge A Bard H et al (eds) Le Rachis Lombaire Degeneratif Montpellier Sauramps Medical 1998 pp 315-324 59 Murray RO Skeletal trauma Regional In Sutton D (ed) Textbook of Radiology and Imaging ed 3 New York Churchill Livingstone 1980 pp 210-231 60 Nachemson A Lumbar disc herniation Conclusions Acta Orthop Scand 64(suppl 251)49 1993 Citation

61 Nathan H Osteophytes of the vertebral column An anatomical study of their development according to age race and sex with consideration as to their etiology and significance J Bone Joint Surg Am 44243-268 1962 62 Nygaard OP Mellgren SI Osterud B The inflammatory properties of contained and noncontained lumbar disc herniations Spine 222584-2488 1997 Abstract 63 Ohshima H Hirano N Osada R et al Morphologic variation of lumbar posterior longitudinal ligament and the modality of disc herniation Spine 182408-2411 1993 Abstract 64 Osti OL Fraser RD MRI and discography of annular tears and intervertebral disc degeneration A prospective clinical comparison J Bone Joint Surg Br 74431-435 1992 Abstract 65 Palmgren T Gronblad M Virri J et al Immunohistochemical demonstration of sensory and autonomic nerve terminals in herniated lumbar disc tissue Spine 211301-1306 1996 Abstract 66 Resnick D Niwayama G Degenerative disease of the spine In Resnick D (ed) Diagnosis of Bone and Joint Disorders ed 3 Philadelphia WB Saunders 1995 pp 1372-1462 67 Resnick D Niwayama G Intravertebral disk herniations Cartilaginous (Schmorls) nodes Radiology 12657-65 1978 Abstract 68 Ross JS Modic MT Masaryk TJ Tears of the anulus fibrosus Assessment with Gd-DTPA-enhanced MR imaging AJR Am J Roentgenol 154159-162 1990 Abstract 69 Saal JS The role of inflammation in lumbar pain Spine 201821-1827 1995 Abstract 70 Sachs BL Vanharanta H Spivey MA et al Dallas discogram description A new classification of CTdiscography in low-back disorders Spine 12287-294 1987 Abstract 71 Sauser DD Goldman AB Kaye JJ Discogenic vertebral sclerosis J Can Assoc Radiol 2944-50 1978 Abstract 72 Schellhas KP Pollei SR Gundry CR et al Lumbar disc high-intensity zone Correlation of magnetic resonance imaging and discography Spine 2179-86 1996 Abstract 73 Schellinger D Manz HJ Vidic B et al Disk fragment migration Radiology 175831-836 1990 Abstract 74 Schipper J Kardaun JW Braakman R et al Lumbar disk herniation Diagnosis with CT or myelography Radiology 165227-231 1987 Abstract 75 Schmorl G Junghanns H The Human Spine in Health and Disease ed 2 New York Grune and Stratton 1971 76 Silverman CS Lenchik L Shimkin PM et al The value of MR in differentiating subligamentous from supraligamentous lumbar disk herniations AJNR Am J Neuroradiol 16571-579 1995 Abstract 77 Simmons JW Emery SF McMillin JN et al Awake discography A comparison study with magnetic

resonance imaging Spine 16S216-221 1991 Abstract 78 Smyth MJ Wright V Sciatica and the intervertebral disc J Bone Joint Surg Am 401401-1418 1958 79 Taveras JM Radiologic aspects of low back pain and sciatic syndromes [editorial] AJNR Am J Neuroradiol 9351-358 1989 80 Tehranzadeh J Discography 2000 Radiol Clin North Am 36463-495 1998 Full Text 81 Thelander U Fagerlund M Friberg S et al Describing the size of lumbar disc herniations using computed tomography A comparison of different size index calculations and their relation to sciatica Spine 191979-1984 1994 Abstract 82 Thornbury JR Fryback DG Turski PA et al Disk-caused nerve compression in patients with acute low-back pain Diagnosis with MR CT myelography and plain CT Radiology 186731-738 1993 Abstract 83 Twomey L Taylor J Age changes in lumbar intervertebral discs Acta Orthop Scand 56496-499 1985 Abstract 84 Twomey LT Taylor JR Age changes in lumbar vertebrae and intervertebral discs Clin Orthop 22497-104 1987 85 Williams AL CT diagnosis of degenerative disc disease The bulging annulus Radiol Clin North Am 21289-300 1983 Abstract 86 Williams AL Haughton VM Meyer GA et al Computed tomographic appearance of the bulging annulus Radiology 142403-408 1982 Abstract 87 Williams AL Haughton VM Syvertsen A Computed tomography in the diagnosis of herniated nucleus pulposus Radiology 13595-99 1980 Abstract 88 Wiltse LL Berger PE McCulloch JA A system for reporting the size and location of lesions in the spine Spine 221534-1537 1997 Abstract 89 Wiltse LL Fonseca AS Amster J et al Relationship of the dura Hofmanns ligaments Batsons plexus and a fibrovascular membrane lying on the posterior surface of the vertebral bodies and attaching to the deep layer of the posterior longitudinal ligament An anatomical radiologic and clinical study Spine 181030-1043 1993 Abstract 90 Yamashita K Hiroshima K Kurata A Gadolinium-DTPA-enhanced magnetic resonance imaging of a sequestered lumbar intervertebral disc and its correlation with pathologic findings Spine 19479-482 1994 Abstract 91 Yu SW Haughton VM Sether LA et al Comparison of MR and diskography in detecting radial tears of the anulus A postmortem study AJNR Am J Neuroradiol 101077-1081 1989 Abstract 92 Yu SW Sether LA Ho PS et al Tears of the anulus fibrosus Correlation between MR and pathologic findings in cadavers AJNR Am J Neuroradiol 9367-370 1988 Abstract

93 Yussen PS Swartz JD The acute lumbar disc herniation Imaging diagnosis Semin Ultrasound CT MR 14389-398 1993 Abstract 94 Zucherman J Derby R Hsu K et al Normal magnetic resonance imaging with abnormal discography Spine 131355-1359 1988 Abstract

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  • CLASSIFICATION DIAGNOSTIC IMAGING AND IMAGING CHARACTERIZATION OF A LUMBAR HERNIATED DISK
    • IMAGING OF LOW BACK PAIN I
      • CLASSIFICATION DIAGNOSTIC IMAGING AND IMAGING CHARACTERIZATION OF A LUMBAR HERNIATED DISK
        • DEFINITION OF A DISK HERNIATION
        • CLASSIFICATION OF A HERNIATED LUMBAR DISK
          • Main Categories of Noninfectious Disk Abnormalities
          • Further Qualifying the Displaced Disk Material Beyond the Disk Space
            • DIAGNOSTIC IMAGING AND CHARACTERIZATION OF A HERNIATED LUMBAR DISK
              • Conventional Radiographs
              • Myelography
              • CT
              • CT Myelography
              • MR Imaging
              • Diskography and CT Diskography
                • SUMMARY
                  • References
Page 8: CLASSIFICATION, DIAGNOSTIC IMAGING, AND IMAGING ... · PDF fileclassification, diagnostic imaging, and imaging characterization of a lumbar herniated disk ... classification, diagnostic

Figure 5 A Bulging disk appearance of the L4-L5 disk shown on a 5-mm-thickness axial CT scan section in a 57-year-old woman The height of the intervertebral space was preserved and there was no reactive vertebral body end-plate modifications This aspect is probably partly due to vertebral body remodeling caused by osteoporosis but is mostly created by volume averaging (From Milette PC Fontaine S Daniels C et al Imaging of Low Back Pain CD-ROM SSB Multimedia Medical Series Montreal 1997 with permission) B Using 4- or 5-mm-thickness CT sections an intermediate gray shade halo is often computer generated by volume averaging of tissues with different attenuation coefficients in voxels represented by two-dimensional pixels located at the disk space periphery This creates the illusion of a three-dimensional image demonstrating diffuse disk bulging ST = slice thickness

Figure 6 Axial CT scan section of a L4-L5 disk in a 78-year-old man demonstrating diffuse disk bulging caused by remodeling of the adjacent vertebral bodies due to osteoporosis The intervertebral space was normal in height and there were no reactive adjacent bony endplate modifications

Figure 7 A T2-weighted axial section of a L5-S1 disk showing a left posterolateral wide base protrusion that can be easily confused with diffuse circumferential bulging B Corresponding T2-weighted left paracentral and central sagittal sections demonstrating loss of the L5-S1 disk signal intensity with posterior small left-central protrusion the anterior aspect of the disk does not extend beyond the endplates and therefore such a disk should not be labeled bulging disk

The Pathoanatomic Model

As opposed to the previous model that can be applied only to the interpretation of CT and MR imaging studies this model can be used for the interpretation of all imaging modalities including plain films and diskograms[ ]47 [ ]51 It consists of five categories that are not mutually exclusive so that different combinations are possible (Fig 8) (Figure Not Available) The first three refer to the general state of the disk (1) normal young disk (2) normal aging disk and (3) deteriorated disk (formerly called the scarred disk) The last two refer to localized lesions anular tear and herniated disk In this model the previously discussed definition of disk herniation proposed by Herzog[ ]30 is applicable The use of this system requires an effort to distinguish the normal aging changes from those of pathologic degeneration Resnick and Niwayama[ ]66 have emphasized the differentiating features of two degenerative processes involving the intervertebral disk which had been previously described by Schmorl and Junghanns[ ]75 (1) spondylosis deformans which affects primarily the anulus fibrosus and bony ring epiphysis and (2) intervertebral osteochondrosis which affects essentially the nucleus pulposus and the vertebral body end plates

Figure 8 (Figure Not Available) Schematic representation of a nomenclature based on a three-dimensional assessment of the anatomic and pathologic characteristics of both disk and adjacent vertebral bodies The categories are not mutually exclusive and some combinations are possible A Categories related to the general aspect of the disk normal young disk (a) normal aging disk (b) deteriorated disk (c) B Categories related to local lesions normal young disk (a) anular tear (b) herniated disk (c) (Adapted from Milette PC The proper terminology for reporting lumbar intervertebral disk disorders AJNR Am J Neuroradiol 181859-1866 1997 with permission)

There is convincing evidence in the scientific literature that the features of spondylosis deformans represent the normal aging process whereas intervertebral osteochondrosis denotes true pathologic disk degeneration[ ]61 [ ]71 [ ]75 [ ]83 [ ]84 Schmorl and Junghanns[ ]75 found spondylotic changes in 60 of women and almost 80 of men over the age of 50 In a series of 400 dried skeletons Nathan[ ]61 found anterior vertebral body osteophytes which constitute the main feature of spondylosis deformans in 100 of individuals over age 40 whereas posterior osteophytes were found in only 39 of individuals even after the age of 80 Twomey and Taylor[ ]83 [ ]84 have found that loss of disk height is unusual in a normal aging population and that loss of stature in the elderly is attributable to loss of intervertebral body height rather than loss in disk height During the normal aging process the mucoid matrix of the nucleus pulposus is progressively replaced by fibrous tissue[ ]37 but the intervertebral height is preserved and the disk margins remain regular Dessication and thining of disks or disks that bulge like an underinflated automobile tire are not typical of elderly spines Slight symmetric bulging may occur if there has been vertebral body remodeling resulting from osteoporosis Small amounts of gas can be detected on plain films or CT images near the insertion of the anulus on the ring epiphysis and this gas is probably located in transverse anular tears adjacent to the ring epiphysis During the fourth decade anterior and lateral marginal vertebral body osteophytes constitute normal findings comparable with having gray hair but end plate erosions with osteosclerosis or chronic reactive bone marrow changes type 2 or 3 as described by Modic et al[ ]57 should not be seen Slight to moderate decrease in central signal intensity can be detected on T2-weighted MR images as part of the normal aging process but the changes should involve uniformly all lumbar disks

Deteriorated disks represent real pathologic degeneration which is sometimes referred to as chronic diskopathy On microscopic examination they show total structural disorganization and general replacement of normal disk material by scar tissue For this reason they were initially labeled scarred disks by the members of a joint committee on spinal nomenclature created by the Quebec Association of Radiologists[ ]14 Because of possible confusion with postoperative changes the term deteriorated disk has been proposed as an acceptable substitute Strictly speaking the term degeneration could be used to designate this entity but this latter term has such a broad nonspecific meaning that it is best avoided The deteriorated disk is characterized by narrowing of the intervertebral space irregular disk contour generally associated with symmetric or asymmetric bulging abundant presence of gas in the central portion of the intervertebral disk space multidirectional osteophytes that do not respect the central spinal canal or the foramina end plate erosions with reactive osteosclerosis and chronic bone marrow changes On T2-weighted MR images the central disk signal intensity is usually markedly decreased and the number of affected lumbar disks is variable Even though transverse concentric and radial anular tears have been identified on postmortem specimens[ ]92 the anular tear category in this model refers essentially to the radial tears that are generally demonstrated by diskography in symptomatic patients For a more precise description of those tears this model may be supplemented by the Dallas Discogram Description system[ ]70 with or without its recently proposed updates[ ]4 [ ]72 [ ]80

It should be emphasized that the pathoanatomic model is not based on direct identification of a particular geometric pattern but on the anatomy and pathology that are expected as a result of the analysis of specific criteria Using this model the conclusion of any imaging report does not consist of terms related to the shape of the disk contour or the displaced disk material but on a pathologic diagnosis that should be presented with an appropriate confidence level (possible probable or definite) The diagnosis of a probable major radial anular tear may be inferred from the presence of a definite central signal intensity loss because as a result of diskographic MR imaging correlations the positive predictive value of this sign has been estimated at 96[ ]48 The use of this model requires an effort to understand the criteria allowing differentiation of normal aging from true pathologic degeneration so this system is slightly more complicated than the morphologic model Its reliability has never been tested Some intraobserver or interobserver disagreement would probably occur trying to distinguish anular tears without herniation from anular tears with small herniations With respect to correspondance to clinical situations this scheme like the morphologic model has limited interest it has been shown that disks demonstrating the features of the deteriorated disk are likely to be responsible for symptoms but this relationship has been statistically established to be significant only for the L4-L5 disk[ ]24

Which Model Should Be Used

In other areas of diagnostic radiology the aim of image analysis is always to predict what the pathologist would find if he or she could be provided with an adequate specimen immediately following the imaging study radiologic diagnoses are presented with a pathologic perspective There is no reason why the reporting of disk disorders should be

any different Terms like bulging disk are meaningless to a pathologist and I personally favor the pathoanatomic model Nomenclature standardization however is not a task that can be achieved by an individual or even a single group of authors[ ]12 To have any impact recommendations have to emanate from well established national or international societies The multiplicity of scientific societies with an interest in the spine all over the world creates a special problem but new joint committees have recently been set up combining efforts to come up with a practical unified system that it is hoped could be proposed jointly by the North American Spine Society the American Academy of Orthopedic Surgeons the American Academy of Neurological Surgeons the American Society of Spine Radiology and the American Society of Neuroradiology Agreeing in North America on a classification of disk disorders that could gain universal acceptance like the TNM classification of neoplastic diseases would be a major achievement Meanwhile the choice of the nomenclature is up to the best judgement of each practicing radiologist and the essential issue in a given hospital or community practice remains clear communication between radiologists and referring physicians by way of a local agreement as to the meaning of words

A major problem frequently occurs because observers of imaging studies try to combine elements of the morphologic classification with those of the pathoanatomic classification Trying to differentiate a bulging disk (morphologic qualifier) from a disk herniation (pathologic diagnosis) cannot work because a bulging disk aspect is a common feature of the aging disk the deteriorated disk and some posterior central disk herniations (Fig 9) Trying to make the distinction is doomed to failure because it defies formal logic On the other hand it is theoretically possible to differentiate a radial anular tear (without herniation) from a disk herniation because these are two different pathologic entities although one may be the continuum of the other It is best to adopt either one of the two systems and avoid trying to straddle the two A general classification of disk disorders attempting to conciliate the morphologic and the pathoanatomic model is proposed in Table 1

Figure 9 A bulging disk aspect often conceals a posterior central herniation A Complete rupture of the outer anular fibers allowing nuclear material to escape and peel off the posterior longitudinal ligament (and sometimes a few intact peripheral anular fibers) from the torn disk creating a detectable focal or asymmetric extension of the disk margin beyond the interspace which qualifies as a protrusion B With more gelatinous nuclear material escaping underneath the rigid posterior longitudinal ligament the focal bulge is no longer detectable as its radius increases and if the tear occurs in the posterior midline or para-medial direction the aspect mimics symmetric disk extension beyond the interspace C Since in most cases only the outline of a diffusely hypointense disk is perceived on MR images this creates the illusion of circumferential disk bulging on axial sections D The real nature of a bulging disk of this type may be suspected by scrutinizing the sagittal sections and appreciating that unless one is dealing with a chronically degenerated scarred disk the bulge is not symmetric but limited to the posterior aspect of the disk

TABLE 1 -- GENERAL

CLASSIFICATION OF DISK LESIONS Normal (excluding aging changes)

Congenitaldevelopmental variants

Inflammationinfection

Neoplasia

Degenerativetraumatic

Degeneration

Anular tear

Herniation Protrusion

Extrusion

Degeneration Spondylosis deformans

Intervertebral osteochondrosis

Further Qualifying the Displaced Disk Material Beyond the Disk Space

Regardless of the basic system that is used the type of herniation should be assessed The volume and location of the displaced disk material beyond the normal peripheral margin of the intervertebral space also need to be specified In certain cases it is also possible to determine the composition of this material For the sake of simplicity the term herniation is used consistently in the remainder of this article to refer to all displaced disk material but what is discussed can also be applied to protrusions and extrusions if one wants to use the morphologic nomenclature

Type of Herniation

Upward or downward migration of nuclear material may occur through a break in a vertebral body end plate creating an intravertebral herniation sometimes referred to as an intraspongy herniation or a Schmorls node[ ]67 (Fig 10) Although a herniation occurring in any horizontal direction is likely to cause symptoms because of the presence of pain-sensitive nerve endings in the outer anulus[ ]7 [ ]8 [ ]65 herniations occurring in a posterior or posterolateral direction deserve special consideration because of the added possibility of dural sac or individual nerve root compression

Figure 10 Various types of intravertebral herniations (Schmorls nodes) A Intravertebral herniation through the inferior end plate of the L3 vertebral body demonstrated by diskography in a 35-year-old man suffering from chronic low back pain The patients typical pain was reproduced during injection and the lesion was considered responsible for the patients symptoms B T2-weighted sagittal section demonstrating an intravertebral herniation through the inferior end plate of the L4 vertebral body in a 24-year-old woman presenting with chronic low back pain The high signal intensity of the lesion associated with the loss of normal central signal intensity of the parent disk suggests that the lesion is a bona fide acquired intraspongy herniation and not just a developmental defect C T2-weighted sagittal section demonstrating an intravertebral herniation through the inferior end plate of the L3 vertebral body (arrow) Because both the herniation and the parent disk show normal signal intensity the abnormality was

considered a probably asymptomatic developmental defect

Other characteristics of disk herniations have become relevant with the development of new therapeutic possibilities (eg chemonucleolysis and percutaneous diskectomy) The term sequestration is confusing and has often been used to indicate displacement of disk material away from the parent disk The term sequestered disk should be used restrictedly to designate a fragment of diskal tissue that has migrated from the disk space and has no connection by diskal tissue to the disk of origin[ ]20 [ ]21 [ ]42 Sequestration refers to loss of continuity with disk tissue still present in the intervertebral disk space The term migration has a broader meaning indicating displacement of disk material away from the edge of the rent in the outer anulus either in the central spinal canal at the disk level or above or below the disk level This difference is illustrated in Figure 11 The terms communicating and noncommunicating derive from a different perspective and are mostly used in the context of intradiskal therapeutic injections They refer to the interruption of the periphery of the disk allowing fluid injected into the disk to leak into the spinal canal and reach displaced disk material[ ]20 [ ]51 The terms contained and uncontained are unfamiliar to most radiologists in a contained herniation the displaced disk material is still covered by a few intact but distended outer anular fibers or by a capsule formed by outer anular fibers and the adherent posterior longitudinal ligament

Figure 11 Various types of posterior central herniations A Small subligamentous herniation (protrusion) without significant disk material migration B Subligamentous herniation with downward migration of disk material under the PLLC C Sub-ligamentous herniation with downward migration of disk material and sequestered fragment (arrow)

The terms subligamentous and extraligamentous (or transligamentous) refer to the position of the displaced disk material with respect to the posterior longitudinal ligament The anatomy of the posterior longitudinal ligament has been recently revised[ ]73 [ ]89 It is a membranous structure that has multiple components a deep layer attached to disks and vertebral bodies a superficial layer attached to the dura by fibrous tissue (Hoffmanns

ligament) and lateral extensions known as the lateral membranes or peridural membranes (Fig 12) (Figure Not Available) It should probably be referred to as the posterior longitudinal ligament complex (PLLC) It actually divides the epidural space into the perithecal space and the anterior epidural space where displaced disk material can be entrapped (Fig 13) A potential space allowing accumulation of displaced disk material has also been detected between the outer anular fibers and the deep fibers of the PLLC on the posterior central aspect of the disk[ ]63 Posterior midline herniations seldom rupture the PLLC and are generally subligamentous The lateral membranes are less resistant and transligamentous herniations are usually the result of posterior off-center herniations or posterolateral herniations

Figure 12 (Figure Not Available) The PLLC is portrayed here in relation to various types of subligamentous disk displacement At the disk level posteriorly displaced disk material frequently occupies the midline Below and above the disk an anterior epidural space (AES) exists between the PLLC and the posterior aspect of the vertebral bodies In this space disk fragment motion across the midline is curtailed by a sagittal midline septum (dashed line) A delicate translucent membrane (shown only on left side of drawing) is stretched between the free edge of the deep layer of the posterior longitudinal ligament and the lateral spinal canal (From Schellinger D Manz HJ Vidic B et al Disk fragment migration Radiology 175831-836 1990 with permission)

Figure 13 Relationship of typical posterior disk herniations with the PLLC A Midline sagittal section unless very large a posterior midline herniation usually remains entrapped underneath the deep layer of the PLL C and sometimes a few intact outer anulus fibers joining with the PLL C to form a capsule The deep layer of the PLL C (arrow) also attaches to the posterior aspect of the vertebral body so that no potential space is present underneath B Sagittal para-central section the PLL C extends laterally at the disk level (arrowhead) but above and below the disk an anterior epidural space (as) where disk fragments are frequently entrapped is present between the lateral (peridural) membranes and the posterior aspect of the vertebral bodies

Volume of Herniated Material

Quantifying the herniated disk material by measuring in millimeters its greatest diameter or by evaluating its cross-sectional area in square millimeters is rarely done The resulting figures could be misleading without relating this measurement to the size of the spinal canal and the exact location of the lesion[ ]88 A purely qualitative and subjective statement that a mild moderate or severe herniation is present however does not give the person reading the imaging report any indication as to the potential of the lesion to cause significant compression of the dural sac or individual exiting nerve roots A reasonably precise scheme has been proposed in 1995 by the Nomenclature Committee of the North American Spine Society[ ]20 Measurements are taken from an axial CT or MR imaging section at the site of most severe compromise canal compromise of less than 25 at that section is qualified as mild 25 to 75 is moderate 76 to 90 is moderately severe and greater than 90 is severe It is understood that such characterizations describe only the cross-sectional area at one level and do not account for the total volume of displaced material displacement of neural tissue or clinical significance The usefulness of having four categories is questionable and can likely generate poor interobserver or intraobserver agreement especially in situations where the central spinal canal is relatively narrow Bonnevilles scheme[ ]9 [ ]10 [ ]11 should generate greater reliability (Fig 14) (Figure Not Available) Separation of the cross-sectional area in three thirds can be applied to both the central spinal canal and the foramina It can be agreed by way of convention that the terms mild moderate and severe lumen compromise by a disk herniation designate extension of the displaced disk material in the anterior middle or posterior third of the central canal or foramen depending on the specified location of the herniation

Figure 14 (Figure Not Available) The size of the herniation in the horizontal plane is assessed and designated by the numbers 1 2 or 3 by establishing its extension in the anterior middle or posterior third of the spinal canal (From Bonneville JF Plaidoyer pour une classification par limage des hernies discales lombaires la carte-image Rev Imag Med 2557-560 1990 with permission)

Location of Herniated Material

Bonneville[ ]9 [ ]10 [ ]11 has also proposed an interesting and simple alpha-numerical system to classify according to their location the position of disk fragments that have migrated in the horizontal or sagittal plane (Figs 15 (Figure Not Available) and 16) (Figure Not Available) Using more precise anatomic boundaries unfortunately more familiar to surgeons than radiologists Wiltse et al[ ]88 have proposed another system which has been supported by the North American Spine Society[ ]20 [ ]21 Anatomic zones and levels are defined using the following anatomic landmarks medial edge of the articular facets medial lateral upper and lower border of the pedicles and coronal plane at the disk center On the horizontal plane (Fig 17) (Figure Not Available) these landmarks determine the bounderies of the central zone the subarticular zone the foraminal zone the extraforaminal zone and the anterior zone (anterior to the coronal plane at the center of the disk) In the sagittal plane they determine the boundaries of the diskal level the infrapedicular level the pedicular level and the suprapedicular level (Figs 18 (Figure

Not Available) and 19) (Figure Not Available) Radiologists interpreting axial CT or MR images may find it difficult to use the medial edge of the facets as the landmark that separates the central zone from the subarticular zone because the superior articular facets are generally not included in axial sections at the disk level The alternative is to use the expression posterolateral to designate collectively all posterior herniations that are not midline but do not extend into a foramen as was proposed by Bonneville[ ]9 [ ]10 [ ]11

Figure 15 (Figure Not Available) In the horizontal plane herniations are labeled midline (a) posterolateral (b) foraminal (c) and extra-foraminal (d) (From Bonneville JF Plaidoyer pour une classification par limage des hernies discales lombaires la carte-image Rev Imag Med 2557-560 1990 with permission)

Figure 16 (Figure Not Available) In the craniocaudal direction disk migration is labeled +1 +2 +3 or -1 -2 -3 by referring to the height of a vertebral body divided in thirds (From Bonneville JF Plaidoyer pour une classification par limage des hernies discales lombaires la carte-image Rev Imag Med 2557-560 1990 with permission)

Figure 17 (Figure Not Available) The anatomic zones identified on axial images The anterior zone (not shown) is delineated from the extraforaminal zone by an imaginary coronal line in the center of the vertebral body (From Wiltse LL Berger PE McCulloch JA A system for reporting the size and location of lesions in the spine Spine 221534-1537 1997 with permission)

Figure 18 (Figure Not Available) The anatomical levels identified on craniocaudal images (From Wiltse LL Berger PE McCulloch AJ A system for reporting the size and location of lesions in the spine Spine 221534-1537 1997 with permission)

Figure 19 (Figure Not Available) Coronal view of the main zones and levels (From Wiltse LL Berger PE McCulloch JA A system for reporting the size and location of lesions in the spine Spine 221534-1537 1997 with permission)

Composition of Herniated Material

Displaced disk material may consist of glycosaminoglycans type 1 or 2 collagen end plate cartilage and bone fragments avulsed from the ring epiphysis A reactive inflammatory reaction usually results in edematous tissue followed by granulation tissue which may undergo calcification (Fig 20) Necrotic and partially resorbed displaced disk material sometimes produces a large fluid-filled pouch distinguishable from the common high-intensity zone because of its size (Fig 21) or a gas-filled cavity generally in continuity with gas in the intervertebral space (Fig 22) [ ]42 These characteristics may be meaningful if intradiskal injection therapy is considered In imaging reports herniations exhibiting calcium deposits and those exhibiting replacement of disk material by gas or a relatively large fluid collection can be qualified as chronic herniations

Figure 20 A CT scan demonstration of a small posterior central L4-L5 calcified subligamentous herniation The resistant deep layer of the PLLC restrains displacement of the disk material in the posterior central direction and does not allow a detectable distortion of the disk contour In this particular case the presence of the calcification is actually the only evidence that a posterior midline anular tear and a small subligamentous herniation are present B Posterior right central and sub-articular L5-S1 calcified disk herniation in same patient Posterolateral herniations are generally more conspicuous than posterior midline herniations because the deep layer of the PLLC gets thinner away from the midline

Figure 21 Posterior central midline L4-L5 herniation in a 52-year-old man demonstrated on a T2-weighted midline MR sagittal section There is intervertebral space narrowing with loss of normal central disk signal

intensity while the herniated disk material demonstrates high signal intensity consistent with a predominantly fluid consistency

Figure 22 CT scan demonstration in a 51-year-old woman of a left posterolateral L5-S1 disk hernation consisting essentially in a gas-filled pouch (white arrow) Gas is also present in the central portion of the intervertebral disk space (black arrow)

DIAGNOSTIC IMAGING AND CHARACTERIZATION OF A HERNIATED LUMBAR DISK

Assessing the validity of the currently used imaging procedures to diagnose a herniated lumbar disk is not an easy endeavor The validity of a measurement is the extent to which it corresponds to the true biologic value or some accepted gold standard[ ]40 With the exception of postmortem studies evaluation of the pathoanatomy by the surgeon in the operating room has always been considered the gold standard but this does not constitute an ideal situation Inspection of the disk through a small laminectomy incision to determine for instance if nuclear fragments lie within or outside the anular fibers may not be very reliable Also unbiased intraoperative determination of a normal degenerated or herniated disk in a patient with sciatica may also be difficult[ ]86 Because the validity of diskography has been previously established by postmortem studies and surgical correlations[ ]48 it is sometimes used as a gold standard in situations where no surgery has been performed

Conventional Radiographs

Lumbar disk herniations can exceptionally be diagnosed directly on good quality lateral projections because the x-ray attenuation is slightly greater in displaced disk material than in epidural fat Occasionally a calcified rim outlines the displaced disk fragment

(Fig 23) In most situations however narrowing of an intervertebral disk space in the absence of other evidence of chronic diskopathy is the only detectable sign suggesting the presence of a disk herniation To my knowledge the sensitivity and specificity of this sign has never been assessed The accepted rule of thumb is that the height of a given lumbar intervertebral disk space should always be slightly greater than the height of the above located interspace This rule does not apply to the transition disk immediately above the sacrum (usually L5-S1) The specificity of this sign is probably quite high but a few false-positives are seen especially at the L4-L5 level because of minor congenital hypoplasia The presence of posterior or foraminal vertebral body osteophytes associated or not with disk space narrowing is a definite sign of a chronic disk herniation

Figure 23 A Chronic left L3-L4 extraforaminal disk hernation in a 54-year-old man suspected on an AP radiograph demonstrating a calcified shell on the left side of the intervertebral disk space (white arrow) B Axial CT scan section confirming the diagnosis of a chronic extraforaminal L3-L4 herniation

Myelography

Myelography is essentially an exploration of the subarachnoid space Disk herniations are demonstrated only indirectly because they can cause thecal sac deformity and individual nerve root sleeve filling defects (Fig 24) Of all the special imaging procedures

myelography is the only one that allows upright projections with full weight bearing It is not unusual to demonstrate in this way small posterior central or posterolateral herniations that are undetectable on CT sections Interestingly the overall sensitivity of myelography to detect disk herniations has been found to be higher than that of CT whereas its specificity has been found to be lower[ ]74 In comparison with standard CT examination which usually includes only the three or four lower lumbar disks myelography easily allows coverage of the entire lumbar area and assessment of the intrathecal structures (cauda equina and conus medullaris) Far lateral foraminal herniations extraforaminal herniations and anterior herniations however are not detected The sensitivity for detection of posterior central L5-S1 herniations is also relatively poor because of the greater distance between the thecal sac and the posterior aspect of this particular disk

Figure 24 L5-S1 disk herniation in a 25-year-old man detected by indirect signs using lumbosacral myelography A Upright oblique projections showing a filling defect of the left S1 root sleeve (white arrow) suggesting significant nerve root compression by a left posterolateral disk hernation The right S1 root sleeve fills normally with contrast (black arrow) B Subtle compression of the anterior wall of the dural sac by displaced disk material (small arrows) demonstrated on upright lateral projection This sign is usually absent in the presence of a large amount of fat and venous structures in the anterior epidural compartment

CT

The sensitivity of CT to diagnose a herniation of the nucleus pulposus at the L5-S1 interspace is greater than that of myelography if images in the exact plane of the disk can be obtained[ ]23 [ ]39 Otherwise the superiority of plain CT over myelography to demonstrate disk herniations has not been established but CT has the distinct advantage of being

noninvasive and provides direct anatomic information[ ]23 Large herniations are easily detected but as explained previously the distinction between protrusions and extrusions is often difficult without sagittal reconstructions CT essentially allows an assessment of the contour of the disk The diagnosis of very small herniations in the absence of direct or indirect evidence of a radial tear is hazardous and associated with a high percentage of false-positives and false-negatives[ ]52 The diagnosis of moderate and large size herniations in different directions is usually possible but anterior herniations are rarely diagnosed not because they are not detectable but because observers pay little attention to the anterior contour of the disk (Fig 25) Because the PLLC cannot usually be identified the distinction of subligamentous from transligamentous herniation can only be suggested in most cases by the size of the herniated material A definite diagnosis of sequestration is rarely possible Calcifications within the displaced material are readily seen but may be difficult at times to differentiate from an accompanying osteophyte or an avulsed bone fragment from the vertebral body ring epiphysis (Fig 26) The presence of gas in the herniated material is easily detected

Figure 25 Anterior L4-L5 herniation demonstrated by CT scan in a 51-year-old woman with chronic low back pain Although sometimes quite conspicuous such herniations are rarely reported because observers pay little attention to the anterior contour of the disk

Figure 26 CT scan demonstration of a posterior right central L4-L5 disk herniation in a 38-year-old woman with avulsion of a bone fragment from the ring epiphysis and adjacent part of the superior L5 end plate Reactive osteosclerosis is seen around the vertebral body defect (arrows) suggesting a chronic lesion

CT Myelography

This association combines the advantages of both imaging modalities The fact that its accuracy has been reported as being less[ ]22 [ ]32 higher[ ]1 [ ]6 or equivalent[ ]82 to MR imaging is a reflection of the differences in technologic advancement and pathologic nomenclature that hamper valid comparisons between different studies

MR Imaging

Most reported studies establish MR imaging as the first choice modality to diagnose a herniated lumbar disk[ ]5 [ ]22 [ ]32 [ ]46 The associated intravenous injection of a paramagnetic agent has been found useful to demonstrate some anatomic features of disk disease in patients with no previous lumbar disk surgery[ ]56 [ ]68 [ ]90 MR imaging provides a better assessment of disk morphology than CT or CT myelography because sagittal sections are routinely obtained Assessment of foraminal involvement by displaced disk material is more accurate (Fig 27) and anterior disk herniations can be detected more easily than with CT or CT myelography If one is looking specifically for herniated lumbar disks associated with nerve root compression however it has been demonstrated that CT is equally accurate[ ]82 Alterations of the central or peripheral disk signal intensity on T2-weighted images are seen in most disks afflicted with an anular tear[ ]48 and alert the observer to scrutinize the disk contour in search for local modifications indicative of a herniation Because the signal of the displaced disk material is usually very similar to that of the outer anulus PLLC and vertebral body cortical bone small herniations are generally more conspicuous on axial CT sections than on corresponding axial MR imaging sections Gas and calcium deposits within the displaced fragment cannot usually

be detected but associated vertebral body bone marrow changes are typically seen and are helpful in differentiating acute from chronic processes[ ]57 The occasional presence of a high-intensity zone in the herniated material with an occasionally enhancing border after contrast injection is probably caused by a mixture of displaced nuclear material acute and subacute inflammatory tissue and neovascularized reactive tissue[ ]4 [ ]48 [ ]72 Contradictory reports have been published regarding the accuracy of MR imaging to differentiate subligamentous from transligamentous herniations[ ]26 [ ]38 [ ]73 [ ]76 Understanding the anatomy of the PLLC is helpful to make the distinction (Fig 28) (Figure Not Available) Masaryk et al[ ]46 have suggested that MR imaging is accurate to distinguish sequestered disks from other forms of lumbar disk herniations but most observers find this distinction difficult to establish[ ]42

Figure 27 A Left L4-L5 foraminal herniation well seen on an intermediate-weighted left parasagittal MR section (arrow) in a 47-year-old man B The lesion is much less obvious on intermediate-weighted (left) and T2-weighted (right) axial sections and was in fact more conspicuous on the corresponding CT scan section

Figure 28 (Figure Not Available) A Subligamentous disk herniation Left T1-weighted image demonstrating displaced disk material with a smooth outline imposed by the demarcation of the anterior epidural space (AES) by the lateral membrane of the PLLC Right Correlative drawing B Transligamentous disk herniation Left T1-weighted image of a large disk herniation (cervical in this case) which has ruptured through the posterior confines of the AES Penetration of the right lateral membrane can be observed (arrow) and the disk fragment contour is serrated Right Correlative drawing (From Schellinger D Manz HJ Vidic B et al Disk fragment migration Radiology 175831-836 1990 with permission)

Diskography and CT Diskography

During 30 years (1950 to 1980) when myelography was the only available imaging technique to demonstrate lumbar disk herniations diskography was an invasive but efficient way to demonstrate posterior central L5-S1 herniations and other large herniations (other than posterior central and paramedial) that could not be detected by myelography[ ]50 These herniations are now usually well demonstrated by CT and MR imaging Comparing the accuracy of five imaging modalities (excluding MR imaging) for the diagnosis of lumbar disk herniation Jackson et al[ ]31 found that CT diskography (Fig 29) was the most accurate test (87) compared with 77 for CT myelography 74 for CT 70 for myelography 64 for pain reproduction during diskography and 58 for diskography without CT Disk injection reproduced the patients clinical pain pattern in only 36 of herniated disks This clinical test isolated from the images had high specificity (89) but low sensitivity (43) for the diagnosis of disk herniation The reported low sensitivity of diskography images (unassociated with CT) to diagnose disk herniation is to be expected the purpose of the intradiskal injection being primarily the demonstration of an anular tear the contrast leaking through the tear only occasionally delineates an extruded fragment When a disk herniation has been diagnosed by other imaging modalities diskography allows to determine if the herniation is contained or noncontained (Figs 30 and 31) this information may have clinical relevance[ ]62 It also allows to establish if the displaced disk material is communicating or not with the parent disk and establishes the likelihood that it is sequestered or not There always remains a possibility that the contrast injected under pressure may reach a disk fragment that is nevertheless sequestered by leaking through the associated anular tear CT diskography also allows assessment in most cases of the integrity of the PLLC[ ]89 The superior sensitivity of diskography over MR imaging to demonstrate anular tears has been well established[ ]27 [ ]44 [ ]48 [ ]64 [ ]77 [ ]91 [ ]94 The presence of a radial tear and the inflammatory reaction it creates may be symptomatic despite the absence of true disk herniation[ ]29 [ ]48 [ ]49 [ ]69

Figure 29 L4-L5 CT diskogram demonstrating a large left posterolateral radial anular tear associated with

a left foraminal and extraforaminal herniaton (same patient as in Figure 28) (Figure Not Available)

Figure 30 Contained posterior L4-L5 and L5-S1 disk herniations in a 57-year-old man demonstrated by diskography The L3-L4 disk is normal

Figure 31 Noncontained L4-L5 disk herniation in a 23-year-old woman Reflux of injected contrast is seen in the anterior epidural space above and below the disk space The L5-S1 disk also demonstrates incomplete anterior and posterior radial anular tears

SUMMARY

The absence of universal nomenclature standardization with respect to the definition of a disk herniation and its different categories especially regarding type and location is still a major problem that will only be overcome when major national or international scientific societies join efforts to support a particular scheme Meanwhile it is important to realize that the two models that are currently most used are based on a different perspective Trying to straddle the two by opposing for instance bulging disk and herniation is doomed to failure because this exercise defies formal logic MR imaging is currently the most accurate noninvasive imaging modality to diagnose a disk herniation and to determine its exact location The determination of some pathoanatomic characteristics of herniated disks (type and composition) may require the use of CT diskography or CT diskography

References

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  • CLASSIFICATION DIAGNOSTIC IMAGING AND IMAGING CHARACTERIZATION OF A LUMBAR HERNIATED DISK
    • IMAGING OF LOW BACK PAIN I
      • CLASSIFICATION DIAGNOSTIC IMAGING AND IMAGING CHARACTERIZATION OF A LUMBAR HERNIATED DISK
        • DEFINITION OF A DISK HERNIATION
        • CLASSIFICATION OF A HERNIATED LUMBAR DISK
          • Main Categories of Noninfectious Disk Abnormalities
          • Further Qualifying the Displaced Disk Material Beyond the Disk Space
            • DIAGNOSTIC IMAGING AND CHARACTERIZATION OF A HERNIATED LUMBAR DISK
              • Conventional Radiographs
              • Myelography
              • CT
              • CT Myelography
              • MR Imaging
              • Diskography and CT Diskography
                • SUMMARY
                  • References
Page 9: CLASSIFICATION, DIAGNOSTIC IMAGING, AND IMAGING ... · PDF fileclassification, diagnostic imaging, and imaging characterization of a lumbar herniated disk ... classification, diagnostic

Figure 6 Axial CT scan section of a L4-L5 disk in a 78-year-old man demonstrating diffuse disk bulging caused by remodeling of the adjacent vertebral bodies due to osteoporosis The intervertebral space was normal in height and there were no reactive adjacent bony endplate modifications

Figure 7 A T2-weighted axial section of a L5-S1 disk showing a left posterolateral wide base protrusion that can be easily confused with diffuse circumferential bulging B Corresponding T2-weighted left paracentral and central sagittal sections demonstrating loss of the L5-S1 disk signal intensity with posterior small left-central protrusion the anterior aspect of the disk does not extend beyond the endplates and therefore such a disk should not be labeled bulging disk

The Pathoanatomic Model

As opposed to the previous model that can be applied only to the interpretation of CT and MR imaging studies this model can be used for the interpretation of all imaging modalities including plain films and diskograms[ ]47 [ ]51 It consists of five categories that are not mutually exclusive so that different combinations are possible (Fig 8) (Figure Not Available) The first three refer to the general state of the disk (1) normal young disk (2) normal aging disk and (3) deteriorated disk (formerly called the scarred disk) The last two refer to localized lesions anular tear and herniated disk In this model the previously discussed definition of disk herniation proposed by Herzog[ ]30 is applicable The use of this system requires an effort to distinguish the normal aging changes from those of pathologic degeneration Resnick and Niwayama[ ]66 have emphasized the differentiating features of two degenerative processes involving the intervertebral disk which had been previously described by Schmorl and Junghanns[ ]75 (1) spondylosis deformans which affects primarily the anulus fibrosus and bony ring epiphysis and (2) intervertebral osteochondrosis which affects essentially the nucleus pulposus and the vertebral body end plates

Figure 8 (Figure Not Available) Schematic representation of a nomenclature based on a three-dimensional assessment of the anatomic and pathologic characteristics of both disk and adjacent vertebral bodies The categories are not mutually exclusive and some combinations are possible A Categories related to the general aspect of the disk normal young disk (a) normal aging disk (b) deteriorated disk (c) B Categories related to local lesions normal young disk (a) anular tear (b) herniated disk (c) (Adapted from Milette PC The proper terminology for reporting lumbar intervertebral disk disorders AJNR Am J Neuroradiol 181859-1866 1997 with permission)

There is convincing evidence in the scientific literature that the features of spondylosis deformans represent the normal aging process whereas intervertebral osteochondrosis denotes true pathologic disk degeneration[ ]61 [ ]71 [ ]75 [ ]83 [ ]84 Schmorl and Junghanns[ ]75 found spondylotic changes in 60 of women and almost 80 of men over the age of 50 In a series of 400 dried skeletons Nathan[ ]61 found anterior vertebral body osteophytes which constitute the main feature of spondylosis deformans in 100 of individuals over age 40 whereas posterior osteophytes were found in only 39 of individuals even after the age of 80 Twomey and Taylor[ ]83 [ ]84 have found that loss of disk height is unusual in a normal aging population and that loss of stature in the elderly is attributable to loss of intervertebral body height rather than loss in disk height During the normal aging process the mucoid matrix of the nucleus pulposus is progressively replaced by fibrous tissue[ ]37 but the intervertebral height is preserved and the disk margins remain regular Dessication and thining of disks or disks that bulge like an underinflated automobile tire are not typical of elderly spines Slight symmetric bulging may occur if there has been vertebral body remodeling resulting from osteoporosis Small amounts of gas can be detected on plain films or CT images near the insertion of the anulus on the ring epiphysis and this gas is probably located in transverse anular tears adjacent to the ring epiphysis During the fourth decade anterior and lateral marginal vertebral body osteophytes constitute normal findings comparable with having gray hair but end plate erosions with osteosclerosis or chronic reactive bone marrow changes type 2 or 3 as described by Modic et al[ ]57 should not be seen Slight to moderate decrease in central signal intensity can be detected on T2-weighted MR images as part of the normal aging process but the changes should involve uniformly all lumbar disks

Deteriorated disks represent real pathologic degeneration which is sometimes referred to as chronic diskopathy On microscopic examination they show total structural disorganization and general replacement of normal disk material by scar tissue For this reason they were initially labeled scarred disks by the members of a joint committee on spinal nomenclature created by the Quebec Association of Radiologists[ ]14 Because of possible confusion with postoperative changes the term deteriorated disk has been proposed as an acceptable substitute Strictly speaking the term degeneration could be used to designate this entity but this latter term has such a broad nonspecific meaning that it is best avoided The deteriorated disk is characterized by narrowing of the intervertebral space irregular disk contour generally associated with symmetric or asymmetric bulging abundant presence of gas in the central portion of the intervertebral disk space multidirectional osteophytes that do not respect the central spinal canal or the foramina end plate erosions with reactive osteosclerosis and chronic bone marrow changes On T2-weighted MR images the central disk signal intensity is usually markedly decreased and the number of affected lumbar disks is variable Even though transverse concentric and radial anular tears have been identified on postmortem specimens[ ]92 the anular tear category in this model refers essentially to the radial tears that are generally demonstrated by diskography in symptomatic patients For a more precise description of those tears this model may be supplemented by the Dallas Discogram Description system[ ]70 with or without its recently proposed updates[ ]4 [ ]72 [ ]80

It should be emphasized that the pathoanatomic model is not based on direct identification of a particular geometric pattern but on the anatomy and pathology that are expected as a result of the analysis of specific criteria Using this model the conclusion of any imaging report does not consist of terms related to the shape of the disk contour or the displaced disk material but on a pathologic diagnosis that should be presented with an appropriate confidence level (possible probable or definite) The diagnosis of a probable major radial anular tear may be inferred from the presence of a definite central signal intensity loss because as a result of diskographic MR imaging correlations the positive predictive value of this sign has been estimated at 96[ ]48 The use of this model requires an effort to understand the criteria allowing differentiation of normal aging from true pathologic degeneration so this system is slightly more complicated than the morphologic model Its reliability has never been tested Some intraobserver or interobserver disagreement would probably occur trying to distinguish anular tears without herniation from anular tears with small herniations With respect to correspondance to clinical situations this scheme like the morphologic model has limited interest it has been shown that disks demonstrating the features of the deteriorated disk are likely to be responsible for symptoms but this relationship has been statistically established to be significant only for the L4-L5 disk[ ]24

Which Model Should Be Used

In other areas of diagnostic radiology the aim of image analysis is always to predict what the pathologist would find if he or she could be provided with an adequate specimen immediately following the imaging study radiologic diagnoses are presented with a pathologic perspective There is no reason why the reporting of disk disorders should be

any different Terms like bulging disk are meaningless to a pathologist and I personally favor the pathoanatomic model Nomenclature standardization however is not a task that can be achieved by an individual or even a single group of authors[ ]12 To have any impact recommendations have to emanate from well established national or international societies The multiplicity of scientific societies with an interest in the spine all over the world creates a special problem but new joint committees have recently been set up combining efforts to come up with a practical unified system that it is hoped could be proposed jointly by the North American Spine Society the American Academy of Orthopedic Surgeons the American Academy of Neurological Surgeons the American Society of Spine Radiology and the American Society of Neuroradiology Agreeing in North America on a classification of disk disorders that could gain universal acceptance like the TNM classification of neoplastic diseases would be a major achievement Meanwhile the choice of the nomenclature is up to the best judgement of each practicing radiologist and the essential issue in a given hospital or community practice remains clear communication between radiologists and referring physicians by way of a local agreement as to the meaning of words

A major problem frequently occurs because observers of imaging studies try to combine elements of the morphologic classification with those of the pathoanatomic classification Trying to differentiate a bulging disk (morphologic qualifier) from a disk herniation (pathologic diagnosis) cannot work because a bulging disk aspect is a common feature of the aging disk the deteriorated disk and some posterior central disk herniations (Fig 9) Trying to make the distinction is doomed to failure because it defies formal logic On the other hand it is theoretically possible to differentiate a radial anular tear (without herniation) from a disk herniation because these are two different pathologic entities although one may be the continuum of the other It is best to adopt either one of the two systems and avoid trying to straddle the two A general classification of disk disorders attempting to conciliate the morphologic and the pathoanatomic model is proposed in Table 1

Figure 9 A bulging disk aspect often conceals a posterior central herniation A Complete rupture of the outer anular fibers allowing nuclear material to escape and peel off the posterior longitudinal ligament (and sometimes a few intact peripheral anular fibers) from the torn disk creating a detectable focal or asymmetric extension of the disk margin beyond the interspace which qualifies as a protrusion B With more gelatinous nuclear material escaping underneath the rigid posterior longitudinal ligament the focal bulge is no longer detectable as its radius increases and if the tear occurs in the posterior midline or para-medial direction the aspect mimics symmetric disk extension beyond the interspace C Since in most cases only the outline of a diffusely hypointense disk is perceived on MR images this creates the illusion of circumferential disk bulging on axial sections D The real nature of a bulging disk of this type may be suspected by scrutinizing the sagittal sections and appreciating that unless one is dealing with a chronically degenerated scarred disk the bulge is not symmetric but limited to the posterior aspect of the disk

TABLE 1 -- GENERAL

CLASSIFICATION OF DISK LESIONS Normal (excluding aging changes)

Congenitaldevelopmental variants

Inflammationinfection

Neoplasia

Degenerativetraumatic

Degeneration

Anular tear

Herniation Protrusion

Extrusion

Degeneration Spondylosis deformans

Intervertebral osteochondrosis

Further Qualifying the Displaced Disk Material Beyond the Disk Space

Regardless of the basic system that is used the type of herniation should be assessed The volume and location of the displaced disk material beyond the normal peripheral margin of the intervertebral space also need to be specified In certain cases it is also possible to determine the composition of this material For the sake of simplicity the term herniation is used consistently in the remainder of this article to refer to all displaced disk material but what is discussed can also be applied to protrusions and extrusions if one wants to use the morphologic nomenclature

Type of Herniation

Upward or downward migration of nuclear material may occur through a break in a vertebral body end plate creating an intravertebral herniation sometimes referred to as an intraspongy herniation or a Schmorls node[ ]67 (Fig 10) Although a herniation occurring in any horizontal direction is likely to cause symptoms because of the presence of pain-sensitive nerve endings in the outer anulus[ ]7 [ ]8 [ ]65 herniations occurring in a posterior or posterolateral direction deserve special consideration because of the added possibility of dural sac or individual nerve root compression

Figure 10 Various types of intravertebral herniations (Schmorls nodes) A Intravertebral herniation through the inferior end plate of the L3 vertebral body demonstrated by diskography in a 35-year-old man suffering from chronic low back pain The patients typical pain was reproduced during injection and the lesion was considered responsible for the patients symptoms B T2-weighted sagittal section demonstrating an intravertebral herniation through the inferior end plate of the L4 vertebral body in a 24-year-old woman presenting with chronic low back pain The high signal intensity of the lesion associated with the loss of normal central signal intensity of the parent disk suggests that the lesion is a bona fide acquired intraspongy herniation and not just a developmental defect C T2-weighted sagittal section demonstrating an intravertebral herniation through the inferior end plate of the L3 vertebral body (arrow) Because both the herniation and the parent disk show normal signal intensity the abnormality was

considered a probably asymptomatic developmental defect

Other characteristics of disk herniations have become relevant with the development of new therapeutic possibilities (eg chemonucleolysis and percutaneous diskectomy) The term sequestration is confusing and has often been used to indicate displacement of disk material away from the parent disk The term sequestered disk should be used restrictedly to designate a fragment of diskal tissue that has migrated from the disk space and has no connection by diskal tissue to the disk of origin[ ]20 [ ]21 [ ]42 Sequestration refers to loss of continuity with disk tissue still present in the intervertebral disk space The term migration has a broader meaning indicating displacement of disk material away from the edge of the rent in the outer anulus either in the central spinal canal at the disk level or above or below the disk level This difference is illustrated in Figure 11 The terms communicating and noncommunicating derive from a different perspective and are mostly used in the context of intradiskal therapeutic injections They refer to the interruption of the periphery of the disk allowing fluid injected into the disk to leak into the spinal canal and reach displaced disk material[ ]20 [ ]51 The terms contained and uncontained are unfamiliar to most radiologists in a contained herniation the displaced disk material is still covered by a few intact but distended outer anular fibers or by a capsule formed by outer anular fibers and the adherent posterior longitudinal ligament

Figure 11 Various types of posterior central herniations A Small subligamentous herniation (protrusion) without significant disk material migration B Subligamentous herniation with downward migration of disk material under the PLLC C Sub-ligamentous herniation with downward migration of disk material and sequestered fragment (arrow)

The terms subligamentous and extraligamentous (or transligamentous) refer to the position of the displaced disk material with respect to the posterior longitudinal ligament The anatomy of the posterior longitudinal ligament has been recently revised[ ]73 [ ]89 It is a membranous structure that has multiple components a deep layer attached to disks and vertebral bodies a superficial layer attached to the dura by fibrous tissue (Hoffmanns

ligament) and lateral extensions known as the lateral membranes or peridural membranes (Fig 12) (Figure Not Available) It should probably be referred to as the posterior longitudinal ligament complex (PLLC) It actually divides the epidural space into the perithecal space and the anterior epidural space where displaced disk material can be entrapped (Fig 13) A potential space allowing accumulation of displaced disk material has also been detected between the outer anular fibers and the deep fibers of the PLLC on the posterior central aspect of the disk[ ]63 Posterior midline herniations seldom rupture the PLLC and are generally subligamentous The lateral membranes are less resistant and transligamentous herniations are usually the result of posterior off-center herniations or posterolateral herniations

Figure 12 (Figure Not Available) The PLLC is portrayed here in relation to various types of subligamentous disk displacement At the disk level posteriorly displaced disk material frequently occupies the midline Below and above the disk an anterior epidural space (AES) exists between the PLLC and the posterior aspect of the vertebral bodies In this space disk fragment motion across the midline is curtailed by a sagittal midline septum (dashed line) A delicate translucent membrane (shown only on left side of drawing) is stretched between the free edge of the deep layer of the posterior longitudinal ligament and the lateral spinal canal (From Schellinger D Manz HJ Vidic B et al Disk fragment migration Radiology 175831-836 1990 with permission)

Figure 13 Relationship of typical posterior disk herniations with the PLLC A Midline sagittal section unless very large a posterior midline herniation usually remains entrapped underneath the deep layer of the PLL C and sometimes a few intact outer anulus fibers joining with the PLL C to form a capsule The deep layer of the PLL C (arrow) also attaches to the posterior aspect of the vertebral body so that no potential space is present underneath B Sagittal para-central section the PLL C extends laterally at the disk level (arrowhead) but above and below the disk an anterior epidural space (as) where disk fragments are frequently entrapped is present between the lateral (peridural) membranes and the posterior aspect of the vertebral bodies

Volume of Herniated Material

Quantifying the herniated disk material by measuring in millimeters its greatest diameter or by evaluating its cross-sectional area in square millimeters is rarely done The resulting figures could be misleading without relating this measurement to the size of the spinal canal and the exact location of the lesion[ ]88 A purely qualitative and subjective statement that a mild moderate or severe herniation is present however does not give the person reading the imaging report any indication as to the potential of the lesion to cause significant compression of the dural sac or individual exiting nerve roots A reasonably precise scheme has been proposed in 1995 by the Nomenclature Committee of the North American Spine Society[ ]20 Measurements are taken from an axial CT or MR imaging section at the site of most severe compromise canal compromise of less than 25 at that section is qualified as mild 25 to 75 is moderate 76 to 90 is moderately severe and greater than 90 is severe It is understood that such characterizations describe only the cross-sectional area at one level and do not account for the total volume of displaced material displacement of neural tissue or clinical significance The usefulness of having four categories is questionable and can likely generate poor interobserver or intraobserver agreement especially in situations where the central spinal canal is relatively narrow Bonnevilles scheme[ ]9 [ ]10 [ ]11 should generate greater reliability (Fig 14) (Figure Not Available) Separation of the cross-sectional area in three thirds can be applied to both the central spinal canal and the foramina It can be agreed by way of convention that the terms mild moderate and severe lumen compromise by a disk herniation designate extension of the displaced disk material in the anterior middle or posterior third of the central canal or foramen depending on the specified location of the herniation

Figure 14 (Figure Not Available) The size of the herniation in the horizontal plane is assessed and designated by the numbers 1 2 or 3 by establishing its extension in the anterior middle or posterior third of the spinal canal (From Bonneville JF Plaidoyer pour une classification par limage des hernies discales lombaires la carte-image Rev Imag Med 2557-560 1990 with permission)

Location of Herniated Material

Bonneville[ ]9 [ ]10 [ ]11 has also proposed an interesting and simple alpha-numerical system to classify according to their location the position of disk fragments that have migrated in the horizontal or sagittal plane (Figs 15 (Figure Not Available) and 16) (Figure Not Available) Using more precise anatomic boundaries unfortunately more familiar to surgeons than radiologists Wiltse et al[ ]88 have proposed another system which has been supported by the North American Spine Society[ ]20 [ ]21 Anatomic zones and levels are defined using the following anatomic landmarks medial edge of the articular facets medial lateral upper and lower border of the pedicles and coronal plane at the disk center On the horizontal plane (Fig 17) (Figure Not Available) these landmarks determine the bounderies of the central zone the subarticular zone the foraminal zone the extraforaminal zone and the anterior zone (anterior to the coronal plane at the center of the disk) In the sagittal plane they determine the boundaries of the diskal level the infrapedicular level the pedicular level and the suprapedicular level (Figs 18 (Figure

Not Available) and 19) (Figure Not Available) Radiologists interpreting axial CT or MR images may find it difficult to use the medial edge of the facets as the landmark that separates the central zone from the subarticular zone because the superior articular facets are generally not included in axial sections at the disk level The alternative is to use the expression posterolateral to designate collectively all posterior herniations that are not midline but do not extend into a foramen as was proposed by Bonneville[ ]9 [ ]10 [ ]11

Figure 15 (Figure Not Available) In the horizontal plane herniations are labeled midline (a) posterolateral (b) foraminal (c) and extra-foraminal (d) (From Bonneville JF Plaidoyer pour une classification par limage des hernies discales lombaires la carte-image Rev Imag Med 2557-560 1990 with permission)

Figure 16 (Figure Not Available) In the craniocaudal direction disk migration is labeled +1 +2 +3 or -1 -2 -3 by referring to the height of a vertebral body divided in thirds (From Bonneville JF Plaidoyer pour une classification par limage des hernies discales lombaires la carte-image Rev Imag Med 2557-560 1990 with permission)

Figure 17 (Figure Not Available) The anatomic zones identified on axial images The anterior zone (not shown) is delineated from the extraforaminal zone by an imaginary coronal line in the center of the vertebral body (From Wiltse LL Berger PE McCulloch JA A system for reporting the size and location of lesions in the spine Spine 221534-1537 1997 with permission)

Figure 18 (Figure Not Available) The anatomical levels identified on craniocaudal images (From Wiltse LL Berger PE McCulloch AJ A system for reporting the size and location of lesions in the spine Spine 221534-1537 1997 with permission)

Figure 19 (Figure Not Available) Coronal view of the main zones and levels (From Wiltse LL Berger PE McCulloch JA A system for reporting the size and location of lesions in the spine Spine 221534-1537 1997 with permission)

Composition of Herniated Material

Displaced disk material may consist of glycosaminoglycans type 1 or 2 collagen end plate cartilage and bone fragments avulsed from the ring epiphysis A reactive inflammatory reaction usually results in edematous tissue followed by granulation tissue which may undergo calcification (Fig 20) Necrotic and partially resorbed displaced disk material sometimes produces a large fluid-filled pouch distinguishable from the common high-intensity zone because of its size (Fig 21) or a gas-filled cavity generally in continuity with gas in the intervertebral space (Fig 22) [ ]42 These characteristics may be meaningful if intradiskal injection therapy is considered In imaging reports herniations exhibiting calcium deposits and those exhibiting replacement of disk material by gas or a relatively large fluid collection can be qualified as chronic herniations

Figure 20 A CT scan demonstration of a small posterior central L4-L5 calcified subligamentous herniation The resistant deep layer of the PLLC restrains displacement of the disk material in the posterior central direction and does not allow a detectable distortion of the disk contour In this particular case the presence of the calcification is actually the only evidence that a posterior midline anular tear and a small subligamentous herniation are present B Posterior right central and sub-articular L5-S1 calcified disk herniation in same patient Posterolateral herniations are generally more conspicuous than posterior midline herniations because the deep layer of the PLLC gets thinner away from the midline

Figure 21 Posterior central midline L4-L5 herniation in a 52-year-old man demonstrated on a T2-weighted midline MR sagittal section There is intervertebral space narrowing with loss of normal central disk signal

intensity while the herniated disk material demonstrates high signal intensity consistent with a predominantly fluid consistency

Figure 22 CT scan demonstration in a 51-year-old woman of a left posterolateral L5-S1 disk hernation consisting essentially in a gas-filled pouch (white arrow) Gas is also present in the central portion of the intervertebral disk space (black arrow)

DIAGNOSTIC IMAGING AND CHARACTERIZATION OF A HERNIATED LUMBAR DISK

Assessing the validity of the currently used imaging procedures to diagnose a herniated lumbar disk is not an easy endeavor The validity of a measurement is the extent to which it corresponds to the true biologic value or some accepted gold standard[ ]40 With the exception of postmortem studies evaluation of the pathoanatomy by the surgeon in the operating room has always been considered the gold standard but this does not constitute an ideal situation Inspection of the disk through a small laminectomy incision to determine for instance if nuclear fragments lie within or outside the anular fibers may not be very reliable Also unbiased intraoperative determination of a normal degenerated or herniated disk in a patient with sciatica may also be difficult[ ]86 Because the validity of diskography has been previously established by postmortem studies and surgical correlations[ ]48 it is sometimes used as a gold standard in situations where no surgery has been performed

Conventional Radiographs

Lumbar disk herniations can exceptionally be diagnosed directly on good quality lateral projections because the x-ray attenuation is slightly greater in displaced disk material than in epidural fat Occasionally a calcified rim outlines the displaced disk fragment

(Fig 23) In most situations however narrowing of an intervertebral disk space in the absence of other evidence of chronic diskopathy is the only detectable sign suggesting the presence of a disk herniation To my knowledge the sensitivity and specificity of this sign has never been assessed The accepted rule of thumb is that the height of a given lumbar intervertebral disk space should always be slightly greater than the height of the above located interspace This rule does not apply to the transition disk immediately above the sacrum (usually L5-S1) The specificity of this sign is probably quite high but a few false-positives are seen especially at the L4-L5 level because of minor congenital hypoplasia The presence of posterior or foraminal vertebral body osteophytes associated or not with disk space narrowing is a definite sign of a chronic disk herniation

Figure 23 A Chronic left L3-L4 extraforaminal disk hernation in a 54-year-old man suspected on an AP radiograph demonstrating a calcified shell on the left side of the intervertebral disk space (white arrow) B Axial CT scan section confirming the diagnosis of a chronic extraforaminal L3-L4 herniation

Myelography

Myelography is essentially an exploration of the subarachnoid space Disk herniations are demonstrated only indirectly because they can cause thecal sac deformity and individual nerve root sleeve filling defects (Fig 24) Of all the special imaging procedures

myelography is the only one that allows upright projections with full weight bearing It is not unusual to demonstrate in this way small posterior central or posterolateral herniations that are undetectable on CT sections Interestingly the overall sensitivity of myelography to detect disk herniations has been found to be higher than that of CT whereas its specificity has been found to be lower[ ]74 In comparison with standard CT examination which usually includes only the three or four lower lumbar disks myelography easily allows coverage of the entire lumbar area and assessment of the intrathecal structures (cauda equina and conus medullaris) Far lateral foraminal herniations extraforaminal herniations and anterior herniations however are not detected The sensitivity for detection of posterior central L5-S1 herniations is also relatively poor because of the greater distance between the thecal sac and the posterior aspect of this particular disk

Figure 24 L5-S1 disk herniation in a 25-year-old man detected by indirect signs using lumbosacral myelography A Upright oblique projections showing a filling defect of the left S1 root sleeve (white arrow) suggesting significant nerve root compression by a left posterolateral disk hernation The right S1 root sleeve fills normally with contrast (black arrow) B Subtle compression of the anterior wall of the dural sac by displaced disk material (small arrows) demonstrated on upright lateral projection This sign is usually absent in the presence of a large amount of fat and venous structures in the anterior epidural compartment

CT

The sensitivity of CT to diagnose a herniation of the nucleus pulposus at the L5-S1 interspace is greater than that of myelography if images in the exact plane of the disk can be obtained[ ]23 [ ]39 Otherwise the superiority of plain CT over myelography to demonstrate disk herniations has not been established but CT has the distinct advantage of being

noninvasive and provides direct anatomic information[ ]23 Large herniations are easily detected but as explained previously the distinction between protrusions and extrusions is often difficult without sagittal reconstructions CT essentially allows an assessment of the contour of the disk The diagnosis of very small herniations in the absence of direct or indirect evidence of a radial tear is hazardous and associated with a high percentage of false-positives and false-negatives[ ]52 The diagnosis of moderate and large size herniations in different directions is usually possible but anterior herniations are rarely diagnosed not because they are not detectable but because observers pay little attention to the anterior contour of the disk (Fig 25) Because the PLLC cannot usually be identified the distinction of subligamentous from transligamentous herniation can only be suggested in most cases by the size of the herniated material A definite diagnosis of sequestration is rarely possible Calcifications within the displaced material are readily seen but may be difficult at times to differentiate from an accompanying osteophyte or an avulsed bone fragment from the vertebral body ring epiphysis (Fig 26) The presence of gas in the herniated material is easily detected

Figure 25 Anterior L4-L5 herniation demonstrated by CT scan in a 51-year-old woman with chronic low back pain Although sometimes quite conspicuous such herniations are rarely reported because observers pay little attention to the anterior contour of the disk

Figure 26 CT scan demonstration of a posterior right central L4-L5 disk herniation in a 38-year-old woman with avulsion of a bone fragment from the ring epiphysis and adjacent part of the superior L5 end plate Reactive osteosclerosis is seen around the vertebral body defect (arrows) suggesting a chronic lesion

CT Myelography

This association combines the advantages of both imaging modalities The fact that its accuracy has been reported as being less[ ]22 [ ]32 higher[ ]1 [ ]6 or equivalent[ ]82 to MR imaging is a reflection of the differences in technologic advancement and pathologic nomenclature that hamper valid comparisons between different studies

MR Imaging

Most reported studies establish MR imaging as the first choice modality to diagnose a herniated lumbar disk[ ]5 [ ]22 [ ]32 [ ]46 The associated intravenous injection of a paramagnetic agent has been found useful to demonstrate some anatomic features of disk disease in patients with no previous lumbar disk surgery[ ]56 [ ]68 [ ]90 MR imaging provides a better assessment of disk morphology than CT or CT myelography because sagittal sections are routinely obtained Assessment of foraminal involvement by displaced disk material is more accurate (Fig 27) and anterior disk herniations can be detected more easily than with CT or CT myelography If one is looking specifically for herniated lumbar disks associated with nerve root compression however it has been demonstrated that CT is equally accurate[ ]82 Alterations of the central or peripheral disk signal intensity on T2-weighted images are seen in most disks afflicted with an anular tear[ ]48 and alert the observer to scrutinize the disk contour in search for local modifications indicative of a herniation Because the signal of the displaced disk material is usually very similar to that of the outer anulus PLLC and vertebral body cortical bone small herniations are generally more conspicuous on axial CT sections than on corresponding axial MR imaging sections Gas and calcium deposits within the displaced fragment cannot usually

be detected but associated vertebral body bone marrow changes are typically seen and are helpful in differentiating acute from chronic processes[ ]57 The occasional presence of a high-intensity zone in the herniated material with an occasionally enhancing border after contrast injection is probably caused by a mixture of displaced nuclear material acute and subacute inflammatory tissue and neovascularized reactive tissue[ ]4 [ ]48 [ ]72 Contradictory reports have been published regarding the accuracy of MR imaging to differentiate subligamentous from transligamentous herniations[ ]26 [ ]38 [ ]73 [ ]76 Understanding the anatomy of the PLLC is helpful to make the distinction (Fig 28) (Figure Not Available) Masaryk et al[ ]46 have suggested that MR imaging is accurate to distinguish sequestered disks from other forms of lumbar disk herniations but most observers find this distinction difficult to establish[ ]42

Figure 27 A Left L4-L5 foraminal herniation well seen on an intermediate-weighted left parasagittal MR section (arrow) in a 47-year-old man B The lesion is much less obvious on intermediate-weighted (left) and T2-weighted (right) axial sections and was in fact more conspicuous on the corresponding CT scan section

Figure 28 (Figure Not Available) A Subligamentous disk herniation Left T1-weighted image demonstrating displaced disk material with a smooth outline imposed by the demarcation of the anterior epidural space (AES) by the lateral membrane of the PLLC Right Correlative drawing B Transligamentous disk herniation Left T1-weighted image of a large disk herniation (cervical in this case) which has ruptured through the posterior confines of the AES Penetration of the right lateral membrane can be observed (arrow) and the disk fragment contour is serrated Right Correlative drawing (From Schellinger D Manz HJ Vidic B et al Disk fragment migration Radiology 175831-836 1990 with permission)

Diskography and CT Diskography

During 30 years (1950 to 1980) when myelography was the only available imaging technique to demonstrate lumbar disk herniations diskography was an invasive but efficient way to demonstrate posterior central L5-S1 herniations and other large herniations (other than posterior central and paramedial) that could not be detected by myelography[ ]50 These herniations are now usually well demonstrated by CT and MR imaging Comparing the accuracy of five imaging modalities (excluding MR imaging) for the diagnosis of lumbar disk herniation Jackson et al[ ]31 found that CT diskography (Fig 29) was the most accurate test (87) compared with 77 for CT myelography 74 for CT 70 for myelography 64 for pain reproduction during diskography and 58 for diskography without CT Disk injection reproduced the patients clinical pain pattern in only 36 of herniated disks This clinical test isolated from the images had high specificity (89) but low sensitivity (43) for the diagnosis of disk herniation The reported low sensitivity of diskography images (unassociated with CT) to diagnose disk herniation is to be expected the purpose of the intradiskal injection being primarily the demonstration of an anular tear the contrast leaking through the tear only occasionally delineates an extruded fragment When a disk herniation has been diagnosed by other imaging modalities diskography allows to determine if the herniation is contained or noncontained (Figs 30 and 31) this information may have clinical relevance[ ]62 It also allows to establish if the displaced disk material is communicating or not with the parent disk and establishes the likelihood that it is sequestered or not There always remains a possibility that the contrast injected under pressure may reach a disk fragment that is nevertheless sequestered by leaking through the associated anular tear CT diskography also allows assessment in most cases of the integrity of the PLLC[ ]89 The superior sensitivity of diskography over MR imaging to demonstrate anular tears has been well established[ ]27 [ ]44 [ ]48 [ ]64 [ ]77 [ ]91 [ ]94 The presence of a radial tear and the inflammatory reaction it creates may be symptomatic despite the absence of true disk herniation[ ]29 [ ]48 [ ]49 [ ]69

Figure 29 L4-L5 CT diskogram demonstrating a large left posterolateral radial anular tear associated with

a left foraminal and extraforaminal herniaton (same patient as in Figure 28) (Figure Not Available)

Figure 30 Contained posterior L4-L5 and L5-S1 disk herniations in a 57-year-old man demonstrated by diskography The L3-L4 disk is normal

Figure 31 Noncontained L4-L5 disk herniation in a 23-year-old woman Reflux of injected contrast is seen in the anterior epidural space above and below the disk space The L5-S1 disk also demonstrates incomplete anterior and posterior radial anular tears

SUMMARY

The absence of universal nomenclature standardization with respect to the definition of a disk herniation and its different categories especially regarding type and location is still a major problem that will only be overcome when major national or international scientific societies join efforts to support a particular scheme Meanwhile it is important to realize that the two models that are currently most used are based on a different perspective Trying to straddle the two by opposing for instance bulging disk and herniation is doomed to failure because this exercise defies formal logic MR imaging is currently the most accurate noninvasive imaging modality to diagnose a disk herniation and to determine its exact location The determination of some pathoanatomic characteristics of herniated disks (type and composition) may require the use of CT diskography or CT diskography

References

1 Albeck MJ Hilden J Kjaer L et al A controlled comparison of myelography computed tomography and magnetic resonance imaging in clinically suspected lumbar disc herniation Spine 20443-448 1995 Abstract 2 American Academy of Orthopedic Surgeons Glossary on Spinal Terminology Chicago American Academy of Orthopedic Surgeons 1981 3 Andersson GB Weinstein JN Disc herniation [editorial] Spine 211S 1996 Citation 4 Aprill C Bogduk N High-intensity zone A diagnostic sign of painful lumbar disc on magnetic resonance imaging Br J Radiol 65361-369 1992 Abstract 5 Birney TJ White JJ Jr Berens D et al Comparison of MRI and discography in the diagnosis of lumbar degenerative disc disease J Spinal Disord 5417-423 1992 Abstract 6 Bischoff RJ Rodriguez RP Gupta K et al A comparison of computed tomography-myelography magnetic resonance imaging and myelography in the diagnosis of herniated nucleus pulposus and spinal stenosis J Spinal Disord 6289-295 1993 Abstract 7 Bogduk N The innervation of the lumbar spine Spine 8286-293 1983 Abstract 8 Bogduk N Tynan W Wilson AS The nerve supply to the human lumbar intervertebral discs J Anat 13239-56 1981 Abstract 9 Bonneville JF La carte-image des hernies discales lombaires Rachis 2255-257 1990 10 Bonneville JF La topografia simbolica delle ernie discali lombari Riv Neuroradiol 5427-431 1992 11 Bonneville JF Plaidoyer pour une classification par limage des hernies discales lombaires La carte-image Rev Imag Med 2557-560 1990 12 Brant-Zawadzki M Jensen M Spinal nomenclature Spine 20388-390 1995 Abstract

13 Brant-Zawadzki MN Jensen MC Obuchowski N et al Interobserver and intraobserver variability in interpretation of lumbar disc abnormalities A comparison of two nomenclatures Spine 201257-1263 1995 Abstract 14 Breton G Is that a bulging disk a small herniation or a moderate protrusion [editorial] Can Assoc Radiol J 42318 1991 Citation 15 Czervionke LF Lumbar intervertebral disc disease Neuroimaging Clin North Am 3465-485 1993 16 Deyo RA Nonsurgical care of low back pain Neurosurg Clin North Am 2851-862 1991 17 Deyo RA Loeser JD Bigos SJ Herniated lumbar intervertebral disk Ann Intern Med 112598-603 1990 Abstract 18 Dorlands Illustrated Medical Dictionary ed 28 Philadelphia WB Saunders 1994 19 Fardon D Pinkerton S Balderston R et al Terms used for diagnosis by English speaking spine surgeons Spine 18274-277 1993 Citation 20 Fardon DF Herzog RJ Mink JH et al Nomenclature of Lumbar Disc Disorders Contemporary Concepts in Spine Care Rosemont IL North American Spine Society 1995 21 Fardon DF Herzog RJ Mink JH et al Nomenclature of lumbar disc disorders In Garfin S Vaccaro A (eds) Orthopedic Knowledge Update Spine Rosemont IL American Academy of Orthopedic Surgeons 1997 pp A3-A14 22 Forristall RM Marsh HO Pay NT Magnetic resonance imaging and contrast CT of the lumbar spine Comparison of diagnostic methods and correlation with surgical findings Spine 131049-1054 1988 Abstract 23 Fries JW Abodeely DA Vijungco JG et al Computed tomography of herniated and extruded nucleus pulposus J Comput Assist Tomogr 6874-887 1982 Abstract 24 Frymoyer JW Newberg A Pope MH et al Spine radiographs in patients with low-back pain An epidemiological study in men J Bone Joint Surg Am 661048-1055 1984 Abstract 25 Gospodarowicz M Benedet L Hutter RV et al History and international developments in cancer staging Cancer Prev Control 2262-268 1998 Abstract 26 Grenier N Greselle JF Vital JM et al Normal and disrupted lumbar longitudinal ligaments Correlative MR and anatomic study Radiology 171197-205 1989 Abstract 27 Gunzburg R Parkinson R Moore R et al A cadaveric study comparing discography magnetic resonance imaging histology and mechanical behavior of the human lumbar disc Spine 17417-426 1992 Abstract 28 Haughton VM Eldevik OP Magnaes B et al A prospective comparison of computed tomography and myelography in the diagnosis of herniated lumbar disks Radiology 142103-110 1982 Abstract

29 Haughton VM Lim TH An H Intervertebral disk appearance correlated with stiffness of lumbar spinal motion segments AJNR Am J Neuroradiol 201161-1165 1999 Abstract 30 Herzog RJ The radiologic assessment for a lumbar disc herniation Spine 2119S-38S 1996 Abstract 31 Jackson RP Becker GJ Jacobs RR et al The neuroradiographic diagnosis of lumbar herniated nucleus pulposus I A comparison of computed tomography (CT) myelography CT-myelography discography and CT-discography Spine 141356-1361 1989 Abstract 32 Jackson RP Cain JE Jr Jacobs RR et al The neuroradiographic diagnosis of lumbar herniated nucleus pulposus II A comparison of computed tomography (CT) myelography CT-myelography and magnetic resonance imaging Spine 141362-1367 1989 Abstract 33 Jarvik JG Haynor DR Koepsell TD et al Interreader reliability for a new classification of lumbar disk disease Acad Radiol 3537-544 1996 Abstract 34 Jensen MC Brant-Zawadzki MN Obuchowski N et al Magnetic resonance imaging of the lumbar spine in people without back pain N Engl J Med 33169-73 1994 Abstract 35 Kent DL Haynor DR Larson EB et al Diagnosis of lumbar spinal stenosis in adults A meta-analysis of the accuracy of CT MR and myelography AJR Am J Roentgenol 1581135-1144 1992 Abstract 36 Kieffer SA Sherry RG Wellenstein DE et al Bulging lumbar intervertebral disk Myelographic differentiation from herniated disk with nerve root compression AJR Am J Roentgenol 138709-716 1982 Abstract 37 Kieffer SA Stadlan EM Mohandas A et al Discographic-anatomical correlation of developmental changes with age in the intervertebral disc Acta Radiol 9733-739 1969 38 Kim KY Kim YT Lee CS et al MRI classification of lumbar herniated intervertebral disc Orthopedics 15493-497 1992 Abstract 39 Kornberg M Rechtine GR Dupuy TE Computed tomography in the diagnosis of a herniated disk at the L5-S1 level Spine 9433-436 1984 Abstract 40 Kramer MS Clinical Epidemiology and Biostatistics New York Springer-Verlag 1988 41 Landis JR Koch GG The measurement of observer agreement agreement for categorical data Biometrics 33159-174 1977 Abstract 42 Laredo JD Bossard P Vuillemin-Bodaghi Formes anatomo-radiologiques des hernies discales In Morvan G Deburge A Bard H et al (eds) Le Rachis Lombaire Degeneratif Montpellier Sauramps Medical 1998 pp 37-49 43 Lee SH Coleman PE Hahn FJ Magnetic resonance imaging of degenerative disk disease of the spine Radiol Clin North Am 26949-964 1988 Abstract 44 Linson MA Crowe CH Comparison of magnetic resonance imaging and lumbar discography in the diagnosis of disc degeneration Clin Orthop 160-163 1990

45 Marchand F Ahmed AM Investigation of the laminate structure of lumbar disc anulus fibrosus Spine 15402-410 1990 Abstract 46 Masaryk TJ Ross JS Modic MT et al High-resolution MR imaging of sequestered lumbar intervertebral disks AJR Am J Roentgenol 1501155-1162 1988 Abstract 47 Milette PC The proper terminology for reporting lumbar intervertebral disk disorders AJNR Am J Neuroradiol 181859-1866 1997 Citation 48 Milette PC Fontaine S Lepanto L et al Differentiating lumbar disc protrusions disk bulges and discs with normal contour but abnormal signal intensity Magnetic resonance imaging with discographic correlations Spine 2444-53 1999 Abstract 49 Milette PC Fontaine S Lepanto L et al Radiating pain to the lower extremities caused by lumbar disk rupture without spinal nerve root involvement AJNR Am J Neuroradiol 161605-1613 1995 Abstract 50 Milette PC Melancon D A reappraisal of lumbar discography Can Assoc Radiol J 33176-182 1982 51 Milette PC Melancon D Dupuis PR et al A simplified terminology for abnormalities of the lumbar disk Can Assoc Radiol J 42319-325 1991 Abstract 52 Milette PC Raymond J Fontaine S Comparison of high-resolution computed tomography with discography in the evaluation of lumbar disc herniations Spine 15525-533 1990 Abstract 53 Mink JH Deutsch AL Goldstein TB et al Spinal imaging and intervention 1998 Phys Med Rehabil Clin North Am 9343-380 1998 54 Mixter WJ Barr JS Rupture of the intervertebral disc with involvement of the spinal canal N Engl J Med 211210-234 1934 55 Modic MT Masaryk TJ Ross JS et al Imaging of degenerative disk disease Radiology 168177-186 1988 Citation 56 Modic MT Ross JS Obuchowski NA et al Contrast-enhanced MR imaging in acute lumbar radiculopathy A pilot study of the natural history Radiology 195429-435 1995 Abstract 57 Modic MT Steinberg PM Ross JS et al Degenerative disk disease Assessment of changes in vertebral body marrow with MR imaging Radiology 166193-199 1988 58 Morvan G Mathieu P Les stenoses laterales In Morvan G Deburge A Bard H et al (eds) Le Rachis Lombaire Degeneratif Montpellier Sauramps Medical 1998 pp 315-324 59 Murray RO Skeletal trauma Regional In Sutton D (ed) Textbook of Radiology and Imaging ed 3 New York Churchill Livingstone 1980 pp 210-231 60 Nachemson A Lumbar disc herniation Conclusions Acta Orthop Scand 64(suppl 251)49 1993 Citation

61 Nathan H Osteophytes of the vertebral column An anatomical study of their development according to age race and sex with consideration as to their etiology and significance J Bone Joint Surg Am 44243-268 1962 62 Nygaard OP Mellgren SI Osterud B The inflammatory properties of contained and noncontained lumbar disc herniations Spine 222584-2488 1997 Abstract 63 Ohshima H Hirano N Osada R et al Morphologic variation of lumbar posterior longitudinal ligament and the modality of disc herniation Spine 182408-2411 1993 Abstract 64 Osti OL Fraser RD MRI and discography of annular tears and intervertebral disc degeneration A prospective clinical comparison J Bone Joint Surg Br 74431-435 1992 Abstract 65 Palmgren T Gronblad M Virri J et al Immunohistochemical demonstration of sensory and autonomic nerve terminals in herniated lumbar disc tissue Spine 211301-1306 1996 Abstract 66 Resnick D Niwayama G Degenerative disease of the spine In Resnick D (ed) Diagnosis of Bone and Joint Disorders ed 3 Philadelphia WB Saunders 1995 pp 1372-1462 67 Resnick D Niwayama G Intravertebral disk herniations Cartilaginous (Schmorls) nodes Radiology 12657-65 1978 Abstract 68 Ross JS Modic MT Masaryk TJ Tears of the anulus fibrosus Assessment with Gd-DTPA-enhanced MR imaging AJR Am J Roentgenol 154159-162 1990 Abstract 69 Saal JS The role of inflammation in lumbar pain Spine 201821-1827 1995 Abstract 70 Sachs BL Vanharanta H Spivey MA et al Dallas discogram description A new classification of CTdiscography in low-back disorders Spine 12287-294 1987 Abstract 71 Sauser DD Goldman AB Kaye JJ Discogenic vertebral sclerosis J Can Assoc Radiol 2944-50 1978 Abstract 72 Schellhas KP Pollei SR Gundry CR et al Lumbar disc high-intensity zone Correlation of magnetic resonance imaging and discography Spine 2179-86 1996 Abstract 73 Schellinger D Manz HJ Vidic B et al Disk fragment migration Radiology 175831-836 1990 Abstract 74 Schipper J Kardaun JW Braakman R et al Lumbar disk herniation Diagnosis with CT or myelography Radiology 165227-231 1987 Abstract 75 Schmorl G Junghanns H The Human Spine in Health and Disease ed 2 New York Grune and Stratton 1971 76 Silverman CS Lenchik L Shimkin PM et al The value of MR in differentiating subligamentous from supraligamentous lumbar disk herniations AJNR Am J Neuroradiol 16571-579 1995 Abstract 77 Simmons JW Emery SF McMillin JN et al Awake discography A comparison study with magnetic

resonance imaging Spine 16S216-221 1991 Abstract 78 Smyth MJ Wright V Sciatica and the intervertebral disc J Bone Joint Surg Am 401401-1418 1958 79 Taveras JM Radiologic aspects of low back pain and sciatic syndromes [editorial] AJNR Am J Neuroradiol 9351-358 1989 80 Tehranzadeh J Discography 2000 Radiol Clin North Am 36463-495 1998 Full Text 81 Thelander U Fagerlund M Friberg S et al Describing the size of lumbar disc herniations using computed tomography A comparison of different size index calculations and their relation to sciatica Spine 191979-1984 1994 Abstract 82 Thornbury JR Fryback DG Turski PA et al Disk-caused nerve compression in patients with acute low-back pain Diagnosis with MR CT myelography and plain CT Radiology 186731-738 1993 Abstract 83 Twomey L Taylor J Age changes in lumbar intervertebral discs Acta Orthop Scand 56496-499 1985 Abstract 84 Twomey LT Taylor JR Age changes in lumbar vertebrae and intervertebral discs Clin Orthop 22497-104 1987 85 Williams AL CT diagnosis of degenerative disc disease The bulging annulus Radiol Clin North Am 21289-300 1983 Abstract 86 Williams AL Haughton VM Meyer GA et al Computed tomographic appearance of the bulging annulus Radiology 142403-408 1982 Abstract 87 Williams AL Haughton VM Syvertsen A Computed tomography in the diagnosis of herniated nucleus pulposus Radiology 13595-99 1980 Abstract 88 Wiltse LL Berger PE McCulloch JA A system for reporting the size and location of lesions in the spine Spine 221534-1537 1997 Abstract 89 Wiltse LL Fonseca AS Amster J et al Relationship of the dura Hofmanns ligaments Batsons plexus and a fibrovascular membrane lying on the posterior surface of the vertebral bodies and attaching to the deep layer of the posterior longitudinal ligament An anatomical radiologic and clinical study Spine 181030-1043 1993 Abstract 90 Yamashita K Hiroshima K Kurata A Gadolinium-DTPA-enhanced magnetic resonance imaging of a sequestered lumbar intervertebral disc and its correlation with pathologic findings Spine 19479-482 1994 Abstract 91 Yu SW Haughton VM Sether LA et al Comparison of MR and diskography in detecting radial tears of the anulus A postmortem study AJNR Am J Neuroradiol 101077-1081 1989 Abstract 92 Yu SW Sether LA Ho PS et al Tears of the anulus fibrosus Correlation between MR and pathologic findings in cadavers AJNR Am J Neuroradiol 9367-370 1988 Abstract

93 Yussen PS Swartz JD The acute lumbar disc herniation Imaging diagnosis Semin Ultrasound CT MR 14389-398 1993 Abstract 94 Zucherman J Derby R Hsu K et al Normal magnetic resonance imaging with abnormal discography Spine 131355-1359 1988 Abstract

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  • CLASSIFICATION DIAGNOSTIC IMAGING AND IMAGING CHARACTERIZATION OF A LUMBAR HERNIATED DISK
    • IMAGING OF LOW BACK PAIN I
      • CLASSIFICATION DIAGNOSTIC IMAGING AND IMAGING CHARACTERIZATION OF A LUMBAR HERNIATED DISK
        • DEFINITION OF A DISK HERNIATION
        • CLASSIFICATION OF A HERNIATED LUMBAR DISK
          • Main Categories of Noninfectious Disk Abnormalities
          • Further Qualifying the Displaced Disk Material Beyond the Disk Space
            • DIAGNOSTIC IMAGING AND CHARACTERIZATION OF A HERNIATED LUMBAR DISK
              • Conventional Radiographs
              • Myelography
              • CT
              • CT Myelography
              • MR Imaging
              • Diskography and CT Diskography
                • SUMMARY
                  • References
Page 10: CLASSIFICATION, DIAGNOSTIC IMAGING, AND IMAGING ... · PDF fileclassification, diagnostic imaging, and imaging characterization of a lumbar herniated disk ... classification, diagnostic

As opposed to the previous model that can be applied only to the interpretation of CT and MR imaging studies this model can be used for the interpretation of all imaging modalities including plain films and diskograms[ ]47 [ ]51 It consists of five categories that are not mutually exclusive so that different combinations are possible (Fig 8) (Figure Not Available) The first three refer to the general state of the disk (1) normal young disk (2) normal aging disk and (3) deteriorated disk (formerly called the scarred disk) The last two refer to localized lesions anular tear and herniated disk In this model the previously discussed definition of disk herniation proposed by Herzog[ ]30 is applicable The use of this system requires an effort to distinguish the normal aging changes from those of pathologic degeneration Resnick and Niwayama[ ]66 have emphasized the differentiating features of two degenerative processes involving the intervertebral disk which had been previously described by Schmorl and Junghanns[ ]75 (1) spondylosis deformans which affects primarily the anulus fibrosus and bony ring epiphysis and (2) intervertebral osteochondrosis which affects essentially the nucleus pulposus and the vertebral body end plates

Figure 8 (Figure Not Available) Schematic representation of a nomenclature based on a three-dimensional assessment of the anatomic and pathologic characteristics of both disk and adjacent vertebral bodies The categories are not mutually exclusive and some combinations are possible A Categories related to the general aspect of the disk normal young disk (a) normal aging disk (b) deteriorated disk (c) B Categories related to local lesions normal young disk (a) anular tear (b) herniated disk (c) (Adapted from Milette PC The proper terminology for reporting lumbar intervertebral disk disorders AJNR Am J Neuroradiol 181859-1866 1997 with permission)

There is convincing evidence in the scientific literature that the features of spondylosis deformans represent the normal aging process whereas intervertebral osteochondrosis denotes true pathologic disk degeneration[ ]61 [ ]71 [ ]75 [ ]83 [ ]84 Schmorl and Junghanns[ ]75 found spondylotic changes in 60 of women and almost 80 of men over the age of 50 In a series of 400 dried skeletons Nathan[ ]61 found anterior vertebral body osteophytes which constitute the main feature of spondylosis deformans in 100 of individuals over age 40 whereas posterior osteophytes were found in only 39 of individuals even after the age of 80 Twomey and Taylor[ ]83 [ ]84 have found that loss of disk height is unusual in a normal aging population and that loss of stature in the elderly is attributable to loss of intervertebral body height rather than loss in disk height During the normal aging process the mucoid matrix of the nucleus pulposus is progressively replaced by fibrous tissue[ ]37 but the intervertebral height is preserved and the disk margins remain regular Dessication and thining of disks or disks that bulge like an underinflated automobile tire are not typical of elderly spines Slight symmetric bulging may occur if there has been vertebral body remodeling resulting from osteoporosis Small amounts of gas can be detected on plain films or CT images near the insertion of the anulus on the ring epiphysis and this gas is probably located in transverse anular tears adjacent to the ring epiphysis During the fourth decade anterior and lateral marginal vertebral body osteophytes constitute normal findings comparable with having gray hair but end plate erosions with osteosclerosis or chronic reactive bone marrow changes type 2 or 3 as described by Modic et al[ ]57 should not be seen Slight to moderate decrease in central signal intensity can be detected on T2-weighted MR images as part of the normal aging process but the changes should involve uniformly all lumbar disks

Deteriorated disks represent real pathologic degeneration which is sometimes referred to as chronic diskopathy On microscopic examination they show total structural disorganization and general replacement of normal disk material by scar tissue For this reason they were initially labeled scarred disks by the members of a joint committee on spinal nomenclature created by the Quebec Association of Radiologists[ ]14 Because of possible confusion with postoperative changes the term deteriorated disk has been proposed as an acceptable substitute Strictly speaking the term degeneration could be used to designate this entity but this latter term has such a broad nonspecific meaning that it is best avoided The deteriorated disk is characterized by narrowing of the intervertebral space irregular disk contour generally associated with symmetric or asymmetric bulging abundant presence of gas in the central portion of the intervertebral disk space multidirectional osteophytes that do not respect the central spinal canal or the foramina end plate erosions with reactive osteosclerosis and chronic bone marrow changes On T2-weighted MR images the central disk signal intensity is usually markedly decreased and the number of affected lumbar disks is variable Even though transverse concentric and radial anular tears have been identified on postmortem specimens[ ]92 the anular tear category in this model refers essentially to the radial tears that are generally demonstrated by diskography in symptomatic patients For a more precise description of those tears this model may be supplemented by the Dallas Discogram Description system[ ]70 with or without its recently proposed updates[ ]4 [ ]72 [ ]80

It should be emphasized that the pathoanatomic model is not based on direct identification of a particular geometric pattern but on the anatomy and pathology that are expected as a result of the analysis of specific criteria Using this model the conclusion of any imaging report does not consist of terms related to the shape of the disk contour or the displaced disk material but on a pathologic diagnosis that should be presented with an appropriate confidence level (possible probable or definite) The diagnosis of a probable major radial anular tear may be inferred from the presence of a definite central signal intensity loss because as a result of diskographic MR imaging correlations the positive predictive value of this sign has been estimated at 96[ ]48 The use of this model requires an effort to understand the criteria allowing differentiation of normal aging from true pathologic degeneration so this system is slightly more complicated than the morphologic model Its reliability has never been tested Some intraobserver or interobserver disagreement would probably occur trying to distinguish anular tears without herniation from anular tears with small herniations With respect to correspondance to clinical situations this scheme like the morphologic model has limited interest it has been shown that disks demonstrating the features of the deteriorated disk are likely to be responsible for symptoms but this relationship has been statistically established to be significant only for the L4-L5 disk[ ]24

Which Model Should Be Used

In other areas of diagnostic radiology the aim of image analysis is always to predict what the pathologist would find if he or she could be provided with an adequate specimen immediately following the imaging study radiologic diagnoses are presented with a pathologic perspective There is no reason why the reporting of disk disorders should be

any different Terms like bulging disk are meaningless to a pathologist and I personally favor the pathoanatomic model Nomenclature standardization however is not a task that can be achieved by an individual or even a single group of authors[ ]12 To have any impact recommendations have to emanate from well established national or international societies The multiplicity of scientific societies with an interest in the spine all over the world creates a special problem but new joint committees have recently been set up combining efforts to come up with a practical unified system that it is hoped could be proposed jointly by the North American Spine Society the American Academy of Orthopedic Surgeons the American Academy of Neurological Surgeons the American Society of Spine Radiology and the American Society of Neuroradiology Agreeing in North America on a classification of disk disorders that could gain universal acceptance like the TNM classification of neoplastic diseases would be a major achievement Meanwhile the choice of the nomenclature is up to the best judgement of each practicing radiologist and the essential issue in a given hospital or community practice remains clear communication between radiologists and referring physicians by way of a local agreement as to the meaning of words

A major problem frequently occurs because observers of imaging studies try to combine elements of the morphologic classification with those of the pathoanatomic classification Trying to differentiate a bulging disk (morphologic qualifier) from a disk herniation (pathologic diagnosis) cannot work because a bulging disk aspect is a common feature of the aging disk the deteriorated disk and some posterior central disk herniations (Fig 9) Trying to make the distinction is doomed to failure because it defies formal logic On the other hand it is theoretically possible to differentiate a radial anular tear (without herniation) from a disk herniation because these are two different pathologic entities although one may be the continuum of the other It is best to adopt either one of the two systems and avoid trying to straddle the two A general classification of disk disorders attempting to conciliate the morphologic and the pathoanatomic model is proposed in Table 1

Figure 9 A bulging disk aspect often conceals a posterior central herniation A Complete rupture of the outer anular fibers allowing nuclear material to escape and peel off the posterior longitudinal ligament (and sometimes a few intact peripheral anular fibers) from the torn disk creating a detectable focal or asymmetric extension of the disk margin beyond the interspace which qualifies as a protrusion B With more gelatinous nuclear material escaping underneath the rigid posterior longitudinal ligament the focal bulge is no longer detectable as its radius increases and if the tear occurs in the posterior midline or para-medial direction the aspect mimics symmetric disk extension beyond the interspace C Since in most cases only the outline of a diffusely hypointense disk is perceived on MR images this creates the illusion of circumferential disk bulging on axial sections D The real nature of a bulging disk of this type may be suspected by scrutinizing the sagittal sections and appreciating that unless one is dealing with a chronically degenerated scarred disk the bulge is not symmetric but limited to the posterior aspect of the disk

TABLE 1 -- GENERAL

CLASSIFICATION OF DISK LESIONS Normal (excluding aging changes)

Congenitaldevelopmental variants

Inflammationinfection

Neoplasia

Degenerativetraumatic

Degeneration

Anular tear

Herniation Protrusion

Extrusion

Degeneration Spondylosis deformans

Intervertebral osteochondrosis

Further Qualifying the Displaced Disk Material Beyond the Disk Space

Regardless of the basic system that is used the type of herniation should be assessed The volume and location of the displaced disk material beyond the normal peripheral margin of the intervertebral space also need to be specified In certain cases it is also possible to determine the composition of this material For the sake of simplicity the term herniation is used consistently in the remainder of this article to refer to all displaced disk material but what is discussed can also be applied to protrusions and extrusions if one wants to use the morphologic nomenclature

Type of Herniation

Upward or downward migration of nuclear material may occur through a break in a vertebral body end plate creating an intravertebral herniation sometimes referred to as an intraspongy herniation or a Schmorls node[ ]67 (Fig 10) Although a herniation occurring in any horizontal direction is likely to cause symptoms because of the presence of pain-sensitive nerve endings in the outer anulus[ ]7 [ ]8 [ ]65 herniations occurring in a posterior or posterolateral direction deserve special consideration because of the added possibility of dural sac or individual nerve root compression

Figure 10 Various types of intravertebral herniations (Schmorls nodes) A Intravertebral herniation through the inferior end plate of the L3 vertebral body demonstrated by diskography in a 35-year-old man suffering from chronic low back pain The patients typical pain was reproduced during injection and the lesion was considered responsible for the patients symptoms B T2-weighted sagittal section demonstrating an intravertebral herniation through the inferior end plate of the L4 vertebral body in a 24-year-old woman presenting with chronic low back pain The high signal intensity of the lesion associated with the loss of normal central signal intensity of the parent disk suggests that the lesion is a bona fide acquired intraspongy herniation and not just a developmental defect C T2-weighted sagittal section demonstrating an intravertebral herniation through the inferior end plate of the L3 vertebral body (arrow) Because both the herniation and the parent disk show normal signal intensity the abnormality was

considered a probably asymptomatic developmental defect

Other characteristics of disk herniations have become relevant with the development of new therapeutic possibilities (eg chemonucleolysis and percutaneous diskectomy) The term sequestration is confusing and has often been used to indicate displacement of disk material away from the parent disk The term sequestered disk should be used restrictedly to designate a fragment of diskal tissue that has migrated from the disk space and has no connection by diskal tissue to the disk of origin[ ]20 [ ]21 [ ]42 Sequestration refers to loss of continuity with disk tissue still present in the intervertebral disk space The term migration has a broader meaning indicating displacement of disk material away from the edge of the rent in the outer anulus either in the central spinal canal at the disk level or above or below the disk level This difference is illustrated in Figure 11 The terms communicating and noncommunicating derive from a different perspective and are mostly used in the context of intradiskal therapeutic injections They refer to the interruption of the periphery of the disk allowing fluid injected into the disk to leak into the spinal canal and reach displaced disk material[ ]20 [ ]51 The terms contained and uncontained are unfamiliar to most radiologists in a contained herniation the displaced disk material is still covered by a few intact but distended outer anular fibers or by a capsule formed by outer anular fibers and the adherent posterior longitudinal ligament

Figure 11 Various types of posterior central herniations A Small subligamentous herniation (protrusion) without significant disk material migration B Subligamentous herniation with downward migration of disk material under the PLLC C Sub-ligamentous herniation with downward migration of disk material and sequestered fragment (arrow)

The terms subligamentous and extraligamentous (or transligamentous) refer to the position of the displaced disk material with respect to the posterior longitudinal ligament The anatomy of the posterior longitudinal ligament has been recently revised[ ]73 [ ]89 It is a membranous structure that has multiple components a deep layer attached to disks and vertebral bodies a superficial layer attached to the dura by fibrous tissue (Hoffmanns

ligament) and lateral extensions known as the lateral membranes or peridural membranes (Fig 12) (Figure Not Available) It should probably be referred to as the posterior longitudinal ligament complex (PLLC) It actually divides the epidural space into the perithecal space and the anterior epidural space where displaced disk material can be entrapped (Fig 13) A potential space allowing accumulation of displaced disk material has also been detected between the outer anular fibers and the deep fibers of the PLLC on the posterior central aspect of the disk[ ]63 Posterior midline herniations seldom rupture the PLLC and are generally subligamentous The lateral membranes are less resistant and transligamentous herniations are usually the result of posterior off-center herniations or posterolateral herniations

Figure 12 (Figure Not Available) The PLLC is portrayed here in relation to various types of subligamentous disk displacement At the disk level posteriorly displaced disk material frequently occupies the midline Below and above the disk an anterior epidural space (AES) exists between the PLLC and the posterior aspect of the vertebral bodies In this space disk fragment motion across the midline is curtailed by a sagittal midline septum (dashed line) A delicate translucent membrane (shown only on left side of drawing) is stretched between the free edge of the deep layer of the posterior longitudinal ligament and the lateral spinal canal (From Schellinger D Manz HJ Vidic B et al Disk fragment migration Radiology 175831-836 1990 with permission)

Figure 13 Relationship of typical posterior disk herniations with the PLLC A Midline sagittal section unless very large a posterior midline herniation usually remains entrapped underneath the deep layer of the PLL C and sometimes a few intact outer anulus fibers joining with the PLL C to form a capsule The deep layer of the PLL C (arrow) also attaches to the posterior aspect of the vertebral body so that no potential space is present underneath B Sagittal para-central section the PLL C extends laterally at the disk level (arrowhead) but above and below the disk an anterior epidural space (as) where disk fragments are frequently entrapped is present between the lateral (peridural) membranes and the posterior aspect of the vertebral bodies

Volume of Herniated Material

Quantifying the herniated disk material by measuring in millimeters its greatest diameter or by evaluating its cross-sectional area in square millimeters is rarely done The resulting figures could be misleading without relating this measurement to the size of the spinal canal and the exact location of the lesion[ ]88 A purely qualitative and subjective statement that a mild moderate or severe herniation is present however does not give the person reading the imaging report any indication as to the potential of the lesion to cause significant compression of the dural sac or individual exiting nerve roots A reasonably precise scheme has been proposed in 1995 by the Nomenclature Committee of the North American Spine Society[ ]20 Measurements are taken from an axial CT or MR imaging section at the site of most severe compromise canal compromise of less than 25 at that section is qualified as mild 25 to 75 is moderate 76 to 90 is moderately severe and greater than 90 is severe It is understood that such characterizations describe only the cross-sectional area at one level and do not account for the total volume of displaced material displacement of neural tissue or clinical significance The usefulness of having four categories is questionable and can likely generate poor interobserver or intraobserver agreement especially in situations where the central spinal canal is relatively narrow Bonnevilles scheme[ ]9 [ ]10 [ ]11 should generate greater reliability (Fig 14) (Figure Not Available) Separation of the cross-sectional area in three thirds can be applied to both the central spinal canal and the foramina It can be agreed by way of convention that the terms mild moderate and severe lumen compromise by a disk herniation designate extension of the displaced disk material in the anterior middle or posterior third of the central canal or foramen depending on the specified location of the herniation

Figure 14 (Figure Not Available) The size of the herniation in the horizontal plane is assessed and designated by the numbers 1 2 or 3 by establishing its extension in the anterior middle or posterior third of the spinal canal (From Bonneville JF Plaidoyer pour une classification par limage des hernies discales lombaires la carte-image Rev Imag Med 2557-560 1990 with permission)

Location of Herniated Material

Bonneville[ ]9 [ ]10 [ ]11 has also proposed an interesting and simple alpha-numerical system to classify according to their location the position of disk fragments that have migrated in the horizontal or sagittal plane (Figs 15 (Figure Not Available) and 16) (Figure Not Available) Using more precise anatomic boundaries unfortunately more familiar to surgeons than radiologists Wiltse et al[ ]88 have proposed another system which has been supported by the North American Spine Society[ ]20 [ ]21 Anatomic zones and levels are defined using the following anatomic landmarks medial edge of the articular facets medial lateral upper and lower border of the pedicles and coronal plane at the disk center On the horizontal plane (Fig 17) (Figure Not Available) these landmarks determine the bounderies of the central zone the subarticular zone the foraminal zone the extraforaminal zone and the anterior zone (anterior to the coronal plane at the center of the disk) In the sagittal plane they determine the boundaries of the diskal level the infrapedicular level the pedicular level and the suprapedicular level (Figs 18 (Figure

Not Available) and 19) (Figure Not Available) Radiologists interpreting axial CT or MR images may find it difficult to use the medial edge of the facets as the landmark that separates the central zone from the subarticular zone because the superior articular facets are generally not included in axial sections at the disk level The alternative is to use the expression posterolateral to designate collectively all posterior herniations that are not midline but do not extend into a foramen as was proposed by Bonneville[ ]9 [ ]10 [ ]11

Figure 15 (Figure Not Available) In the horizontal plane herniations are labeled midline (a) posterolateral (b) foraminal (c) and extra-foraminal (d) (From Bonneville JF Plaidoyer pour une classification par limage des hernies discales lombaires la carte-image Rev Imag Med 2557-560 1990 with permission)

Figure 16 (Figure Not Available) In the craniocaudal direction disk migration is labeled +1 +2 +3 or -1 -2 -3 by referring to the height of a vertebral body divided in thirds (From Bonneville JF Plaidoyer pour une classification par limage des hernies discales lombaires la carte-image Rev Imag Med 2557-560 1990 with permission)

Figure 17 (Figure Not Available) The anatomic zones identified on axial images The anterior zone (not shown) is delineated from the extraforaminal zone by an imaginary coronal line in the center of the vertebral body (From Wiltse LL Berger PE McCulloch JA A system for reporting the size and location of lesions in the spine Spine 221534-1537 1997 with permission)

Figure 18 (Figure Not Available) The anatomical levels identified on craniocaudal images (From Wiltse LL Berger PE McCulloch AJ A system for reporting the size and location of lesions in the spine Spine 221534-1537 1997 with permission)

Figure 19 (Figure Not Available) Coronal view of the main zones and levels (From Wiltse LL Berger PE McCulloch JA A system for reporting the size and location of lesions in the spine Spine 221534-1537 1997 with permission)

Composition of Herniated Material

Displaced disk material may consist of glycosaminoglycans type 1 or 2 collagen end plate cartilage and bone fragments avulsed from the ring epiphysis A reactive inflammatory reaction usually results in edematous tissue followed by granulation tissue which may undergo calcification (Fig 20) Necrotic and partially resorbed displaced disk material sometimes produces a large fluid-filled pouch distinguishable from the common high-intensity zone because of its size (Fig 21) or a gas-filled cavity generally in continuity with gas in the intervertebral space (Fig 22) [ ]42 These characteristics may be meaningful if intradiskal injection therapy is considered In imaging reports herniations exhibiting calcium deposits and those exhibiting replacement of disk material by gas or a relatively large fluid collection can be qualified as chronic herniations

Figure 20 A CT scan demonstration of a small posterior central L4-L5 calcified subligamentous herniation The resistant deep layer of the PLLC restrains displacement of the disk material in the posterior central direction and does not allow a detectable distortion of the disk contour In this particular case the presence of the calcification is actually the only evidence that a posterior midline anular tear and a small subligamentous herniation are present B Posterior right central and sub-articular L5-S1 calcified disk herniation in same patient Posterolateral herniations are generally more conspicuous than posterior midline herniations because the deep layer of the PLLC gets thinner away from the midline

Figure 21 Posterior central midline L4-L5 herniation in a 52-year-old man demonstrated on a T2-weighted midline MR sagittal section There is intervertebral space narrowing with loss of normal central disk signal

intensity while the herniated disk material demonstrates high signal intensity consistent with a predominantly fluid consistency

Figure 22 CT scan demonstration in a 51-year-old woman of a left posterolateral L5-S1 disk hernation consisting essentially in a gas-filled pouch (white arrow) Gas is also present in the central portion of the intervertebral disk space (black arrow)

DIAGNOSTIC IMAGING AND CHARACTERIZATION OF A HERNIATED LUMBAR DISK

Assessing the validity of the currently used imaging procedures to diagnose a herniated lumbar disk is not an easy endeavor The validity of a measurement is the extent to which it corresponds to the true biologic value or some accepted gold standard[ ]40 With the exception of postmortem studies evaluation of the pathoanatomy by the surgeon in the operating room has always been considered the gold standard but this does not constitute an ideal situation Inspection of the disk through a small laminectomy incision to determine for instance if nuclear fragments lie within or outside the anular fibers may not be very reliable Also unbiased intraoperative determination of a normal degenerated or herniated disk in a patient with sciatica may also be difficult[ ]86 Because the validity of diskography has been previously established by postmortem studies and surgical correlations[ ]48 it is sometimes used as a gold standard in situations where no surgery has been performed

Conventional Radiographs

Lumbar disk herniations can exceptionally be diagnosed directly on good quality lateral projections because the x-ray attenuation is slightly greater in displaced disk material than in epidural fat Occasionally a calcified rim outlines the displaced disk fragment

(Fig 23) In most situations however narrowing of an intervertebral disk space in the absence of other evidence of chronic diskopathy is the only detectable sign suggesting the presence of a disk herniation To my knowledge the sensitivity and specificity of this sign has never been assessed The accepted rule of thumb is that the height of a given lumbar intervertebral disk space should always be slightly greater than the height of the above located interspace This rule does not apply to the transition disk immediately above the sacrum (usually L5-S1) The specificity of this sign is probably quite high but a few false-positives are seen especially at the L4-L5 level because of minor congenital hypoplasia The presence of posterior or foraminal vertebral body osteophytes associated or not with disk space narrowing is a definite sign of a chronic disk herniation

Figure 23 A Chronic left L3-L4 extraforaminal disk hernation in a 54-year-old man suspected on an AP radiograph demonstrating a calcified shell on the left side of the intervertebral disk space (white arrow) B Axial CT scan section confirming the diagnosis of a chronic extraforaminal L3-L4 herniation

Myelography

Myelography is essentially an exploration of the subarachnoid space Disk herniations are demonstrated only indirectly because they can cause thecal sac deformity and individual nerve root sleeve filling defects (Fig 24) Of all the special imaging procedures

myelography is the only one that allows upright projections with full weight bearing It is not unusual to demonstrate in this way small posterior central or posterolateral herniations that are undetectable on CT sections Interestingly the overall sensitivity of myelography to detect disk herniations has been found to be higher than that of CT whereas its specificity has been found to be lower[ ]74 In comparison with standard CT examination which usually includes only the three or four lower lumbar disks myelography easily allows coverage of the entire lumbar area and assessment of the intrathecal structures (cauda equina and conus medullaris) Far lateral foraminal herniations extraforaminal herniations and anterior herniations however are not detected The sensitivity for detection of posterior central L5-S1 herniations is also relatively poor because of the greater distance between the thecal sac and the posterior aspect of this particular disk

Figure 24 L5-S1 disk herniation in a 25-year-old man detected by indirect signs using lumbosacral myelography A Upright oblique projections showing a filling defect of the left S1 root sleeve (white arrow) suggesting significant nerve root compression by a left posterolateral disk hernation The right S1 root sleeve fills normally with contrast (black arrow) B Subtle compression of the anterior wall of the dural sac by displaced disk material (small arrows) demonstrated on upright lateral projection This sign is usually absent in the presence of a large amount of fat and venous structures in the anterior epidural compartment

CT

The sensitivity of CT to diagnose a herniation of the nucleus pulposus at the L5-S1 interspace is greater than that of myelography if images in the exact plane of the disk can be obtained[ ]23 [ ]39 Otherwise the superiority of plain CT over myelography to demonstrate disk herniations has not been established but CT has the distinct advantage of being

noninvasive and provides direct anatomic information[ ]23 Large herniations are easily detected but as explained previously the distinction between protrusions and extrusions is often difficult without sagittal reconstructions CT essentially allows an assessment of the contour of the disk The diagnosis of very small herniations in the absence of direct or indirect evidence of a radial tear is hazardous and associated with a high percentage of false-positives and false-negatives[ ]52 The diagnosis of moderate and large size herniations in different directions is usually possible but anterior herniations are rarely diagnosed not because they are not detectable but because observers pay little attention to the anterior contour of the disk (Fig 25) Because the PLLC cannot usually be identified the distinction of subligamentous from transligamentous herniation can only be suggested in most cases by the size of the herniated material A definite diagnosis of sequestration is rarely possible Calcifications within the displaced material are readily seen but may be difficult at times to differentiate from an accompanying osteophyte or an avulsed bone fragment from the vertebral body ring epiphysis (Fig 26) The presence of gas in the herniated material is easily detected

Figure 25 Anterior L4-L5 herniation demonstrated by CT scan in a 51-year-old woman with chronic low back pain Although sometimes quite conspicuous such herniations are rarely reported because observers pay little attention to the anterior contour of the disk

Figure 26 CT scan demonstration of a posterior right central L4-L5 disk herniation in a 38-year-old woman with avulsion of a bone fragment from the ring epiphysis and adjacent part of the superior L5 end plate Reactive osteosclerosis is seen around the vertebral body defect (arrows) suggesting a chronic lesion

CT Myelography

This association combines the advantages of both imaging modalities The fact that its accuracy has been reported as being less[ ]22 [ ]32 higher[ ]1 [ ]6 or equivalent[ ]82 to MR imaging is a reflection of the differences in technologic advancement and pathologic nomenclature that hamper valid comparisons between different studies

MR Imaging

Most reported studies establish MR imaging as the first choice modality to diagnose a herniated lumbar disk[ ]5 [ ]22 [ ]32 [ ]46 The associated intravenous injection of a paramagnetic agent has been found useful to demonstrate some anatomic features of disk disease in patients with no previous lumbar disk surgery[ ]56 [ ]68 [ ]90 MR imaging provides a better assessment of disk morphology than CT or CT myelography because sagittal sections are routinely obtained Assessment of foraminal involvement by displaced disk material is more accurate (Fig 27) and anterior disk herniations can be detected more easily than with CT or CT myelography If one is looking specifically for herniated lumbar disks associated with nerve root compression however it has been demonstrated that CT is equally accurate[ ]82 Alterations of the central or peripheral disk signal intensity on T2-weighted images are seen in most disks afflicted with an anular tear[ ]48 and alert the observer to scrutinize the disk contour in search for local modifications indicative of a herniation Because the signal of the displaced disk material is usually very similar to that of the outer anulus PLLC and vertebral body cortical bone small herniations are generally more conspicuous on axial CT sections than on corresponding axial MR imaging sections Gas and calcium deposits within the displaced fragment cannot usually

be detected but associated vertebral body bone marrow changes are typically seen and are helpful in differentiating acute from chronic processes[ ]57 The occasional presence of a high-intensity zone in the herniated material with an occasionally enhancing border after contrast injection is probably caused by a mixture of displaced nuclear material acute and subacute inflammatory tissue and neovascularized reactive tissue[ ]4 [ ]48 [ ]72 Contradictory reports have been published regarding the accuracy of MR imaging to differentiate subligamentous from transligamentous herniations[ ]26 [ ]38 [ ]73 [ ]76 Understanding the anatomy of the PLLC is helpful to make the distinction (Fig 28) (Figure Not Available) Masaryk et al[ ]46 have suggested that MR imaging is accurate to distinguish sequestered disks from other forms of lumbar disk herniations but most observers find this distinction difficult to establish[ ]42

Figure 27 A Left L4-L5 foraminal herniation well seen on an intermediate-weighted left parasagittal MR section (arrow) in a 47-year-old man B The lesion is much less obvious on intermediate-weighted (left) and T2-weighted (right) axial sections and was in fact more conspicuous on the corresponding CT scan section

Figure 28 (Figure Not Available) A Subligamentous disk herniation Left T1-weighted image demonstrating displaced disk material with a smooth outline imposed by the demarcation of the anterior epidural space (AES) by the lateral membrane of the PLLC Right Correlative drawing B Transligamentous disk herniation Left T1-weighted image of a large disk herniation (cervical in this case) which has ruptured through the posterior confines of the AES Penetration of the right lateral membrane can be observed (arrow) and the disk fragment contour is serrated Right Correlative drawing (From Schellinger D Manz HJ Vidic B et al Disk fragment migration Radiology 175831-836 1990 with permission)

Diskography and CT Diskography

During 30 years (1950 to 1980) when myelography was the only available imaging technique to demonstrate lumbar disk herniations diskography was an invasive but efficient way to demonstrate posterior central L5-S1 herniations and other large herniations (other than posterior central and paramedial) that could not be detected by myelography[ ]50 These herniations are now usually well demonstrated by CT and MR imaging Comparing the accuracy of five imaging modalities (excluding MR imaging) for the diagnosis of lumbar disk herniation Jackson et al[ ]31 found that CT diskography (Fig 29) was the most accurate test (87) compared with 77 for CT myelography 74 for CT 70 for myelography 64 for pain reproduction during diskography and 58 for diskography without CT Disk injection reproduced the patients clinical pain pattern in only 36 of herniated disks This clinical test isolated from the images had high specificity (89) but low sensitivity (43) for the diagnosis of disk herniation The reported low sensitivity of diskography images (unassociated with CT) to diagnose disk herniation is to be expected the purpose of the intradiskal injection being primarily the demonstration of an anular tear the contrast leaking through the tear only occasionally delineates an extruded fragment When a disk herniation has been diagnosed by other imaging modalities diskography allows to determine if the herniation is contained or noncontained (Figs 30 and 31) this information may have clinical relevance[ ]62 It also allows to establish if the displaced disk material is communicating or not with the parent disk and establishes the likelihood that it is sequestered or not There always remains a possibility that the contrast injected under pressure may reach a disk fragment that is nevertheless sequestered by leaking through the associated anular tear CT diskography also allows assessment in most cases of the integrity of the PLLC[ ]89 The superior sensitivity of diskography over MR imaging to demonstrate anular tears has been well established[ ]27 [ ]44 [ ]48 [ ]64 [ ]77 [ ]91 [ ]94 The presence of a radial tear and the inflammatory reaction it creates may be symptomatic despite the absence of true disk herniation[ ]29 [ ]48 [ ]49 [ ]69

Figure 29 L4-L5 CT diskogram demonstrating a large left posterolateral radial anular tear associated with

a left foraminal and extraforaminal herniaton (same patient as in Figure 28) (Figure Not Available)

Figure 30 Contained posterior L4-L5 and L5-S1 disk herniations in a 57-year-old man demonstrated by diskography The L3-L4 disk is normal

Figure 31 Noncontained L4-L5 disk herniation in a 23-year-old woman Reflux of injected contrast is seen in the anterior epidural space above and below the disk space The L5-S1 disk also demonstrates incomplete anterior and posterior radial anular tears

SUMMARY

The absence of universal nomenclature standardization with respect to the definition of a disk herniation and its different categories especially regarding type and location is still a major problem that will only be overcome when major national or international scientific societies join efforts to support a particular scheme Meanwhile it is important to realize that the two models that are currently most used are based on a different perspective Trying to straddle the two by opposing for instance bulging disk and herniation is doomed to failure because this exercise defies formal logic MR imaging is currently the most accurate noninvasive imaging modality to diagnose a disk herniation and to determine its exact location The determination of some pathoanatomic characteristics of herniated disks (type and composition) may require the use of CT diskography or CT diskography

References

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13 Brant-Zawadzki MN Jensen MC Obuchowski N et al Interobserver and intraobserver variability in interpretation of lumbar disc abnormalities A comparison of two nomenclatures Spine 201257-1263 1995 Abstract 14 Breton G Is that a bulging disk a small herniation or a moderate protrusion [editorial] Can Assoc Radiol J 42318 1991 Citation 15 Czervionke LF Lumbar intervertebral disc disease Neuroimaging Clin North Am 3465-485 1993 16 Deyo RA Nonsurgical care of low back pain Neurosurg Clin North Am 2851-862 1991 17 Deyo RA Loeser JD Bigos SJ Herniated lumbar intervertebral disk Ann Intern Med 112598-603 1990 Abstract 18 Dorlands Illustrated Medical Dictionary ed 28 Philadelphia WB Saunders 1994 19 Fardon D Pinkerton S Balderston R et al Terms used for diagnosis by English speaking spine surgeons Spine 18274-277 1993 Citation 20 Fardon DF Herzog RJ Mink JH et al Nomenclature of Lumbar Disc Disorders Contemporary Concepts in Spine Care Rosemont IL North American Spine Society 1995 21 Fardon DF Herzog RJ Mink JH et al Nomenclature of lumbar disc disorders In Garfin S Vaccaro A (eds) Orthopedic Knowledge Update Spine Rosemont IL American Academy of Orthopedic Surgeons 1997 pp A3-A14 22 Forristall RM Marsh HO Pay NT Magnetic resonance imaging and contrast CT of the lumbar spine Comparison of diagnostic methods and correlation with surgical findings Spine 131049-1054 1988 Abstract 23 Fries JW Abodeely DA Vijungco JG et al Computed tomography of herniated and extruded nucleus pulposus J Comput Assist Tomogr 6874-887 1982 Abstract 24 Frymoyer JW Newberg A Pope MH et al Spine radiographs in patients with low-back pain An epidemiological study in men J Bone Joint Surg Am 661048-1055 1984 Abstract 25 Gospodarowicz M Benedet L Hutter RV et al History and international developments in cancer staging Cancer Prev Control 2262-268 1998 Abstract 26 Grenier N Greselle JF Vital JM et al Normal and disrupted lumbar longitudinal ligaments Correlative MR and anatomic study Radiology 171197-205 1989 Abstract 27 Gunzburg R Parkinson R Moore R et al A cadaveric study comparing discography magnetic resonance imaging histology and mechanical behavior of the human lumbar disc Spine 17417-426 1992 Abstract 28 Haughton VM Eldevik OP Magnaes B et al A prospective comparison of computed tomography and myelography in the diagnosis of herniated lumbar disks Radiology 142103-110 1982 Abstract

29 Haughton VM Lim TH An H Intervertebral disk appearance correlated with stiffness of lumbar spinal motion segments AJNR Am J Neuroradiol 201161-1165 1999 Abstract 30 Herzog RJ The radiologic assessment for a lumbar disc herniation Spine 2119S-38S 1996 Abstract 31 Jackson RP Becker GJ Jacobs RR et al The neuroradiographic diagnosis of lumbar herniated nucleus pulposus I A comparison of computed tomography (CT) myelography CT-myelography discography and CT-discography Spine 141356-1361 1989 Abstract 32 Jackson RP Cain JE Jr Jacobs RR et al The neuroradiographic diagnosis of lumbar herniated nucleus pulposus II A comparison of computed tomography (CT) myelography CT-myelography and magnetic resonance imaging Spine 141362-1367 1989 Abstract 33 Jarvik JG Haynor DR Koepsell TD et al Interreader reliability for a new classification of lumbar disk disease Acad Radiol 3537-544 1996 Abstract 34 Jensen MC Brant-Zawadzki MN Obuchowski N et al Magnetic resonance imaging of the lumbar spine in people without back pain N Engl J Med 33169-73 1994 Abstract 35 Kent DL Haynor DR Larson EB et al Diagnosis of lumbar spinal stenosis in adults A meta-analysis of the accuracy of CT MR and myelography AJR Am J Roentgenol 1581135-1144 1992 Abstract 36 Kieffer SA Sherry RG Wellenstein DE et al Bulging lumbar intervertebral disk Myelographic differentiation from herniated disk with nerve root compression AJR Am J Roentgenol 138709-716 1982 Abstract 37 Kieffer SA Stadlan EM Mohandas A et al Discographic-anatomical correlation of developmental changes with age in the intervertebral disc Acta Radiol 9733-739 1969 38 Kim KY Kim YT Lee CS et al MRI classification of lumbar herniated intervertebral disc Orthopedics 15493-497 1992 Abstract 39 Kornberg M Rechtine GR Dupuy TE Computed tomography in the diagnosis of a herniated disk at the L5-S1 level Spine 9433-436 1984 Abstract 40 Kramer MS Clinical Epidemiology and Biostatistics New York Springer-Verlag 1988 41 Landis JR Koch GG The measurement of observer agreement agreement for categorical data Biometrics 33159-174 1977 Abstract 42 Laredo JD Bossard P Vuillemin-Bodaghi Formes anatomo-radiologiques des hernies discales In Morvan G Deburge A Bard H et al (eds) Le Rachis Lombaire Degeneratif Montpellier Sauramps Medical 1998 pp 37-49 43 Lee SH Coleman PE Hahn FJ Magnetic resonance imaging of degenerative disk disease of the spine Radiol Clin North Am 26949-964 1988 Abstract 44 Linson MA Crowe CH Comparison of magnetic resonance imaging and lumbar discography in the diagnosis of disc degeneration Clin Orthop 160-163 1990

45 Marchand F Ahmed AM Investigation of the laminate structure of lumbar disc anulus fibrosus Spine 15402-410 1990 Abstract 46 Masaryk TJ Ross JS Modic MT et al High-resolution MR imaging of sequestered lumbar intervertebral disks AJR Am J Roentgenol 1501155-1162 1988 Abstract 47 Milette PC The proper terminology for reporting lumbar intervertebral disk disorders AJNR Am J Neuroradiol 181859-1866 1997 Citation 48 Milette PC Fontaine S Lepanto L et al Differentiating lumbar disc protrusions disk bulges and discs with normal contour but abnormal signal intensity Magnetic resonance imaging with discographic correlations Spine 2444-53 1999 Abstract 49 Milette PC Fontaine S Lepanto L et al Radiating pain to the lower extremities caused by lumbar disk rupture without spinal nerve root involvement AJNR Am J Neuroradiol 161605-1613 1995 Abstract 50 Milette PC Melancon D A reappraisal of lumbar discography Can Assoc Radiol J 33176-182 1982 51 Milette PC Melancon D Dupuis PR et al A simplified terminology for abnormalities of the lumbar disk Can Assoc Radiol J 42319-325 1991 Abstract 52 Milette PC Raymond J Fontaine S Comparison of high-resolution computed tomography with discography in the evaluation of lumbar disc herniations Spine 15525-533 1990 Abstract 53 Mink JH Deutsch AL Goldstein TB et al Spinal imaging and intervention 1998 Phys Med Rehabil Clin North Am 9343-380 1998 54 Mixter WJ Barr JS Rupture of the intervertebral disc with involvement of the spinal canal N Engl J Med 211210-234 1934 55 Modic MT Masaryk TJ Ross JS et al Imaging of degenerative disk disease Radiology 168177-186 1988 Citation 56 Modic MT Ross JS Obuchowski NA et al Contrast-enhanced MR imaging in acute lumbar radiculopathy A pilot study of the natural history Radiology 195429-435 1995 Abstract 57 Modic MT Steinberg PM Ross JS et al Degenerative disk disease Assessment of changes in vertebral body marrow with MR imaging Radiology 166193-199 1988 58 Morvan G Mathieu P Les stenoses laterales In Morvan G Deburge A Bard H et al (eds) Le Rachis Lombaire Degeneratif Montpellier Sauramps Medical 1998 pp 315-324 59 Murray RO Skeletal trauma Regional In Sutton D (ed) Textbook of Radiology and Imaging ed 3 New York Churchill Livingstone 1980 pp 210-231 60 Nachemson A Lumbar disc herniation Conclusions Acta Orthop Scand 64(suppl 251)49 1993 Citation

61 Nathan H Osteophytes of the vertebral column An anatomical study of their development according to age race and sex with consideration as to their etiology and significance J Bone Joint Surg Am 44243-268 1962 62 Nygaard OP Mellgren SI Osterud B The inflammatory properties of contained and noncontained lumbar disc herniations Spine 222584-2488 1997 Abstract 63 Ohshima H Hirano N Osada R et al Morphologic variation of lumbar posterior longitudinal ligament and the modality of disc herniation Spine 182408-2411 1993 Abstract 64 Osti OL Fraser RD MRI and discography of annular tears and intervertebral disc degeneration A prospective clinical comparison J Bone Joint Surg Br 74431-435 1992 Abstract 65 Palmgren T Gronblad M Virri J et al Immunohistochemical demonstration of sensory and autonomic nerve terminals in herniated lumbar disc tissue Spine 211301-1306 1996 Abstract 66 Resnick D Niwayama G Degenerative disease of the spine In Resnick D (ed) Diagnosis of Bone and Joint Disorders ed 3 Philadelphia WB Saunders 1995 pp 1372-1462 67 Resnick D Niwayama G Intravertebral disk herniations Cartilaginous (Schmorls) nodes Radiology 12657-65 1978 Abstract 68 Ross JS Modic MT Masaryk TJ Tears of the anulus fibrosus Assessment with Gd-DTPA-enhanced MR imaging AJR Am J Roentgenol 154159-162 1990 Abstract 69 Saal JS The role of inflammation in lumbar pain Spine 201821-1827 1995 Abstract 70 Sachs BL Vanharanta H Spivey MA et al Dallas discogram description A new classification of CTdiscography in low-back disorders Spine 12287-294 1987 Abstract 71 Sauser DD Goldman AB Kaye JJ Discogenic vertebral sclerosis J Can Assoc Radiol 2944-50 1978 Abstract 72 Schellhas KP Pollei SR Gundry CR et al Lumbar disc high-intensity zone Correlation of magnetic resonance imaging and discography Spine 2179-86 1996 Abstract 73 Schellinger D Manz HJ Vidic B et al Disk fragment migration Radiology 175831-836 1990 Abstract 74 Schipper J Kardaun JW Braakman R et al Lumbar disk herniation Diagnosis with CT or myelography Radiology 165227-231 1987 Abstract 75 Schmorl G Junghanns H The Human Spine in Health and Disease ed 2 New York Grune and Stratton 1971 76 Silverman CS Lenchik L Shimkin PM et al The value of MR in differentiating subligamentous from supraligamentous lumbar disk herniations AJNR Am J Neuroradiol 16571-579 1995 Abstract 77 Simmons JW Emery SF McMillin JN et al Awake discography A comparison study with magnetic

resonance imaging Spine 16S216-221 1991 Abstract 78 Smyth MJ Wright V Sciatica and the intervertebral disc J Bone Joint Surg Am 401401-1418 1958 79 Taveras JM Radiologic aspects of low back pain and sciatic syndromes [editorial] AJNR Am J Neuroradiol 9351-358 1989 80 Tehranzadeh J Discography 2000 Radiol Clin North Am 36463-495 1998 Full Text 81 Thelander U Fagerlund M Friberg S et al Describing the size of lumbar disc herniations using computed tomography A comparison of different size index calculations and their relation to sciatica Spine 191979-1984 1994 Abstract 82 Thornbury JR Fryback DG Turski PA et al Disk-caused nerve compression in patients with acute low-back pain Diagnosis with MR CT myelography and plain CT Radiology 186731-738 1993 Abstract 83 Twomey L Taylor J Age changes in lumbar intervertebral discs Acta Orthop Scand 56496-499 1985 Abstract 84 Twomey LT Taylor JR Age changes in lumbar vertebrae and intervertebral discs Clin Orthop 22497-104 1987 85 Williams AL CT diagnosis of degenerative disc disease The bulging annulus Radiol Clin North Am 21289-300 1983 Abstract 86 Williams AL Haughton VM Meyer GA et al Computed tomographic appearance of the bulging annulus Radiology 142403-408 1982 Abstract 87 Williams AL Haughton VM Syvertsen A Computed tomography in the diagnosis of herniated nucleus pulposus Radiology 13595-99 1980 Abstract 88 Wiltse LL Berger PE McCulloch JA A system for reporting the size and location of lesions in the spine Spine 221534-1537 1997 Abstract 89 Wiltse LL Fonseca AS Amster J et al Relationship of the dura Hofmanns ligaments Batsons plexus and a fibrovascular membrane lying on the posterior surface of the vertebral bodies and attaching to the deep layer of the posterior longitudinal ligament An anatomical radiologic and clinical study Spine 181030-1043 1993 Abstract 90 Yamashita K Hiroshima K Kurata A Gadolinium-DTPA-enhanced magnetic resonance imaging of a sequestered lumbar intervertebral disc and its correlation with pathologic findings Spine 19479-482 1994 Abstract 91 Yu SW Haughton VM Sether LA et al Comparison of MR and diskography in detecting radial tears of the anulus A postmortem study AJNR Am J Neuroradiol 101077-1081 1989 Abstract 92 Yu SW Sether LA Ho PS et al Tears of the anulus fibrosus Correlation between MR and pathologic findings in cadavers AJNR Am J Neuroradiol 9367-370 1988 Abstract

93 Yussen PS Swartz JD The acute lumbar disc herniation Imaging diagnosis Semin Ultrasound CT MR 14389-398 1993 Abstract 94 Zucherman J Derby R Hsu K et al Normal magnetic resonance imaging with abnormal discography Spine 131355-1359 1988 Abstract

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  • CLASSIFICATION DIAGNOSTIC IMAGING AND IMAGING CHARACTERIZATION OF A LUMBAR HERNIATED DISK
    • IMAGING OF LOW BACK PAIN I
      • CLASSIFICATION DIAGNOSTIC IMAGING AND IMAGING CHARACTERIZATION OF A LUMBAR HERNIATED DISK
        • DEFINITION OF A DISK HERNIATION
        • CLASSIFICATION OF A HERNIATED LUMBAR DISK
          • Main Categories of Noninfectious Disk Abnormalities
          • Further Qualifying the Displaced Disk Material Beyond the Disk Space
            • DIAGNOSTIC IMAGING AND CHARACTERIZATION OF A HERNIATED LUMBAR DISK
              • Conventional Radiographs
              • Myelography
              • CT
              • CT Myelography
              • MR Imaging
              • Diskography and CT Diskography
                • SUMMARY
                  • References
Page 11: CLASSIFICATION, DIAGNOSTIC IMAGING, AND IMAGING ... · PDF fileclassification, diagnostic imaging, and imaging characterization of a lumbar herniated disk ... classification, diagnostic

Deteriorated disks represent real pathologic degeneration which is sometimes referred to as chronic diskopathy On microscopic examination they show total structural disorganization and general replacement of normal disk material by scar tissue For this reason they were initially labeled scarred disks by the members of a joint committee on spinal nomenclature created by the Quebec Association of Radiologists[ ]14 Because of possible confusion with postoperative changes the term deteriorated disk has been proposed as an acceptable substitute Strictly speaking the term degeneration could be used to designate this entity but this latter term has such a broad nonspecific meaning that it is best avoided The deteriorated disk is characterized by narrowing of the intervertebral space irregular disk contour generally associated with symmetric or asymmetric bulging abundant presence of gas in the central portion of the intervertebral disk space multidirectional osteophytes that do not respect the central spinal canal or the foramina end plate erosions with reactive osteosclerosis and chronic bone marrow changes On T2-weighted MR images the central disk signal intensity is usually markedly decreased and the number of affected lumbar disks is variable Even though transverse concentric and radial anular tears have been identified on postmortem specimens[ ]92 the anular tear category in this model refers essentially to the radial tears that are generally demonstrated by diskography in symptomatic patients For a more precise description of those tears this model may be supplemented by the Dallas Discogram Description system[ ]70 with or without its recently proposed updates[ ]4 [ ]72 [ ]80

It should be emphasized that the pathoanatomic model is not based on direct identification of a particular geometric pattern but on the anatomy and pathology that are expected as a result of the analysis of specific criteria Using this model the conclusion of any imaging report does not consist of terms related to the shape of the disk contour or the displaced disk material but on a pathologic diagnosis that should be presented with an appropriate confidence level (possible probable or definite) The diagnosis of a probable major radial anular tear may be inferred from the presence of a definite central signal intensity loss because as a result of diskographic MR imaging correlations the positive predictive value of this sign has been estimated at 96[ ]48 The use of this model requires an effort to understand the criteria allowing differentiation of normal aging from true pathologic degeneration so this system is slightly more complicated than the morphologic model Its reliability has never been tested Some intraobserver or interobserver disagreement would probably occur trying to distinguish anular tears without herniation from anular tears with small herniations With respect to correspondance to clinical situations this scheme like the morphologic model has limited interest it has been shown that disks demonstrating the features of the deteriorated disk are likely to be responsible for symptoms but this relationship has been statistically established to be significant only for the L4-L5 disk[ ]24

Which Model Should Be Used

In other areas of diagnostic radiology the aim of image analysis is always to predict what the pathologist would find if he or she could be provided with an adequate specimen immediately following the imaging study radiologic diagnoses are presented with a pathologic perspective There is no reason why the reporting of disk disorders should be

any different Terms like bulging disk are meaningless to a pathologist and I personally favor the pathoanatomic model Nomenclature standardization however is not a task that can be achieved by an individual or even a single group of authors[ ]12 To have any impact recommendations have to emanate from well established national or international societies The multiplicity of scientific societies with an interest in the spine all over the world creates a special problem but new joint committees have recently been set up combining efforts to come up with a practical unified system that it is hoped could be proposed jointly by the North American Spine Society the American Academy of Orthopedic Surgeons the American Academy of Neurological Surgeons the American Society of Spine Radiology and the American Society of Neuroradiology Agreeing in North America on a classification of disk disorders that could gain universal acceptance like the TNM classification of neoplastic diseases would be a major achievement Meanwhile the choice of the nomenclature is up to the best judgement of each practicing radiologist and the essential issue in a given hospital or community practice remains clear communication between radiologists and referring physicians by way of a local agreement as to the meaning of words

A major problem frequently occurs because observers of imaging studies try to combine elements of the morphologic classification with those of the pathoanatomic classification Trying to differentiate a bulging disk (morphologic qualifier) from a disk herniation (pathologic diagnosis) cannot work because a bulging disk aspect is a common feature of the aging disk the deteriorated disk and some posterior central disk herniations (Fig 9) Trying to make the distinction is doomed to failure because it defies formal logic On the other hand it is theoretically possible to differentiate a radial anular tear (without herniation) from a disk herniation because these are two different pathologic entities although one may be the continuum of the other It is best to adopt either one of the two systems and avoid trying to straddle the two A general classification of disk disorders attempting to conciliate the morphologic and the pathoanatomic model is proposed in Table 1

Figure 9 A bulging disk aspect often conceals a posterior central herniation A Complete rupture of the outer anular fibers allowing nuclear material to escape and peel off the posterior longitudinal ligament (and sometimes a few intact peripheral anular fibers) from the torn disk creating a detectable focal or asymmetric extension of the disk margin beyond the interspace which qualifies as a protrusion B With more gelatinous nuclear material escaping underneath the rigid posterior longitudinal ligament the focal bulge is no longer detectable as its radius increases and if the tear occurs in the posterior midline or para-medial direction the aspect mimics symmetric disk extension beyond the interspace C Since in most cases only the outline of a diffusely hypointense disk is perceived on MR images this creates the illusion of circumferential disk bulging on axial sections D The real nature of a bulging disk of this type may be suspected by scrutinizing the sagittal sections and appreciating that unless one is dealing with a chronically degenerated scarred disk the bulge is not symmetric but limited to the posterior aspect of the disk

TABLE 1 -- GENERAL

CLASSIFICATION OF DISK LESIONS Normal (excluding aging changes)

Congenitaldevelopmental variants

Inflammationinfection

Neoplasia

Degenerativetraumatic

Degeneration

Anular tear

Herniation Protrusion

Extrusion

Degeneration Spondylosis deformans

Intervertebral osteochondrosis

Further Qualifying the Displaced Disk Material Beyond the Disk Space

Regardless of the basic system that is used the type of herniation should be assessed The volume and location of the displaced disk material beyond the normal peripheral margin of the intervertebral space also need to be specified In certain cases it is also possible to determine the composition of this material For the sake of simplicity the term herniation is used consistently in the remainder of this article to refer to all displaced disk material but what is discussed can also be applied to protrusions and extrusions if one wants to use the morphologic nomenclature

Type of Herniation

Upward or downward migration of nuclear material may occur through a break in a vertebral body end plate creating an intravertebral herniation sometimes referred to as an intraspongy herniation or a Schmorls node[ ]67 (Fig 10) Although a herniation occurring in any horizontal direction is likely to cause symptoms because of the presence of pain-sensitive nerve endings in the outer anulus[ ]7 [ ]8 [ ]65 herniations occurring in a posterior or posterolateral direction deserve special consideration because of the added possibility of dural sac or individual nerve root compression

Figure 10 Various types of intravertebral herniations (Schmorls nodes) A Intravertebral herniation through the inferior end plate of the L3 vertebral body demonstrated by diskography in a 35-year-old man suffering from chronic low back pain The patients typical pain was reproduced during injection and the lesion was considered responsible for the patients symptoms B T2-weighted sagittal section demonstrating an intravertebral herniation through the inferior end plate of the L4 vertebral body in a 24-year-old woman presenting with chronic low back pain The high signal intensity of the lesion associated with the loss of normal central signal intensity of the parent disk suggests that the lesion is a bona fide acquired intraspongy herniation and not just a developmental defect C T2-weighted sagittal section demonstrating an intravertebral herniation through the inferior end plate of the L3 vertebral body (arrow) Because both the herniation and the parent disk show normal signal intensity the abnormality was

considered a probably asymptomatic developmental defect

Other characteristics of disk herniations have become relevant with the development of new therapeutic possibilities (eg chemonucleolysis and percutaneous diskectomy) The term sequestration is confusing and has often been used to indicate displacement of disk material away from the parent disk The term sequestered disk should be used restrictedly to designate a fragment of diskal tissue that has migrated from the disk space and has no connection by diskal tissue to the disk of origin[ ]20 [ ]21 [ ]42 Sequestration refers to loss of continuity with disk tissue still present in the intervertebral disk space The term migration has a broader meaning indicating displacement of disk material away from the edge of the rent in the outer anulus either in the central spinal canal at the disk level or above or below the disk level This difference is illustrated in Figure 11 The terms communicating and noncommunicating derive from a different perspective and are mostly used in the context of intradiskal therapeutic injections They refer to the interruption of the periphery of the disk allowing fluid injected into the disk to leak into the spinal canal and reach displaced disk material[ ]20 [ ]51 The terms contained and uncontained are unfamiliar to most radiologists in a contained herniation the displaced disk material is still covered by a few intact but distended outer anular fibers or by a capsule formed by outer anular fibers and the adherent posterior longitudinal ligament

Figure 11 Various types of posterior central herniations A Small subligamentous herniation (protrusion) without significant disk material migration B Subligamentous herniation with downward migration of disk material under the PLLC C Sub-ligamentous herniation with downward migration of disk material and sequestered fragment (arrow)

The terms subligamentous and extraligamentous (or transligamentous) refer to the position of the displaced disk material with respect to the posterior longitudinal ligament The anatomy of the posterior longitudinal ligament has been recently revised[ ]73 [ ]89 It is a membranous structure that has multiple components a deep layer attached to disks and vertebral bodies a superficial layer attached to the dura by fibrous tissue (Hoffmanns

ligament) and lateral extensions known as the lateral membranes or peridural membranes (Fig 12) (Figure Not Available) It should probably be referred to as the posterior longitudinal ligament complex (PLLC) It actually divides the epidural space into the perithecal space and the anterior epidural space where displaced disk material can be entrapped (Fig 13) A potential space allowing accumulation of displaced disk material has also been detected between the outer anular fibers and the deep fibers of the PLLC on the posterior central aspect of the disk[ ]63 Posterior midline herniations seldom rupture the PLLC and are generally subligamentous The lateral membranes are less resistant and transligamentous herniations are usually the result of posterior off-center herniations or posterolateral herniations

Figure 12 (Figure Not Available) The PLLC is portrayed here in relation to various types of subligamentous disk displacement At the disk level posteriorly displaced disk material frequently occupies the midline Below and above the disk an anterior epidural space (AES) exists between the PLLC and the posterior aspect of the vertebral bodies In this space disk fragment motion across the midline is curtailed by a sagittal midline septum (dashed line) A delicate translucent membrane (shown only on left side of drawing) is stretched between the free edge of the deep layer of the posterior longitudinal ligament and the lateral spinal canal (From Schellinger D Manz HJ Vidic B et al Disk fragment migration Radiology 175831-836 1990 with permission)

Figure 13 Relationship of typical posterior disk herniations with the PLLC A Midline sagittal section unless very large a posterior midline herniation usually remains entrapped underneath the deep layer of the PLL C and sometimes a few intact outer anulus fibers joining with the PLL C to form a capsule The deep layer of the PLL C (arrow) also attaches to the posterior aspect of the vertebral body so that no potential space is present underneath B Sagittal para-central section the PLL C extends laterally at the disk level (arrowhead) but above and below the disk an anterior epidural space (as) where disk fragments are frequently entrapped is present between the lateral (peridural) membranes and the posterior aspect of the vertebral bodies

Volume of Herniated Material

Quantifying the herniated disk material by measuring in millimeters its greatest diameter or by evaluating its cross-sectional area in square millimeters is rarely done The resulting figures could be misleading without relating this measurement to the size of the spinal canal and the exact location of the lesion[ ]88 A purely qualitative and subjective statement that a mild moderate or severe herniation is present however does not give the person reading the imaging report any indication as to the potential of the lesion to cause significant compression of the dural sac or individual exiting nerve roots A reasonably precise scheme has been proposed in 1995 by the Nomenclature Committee of the North American Spine Society[ ]20 Measurements are taken from an axial CT or MR imaging section at the site of most severe compromise canal compromise of less than 25 at that section is qualified as mild 25 to 75 is moderate 76 to 90 is moderately severe and greater than 90 is severe It is understood that such characterizations describe only the cross-sectional area at one level and do not account for the total volume of displaced material displacement of neural tissue or clinical significance The usefulness of having four categories is questionable and can likely generate poor interobserver or intraobserver agreement especially in situations where the central spinal canal is relatively narrow Bonnevilles scheme[ ]9 [ ]10 [ ]11 should generate greater reliability (Fig 14) (Figure Not Available) Separation of the cross-sectional area in three thirds can be applied to both the central spinal canal and the foramina It can be agreed by way of convention that the terms mild moderate and severe lumen compromise by a disk herniation designate extension of the displaced disk material in the anterior middle or posterior third of the central canal or foramen depending on the specified location of the herniation

Figure 14 (Figure Not Available) The size of the herniation in the horizontal plane is assessed and designated by the numbers 1 2 or 3 by establishing its extension in the anterior middle or posterior third of the spinal canal (From Bonneville JF Plaidoyer pour une classification par limage des hernies discales lombaires la carte-image Rev Imag Med 2557-560 1990 with permission)

Location of Herniated Material

Bonneville[ ]9 [ ]10 [ ]11 has also proposed an interesting and simple alpha-numerical system to classify according to their location the position of disk fragments that have migrated in the horizontal or sagittal plane (Figs 15 (Figure Not Available) and 16) (Figure Not Available) Using more precise anatomic boundaries unfortunately more familiar to surgeons than radiologists Wiltse et al[ ]88 have proposed another system which has been supported by the North American Spine Society[ ]20 [ ]21 Anatomic zones and levels are defined using the following anatomic landmarks medial edge of the articular facets medial lateral upper and lower border of the pedicles and coronal plane at the disk center On the horizontal plane (Fig 17) (Figure Not Available) these landmarks determine the bounderies of the central zone the subarticular zone the foraminal zone the extraforaminal zone and the anterior zone (anterior to the coronal plane at the center of the disk) In the sagittal plane they determine the boundaries of the diskal level the infrapedicular level the pedicular level and the suprapedicular level (Figs 18 (Figure

Not Available) and 19) (Figure Not Available) Radiologists interpreting axial CT or MR images may find it difficult to use the medial edge of the facets as the landmark that separates the central zone from the subarticular zone because the superior articular facets are generally not included in axial sections at the disk level The alternative is to use the expression posterolateral to designate collectively all posterior herniations that are not midline but do not extend into a foramen as was proposed by Bonneville[ ]9 [ ]10 [ ]11

Figure 15 (Figure Not Available) In the horizontal plane herniations are labeled midline (a) posterolateral (b) foraminal (c) and extra-foraminal (d) (From Bonneville JF Plaidoyer pour une classification par limage des hernies discales lombaires la carte-image Rev Imag Med 2557-560 1990 with permission)

Figure 16 (Figure Not Available) In the craniocaudal direction disk migration is labeled +1 +2 +3 or -1 -2 -3 by referring to the height of a vertebral body divided in thirds (From Bonneville JF Plaidoyer pour une classification par limage des hernies discales lombaires la carte-image Rev Imag Med 2557-560 1990 with permission)

Figure 17 (Figure Not Available) The anatomic zones identified on axial images The anterior zone (not shown) is delineated from the extraforaminal zone by an imaginary coronal line in the center of the vertebral body (From Wiltse LL Berger PE McCulloch JA A system for reporting the size and location of lesions in the spine Spine 221534-1537 1997 with permission)

Figure 18 (Figure Not Available) The anatomical levels identified on craniocaudal images (From Wiltse LL Berger PE McCulloch AJ A system for reporting the size and location of lesions in the spine Spine 221534-1537 1997 with permission)

Figure 19 (Figure Not Available) Coronal view of the main zones and levels (From Wiltse LL Berger PE McCulloch JA A system for reporting the size and location of lesions in the spine Spine 221534-1537 1997 with permission)

Composition of Herniated Material

Displaced disk material may consist of glycosaminoglycans type 1 or 2 collagen end plate cartilage and bone fragments avulsed from the ring epiphysis A reactive inflammatory reaction usually results in edematous tissue followed by granulation tissue which may undergo calcification (Fig 20) Necrotic and partially resorbed displaced disk material sometimes produces a large fluid-filled pouch distinguishable from the common high-intensity zone because of its size (Fig 21) or a gas-filled cavity generally in continuity with gas in the intervertebral space (Fig 22) [ ]42 These characteristics may be meaningful if intradiskal injection therapy is considered In imaging reports herniations exhibiting calcium deposits and those exhibiting replacement of disk material by gas or a relatively large fluid collection can be qualified as chronic herniations

Figure 20 A CT scan demonstration of a small posterior central L4-L5 calcified subligamentous herniation The resistant deep layer of the PLLC restrains displacement of the disk material in the posterior central direction and does not allow a detectable distortion of the disk contour In this particular case the presence of the calcification is actually the only evidence that a posterior midline anular tear and a small subligamentous herniation are present B Posterior right central and sub-articular L5-S1 calcified disk herniation in same patient Posterolateral herniations are generally more conspicuous than posterior midline herniations because the deep layer of the PLLC gets thinner away from the midline

Figure 21 Posterior central midline L4-L5 herniation in a 52-year-old man demonstrated on a T2-weighted midline MR sagittal section There is intervertebral space narrowing with loss of normal central disk signal

intensity while the herniated disk material demonstrates high signal intensity consistent with a predominantly fluid consistency

Figure 22 CT scan demonstration in a 51-year-old woman of a left posterolateral L5-S1 disk hernation consisting essentially in a gas-filled pouch (white arrow) Gas is also present in the central portion of the intervertebral disk space (black arrow)

DIAGNOSTIC IMAGING AND CHARACTERIZATION OF A HERNIATED LUMBAR DISK

Assessing the validity of the currently used imaging procedures to diagnose a herniated lumbar disk is not an easy endeavor The validity of a measurement is the extent to which it corresponds to the true biologic value or some accepted gold standard[ ]40 With the exception of postmortem studies evaluation of the pathoanatomy by the surgeon in the operating room has always been considered the gold standard but this does not constitute an ideal situation Inspection of the disk through a small laminectomy incision to determine for instance if nuclear fragments lie within or outside the anular fibers may not be very reliable Also unbiased intraoperative determination of a normal degenerated or herniated disk in a patient with sciatica may also be difficult[ ]86 Because the validity of diskography has been previously established by postmortem studies and surgical correlations[ ]48 it is sometimes used as a gold standard in situations where no surgery has been performed

Conventional Radiographs

Lumbar disk herniations can exceptionally be diagnosed directly on good quality lateral projections because the x-ray attenuation is slightly greater in displaced disk material than in epidural fat Occasionally a calcified rim outlines the displaced disk fragment

(Fig 23) In most situations however narrowing of an intervertebral disk space in the absence of other evidence of chronic diskopathy is the only detectable sign suggesting the presence of a disk herniation To my knowledge the sensitivity and specificity of this sign has never been assessed The accepted rule of thumb is that the height of a given lumbar intervertebral disk space should always be slightly greater than the height of the above located interspace This rule does not apply to the transition disk immediately above the sacrum (usually L5-S1) The specificity of this sign is probably quite high but a few false-positives are seen especially at the L4-L5 level because of minor congenital hypoplasia The presence of posterior or foraminal vertebral body osteophytes associated or not with disk space narrowing is a definite sign of a chronic disk herniation

Figure 23 A Chronic left L3-L4 extraforaminal disk hernation in a 54-year-old man suspected on an AP radiograph demonstrating a calcified shell on the left side of the intervertebral disk space (white arrow) B Axial CT scan section confirming the diagnosis of a chronic extraforaminal L3-L4 herniation

Myelography

Myelography is essentially an exploration of the subarachnoid space Disk herniations are demonstrated only indirectly because they can cause thecal sac deformity and individual nerve root sleeve filling defects (Fig 24) Of all the special imaging procedures

myelography is the only one that allows upright projections with full weight bearing It is not unusual to demonstrate in this way small posterior central or posterolateral herniations that are undetectable on CT sections Interestingly the overall sensitivity of myelography to detect disk herniations has been found to be higher than that of CT whereas its specificity has been found to be lower[ ]74 In comparison with standard CT examination which usually includes only the three or four lower lumbar disks myelography easily allows coverage of the entire lumbar area and assessment of the intrathecal structures (cauda equina and conus medullaris) Far lateral foraminal herniations extraforaminal herniations and anterior herniations however are not detected The sensitivity for detection of posterior central L5-S1 herniations is also relatively poor because of the greater distance between the thecal sac and the posterior aspect of this particular disk

Figure 24 L5-S1 disk herniation in a 25-year-old man detected by indirect signs using lumbosacral myelography A Upright oblique projections showing a filling defect of the left S1 root sleeve (white arrow) suggesting significant nerve root compression by a left posterolateral disk hernation The right S1 root sleeve fills normally with contrast (black arrow) B Subtle compression of the anterior wall of the dural sac by displaced disk material (small arrows) demonstrated on upright lateral projection This sign is usually absent in the presence of a large amount of fat and venous structures in the anterior epidural compartment

CT

The sensitivity of CT to diagnose a herniation of the nucleus pulposus at the L5-S1 interspace is greater than that of myelography if images in the exact plane of the disk can be obtained[ ]23 [ ]39 Otherwise the superiority of plain CT over myelography to demonstrate disk herniations has not been established but CT has the distinct advantage of being

noninvasive and provides direct anatomic information[ ]23 Large herniations are easily detected but as explained previously the distinction between protrusions and extrusions is often difficult without sagittal reconstructions CT essentially allows an assessment of the contour of the disk The diagnosis of very small herniations in the absence of direct or indirect evidence of a radial tear is hazardous and associated with a high percentage of false-positives and false-negatives[ ]52 The diagnosis of moderate and large size herniations in different directions is usually possible but anterior herniations are rarely diagnosed not because they are not detectable but because observers pay little attention to the anterior contour of the disk (Fig 25) Because the PLLC cannot usually be identified the distinction of subligamentous from transligamentous herniation can only be suggested in most cases by the size of the herniated material A definite diagnosis of sequestration is rarely possible Calcifications within the displaced material are readily seen but may be difficult at times to differentiate from an accompanying osteophyte or an avulsed bone fragment from the vertebral body ring epiphysis (Fig 26) The presence of gas in the herniated material is easily detected

Figure 25 Anterior L4-L5 herniation demonstrated by CT scan in a 51-year-old woman with chronic low back pain Although sometimes quite conspicuous such herniations are rarely reported because observers pay little attention to the anterior contour of the disk

Figure 26 CT scan demonstration of a posterior right central L4-L5 disk herniation in a 38-year-old woman with avulsion of a bone fragment from the ring epiphysis and adjacent part of the superior L5 end plate Reactive osteosclerosis is seen around the vertebral body defect (arrows) suggesting a chronic lesion

CT Myelography

This association combines the advantages of both imaging modalities The fact that its accuracy has been reported as being less[ ]22 [ ]32 higher[ ]1 [ ]6 or equivalent[ ]82 to MR imaging is a reflection of the differences in technologic advancement and pathologic nomenclature that hamper valid comparisons between different studies

MR Imaging

Most reported studies establish MR imaging as the first choice modality to diagnose a herniated lumbar disk[ ]5 [ ]22 [ ]32 [ ]46 The associated intravenous injection of a paramagnetic agent has been found useful to demonstrate some anatomic features of disk disease in patients with no previous lumbar disk surgery[ ]56 [ ]68 [ ]90 MR imaging provides a better assessment of disk morphology than CT or CT myelography because sagittal sections are routinely obtained Assessment of foraminal involvement by displaced disk material is more accurate (Fig 27) and anterior disk herniations can be detected more easily than with CT or CT myelography If one is looking specifically for herniated lumbar disks associated with nerve root compression however it has been demonstrated that CT is equally accurate[ ]82 Alterations of the central or peripheral disk signal intensity on T2-weighted images are seen in most disks afflicted with an anular tear[ ]48 and alert the observer to scrutinize the disk contour in search for local modifications indicative of a herniation Because the signal of the displaced disk material is usually very similar to that of the outer anulus PLLC and vertebral body cortical bone small herniations are generally more conspicuous on axial CT sections than on corresponding axial MR imaging sections Gas and calcium deposits within the displaced fragment cannot usually

be detected but associated vertebral body bone marrow changes are typically seen and are helpful in differentiating acute from chronic processes[ ]57 The occasional presence of a high-intensity zone in the herniated material with an occasionally enhancing border after contrast injection is probably caused by a mixture of displaced nuclear material acute and subacute inflammatory tissue and neovascularized reactive tissue[ ]4 [ ]48 [ ]72 Contradictory reports have been published regarding the accuracy of MR imaging to differentiate subligamentous from transligamentous herniations[ ]26 [ ]38 [ ]73 [ ]76 Understanding the anatomy of the PLLC is helpful to make the distinction (Fig 28) (Figure Not Available) Masaryk et al[ ]46 have suggested that MR imaging is accurate to distinguish sequestered disks from other forms of lumbar disk herniations but most observers find this distinction difficult to establish[ ]42

Figure 27 A Left L4-L5 foraminal herniation well seen on an intermediate-weighted left parasagittal MR section (arrow) in a 47-year-old man B The lesion is much less obvious on intermediate-weighted (left) and T2-weighted (right) axial sections and was in fact more conspicuous on the corresponding CT scan section

Figure 28 (Figure Not Available) A Subligamentous disk herniation Left T1-weighted image demonstrating displaced disk material with a smooth outline imposed by the demarcation of the anterior epidural space (AES) by the lateral membrane of the PLLC Right Correlative drawing B Transligamentous disk herniation Left T1-weighted image of a large disk herniation (cervical in this case) which has ruptured through the posterior confines of the AES Penetration of the right lateral membrane can be observed (arrow) and the disk fragment contour is serrated Right Correlative drawing (From Schellinger D Manz HJ Vidic B et al Disk fragment migration Radiology 175831-836 1990 with permission)

Diskography and CT Diskography

During 30 years (1950 to 1980) when myelography was the only available imaging technique to demonstrate lumbar disk herniations diskography was an invasive but efficient way to demonstrate posterior central L5-S1 herniations and other large herniations (other than posterior central and paramedial) that could not be detected by myelography[ ]50 These herniations are now usually well demonstrated by CT and MR imaging Comparing the accuracy of five imaging modalities (excluding MR imaging) for the diagnosis of lumbar disk herniation Jackson et al[ ]31 found that CT diskography (Fig 29) was the most accurate test (87) compared with 77 for CT myelography 74 for CT 70 for myelography 64 for pain reproduction during diskography and 58 for diskography without CT Disk injection reproduced the patients clinical pain pattern in only 36 of herniated disks This clinical test isolated from the images had high specificity (89) but low sensitivity (43) for the diagnosis of disk herniation The reported low sensitivity of diskography images (unassociated with CT) to diagnose disk herniation is to be expected the purpose of the intradiskal injection being primarily the demonstration of an anular tear the contrast leaking through the tear only occasionally delineates an extruded fragment When a disk herniation has been diagnosed by other imaging modalities diskography allows to determine if the herniation is contained or noncontained (Figs 30 and 31) this information may have clinical relevance[ ]62 It also allows to establish if the displaced disk material is communicating or not with the parent disk and establishes the likelihood that it is sequestered or not There always remains a possibility that the contrast injected under pressure may reach a disk fragment that is nevertheless sequestered by leaking through the associated anular tear CT diskography also allows assessment in most cases of the integrity of the PLLC[ ]89 The superior sensitivity of diskography over MR imaging to demonstrate anular tears has been well established[ ]27 [ ]44 [ ]48 [ ]64 [ ]77 [ ]91 [ ]94 The presence of a radial tear and the inflammatory reaction it creates may be symptomatic despite the absence of true disk herniation[ ]29 [ ]48 [ ]49 [ ]69

Figure 29 L4-L5 CT diskogram demonstrating a large left posterolateral radial anular tear associated with

a left foraminal and extraforaminal herniaton (same patient as in Figure 28) (Figure Not Available)

Figure 30 Contained posterior L4-L5 and L5-S1 disk herniations in a 57-year-old man demonstrated by diskography The L3-L4 disk is normal

Figure 31 Noncontained L4-L5 disk herniation in a 23-year-old woman Reflux of injected contrast is seen in the anterior epidural space above and below the disk space The L5-S1 disk also demonstrates incomplete anterior and posterior radial anular tears

SUMMARY

The absence of universal nomenclature standardization with respect to the definition of a disk herniation and its different categories especially regarding type and location is still a major problem that will only be overcome when major national or international scientific societies join efforts to support a particular scheme Meanwhile it is important to realize that the two models that are currently most used are based on a different perspective Trying to straddle the two by opposing for instance bulging disk and herniation is doomed to failure because this exercise defies formal logic MR imaging is currently the most accurate noninvasive imaging modality to diagnose a disk herniation and to determine its exact location The determination of some pathoanatomic characteristics of herniated disks (type and composition) may require the use of CT diskography or CT diskography

References

1 Albeck MJ Hilden J Kjaer L et al A controlled comparison of myelography computed tomography and magnetic resonance imaging in clinically suspected lumbar disc herniation Spine 20443-448 1995 Abstract 2 American Academy of Orthopedic Surgeons Glossary on Spinal Terminology Chicago American Academy of Orthopedic Surgeons 1981 3 Andersson GB Weinstein JN Disc herniation [editorial] Spine 211S 1996 Citation 4 Aprill C Bogduk N High-intensity zone A diagnostic sign of painful lumbar disc on magnetic resonance imaging Br J Radiol 65361-369 1992 Abstract 5 Birney TJ White JJ Jr Berens D et al Comparison of MRI and discography in the diagnosis of lumbar degenerative disc disease J Spinal Disord 5417-423 1992 Abstract 6 Bischoff RJ Rodriguez RP Gupta K et al A comparison of computed tomography-myelography magnetic resonance imaging and myelography in the diagnosis of herniated nucleus pulposus and spinal stenosis J Spinal Disord 6289-295 1993 Abstract 7 Bogduk N The innervation of the lumbar spine Spine 8286-293 1983 Abstract 8 Bogduk N Tynan W Wilson AS The nerve supply to the human lumbar intervertebral discs J Anat 13239-56 1981 Abstract 9 Bonneville JF La carte-image des hernies discales lombaires Rachis 2255-257 1990 10 Bonneville JF La topografia simbolica delle ernie discali lombari Riv Neuroradiol 5427-431 1992 11 Bonneville JF Plaidoyer pour une classification par limage des hernies discales lombaires La carte-image Rev Imag Med 2557-560 1990 12 Brant-Zawadzki M Jensen M Spinal nomenclature Spine 20388-390 1995 Abstract

13 Brant-Zawadzki MN Jensen MC Obuchowski N et al Interobserver and intraobserver variability in interpretation of lumbar disc abnormalities A comparison of two nomenclatures Spine 201257-1263 1995 Abstract 14 Breton G Is that a bulging disk a small herniation or a moderate protrusion [editorial] Can Assoc Radiol J 42318 1991 Citation 15 Czervionke LF Lumbar intervertebral disc disease Neuroimaging Clin North Am 3465-485 1993 16 Deyo RA Nonsurgical care of low back pain Neurosurg Clin North Am 2851-862 1991 17 Deyo RA Loeser JD Bigos SJ Herniated lumbar intervertebral disk Ann Intern Med 112598-603 1990 Abstract 18 Dorlands Illustrated Medical Dictionary ed 28 Philadelphia WB Saunders 1994 19 Fardon D Pinkerton S Balderston R et al Terms used for diagnosis by English speaking spine surgeons Spine 18274-277 1993 Citation 20 Fardon DF Herzog RJ Mink JH et al Nomenclature of Lumbar Disc Disorders Contemporary Concepts in Spine Care Rosemont IL North American Spine Society 1995 21 Fardon DF Herzog RJ Mink JH et al Nomenclature of lumbar disc disorders In Garfin S Vaccaro A (eds) Orthopedic Knowledge Update Spine Rosemont IL American Academy of Orthopedic Surgeons 1997 pp A3-A14 22 Forristall RM Marsh HO Pay NT Magnetic resonance imaging and contrast CT of the lumbar spine Comparison of diagnostic methods and correlation with surgical findings Spine 131049-1054 1988 Abstract 23 Fries JW Abodeely DA Vijungco JG et al Computed tomography of herniated and extruded nucleus pulposus J Comput Assist Tomogr 6874-887 1982 Abstract 24 Frymoyer JW Newberg A Pope MH et al Spine radiographs in patients with low-back pain An epidemiological study in men J Bone Joint Surg Am 661048-1055 1984 Abstract 25 Gospodarowicz M Benedet L Hutter RV et al History and international developments in cancer staging Cancer Prev Control 2262-268 1998 Abstract 26 Grenier N Greselle JF Vital JM et al Normal and disrupted lumbar longitudinal ligaments Correlative MR and anatomic study Radiology 171197-205 1989 Abstract 27 Gunzburg R Parkinson R Moore R et al A cadaveric study comparing discography magnetic resonance imaging histology and mechanical behavior of the human lumbar disc Spine 17417-426 1992 Abstract 28 Haughton VM Eldevik OP Magnaes B et al A prospective comparison of computed tomography and myelography in the diagnosis of herniated lumbar disks Radiology 142103-110 1982 Abstract

29 Haughton VM Lim TH An H Intervertebral disk appearance correlated with stiffness of lumbar spinal motion segments AJNR Am J Neuroradiol 201161-1165 1999 Abstract 30 Herzog RJ The radiologic assessment for a lumbar disc herniation Spine 2119S-38S 1996 Abstract 31 Jackson RP Becker GJ Jacobs RR et al The neuroradiographic diagnosis of lumbar herniated nucleus pulposus I A comparison of computed tomography (CT) myelography CT-myelography discography and CT-discography Spine 141356-1361 1989 Abstract 32 Jackson RP Cain JE Jr Jacobs RR et al The neuroradiographic diagnosis of lumbar herniated nucleus pulposus II A comparison of computed tomography (CT) myelography CT-myelography and magnetic resonance imaging Spine 141362-1367 1989 Abstract 33 Jarvik JG Haynor DR Koepsell TD et al Interreader reliability for a new classification of lumbar disk disease Acad Radiol 3537-544 1996 Abstract 34 Jensen MC Brant-Zawadzki MN Obuchowski N et al Magnetic resonance imaging of the lumbar spine in people without back pain N Engl J Med 33169-73 1994 Abstract 35 Kent DL Haynor DR Larson EB et al Diagnosis of lumbar spinal stenosis in adults A meta-analysis of the accuracy of CT MR and myelography AJR Am J Roentgenol 1581135-1144 1992 Abstract 36 Kieffer SA Sherry RG Wellenstein DE et al Bulging lumbar intervertebral disk Myelographic differentiation from herniated disk with nerve root compression AJR Am J Roentgenol 138709-716 1982 Abstract 37 Kieffer SA Stadlan EM Mohandas A et al Discographic-anatomical correlation of developmental changes with age in the intervertebral disc Acta Radiol 9733-739 1969 38 Kim KY Kim YT Lee CS et al MRI classification of lumbar herniated intervertebral disc Orthopedics 15493-497 1992 Abstract 39 Kornberg M Rechtine GR Dupuy TE Computed tomography in the diagnosis of a herniated disk at the L5-S1 level Spine 9433-436 1984 Abstract 40 Kramer MS Clinical Epidemiology and Biostatistics New York Springer-Verlag 1988 41 Landis JR Koch GG The measurement of observer agreement agreement for categorical data Biometrics 33159-174 1977 Abstract 42 Laredo JD Bossard P Vuillemin-Bodaghi Formes anatomo-radiologiques des hernies discales In Morvan G Deburge A Bard H et al (eds) Le Rachis Lombaire Degeneratif Montpellier Sauramps Medical 1998 pp 37-49 43 Lee SH Coleman PE Hahn FJ Magnetic resonance imaging of degenerative disk disease of the spine Radiol Clin North Am 26949-964 1988 Abstract 44 Linson MA Crowe CH Comparison of magnetic resonance imaging and lumbar discography in the diagnosis of disc degeneration Clin Orthop 160-163 1990

45 Marchand F Ahmed AM Investigation of the laminate structure of lumbar disc anulus fibrosus Spine 15402-410 1990 Abstract 46 Masaryk TJ Ross JS Modic MT et al High-resolution MR imaging of sequestered lumbar intervertebral disks AJR Am J Roentgenol 1501155-1162 1988 Abstract 47 Milette PC The proper terminology for reporting lumbar intervertebral disk disorders AJNR Am J Neuroradiol 181859-1866 1997 Citation 48 Milette PC Fontaine S Lepanto L et al Differentiating lumbar disc protrusions disk bulges and discs with normal contour but abnormal signal intensity Magnetic resonance imaging with discographic correlations Spine 2444-53 1999 Abstract 49 Milette PC Fontaine S Lepanto L et al Radiating pain to the lower extremities caused by lumbar disk rupture without spinal nerve root involvement AJNR Am J Neuroradiol 161605-1613 1995 Abstract 50 Milette PC Melancon D A reappraisal of lumbar discography Can Assoc Radiol J 33176-182 1982 51 Milette PC Melancon D Dupuis PR et al A simplified terminology for abnormalities of the lumbar disk Can Assoc Radiol J 42319-325 1991 Abstract 52 Milette PC Raymond J Fontaine S Comparison of high-resolution computed tomography with discography in the evaluation of lumbar disc herniations Spine 15525-533 1990 Abstract 53 Mink JH Deutsch AL Goldstein TB et al Spinal imaging and intervention 1998 Phys Med Rehabil Clin North Am 9343-380 1998 54 Mixter WJ Barr JS Rupture of the intervertebral disc with involvement of the spinal canal N Engl J Med 211210-234 1934 55 Modic MT Masaryk TJ Ross JS et al Imaging of degenerative disk disease Radiology 168177-186 1988 Citation 56 Modic MT Ross JS Obuchowski NA et al Contrast-enhanced MR imaging in acute lumbar radiculopathy A pilot study of the natural history Radiology 195429-435 1995 Abstract 57 Modic MT Steinberg PM Ross JS et al Degenerative disk disease Assessment of changes in vertebral body marrow with MR imaging Radiology 166193-199 1988 58 Morvan G Mathieu P Les stenoses laterales In Morvan G Deburge A Bard H et al (eds) Le Rachis Lombaire Degeneratif Montpellier Sauramps Medical 1998 pp 315-324 59 Murray RO Skeletal trauma Regional In Sutton D (ed) Textbook of Radiology and Imaging ed 3 New York Churchill Livingstone 1980 pp 210-231 60 Nachemson A Lumbar disc herniation Conclusions Acta Orthop Scand 64(suppl 251)49 1993 Citation

61 Nathan H Osteophytes of the vertebral column An anatomical study of their development according to age race and sex with consideration as to their etiology and significance J Bone Joint Surg Am 44243-268 1962 62 Nygaard OP Mellgren SI Osterud B The inflammatory properties of contained and noncontained lumbar disc herniations Spine 222584-2488 1997 Abstract 63 Ohshima H Hirano N Osada R et al Morphologic variation of lumbar posterior longitudinal ligament and the modality of disc herniation Spine 182408-2411 1993 Abstract 64 Osti OL Fraser RD MRI and discography of annular tears and intervertebral disc degeneration A prospective clinical comparison J Bone Joint Surg Br 74431-435 1992 Abstract 65 Palmgren T Gronblad M Virri J et al Immunohistochemical demonstration of sensory and autonomic nerve terminals in herniated lumbar disc tissue Spine 211301-1306 1996 Abstract 66 Resnick D Niwayama G Degenerative disease of the spine In Resnick D (ed) Diagnosis of Bone and Joint Disorders ed 3 Philadelphia WB Saunders 1995 pp 1372-1462 67 Resnick D Niwayama G Intravertebral disk herniations Cartilaginous (Schmorls) nodes Radiology 12657-65 1978 Abstract 68 Ross JS Modic MT Masaryk TJ Tears of the anulus fibrosus Assessment with Gd-DTPA-enhanced MR imaging AJR Am J Roentgenol 154159-162 1990 Abstract 69 Saal JS The role of inflammation in lumbar pain Spine 201821-1827 1995 Abstract 70 Sachs BL Vanharanta H Spivey MA et al Dallas discogram description A new classification of CTdiscography in low-back disorders Spine 12287-294 1987 Abstract 71 Sauser DD Goldman AB Kaye JJ Discogenic vertebral sclerosis J Can Assoc Radiol 2944-50 1978 Abstract 72 Schellhas KP Pollei SR Gundry CR et al Lumbar disc high-intensity zone Correlation of magnetic resonance imaging and discography Spine 2179-86 1996 Abstract 73 Schellinger D Manz HJ Vidic B et al Disk fragment migration Radiology 175831-836 1990 Abstract 74 Schipper J Kardaun JW Braakman R et al Lumbar disk herniation Diagnosis with CT or myelography Radiology 165227-231 1987 Abstract 75 Schmorl G Junghanns H The Human Spine in Health and Disease ed 2 New York Grune and Stratton 1971 76 Silverman CS Lenchik L Shimkin PM et al The value of MR in differentiating subligamentous from supraligamentous lumbar disk herniations AJNR Am J Neuroradiol 16571-579 1995 Abstract 77 Simmons JW Emery SF McMillin JN et al Awake discography A comparison study with magnetic

resonance imaging Spine 16S216-221 1991 Abstract 78 Smyth MJ Wright V Sciatica and the intervertebral disc J Bone Joint Surg Am 401401-1418 1958 79 Taveras JM Radiologic aspects of low back pain and sciatic syndromes [editorial] AJNR Am J Neuroradiol 9351-358 1989 80 Tehranzadeh J Discography 2000 Radiol Clin North Am 36463-495 1998 Full Text 81 Thelander U Fagerlund M Friberg S et al Describing the size of lumbar disc herniations using computed tomography A comparison of different size index calculations and their relation to sciatica Spine 191979-1984 1994 Abstract 82 Thornbury JR Fryback DG Turski PA et al Disk-caused nerve compression in patients with acute low-back pain Diagnosis with MR CT myelography and plain CT Radiology 186731-738 1993 Abstract 83 Twomey L Taylor J Age changes in lumbar intervertebral discs Acta Orthop Scand 56496-499 1985 Abstract 84 Twomey LT Taylor JR Age changes in lumbar vertebrae and intervertebral discs Clin Orthop 22497-104 1987 85 Williams AL CT diagnosis of degenerative disc disease The bulging annulus Radiol Clin North Am 21289-300 1983 Abstract 86 Williams AL Haughton VM Meyer GA et al Computed tomographic appearance of the bulging annulus Radiology 142403-408 1982 Abstract 87 Williams AL Haughton VM Syvertsen A Computed tomography in the diagnosis of herniated nucleus pulposus Radiology 13595-99 1980 Abstract 88 Wiltse LL Berger PE McCulloch JA A system for reporting the size and location of lesions in the spine Spine 221534-1537 1997 Abstract 89 Wiltse LL Fonseca AS Amster J et al Relationship of the dura Hofmanns ligaments Batsons plexus and a fibrovascular membrane lying on the posterior surface of the vertebral bodies and attaching to the deep layer of the posterior longitudinal ligament An anatomical radiologic and clinical study Spine 181030-1043 1993 Abstract 90 Yamashita K Hiroshima K Kurata A Gadolinium-DTPA-enhanced magnetic resonance imaging of a sequestered lumbar intervertebral disc and its correlation with pathologic findings Spine 19479-482 1994 Abstract 91 Yu SW Haughton VM Sether LA et al Comparison of MR and diskography in detecting radial tears of the anulus A postmortem study AJNR Am J Neuroradiol 101077-1081 1989 Abstract 92 Yu SW Sether LA Ho PS et al Tears of the anulus fibrosus Correlation between MR and pathologic findings in cadavers AJNR Am J Neuroradiol 9367-370 1988 Abstract

93 Yussen PS Swartz JD The acute lumbar disc herniation Imaging diagnosis Semin Ultrasound CT MR 14389-398 1993 Abstract 94 Zucherman J Derby R Hsu K et al Normal magnetic resonance imaging with abnormal discography Spine 131355-1359 1988 Abstract

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  • CLASSIFICATION DIAGNOSTIC IMAGING AND IMAGING CHARACTERIZATION OF A LUMBAR HERNIATED DISK
    • IMAGING OF LOW BACK PAIN I
      • CLASSIFICATION DIAGNOSTIC IMAGING AND IMAGING CHARACTERIZATION OF A LUMBAR HERNIATED DISK
        • DEFINITION OF A DISK HERNIATION
        • CLASSIFICATION OF A HERNIATED LUMBAR DISK
          • Main Categories of Noninfectious Disk Abnormalities
          • Further Qualifying the Displaced Disk Material Beyond the Disk Space
            • DIAGNOSTIC IMAGING AND CHARACTERIZATION OF A HERNIATED LUMBAR DISK
              • Conventional Radiographs
              • Myelography
              • CT
              • CT Myelography
              • MR Imaging
              • Diskography and CT Diskography
                • SUMMARY
                  • References
Page 12: CLASSIFICATION, DIAGNOSTIC IMAGING, AND IMAGING ... · PDF fileclassification, diagnostic imaging, and imaging characterization of a lumbar herniated disk ... classification, diagnostic

any different Terms like bulging disk are meaningless to a pathologist and I personally favor the pathoanatomic model Nomenclature standardization however is not a task that can be achieved by an individual or even a single group of authors[ ]12 To have any impact recommendations have to emanate from well established national or international societies The multiplicity of scientific societies with an interest in the spine all over the world creates a special problem but new joint committees have recently been set up combining efforts to come up with a practical unified system that it is hoped could be proposed jointly by the North American Spine Society the American Academy of Orthopedic Surgeons the American Academy of Neurological Surgeons the American Society of Spine Radiology and the American Society of Neuroradiology Agreeing in North America on a classification of disk disorders that could gain universal acceptance like the TNM classification of neoplastic diseases would be a major achievement Meanwhile the choice of the nomenclature is up to the best judgement of each practicing radiologist and the essential issue in a given hospital or community practice remains clear communication between radiologists and referring physicians by way of a local agreement as to the meaning of words

A major problem frequently occurs because observers of imaging studies try to combine elements of the morphologic classification with those of the pathoanatomic classification Trying to differentiate a bulging disk (morphologic qualifier) from a disk herniation (pathologic diagnosis) cannot work because a bulging disk aspect is a common feature of the aging disk the deteriorated disk and some posterior central disk herniations (Fig 9) Trying to make the distinction is doomed to failure because it defies formal logic On the other hand it is theoretically possible to differentiate a radial anular tear (without herniation) from a disk herniation because these are two different pathologic entities although one may be the continuum of the other It is best to adopt either one of the two systems and avoid trying to straddle the two A general classification of disk disorders attempting to conciliate the morphologic and the pathoanatomic model is proposed in Table 1

Figure 9 A bulging disk aspect often conceals a posterior central herniation A Complete rupture of the outer anular fibers allowing nuclear material to escape and peel off the posterior longitudinal ligament (and sometimes a few intact peripheral anular fibers) from the torn disk creating a detectable focal or asymmetric extension of the disk margin beyond the interspace which qualifies as a protrusion B With more gelatinous nuclear material escaping underneath the rigid posterior longitudinal ligament the focal bulge is no longer detectable as its radius increases and if the tear occurs in the posterior midline or para-medial direction the aspect mimics symmetric disk extension beyond the interspace C Since in most cases only the outline of a diffusely hypointense disk is perceived on MR images this creates the illusion of circumferential disk bulging on axial sections D The real nature of a bulging disk of this type may be suspected by scrutinizing the sagittal sections and appreciating that unless one is dealing with a chronically degenerated scarred disk the bulge is not symmetric but limited to the posterior aspect of the disk

TABLE 1 -- GENERAL

CLASSIFICATION OF DISK LESIONS Normal (excluding aging changes)

Congenitaldevelopmental variants

Inflammationinfection

Neoplasia

Degenerativetraumatic

Degeneration

Anular tear

Herniation Protrusion

Extrusion

Degeneration Spondylosis deformans

Intervertebral osteochondrosis

Further Qualifying the Displaced Disk Material Beyond the Disk Space

Regardless of the basic system that is used the type of herniation should be assessed The volume and location of the displaced disk material beyond the normal peripheral margin of the intervertebral space also need to be specified In certain cases it is also possible to determine the composition of this material For the sake of simplicity the term herniation is used consistently in the remainder of this article to refer to all displaced disk material but what is discussed can also be applied to protrusions and extrusions if one wants to use the morphologic nomenclature

Type of Herniation

Upward or downward migration of nuclear material may occur through a break in a vertebral body end plate creating an intravertebral herniation sometimes referred to as an intraspongy herniation or a Schmorls node[ ]67 (Fig 10) Although a herniation occurring in any horizontal direction is likely to cause symptoms because of the presence of pain-sensitive nerve endings in the outer anulus[ ]7 [ ]8 [ ]65 herniations occurring in a posterior or posterolateral direction deserve special consideration because of the added possibility of dural sac or individual nerve root compression

Figure 10 Various types of intravertebral herniations (Schmorls nodes) A Intravertebral herniation through the inferior end plate of the L3 vertebral body demonstrated by diskography in a 35-year-old man suffering from chronic low back pain The patients typical pain was reproduced during injection and the lesion was considered responsible for the patients symptoms B T2-weighted sagittal section demonstrating an intravertebral herniation through the inferior end plate of the L4 vertebral body in a 24-year-old woman presenting with chronic low back pain The high signal intensity of the lesion associated with the loss of normal central signal intensity of the parent disk suggests that the lesion is a bona fide acquired intraspongy herniation and not just a developmental defect C T2-weighted sagittal section demonstrating an intravertebral herniation through the inferior end plate of the L3 vertebral body (arrow) Because both the herniation and the parent disk show normal signal intensity the abnormality was

considered a probably asymptomatic developmental defect

Other characteristics of disk herniations have become relevant with the development of new therapeutic possibilities (eg chemonucleolysis and percutaneous diskectomy) The term sequestration is confusing and has often been used to indicate displacement of disk material away from the parent disk The term sequestered disk should be used restrictedly to designate a fragment of diskal tissue that has migrated from the disk space and has no connection by diskal tissue to the disk of origin[ ]20 [ ]21 [ ]42 Sequestration refers to loss of continuity with disk tissue still present in the intervertebral disk space The term migration has a broader meaning indicating displacement of disk material away from the edge of the rent in the outer anulus either in the central spinal canal at the disk level or above or below the disk level This difference is illustrated in Figure 11 The terms communicating and noncommunicating derive from a different perspective and are mostly used in the context of intradiskal therapeutic injections They refer to the interruption of the periphery of the disk allowing fluid injected into the disk to leak into the spinal canal and reach displaced disk material[ ]20 [ ]51 The terms contained and uncontained are unfamiliar to most radiologists in a contained herniation the displaced disk material is still covered by a few intact but distended outer anular fibers or by a capsule formed by outer anular fibers and the adherent posterior longitudinal ligament

Figure 11 Various types of posterior central herniations A Small subligamentous herniation (protrusion) without significant disk material migration B Subligamentous herniation with downward migration of disk material under the PLLC C Sub-ligamentous herniation with downward migration of disk material and sequestered fragment (arrow)

The terms subligamentous and extraligamentous (or transligamentous) refer to the position of the displaced disk material with respect to the posterior longitudinal ligament The anatomy of the posterior longitudinal ligament has been recently revised[ ]73 [ ]89 It is a membranous structure that has multiple components a deep layer attached to disks and vertebral bodies a superficial layer attached to the dura by fibrous tissue (Hoffmanns

ligament) and lateral extensions known as the lateral membranes or peridural membranes (Fig 12) (Figure Not Available) It should probably be referred to as the posterior longitudinal ligament complex (PLLC) It actually divides the epidural space into the perithecal space and the anterior epidural space where displaced disk material can be entrapped (Fig 13) A potential space allowing accumulation of displaced disk material has also been detected between the outer anular fibers and the deep fibers of the PLLC on the posterior central aspect of the disk[ ]63 Posterior midline herniations seldom rupture the PLLC and are generally subligamentous The lateral membranes are less resistant and transligamentous herniations are usually the result of posterior off-center herniations or posterolateral herniations

Figure 12 (Figure Not Available) The PLLC is portrayed here in relation to various types of subligamentous disk displacement At the disk level posteriorly displaced disk material frequently occupies the midline Below and above the disk an anterior epidural space (AES) exists between the PLLC and the posterior aspect of the vertebral bodies In this space disk fragment motion across the midline is curtailed by a sagittal midline septum (dashed line) A delicate translucent membrane (shown only on left side of drawing) is stretched between the free edge of the deep layer of the posterior longitudinal ligament and the lateral spinal canal (From Schellinger D Manz HJ Vidic B et al Disk fragment migration Radiology 175831-836 1990 with permission)

Figure 13 Relationship of typical posterior disk herniations with the PLLC A Midline sagittal section unless very large a posterior midline herniation usually remains entrapped underneath the deep layer of the PLL C and sometimes a few intact outer anulus fibers joining with the PLL C to form a capsule The deep layer of the PLL C (arrow) also attaches to the posterior aspect of the vertebral body so that no potential space is present underneath B Sagittal para-central section the PLL C extends laterally at the disk level (arrowhead) but above and below the disk an anterior epidural space (as) where disk fragments are frequently entrapped is present between the lateral (peridural) membranes and the posterior aspect of the vertebral bodies

Volume of Herniated Material

Quantifying the herniated disk material by measuring in millimeters its greatest diameter or by evaluating its cross-sectional area in square millimeters is rarely done The resulting figures could be misleading without relating this measurement to the size of the spinal canal and the exact location of the lesion[ ]88 A purely qualitative and subjective statement that a mild moderate or severe herniation is present however does not give the person reading the imaging report any indication as to the potential of the lesion to cause significant compression of the dural sac or individual exiting nerve roots A reasonably precise scheme has been proposed in 1995 by the Nomenclature Committee of the North American Spine Society[ ]20 Measurements are taken from an axial CT or MR imaging section at the site of most severe compromise canal compromise of less than 25 at that section is qualified as mild 25 to 75 is moderate 76 to 90 is moderately severe and greater than 90 is severe It is understood that such characterizations describe only the cross-sectional area at one level and do not account for the total volume of displaced material displacement of neural tissue or clinical significance The usefulness of having four categories is questionable and can likely generate poor interobserver or intraobserver agreement especially in situations where the central spinal canal is relatively narrow Bonnevilles scheme[ ]9 [ ]10 [ ]11 should generate greater reliability (Fig 14) (Figure Not Available) Separation of the cross-sectional area in three thirds can be applied to both the central spinal canal and the foramina It can be agreed by way of convention that the terms mild moderate and severe lumen compromise by a disk herniation designate extension of the displaced disk material in the anterior middle or posterior third of the central canal or foramen depending on the specified location of the herniation

Figure 14 (Figure Not Available) The size of the herniation in the horizontal plane is assessed and designated by the numbers 1 2 or 3 by establishing its extension in the anterior middle or posterior third of the spinal canal (From Bonneville JF Plaidoyer pour une classification par limage des hernies discales lombaires la carte-image Rev Imag Med 2557-560 1990 with permission)

Location of Herniated Material

Bonneville[ ]9 [ ]10 [ ]11 has also proposed an interesting and simple alpha-numerical system to classify according to their location the position of disk fragments that have migrated in the horizontal or sagittal plane (Figs 15 (Figure Not Available) and 16) (Figure Not Available) Using more precise anatomic boundaries unfortunately more familiar to surgeons than radiologists Wiltse et al[ ]88 have proposed another system which has been supported by the North American Spine Society[ ]20 [ ]21 Anatomic zones and levels are defined using the following anatomic landmarks medial edge of the articular facets medial lateral upper and lower border of the pedicles and coronal plane at the disk center On the horizontal plane (Fig 17) (Figure Not Available) these landmarks determine the bounderies of the central zone the subarticular zone the foraminal zone the extraforaminal zone and the anterior zone (anterior to the coronal plane at the center of the disk) In the sagittal plane they determine the boundaries of the diskal level the infrapedicular level the pedicular level and the suprapedicular level (Figs 18 (Figure

Not Available) and 19) (Figure Not Available) Radiologists interpreting axial CT or MR images may find it difficult to use the medial edge of the facets as the landmark that separates the central zone from the subarticular zone because the superior articular facets are generally not included in axial sections at the disk level The alternative is to use the expression posterolateral to designate collectively all posterior herniations that are not midline but do not extend into a foramen as was proposed by Bonneville[ ]9 [ ]10 [ ]11

Figure 15 (Figure Not Available) In the horizontal plane herniations are labeled midline (a) posterolateral (b) foraminal (c) and extra-foraminal (d) (From Bonneville JF Plaidoyer pour une classification par limage des hernies discales lombaires la carte-image Rev Imag Med 2557-560 1990 with permission)

Figure 16 (Figure Not Available) In the craniocaudal direction disk migration is labeled +1 +2 +3 or -1 -2 -3 by referring to the height of a vertebral body divided in thirds (From Bonneville JF Plaidoyer pour une classification par limage des hernies discales lombaires la carte-image Rev Imag Med 2557-560 1990 with permission)

Figure 17 (Figure Not Available) The anatomic zones identified on axial images The anterior zone (not shown) is delineated from the extraforaminal zone by an imaginary coronal line in the center of the vertebral body (From Wiltse LL Berger PE McCulloch JA A system for reporting the size and location of lesions in the spine Spine 221534-1537 1997 with permission)

Figure 18 (Figure Not Available) The anatomical levels identified on craniocaudal images (From Wiltse LL Berger PE McCulloch AJ A system for reporting the size and location of lesions in the spine Spine 221534-1537 1997 with permission)

Figure 19 (Figure Not Available) Coronal view of the main zones and levels (From Wiltse LL Berger PE McCulloch JA A system for reporting the size and location of lesions in the spine Spine 221534-1537 1997 with permission)

Composition of Herniated Material

Displaced disk material may consist of glycosaminoglycans type 1 or 2 collagen end plate cartilage and bone fragments avulsed from the ring epiphysis A reactive inflammatory reaction usually results in edematous tissue followed by granulation tissue which may undergo calcification (Fig 20) Necrotic and partially resorbed displaced disk material sometimes produces a large fluid-filled pouch distinguishable from the common high-intensity zone because of its size (Fig 21) or a gas-filled cavity generally in continuity with gas in the intervertebral space (Fig 22) [ ]42 These characteristics may be meaningful if intradiskal injection therapy is considered In imaging reports herniations exhibiting calcium deposits and those exhibiting replacement of disk material by gas or a relatively large fluid collection can be qualified as chronic herniations

Figure 20 A CT scan demonstration of a small posterior central L4-L5 calcified subligamentous herniation The resistant deep layer of the PLLC restrains displacement of the disk material in the posterior central direction and does not allow a detectable distortion of the disk contour In this particular case the presence of the calcification is actually the only evidence that a posterior midline anular tear and a small subligamentous herniation are present B Posterior right central and sub-articular L5-S1 calcified disk herniation in same patient Posterolateral herniations are generally more conspicuous than posterior midline herniations because the deep layer of the PLLC gets thinner away from the midline

Figure 21 Posterior central midline L4-L5 herniation in a 52-year-old man demonstrated on a T2-weighted midline MR sagittal section There is intervertebral space narrowing with loss of normal central disk signal

intensity while the herniated disk material demonstrates high signal intensity consistent with a predominantly fluid consistency

Figure 22 CT scan demonstration in a 51-year-old woman of a left posterolateral L5-S1 disk hernation consisting essentially in a gas-filled pouch (white arrow) Gas is also present in the central portion of the intervertebral disk space (black arrow)

DIAGNOSTIC IMAGING AND CHARACTERIZATION OF A HERNIATED LUMBAR DISK

Assessing the validity of the currently used imaging procedures to diagnose a herniated lumbar disk is not an easy endeavor The validity of a measurement is the extent to which it corresponds to the true biologic value or some accepted gold standard[ ]40 With the exception of postmortem studies evaluation of the pathoanatomy by the surgeon in the operating room has always been considered the gold standard but this does not constitute an ideal situation Inspection of the disk through a small laminectomy incision to determine for instance if nuclear fragments lie within or outside the anular fibers may not be very reliable Also unbiased intraoperative determination of a normal degenerated or herniated disk in a patient with sciatica may also be difficult[ ]86 Because the validity of diskography has been previously established by postmortem studies and surgical correlations[ ]48 it is sometimes used as a gold standard in situations where no surgery has been performed

Conventional Radiographs

Lumbar disk herniations can exceptionally be diagnosed directly on good quality lateral projections because the x-ray attenuation is slightly greater in displaced disk material than in epidural fat Occasionally a calcified rim outlines the displaced disk fragment

(Fig 23) In most situations however narrowing of an intervertebral disk space in the absence of other evidence of chronic diskopathy is the only detectable sign suggesting the presence of a disk herniation To my knowledge the sensitivity and specificity of this sign has never been assessed The accepted rule of thumb is that the height of a given lumbar intervertebral disk space should always be slightly greater than the height of the above located interspace This rule does not apply to the transition disk immediately above the sacrum (usually L5-S1) The specificity of this sign is probably quite high but a few false-positives are seen especially at the L4-L5 level because of minor congenital hypoplasia The presence of posterior or foraminal vertebral body osteophytes associated or not with disk space narrowing is a definite sign of a chronic disk herniation

Figure 23 A Chronic left L3-L4 extraforaminal disk hernation in a 54-year-old man suspected on an AP radiograph demonstrating a calcified shell on the left side of the intervertebral disk space (white arrow) B Axial CT scan section confirming the diagnosis of a chronic extraforaminal L3-L4 herniation

Myelography

Myelography is essentially an exploration of the subarachnoid space Disk herniations are demonstrated only indirectly because they can cause thecal sac deformity and individual nerve root sleeve filling defects (Fig 24) Of all the special imaging procedures

myelography is the only one that allows upright projections with full weight bearing It is not unusual to demonstrate in this way small posterior central or posterolateral herniations that are undetectable on CT sections Interestingly the overall sensitivity of myelography to detect disk herniations has been found to be higher than that of CT whereas its specificity has been found to be lower[ ]74 In comparison with standard CT examination which usually includes only the three or four lower lumbar disks myelography easily allows coverage of the entire lumbar area and assessment of the intrathecal structures (cauda equina and conus medullaris) Far lateral foraminal herniations extraforaminal herniations and anterior herniations however are not detected The sensitivity for detection of posterior central L5-S1 herniations is also relatively poor because of the greater distance between the thecal sac and the posterior aspect of this particular disk

Figure 24 L5-S1 disk herniation in a 25-year-old man detected by indirect signs using lumbosacral myelography A Upright oblique projections showing a filling defect of the left S1 root sleeve (white arrow) suggesting significant nerve root compression by a left posterolateral disk hernation The right S1 root sleeve fills normally with contrast (black arrow) B Subtle compression of the anterior wall of the dural sac by displaced disk material (small arrows) demonstrated on upright lateral projection This sign is usually absent in the presence of a large amount of fat and venous structures in the anterior epidural compartment

CT

The sensitivity of CT to diagnose a herniation of the nucleus pulposus at the L5-S1 interspace is greater than that of myelography if images in the exact plane of the disk can be obtained[ ]23 [ ]39 Otherwise the superiority of plain CT over myelography to demonstrate disk herniations has not been established but CT has the distinct advantage of being

noninvasive and provides direct anatomic information[ ]23 Large herniations are easily detected but as explained previously the distinction between protrusions and extrusions is often difficult without sagittal reconstructions CT essentially allows an assessment of the contour of the disk The diagnosis of very small herniations in the absence of direct or indirect evidence of a radial tear is hazardous and associated with a high percentage of false-positives and false-negatives[ ]52 The diagnosis of moderate and large size herniations in different directions is usually possible but anterior herniations are rarely diagnosed not because they are not detectable but because observers pay little attention to the anterior contour of the disk (Fig 25) Because the PLLC cannot usually be identified the distinction of subligamentous from transligamentous herniation can only be suggested in most cases by the size of the herniated material A definite diagnosis of sequestration is rarely possible Calcifications within the displaced material are readily seen but may be difficult at times to differentiate from an accompanying osteophyte or an avulsed bone fragment from the vertebral body ring epiphysis (Fig 26) The presence of gas in the herniated material is easily detected

Figure 25 Anterior L4-L5 herniation demonstrated by CT scan in a 51-year-old woman with chronic low back pain Although sometimes quite conspicuous such herniations are rarely reported because observers pay little attention to the anterior contour of the disk

Figure 26 CT scan demonstration of a posterior right central L4-L5 disk herniation in a 38-year-old woman with avulsion of a bone fragment from the ring epiphysis and adjacent part of the superior L5 end plate Reactive osteosclerosis is seen around the vertebral body defect (arrows) suggesting a chronic lesion

CT Myelography

This association combines the advantages of both imaging modalities The fact that its accuracy has been reported as being less[ ]22 [ ]32 higher[ ]1 [ ]6 or equivalent[ ]82 to MR imaging is a reflection of the differences in technologic advancement and pathologic nomenclature that hamper valid comparisons between different studies

MR Imaging

Most reported studies establish MR imaging as the first choice modality to diagnose a herniated lumbar disk[ ]5 [ ]22 [ ]32 [ ]46 The associated intravenous injection of a paramagnetic agent has been found useful to demonstrate some anatomic features of disk disease in patients with no previous lumbar disk surgery[ ]56 [ ]68 [ ]90 MR imaging provides a better assessment of disk morphology than CT or CT myelography because sagittal sections are routinely obtained Assessment of foraminal involvement by displaced disk material is more accurate (Fig 27) and anterior disk herniations can be detected more easily than with CT or CT myelography If one is looking specifically for herniated lumbar disks associated with nerve root compression however it has been demonstrated that CT is equally accurate[ ]82 Alterations of the central or peripheral disk signal intensity on T2-weighted images are seen in most disks afflicted with an anular tear[ ]48 and alert the observer to scrutinize the disk contour in search for local modifications indicative of a herniation Because the signal of the displaced disk material is usually very similar to that of the outer anulus PLLC and vertebral body cortical bone small herniations are generally more conspicuous on axial CT sections than on corresponding axial MR imaging sections Gas and calcium deposits within the displaced fragment cannot usually

be detected but associated vertebral body bone marrow changes are typically seen and are helpful in differentiating acute from chronic processes[ ]57 The occasional presence of a high-intensity zone in the herniated material with an occasionally enhancing border after contrast injection is probably caused by a mixture of displaced nuclear material acute and subacute inflammatory tissue and neovascularized reactive tissue[ ]4 [ ]48 [ ]72 Contradictory reports have been published regarding the accuracy of MR imaging to differentiate subligamentous from transligamentous herniations[ ]26 [ ]38 [ ]73 [ ]76 Understanding the anatomy of the PLLC is helpful to make the distinction (Fig 28) (Figure Not Available) Masaryk et al[ ]46 have suggested that MR imaging is accurate to distinguish sequestered disks from other forms of lumbar disk herniations but most observers find this distinction difficult to establish[ ]42

Figure 27 A Left L4-L5 foraminal herniation well seen on an intermediate-weighted left parasagittal MR section (arrow) in a 47-year-old man B The lesion is much less obvious on intermediate-weighted (left) and T2-weighted (right) axial sections and was in fact more conspicuous on the corresponding CT scan section

Figure 28 (Figure Not Available) A Subligamentous disk herniation Left T1-weighted image demonstrating displaced disk material with a smooth outline imposed by the demarcation of the anterior epidural space (AES) by the lateral membrane of the PLLC Right Correlative drawing B Transligamentous disk herniation Left T1-weighted image of a large disk herniation (cervical in this case) which has ruptured through the posterior confines of the AES Penetration of the right lateral membrane can be observed (arrow) and the disk fragment contour is serrated Right Correlative drawing (From Schellinger D Manz HJ Vidic B et al Disk fragment migration Radiology 175831-836 1990 with permission)

Diskography and CT Diskography

During 30 years (1950 to 1980) when myelography was the only available imaging technique to demonstrate lumbar disk herniations diskography was an invasive but efficient way to demonstrate posterior central L5-S1 herniations and other large herniations (other than posterior central and paramedial) that could not be detected by myelography[ ]50 These herniations are now usually well demonstrated by CT and MR imaging Comparing the accuracy of five imaging modalities (excluding MR imaging) for the diagnosis of lumbar disk herniation Jackson et al[ ]31 found that CT diskography (Fig 29) was the most accurate test (87) compared with 77 for CT myelography 74 for CT 70 for myelography 64 for pain reproduction during diskography and 58 for diskography without CT Disk injection reproduced the patients clinical pain pattern in only 36 of herniated disks This clinical test isolated from the images had high specificity (89) but low sensitivity (43) for the diagnosis of disk herniation The reported low sensitivity of diskography images (unassociated with CT) to diagnose disk herniation is to be expected the purpose of the intradiskal injection being primarily the demonstration of an anular tear the contrast leaking through the tear only occasionally delineates an extruded fragment When a disk herniation has been diagnosed by other imaging modalities diskography allows to determine if the herniation is contained or noncontained (Figs 30 and 31) this information may have clinical relevance[ ]62 It also allows to establish if the displaced disk material is communicating or not with the parent disk and establishes the likelihood that it is sequestered or not There always remains a possibility that the contrast injected under pressure may reach a disk fragment that is nevertheless sequestered by leaking through the associated anular tear CT diskography also allows assessment in most cases of the integrity of the PLLC[ ]89 The superior sensitivity of diskography over MR imaging to demonstrate anular tears has been well established[ ]27 [ ]44 [ ]48 [ ]64 [ ]77 [ ]91 [ ]94 The presence of a radial tear and the inflammatory reaction it creates may be symptomatic despite the absence of true disk herniation[ ]29 [ ]48 [ ]49 [ ]69

Figure 29 L4-L5 CT diskogram demonstrating a large left posterolateral radial anular tear associated with

a left foraminal and extraforaminal herniaton (same patient as in Figure 28) (Figure Not Available)

Figure 30 Contained posterior L4-L5 and L5-S1 disk herniations in a 57-year-old man demonstrated by diskography The L3-L4 disk is normal

Figure 31 Noncontained L4-L5 disk herniation in a 23-year-old woman Reflux of injected contrast is seen in the anterior epidural space above and below the disk space The L5-S1 disk also demonstrates incomplete anterior and posterior radial anular tears

SUMMARY

The absence of universal nomenclature standardization with respect to the definition of a disk herniation and its different categories especially regarding type and location is still a major problem that will only be overcome when major national or international scientific societies join efforts to support a particular scheme Meanwhile it is important to realize that the two models that are currently most used are based on a different perspective Trying to straddle the two by opposing for instance bulging disk and herniation is doomed to failure because this exercise defies formal logic MR imaging is currently the most accurate noninvasive imaging modality to diagnose a disk herniation and to determine its exact location The determination of some pathoanatomic characteristics of herniated disks (type and composition) may require the use of CT diskography or CT diskography

References

1 Albeck MJ Hilden J Kjaer L et al A controlled comparison of myelography computed tomography and magnetic resonance imaging in clinically suspected lumbar disc herniation Spine 20443-448 1995 Abstract 2 American Academy of Orthopedic Surgeons Glossary on Spinal Terminology Chicago American Academy of Orthopedic Surgeons 1981 3 Andersson GB Weinstein JN Disc herniation [editorial] Spine 211S 1996 Citation 4 Aprill C Bogduk N High-intensity zone A diagnostic sign of painful lumbar disc on magnetic resonance imaging Br J Radiol 65361-369 1992 Abstract 5 Birney TJ White JJ Jr Berens D et al Comparison of MRI and discography in the diagnosis of lumbar degenerative disc disease J Spinal Disord 5417-423 1992 Abstract 6 Bischoff RJ Rodriguez RP Gupta K et al A comparison of computed tomography-myelography magnetic resonance imaging and myelography in the diagnosis of herniated nucleus pulposus and spinal stenosis J Spinal Disord 6289-295 1993 Abstract 7 Bogduk N The innervation of the lumbar spine Spine 8286-293 1983 Abstract 8 Bogduk N Tynan W Wilson AS The nerve supply to the human lumbar intervertebral discs J Anat 13239-56 1981 Abstract 9 Bonneville JF La carte-image des hernies discales lombaires Rachis 2255-257 1990 10 Bonneville JF La topografia simbolica delle ernie discali lombari Riv Neuroradiol 5427-431 1992 11 Bonneville JF Plaidoyer pour une classification par limage des hernies discales lombaires La carte-image Rev Imag Med 2557-560 1990 12 Brant-Zawadzki M Jensen M Spinal nomenclature Spine 20388-390 1995 Abstract

13 Brant-Zawadzki MN Jensen MC Obuchowski N et al Interobserver and intraobserver variability in interpretation of lumbar disc abnormalities A comparison of two nomenclatures Spine 201257-1263 1995 Abstract 14 Breton G Is that a bulging disk a small herniation or a moderate protrusion [editorial] Can Assoc Radiol J 42318 1991 Citation 15 Czervionke LF Lumbar intervertebral disc disease Neuroimaging Clin North Am 3465-485 1993 16 Deyo RA Nonsurgical care of low back pain Neurosurg Clin North Am 2851-862 1991 17 Deyo RA Loeser JD Bigos SJ Herniated lumbar intervertebral disk Ann Intern Med 112598-603 1990 Abstract 18 Dorlands Illustrated Medical Dictionary ed 28 Philadelphia WB Saunders 1994 19 Fardon D Pinkerton S Balderston R et al Terms used for diagnosis by English speaking spine surgeons Spine 18274-277 1993 Citation 20 Fardon DF Herzog RJ Mink JH et al Nomenclature of Lumbar Disc Disorders Contemporary Concepts in Spine Care Rosemont IL North American Spine Society 1995 21 Fardon DF Herzog RJ Mink JH et al Nomenclature of lumbar disc disorders In Garfin S Vaccaro A (eds) Orthopedic Knowledge Update Spine Rosemont IL American Academy of Orthopedic Surgeons 1997 pp A3-A14 22 Forristall RM Marsh HO Pay NT Magnetic resonance imaging and contrast CT of the lumbar spine Comparison of diagnostic methods and correlation with surgical findings Spine 131049-1054 1988 Abstract 23 Fries JW Abodeely DA Vijungco JG et al Computed tomography of herniated and extruded nucleus pulposus J Comput Assist Tomogr 6874-887 1982 Abstract 24 Frymoyer JW Newberg A Pope MH et al Spine radiographs in patients with low-back pain An epidemiological study in men J Bone Joint Surg Am 661048-1055 1984 Abstract 25 Gospodarowicz M Benedet L Hutter RV et al History and international developments in cancer staging Cancer Prev Control 2262-268 1998 Abstract 26 Grenier N Greselle JF Vital JM et al Normal and disrupted lumbar longitudinal ligaments Correlative MR and anatomic study Radiology 171197-205 1989 Abstract 27 Gunzburg R Parkinson R Moore R et al A cadaveric study comparing discography magnetic resonance imaging histology and mechanical behavior of the human lumbar disc Spine 17417-426 1992 Abstract 28 Haughton VM Eldevik OP Magnaes B et al A prospective comparison of computed tomography and myelography in the diagnosis of herniated lumbar disks Radiology 142103-110 1982 Abstract

29 Haughton VM Lim TH An H Intervertebral disk appearance correlated with stiffness of lumbar spinal motion segments AJNR Am J Neuroradiol 201161-1165 1999 Abstract 30 Herzog RJ The radiologic assessment for a lumbar disc herniation Spine 2119S-38S 1996 Abstract 31 Jackson RP Becker GJ Jacobs RR et al The neuroradiographic diagnosis of lumbar herniated nucleus pulposus I A comparison of computed tomography (CT) myelography CT-myelography discography and CT-discography Spine 141356-1361 1989 Abstract 32 Jackson RP Cain JE Jr Jacobs RR et al The neuroradiographic diagnosis of lumbar herniated nucleus pulposus II A comparison of computed tomography (CT) myelography CT-myelography and magnetic resonance imaging Spine 141362-1367 1989 Abstract 33 Jarvik JG Haynor DR Koepsell TD et al Interreader reliability for a new classification of lumbar disk disease Acad Radiol 3537-544 1996 Abstract 34 Jensen MC Brant-Zawadzki MN Obuchowski N et al Magnetic resonance imaging of the lumbar spine in people without back pain N Engl J Med 33169-73 1994 Abstract 35 Kent DL Haynor DR Larson EB et al Diagnosis of lumbar spinal stenosis in adults A meta-analysis of the accuracy of CT MR and myelography AJR Am J Roentgenol 1581135-1144 1992 Abstract 36 Kieffer SA Sherry RG Wellenstein DE et al Bulging lumbar intervertebral disk Myelographic differentiation from herniated disk with nerve root compression AJR Am J Roentgenol 138709-716 1982 Abstract 37 Kieffer SA Stadlan EM Mohandas A et al Discographic-anatomical correlation of developmental changes with age in the intervertebral disc Acta Radiol 9733-739 1969 38 Kim KY Kim YT Lee CS et al MRI classification of lumbar herniated intervertebral disc Orthopedics 15493-497 1992 Abstract 39 Kornberg M Rechtine GR Dupuy TE Computed tomography in the diagnosis of a herniated disk at the L5-S1 level Spine 9433-436 1984 Abstract 40 Kramer MS Clinical Epidemiology and Biostatistics New York Springer-Verlag 1988 41 Landis JR Koch GG The measurement of observer agreement agreement for categorical data Biometrics 33159-174 1977 Abstract 42 Laredo JD Bossard P Vuillemin-Bodaghi Formes anatomo-radiologiques des hernies discales In Morvan G Deburge A Bard H et al (eds) Le Rachis Lombaire Degeneratif Montpellier Sauramps Medical 1998 pp 37-49 43 Lee SH Coleman PE Hahn FJ Magnetic resonance imaging of degenerative disk disease of the spine Radiol Clin North Am 26949-964 1988 Abstract 44 Linson MA Crowe CH Comparison of magnetic resonance imaging and lumbar discography in the diagnosis of disc degeneration Clin Orthop 160-163 1990

45 Marchand F Ahmed AM Investigation of the laminate structure of lumbar disc anulus fibrosus Spine 15402-410 1990 Abstract 46 Masaryk TJ Ross JS Modic MT et al High-resolution MR imaging of sequestered lumbar intervertebral disks AJR Am J Roentgenol 1501155-1162 1988 Abstract 47 Milette PC The proper terminology for reporting lumbar intervertebral disk disorders AJNR Am J Neuroradiol 181859-1866 1997 Citation 48 Milette PC Fontaine S Lepanto L et al Differentiating lumbar disc protrusions disk bulges and discs with normal contour but abnormal signal intensity Magnetic resonance imaging with discographic correlations Spine 2444-53 1999 Abstract 49 Milette PC Fontaine S Lepanto L et al Radiating pain to the lower extremities caused by lumbar disk rupture without spinal nerve root involvement AJNR Am J Neuroradiol 161605-1613 1995 Abstract 50 Milette PC Melancon D A reappraisal of lumbar discography Can Assoc Radiol J 33176-182 1982 51 Milette PC Melancon D Dupuis PR et al A simplified terminology for abnormalities of the lumbar disk Can Assoc Radiol J 42319-325 1991 Abstract 52 Milette PC Raymond J Fontaine S Comparison of high-resolution computed tomography with discography in the evaluation of lumbar disc herniations Spine 15525-533 1990 Abstract 53 Mink JH Deutsch AL Goldstein TB et al Spinal imaging and intervention 1998 Phys Med Rehabil Clin North Am 9343-380 1998 54 Mixter WJ Barr JS Rupture of the intervertebral disc with involvement of the spinal canal N Engl J Med 211210-234 1934 55 Modic MT Masaryk TJ Ross JS et al Imaging of degenerative disk disease Radiology 168177-186 1988 Citation 56 Modic MT Ross JS Obuchowski NA et al Contrast-enhanced MR imaging in acute lumbar radiculopathy A pilot study of the natural history Radiology 195429-435 1995 Abstract 57 Modic MT Steinberg PM Ross JS et al Degenerative disk disease Assessment of changes in vertebral body marrow with MR imaging Radiology 166193-199 1988 58 Morvan G Mathieu P Les stenoses laterales In Morvan G Deburge A Bard H et al (eds) Le Rachis Lombaire Degeneratif Montpellier Sauramps Medical 1998 pp 315-324 59 Murray RO Skeletal trauma Regional In Sutton D (ed) Textbook of Radiology and Imaging ed 3 New York Churchill Livingstone 1980 pp 210-231 60 Nachemson A Lumbar disc herniation Conclusions Acta Orthop Scand 64(suppl 251)49 1993 Citation

61 Nathan H Osteophytes of the vertebral column An anatomical study of their development according to age race and sex with consideration as to their etiology and significance J Bone Joint Surg Am 44243-268 1962 62 Nygaard OP Mellgren SI Osterud B The inflammatory properties of contained and noncontained lumbar disc herniations Spine 222584-2488 1997 Abstract 63 Ohshima H Hirano N Osada R et al Morphologic variation of lumbar posterior longitudinal ligament and the modality of disc herniation Spine 182408-2411 1993 Abstract 64 Osti OL Fraser RD MRI and discography of annular tears and intervertebral disc degeneration A prospective clinical comparison J Bone Joint Surg Br 74431-435 1992 Abstract 65 Palmgren T Gronblad M Virri J et al Immunohistochemical demonstration of sensory and autonomic nerve terminals in herniated lumbar disc tissue Spine 211301-1306 1996 Abstract 66 Resnick D Niwayama G Degenerative disease of the spine In Resnick D (ed) Diagnosis of Bone and Joint Disorders ed 3 Philadelphia WB Saunders 1995 pp 1372-1462 67 Resnick D Niwayama G Intravertebral disk herniations Cartilaginous (Schmorls) nodes Radiology 12657-65 1978 Abstract 68 Ross JS Modic MT Masaryk TJ Tears of the anulus fibrosus Assessment with Gd-DTPA-enhanced MR imaging AJR Am J Roentgenol 154159-162 1990 Abstract 69 Saal JS The role of inflammation in lumbar pain Spine 201821-1827 1995 Abstract 70 Sachs BL Vanharanta H Spivey MA et al Dallas discogram description A new classification of CTdiscography in low-back disorders Spine 12287-294 1987 Abstract 71 Sauser DD Goldman AB Kaye JJ Discogenic vertebral sclerosis J Can Assoc Radiol 2944-50 1978 Abstract 72 Schellhas KP Pollei SR Gundry CR et al Lumbar disc high-intensity zone Correlation of magnetic resonance imaging and discography Spine 2179-86 1996 Abstract 73 Schellinger D Manz HJ Vidic B et al Disk fragment migration Radiology 175831-836 1990 Abstract 74 Schipper J Kardaun JW Braakman R et al Lumbar disk herniation Diagnosis with CT or myelography Radiology 165227-231 1987 Abstract 75 Schmorl G Junghanns H The Human Spine in Health and Disease ed 2 New York Grune and Stratton 1971 76 Silverman CS Lenchik L Shimkin PM et al The value of MR in differentiating subligamentous from supraligamentous lumbar disk herniations AJNR Am J Neuroradiol 16571-579 1995 Abstract 77 Simmons JW Emery SF McMillin JN et al Awake discography A comparison study with magnetic

resonance imaging Spine 16S216-221 1991 Abstract 78 Smyth MJ Wright V Sciatica and the intervertebral disc J Bone Joint Surg Am 401401-1418 1958 79 Taveras JM Radiologic aspects of low back pain and sciatic syndromes [editorial] AJNR Am J Neuroradiol 9351-358 1989 80 Tehranzadeh J Discography 2000 Radiol Clin North Am 36463-495 1998 Full Text 81 Thelander U Fagerlund M Friberg S et al Describing the size of lumbar disc herniations using computed tomography A comparison of different size index calculations and their relation to sciatica Spine 191979-1984 1994 Abstract 82 Thornbury JR Fryback DG Turski PA et al Disk-caused nerve compression in patients with acute low-back pain Diagnosis with MR CT myelography and plain CT Radiology 186731-738 1993 Abstract 83 Twomey L Taylor J Age changes in lumbar intervertebral discs Acta Orthop Scand 56496-499 1985 Abstract 84 Twomey LT Taylor JR Age changes in lumbar vertebrae and intervertebral discs Clin Orthop 22497-104 1987 85 Williams AL CT diagnosis of degenerative disc disease The bulging annulus Radiol Clin North Am 21289-300 1983 Abstract 86 Williams AL Haughton VM Meyer GA et al Computed tomographic appearance of the bulging annulus Radiology 142403-408 1982 Abstract 87 Williams AL Haughton VM Syvertsen A Computed tomography in the diagnosis of herniated nucleus pulposus Radiology 13595-99 1980 Abstract 88 Wiltse LL Berger PE McCulloch JA A system for reporting the size and location of lesions in the spine Spine 221534-1537 1997 Abstract 89 Wiltse LL Fonseca AS Amster J et al Relationship of the dura Hofmanns ligaments Batsons plexus and a fibrovascular membrane lying on the posterior surface of the vertebral bodies and attaching to the deep layer of the posterior longitudinal ligament An anatomical radiologic and clinical study Spine 181030-1043 1993 Abstract 90 Yamashita K Hiroshima K Kurata A Gadolinium-DTPA-enhanced magnetic resonance imaging of a sequestered lumbar intervertebral disc and its correlation with pathologic findings Spine 19479-482 1994 Abstract 91 Yu SW Haughton VM Sether LA et al Comparison of MR and diskography in detecting radial tears of the anulus A postmortem study AJNR Am J Neuroradiol 101077-1081 1989 Abstract 92 Yu SW Sether LA Ho PS et al Tears of the anulus fibrosus Correlation between MR and pathologic findings in cadavers AJNR Am J Neuroradiol 9367-370 1988 Abstract

93 Yussen PS Swartz JD The acute lumbar disc herniation Imaging diagnosis Semin Ultrasound CT MR 14389-398 1993 Abstract 94 Zucherman J Derby R Hsu K et al Normal magnetic resonance imaging with abnormal discography Spine 131355-1359 1988 Abstract

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  • CLASSIFICATION DIAGNOSTIC IMAGING AND IMAGING CHARACTERIZATION OF A LUMBAR HERNIATED DISK
    • IMAGING OF LOW BACK PAIN I
      • CLASSIFICATION DIAGNOSTIC IMAGING AND IMAGING CHARACTERIZATION OF A LUMBAR HERNIATED DISK
        • DEFINITION OF A DISK HERNIATION
        • CLASSIFICATION OF A HERNIATED LUMBAR DISK
          • Main Categories of Noninfectious Disk Abnormalities
          • Further Qualifying the Displaced Disk Material Beyond the Disk Space
            • DIAGNOSTIC IMAGING AND CHARACTERIZATION OF A HERNIATED LUMBAR DISK
              • Conventional Radiographs
              • Myelography
              • CT
              • CT Myelography
              • MR Imaging
              • Diskography and CT Diskography
                • SUMMARY
                  • References
Page 13: CLASSIFICATION, DIAGNOSTIC IMAGING, AND IMAGING ... · PDF fileclassification, diagnostic imaging, and imaging characterization of a lumbar herniated disk ... classification, diagnostic

Figure 9 A bulging disk aspect often conceals a posterior central herniation A Complete rupture of the outer anular fibers allowing nuclear material to escape and peel off the posterior longitudinal ligament (and sometimes a few intact peripheral anular fibers) from the torn disk creating a detectable focal or asymmetric extension of the disk margin beyond the interspace which qualifies as a protrusion B With more gelatinous nuclear material escaping underneath the rigid posterior longitudinal ligament the focal bulge is no longer detectable as its radius increases and if the tear occurs in the posterior midline or para-medial direction the aspect mimics symmetric disk extension beyond the interspace C Since in most cases only the outline of a diffusely hypointense disk is perceived on MR images this creates the illusion of circumferential disk bulging on axial sections D The real nature of a bulging disk of this type may be suspected by scrutinizing the sagittal sections and appreciating that unless one is dealing with a chronically degenerated scarred disk the bulge is not symmetric but limited to the posterior aspect of the disk

TABLE 1 -- GENERAL

CLASSIFICATION OF DISK LESIONS Normal (excluding aging changes)

Congenitaldevelopmental variants

Inflammationinfection

Neoplasia

Degenerativetraumatic

Degeneration

Anular tear

Herniation Protrusion

Extrusion

Degeneration Spondylosis deformans

Intervertebral osteochondrosis

Further Qualifying the Displaced Disk Material Beyond the Disk Space

Regardless of the basic system that is used the type of herniation should be assessed The volume and location of the displaced disk material beyond the normal peripheral margin of the intervertebral space also need to be specified In certain cases it is also possible to determine the composition of this material For the sake of simplicity the term herniation is used consistently in the remainder of this article to refer to all displaced disk material but what is discussed can also be applied to protrusions and extrusions if one wants to use the morphologic nomenclature

Type of Herniation

Upward or downward migration of nuclear material may occur through a break in a vertebral body end plate creating an intravertebral herniation sometimes referred to as an intraspongy herniation or a Schmorls node[ ]67 (Fig 10) Although a herniation occurring in any horizontal direction is likely to cause symptoms because of the presence of pain-sensitive nerve endings in the outer anulus[ ]7 [ ]8 [ ]65 herniations occurring in a posterior or posterolateral direction deserve special consideration because of the added possibility of dural sac or individual nerve root compression

Figure 10 Various types of intravertebral herniations (Schmorls nodes) A Intravertebral herniation through the inferior end plate of the L3 vertebral body demonstrated by diskography in a 35-year-old man suffering from chronic low back pain The patients typical pain was reproduced during injection and the lesion was considered responsible for the patients symptoms B T2-weighted sagittal section demonstrating an intravertebral herniation through the inferior end plate of the L4 vertebral body in a 24-year-old woman presenting with chronic low back pain The high signal intensity of the lesion associated with the loss of normal central signal intensity of the parent disk suggests that the lesion is a bona fide acquired intraspongy herniation and not just a developmental defect C T2-weighted sagittal section demonstrating an intravertebral herniation through the inferior end plate of the L3 vertebral body (arrow) Because both the herniation and the parent disk show normal signal intensity the abnormality was

considered a probably asymptomatic developmental defect

Other characteristics of disk herniations have become relevant with the development of new therapeutic possibilities (eg chemonucleolysis and percutaneous diskectomy) The term sequestration is confusing and has often been used to indicate displacement of disk material away from the parent disk The term sequestered disk should be used restrictedly to designate a fragment of diskal tissue that has migrated from the disk space and has no connection by diskal tissue to the disk of origin[ ]20 [ ]21 [ ]42 Sequestration refers to loss of continuity with disk tissue still present in the intervertebral disk space The term migration has a broader meaning indicating displacement of disk material away from the edge of the rent in the outer anulus either in the central spinal canal at the disk level or above or below the disk level This difference is illustrated in Figure 11 The terms communicating and noncommunicating derive from a different perspective and are mostly used in the context of intradiskal therapeutic injections They refer to the interruption of the periphery of the disk allowing fluid injected into the disk to leak into the spinal canal and reach displaced disk material[ ]20 [ ]51 The terms contained and uncontained are unfamiliar to most radiologists in a contained herniation the displaced disk material is still covered by a few intact but distended outer anular fibers or by a capsule formed by outer anular fibers and the adherent posterior longitudinal ligament

Figure 11 Various types of posterior central herniations A Small subligamentous herniation (protrusion) without significant disk material migration B Subligamentous herniation with downward migration of disk material under the PLLC C Sub-ligamentous herniation with downward migration of disk material and sequestered fragment (arrow)

The terms subligamentous and extraligamentous (or transligamentous) refer to the position of the displaced disk material with respect to the posterior longitudinal ligament The anatomy of the posterior longitudinal ligament has been recently revised[ ]73 [ ]89 It is a membranous structure that has multiple components a deep layer attached to disks and vertebral bodies a superficial layer attached to the dura by fibrous tissue (Hoffmanns

ligament) and lateral extensions known as the lateral membranes or peridural membranes (Fig 12) (Figure Not Available) It should probably be referred to as the posterior longitudinal ligament complex (PLLC) It actually divides the epidural space into the perithecal space and the anterior epidural space where displaced disk material can be entrapped (Fig 13) A potential space allowing accumulation of displaced disk material has also been detected between the outer anular fibers and the deep fibers of the PLLC on the posterior central aspect of the disk[ ]63 Posterior midline herniations seldom rupture the PLLC and are generally subligamentous The lateral membranes are less resistant and transligamentous herniations are usually the result of posterior off-center herniations or posterolateral herniations

Figure 12 (Figure Not Available) The PLLC is portrayed here in relation to various types of subligamentous disk displacement At the disk level posteriorly displaced disk material frequently occupies the midline Below and above the disk an anterior epidural space (AES) exists between the PLLC and the posterior aspect of the vertebral bodies In this space disk fragment motion across the midline is curtailed by a sagittal midline septum (dashed line) A delicate translucent membrane (shown only on left side of drawing) is stretched between the free edge of the deep layer of the posterior longitudinal ligament and the lateral spinal canal (From Schellinger D Manz HJ Vidic B et al Disk fragment migration Radiology 175831-836 1990 with permission)

Figure 13 Relationship of typical posterior disk herniations with the PLLC A Midline sagittal section unless very large a posterior midline herniation usually remains entrapped underneath the deep layer of the PLL C and sometimes a few intact outer anulus fibers joining with the PLL C to form a capsule The deep layer of the PLL C (arrow) also attaches to the posterior aspect of the vertebral body so that no potential space is present underneath B Sagittal para-central section the PLL C extends laterally at the disk level (arrowhead) but above and below the disk an anterior epidural space (as) where disk fragments are frequently entrapped is present between the lateral (peridural) membranes and the posterior aspect of the vertebral bodies

Volume of Herniated Material

Quantifying the herniated disk material by measuring in millimeters its greatest diameter or by evaluating its cross-sectional area in square millimeters is rarely done The resulting figures could be misleading without relating this measurement to the size of the spinal canal and the exact location of the lesion[ ]88 A purely qualitative and subjective statement that a mild moderate or severe herniation is present however does not give the person reading the imaging report any indication as to the potential of the lesion to cause significant compression of the dural sac or individual exiting nerve roots A reasonably precise scheme has been proposed in 1995 by the Nomenclature Committee of the North American Spine Society[ ]20 Measurements are taken from an axial CT or MR imaging section at the site of most severe compromise canal compromise of less than 25 at that section is qualified as mild 25 to 75 is moderate 76 to 90 is moderately severe and greater than 90 is severe It is understood that such characterizations describe only the cross-sectional area at one level and do not account for the total volume of displaced material displacement of neural tissue or clinical significance The usefulness of having four categories is questionable and can likely generate poor interobserver or intraobserver agreement especially in situations where the central spinal canal is relatively narrow Bonnevilles scheme[ ]9 [ ]10 [ ]11 should generate greater reliability (Fig 14) (Figure Not Available) Separation of the cross-sectional area in three thirds can be applied to both the central spinal canal and the foramina It can be agreed by way of convention that the terms mild moderate and severe lumen compromise by a disk herniation designate extension of the displaced disk material in the anterior middle or posterior third of the central canal or foramen depending on the specified location of the herniation

Figure 14 (Figure Not Available) The size of the herniation in the horizontal plane is assessed and designated by the numbers 1 2 or 3 by establishing its extension in the anterior middle or posterior third of the spinal canal (From Bonneville JF Plaidoyer pour une classification par limage des hernies discales lombaires la carte-image Rev Imag Med 2557-560 1990 with permission)

Location of Herniated Material

Bonneville[ ]9 [ ]10 [ ]11 has also proposed an interesting and simple alpha-numerical system to classify according to their location the position of disk fragments that have migrated in the horizontal or sagittal plane (Figs 15 (Figure Not Available) and 16) (Figure Not Available) Using more precise anatomic boundaries unfortunately more familiar to surgeons than radiologists Wiltse et al[ ]88 have proposed another system which has been supported by the North American Spine Society[ ]20 [ ]21 Anatomic zones and levels are defined using the following anatomic landmarks medial edge of the articular facets medial lateral upper and lower border of the pedicles and coronal plane at the disk center On the horizontal plane (Fig 17) (Figure Not Available) these landmarks determine the bounderies of the central zone the subarticular zone the foraminal zone the extraforaminal zone and the anterior zone (anterior to the coronal plane at the center of the disk) In the sagittal plane they determine the boundaries of the diskal level the infrapedicular level the pedicular level and the suprapedicular level (Figs 18 (Figure

Not Available) and 19) (Figure Not Available) Radiologists interpreting axial CT or MR images may find it difficult to use the medial edge of the facets as the landmark that separates the central zone from the subarticular zone because the superior articular facets are generally not included in axial sections at the disk level The alternative is to use the expression posterolateral to designate collectively all posterior herniations that are not midline but do not extend into a foramen as was proposed by Bonneville[ ]9 [ ]10 [ ]11

Figure 15 (Figure Not Available) In the horizontal plane herniations are labeled midline (a) posterolateral (b) foraminal (c) and extra-foraminal (d) (From Bonneville JF Plaidoyer pour une classification par limage des hernies discales lombaires la carte-image Rev Imag Med 2557-560 1990 with permission)

Figure 16 (Figure Not Available) In the craniocaudal direction disk migration is labeled +1 +2 +3 or -1 -2 -3 by referring to the height of a vertebral body divided in thirds (From Bonneville JF Plaidoyer pour une classification par limage des hernies discales lombaires la carte-image Rev Imag Med 2557-560 1990 with permission)

Figure 17 (Figure Not Available) The anatomic zones identified on axial images The anterior zone (not shown) is delineated from the extraforaminal zone by an imaginary coronal line in the center of the vertebral body (From Wiltse LL Berger PE McCulloch JA A system for reporting the size and location of lesions in the spine Spine 221534-1537 1997 with permission)

Figure 18 (Figure Not Available) The anatomical levels identified on craniocaudal images (From Wiltse LL Berger PE McCulloch AJ A system for reporting the size and location of lesions in the spine Spine 221534-1537 1997 with permission)

Figure 19 (Figure Not Available) Coronal view of the main zones and levels (From Wiltse LL Berger PE McCulloch JA A system for reporting the size and location of lesions in the spine Spine 221534-1537 1997 with permission)

Composition of Herniated Material

Displaced disk material may consist of glycosaminoglycans type 1 or 2 collagen end plate cartilage and bone fragments avulsed from the ring epiphysis A reactive inflammatory reaction usually results in edematous tissue followed by granulation tissue which may undergo calcification (Fig 20) Necrotic and partially resorbed displaced disk material sometimes produces a large fluid-filled pouch distinguishable from the common high-intensity zone because of its size (Fig 21) or a gas-filled cavity generally in continuity with gas in the intervertebral space (Fig 22) [ ]42 These characteristics may be meaningful if intradiskal injection therapy is considered In imaging reports herniations exhibiting calcium deposits and those exhibiting replacement of disk material by gas or a relatively large fluid collection can be qualified as chronic herniations

Figure 20 A CT scan demonstration of a small posterior central L4-L5 calcified subligamentous herniation The resistant deep layer of the PLLC restrains displacement of the disk material in the posterior central direction and does not allow a detectable distortion of the disk contour In this particular case the presence of the calcification is actually the only evidence that a posterior midline anular tear and a small subligamentous herniation are present B Posterior right central and sub-articular L5-S1 calcified disk herniation in same patient Posterolateral herniations are generally more conspicuous than posterior midline herniations because the deep layer of the PLLC gets thinner away from the midline

Figure 21 Posterior central midline L4-L5 herniation in a 52-year-old man demonstrated on a T2-weighted midline MR sagittal section There is intervertebral space narrowing with loss of normal central disk signal

intensity while the herniated disk material demonstrates high signal intensity consistent with a predominantly fluid consistency

Figure 22 CT scan demonstration in a 51-year-old woman of a left posterolateral L5-S1 disk hernation consisting essentially in a gas-filled pouch (white arrow) Gas is also present in the central portion of the intervertebral disk space (black arrow)

DIAGNOSTIC IMAGING AND CHARACTERIZATION OF A HERNIATED LUMBAR DISK

Assessing the validity of the currently used imaging procedures to diagnose a herniated lumbar disk is not an easy endeavor The validity of a measurement is the extent to which it corresponds to the true biologic value or some accepted gold standard[ ]40 With the exception of postmortem studies evaluation of the pathoanatomy by the surgeon in the operating room has always been considered the gold standard but this does not constitute an ideal situation Inspection of the disk through a small laminectomy incision to determine for instance if nuclear fragments lie within or outside the anular fibers may not be very reliable Also unbiased intraoperative determination of a normal degenerated or herniated disk in a patient with sciatica may also be difficult[ ]86 Because the validity of diskography has been previously established by postmortem studies and surgical correlations[ ]48 it is sometimes used as a gold standard in situations where no surgery has been performed

Conventional Radiographs

Lumbar disk herniations can exceptionally be diagnosed directly on good quality lateral projections because the x-ray attenuation is slightly greater in displaced disk material than in epidural fat Occasionally a calcified rim outlines the displaced disk fragment

(Fig 23) In most situations however narrowing of an intervertebral disk space in the absence of other evidence of chronic diskopathy is the only detectable sign suggesting the presence of a disk herniation To my knowledge the sensitivity and specificity of this sign has never been assessed The accepted rule of thumb is that the height of a given lumbar intervertebral disk space should always be slightly greater than the height of the above located interspace This rule does not apply to the transition disk immediately above the sacrum (usually L5-S1) The specificity of this sign is probably quite high but a few false-positives are seen especially at the L4-L5 level because of minor congenital hypoplasia The presence of posterior or foraminal vertebral body osteophytes associated or not with disk space narrowing is a definite sign of a chronic disk herniation

Figure 23 A Chronic left L3-L4 extraforaminal disk hernation in a 54-year-old man suspected on an AP radiograph demonstrating a calcified shell on the left side of the intervertebral disk space (white arrow) B Axial CT scan section confirming the diagnosis of a chronic extraforaminal L3-L4 herniation

Myelography

Myelography is essentially an exploration of the subarachnoid space Disk herniations are demonstrated only indirectly because they can cause thecal sac deformity and individual nerve root sleeve filling defects (Fig 24) Of all the special imaging procedures

myelography is the only one that allows upright projections with full weight bearing It is not unusual to demonstrate in this way small posterior central or posterolateral herniations that are undetectable on CT sections Interestingly the overall sensitivity of myelography to detect disk herniations has been found to be higher than that of CT whereas its specificity has been found to be lower[ ]74 In comparison with standard CT examination which usually includes only the three or four lower lumbar disks myelography easily allows coverage of the entire lumbar area and assessment of the intrathecal structures (cauda equina and conus medullaris) Far lateral foraminal herniations extraforaminal herniations and anterior herniations however are not detected The sensitivity for detection of posterior central L5-S1 herniations is also relatively poor because of the greater distance between the thecal sac and the posterior aspect of this particular disk

Figure 24 L5-S1 disk herniation in a 25-year-old man detected by indirect signs using lumbosacral myelography A Upright oblique projections showing a filling defect of the left S1 root sleeve (white arrow) suggesting significant nerve root compression by a left posterolateral disk hernation The right S1 root sleeve fills normally with contrast (black arrow) B Subtle compression of the anterior wall of the dural sac by displaced disk material (small arrows) demonstrated on upright lateral projection This sign is usually absent in the presence of a large amount of fat and venous structures in the anterior epidural compartment

CT

The sensitivity of CT to diagnose a herniation of the nucleus pulposus at the L5-S1 interspace is greater than that of myelography if images in the exact plane of the disk can be obtained[ ]23 [ ]39 Otherwise the superiority of plain CT over myelography to demonstrate disk herniations has not been established but CT has the distinct advantage of being

noninvasive and provides direct anatomic information[ ]23 Large herniations are easily detected but as explained previously the distinction between protrusions and extrusions is often difficult without sagittal reconstructions CT essentially allows an assessment of the contour of the disk The diagnosis of very small herniations in the absence of direct or indirect evidence of a radial tear is hazardous and associated with a high percentage of false-positives and false-negatives[ ]52 The diagnosis of moderate and large size herniations in different directions is usually possible but anterior herniations are rarely diagnosed not because they are not detectable but because observers pay little attention to the anterior contour of the disk (Fig 25) Because the PLLC cannot usually be identified the distinction of subligamentous from transligamentous herniation can only be suggested in most cases by the size of the herniated material A definite diagnosis of sequestration is rarely possible Calcifications within the displaced material are readily seen but may be difficult at times to differentiate from an accompanying osteophyte or an avulsed bone fragment from the vertebral body ring epiphysis (Fig 26) The presence of gas in the herniated material is easily detected

Figure 25 Anterior L4-L5 herniation demonstrated by CT scan in a 51-year-old woman with chronic low back pain Although sometimes quite conspicuous such herniations are rarely reported because observers pay little attention to the anterior contour of the disk

Figure 26 CT scan demonstration of a posterior right central L4-L5 disk herniation in a 38-year-old woman with avulsion of a bone fragment from the ring epiphysis and adjacent part of the superior L5 end plate Reactive osteosclerosis is seen around the vertebral body defect (arrows) suggesting a chronic lesion

CT Myelography

This association combines the advantages of both imaging modalities The fact that its accuracy has been reported as being less[ ]22 [ ]32 higher[ ]1 [ ]6 or equivalent[ ]82 to MR imaging is a reflection of the differences in technologic advancement and pathologic nomenclature that hamper valid comparisons between different studies

MR Imaging

Most reported studies establish MR imaging as the first choice modality to diagnose a herniated lumbar disk[ ]5 [ ]22 [ ]32 [ ]46 The associated intravenous injection of a paramagnetic agent has been found useful to demonstrate some anatomic features of disk disease in patients with no previous lumbar disk surgery[ ]56 [ ]68 [ ]90 MR imaging provides a better assessment of disk morphology than CT or CT myelography because sagittal sections are routinely obtained Assessment of foraminal involvement by displaced disk material is more accurate (Fig 27) and anterior disk herniations can be detected more easily than with CT or CT myelography If one is looking specifically for herniated lumbar disks associated with nerve root compression however it has been demonstrated that CT is equally accurate[ ]82 Alterations of the central or peripheral disk signal intensity on T2-weighted images are seen in most disks afflicted with an anular tear[ ]48 and alert the observer to scrutinize the disk contour in search for local modifications indicative of a herniation Because the signal of the displaced disk material is usually very similar to that of the outer anulus PLLC and vertebral body cortical bone small herniations are generally more conspicuous on axial CT sections than on corresponding axial MR imaging sections Gas and calcium deposits within the displaced fragment cannot usually

be detected but associated vertebral body bone marrow changes are typically seen and are helpful in differentiating acute from chronic processes[ ]57 The occasional presence of a high-intensity zone in the herniated material with an occasionally enhancing border after contrast injection is probably caused by a mixture of displaced nuclear material acute and subacute inflammatory tissue and neovascularized reactive tissue[ ]4 [ ]48 [ ]72 Contradictory reports have been published regarding the accuracy of MR imaging to differentiate subligamentous from transligamentous herniations[ ]26 [ ]38 [ ]73 [ ]76 Understanding the anatomy of the PLLC is helpful to make the distinction (Fig 28) (Figure Not Available) Masaryk et al[ ]46 have suggested that MR imaging is accurate to distinguish sequestered disks from other forms of lumbar disk herniations but most observers find this distinction difficult to establish[ ]42

Figure 27 A Left L4-L5 foraminal herniation well seen on an intermediate-weighted left parasagittal MR section (arrow) in a 47-year-old man B The lesion is much less obvious on intermediate-weighted (left) and T2-weighted (right) axial sections and was in fact more conspicuous on the corresponding CT scan section

Figure 28 (Figure Not Available) A Subligamentous disk herniation Left T1-weighted image demonstrating displaced disk material with a smooth outline imposed by the demarcation of the anterior epidural space (AES) by the lateral membrane of the PLLC Right Correlative drawing B Transligamentous disk herniation Left T1-weighted image of a large disk herniation (cervical in this case) which has ruptured through the posterior confines of the AES Penetration of the right lateral membrane can be observed (arrow) and the disk fragment contour is serrated Right Correlative drawing (From Schellinger D Manz HJ Vidic B et al Disk fragment migration Radiology 175831-836 1990 with permission)

Diskography and CT Diskography

During 30 years (1950 to 1980) when myelography was the only available imaging technique to demonstrate lumbar disk herniations diskography was an invasive but efficient way to demonstrate posterior central L5-S1 herniations and other large herniations (other than posterior central and paramedial) that could not be detected by myelography[ ]50 These herniations are now usually well demonstrated by CT and MR imaging Comparing the accuracy of five imaging modalities (excluding MR imaging) for the diagnosis of lumbar disk herniation Jackson et al[ ]31 found that CT diskography (Fig 29) was the most accurate test (87) compared with 77 for CT myelography 74 for CT 70 for myelography 64 for pain reproduction during diskography and 58 for diskography without CT Disk injection reproduced the patients clinical pain pattern in only 36 of herniated disks This clinical test isolated from the images had high specificity (89) but low sensitivity (43) for the diagnosis of disk herniation The reported low sensitivity of diskography images (unassociated with CT) to diagnose disk herniation is to be expected the purpose of the intradiskal injection being primarily the demonstration of an anular tear the contrast leaking through the tear only occasionally delineates an extruded fragment When a disk herniation has been diagnosed by other imaging modalities diskography allows to determine if the herniation is contained or noncontained (Figs 30 and 31) this information may have clinical relevance[ ]62 It also allows to establish if the displaced disk material is communicating or not with the parent disk and establishes the likelihood that it is sequestered or not There always remains a possibility that the contrast injected under pressure may reach a disk fragment that is nevertheless sequestered by leaking through the associated anular tear CT diskography also allows assessment in most cases of the integrity of the PLLC[ ]89 The superior sensitivity of diskography over MR imaging to demonstrate anular tears has been well established[ ]27 [ ]44 [ ]48 [ ]64 [ ]77 [ ]91 [ ]94 The presence of a radial tear and the inflammatory reaction it creates may be symptomatic despite the absence of true disk herniation[ ]29 [ ]48 [ ]49 [ ]69

Figure 29 L4-L5 CT diskogram demonstrating a large left posterolateral radial anular tear associated with

a left foraminal and extraforaminal herniaton (same patient as in Figure 28) (Figure Not Available)

Figure 30 Contained posterior L4-L5 and L5-S1 disk herniations in a 57-year-old man demonstrated by diskography The L3-L4 disk is normal

Figure 31 Noncontained L4-L5 disk herniation in a 23-year-old woman Reflux of injected contrast is seen in the anterior epidural space above and below the disk space The L5-S1 disk also demonstrates incomplete anterior and posterior radial anular tears

SUMMARY

The absence of universal nomenclature standardization with respect to the definition of a disk herniation and its different categories especially regarding type and location is still a major problem that will only be overcome when major national or international scientific societies join efforts to support a particular scheme Meanwhile it is important to realize that the two models that are currently most used are based on a different perspective Trying to straddle the two by opposing for instance bulging disk and herniation is doomed to failure because this exercise defies formal logic MR imaging is currently the most accurate noninvasive imaging modality to diagnose a disk herniation and to determine its exact location The determination of some pathoanatomic characteristics of herniated disks (type and composition) may require the use of CT diskography or CT diskography

References

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  • CLASSIFICATION DIAGNOSTIC IMAGING AND IMAGING CHARACTERIZATION OF A LUMBAR HERNIATED DISK
    • IMAGING OF LOW BACK PAIN I
      • CLASSIFICATION DIAGNOSTIC IMAGING AND IMAGING CHARACTERIZATION OF A LUMBAR HERNIATED DISK
        • DEFINITION OF A DISK HERNIATION
        • CLASSIFICATION OF A HERNIATED LUMBAR DISK
          • Main Categories of Noninfectious Disk Abnormalities
          • Further Qualifying the Displaced Disk Material Beyond the Disk Space
            • DIAGNOSTIC IMAGING AND CHARACTERIZATION OF A HERNIATED LUMBAR DISK
              • Conventional Radiographs
              • Myelography
              • CT
              • CT Myelography
              • MR Imaging
              • Diskography and CT Diskography
                • SUMMARY
                  • References
Page 14: CLASSIFICATION, DIAGNOSTIC IMAGING, AND IMAGING ... · PDF fileclassification, diagnostic imaging, and imaging characterization of a lumbar herniated disk ... classification, diagnostic

Degeneration Spondylosis deformans

Intervertebral osteochondrosis

Further Qualifying the Displaced Disk Material Beyond the Disk Space

Regardless of the basic system that is used the type of herniation should be assessed The volume and location of the displaced disk material beyond the normal peripheral margin of the intervertebral space also need to be specified In certain cases it is also possible to determine the composition of this material For the sake of simplicity the term herniation is used consistently in the remainder of this article to refer to all displaced disk material but what is discussed can also be applied to protrusions and extrusions if one wants to use the morphologic nomenclature

Type of Herniation

Upward or downward migration of nuclear material may occur through a break in a vertebral body end plate creating an intravertebral herniation sometimes referred to as an intraspongy herniation or a Schmorls node[ ]67 (Fig 10) Although a herniation occurring in any horizontal direction is likely to cause symptoms because of the presence of pain-sensitive nerve endings in the outer anulus[ ]7 [ ]8 [ ]65 herniations occurring in a posterior or posterolateral direction deserve special consideration because of the added possibility of dural sac or individual nerve root compression

Figure 10 Various types of intravertebral herniations (Schmorls nodes) A Intravertebral herniation through the inferior end plate of the L3 vertebral body demonstrated by diskography in a 35-year-old man suffering from chronic low back pain The patients typical pain was reproduced during injection and the lesion was considered responsible for the patients symptoms B T2-weighted sagittal section demonstrating an intravertebral herniation through the inferior end plate of the L4 vertebral body in a 24-year-old woman presenting with chronic low back pain The high signal intensity of the lesion associated with the loss of normal central signal intensity of the parent disk suggests that the lesion is a bona fide acquired intraspongy herniation and not just a developmental defect C T2-weighted sagittal section demonstrating an intravertebral herniation through the inferior end plate of the L3 vertebral body (arrow) Because both the herniation and the parent disk show normal signal intensity the abnormality was

considered a probably asymptomatic developmental defect

Other characteristics of disk herniations have become relevant with the development of new therapeutic possibilities (eg chemonucleolysis and percutaneous diskectomy) The term sequestration is confusing and has often been used to indicate displacement of disk material away from the parent disk The term sequestered disk should be used restrictedly to designate a fragment of diskal tissue that has migrated from the disk space and has no connection by diskal tissue to the disk of origin[ ]20 [ ]21 [ ]42 Sequestration refers to loss of continuity with disk tissue still present in the intervertebral disk space The term migration has a broader meaning indicating displacement of disk material away from the edge of the rent in the outer anulus either in the central spinal canal at the disk level or above or below the disk level This difference is illustrated in Figure 11 The terms communicating and noncommunicating derive from a different perspective and are mostly used in the context of intradiskal therapeutic injections They refer to the interruption of the periphery of the disk allowing fluid injected into the disk to leak into the spinal canal and reach displaced disk material[ ]20 [ ]51 The terms contained and uncontained are unfamiliar to most radiologists in a contained herniation the displaced disk material is still covered by a few intact but distended outer anular fibers or by a capsule formed by outer anular fibers and the adherent posterior longitudinal ligament

Figure 11 Various types of posterior central herniations A Small subligamentous herniation (protrusion) without significant disk material migration B Subligamentous herniation with downward migration of disk material under the PLLC C Sub-ligamentous herniation with downward migration of disk material and sequestered fragment (arrow)

The terms subligamentous and extraligamentous (or transligamentous) refer to the position of the displaced disk material with respect to the posterior longitudinal ligament The anatomy of the posterior longitudinal ligament has been recently revised[ ]73 [ ]89 It is a membranous structure that has multiple components a deep layer attached to disks and vertebral bodies a superficial layer attached to the dura by fibrous tissue (Hoffmanns

ligament) and lateral extensions known as the lateral membranes or peridural membranes (Fig 12) (Figure Not Available) It should probably be referred to as the posterior longitudinal ligament complex (PLLC) It actually divides the epidural space into the perithecal space and the anterior epidural space where displaced disk material can be entrapped (Fig 13) A potential space allowing accumulation of displaced disk material has also been detected between the outer anular fibers and the deep fibers of the PLLC on the posterior central aspect of the disk[ ]63 Posterior midline herniations seldom rupture the PLLC and are generally subligamentous The lateral membranes are less resistant and transligamentous herniations are usually the result of posterior off-center herniations or posterolateral herniations

Figure 12 (Figure Not Available) The PLLC is portrayed here in relation to various types of subligamentous disk displacement At the disk level posteriorly displaced disk material frequently occupies the midline Below and above the disk an anterior epidural space (AES) exists between the PLLC and the posterior aspect of the vertebral bodies In this space disk fragment motion across the midline is curtailed by a sagittal midline septum (dashed line) A delicate translucent membrane (shown only on left side of drawing) is stretched between the free edge of the deep layer of the posterior longitudinal ligament and the lateral spinal canal (From Schellinger D Manz HJ Vidic B et al Disk fragment migration Radiology 175831-836 1990 with permission)

Figure 13 Relationship of typical posterior disk herniations with the PLLC A Midline sagittal section unless very large a posterior midline herniation usually remains entrapped underneath the deep layer of the PLL C and sometimes a few intact outer anulus fibers joining with the PLL C to form a capsule The deep layer of the PLL C (arrow) also attaches to the posterior aspect of the vertebral body so that no potential space is present underneath B Sagittal para-central section the PLL C extends laterally at the disk level (arrowhead) but above and below the disk an anterior epidural space (as) where disk fragments are frequently entrapped is present between the lateral (peridural) membranes and the posterior aspect of the vertebral bodies

Volume of Herniated Material

Quantifying the herniated disk material by measuring in millimeters its greatest diameter or by evaluating its cross-sectional area in square millimeters is rarely done The resulting figures could be misleading without relating this measurement to the size of the spinal canal and the exact location of the lesion[ ]88 A purely qualitative and subjective statement that a mild moderate or severe herniation is present however does not give the person reading the imaging report any indication as to the potential of the lesion to cause significant compression of the dural sac or individual exiting nerve roots A reasonably precise scheme has been proposed in 1995 by the Nomenclature Committee of the North American Spine Society[ ]20 Measurements are taken from an axial CT or MR imaging section at the site of most severe compromise canal compromise of less than 25 at that section is qualified as mild 25 to 75 is moderate 76 to 90 is moderately severe and greater than 90 is severe It is understood that such characterizations describe only the cross-sectional area at one level and do not account for the total volume of displaced material displacement of neural tissue or clinical significance The usefulness of having four categories is questionable and can likely generate poor interobserver or intraobserver agreement especially in situations where the central spinal canal is relatively narrow Bonnevilles scheme[ ]9 [ ]10 [ ]11 should generate greater reliability (Fig 14) (Figure Not Available) Separation of the cross-sectional area in three thirds can be applied to both the central spinal canal and the foramina It can be agreed by way of convention that the terms mild moderate and severe lumen compromise by a disk herniation designate extension of the displaced disk material in the anterior middle or posterior third of the central canal or foramen depending on the specified location of the herniation

Figure 14 (Figure Not Available) The size of the herniation in the horizontal plane is assessed and designated by the numbers 1 2 or 3 by establishing its extension in the anterior middle or posterior third of the spinal canal (From Bonneville JF Plaidoyer pour une classification par limage des hernies discales lombaires la carte-image Rev Imag Med 2557-560 1990 with permission)

Location of Herniated Material

Bonneville[ ]9 [ ]10 [ ]11 has also proposed an interesting and simple alpha-numerical system to classify according to their location the position of disk fragments that have migrated in the horizontal or sagittal plane (Figs 15 (Figure Not Available) and 16) (Figure Not Available) Using more precise anatomic boundaries unfortunately more familiar to surgeons than radiologists Wiltse et al[ ]88 have proposed another system which has been supported by the North American Spine Society[ ]20 [ ]21 Anatomic zones and levels are defined using the following anatomic landmarks medial edge of the articular facets medial lateral upper and lower border of the pedicles and coronal plane at the disk center On the horizontal plane (Fig 17) (Figure Not Available) these landmarks determine the bounderies of the central zone the subarticular zone the foraminal zone the extraforaminal zone and the anterior zone (anterior to the coronal plane at the center of the disk) In the sagittal plane they determine the boundaries of the diskal level the infrapedicular level the pedicular level and the suprapedicular level (Figs 18 (Figure

Not Available) and 19) (Figure Not Available) Radiologists interpreting axial CT or MR images may find it difficult to use the medial edge of the facets as the landmark that separates the central zone from the subarticular zone because the superior articular facets are generally not included in axial sections at the disk level The alternative is to use the expression posterolateral to designate collectively all posterior herniations that are not midline but do not extend into a foramen as was proposed by Bonneville[ ]9 [ ]10 [ ]11

Figure 15 (Figure Not Available) In the horizontal plane herniations are labeled midline (a) posterolateral (b) foraminal (c) and extra-foraminal (d) (From Bonneville JF Plaidoyer pour une classification par limage des hernies discales lombaires la carte-image Rev Imag Med 2557-560 1990 with permission)

Figure 16 (Figure Not Available) In the craniocaudal direction disk migration is labeled +1 +2 +3 or -1 -2 -3 by referring to the height of a vertebral body divided in thirds (From Bonneville JF Plaidoyer pour une classification par limage des hernies discales lombaires la carte-image Rev Imag Med 2557-560 1990 with permission)

Figure 17 (Figure Not Available) The anatomic zones identified on axial images The anterior zone (not shown) is delineated from the extraforaminal zone by an imaginary coronal line in the center of the vertebral body (From Wiltse LL Berger PE McCulloch JA A system for reporting the size and location of lesions in the spine Spine 221534-1537 1997 with permission)

Figure 18 (Figure Not Available) The anatomical levels identified on craniocaudal images (From Wiltse LL Berger PE McCulloch AJ A system for reporting the size and location of lesions in the spine Spine 221534-1537 1997 with permission)

Figure 19 (Figure Not Available) Coronal view of the main zones and levels (From Wiltse LL Berger PE McCulloch JA A system for reporting the size and location of lesions in the spine Spine 221534-1537 1997 with permission)

Composition of Herniated Material

Displaced disk material may consist of glycosaminoglycans type 1 or 2 collagen end plate cartilage and bone fragments avulsed from the ring epiphysis A reactive inflammatory reaction usually results in edematous tissue followed by granulation tissue which may undergo calcification (Fig 20) Necrotic and partially resorbed displaced disk material sometimes produces a large fluid-filled pouch distinguishable from the common high-intensity zone because of its size (Fig 21) or a gas-filled cavity generally in continuity with gas in the intervertebral space (Fig 22) [ ]42 These characteristics may be meaningful if intradiskal injection therapy is considered In imaging reports herniations exhibiting calcium deposits and those exhibiting replacement of disk material by gas or a relatively large fluid collection can be qualified as chronic herniations

Figure 20 A CT scan demonstration of a small posterior central L4-L5 calcified subligamentous herniation The resistant deep layer of the PLLC restrains displacement of the disk material in the posterior central direction and does not allow a detectable distortion of the disk contour In this particular case the presence of the calcification is actually the only evidence that a posterior midline anular tear and a small subligamentous herniation are present B Posterior right central and sub-articular L5-S1 calcified disk herniation in same patient Posterolateral herniations are generally more conspicuous than posterior midline herniations because the deep layer of the PLLC gets thinner away from the midline

Figure 21 Posterior central midline L4-L5 herniation in a 52-year-old man demonstrated on a T2-weighted midline MR sagittal section There is intervertebral space narrowing with loss of normal central disk signal

intensity while the herniated disk material demonstrates high signal intensity consistent with a predominantly fluid consistency

Figure 22 CT scan demonstration in a 51-year-old woman of a left posterolateral L5-S1 disk hernation consisting essentially in a gas-filled pouch (white arrow) Gas is also present in the central portion of the intervertebral disk space (black arrow)

DIAGNOSTIC IMAGING AND CHARACTERIZATION OF A HERNIATED LUMBAR DISK

Assessing the validity of the currently used imaging procedures to diagnose a herniated lumbar disk is not an easy endeavor The validity of a measurement is the extent to which it corresponds to the true biologic value or some accepted gold standard[ ]40 With the exception of postmortem studies evaluation of the pathoanatomy by the surgeon in the operating room has always been considered the gold standard but this does not constitute an ideal situation Inspection of the disk through a small laminectomy incision to determine for instance if nuclear fragments lie within or outside the anular fibers may not be very reliable Also unbiased intraoperative determination of a normal degenerated or herniated disk in a patient with sciatica may also be difficult[ ]86 Because the validity of diskography has been previously established by postmortem studies and surgical correlations[ ]48 it is sometimes used as a gold standard in situations where no surgery has been performed

Conventional Radiographs

Lumbar disk herniations can exceptionally be diagnosed directly on good quality lateral projections because the x-ray attenuation is slightly greater in displaced disk material than in epidural fat Occasionally a calcified rim outlines the displaced disk fragment

(Fig 23) In most situations however narrowing of an intervertebral disk space in the absence of other evidence of chronic diskopathy is the only detectable sign suggesting the presence of a disk herniation To my knowledge the sensitivity and specificity of this sign has never been assessed The accepted rule of thumb is that the height of a given lumbar intervertebral disk space should always be slightly greater than the height of the above located interspace This rule does not apply to the transition disk immediately above the sacrum (usually L5-S1) The specificity of this sign is probably quite high but a few false-positives are seen especially at the L4-L5 level because of minor congenital hypoplasia The presence of posterior or foraminal vertebral body osteophytes associated or not with disk space narrowing is a definite sign of a chronic disk herniation

Figure 23 A Chronic left L3-L4 extraforaminal disk hernation in a 54-year-old man suspected on an AP radiograph demonstrating a calcified shell on the left side of the intervertebral disk space (white arrow) B Axial CT scan section confirming the diagnosis of a chronic extraforaminal L3-L4 herniation

Myelography

Myelography is essentially an exploration of the subarachnoid space Disk herniations are demonstrated only indirectly because they can cause thecal sac deformity and individual nerve root sleeve filling defects (Fig 24) Of all the special imaging procedures

myelography is the only one that allows upright projections with full weight bearing It is not unusual to demonstrate in this way small posterior central or posterolateral herniations that are undetectable on CT sections Interestingly the overall sensitivity of myelography to detect disk herniations has been found to be higher than that of CT whereas its specificity has been found to be lower[ ]74 In comparison with standard CT examination which usually includes only the three or four lower lumbar disks myelography easily allows coverage of the entire lumbar area and assessment of the intrathecal structures (cauda equina and conus medullaris) Far lateral foraminal herniations extraforaminal herniations and anterior herniations however are not detected The sensitivity for detection of posterior central L5-S1 herniations is also relatively poor because of the greater distance between the thecal sac and the posterior aspect of this particular disk

Figure 24 L5-S1 disk herniation in a 25-year-old man detected by indirect signs using lumbosacral myelography A Upright oblique projections showing a filling defect of the left S1 root sleeve (white arrow) suggesting significant nerve root compression by a left posterolateral disk hernation The right S1 root sleeve fills normally with contrast (black arrow) B Subtle compression of the anterior wall of the dural sac by displaced disk material (small arrows) demonstrated on upright lateral projection This sign is usually absent in the presence of a large amount of fat and venous structures in the anterior epidural compartment

CT

The sensitivity of CT to diagnose a herniation of the nucleus pulposus at the L5-S1 interspace is greater than that of myelography if images in the exact plane of the disk can be obtained[ ]23 [ ]39 Otherwise the superiority of plain CT over myelography to demonstrate disk herniations has not been established but CT has the distinct advantage of being

noninvasive and provides direct anatomic information[ ]23 Large herniations are easily detected but as explained previously the distinction between protrusions and extrusions is often difficult without sagittal reconstructions CT essentially allows an assessment of the contour of the disk The diagnosis of very small herniations in the absence of direct or indirect evidence of a radial tear is hazardous and associated with a high percentage of false-positives and false-negatives[ ]52 The diagnosis of moderate and large size herniations in different directions is usually possible but anterior herniations are rarely diagnosed not because they are not detectable but because observers pay little attention to the anterior contour of the disk (Fig 25) Because the PLLC cannot usually be identified the distinction of subligamentous from transligamentous herniation can only be suggested in most cases by the size of the herniated material A definite diagnosis of sequestration is rarely possible Calcifications within the displaced material are readily seen but may be difficult at times to differentiate from an accompanying osteophyte or an avulsed bone fragment from the vertebral body ring epiphysis (Fig 26) The presence of gas in the herniated material is easily detected

Figure 25 Anterior L4-L5 herniation demonstrated by CT scan in a 51-year-old woman with chronic low back pain Although sometimes quite conspicuous such herniations are rarely reported because observers pay little attention to the anterior contour of the disk

Figure 26 CT scan demonstration of a posterior right central L4-L5 disk herniation in a 38-year-old woman with avulsion of a bone fragment from the ring epiphysis and adjacent part of the superior L5 end plate Reactive osteosclerosis is seen around the vertebral body defect (arrows) suggesting a chronic lesion

CT Myelography

This association combines the advantages of both imaging modalities The fact that its accuracy has been reported as being less[ ]22 [ ]32 higher[ ]1 [ ]6 or equivalent[ ]82 to MR imaging is a reflection of the differences in technologic advancement and pathologic nomenclature that hamper valid comparisons between different studies

MR Imaging

Most reported studies establish MR imaging as the first choice modality to diagnose a herniated lumbar disk[ ]5 [ ]22 [ ]32 [ ]46 The associated intravenous injection of a paramagnetic agent has been found useful to demonstrate some anatomic features of disk disease in patients with no previous lumbar disk surgery[ ]56 [ ]68 [ ]90 MR imaging provides a better assessment of disk morphology than CT or CT myelography because sagittal sections are routinely obtained Assessment of foraminal involvement by displaced disk material is more accurate (Fig 27) and anterior disk herniations can be detected more easily than with CT or CT myelography If one is looking specifically for herniated lumbar disks associated with nerve root compression however it has been demonstrated that CT is equally accurate[ ]82 Alterations of the central or peripheral disk signal intensity on T2-weighted images are seen in most disks afflicted with an anular tear[ ]48 and alert the observer to scrutinize the disk contour in search for local modifications indicative of a herniation Because the signal of the displaced disk material is usually very similar to that of the outer anulus PLLC and vertebral body cortical bone small herniations are generally more conspicuous on axial CT sections than on corresponding axial MR imaging sections Gas and calcium deposits within the displaced fragment cannot usually

be detected but associated vertebral body bone marrow changes are typically seen and are helpful in differentiating acute from chronic processes[ ]57 The occasional presence of a high-intensity zone in the herniated material with an occasionally enhancing border after contrast injection is probably caused by a mixture of displaced nuclear material acute and subacute inflammatory tissue and neovascularized reactive tissue[ ]4 [ ]48 [ ]72 Contradictory reports have been published regarding the accuracy of MR imaging to differentiate subligamentous from transligamentous herniations[ ]26 [ ]38 [ ]73 [ ]76 Understanding the anatomy of the PLLC is helpful to make the distinction (Fig 28) (Figure Not Available) Masaryk et al[ ]46 have suggested that MR imaging is accurate to distinguish sequestered disks from other forms of lumbar disk herniations but most observers find this distinction difficult to establish[ ]42

Figure 27 A Left L4-L5 foraminal herniation well seen on an intermediate-weighted left parasagittal MR section (arrow) in a 47-year-old man B The lesion is much less obvious on intermediate-weighted (left) and T2-weighted (right) axial sections and was in fact more conspicuous on the corresponding CT scan section

Figure 28 (Figure Not Available) A Subligamentous disk herniation Left T1-weighted image demonstrating displaced disk material with a smooth outline imposed by the demarcation of the anterior epidural space (AES) by the lateral membrane of the PLLC Right Correlative drawing B Transligamentous disk herniation Left T1-weighted image of a large disk herniation (cervical in this case) which has ruptured through the posterior confines of the AES Penetration of the right lateral membrane can be observed (arrow) and the disk fragment contour is serrated Right Correlative drawing (From Schellinger D Manz HJ Vidic B et al Disk fragment migration Radiology 175831-836 1990 with permission)

Diskography and CT Diskography

During 30 years (1950 to 1980) when myelography was the only available imaging technique to demonstrate lumbar disk herniations diskography was an invasive but efficient way to demonstrate posterior central L5-S1 herniations and other large herniations (other than posterior central and paramedial) that could not be detected by myelography[ ]50 These herniations are now usually well demonstrated by CT and MR imaging Comparing the accuracy of five imaging modalities (excluding MR imaging) for the diagnosis of lumbar disk herniation Jackson et al[ ]31 found that CT diskography (Fig 29) was the most accurate test (87) compared with 77 for CT myelography 74 for CT 70 for myelography 64 for pain reproduction during diskography and 58 for diskography without CT Disk injection reproduced the patients clinical pain pattern in only 36 of herniated disks This clinical test isolated from the images had high specificity (89) but low sensitivity (43) for the diagnosis of disk herniation The reported low sensitivity of diskography images (unassociated with CT) to diagnose disk herniation is to be expected the purpose of the intradiskal injection being primarily the demonstration of an anular tear the contrast leaking through the tear only occasionally delineates an extruded fragment When a disk herniation has been diagnosed by other imaging modalities diskography allows to determine if the herniation is contained or noncontained (Figs 30 and 31) this information may have clinical relevance[ ]62 It also allows to establish if the displaced disk material is communicating or not with the parent disk and establishes the likelihood that it is sequestered or not There always remains a possibility that the contrast injected under pressure may reach a disk fragment that is nevertheless sequestered by leaking through the associated anular tear CT diskography also allows assessment in most cases of the integrity of the PLLC[ ]89 The superior sensitivity of diskography over MR imaging to demonstrate anular tears has been well established[ ]27 [ ]44 [ ]48 [ ]64 [ ]77 [ ]91 [ ]94 The presence of a radial tear and the inflammatory reaction it creates may be symptomatic despite the absence of true disk herniation[ ]29 [ ]48 [ ]49 [ ]69

Figure 29 L4-L5 CT diskogram demonstrating a large left posterolateral radial anular tear associated with

a left foraminal and extraforaminal herniaton (same patient as in Figure 28) (Figure Not Available)

Figure 30 Contained posterior L4-L5 and L5-S1 disk herniations in a 57-year-old man demonstrated by diskography The L3-L4 disk is normal

Figure 31 Noncontained L4-L5 disk herniation in a 23-year-old woman Reflux of injected contrast is seen in the anterior epidural space above and below the disk space The L5-S1 disk also demonstrates incomplete anterior and posterior radial anular tears

SUMMARY

The absence of universal nomenclature standardization with respect to the definition of a disk herniation and its different categories especially regarding type and location is still a major problem that will only be overcome when major national or international scientific societies join efforts to support a particular scheme Meanwhile it is important to realize that the two models that are currently most used are based on a different perspective Trying to straddle the two by opposing for instance bulging disk and herniation is doomed to failure because this exercise defies formal logic MR imaging is currently the most accurate noninvasive imaging modality to diagnose a disk herniation and to determine its exact location The determination of some pathoanatomic characteristics of herniated disks (type and composition) may require the use of CT diskography or CT diskography

References

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29 Haughton VM Lim TH An H Intervertebral disk appearance correlated with stiffness of lumbar spinal motion segments AJNR Am J Neuroradiol 201161-1165 1999 Abstract 30 Herzog RJ The radiologic assessment for a lumbar disc herniation Spine 2119S-38S 1996 Abstract 31 Jackson RP Becker GJ Jacobs RR et al The neuroradiographic diagnosis of lumbar herniated nucleus pulposus I A comparison of computed tomography (CT) myelography CT-myelography discography and CT-discography Spine 141356-1361 1989 Abstract 32 Jackson RP Cain JE Jr Jacobs RR et al The neuroradiographic diagnosis of lumbar herniated nucleus pulposus II A comparison of computed tomography (CT) myelography CT-myelography and magnetic resonance imaging Spine 141362-1367 1989 Abstract 33 Jarvik JG Haynor DR Koepsell TD et al Interreader reliability for a new classification of lumbar disk disease Acad Radiol 3537-544 1996 Abstract 34 Jensen MC Brant-Zawadzki MN Obuchowski N et al Magnetic resonance imaging of the lumbar spine in people without back pain N Engl J Med 33169-73 1994 Abstract 35 Kent DL Haynor DR Larson EB et al Diagnosis of lumbar spinal stenosis in adults A meta-analysis of the accuracy of CT MR and myelography AJR Am J Roentgenol 1581135-1144 1992 Abstract 36 Kieffer SA Sherry RG Wellenstein DE et al Bulging lumbar intervertebral disk Myelographic differentiation from herniated disk with nerve root compression AJR Am J Roentgenol 138709-716 1982 Abstract 37 Kieffer SA Stadlan EM Mohandas A et al Discographic-anatomical correlation of developmental changes with age in the intervertebral disc Acta Radiol 9733-739 1969 38 Kim KY Kim YT Lee CS et al MRI classification of lumbar herniated intervertebral disc Orthopedics 15493-497 1992 Abstract 39 Kornberg M Rechtine GR Dupuy TE Computed tomography in the diagnosis of a herniated disk at the L5-S1 level Spine 9433-436 1984 Abstract 40 Kramer MS Clinical Epidemiology and Biostatistics New York Springer-Verlag 1988 41 Landis JR Koch GG The measurement of observer agreement agreement for categorical data Biometrics 33159-174 1977 Abstract 42 Laredo JD Bossard P Vuillemin-Bodaghi Formes anatomo-radiologiques des hernies discales In Morvan G Deburge A Bard H et al (eds) Le Rachis Lombaire Degeneratif Montpellier Sauramps Medical 1998 pp 37-49 43 Lee SH Coleman PE Hahn FJ Magnetic resonance imaging of degenerative disk disease of the spine Radiol Clin North Am 26949-964 1988 Abstract 44 Linson MA Crowe CH Comparison of magnetic resonance imaging and lumbar discography in the diagnosis of disc degeneration Clin Orthop 160-163 1990

45 Marchand F Ahmed AM Investigation of the laminate structure of lumbar disc anulus fibrosus Spine 15402-410 1990 Abstract 46 Masaryk TJ Ross JS Modic MT et al High-resolution MR imaging of sequestered lumbar intervertebral disks AJR Am J Roentgenol 1501155-1162 1988 Abstract 47 Milette PC The proper terminology for reporting lumbar intervertebral disk disorders AJNR Am J Neuroradiol 181859-1866 1997 Citation 48 Milette PC Fontaine S Lepanto L et al Differentiating lumbar disc protrusions disk bulges and discs with normal contour but abnormal signal intensity Magnetic resonance imaging with discographic correlations Spine 2444-53 1999 Abstract 49 Milette PC Fontaine S Lepanto L et al Radiating pain to the lower extremities caused by lumbar disk rupture without spinal nerve root involvement AJNR Am J Neuroradiol 161605-1613 1995 Abstract 50 Milette PC Melancon D A reappraisal of lumbar discography Can Assoc Radiol J 33176-182 1982 51 Milette PC Melancon D Dupuis PR et al A simplified terminology for abnormalities of the lumbar disk Can Assoc Radiol J 42319-325 1991 Abstract 52 Milette PC Raymond J Fontaine S Comparison of high-resolution computed tomography with discography in the evaluation of lumbar disc herniations Spine 15525-533 1990 Abstract 53 Mink JH Deutsch AL Goldstein TB et al Spinal imaging and intervention 1998 Phys Med Rehabil Clin North Am 9343-380 1998 54 Mixter WJ Barr JS Rupture of the intervertebral disc with involvement of the spinal canal N Engl J Med 211210-234 1934 55 Modic MT Masaryk TJ Ross JS et al Imaging of degenerative disk disease Radiology 168177-186 1988 Citation 56 Modic MT Ross JS Obuchowski NA et al Contrast-enhanced MR imaging in acute lumbar radiculopathy A pilot study of the natural history Radiology 195429-435 1995 Abstract 57 Modic MT Steinberg PM Ross JS et al Degenerative disk disease Assessment of changes in vertebral body marrow with MR imaging Radiology 166193-199 1988 58 Morvan G Mathieu P Les stenoses laterales In Morvan G Deburge A Bard H et al (eds) Le Rachis Lombaire Degeneratif Montpellier Sauramps Medical 1998 pp 315-324 59 Murray RO Skeletal trauma Regional In Sutton D (ed) Textbook of Radiology and Imaging ed 3 New York Churchill Livingstone 1980 pp 210-231 60 Nachemson A Lumbar disc herniation Conclusions Acta Orthop Scand 64(suppl 251)49 1993 Citation

61 Nathan H Osteophytes of the vertebral column An anatomical study of their development according to age race and sex with consideration as to their etiology and significance J Bone Joint Surg Am 44243-268 1962 62 Nygaard OP Mellgren SI Osterud B The inflammatory properties of contained and noncontained lumbar disc herniations Spine 222584-2488 1997 Abstract 63 Ohshima H Hirano N Osada R et al Morphologic variation of lumbar posterior longitudinal ligament and the modality of disc herniation Spine 182408-2411 1993 Abstract 64 Osti OL Fraser RD MRI and discography of annular tears and intervertebral disc degeneration A prospective clinical comparison J Bone Joint Surg Br 74431-435 1992 Abstract 65 Palmgren T Gronblad M Virri J et al Immunohistochemical demonstration of sensory and autonomic nerve terminals in herniated lumbar disc tissue Spine 211301-1306 1996 Abstract 66 Resnick D Niwayama G Degenerative disease of the spine In Resnick D (ed) Diagnosis of Bone and Joint Disorders ed 3 Philadelphia WB Saunders 1995 pp 1372-1462 67 Resnick D Niwayama G Intravertebral disk herniations Cartilaginous (Schmorls) nodes Radiology 12657-65 1978 Abstract 68 Ross JS Modic MT Masaryk TJ Tears of the anulus fibrosus Assessment with Gd-DTPA-enhanced MR imaging AJR Am J Roentgenol 154159-162 1990 Abstract 69 Saal JS The role of inflammation in lumbar pain Spine 201821-1827 1995 Abstract 70 Sachs BL Vanharanta H Spivey MA et al Dallas discogram description A new classification of CTdiscography in low-back disorders Spine 12287-294 1987 Abstract 71 Sauser DD Goldman AB Kaye JJ Discogenic vertebral sclerosis J Can Assoc Radiol 2944-50 1978 Abstract 72 Schellhas KP Pollei SR Gundry CR et al Lumbar disc high-intensity zone Correlation of magnetic resonance imaging and discography Spine 2179-86 1996 Abstract 73 Schellinger D Manz HJ Vidic B et al Disk fragment migration Radiology 175831-836 1990 Abstract 74 Schipper J Kardaun JW Braakman R et al Lumbar disk herniation Diagnosis with CT or myelography Radiology 165227-231 1987 Abstract 75 Schmorl G Junghanns H The Human Spine in Health and Disease ed 2 New York Grune and Stratton 1971 76 Silverman CS Lenchik L Shimkin PM et al The value of MR in differentiating subligamentous from supraligamentous lumbar disk herniations AJNR Am J Neuroradiol 16571-579 1995 Abstract 77 Simmons JW Emery SF McMillin JN et al Awake discography A comparison study with magnetic

resonance imaging Spine 16S216-221 1991 Abstract 78 Smyth MJ Wright V Sciatica and the intervertebral disc J Bone Joint Surg Am 401401-1418 1958 79 Taveras JM Radiologic aspects of low back pain and sciatic syndromes [editorial] AJNR Am J Neuroradiol 9351-358 1989 80 Tehranzadeh J Discography 2000 Radiol Clin North Am 36463-495 1998 Full Text 81 Thelander U Fagerlund M Friberg S et al Describing the size of lumbar disc herniations using computed tomography A comparison of different size index calculations and their relation to sciatica Spine 191979-1984 1994 Abstract 82 Thornbury JR Fryback DG Turski PA et al Disk-caused nerve compression in patients with acute low-back pain Diagnosis with MR CT myelography and plain CT Radiology 186731-738 1993 Abstract 83 Twomey L Taylor J Age changes in lumbar intervertebral discs Acta Orthop Scand 56496-499 1985 Abstract 84 Twomey LT Taylor JR Age changes in lumbar vertebrae and intervertebral discs Clin Orthop 22497-104 1987 85 Williams AL CT diagnosis of degenerative disc disease The bulging annulus Radiol Clin North Am 21289-300 1983 Abstract 86 Williams AL Haughton VM Meyer GA et al Computed tomographic appearance of the bulging annulus Radiology 142403-408 1982 Abstract 87 Williams AL Haughton VM Syvertsen A Computed tomography in the diagnosis of herniated nucleus pulposus Radiology 13595-99 1980 Abstract 88 Wiltse LL Berger PE McCulloch JA A system for reporting the size and location of lesions in the spine Spine 221534-1537 1997 Abstract 89 Wiltse LL Fonseca AS Amster J et al Relationship of the dura Hofmanns ligaments Batsons plexus and a fibrovascular membrane lying on the posterior surface of the vertebral bodies and attaching to the deep layer of the posterior longitudinal ligament An anatomical radiologic and clinical study Spine 181030-1043 1993 Abstract 90 Yamashita K Hiroshima K Kurata A Gadolinium-DTPA-enhanced magnetic resonance imaging of a sequestered lumbar intervertebral disc and its correlation with pathologic findings Spine 19479-482 1994 Abstract 91 Yu SW Haughton VM Sether LA et al Comparison of MR and diskography in detecting radial tears of the anulus A postmortem study AJNR Am J Neuroradiol 101077-1081 1989 Abstract 92 Yu SW Sether LA Ho PS et al Tears of the anulus fibrosus Correlation between MR and pathologic findings in cadavers AJNR Am J Neuroradiol 9367-370 1988 Abstract

93 Yussen PS Swartz JD The acute lumbar disc herniation Imaging diagnosis Semin Ultrasound CT MR 14389-398 1993 Abstract 94 Zucherman J Derby R Hsu K et al Normal magnetic resonance imaging with abnormal discography Spine 131355-1359 1988 Abstract

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  • CLASSIFICATION DIAGNOSTIC IMAGING AND IMAGING CHARACTERIZATION OF A LUMBAR HERNIATED DISK
    • IMAGING OF LOW BACK PAIN I
      • CLASSIFICATION DIAGNOSTIC IMAGING AND IMAGING CHARACTERIZATION OF A LUMBAR HERNIATED DISK
        • DEFINITION OF A DISK HERNIATION
        • CLASSIFICATION OF A HERNIATED LUMBAR DISK
          • Main Categories of Noninfectious Disk Abnormalities
          • Further Qualifying the Displaced Disk Material Beyond the Disk Space
            • DIAGNOSTIC IMAGING AND CHARACTERIZATION OF A HERNIATED LUMBAR DISK
              • Conventional Radiographs
              • Myelography
              • CT
              • CT Myelography
              • MR Imaging
              • Diskography and CT Diskography
                • SUMMARY
                  • References
Page 15: CLASSIFICATION, DIAGNOSTIC IMAGING, AND IMAGING ... · PDF fileclassification, diagnostic imaging, and imaging characterization of a lumbar herniated disk ... classification, diagnostic

Figure 10 Various types of intravertebral herniations (Schmorls nodes) A Intravertebral herniation through the inferior end plate of the L3 vertebral body demonstrated by diskography in a 35-year-old man suffering from chronic low back pain The patients typical pain was reproduced during injection and the lesion was considered responsible for the patients symptoms B T2-weighted sagittal section demonstrating an intravertebral herniation through the inferior end plate of the L4 vertebral body in a 24-year-old woman presenting with chronic low back pain The high signal intensity of the lesion associated with the loss of normal central signal intensity of the parent disk suggests that the lesion is a bona fide acquired intraspongy herniation and not just a developmental defect C T2-weighted sagittal section demonstrating an intravertebral herniation through the inferior end plate of the L3 vertebral body (arrow) Because both the herniation and the parent disk show normal signal intensity the abnormality was

considered a probably asymptomatic developmental defect

Other characteristics of disk herniations have become relevant with the development of new therapeutic possibilities (eg chemonucleolysis and percutaneous diskectomy) The term sequestration is confusing and has often been used to indicate displacement of disk material away from the parent disk The term sequestered disk should be used restrictedly to designate a fragment of diskal tissue that has migrated from the disk space and has no connection by diskal tissue to the disk of origin[ ]20 [ ]21 [ ]42 Sequestration refers to loss of continuity with disk tissue still present in the intervertebral disk space The term migration has a broader meaning indicating displacement of disk material away from the edge of the rent in the outer anulus either in the central spinal canal at the disk level or above or below the disk level This difference is illustrated in Figure 11 The terms communicating and noncommunicating derive from a different perspective and are mostly used in the context of intradiskal therapeutic injections They refer to the interruption of the periphery of the disk allowing fluid injected into the disk to leak into the spinal canal and reach displaced disk material[ ]20 [ ]51 The terms contained and uncontained are unfamiliar to most radiologists in a contained herniation the displaced disk material is still covered by a few intact but distended outer anular fibers or by a capsule formed by outer anular fibers and the adherent posterior longitudinal ligament

Figure 11 Various types of posterior central herniations A Small subligamentous herniation (protrusion) without significant disk material migration B Subligamentous herniation with downward migration of disk material under the PLLC C Sub-ligamentous herniation with downward migration of disk material and sequestered fragment (arrow)

The terms subligamentous and extraligamentous (or transligamentous) refer to the position of the displaced disk material with respect to the posterior longitudinal ligament The anatomy of the posterior longitudinal ligament has been recently revised[ ]73 [ ]89 It is a membranous structure that has multiple components a deep layer attached to disks and vertebral bodies a superficial layer attached to the dura by fibrous tissue (Hoffmanns

ligament) and lateral extensions known as the lateral membranes or peridural membranes (Fig 12) (Figure Not Available) It should probably be referred to as the posterior longitudinal ligament complex (PLLC) It actually divides the epidural space into the perithecal space and the anterior epidural space where displaced disk material can be entrapped (Fig 13) A potential space allowing accumulation of displaced disk material has also been detected between the outer anular fibers and the deep fibers of the PLLC on the posterior central aspect of the disk[ ]63 Posterior midline herniations seldom rupture the PLLC and are generally subligamentous The lateral membranes are less resistant and transligamentous herniations are usually the result of posterior off-center herniations or posterolateral herniations

Figure 12 (Figure Not Available) The PLLC is portrayed here in relation to various types of subligamentous disk displacement At the disk level posteriorly displaced disk material frequently occupies the midline Below and above the disk an anterior epidural space (AES) exists between the PLLC and the posterior aspect of the vertebral bodies In this space disk fragment motion across the midline is curtailed by a sagittal midline septum (dashed line) A delicate translucent membrane (shown only on left side of drawing) is stretched between the free edge of the deep layer of the posterior longitudinal ligament and the lateral spinal canal (From Schellinger D Manz HJ Vidic B et al Disk fragment migration Radiology 175831-836 1990 with permission)

Figure 13 Relationship of typical posterior disk herniations with the PLLC A Midline sagittal section unless very large a posterior midline herniation usually remains entrapped underneath the deep layer of the PLL C and sometimes a few intact outer anulus fibers joining with the PLL C to form a capsule The deep layer of the PLL C (arrow) also attaches to the posterior aspect of the vertebral body so that no potential space is present underneath B Sagittal para-central section the PLL C extends laterally at the disk level (arrowhead) but above and below the disk an anterior epidural space (as) where disk fragments are frequently entrapped is present between the lateral (peridural) membranes and the posterior aspect of the vertebral bodies

Volume of Herniated Material

Quantifying the herniated disk material by measuring in millimeters its greatest diameter or by evaluating its cross-sectional area in square millimeters is rarely done The resulting figures could be misleading without relating this measurement to the size of the spinal canal and the exact location of the lesion[ ]88 A purely qualitative and subjective statement that a mild moderate or severe herniation is present however does not give the person reading the imaging report any indication as to the potential of the lesion to cause significant compression of the dural sac or individual exiting nerve roots A reasonably precise scheme has been proposed in 1995 by the Nomenclature Committee of the North American Spine Society[ ]20 Measurements are taken from an axial CT or MR imaging section at the site of most severe compromise canal compromise of less than 25 at that section is qualified as mild 25 to 75 is moderate 76 to 90 is moderately severe and greater than 90 is severe It is understood that such characterizations describe only the cross-sectional area at one level and do not account for the total volume of displaced material displacement of neural tissue or clinical significance The usefulness of having four categories is questionable and can likely generate poor interobserver or intraobserver agreement especially in situations where the central spinal canal is relatively narrow Bonnevilles scheme[ ]9 [ ]10 [ ]11 should generate greater reliability (Fig 14) (Figure Not Available) Separation of the cross-sectional area in three thirds can be applied to both the central spinal canal and the foramina It can be agreed by way of convention that the terms mild moderate and severe lumen compromise by a disk herniation designate extension of the displaced disk material in the anterior middle or posterior third of the central canal or foramen depending on the specified location of the herniation

Figure 14 (Figure Not Available) The size of the herniation in the horizontal plane is assessed and designated by the numbers 1 2 or 3 by establishing its extension in the anterior middle or posterior third of the spinal canal (From Bonneville JF Plaidoyer pour une classification par limage des hernies discales lombaires la carte-image Rev Imag Med 2557-560 1990 with permission)

Location of Herniated Material

Bonneville[ ]9 [ ]10 [ ]11 has also proposed an interesting and simple alpha-numerical system to classify according to their location the position of disk fragments that have migrated in the horizontal or sagittal plane (Figs 15 (Figure Not Available) and 16) (Figure Not Available) Using more precise anatomic boundaries unfortunately more familiar to surgeons than radiologists Wiltse et al[ ]88 have proposed another system which has been supported by the North American Spine Society[ ]20 [ ]21 Anatomic zones and levels are defined using the following anatomic landmarks medial edge of the articular facets medial lateral upper and lower border of the pedicles and coronal plane at the disk center On the horizontal plane (Fig 17) (Figure Not Available) these landmarks determine the bounderies of the central zone the subarticular zone the foraminal zone the extraforaminal zone and the anterior zone (anterior to the coronal plane at the center of the disk) In the sagittal plane they determine the boundaries of the diskal level the infrapedicular level the pedicular level and the suprapedicular level (Figs 18 (Figure

Not Available) and 19) (Figure Not Available) Radiologists interpreting axial CT or MR images may find it difficult to use the medial edge of the facets as the landmark that separates the central zone from the subarticular zone because the superior articular facets are generally not included in axial sections at the disk level The alternative is to use the expression posterolateral to designate collectively all posterior herniations that are not midline but do not extend into a foramen as was proposed by Bonneville[ ]9 [ ]10 [ ]11

Figure 15 (Figure Not Available) In the horizontal plane herniations are labeled midline (a) posterolateral (b) foraminal (c) and extra-foraminal (d) (From Bonneville JF Plaidoyer pour une classification par limage des hernies discales lombaires la carte-image Rev Imag Med 2557-560 1990 with permission)

Figure 16 (Figure Not Available) In the craniocaudal direction disk migration is labeled +1 +2 +3 or -1 -2 -3 by referring to the height of a vertebral body divided in thirds (From Bonneville JF Plaidoyer pour une classification par limage des hernies discales lombaires la carte-image Rev Imag Med 2557-560 1990 with permission)

Figure 17 (Figure Not Available) The anatomic zones identified on axial images The anterior zone (not shown) is delineated from the extraforaminal zone by an imaginary coronal line in the center of the vertebral body (From Wiltse LL Berger PE McCulloch JA A system for reporting the size and location of lesions in the spine Spine 221534-1537 1997 with permission)

Figure 18 (Figure Not Available) The anatomical levels identified on craniocaudal images (From Wiltse LL Berger PE McCulloch AJ A system for reporting the size and location of lesions in the spine Spine 221534-1537 1997 with permission)

Figure 19 (Figure Not Available) Coronal view of the main zones and levels (From Wiltse LL Berger PE McCulloch JA A system for reporting the size and location of lesions in the spine Spine 221534-1537 1997 with permission)

Composition of Herniated Material

Displaced disk material may consist of glycosaminoglycans type 1 or 2 collagen end plate cartilage and bone fragments avulsed from the ring epiphysis A reactive inflammatory reaction usually results in edematous tissue followed by granulation tissue which may undergo calcification (Fig 20) Necrotic and partially resorbed displaced disk material sometimes produces a large fluid-filled pouch distinguishable from the common high-intensity zone because of its size (Fig 21) or a gas-filled cavity generally in continuity with gas in the intervertebral space (Fig 22) [ ]42 These characteristics may be meaningful if intradiskal injection therapy is considered In imaging reports herniations exhibiting calcium deposits and those exhibiting replacement of disk material by gas or a relatively large fluid collection can be qualified as chronic herniations

Figure 20 A CT scan demonstration of a small posterior central L4-L5 calcified subligamentous herniation The resistant deep layer of the PLLC restrains displacement of the disk material in the posterior central direction and does not allow a detectable distortion of the disk contour In this particular case the presence of the calcification is actually the only evidence that a posterior midline anular tear and a small subligamentous herniation are present B Posterior right central and sub-articular L5-S1 calcified disk herniation in same patient Posterolateral herniations are generally more conspicuous than posterior midline herniations because the deep layer of the PLLC gets thinner away from the midline

Figure 21 Posterior central midline L4-L5 herniation in a 52-year-old man demonstrated on a T2-weighted midline MR sagittal section There is intervertebral space narrowing with loss of normal central disk signal

intensity while the herniated disk material demonstrates high signal intensity consistent with a predominantly fluid consistency

Figure 22 CT scan demonstration in a 51-year-old woman of a left posterolateral L5-S1 disk hernation consisting essentially in a gas-filled pouch (white arrow) Gas is also present in the central portion of the intervertebral disk space (black arrow)

DIAGNOSTIC IMAGING AND CHARACTERIZATION OF A HERNIATED LUMBAR DISK

Assessing the validity of the currently used imaging procedures to diagnose a herniated lumbar disk is not an easy endeavor The validity of a measurement is the extent to which it corresponds to the true biologic value or some accepted gold standard[ ]40 With the exception of postmortem studies evaluation of the pathoanatomy by the surgeon in the operating room has always been considered the gold standard but this does not constitute an ideal situation Inspection of the disk through a small laminectomy incision to determine for instance if nuclear fragments lie within or outside the anular fibers may not be very reliable Also unbiased intraoperative determination of a normal degenerated or herniated disk in a patient with sciatica may also be difficult[ ]86 Because the validity of diskography has been previously established by postmortem studies and surgical correlations[ ]48 it is sometimes used as a gold standard in situations where no surgery has been performed

Conventional Radiographs

Lumbar disk herniations can exceptionally be diagnosed directly on good quality lateral projections because the x-ray attenuation is slightly greater in displaced disk material than in epidural fat Occasionally a calcified rim outlines the displaced disk fragment

(Fig 23) In most situations however narrowing of an intervertebral disk space in the absence of other evidence of chronic diskopathy is the only detectable sign suggesting the presence of a disk herniation To my knowledge the sensitivity and specificity of this sign has never been assessed The accepted rule of thumb is that the height of a given lumbar intervertebral disk space should always be slightly greater than the height of the above located interspace This rule does not apply to the transition disk immediately above the sacrum (usually L5-S1) The specificity of this sign is probably quite high but a few false-positives are seen especially at the L4-L5 level because of minor congenital hypoplasia The presence of posterior or foraminal vertebral body osteophytes associated or not with disk space narrowing is a definite sign of a chronic disk herniation

Figure 23 A Chronic left L3-L4 extraforaminal disk hernation in a 54-year-old man suspected on an AP radiograph demonstrating a calcified shell on the left side of the intervertebral disk space (white arrow) B Axial CT scan section confirming the diagnosis of a chronic extraforaminal L3-L4 herniation

Myelography

Myelography is essentially an exploration of the subarachnoid space Disk herniations are demonstrated only indirectly because they can cause thecal sac deformity and individual nerve root sleeve filling defects (Fig 24) Of all the special imaging procedures

myelography is the only one that allows upright projections with full weight bearing It is not unusual to demonstrate in this way small posterior central or posterolateral herniations that are undetectable on CT sections Interestingly the overall sensitivity of myelography to detect disk herniations has been found to be higher than that of CT whereas its specificity has been found to be lower[ ]74 In comparison with standard CT examination which usually includes only the three or four lower lumbar disks myelography easily allows coverage of the entire lumbar area and assessment of the intrathecal structures (cauda equina and conus medullaris) Far lateral foraminal herniations extraforaminal herniations and anterior herniations however are not detected The sensitivity for detection of posterior central L5-S1 herniations is also relatively poor because of the greater distance between the thecal sac and the posterior aspect of this particular disk

Figure 24 L5-S1 disk herniation in a 25-year-old man detected by indirect signs using lumbosacral myelography A Upright oblique projections showing a filling defect of the left S1 root sleeve (white arrow) suggesting significant nerve root compression by a left posterolateral disk hernation The right S1 root sleeve fills normally with contrast (black arrow) B Subtle compression of the anterior wall of the dural sac by displaced disk material (small arrows) demonstrated on upright lateral projection This sign is usually absent in the presence of a large amount of fat and venous structures in the anterior epidural compartment

CT

The sensitivity of CT to diagnose a herniation of the nucleus pulposus at the L5-S1 interspace is greater than that of myelography if images in the exact plane of the disk can be obtained[ ]23 [ ]39 Otherwise the superiority of plain CT over myelography to demonstrate disk herniations has not been established but CT has the distinct advantage of being

noninvasive and provides direct anatomic information[ ]23 Large herniations are easily detected but as explained previously the distinction between protrusions and extrusions is often difficult without sagittal reconstructions CT essentially allows an assessment of the contour of the disk The diagnosis of very small herniations in the absence of direct or indirect evidence of a radial tear is hazardous and associated with a high percentage of false-positives and false-negatives[ ]52 The diagnosis of moderate and large size herniations in different directions is usually possible but anterior herniations are rarely diagnosed not because they are not detectable but because observers pay little attention to the anterior contour of the disk (Fig 25) Because the PLLC cannot usually be identified the distinction of subligamentous from transligamentous herniation can only be suggested in most cases by the size of the herniated material A definite diagnosis of sequestration is rarely possible Calcifications within the displaced material are readily seen but may be difficult at times to differentiate from an accompanying osteophyte or an avulsed bone fragment from the vertebral body ring epiphysis (Fig 26) The presence of gas in the herniated material is easily detected

Figure 25 Anterior L4-L5 herniation demonstrated by CT scan in a 51-year-old woman with chronic low back pain Although sometimes quite conspicuous such herniations are rarely reported because observers pay little attention to the anterior contour of the disk

Figure 26 CT scan demonstration of a posterior right central L4-L5 disk herniation in a 38-year-old woman with avulsion of a bone fragment from the ring epiphysis and adjacent part of the superior L5 end plate Reactive osteosclerosis is seen around the vertebral body defect (arrows) suggesting a chronic lesion

CT Myelography

This association combines the advantages of both imaging modalities The fact that its accuracy has been reported as being less[ ]22 [ ]32 higher[ ]1 [ ]6 or equivalent[ ]82 to MR imaging is a reflection of the differences in technologic advancement and pathologic nomenclature that hamper valid comparisons between different studies

MR Imaging

Most reported studies establish MR imaging as the first choice modality to diagnose a herniated lumbar disk[ ]5 [ ]22 [ ]32 [ ]46 The associated intravenous injection of a paramagnetic agent has been found useful to demonstrate some anatomic features of disk disease in patients with no previous lumbar disk surgery[ ]56 [ ]68 [ ]90 MR imaging provides a better assessment of disk morphology than CT or CT myelography because sagittal sections are routinely obtained Assessment of foraminal involvement by displaced disk material is more accurate (Fig 27) and anterior disk herniations can be detected more easily than with CT or CT myelography If one is looking specifically for herniated lumbar disks associated with nerve root compression however it has been demonstrated that CT is equally accurate[ ]82 Alterations of the central or peripheral disk signal intensity on T2-weighted images are seen in most disks afflicted with an anular tear[ ]48 and alert the observer to scrutinize the disk contour in search for local modifications indicative of a herniation Because the signal of the displaced disk material is usually very similar to that of the outer anulus PLLC and vertebral body cortical bone small herniations are generally more conspicuous on axial CT sections than on corresponding axial MR imaging sections Gas and calcium deposits within the displaced fragment cannot usually

be detected but associated vertebral body bone marrow changes are typically seen and are helpful in differentiating acute from chronic processes[ ]57 The occasional presence of a high-intensity zone in the herniated material with an occasionally enhancing border after contrast injection is probably caused by a mixture of displaced nuclear material acute and subacute inflammatory tissue and neovascularized reactive tissue[ ]4 [ ]48 [ ]72 Contradictory reports have been published regarding the accuracy of MR imaging to differentiate subligamentous from transligamentous herniations[ ]26 [ ]38 [ ]73 [ ]76 Understanding the anatomy of the PLLC is helpful to make the distinction (Fig 28) (Figure Not Available) Masaryk et al[ ]46 have suggested that MR imaging is accurate to distinguish sequestered disks from other forms of lumbar disk herniations but most observers find this distinction difficult to establish[ ]42

Figure 27 A Left L4-L5 foraminal herniation well seen on an intermediate-weighted left parasagittal MR section (arrow) in a 47-year-old man B The lesion is much less obvious on intermediate-weighted (left) and T2-weighted (right) axial sections and was in fact more conspicuous on the corresponding CT scan section

Figure 28 (Figure Not Available) A Subligamentous disk herniation Left T1-weighted image demonstrating displaced disk material with a smooth outline imposed by the demarcation of the anterior epidural space (AES) by the lateral membrane of the PLLC Right Correlative drawing B Transligamentous disk herniation Left T1-weighted image of a large disk herniation (cervical in this case) which has ruptured through the posterior confines of the AES Penetration of the right lateral membrane can be observed (arrow) and the disk fragment contour is serrated Right Correlative drawing (From Schellinger D Manz HJ Vidic B et al Disk fragment migration Radiology 175831-836 1990 with permission)

Diskography and CT Diskography

During 30 years (1950 to 1980) when myelography was the only available imaging technique to demonstrate lumbar disk herniations diskography was an invasive but efficient way to demonstrate posterior central L5-S1 herniations and other large herniations (other than posterior central and paramedial) that could not be detected by myelography[ ]50 These herniations are now usually well demonstrated by CT and MR imaging Comparing the accuracy of five imaging modalities (excluding MR imaging) for the diagnosis of lumbar disk herniation Jackson et al[ ]31 found that CT diskography (Fig 29) was the most accurate test (87) compared with 77 for CT myelography 74 for CT 70 for myelography 64 for pain reproduction during diskography and 58 for diskography without CT Disk injection reproduced the patients clinical pain pattern in only 36 of herniated disks This clinical test isolated from the images had high specificity (89) but low sensitivity (43) for the diagnosis of disk herniation The reported low sensitivity of diskography images (unassociated with CT) to diagnose disk herniation is to be expected the purpose of the intradiskal injection being primarily the demonstration of an anular tear the contrast leaking through the tear only occasionally delineates an extruded fragment When a disk herniation has been diagnosed by other imaging modalities diskography allows to determine if the herniation is contained or noncontained (Figs 30 and 31) this information may have clinical relevance[ ]62 It also allows to establish if the displaced disk material is communicating or not with the parent disk and establishes the likelihood that it is sequestered or not There always remains a possibility that the contrast injected under pressure may reach a disk fragment that is nevertheless sequestered by leaking through the associated anular tear CT diskography also allows assessment in most cases of the integrity of the PLLC[ ]89 The superior sensitivity of diskography over MR imaging to demonstrate anular tears has been well established[ ]27 [ ]44 [ ]48 [ ]64 [ ]77 [ ]91 [ ]94 The presence of a radial tear and the inflammatory reaction it creates may be symptomatic despite the absence of true disk herniation[ ]29 [ ]48 [ ]49 [ ]69

Figure 29 L4-L5 CT diskogram demonstrating a large left posterolateral radial anular tear associated with

a left foraminal and extraforaminal herniaton (same patient as in Figure 28) (Figure Not Available)

Figure 30 Contained posterior L4-L5 and L5-S1 disk herniations in a 57-year-old man demonstrated by diskography The L3-L4 disk is normal

Figure 31 Noncontained L4-L5 disk herniation in a 23-year-old woman Reflux of injected contrast is seen in the anterior epidural space above and below the disk space The L5-S1 disk also demonstrates incomplete anterior and posterior radial anular tears

SUMMARY

The absence of universal nomenclature standardization with respect to the definition of a disk herniation and its different categories especially regarding type and location is still a major problem that will only be overcome when major national or international scientific societies join efforts to support a particular scheme Meanwhile it is important to realize that the two models that are currently most used are based on a different perspective Trying to straddle the two by opposing for instance bulging disk and herniation is doomed to failure because this exercise defies formal logic MR imaging is currently the most accurate noninvasive imaging modality to diagnose a disk herniation and to determine its exact location The determination of some pathoanatomic characteristics of herniated disks (type and composition) may require the use of CT diskography or CT diskography

References

1 Albeck MJ Hilden J Kjaer L et al A controlled comparison of myelography computed tomography and magnetic resonance imaging in clinically suspected lumbar disc herniation Spine 20443-448 1995 Abstract 2 American Academy of Orthopedic Surgeons Glossary on Spinal Terminology Chicago American Academy of Orthopedic Surgeons 1981 3 Andersson GB Weinstein JN Disc herniation [editorial] Spine 211S 1996 Citation 4 Aprill C Bogduk N High-intensity zone A diagnostic sign of painful lumbar disc on magnetic resonance imaging Br J Radiol 65361-369 1992 Abstract 5 Birney TJ White JJ Jr Berens D et al Comparison of MRI and discography in the diagnosis of lumbar degenerative disc disease J Spinal Disord 5417-423 1992 Abstract 6 Bischoff RJ Rodriguez RP Gupta K et al A comparison of computed tomography-myelography magnetic resonance imaging and myelography in the diagnosis of herniated nucleus pulposus and spinal stenosis J Spinal Disord 6289-295 1993 Abstract 7 Bogduk N The innervation of the lumbar spine Spine 8286-293 1983 Abstract 8 Bogduk N Tynan W Wilson AS The nerve supply to the human lumbar intervertebral discs J Anat 13239-56 1981 Abstract 9 Bonneville JF La carte-image des hernies discales lombaires Rachis 2255-257 1990 10 Bonneville JF La topografia simbolica delle ernie discali lombari Riv Neuroradiol 5427-431 1992 11 Bonneville JF Plaidoyer pour une classification par limage des hernies discales lombaires La carte-image Rev Imag Med 2557-560 1990 12 Brant-Zawadzki M Jensen M Spinal nomenclature Spine 20388-390 1995 Abstract

13 Brant-Zawadzki MN Jensen MC Obuchowski N et al Interobserver and intraobserver variability in interpretation of lumbar disc abnormalities A comparison of two nomenclatures Spine 201257-1263 1995 Abstract 14 Breton G Is that a bulging disk a small herniation or a moderate protrusion [editorial] Can Assoc Radiol J 42318 1991 Citation 15 Czervionke LF Lumbar intervertebral disc disease Neuroimaging Clin North Am 3465-485 1993 16 Deyo RA Nonsurgical care of low back pain Neurosurg Clin North Am 2851-862 1991 17 Deyo RA Loeser JD Bigos SJ Herniated lumbar intervertebral disk Ann Intern Med 112598-603 1990 Abstract 18 Dorlands Illustrated Medical Dictionary ed 28 Philadelphia WB Saunders 1994 19 Fardon D Pinkerton S Balderston R et al Terms used for diagnosis by English speaking spine surgeons Spine 18274-277 1993 Citation 20 Fardon DF Herzog RJ Mink JH et al Nomenclature of Lumbar Disc Disorders Contemporary Concepts in Spine Care Rosemont IL North American Spine Society 1995 21 Fardon DF Herzog RJ Mink JH et al Nomenclature of lumbar disc disorders In Garfin S Vaccaro A (eds) Orthopedic Knowledge Update Spine Rosemont IL American Academy of Orthopedic Surgeons 1997 pp A3-A14 22 Forristall RM Marsh HO Pay NT Magnetic resonance imaging and contrast CT of the lumbar spine Comparison of diagnostic methods and correlation with surgical findings Spine 131049-1054 1988 Abstract 23 Fries JW Abodeely DA Vijungco JG et al Computed tomography of herniated and extruded nucleus pulposus J Comput Assist Tomogr 6874-887 1982 Abstract 24 Frymoyer JW Newberg A Pope MH et al Spine radiographs in patients with low-back pain An epidemiological study in men J Bone Joint Surg Am 661048-1055 1984 Abstract 25 Gospodarowicz M Benedet L Hutter RV et al History and international developments in cancer staging Cancer Prev Control 2262-268 1998 Abstract 26 Grenier N Greselle JF Vital JM et al Normal and disrupted lumbar longitudinal ligaments Correlative MR and anatomic study Radiology 171197-205 1989 Abstract 27 Gunzburg R Parkinson R Moore R et al A cadaveric study comparing discography magnetic resonance imaging histology and mechanical behavior of the human lumbar disc Spine 17417-426 1992 Abstract 28 Haughton VM Eldevik OP Magnaes B et al A prospective comparison of computed tomography and myelography in the diagnosis of herniated lumbar disks Radiology 142103-110 1982 Abstract

29 Haughton VM Lim TH An H Intervertebral disk appearance correlated with stiffness of lumbar spinal motion segments AJNR Am J Neuroradiol 201161-1165 1999 Abstract 30 Herzog RJ The radiologic assessment for a lumbar disc herniation Spine 2119S-38S 1996 Abstract 31 Jackson RP Becker GJ Jacobs RR et al The neuroradiographic diagnosis of lumbar herniated nucleus pulposus I A comparison of computed tomography (CT) myelography CT-myelography discography and CT-discography Spine 141356-1361 1989 Abstract 32 Jackson RP Cain JE Jr Jacobs RR et al The neuroradiographic diagnosis of lumbar herniated nucleus pulposus II A comparison of computed tomography (CT) myelography CT-myelography and magnetic resonance imaging Spine 141362-1367 1989 Abstract 33 Jarvik JG Haynor DR Koepsell TD et al Interreader reliability for a new classification of lumbar disk disease Acad Radiol 3537-544 1996 Abstract 34 Jensen MC Brant-Zawadzki MN Obuchowski N et al Magnetic resonance imaging of the lumbar spine in people without back pain N Engl J Med 33169-73 1994 Abstract 35 Kent DL Haynor DR Larson EB et al Diagnosis of lumbar spinal stenosis in adults A meta-analysis of the accuracy of CT MR and myelography AJR Am J Roentgenol 1581135-1144 1992 Abstract 36 Kieffer SA Sherry RG Wellenstein DE et al Bulging lumbar intervertebral disk Myelographic differentiation from herniated disk with nerve root compression AJR Am J Roentgenol 138709-716 1982 Abstract 37 Kieffer SA Stadlan EM Mohandas A et al Discographic-anatomical correlation of developmental changes with age in the intervertebral disc Acta Radiol 9733-739 1969 38 Kim KY Kim YT Lee CS et al MRI classification of lumbar herniated intervertebral disc Orthopedics 15493-497 1992 Abstract 39 Kornberg M Rechtine GR Dupuy TE Computed tomography in the diagnosis of a herniated disk at the L5-S1 level Spine 9433-436 1984 Abstract 40 Kramer MS Clinical Epidemiology and Biostatistics New York Springer-Verlag 1988 41 Landis JR Koch GG The measurement of observer agreement agreement for categorical data Biometrics 33159-174 1977 Abstract 42 Laredo JD Bossard P Vuillemin-Bodaghi Formes anatomo-radiologiques des hernies discales In Morvan G Deburge A Bard H et al (eds) Le Rachis Lombaire Degeneratif Montpellier Sauramps Medical 1998 pp 37-49 43 Lee SH Coleman PE Hahn FJ Magnetic resonance imaging of degenerative disk disease of the spine Radiol Clin North Am 26949-964 1988 Abstract 44 Linson MA Crowe CH Comparison of magnetic resonance imaging and lumbar discography in the diagnosis of disc degeneration Clin Orthop 160-163 1990

45 Marchand F Ahmed AM Investigation of the laminate structure of lumbar disc anulus fibrosus Spine 15402-410 1990 Abstract 46 Masaryk TJ Ross JS Modic MT et al High-resolution MR imaging of sequestered lumbar intervertebral disks AJR Am J Roentgenol 1501155-1162 1988 Abstract 47 Milette PC The proper terminology for reporting lumbar intervertebral disk disorders AJNR Am J Neuroradiol 181859-1866 1997 Citation 48 Milette PC Fontaine S Lepanto L et al Differentiating lumbar disc protrusions disk bulges and discs with normal contour but abnormal signal intensity Magnetic resonance imaging with discographic correlations Spine 2444-53 1999 Abstract 49 Milette PC Fontaine S Lepanto L et al Radiating pain to the lower extremities caused by lumbar disk rupture without spinal nerve root involvement AJNR Am J Neuroradiol 161605-1613 1995 Abstract 50 Milette PC Melancon D A reappraisal of lumbar discography Can Assoc Radiol J 33176-182 1982 51 Milette PC Melancon D Dupuis PR et al A simplified terminology for abnormalities of the lumbar disk Can Assoc Radiol J 42319-325 1991 Abstract 52 Milette PC Raymond J Fontaine S Comparison of high-resolution computed tomography with discography in the evaluation of lumbar disc herniations Spine 15525-533 1990 Abstract 53 Mink JH Deutsch AL Goldstein TB et al Spinal imaging and intervention 1998 Phys Med Rehabil Clin North Am 9343-380 1998 54 Mixter WJ Barr JS Rupture of the intervertebral disc with involvement of the spinal canal N Engl J Med 211210-234 1934 55 Modic MT Masaryk TJ Ross JS et al Imaging of degenerative disk disease Radiology 168177-186 1988 Citation 56 Modic MT Ross JS Obuchowski NA et al Contrast-enhanced MR imaging in acute lumbar radiculopathy A pilot study of the natural history Radiology 195429-435 1995 Abstract 57 Modic MT Steinberg PM Ross JS et al Degenerative disk disease Assessment of changes in vertebral body marrow with MR imaging Radiology 166193-199 1988 58 Morvan G Mathieu P Les stenoses laterales In Morvan G Deburge A Bard H et al (eds) Le Rachis Lombaire Degeneratif Montpellier Sauramps Medical 1998 pp 315-324 59 Murray RO Skeletal trauma Regional In Sutton D (ed) Textbook of Radiology and Imaging ed 3 New York Churchill Livingstone 1980 pp 210-231 60 Nachemson A Lumbar disc herniation Conclusions Acta Orthop Scand 64(suppl 251)49 1993 Citation

61 Nathan H Osteophytes of the vertebral column An anatomical study of their development according to age race and sex with consideration as to their etiology and significance J Bone Joint Surg Am 44243-268 1962 62 Nygaard OP Mellgren SI Osterud B The inflammatory properties of contained and noncontained lumbar disc herniations Spine 222584-2488 1997 Abstract 63 Ohshima H Hirano N Osada R et al Morphologic variation of lumbar posterior longitudinal ligament and the modality of disc herniation Spine 182408-2411 1993 Abstract 64 Osti OL Fraser RD MRI and discography of annular tears and intervertebral disc degeneration A prospective clinical comparison J Bone Joint Surg Br 74431-435 1992 Abstract 65 Palmgren T Gronblad M Virri J et al Immunohistochemical demonstration of sensory and autonomic nerve terminals in herniated lumbar disc tissue Spine 211301-1306 1996 Abstract 66 Resnick D Niwayama G Degenerative disease of the spine In Resnick D (ed) Diagnosis of Bone and Joint Disorders ed 3 Philadelphia WB Saunders 1995 pp 1372-1462 67 Resnick D Niwayama G Intravertebral disk herniations Cartilaginous (Schmorls) nodes Radiology 12657-65 1978 Abstract 68 Ross JS Modic MT Masaryk TJ Tears of the anulus fibrosus Assessment with Gd-DTPA-enhanced MR imaging AJR Am J Roentgenol 154159-162 1990 Abstract 69 Saal JS The role of inflammation in lumbar pain Spine 201821-1827 1995 Abstract 70 Sachs BL Vanharanta H Spivey MA et al Dallas discogram description A new classification of CTdiscography in low-back disorders Spine 12287-294 1987 Abstract 71 Sauser DD Goldman AB Kaye JJ Discogenic vertebral sclerosis J Can Assoc Radiol 2944-50 1978 Abstract 72 Schellhas KP Pollei SR Gundry CR et al Lumbar disc high-intensity zone Correlation of magnetic resonance imaging and discography Spine 2179-86 1996 Abstract 73 Schellinger D Manz HJ Vidic B et al Disk fragment migration Radiology 175831-836 1990 Abstract 74 Schipper J Kardaun JW Braakman R et al Lumbar disk herniation Diagnosis with CT or myelography Radiology 165227-231 1987 Abstract 75 Schmorl G Junghanns H The Human Spine in Health and Disease ed 2 New York Grune and Stratton 1971 76 Silverman CS Lenchik L Shimkin PM et al The value of MR in differentiating subligamentous from supraligamentous lumbar disk herniations AJNR Am J Neuroradiol 16571-579 1995 Abstract 77 Simmons JW Emery SF McMillin JN et al Awake discography A comparison study with magnetic

resonance imaging Spine 16S216-221 1991 Abstract 78 Smyth MJ Wright V Sciatica and the intervertebral disc J Bone Joint Surg Am 401401-1418 1958 79 Taveras JM Radiologic aspects of low back pain and sciatic syndromes [editorial] AJNR Am J Neuroradiol 9351-358 1989 80 Tehranzadeh J Discography 2000 Radiol Clin North Am 36463-495 1998 Full Text 81 Thelander U Fagerlund M Friberg S et al Describing the size of lumbar disc herniations using computed tomography A comparison of different size index calculations and their relation to sciatica Spine 191979-1984 1994 Abstract 82 Thornbury JR Fryback DG Turski PA et al Disk-caused nerve compression in patients with acute low-back pain Diagnosis with MR CT myelography and plain CT Radiology 186731-738 1993 Abstract 83 Twomey L Taylor J Age changes in lumbar intervertebral discs Acta Orthop Scand 56496-499 1985 Abstract 84 Twomey LT Taylor JR Age changes in lumbar vertebrae and intervertebral discs Clin Orthop 22497-104 1987 85 Williams AL CT diagnosis of degenerative disc disease The bulging annulus Radiol Clin North Am 21289-300 1983 Abstract 86 Williams AL Haughton VM Meyer GA et al Computed tomographic appearance of the bulging annulus Radiology 142403-408 1982 Abstract 87 Williams AL Haughton VM Syvertsen A Computed tomography in the diagnosis of herniated nucleus pulposus Radiology 13595-99 1980 Abstract 88 Wiltse LL Berger PE McCulloch JA A system for reporting the size and location of lesions in the spine Spine 221534-1537 1997 Abstract 89 Wiltse LL Fonseca AS Amster J et al Relationship of the dura Hofmanns ligaments Batsons plexus and a fibrovascular membrane lying on the posterior surface of the vertebral bodies and attaching to the deep layer of the posterior longitudinal ligament An anatomical radiologic and clinical study Spine 181030-1043 1993 Abstract 90 Yamashita K Hiroshima K Kurata A Gadolinium-DTPA-enhanced magnetic resonance imaging of a sequestered lumbar intervertebral disc and its correlation with pathologic findings Spine 19479-482 1994 Abstract 91 Yu SW Haughton VM Sether LA et al Comparison of MR and diskography in detecting radial tears of the anulus A postmortem study AJNR Am J Neuroradiol 101077-1081 1989 Abstract 92 Yu SW Sether LA Ho PS et al Tears of the anulus fibrosus Correlation between MR and pathologic findings in cadavers AJNR Am J Neuroradiol 9367-370 1988 Abstract

93 Yussen PS Swartz JD The acute lumbar disc herniation Imaging diagnosis Semin Ultrasound CT MR 14389-398 1993 Abstract 94 Zucherman J Derby R Hsu K et al Normal magnetic resonance imaging with abnormal discography Spine 131355-1359 1988 Abstract

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  • CLASSIFICATION DIAGNOSTIC IMAGING AND IMAGING CHARACTERIZATION OF A LUMBAR HERNIATED DISK
    • IMAGING OF LOW BACK PAIN I
      • CLASSIFICATION DIAGNOSTIC IMAGING AND IMAGING CHARACTERIZATION OF A LUMBAR HERNIATED DISK
        • DEFINITION OF A DISK HERNIATION
        • CLASSIFICATION OF A HERNIATED LUMBAR DISK
          • Main Categories of Noninfectious Disk Abnormalities
          • Further Qualifying the Displaced Disk Material Beyond the Disk Space
            • DIAGNOSTIC IMAGING AND CHARACTERIZATION OF A HERNIATED LUMBAR DISK
              • Conventional Radiographs
              • Myelography
              • CT
              • CT Myelography
              • MR Imaging
              • Diskography and CT Diskography
                • SUMMARY
                  • References
Page 16: CLASSIFICATION, DIAGNOSTIC IMAGING, AND IMAGING ... · PDF fileclassification, diagnostic imaging, and imaging characterization of a lumbar herniated disk ... classification, diagnostic

considered a probably asymptomatic developmental defect

Other characteristics of disk herniations have become relevant with the development of new therapeutic possibilities (eg chemonucleolysis and percutaneous diskectomy) The term sequestration is confusing and has often been used to indicate displacement of disk material away from the parent disk The term sequestered disk should be used restrictedly to designate a fragment of diskal tissue that has migrated from the disk space and has no connection by diskal tissue to the disk of origin[ ]20 [ ]21 [ ]42 Sequestration refers to loss of continuity with disk tissue still present in the intervertebral disk space The term migration has a broader meaning indicating displacement of disk material away from the edge of the rent in the outer anulus either in the central spinal canal at the disk level or above or below the disk level This difference is illustrated in Figure 11 The terms communicating and noncommunicating derive from a different perspective and are mostly used in the context of intradiskal therapeutic injections They refer to the interruption of the periphery of the disk allowing fluid injected into the disk to leak into the spinal canal and reach displaced disk material[ ]20 [ ]51 The terms contained and uncontained are unfamiliar to most radiologists in a contained herniation the displaced disk material is still covered by a few intact but distended outer anular fibers or by a capsule formed by outer anular fibers and the adherent posterior longitudinal ligament

Figure 11 Various types of posterior central herniations A Small subligamentous herniation (protrusion) without significant disk material migration B Subligamentous herniation with downward migration of disk material under the PLLC C Sub-ligamentous herniation with downward migration of disk material and sequestered fragment (arrow)

The terms subligamentous and extraligamentous (or transligamentous) refer to the position of the displaced disk material with respect to the posterior longitudinal ligament The anatomy of the posterior longitudinal ligament has been recently revised[ ]73 [ ]89 It is a membranous structure that has multiple components a deep layer attached to disks and vertebral bodies a superficial layer attached to the dura by fibrous tissue (Hoffmanns

ligament) and lateral extensions known as the lateral membranes or peridural membranes (Fig 12) (Figure Not Available) It should probably be referred to as the posterior longitudinal ligament complex (PLLC) It actually divides the epidural space into the perithecal space and the anterior epidural space where displaced disk material can be entrapped (Fig 13) A potential space allowing accumulation of displaced disk material has also been detected between the outer anular fibers and the deep fibers of the PLLC on the posterior central aspect of the disk[ ]63 Posterior midline herniations seldom rupture the PLLC and are generally subligamentous The lateral membranes are less resistant and transligamentous herniations are usually the result of posterior off-center herniations or posterolateral herniations

Figure 12 (Figure Not Available) The PLLC is portrayed here in relation to various types of subligamentous disk displacement At the disk level posteriorly displaced disk material frequently occupies the midline Below and above the disk an anterior epidural space (AES) exists between the PLLC and the posterior aspect of the vertebral bodies In this space disk fragment motion across the midline is curtailed by a sagittal midline septum (dashed line) A delicate translucent membrane (shown only on left side of drawing) is stretched between the free edge of the deep layer of the posterior longitudinal ligament and the lateral spinal canal (From Schellinger D Manz HJ Vidic B et al Disk fragment migration Radiology 175831-836 1990 with permission)

Figure 13 Relationship of typical posterior disk herniations with the PLLC A Midline sagittal section unless very large a posterior midline herniation usually remains entrapped underneath the deep layer of the PLL C and sometimes a few intact outer anulus fibers joining with the PLL C to form a capsule The deep layer of the PLL C (arrow) also attaches to the posterior aspect of the vertebral body so that no potential space is present underneath B Sagittal para-central section the PLL C extends laterally at the disk level (arrowhead) but above and below the disk an anterior epidural space (as) where disk fragments are frequently entrapped is present between the lateral (peridural) membranes and the posterior aspect of the vertebral bodies

Volume of Herniated Material

Quantifying the herniated disk material by measuring in millimeters its greatest diameter or by evaluating its cross-sectional area in square millimeters is rarely done The resulting figures could be misleading without relating this measurement to the size of the spinal canal and the exact location of the lesion[ ]88 A purely qualitative and subjective statement that a mild moderate or severe herniation is present however does not give the person reading the imaging report any indication as to the potential of the lesion to cause significant compression of the dural sac or individual exiting nerve roots A reasonably precise scheme has been proposed in 1995 by the Nomenclature Committee of the North American Spine Society[ ]20 Measurements are taken from an axial CT or MR imaging section at the site of most severe compromise canal compromise of less than 25 at that section is qualified as mild 25 to 75 is moderate 76 to 90 is moderately severe and greater than 90 is severe It is understood that such characterizations describe only the cross-sectional area at one level and do not account for the total volume of displaced material displacement of neural tissue or clinical significance The usefulness of having four categories is questionable and can likely generate poor interobserver or intraobserver agreement especially in situations where the central spinal canal is relatively narrow Bonnevilles scheme[ ]9 [ ]10 [ ]11 should generate greater reliability (Fig 14) (Figure Not Available) Separation of the cross-sectional area in three thirds can be applied to both the central spinal canal and the foramina It can be agreed by way of convention that the terms mild moderate and severe lumen compromise by a disk herniation designate extension of the displaced disk material in the anterior middle or posterior third of the central canal or foramen depending on the specified location of the herniation

Figure 14 (Figure Not Available) The size of the herniation in the horizontal plane is assessed and designated by the numbers 1 2 or 3 by establishing its extension in the anterior middle or posterior third of the spinal canal (From Bonneville JF Plaidoyer pour une classification par limage des hernies discales lombaires la carte-image Rev Imag Med 2557-560 1990 with permission)

Location of Herniated Material

Bonneville[ ]9 [ ]10 [ ]11 has also proposed an interesting and simple alpha-numerical system to classify according to their location the position of disk fragments that have migrated in the horizontal or sagittal plane (Figs 15 (Figure Not Available) and 16) (Figure Not Available) Using more precise anatomic boundaries unfortunately more familiar to surgeons than radiologists Wiltse et al[ ]88 have proposed another system which has been supported by the North American Spine Society[ ]20 [ ]21 Anatomic zones and levels are defined using the following anatomic landmarks medial edge of the articular facets medial lateral upper and lower border of the pedicles and coronal plane at the disk center On the horizontal plane (Fig 17) (Figure Not Available) these landmarks determine the bounderies of the central zone the subarticular zone the foraminal zone the extraforaminal zone and the anterior zone (anterior to the coronal plane at the center of the disk) In the sagittal plane they determine the boundaries of the diskal level the infrapedicular level the pedicular level and the suprapedicular level (Figs 18 (Figure

Not Available) and 19) (Figure Not Available) Radiologists interpreting axial CT or MR images may find it difficult to use the medial edge of the facets as the landmark that separates the central zone from the subarticular zone because the superior articular facets are generally not included in axial sections at the disk level The alternative is to use the expression posterolateral to designate collectively all posterior herniations that are not midline but do not extend into a foramen as was proposed by Bonneville[ ]9 [ ]10 [ ]11

Figure 15 (Figure Not Available) In the horizontal plane herniations are labeled midline (a) posterolateral (b) foraminal (c) and extra-foraminal (d) (From Bonneville JF Plaidoyer pour une classification par limage des hernies discales lombaires la carte-image Rev Imag Med 2557-560 1990 with permission)

Figure 16 (Figure Not Available) In the craniocaudal direction disk migration is labeled +1 +2 +3 or -1 -2 -3 by referring to the height of a vertebral body divided in thirds (From Bonneville JF Plaidoyer pour une classification par limage des hernies discales lombaires la carte-image Rev Imag Med 2557-560 1990 with permission)

Figure 17 (Figure Not Available) The anatomic zones identified on axial images The anterior zone (not shown) is delineated from the extraforaminal zone by an imaginary coronal line in the center of the vertebral body (From Wiltse LL Berger PE McCulloch JA A system for reporting the size and location of lesions in the spine Spine 221534-1537 1997 with permission)

Figure 18 (Figure Not Available) The anatomical levels identified on craniocaudal images (From Wiltse LL Berger PE McCulloch AJ A system for reporting the size and location of lesions in the spine Spine 221534-1537 1997 with permission)

Figure 19 (Figure Not Available) Coronal view of the main zones and levels (From Wiltse LL Berger PE McCulloch JA A system for reporting the size and location of lesions in the spine Spine 221534-1537 1997 with permission)

Composition of Herniated Material

Displaced disk material may consist of glycosaminoglycans type 1 or 2 collagen end plate cartilage and bone fragments avulsed from the ring epiphysis A reactive inflammatory reaction usually results in edematous tissue followed by granulation tissue which may undergo calcification (Fig 20) Necrotic and partially resorbed displaced disk material sometimes produces a large fluid-filled pouch distinguishable from the common high-intensity zone because of its size (Fig 21) or a gas-filled cavity generally in continuity with gas in the intervertebral space (Fig 22) [ ]42 These characteristics may be meaningful if intradiskal injection therapy is considered In imaging reports herniations exhibiting calcium deposits and those exhibiting replacement of disk material by gas or a relatively large fluid collection can be qualified as chronic herniations

Figure 20 A CT scan demonstration of a small posterior central L4-L5 calcified subligamentous herniation The resistant deep layer of the PLLC restrains displacement of the disk material in the posterior central direction and does not allow a detectable distortion of the disk contour In this particular case the presence of the calcification is actually the only evidence that a posterior midline anular tear and a small subligamentous herniation are present B Posterior right central and sub-articular L5-S1 calcified disk herniation in same patient Posterolateral herniations are generally more conspicuous than posterior midline herniations because the deep layer of the PLLC gets thinner away from the midline

Figure 21 Posterior central midline L4-L5 herniation in a 52-year-old man demonstrated on a T2-weighted midline MR sagittal section There is intervertebral space narrowing with loss of normal central disk signal

intensity while the herniated disk material demonstrates high signal intensity consistent with a predominantly fluid consistency

Figure 22 CT scan demonstration in a 51-year-old woman of a left posterolateral L5-S1 disk hernation consisting essentially in a gas-filled pouch (white arrow) Gas is also present in the central portion of the intervertebral disk space (black arrow)

DIAGNOSTIC IMAGING AND CHARACTERIZATION OF A HERNIATED LUMBAR DISK

Assessing the validity of the currently used imaging procedures to diagnose a herniated lumbar disk is not an easy endeavor The validity of a measurement is the extent to which it corresponds to the true biologic value or some accepted gold standard[ ]40 With the exception of postmortem studies evaluation of the pathoanatomy by the surgeon in the operating room has always been considered the gold standard but this does not constitute an ideal situation Inspection of the disk through a small laminectomy incision to determine for instance if nuclear fragments lie within or outside the anular fibers may not be very reliable Also unbiased intraoperative determination of a normal degenerated or herniated disk in a patient with sciatica may also be difficult[ ]86 Because the validity of diskography has been previously established by postmortem studies and surgical correlations[ ]48 it is sometimes used as a gold standard in situations where no surgery has been performed

Conventional Radiographs

Lumbar disk herniations can exceptionally be diagnosed directly on good quality lateral projections because the x-ray attenuation is slightly greater in displaced disk material than in epidural fat Occasionally a calcified rim outlines the displaced disk fragment

(Fig 23) In most situations however narrowing of an intervertebral disk space in the absence of other evidence of chronic diskopathy is the only detectable sign suggesting the presence of a disk herniation To my knowledge the sensitivity and specificity of this sign has never been assessed The accepted rule of thumb is that the height of a given lumbar intervertebral disk space should always be slightly greater than the height of the above located interspace This rule does not apply to the transition disk immediately above the sacrum (usually L5-S1) The specificity of this sign is probably quite high but a few false-positives are seen especially at the L4-L5 level because of minor congenital hypoplasia The presence of posterior or foraminal vertebral body osteophytes associated or not with disk space narrowing is a definite sign of a chronic disk herniation

Figure 23 A Chronic left L3-L4 extraforaminal disk hernation in a 54-year-old man suspected on an AP radiograph demonstrating a calcified shell on the left side of the intervertebral disk space (white arrow) B Axial CT scan section confirming the diagnosis of a chronic extraforaminal L3-L4 herniation

Myelography

Myelography is essentially an exploration of the subarachnoid space Disk herniations are demonstrated only indirectly because they can cause thecal sac deformity and individual nerve root sleeve filling defects (Fig 24) Of all the special imaging procedures

myelography is the only one that allows upright projections with full weight bearing It is not unusual to demonstrate in this way small posterior central or posterolateral herniations that are undetectable on CT sections Interestingly the overall sensitivity of myelography to detect disk herniations has been found to be higher than that of CT whereas its specificity has been found to be lower[ ]74 In comparison with standard CT examination which usually includes only the three or four lower lumbar disks myelography easily allows coverage of the entire lumbar area and assessment of the intrathecal structures (cauda equina and conus medullaris) Far lateral foraminal herniations extraforaminal herniations and anterior herniations however are not detected The sensitivity for detection of posterior central L5-S1 herniations is also relatively poor because of the greater distance between the thecal sac and the posterior aspect of this particular disk

Figure 24 L5-S1 disk herniation in a 25-year-old man detected by indirect signs using lumbosacral myelography A Upright oblique projections showing a filling defect of the left S1 root sleeve (white arrow) suggesting significant nerve root compression by a left posterolateral disk hernation The right S1 root sleeve fills normally with contrast (black arrow) B Subtle compression of the anterior wall of the dural sac by displaced disk material (small arrows) demonstrated on upright lateral projection This sign is usually absent in the presence of a large amount of fat and venous structures in the anterior epidural compartment

CT

The sensitivity of CT to diagnose a herniation of the nucleus pulposus at the L5-S1 interspace is greater than that of myelography if images in the exact plane of the disk can be obtained[ ]23 [ ]39 Otherwise the superiority of plain CT over myelography to demonstrate disk herniations has not been established but CT has the distinct advantage of being

noninvasive and provides direct anatomic information[ ]23 Large herniations are easily detected but as explained previously the distinction between protrusions and extrusions is often difficult without sagittal reconstructions CT essentially allows an assessment of the contour of the disk The diagnosis of very small herniations in the absence of direct or indirect evidence of a radial tear is hazardous and associated with a high percentage of false-positives and false-negatives[ ]52 The diagnosis of moderate and large size herniations in different directions is usually possible but anterior herniations are rarely diagnosed not because they are not detectable but because observers pay little attention to the anterior contour of the disk (Fig 25) Because the PLLC cannot usually be identified the distinction of subligamentous from transligamentous herniation can only be suggested in most cases by the size of the herniated material A definite diagnosis of sequestration is rarely possible Calcifications within the displaced material are readily seen but may be difficult at times to differentiate from an accompanying osteophyte or an avulsed bone fragment from the vertebral body ring epiphysis (Fig 26) The presence of gas in the herniated material is easily detected

Figure 25 Anterior L4-L5 herniation demonstrated by CT scan in a 51-year-old woman with chronic low back pain Although sometimes quite conspicuous such herniations are rarely reported because observers pay little attention to the anterior contour of the disk

Figure 26 CT scan demonstration of a posterior right central L4-L5 disk herniation in a 38-year-old woman with avulsion of a bone fragment from the ring epiphysis and adjacent part of the superior L5 end plate Reactive osteosclerosis is seen around the vertebral body defect (arrows) suggesting a chronic lesion

CT Myelography

This association combines the advantages of both imaging modalities The fact that its accuracy has been reported as being less[ ]22 [ ]32 higher[ ]1 [ ]6 or equivalent[ ]82 to MR imaging is a reflection of the differences in technologic advancement and pathologic nomenclature that hamper valid comparisons between different studies

MR Imaging

Most reported studies establish MR imaging as the first choice modality to diagnose a herniated lumbar disk[ ]5 [ ]22 [ ]32 [ ]46 The associated intravenous injection of a paramagnetic agent has been found useful to demonstrate some anatomic features of disk disease in patients with no previous lumbar disk surgery[ ]56 [ ]68 [ ]90 MR imaging provides a better assessment of disk morphology than CT or CT myelography because sagittal sections are routinely obtained Assessment of foraminal involvement by displaced disk material is more accurate (Fig 27) and anterior disk herniations can be detected more easily than with CT or CT myelography If one is looking specifically for herniated lumbar disks associated with nerve root compression however it has been demonstrated that CT is equally accurate[ ]82 Alterations of the central or peripheral disk signal intensity on T2-weighted images are seen in most disks afflicted with an anular tear[ ]48 and alert the observer to scrutinize the disk contour in search for local modifications indicative of a herniation Because the signal of the displaced disk material is usually very similar to that of the outer anulus PLLC and vertebral body cortical bone small herniations are generally more conspicuous on axial CT sections than on corresponding axial MR imaging sections Gas and calcium deposits within the displaced fragment cannot usually

be detected but associated vertebral body bone marrow changes are typically seen and are helpful in differentiating acute from chronic processes[ ]57 The occasional presence of a high-intensity zone in the herniated material with an occasionally enhancing border after contrast injection is probably caused by a mixture of displaced nuclear material acute and subacute inflammatory tissue and neovascularized reactive tissue[ ]4 [ ]48 [ ]72 Contradictory reports have been published regarding the accuracy of MR imaging to differentiate subligamentous from transligamentous herniations[ ]26 [ ]38 [ ]73 [ ]76 Understanding the anatomy of the PLLC is helpful to make the distinction (Fig 28) (Figure Not Available) Masaryk et al[ ]46 have suggested that MR imaging is accurate to distinguish sequestered disks from other forms of lumbar disk herniations but most observers find this distinction difficult to establish[ ]42

Figure 27 A Left L4-L5 foraminal herniation well seen on an intermediate-weighted left parasagittal MR section (arrow) in a 47-year-old man B The lesion is much less obvious on intermediate-weighted (left) and T2-weighted (right) axial sections and was in fact more conspicuous on the corresponding CT scan section

Figure 28 (Figure Not Available) A Subligamentous disk herniation Left T1-weighted image demonstrating displaced disk material with a smooth outline imposed by the demarcation of the anterior epidural space (AES) by the lateral membrane of the PLLC Right Correlative drawing B Transligamentous disk herniation Left T1-weighted image of a large disk herniation (cervical in this case) which has ruptured through the posterior confines of the AES Penetration of the right lateral membrane can be observed (arrow) and the disk fragment contour is serrated Right Correlative drawing (From Schellinger D Manz HJ Vidic B et al Disk fragment migration Radiology 175831-836 1990 with permission)

Diskography and CT Diskography

During 30 years (1950 to 1980) when myelography was the only available imaging technique to demonstrate lumbar disk herniations diskography was an invasive but efficient way to demonstrate posterior central L5-S1 herniations and other large herniations (other than posterior central and paramedial) that could not be detected by myelography[ ]50 These herniations are now usually well demonstrated by CT and MR imaging Comparing the accuracy of five imaging modalities (excluding MR imaging) for the diagnosis of lumbar disk herniation Jackson et al[ ]31 found that CT diskography (Fig 29) was the most accurate test (87) compared with 77 for CT myelography 74 for CT 70 for myelography 64 for pain reproduction during diskography and 58 for diskography without CT Disk injection reproduced the patients clinical pain pattern in only 36 of herniated disks This clinical test isolated from the images had high specificity (89) but low sensitivity (43) for the diagnosis of disk herniation The reported low sensitivity of diskography images (unassociated with CT) to diagnose disk herniation is to be expected the purpose of the intradiskal injection being primarily the demonstration of an anular tear the contrast leaking through the tear only occasionally delineates an extruded fragment When a disk herniation has been diagnosed by other imaging modalities diskography allows to determine if the herniation is contained or noncontained (Figs 30 and 31) this information may have clinical relevance[ ]62 It also allows to establish if the displaced disk material is communicating or not with the parent disk and establishes the likelihood that it is sequestered or not There always remains a possibility that the contrast injected under pressure may reach a disk fragment that is nevertheless sequestered by leaking through the associated anular tear CT diskography also allows assessment in most cases of the integrity of the PLLC[ ]89 The superior sensitivity of diskography over MR imaging to demonstrate anular tears has been well established[ ]27 [ ]44 [ ]48 [ ]64 [ ]77 [ ]91 [ ]94 The presence of a radial tear and the inflammatory reaction it creates may be symptomatic despite the absence of true disk herniation[ ]29 [ ]48 [ ]49 [ ]69

Figure 29 L4-L5 CT diskogram demonstrating a large left posterolateral radial anular tear associated with

a left foraminal and extraforaminal herniaton (same patient as in Figure 28) (Figure Not Available)

Figure 30 Contained posterior L4-L5 and L5-S1 disk herniations in a 57-year-old man demonstrated by diskography The L3-L4 disk is normal

Figure 31 Noncontained L4-L5 disk herniation in a 23-year-old woman Reflux of injected contrast is seen in the anterior epidural space above and below the disk space The L5-S1 disk also demonstrates incomplete anterior and posterior radial anular tears

SUMMARY

The absence of universal nomenclature standardization with respect to the definition of a disk herniation and its different categories especially regarding type and location is still a major problem that will only be overcome when major national or international scientific societies join efforts to support a particular scheme Meanwhile it is important to realize that the two models that are currently most used are based on a different perspective Trying to straddle the two by opposing for instance bulging disk and herniation is doomed to failure because this exercise defies formal logic MR imaging is currently the most accurate noninvasive imaging modality to diagnose a disk herniation and to determine its exact location The determination of some pathoanatomic characteristics of herniated disks (type and composition) may require the use of CT diskography or CT diskography

References

1 Albeck MJ Hilden J Kjaer L et al A controlled comparison of myelography computed tomography and magnetic resonance imaging in clinically suspected lumbar disc herniation Spine 20443-448 1995 Abstract 2 American Academy of Orthopedic Surgeons Glossary on Spinal Terminology Chicago American Academy of Orthopedic Surgeons 1981 3 Andersson GB Weinstein JN Disc herniation [editorial] Spine 211S 1996 Citation 4 Aprill C Bogduk N High-intensity zone A diagnostic sign of painful lumbar disc on magnetic resonance imaging Br J Radiol 65361-369 1992 Abstract 5 Birney TJ White JJ Jr Berens D et al Comparison of MRI and discography in the diagnosis of lumbar degenerative disc disease J Spinal Disord 5417-423 1992 Abstract 6 Bischoff RJ Rodriguez RP Gupta K et al A comparison of computed tomography-myelography magnetic resonance imaging and myelography in the diagnosis of herniated nucleus pulposus and spinal stenosis J Spinal Disord 6289-295 1993 Abstract 7 Bogduk N The innervation of the lumbar spine Spine 8286-293 1983 Abstract 8 Bogduk N Tynan W Wilson AS The nerve supply to the human lumbar intervertebral discs J Anat 13239-56 1981 Abstract 9 Bonneville JF La carte-image des hernies discales lombaires Rachis 2255-257 1990 10 Bonneville JF La topografia simbolica delle ernie discali lombari Riv Neuroradiol 5427-431 1992 11 Bonneville JF Plaidoyer pour une classification par limage des hernies discales lombaires La carte-image Rev Imag Med 2557-560 1990 12 Brant-Zawadzki M Jensen M Spinal nomenclature Spine 20388-390 1995 Abstract

13 Brant-Zawadzki MN Jensen MC Obuchowski N et al Interobserver and intraobserver variability in interpretation of lumbar disc abnormalities A comparison of two nomenclatures Spine 201257-1263 1995 Abstract 14 Breton G Is that a bulging disk a small herniation or a moderate protrusion [editorial] Can Assoc Radiol J 42318 1991 Citation 15 Czervionke LF Lumbar intervertebral disc disease Neuroimaging Clin North Am 3465-485 1993 16 Deyo RA Nonsurgical care of low back pain Neurosurg Clin North Am 2851-862 1991 17 Deyo RA Loeser JD Bigos SJ Herniated lumbar intervertebral disk Ann Intern Med 112598-603 1990 Abstract 18 Dorlands Illustrated Medical Dictionary ed 28 Philadelphia WB Saunders 1994 19 Fardon D Pinkerton S Balderston R et al Terms used for diagnosis by English speaking spine surgeons Spine 18274-277 1993 Citation 20 Fardon DF Herzog RJ Mink JH et al Nomenclature of Lumbar Disc Disorders Contemporary Concepts in Spine Care Rosemont IL North American Spine Society 1995 21 Fardon DF Herzog RJ Mink JH et al Nomenclature of lumbar disc disorders In Garfin S Vaccaro A (eds) Orthopedic Knowledge Update Spine Rosemont IL American Academy of Orthopedic Surgeons 1997 pp A3-A14 22 Forristall RM Marsh HO Pay NT Magnetic resonance imaging and contrast CT of the lumbar spine Comparison of diagnostic methods and correlation with surgical findings Spine 131049-1054 1988 Abstract 23 Fries JW Abodeely DA Vijungco JG et al Computed tomography of herniated and extruded nucleus pulposus J Comput Assist Tomogr 6874-887 1982 Abstract 24 Frymoyer JW Newberg A Pope MH et al Spine radiographs in patients with low-back pain An epidemiological study in men J Bone Joint Surg Am 661048-1055 1984 Abstract 25 Gospodarowicz M Benedet L Hutter RV et al History and international developments in cancer staging Cancer Prev Control 2262-268 1998 Abstract 26 Grenier N Greselle JF Vital JM et al Normal and disrupted lumbar longitudinal ligaments Correlative MR and anatomic study Radiology 171197-205 1989 Abstract 27 Gunzburg R Parkinson R Moore R et al A cadaveric study comparing discography magnetic resonance imaging histology and mechanical behavior of the human lumbar disc Spine 17417-426 1992 Abstract 28 Haughton VM Eldevik OP Magnaes B et al A prospective comparison of computed tomography and myelography in the diagnosis of herniated lumbar disks Radiology 142103-110 1982 Abstract

29 Haughton VM Lim TH An H Intervertebral disk appearance correlated with stiffness of lumbar spinal motion segments AJNR Am J Neuroradiol 201161-1165 1999 Abstract 30 Herzog RJ The radiologic assessment for a lumbar disc herniation Spine 2119S-38S 1996 Abstract 31 Jackson RP Becker GJ Jacobs RR et al The neuroradiographic diagnosis of lumbar herniated nucleus pulposus I A comparison of computed tomography (CT) myelography CT-myelography discography and CT-discography Spine 141356-1361 1989 Abstract 32 Jackson RP Cain JE Jr Jacobs RR et al The neuroradiographic diagnosis of lumbar herniated nucleus pulposus II A comparison of computed tomography (CT) myelography CT-myelography and magnetic resonance imaging Spine 141362-1367 1989 Abstract 33 Jarvik JG Haynor DR Koepsell TD et al Interreader reliability for a new classification of lumbar disk disease Acad Radiol 3537-544 1996 Abstract 34 Jensen MC Brant-Zawadzki MN Obuchowski N et al Magnetic resonance imaging of the lumbar spine in people without back pain N Engl J Med 33169-73 1994 Abstract 35 Kent DL Haynor DR Larson EB et al Diagnosis of lumbar spinal stenosis in adults A meta-analysis of the accuracy of CT MR and myelography AJR Am J Roentgenol 1581135-1144 1992 Abstract 36 Kieffer SA Sherry RG Wellenstein DE et al Bulging lumbar intervertebral disk Myelographic differentiation from herniated disk with nerve root compression AJR Am J Roentgenol 138709-716 1982 Abstract 37 Kieffer SA Stadlan EM Mohandas A et al Discographic-anatomical correlation of developmental changes with age in the intervertebral disc Acta Radiol 9733-739 1969 38 Kim KY Kim YT Lee CS et al MRI classification of lumbar herniated intervertebral disc Orthopedics 15493-497 1992 Abstract 39 Kornberg M Rechtine GR Dupuy TE Computed tomography in the diagnosis of a herniated disk at the L5-S1 level Spine 9433-436 1984 Abstract 40 Kramer MS Clinical Epidemiology and Biostatistics New York Springer-Verlag 1988 41 Landis JR Koch GG The measurement of observer agreement agreement for categorical data Biometrics 33159-174 1977 Abstract 42 Laredo JD Bossard P Vuillemin-Bodaghi Formes anatomo-radiologiques des hernies discales In Morvan G Deburge A Bard H et al (eds) Le Rachis Lombaire Degeneratif Montpellier Sauramps Medical 1998 pp 37-49 43 Lee SH Coleman PE Hahn FJ Magnetic resonance imaging of degenerative disk disease of the spine Radiol Clin North Am 26949-964 1988 Abstract 44 Linson MA Crowe CH Comparison of magnetic resonance imaging and lumbar discography in the diagnosis of disc degeneration Clin Orthop 160-163 1990

45 Marchand F Ahmed AM Investigation of the laminate structure of lumbar disc anulus fibrosus Spine 15402-410 1990 Abstract 46 Masaryk TJ Ross JS Modic MT et al High-resolution MR imaging of sequestered lumbar intervertebral disks AJR Am J Roentgenol 1501155-1162 1988 Abstract 47 Milette PC The proper terminology for reporting lumbar intervertebral disk disorders AJNR Am J Neuroradiol 181859-1866 1997 Citation 48 Milette PC Fontaine S Lepanto L et al Differentiating lumbar disc protrusions disk bulges and discs with normal contour but abnormal signal intensity Magnetic resonance imaging with discographic correlations Spine 2444-53 1999 Abstract 49 Milette PC Fontaine S Lepanto L et al Radiating pain to the lower extremities caused by lumbar disk rupture without spinal nerve root involvement AJNR Am J Neuroradiol 161605-1613 1995 Abstract 50 Milette PC Melancon D A reappraisal of lumbar discography Can Assoc Radiol J 33176-182 1982 51 Milette PC Melancon D Dupuis PR et al A simplified terminology for abnormalities of the lumbar disk Can Assoc Radiol J 42319-325 1991 Abstract 52 Milette PC Raymond J Fontaine S Comparison of high-resolution computed tomography with discography in the evaluation of lumbar disc herniations Spine 15525-533 1990 Abstract 53 Mink JH Deutsch AL Goldstein TB et al Spinal imaging and intervention 1998 Phys Med Rehabil Clin North Am 9343-380 1998 54 Mixter WJ Barr JS Rupture of the intervertebral disc with involvement of the spinal canal N Engl J Med 211210-234 1934 55 Modic MT Masaryk TJ Ross JS et al Imaging of degenerative disk disease Radiology 168177-186 1988 Citation 56 Modic MT Ross JS Obuchowski NA et al Contrast-enhanced MR imaging in acute lumbar radiculopathy A pilot study of the natural history Radiology 195429-435 1995 Abstract 57 Modic MT Steinberg PM Ross JS et al Degenerative disk disease Assessment of changes in vertebral body marrow with MR imaging Radiology 166193-199 1988 58 Morvan G Mathieu P Les stenoses laterales In Morvan G Deburge A Bard H et al (eds) Le Rachis Lombaire Degeneratif Montpellier Sauramps Medical 1998 pp 315-324 59 Murray RO Skeletal trauma Regional In Sutton D (ed) Textbook of Radiology and Imaging ed 3 New York Churchill Livingstone 1980 pp 210-231 60 Nachemson A Lumbar disc herniation Conclusions Acta Orthop Scand 64(suppl 251)49 1993 Citation

61 Nathan H Osteophytes of the vertebral column An anatomical study of their development according to age race and sex with consideration as to their etiology and significance J Bone Joint Surg Am 44243-268 1962 62 Nygaard OP Mellgren SI Osterud B The inflammatory properties of contained and noncontained lumbar disc herniations Spine 222584-2488 1997 Abstract 63 Ohshima H Hirano N Osada R et al Morphologic variation of lumbar posterior longitudinal ligament and the modality of disc herniation Spine 182408-2411 1993 Abstract 64 Osti OL Fraser RD MRI and discography of annular tears and intervertebral disc degeneration A prospective clinical comparison J Bone Joint Surg Br 74431-435 1992 Abstract 65 Palmgren T Gronblad M Virri J et al Immunohistochemical demonstration of sensory and autonomic nerve terminals in herniated lumbar disc tissue Spine 211301-1306 1996 Abstract 66 Resnick D Niwayama G Degenerative disease of the spine In Resnick D (ed) Diagnosis of Bone and Joint Disorders ed 3 Philadelphia WB Saunders 1995 pp 1372-1462 67 Resnick D Niwayama G Intravertebral disk herniations Cartilaginous (Schmorls) nodes Radiology 12657-65 1978 Abstract 68 Ross JS Modic MT Masaryk TJ Tears of the anulus fibrosus Assessment with Gd-DTPA-enhanced MR imaging AJR Am J Roentgenol 154159-162 1990 Abstract 69 Saal JS The role of inflammation in lumbar pain Spine 201821-1827 1995 Abstract 70 Sachs BL Vanharanta H Spivey MA et al Dallas discogram description A new classification of CTdiscography in low-back disorders Spine 12287-294 1987 Abstract 71 Sauser DD Goldman AB Kaye JJ Discogenic vertebral sclerosis J Can Assoc Radiol 2944-50 1978 Abstract 72 Schellhas KP Pollei SR Gundry CR et al Lumbar disc high-intensity zone Correlation of magnetic resonance imaging and discography Spine 2179-86 1996 Abstract 73 Schellinger D Manz HJ Vidic B et al Disk fragment migration Radiology 175831-836 1990 Abstract 74 Schipper J Kardaun JW Braakman R et al Lumbar disk herniation Diagnosis with CT or myelography Radiology 165227-231 1987 Abstract 75 Schmorl G Junghanns H The Human Spine in Health and Disease ed 2 New York Grune and Stratton 1971 76 Silverman CS Lenchik L Shimkin PM et al The value of MR in differentiating subligamentous from supraligamentous lumbar disk herniations AJNR Am J Neuroradiol 16571-579 1995 Abstract 77 Simmons JW Emery SF McMillin JN et al Awake discography A comparison study with magnetic

resonance imaging Spine 16S216-221 1991 Abstract 78 Smyth MJ Wright V Sciatica and the intervertebral disc J Bone Joint Surg Am 401401-1418 1958 79 Taveras JM Radiologic aspects of low back pain and sciatic syndromes [editorial] AJNR Am J Neuroradiol 9351-358 1989 80 Tehranzadeh J Discography 2000 Radiol Clin North Am 36463-495 1998 Full Text 81 Thelander U Fagerlund M Friberg S et al Describing the size of lumbar disc herniations using computed tomography A comparison of different size index calculations and their relation to sciatica Spine 191979-1984 1994 Abstract 82 Thornbury JR Fryback DG Turski PA et al Disk-caused nerve compression in patients with acute low-back pain Diagnosis with MR CT myelography and plain CT Radiology 186731-738 1993 Abstract 83 Twomey L Taylor J Age changes in lumbar intervertebral discs Acta Orthop Scand 56496-499 1985 Abstract 84 Twomey LT Taylor JR Age changes in lumbar vertebrae and intervertebral discs Clin Orthop 22497-104 1987 85 Williams AL CT diagnosis of degenerative disc disease The bulging annulus Radiol Clin North Am 21289-300 1983 Abstract 86 Williams AL Haughton VM Meyer GA et al Computed tomographic appearance of the bulging annulus Radiology 142403-408 1982 Abstract 87 Williams AL Haughton VM Syvertsen A Computed tomography in the diagnosis of herniated nucleus pulposus Radiology 13595-99 1980 Abstract 88 Wiltse LL Berger PE McCulloch JA A system for reporting the size and location of lesions in the spine Spine 221534-1537 1997 Abstract 89 Wiltse LL Fonseca AS Amster J et al Relationship of the dura Hofmanns ligaments Batsons plexus and a fibrovascular membrane lying on the posterior surface of the vertebral bodies and attaching to the deep layer of the posterior longitudinal ligament An anatomical radiologic and clinical study Spine 181030-1043 1993 Abstract 90 Yamashita K Hiroshima K Kurata A Gadolinium-DTPA-enhanced magnetic resonance imaging of a sequestered lumbar intervertebral disc and its correlation with pathologic findings Spine 19479-482 1994 Abstract 91 Yu SW Haughton VM Sether LA et al Comparison of MR and diskography in detecting radial tears of the anulus A postmortem study AJNR Am J Neuroradiol 101077-1081 1989 Abstract 92 Yu SW Sether LA Ho PS et al Tears of the anulus fibrosus Correlation between MR and pathologic findings in cadavers AJNR Am J Neuroradiol 9367-370 1988 Abstract

93 Yussen PS Swartz JD The acute lumbar disc herniation Imaging diagnosis Semin Ultrasound CT MR 14389-398 1993 Abstract 94 Zucherman J Derby R Hsu K et al Normal magnetic resonance imaging with abnormal discography Spine 131355-1359 1988 Abstract

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  • CLASSIFICATION DIAGNOSTIC IMAGING AND IMAGING CHARACTERIZATION OF A LUMBAR HERNIATED DISK
    • IMAGING OF LOW BACK PAIN I
      • CLASSIFICATION DIAGNOSTIC IMAGING AND IMAGING CHARACTERIZATION OF A LUMBAR HERNIATED DISK
        • DEFINITION OF A DISK HERNIATION
        • CLASSIFICATION OF A HERNIATED LUMBAR DISK
          • Main Categories of Noninfectious Disk Abnormalities
          • Further Qualifying the Displaced Disk Material Beyond the Disk Space
            • DIAGNOSTIC IMAGING AND CHARACTERIZATION OF A HERNIATED LUMBAR DISK
              • Conventional Radiographs
              • Myelography
              • CT
              • CT Myelography
              • MR Imaging
              • Diskography and CT Diskography
                • SUMMARY
                  • References
Page 17: CLASSIFICATION, DIAGNOSTIC IMAGING, AND IMAGING ... · PDF fileclassification, diagnostic imaging, and imaging characterization of a lumbar herniated disk ... classification, diagnostic

ligament) and lateral extensions known as the lateral membranes or peridural membranes (Fig 12) (Figure Not Available) It should probably be referred to as the posterior longitudinal ligament complex (PLLC) It actually divides the epidural space into the perithecal space and the anterior epidural space where displaced disk material can be entrapped (Fig 13) A potential space allowing accumulation of displaced disk material has also been detected between the outer anular fibers and the deep fibers of the PLLC on the posterior central aspect of the disk[ ]63 Posterior midline herniations seldom rupture the PLLC and are generally subligamentous The lateral membranes are less resistant and transligamentous herniations are usually the result of posterior off-center herniations or posterolateral herniations

Figure 12 (Figure Not Available) The PLLC is portrayed here in relation to various types of subligamentous disk displacement At the disk level posteriorly displaced disk material frequently occupies the midline Below and above the disk an anterior epidural space (AES) exists between the PLLC and the posterior aspect of the vertebral bodies In this space disk fragment motion across the midline is curtailed by a sagittal midline septum (dashed line) A delicate translucent membrane (shown only on left side of drawing) is stretched between the free edge of the deep layer of the posterior longitudinal ligament and the lateral spinal canal (From Schellinger D Manz HJ Vidic B et al Disk fragment migration Radiology 175831-836 1990 with permission)

Figure 13 Relationship of typical posterior disk herniations with the PLLC A Midline sagittal section unless very large a posterior midline herniation usually remains entrapped underneath the deep layer of the PLL C and sometimes a few intact outer anulus fibers joining with the PLL C to form a capsule The deep layer of the PLL C (arrow) also attaches to the posterior aspect of the vertebral body so that no potential space is present underneath B Sagittal para-central section the PLL C extends laterally at the disk level (arrowhead) but above and below the disk an anterior epidural space (as) where disk fragments are frequently entrapped is present between the lateral (peridural) membranes and the posterior aspect of the vertebral bodies

Volume of Herniated Material

Quantifying the herniated disk material by measuring in millimeters its greatest diameter or by evaluating its cross-sectional area in square millimeters is rarely done The resulting figures could be misleading without relating this measurement to the size of the spinal canal and the exact location of the lesion[ ]88 A purely qualitative and subjective statement that a mild moderate or severe herniation is present however does not give the person reading the imaging report any indication as to the potential of the lesion to cause significant compression of the dural sac or individual exiting nerve roots A reasonably precise scheme has been proposed in 1995 by the Nomenclature Committee of the North American Spine Society[ ]20 Measurements are taken from an axial CT or MR imaging section at the site of most severe compromise canal compromise of less than 25 at that section is qualified as mild 25 to 75 is moderate 76 to 90 is moderately severe and greater than 90 is severe It is understood that such characterizations describe only the cross-sectional area at one level and do not account for the total volume of displaced material displacement of neural tissue or clinical significance The usefulness of having four categories is questionable and can likely generate poor interobserver or intraobserver agreement especially in situations where the central spinal canal is relatively narrow Bonnevilles scheme[ ]9 [ ]10 [ ]11 should generate greater reliability (Fig 14) (Figure Not Available) Separation of the cross-sectional area in three thirds can be applied to both the central spinal canal and the foramina It can be agreed by way of convention that the terms mild moderate and severe lumen compromise by a disk herniation designate extension of the displaced disk material in the anterior middle or posterior third of the central canal or foramen depending on the specified location of the herniation

Figure 14 (Figure Not Available) The size of the herniation in the horizontal plane is assessed and designated by the numbers 1 2 or 3 by establishing its extension in the anterior middle or posterior third of the spinal canal (From Bonneville JF Plaidoyer pour une classification par limage des hernies discales lombaires la carte-image Rev Imag Med 2557-560 1990 with permission)

Location of Herniated Material

Bonneville[ ]9 [ ]10 [ ]11 has also proposed an interesting and simple alpha-numerical system to classify according to their location the position of disk fragments that have migrated in the horizontal or sagittal plane (Figs 15 (Figure Not Available) and 16) (Figure Not Available) Using more precise anatomic boundaries unfortunately more familiar to surgeons than radiologists Wiltse et al[ ]88 have proposed another system which has been supported by the North American Spine Society[ ]20 [ ]21 Anatomic zones and levels are defined using the following anatomic landmarks medial edge of the articular facets medial lateral upper and lower border of the pedicles and coronal plane at the disk center On the horizontal plane (Fig 17) (Figure Not Available) these landmarks determine the bounderies of the central zone the subarticular zone the foraminal zone the extraforaminal zone and the anterior zone (anterior to the coronal plane at the center of the disk) In the sagittal plane they determine the boundaries of the diskal level the infrapedicular level the pedicular level and the suprapedicular level (Figs 18 (Figure

Not Available) and 19) (Figure Not Available) Radiologists interpreting axial CT or MR images may find it difficult to use the medial edge of the facets as the landmark that separates the central zone from the subarticular zone because the superior articular facets are generally not included in axial sections at the disk level The alternative is to use the expression posterolateral to designate collectively all posterior herniations that are not midline but do not extend into a foramen as was proposed by Bonneville[ ]9 [ ]10 [ ]11

Figure 15 (Figure Not Available) In the horizontal plane herniations are labeled midline (a) posterolateral (b) foraminal (c) and extra-foraminal (d) (From Bonneville JF Plaidoyer pour une classification par limage des hernies discales lombaires la carte-image Rev Imag Med 2557-560 1990 with permission)

Figure 16 (Figure Not Available) In the craniocaudal direction disk migration is labeled +1 +2 +3 or -1 -2 -3 by referring to the height of a vertebral body divided in thirds (From Bonneville JF Plaidoyer pour une classification par limage des hernies discales lombaires la carte-image Rev Imag Med 2557-560 1990 with permission)

Figure 17 (Figure Not Available) The anatomic zones identified on axial images The anterior zone (not shown) is delineated from the extraforaminal zone by an imaginary coronal line in the center of the vertebral body (From Wiltse LL Berger PE McCulloch JA A system for reporting the size and location of lesions in the spine Spine 221534-1537 1997 with permission)

Figure 18 (Figure Not Available) The anatomical levels identified on craniocaudal images (From Wiltse LL Berger PE McCulloch AJ A system for reporting the size and location of lesions in the spine Spine 221534-1537 1997 with permission)

Figure 19 (Figure Not Available) Coronal view of the main zones and levels (From Wiltse LL Berger PE McCulloch JA A system for reporting the size and location of lesions in the spine Spine 221534-1537 1997 with permission)

Composition of Herniated Material

Displaced disk material may consist of glycosaminoglycans type 1 or 2 collagen end plate cartilage and bone fragments avulsed from the ring epiphysis A reactive inflammatory reaction usually results in edematous tissue followed by granulation tissue which may undergo calcification (Fig 20) Necrotic and partially resorbed displaced disk material sometimes produces a large fluid-filled pouch distinguishable from the common high-intensity zone because of its size (Fig 21) or a gas-filled cavity generally in continuity with gas in the intervertebral space (Fig 22) [ ]42 These characteristics may be meaningful if intradiskal injection therapy is considered In imaging reports herniations exhibiting calcium deposits and those exhibiting replacement of disk material by gas or a relatively large fluid collection can be qualified as chronic herniations

Figure 20 A CT scan demonstration of a small posterior central L4-L5 calcified subligamentous herniation The resistant deep layer of the PLLC restrains displacement of the disk material in the posterior central direction and does not allow a detectable distortion of the disk contour In this particular case the presence of the calcification is actually the only evidence that a posterior midline anular tear and a small subligamentous herniation are present B Posterior right central and sub-articular L5-S1 calcified disk herniation in same patient Posterolateral herniations are generally more conspicuous than posterior midline herniations because the deep layer of the PLLC gets thinner away from the midline

Figure 21 Posterior central midline L4-L5 herniation in a 52-year-old man demonstrated on a T2-weighted midline MR sagittal section There is intervertebral space narrowing with loss of normal central disk signal

intensity while the herniated disk material demonstrates high signal intensity consistent with a predominantly fluid consistency

Figure 22 CT scan demonstration in a 51-year-old woman of a left posterolateral L5-S1 disk hernation consisting essentially in a gas-filled pouch (white arrow) Gas is also present in the central portion of the intervertebral disk space (black arrow)

DIAGNOSTIC IMAGING AND CHARACTERIZATION OF A HERNIATED LUMBAR DISK

Assessing the validity of the currently used imaging procedures to diagnose a herniated lumbar disk is not an easy endeavor The validity of a measurement is the extent to which it corresponds to the true biologic value or some accepted gold standard[ ]40 With the exception of postmortem studies evaluation of the pathoanatomy by the surgeon in the operating room has always been considered the gold standard but this does not constitute an ideal situation Inspection of the disk through a small laminectomy incision to determine for instance if nuclear fragments lie within or outside the anular fibers may not be very reliable Also unbiased intraoperative determination of a normal degenerated or herniated disk in a patient with sciatica may also be difficult[ ]86 Because the validity of diskography has been previously established by postmortem studies and surgical correlations[ ]48 it is sometimes used as a gold standard in situations where no surgery has been performed

Conventional Radiographs

Lumbar disk herniations can exceptionally be diagnosed directly on good quality lateral projections because the x-ray attenuation is slightly greater in displaced disk material than in epidural fat Occasionally a calcified rim outlines the displaced disk fragment

(Fig 23) In most situations however narrowing of an intervertebral disk space in the absence of other evidence of chronic diskopathy is the only detectable sign suggesting the presence of a disk herniation To my knowledge the sensitivity and specificity of this sign has never been assessed The accepted rule of thumb is that the height of a given lumbar intervertebral disk space should always be slightly greater than the height of the above located interspace This rule does not apply to the transition disk immediately above the sacrum (usually L5-S1) The specificity of this sign is probably quite high but a few false-positives are seen especially at the L4-L5 level because of minor congenital hypoplasia The presence of posterior or foraminal vertebral body osteophytes associated or not with disk space narrowing is a definite sign of a chronic disk herniation

Figure 23 A Chronic left L3-L4 extraforaminal disk hernation in a 54-year-old man suspected on an AP radiograph demonstrating a calcified shell on the left side of the intervertebral disk space (white arrow) B Axial CT scan section confirming the diagnosis of a chronic extraforaminal L3-L4 herniation

Myelography

Myelography is essentially an exploration of the subarachnoid space Disk herniations are demonstrated only indirectly because they can cause thecal sac deformity and individual nerve root sleeve filling defects (Fig 24) Of all the special imaging procedures

myelography is the only one that allows upright projections with full weight bearing It is not unusual to demonstrate in this way small posterior central or posterolateral herniations that are undetectable on CT sections Interestingly the overall sensitivity of myelography to detect disk herniations has been found to be higher than that of CT whereas its specificity has been found to be lower[ ]74 In comparison with standard CT examination which usually includes only the three or four lower lumbar disks myelography easily allows coverage of the entire lumbar area and assessment of the intrathecal structures (cauda equina and conus medullaris) Far lateral foraminal herniations extraforaminal herniations and anterior herniations however are not detected The sensitivity for detection of posterior central L5-S1 herniations is also relatively poor because of the greater distance between the thecal sac and the posterior aspect of this particular disk

Figure 24 L5-S1 disk herniation in a 25-year-old man detected by indirect signs using lumbosacral myelography A Upright oblique projections showing a filling defect of the left S1 root sleeve (white arrow) suggesting significant nerve root compression by a left posterolateral disk hernation The right S1 root sleeve fills normally with contrast (black arrow) B Subtle compression of the anterior wall of the dural sac by displaced disk material (small arrows) demonstrated on upright lateral projection This sign is usually absent in the presence of a large amount of fat and venous structures in the anterior epidural compartment

CT

The sensitivity of CT to diagnose a herniation of the nucleus pulposus at the L5-S1 interspace is greater than that of myelography if images in the exact plane of the disk can be obtained[ ]23 [ ]39 Otherwise the superiority of plain CT over myelography to demonstrate disk herniations has not been established but CT has the distinct advantage of being

noninvasive and provides direct anatomic information[ ]23 Large herniations are easily detected but as explained previously the distinction between protrusions and extrusions is often difficult without sagittal reconstructions CT essentially allows an assessment of the contour of the disk The diagnosis of very small herniations in the absence of direct or indirect evidence of a radial tear is hazardous and associated with a high percentage of false-positives and false-negatives[ ]52 The diagnosis of moderate and large size herniations in different directions is usually possible but anterior herniations are rarely diagnosed not because they are not detectable but because observers pay little attention to the anterior contour of the disk (Fig 25) Because the PLLC cannot usually be identified the distinction of subligamentous from transligamentous herniation can only be suggested in most cases by the size of the herniated material A definite diagnosis of sequestration is rarely possible Calcifications within the displaced material are readily seen but may be difficult at times to differentiate from an accompanying osteophyte or an avulsed bone fragment from the vertebral body ring epiphysis (Fig 26) The presence of gas in the herniated material is easily detected

Figure 25 Anterior L4-L5 herniation demonstrated by CT scan in a 51-year-old woman with chronic low back pain Although sometimes quite conspicuous such herniations are rarely reported because observers pay little attention to the anterior contour of the disk

Figure 26 CT scan demonstration of a posterior right central L4-L5 disk herniation in a 38-year-old woman with avulsion of a bone fragment from the ring epiphysis and adjacent part of the superior L5 end plate Reactive osteosclerosis is seen around the vertebral body defect (arrows) suggesting a chronic lesion

CT Myelography

This association combines the advantages of both imaging modalities The fact that its accuracy has been reported as being less[ ]22 [ ]32 higher[ ]1 [ ]6 or equivalent[ ]82 to MR imaging is a reflection of the differences in technologic advancement and pathologic nomenclature that hamper valid comparisons between different studies

MR Imaging

Most reported studies establish MR imaging as the first choice modality to diagnose a herniated lumbar disk[ ]5 [ ]22 [ ]32 [ ]46 The associated intravenous injection of a paramagnetic agent has been found useful to demonstrate some anatomic features of disk disease in patients with no previous lumbar disk surgery[ ]56 [ ]68 [ ]90 MR imaging provides a better assessment of disk morphology than CT or CT myelography because sagittal sections are routinely obtained Assessment of foraminal involvement by displaced disk material is more accurate (Fig 27) and anterior disk herniations can be detected more easily than with CT or CT myelography If one is looking specifically for herniated lumbar disks associated with nerve root compression however it has been demonstrated that CT is equally accurate[ ]82 Alterations of the central or peripheral disk signal intensity on T2-weighted images are seen in most disks afflicted with an anular tear[ ]48 and alert the observer to scrutinize the disk contour in search for local modifications indicative of a herniation Because the signal of the displaced disk material is usually very similar to that of the outer anulus PLLC and vertebral body cortical bone small herniations are generally more conspicuous on axial CT sections than on corresponding axial MR imaging sections Gas and calcium deposits within the displaced fragment cannot usually

be detected but associated vertebral body bone marrow changes are typically seen and are helpful in differentiating acute from chronic processes[ ]57 The occasional presence of a high-intensity zone in the herniated material with an occasionally enhancing border after contrast injection is probably caused by a mixture of displaced nuclear material acute and subacute inflammatory tissue and neovascularized reactive tissue[ ]4 [ ]48 [ ]72 Contradictory reports have been published regarding the accuracy of MR imaging to differentiate subligamentous from transligamentous herniations[ ]26 [ ]38 [ ]73 [ ]76 Understanding the anatomy of the PLLC is helpful to make the distinction (Fig 28) (Figure Not Available) Masaryk et al[ ]46 have suggested that MR imaging is accurate to distinguish sequestered disks from other forms of lumbar disk herniations but most observers find this distinction difficult to establish[ ]42

Figure 27 A Left L4-L5 foraminal herniation well seen on an intermediate-weighted left parasagittal MR section (arrow) in a 47-year-old man B The lesion is much less obvious on intermediate-weighted (left) and T2-weighted (right) axial sections and was in fact more conspicuous on the corresponding CT scan section

Figure 28 (Figure Not Available) A Subligamentous disk herniation Left T1-weighted image demonstrating displaced disk material with a smooth outline imposed by the demarcation of the anterior epidural space (AES) by the lateral membrane of the PLLC Right Correlative drawing B Transligamentous disk herniation Left T1-weighted image of a large disk herniation (cervical in this case) which has ruptured through the posterior confines of the AES Penetration of the right lateral membrane can be observed (arrow) and the disk fragment contour is serrated Right Correlative drawing (From Schellinger D Manz HJ Vidic B et al Disk fragment migration Radiology 175831-836 1990 with permission)

Diskography and CT Diskography

During 30 years (1950 to 1980) when myelography was the only available imaging technique to demonstrate lumbar disk herniations diskography was an invasive but efficient way to demonstrate posterior central L5-S1 herniations and other large herniations (other than posterior central and paramedial) that could not be detected by myelography[ ]50 These herniations are now usually well demonstrated by CT and MR imaging Comparing the accuracy of five imaging modalities (excluding MR imaging) for the diagnosis of lumbar disk herniation Jackson et al[ ]31 found that CT diskography (Fig 29) was the most accurate test (87) compared with 77 for CT myelography 74 for CT 70 for myelography 64 for pain reproduction during diskography and 58 for diskography without CT Disk injection reproduced the patients clinical pain pattern in only 36 of herniated disks This clinical test isolated from the images had high specificity (89) but low sensitivity (43) for the diagnosis of disk herniation The reported low sensitivity of diskography images (unassociated with CT) to diagnose disk herniation is to be expected the purpose of the intradiskal injection being primarily the demonstration of an anular tear the contrast leaking through the tear only occasionally delineates an extruded fragment When a disk herniation has been diagnosed by other imaging modalities diskography allows to determine if the herniation is contained or noncontained (Figs 30 and 31) this information may have clinical relevance[ ]62 It also allows to establish if the displaced disk material is communicating or not with the parent disk and establishes the likelihood that it is sequestered or not There always remains a possibility that the contrast injected under pressure may reach a disk fragment that is nevertheless sequestered by leaking through the associated anular tear CT diskography also allows assessment in most cases of the integrity of the PLLC[ ]89 The superior sensitivity of diskography over MR imaging to demonstrate anular tears has been well established[ ]27 [ ]44 [ ]48 [ ]64 [ ]77 [ ]91 [ ]94 The presence of a radial tear and the inflammatory reaction it creates may be symptomatic despite the absence of true disk herniation[ ]29 [ ]48 [ ]49 [ ]69

Figure 29 L4-L5 CT diskogram demonstrating a large left posterolateral radial anular tear associated with

a left foraminal and extraforaminal herniaton (same patient as in Figure 28) (Figure Not Available)

Figure 30 Contained posterior L4-L5 and L5-S1 disk herniations in a 57-year-old man demonstrated by diskography The L3-L4 disk is normal

Figure 31 Noncontained L4-L5 disk herniation in a 23-year-old woman Reflux of injected contrast is seen in the anterior epidural space above and below the disk space The L5-S1 disk also demonstrates incomplete anterior and posterior radial anular tears

SUMMARY

The absence of universal nomenclature standardization with respect to the definition of a disk herniation and its different categories especially regarding type and location is still a major problem that will only be overcome when major national or international scientific societies join efforts to support a particular scheme Meanwhile it is important to realize that the two models that are currently most used are based on a different perspective Trying to straddle the two by opposing for instance bulging disk and herniation is doomed to failure because this exercise defies formal logic MR imaging is currently the most accurate noninvasive imaging modality to diagnose a disk herniation and to determine its exact location The determination of some pathoanatomic characteristics of herniated disks (type and composition) may require the use of CT diskography or CT diskography

References

1 Albeck MJ Hilden J Kjaer L et al A controlled comparison of myelography computed tomography and magnetic resonance imaging in clinically suspected lumbar disc herniation Spine 20443-448 1995 Abstract 2 American Academy of Orthopedic Surgeons Glossary on Spinal Terminology Chicago American Academy of Orthopedic Surgeons 1981 3 Andersson GB Weinstein JN Disc herniation [editorial] Spine 211S 1996 Citation 4 Aprill C Bogduk N High-intensity zone A diagnostic sign of painful lumbar disc on magnetic resonance imaging Br J Radiol 65361-369 1992 Abstract 5 Birney TJ White JJ Jr Berens D et al Comparison of MRI and discography in the diagnosis of lumbar degenerative disc disease J Spinal Disord 5417-423 1992 Abstract 6 Bischoff RJ Rodriguez RP Gupta K et al A comparison of computed tomography-myelography magnetic resonance imaging and myelography in the diagnosis of herniated nucleus pulposus and spinal stenosis J Spinal Disord 6289-295 1993 Abstract 7 Bogduk N The innervation of the lumbar spine Spine 8286-293 1983 Abstract 8 Bogduk N Tynan W Wilson AS The nerve supply to the human lumbar intervertebral discs J Anat 13239-56 1981 Abstract 9 Bonneville JF La carte-image des hernies discales lombaires Rachis 2255-257 1990 10 Bonneville JF La topografia simbolica delle ernie discali lombari Riv Neuroradiol 5427-431 1992 11 Bonneville JF Plaidoyer pour une classification par limage des hernies discales lombaires La carte-image Rev Imag Med 2557-560 1990 12 Brant-Zawadzki M Jensen M Spinal nomenclature Spine 20388-390 1995 Abstract

13 Brant-Zawadzki MN Jensen MC Obuchowski N et al Interobserver and intraobserver variability in interpretation of lumbar disc abnormalities A comparison of two nomenclatures Spine 201257-1263 1995 Abstract 14 Breton G Is that a bulging disk a small herniation or a moderate protrusion [editorial] Can Assoc Radiol J 42318 1991 Citation 15 Czervionke LF Lumbar intervertebral disc disease Neuroimaging Clin North Am 3465-485 1993 16 Deyo RA Nonsurgical care of low back pain Neurosurg Clin North Am 2851-862 1991 17 Deyo RA Loeser JD Bigos SJ Herniated lumbar intervertebral disk Ann Intern Med 112598-603 1990 Abstract 18 Dorlands Illustrated Medical Dictionary ed 28 Philadelphia WB Saunders 1994 19 Fardon D Pinkerton S Balderston R et al Terms used for diagnosis by English speaking spine surgeons Spine 18274-277 1993 Citation 20 Fardon DF Herzog RJ Mink JH et al Nomenclature of Lumbar Disc Disorders Contemporary Concepts in Spine Care Rosemont IL North American Spine Society 1995 21 Fardon DF Herzog RJ Mink JH et al Nomenclature of lumbar disc disorders In Garfin S Vaccaro A (eds) Orthopedic Knowledge Update Spine Rosemont IL American Academy of Orthopedic Surgeons 1997 pp A3-A14 22 Forristall RM Marsh HO Pay NT Magnetic resonance imaging and contrast CT of the lumbar spine Comparison of diagnostic methods and correlation with surgical findings Spine 131049-1054 1988 Abstract 23 Fries JW Abodeely DA Vijungco JG et al Computed tomography of herniated and extruded nucleus pulposus J Comput Assist Tomogr 6874-887 1982 Abstract 24 Frymoyer JW Newberg A Pope MH et al Spine radiographs in patients with low-back pain An epidemiological study in men J Bone Joint Surg Am 661048-1055 1984 Abstract 25 Gospodarowicz M Benedet L Hutter RV et al History and international developments in cancer staging Cancer Prev Control 2262-268 1998 Abstract 26 Grenier N Greselle JF Vital JM et al Normal and disrupted lumbar longitudinal ligaments Correlative MR and anatomic study Radiology 171197-205 1989 Abstract 27 Gunzburg R Parkinson R Moore R et al A cadaveric study comparing discography magnetic resonance imaging histology and mechanical behavior of the human lumbar disc Spine 17417-426 1992 Abstract 28 Haughton VM Eldevik OP Magnaes B et al A prospective comparison of computed tomography and myelography in the diagnosis of herniated lumbar disks Radiology 142103-110 1982 Abstract

29 Haughton VM Lim TH An H Intervertebral disk appearance correlated with stiffness of lumbar spinal motion segments AJNR Am J Neuroradiol 201161-1165 1999 Abstract 30 Herzog RJ The radiologic assessment for a lumbar disc herniation Spine 2119S-38S 1996 Abstract 31 Jackson RP Becker GJ Jacobs RR et al The neuroradiographic diagnosis of lumbar herniated nucleus pulposus I A comparison of computed tomography (CT) myelography CT-myelography discography and CT-discography Spine 141356-1361 1989 Abstract 32 Jackson RP Cain JE Jr Jacobs RR et al The neuroradiographic diagnosis of lumbar herniated nucleus pulposus II A comparison of computed tomography (CT) myelography CT-myelography and magnetic resonance imaging Spine 141362-1367 1989 Abstract 33 Jarvik JG Haynor DR Koepsell TD et al Interreader reliability for a new classification of lumbar disk disease Acad Radiol 3537-544 1996 Abstract 34 Jensen MC Brant-Zawadzki MN Obuchowski N et al Magnetic resonance imaging of the lumbar spine in people without back pain N Engl J Med 33169-73 1994 Abstract 35 Kent DL Haynor DR Larson EB et al Diagnosis of lumbar spinal stenosis in adults A meta-analysis of the accuracy of CT MR and myelography AJR Am J Roentgenol 1581135-1144 1992 Abstract 36 Kieffer SA Sherry RG Wellenstein DE et al Bulging lumbar intervertebral disk Myelographic differentiation from herniated disk with nerve root compression AJR Am J Roentgenol 138709-716 1982 Abstract 37 Kieffer SA Stadlan EM Mohandas A et al Discographic-anatomical correlation of developmental changes with age in the intervertebral disc Acta Radiol 9733-739 1969 38 Kim KY Kim YT Lee CS et al MRI classification of lumbar herniated intervertebral disc Orthopedics 15493-497 1992 Abstract 39 Kornberg M Rechtine GR Dupuy TE Computed tomography in the diagnosis of a herniated disk at the L5-S1 level Spine 9433-436 1984 Abstract 40 Kramer MS Clinical Epidemiology and Biostatistics New York Springer-Verlag 1988 41 Landis JR Koch GG The measurement of observer agreement agreement for categorical data Biometrics 33159-174 1977 Abstract 42 Laredo JD Bossard P Vuillemin-Bodaghi Formes anatomo-radiologiques des hernies discales In Morvan G Deburge A Bard H et al (eds) Le Rachis Lombaire Degeneratif Montpellier Sauramps Medical 1998 pp 37-49 43 Lee SH Coleman PE Hahn FJ Magnetic resonance imaging of degenerative disk disease of the spine Radiol Clin North Am 26949-964 1988 Abstract 44 Linson MA Crowe CH Comparison of magnetic resonance imaging and lumbar discography in the diagnosis of disc degeneration Clin Orthop 160-163 1990

45 Marchand F Ahmed AM Investigation of the laminate structure of lumbar disc anulus fibrosus Spine 15402-410 1990 Abstract 46 Masaryk TJ Ross JS Modic MT et al High-resolution MR imaging of sequestered lumbar intervertebral disks AJR Am J Roentgenol 1501155-1162 1988 Abstract 47 Milette PC The proper terminology for reporting lumbar intervertebral disk disorders AJNR Am J Neuroradiol 181859-1866 1997 Citation 48 Milette PC Fontaine S Lepanto L et al Differentiating lumbar disc protrusions disk bulges and discs with normal contour but abnormal signal intensity Magnetic resonance imaging with discographic correlations Spine 2444-53 1999 Abstract 49 Milette PC Fontaine S Lepanto L et al Radiating pain to the lower extremities caused by lumbar disk rupture without spinal nerve root involvement AJNR Am J Neuroradiol 161605-1613 1995 Abstract 50 Milette PC Melancon D A reappraisal of lumbar discography Can Assoc Radiol J 33176-182 1982 51 Milette PC Melancon D Dupuis PR et al A simplified terminology for abnormalities of the lumbar disk Can Assoc Radiol J 42319-325 1991 Abstract 52 Milette PC Raymond J Fontaine S Comparison of high-resolution computed tomography with discography in the evaluation of lumbar disc herniations Spine 15525-533 1990 Abstract 53 Mink JH Deutsch AL Goldstein TB et al Spinal imaging and intervention 1998 Phys Med Rehabil Clin North Am 9343-380 1998 54 Mixter WJ Barr JS Rupture of the intervertebral disc with involvement of the spinal canal N Engl J Med 211210-234 1934 55 Modic MT Masaryk TJ Ross JS et al Imaging of degenerative disk disease Radiology 168177-186 1988 Citation 56 Modic MT Ross JS Obuchowski NA et al Contrast-enhanced MR imaging in acute lumbar radiculopathy A pilot study of the natural history Radiology 195429-435 1995 Abstract 57 Modic MT Steinberg PM Ross JS et al Degenerative disk disease Assessment of changes in vertebral body marrow with MR imaging Radiology 166193-199 1988 58 Morvan G Mathieu P Les stenoses laterales In Morvan G Deburge A Bard H et al (eds) Le Rachis Lombaire Degeneratif Montpellier Sauramps Medical 1998 pp 315-324 59 Murray RO Skeletal trauma Regional In Sutton D (ed) Textbook of Radiology and Imaging ed 3 New York Churchill Livingstone 1980 pp 210-231 60 Nachemson A Lumbar disc herniation Conclusions Acta Orthop Scand 64(suppl 251)49 1993 Citation

61 Nathan H Osteophytes of the vertebral column An anatomical study of their development according to age race and sex with consideration as to their etiology and significance J Bone Joint Surg Am 44243-268 1962 62 Nygaard OP Mellgren SI Osterud B The inflammatory properties of contained and noncontained lumbar disc herniations Spine 222584-2488 1997 Abstract 63 Ohshima H Hirano N Osada R et al Morphologic variation of lumbar posterior longitudinal ligament and the modality of disc herniation Spine 182408-2411 1993 Abstract 64 Osti OL Fraser RD MRI and discography of annular tears and intervertebral disc degeneration A prospective clinical comparison J Bone Joint Surg Br 74431-435 1992 Abstract 65 Palmgren T Gronblad M Virri J et al Immunohistochemical demonstration of sensory and autonomic nerve terminals in herniated lumbar disc tissue Spine 211301-1306 1996 Abstract 66 Resnick D Niwayama G Degenerative disease of the spine In Resnick D (ed) Diagnosis of Bone and Joint Disorders ed 3 Philadelphia WB Saunders 1995 pp 1372-1462 67 Resnick D Niwayama G Intravertebral disk herniations Cartilaginous (Schmorls) nodes Radiology 12657-65 1978 Abstract 68 Ross JS Modic MT Masaryk TJ Tears of the anulus fibrosus Assessment with Gd-DTPA-enhanced MR imaging AJR Am J Roentgenol 154159-162 1990 Abstract 69 Saal JS The role of inflammation in lumbar pain Spine 201821-1827 1995 Abstract 70 Sachs BL Vanharanta H Spivey MA et al Dallas discogram description A new classification of CTdiscography in low-back disorders Spine 12287-294 1987 Abstract 71 Sauser DD Goldman AB Kaye JJ Discogenic vertebral sclerosis J Can Assoc Radiol 2944-50 1978 Abstract 72 Schellhas KP Pollei SR Gundry CR et al Lumbar disc high-intensity zone Correlation of magnetic resonance imaging and discography Spine 2179-86 1996 Abstract 73 Schellinger D Manz HJ Vidic B et al Disk fragment migration Radiology 175831-836 1990 Abstract 74 Schipper J Kardaun JW Braakman R et al Lumbar disk herniation Diagnosis with CT or myelography Radiology 165227-231 1987 Abstract 75 Schmorl G Junghanns H The Human Spine in Health and Disease ed 2 New York Grune and Stratton 1971 76 Silverman CS Lenchik L Shimkin PM et al The value of MR in differentiating subligamentous from supraligamentous lumbar disk herniations AJNR Am J Neuroradiol 16571-579 1995 Abstract 77 Simmons JW Emery SF McMillin JN et al Awake discography A comparison study with magnetic

resonance imaging Spine 16S216-221 1991 Abstract 78 Smyth MJ Wright V Sciatica and the intervertebral disc J Bone Joint Surg Am 401401-1418 1958 79 Taveras JM Radiologic aspects of low back pain and sciatic syndromes [editorial] AJNR Am J Neuroradiol 9351-358 1989 80 Tehranzadeh J Discography 2000 Radiol Clin North Am 36463-495 1998 Full Text 81 Thelander U Fagerlund M Friberg S et al Describing the size of lumbar disc herniations using computed tomography A comparison of different size index calculations and their relation to sciatica Spine 191979-1984 1994 Abstract 82 Thornbury JR Fryback DG Turski PA et al Disk-caused nerve compression in patients with acute low-back pain Diagnosis with MR CT myelography and plain CT Radiology 186731-738 1993 Abstract 83 Twomey L Taylor J Age changes in lumbar intervertebral discs Acta Orthop Scand 56496-499 1985 Abstract 84 Twomey LT Taylor JR Age changes in lumbar vertebrae and intervertebral discs Clin Orthop 22497-104 1987 85 Williams AL CT diagnosis of degenerative disc disease The bulging annulus Radiol Clin North Am 21289-300 1983 Abstract 86 Williams AL Haughton VM Meyer GA et al Computed tomographic appearance of the bulging annulus Radiology 142403-408 1982 Abstract 87 Williams AL Haughton VM Syvertsen A Computed tomography in the diagnosis of herniated nucleus pulposus Radiology 13595-99 1980 Abstract 88 Wiltse LL Berger PE McCulloch JA A system for reporting the size and location of lesions in the spine Spine 221534-1537 1997 Abstract 89 Wiltse LL Fonseca AS Amster J et al Relationship of the dura Hofmanns ligaments Batsons plexus and a fibrovascular membrane lying on the posterior surface of the vertebral bodies and attaching to the deep layer of the posterior longitudinal ligament An anatomical radiologic and clinical study Spine 181030-1043 1993 Abstract 90 Yamashita K Hiroshima K Kurata A Gadolinium-DTPA-enhanced magnetic resonance imaging of a sequestered lumbar intervertebral disc and its correlation with pathologic findings Spine 19479-482 1994 Abstract 91 Yu SW Haughton VM Sether LA et al Comparison of MR and diskography in detecting radial tears of the anulus A postmortem study AJNR Am J Neuroradiol 101077-1081 1989 Abstract 92 Yu SW Sether LA Ho PS et al Tears of the anulus fibrosus Correlation between MR and pathologic findings in cadavers AJNR Am J Neuroradiol 9367-370 1988 Abstract

93 Yussen PS Swartz JD The acute lumbar disc herniation Imaging diagnosis Semin Ultrasound CT MR 14389-398 1993 Abstract 94 Zucherman J Derby R Hsu K et al Normal magnetic resonance imaging with abnormal discography Spine 131355-1359 1988 Abstract

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  • CLASSIFICATION DIAGNOSTIC IMAGING AND IMAGING CHARACTERIZATION OF A LUMBAR HERNIATED DISK
    • IMAGING OF LOW BACK PAIN I
      • CLASSIFICATION DIAGNOSTIC IMAGING AND IMAGING CHARACTERIZATION OF A LUMBAR HERNIATED DISK
        • DEFINITION OF A DISK HERNIATION
        • CLASSIFICATION OF A HERNIATED LUMBAR DISK
          • Main Categories of Noninfectious Disk Abnormalities
          • Further Qualifying the Displaced Disk Material Beyond the Disk Space
            • DIAGNOSTIC IMAGING AND CHARACTERIZATION OF A HERNIATED LUMBAR DISK
              • Conventional Radiographs
              • Myelography
              • CT
              • CT Myelography
              • MR Imaging
              • Diskography and CT Diskography
                • SUMMARY
                  • References
Page 18: CLASSIFICATION, DIAGNOSTIC IMAGING, AND IMAGING ... · PDF fileclassification, diagnostic imaging, and imaging characterization of a lumbar herniated disk ... classification, diagnostic

Volume of Herniated Material

Quantifying the herniated disk material by measuring in millimeters its greatest diameter or by evaluating its cross-sectional area in square millimeters is rarely done The resulting figures could be misleading without relating this measurement to the size of the spinal canal and the exact location of the lesion[ ]88 A purely qualitative and subjective statement that a mild moderate or severe herniation is present however does not give the person reading the imaging report any indication as to the potential of the lesion to cause significant compression of the dural sac or individual exiting nerve roots A reasonably precise scheme has been proposed in 1995 by the Nomenclature Committee of the North American Spine Society[ ]20 Measurements are taken from an axial CT or MR imaging section at the site of most severe compromise canal compromise of less than 25 at that section is qualified as mild 25 to 75 is moderate 76 to 90 is moderately severe and greater than 90 is severe It is understood that such characterizations describe only the cross-sectional area at one level and do not account for the total volume of displaced material displacement of neural tissue or clinical significance The usefulness of having four categories is questionable and can likely generate poor interobserver or intraobserver agreement especially in situations where the central spinal canal is relatively narrow Bonnevilles scheme[ ]9 [ ]10 [ ]11 should generate greater reliability (Fig 14) (Figure Not Available) Separation of the cross-sectional area in three thirds can be applied to both the central spinal canal and the foramina It can be agreed by way of convention that the terms mild moderate and severe lumen compromise by a disk herniation designate extension of the displaced disk material in the anterior middle or posterior third of the central canal or foramen depending on the specified location of the herniation

Figure 14 (Figure Not Available) The size of the herniation in the horizontal plane is assessed and designated by the numbers 1 2 or 3 by establishing its extension in the anterior middle or posterior third of the spinal canal (From Bonneville JF Plaidoyer pour une classification par limage des hernies discales lombaires la carte-image Rev Imag Med 2557-560 1990 with permission)

Location of Herniated Material

Bonneville[ ]9 [ ]10 [ ]11 has also proposed an interesting and simple alpha-numerical system to classify according to their location the position of disk fragments that have migrated in the horizontal or sagittal plane (Figs 15 (Figure Not Available) and 16) (Figure Not Available) Using more precise anatomic boundaries unfortunately more familiar to surgeons than radiologists Wiltse et al[ ]88 have proposed another system which has been supported by the North American Spine Society[ ]20 [ ]21 Anatomic zones and levels are defined using the following anatomic landmarks medial edge of the articular facets medial lateral upper and lower border of the pedicles and coronal plane at the disk center On the horizontal plane (Fig 17) (Figure Not Available) these landmarks determine the bounderies of the central zone the subarticular zone the foraminal zone the extraforaminal zone and the anterior zone (anterior to the coronal plane at the center of the disk) In the sagittal plane they determine the boundaries of the diskal level the infrapedicular level the pedicular level and the suprapedicular level (Figs 18 (Figure

Not Available) and 19) (Figure Not Available) Radiologists interpreting axial CT or MR images may find it difficult to use the medial edge of the facets as the landmark that separates the central zone from the subarticular zone because the superior articular facets are generally not included in axial sections at the disk level The alternative is to use the expression posterolateral to designate collectively all posterior herniations that are not midline but do not extend into a foramen as was proposed by Bonneville[ ]9 [ ]10 [ ]11

Figure 15 (Figure Not Available) In the horizontal plane herniations are labeled midline (a) posterolateral (b) foraminal (c) and extra-foraminal (d) (From Bonneville JF Plaidoyer pour une classification par limage des hernies discales lombaires la carte-image Rev Imag Med 2557-560 1990 with permission)

Figure 16 (Figure Not Available) In the craniocaudal direction disk migration is labeled +1 +2 +3 or -1 -2 -3 by referring to the height of a vertebral body divided in thirds (From Bonneville JF Plaidoyer pour une classification par limage des hernies discales lombaires la carte-image Rev Imag Med 2557-560 1990 with permission)

Figure 17 (Figure Not Available) The anatomic zones identified on axial images The anterior zone (not shown) is delineated from the extraforaminal zone by an imaginary coronal line in the center of the vertebral body (From Wiltse LL Berger PE McCulloch JA A system for reporting the size and location of lesions in the spine Spine 221534-1537 1997 with permission)

Figure 18 (Figure Not Available) The anatomical levels identified on craniocaudal images (From Wiltse LL Berger PE McCulloch AJ A system for reporting the size and location of lesions in the spine Spine 221534-1537 1997 with permission)

Figure 19 (Figure Not Available) Coronal view of the main zones and levels (From Wiltse LL Berger PE McCulloch JA A system for reporting the size and location of lesions in the spine Spine 221534-1537 1997 with permission)

Composition of Herniated Material

Displaced disk material may consist of glycosaminoglycans type 1 or 2 collagen end plate cartilage and bone fragments avulsed from the ring epiphysis A reactive inflammatory reaction usually results in edematous tissue followed by granulation tissue which may undergo calcification (Fig 20) Necrotic and partially resorbed displaced disk material sometimes produces a large fluid-filled pouch distinguishable from the common high-intensity zone because of its size (Fig 21) or a gas-filled cavity generally in continuity with gas in the intervertebral space (Fig 22) [ ]42 These characteristics may be meaningful if intradiskal injection therapy is considered In imaging reports herniations exhibiting calcium deposits and those exhibiting replacement of disk material by gas or a relatively large fluid collection can be qualified as chronic herniations

Figure 20 A CT scan demonstration of a small posterior central L4-L5 calcified subligamentous herniation The resistant deep layer of the PLLC restrains displacement of the disk material in the posterior central direction and does not allow a detectable distortion of the disk contour In this particular case the presence of the calcification is actually the only evidence that a posterior midline anular tear and a small subligamentous herniation are present B Posterior right central and sub-articular L5-S1 calcified disk herniation in same patient Posterolateral herniations are generally more conspicuous than posterior midline herniations because the deep layer of the PLLC gets thinner away from the midline

Figure 21 Posterior central midline L4-L5 herniation in a 52-year-old man demonstrated on a T2-weighted midline MR sagittal section There is intervertebral space narrowing with loss of normal central disk signal

intensity while the herniated disk material demonstrates high signal intensity consistent with a predominantly fluid consistency

Figure 22 CT scan demonstration in a 51-year-old woman of a left posterolateral L5-S1 disk hernation consisting essentially in a gas-filled pouch (white arrow) Gas is also present in the central portion of the intervertebral disk space (black arrow)

DIAGNOSTIC IMAGING AND CHARACTERIZATION OF A HERNIATED LUMBAR DISK

Assessing the validity of the currently used imaging procedures to diagnose a herniated lumbar disk is not an easy endeavor The validity of a measurement is the extent to which it corresponds to the true biologic value or some accepted gold standard[ ]40 With the exception of postmortem studies evaluation of the pathoanatomy by the surgeon in the operating room has always been considered the gold standard but this does not constitute an ideal situation Inspection of the disk through a small laminectomy incision to determine for instance if nuclear fragments lie within or outside the anular fibers may not be very reliable Also unbiased intraoperative determination of a normal degenerated or herniated disk in a patient with sciatica may also be difficult[ ]86 Because the validity of diskography has been previously established by postmortem studies and surgical correlations[ ]48 it is sometimes used as a gold standard in situations where no surgery has been performed

Conventional Radiographs

Lumbar disk herniations can exceptionally be diagnosed directly on good quality lateral projections because the x-ray attenuation is slightly greater in displaced disk material than in epidural fat Occasionally a calcified rim outlines the displaced disk fragment

(Fig 23) In most situations however narrowing of an intervertebral disk space in the absence of other evidence of chronic diskopathy is the only detectable sign suggesting the presence of a disk herniation To my knowledge the sensitivity and specificity of this sign has never been assessed The accepted rule of thumb is that the height of a given lumbar intervertebral disk space should always be slightly greater than the height of the above located interspace This rule does not apply to the transition disk immediately above the sacrum (usually L5-S1) The specificity of this sign is probably quite high but a few false-positives are seen especially at the L4-L5 level because of minor congenital hypoplasia The presence of posterior or foraminal vertebral body osteophytes associated or not with disk space narrowing is a definite sign of a chronic disk herniation

Figure 23 A Chronic left L3-L4 extraforaminal disk hernation in a 54-year-old man suspected on an AP radiograph demonstrating a calcified shell on the left side of the intervertebral disk space (white arrow) B Axial CT scan section confirming the diagnosis of a chronic extraforaminal L3-L4 herniation

Myelography

Myelography is essentially an exploration of the subarachnoid space Disk herniations are demonstrated only indirectly because they can cause thecal sac deformity and individual nerve root sleeve filling defects (Fig 24) Of all the special imaging procedures

myelography is the only one that allows upright projections with full weight bearing It is not unusual to demonstrate in this way small posterior central or posterolateral herniations that are undetectable on CT sections Interestingly the overall sensitivity of myelography to detect disk herniations has been found to be higher than that of CT whereas its specificity has been found to be lower[ ]74 In comparison with standard CT examination which usually includes only the three or four lower lumbar disks myelography easily allows coverage of the entire lumbar area and assessment of the intrathecal structures (cauda equina and conus medullaris) Far lateral foraminal herniations extraforaminal herniations and anterior herniations however are not detected The sensitivity for detection of posterior central L5-S1 herniations is also relatively poor because of the greater distance between the thecal sac and the posterior aspect of this particular disk

Figure 24 L5-S1 disk herniation in a 25-year-old man detected by indirect signs using lumbosacral myelography A Upright oblique projections showing a filling defect of the left S1 root sleeve (white arrow) suggesting significant nerve root compression by a left posterolateral disk hernation The right S1 root sleeve fills normally with contrast (black arrow) B Subtle compression of the anterior wall of the dural sac by displaced disk material (small arrows) demonstrated on upright lateral projection This sign is usually absent in the presence of a large amount of fat and venous structures in the anterior epidural compartment

CT

The sensitivity of CT to diagnose a herniation of the nucleus pulposus at the L5-S1 interspace is greater than that of myelography if images in the exact plane of the disk can be obtained[ ]23 [ ]39 Otherwise the superiority of plain CT over myelography to demonstrate disk herniations has not been established but CT has the distinct advantage of being

noninvasive and provides direct anatomic information[ ]23 Large herniations are easily detected but as explained previously the distinction between protrusions and extrusions is often difficult without sagittal reconstructions CT essentially allows an assessment of the contour of the disk The diagnosis of very small herniations in the absence of direct or indirect evidence of a radial tear is hazardous and associated with a high percentage of false-positives and false-negatives[ ]52 The diagnosis of moderate and large size herniations in different directions is usually possible but anterior herniations are rarely diagnosed not because they are not detectable but because observers pay little attention to the anterior contour of the disk (Fig 25) Because the PLLC cannot usually be identified the distinction of subligamentous from transligamentous herniation can only be suggested in most cases by the size of the herniated material A definite diagnosis of sequestration is rarely possible Calcifications within the displaced material are readily seen but may be difficult at times to differentiate from an accompanying osteophyte or an avulsed bone fragment from the vertebral body ring epiphysis (Fig 26) The presence of gas in the herniated material is easily detected

Figure 25 Anterior L4-L5 herniation demonstrated by CT scan in a 51-year-old woman with chronic low back pain Although sometimes quite conspicuous such herniations are rarely reported because observers pay little attention to the anterior contour of the disk

Figure 26 CT scan demonstration of a posterior right central L4-L5 disk herniation in a 38-year-old woman with avulsion of a bone fragment from the ring epiphysis and adjacent part of the superior L5 end plate Reactive osteosclerosis is seen around the vertebral body defect (arrows) suggesting a chronic lesion

CT Myelography

This association combines the advantages of both imaging modalities The fact that its accuracy has been reported as being less[ ]22 [ ]32 higher[ ]1 [ ]6 or equivalent[ ]82 to MR imaging is a reflection of the differences in technologic advancement and pathologic nomenclature that hamper valid comparisons between different studies

MR Imaging

Most reported studies establish MR imaging as the first choice modality to diagnose a herniated lumbar disk[ ]5 [ ]22 [ ]32 [ ]46 The associated intravenous injection of a paramagnetic agent has been found useful to demonstrate some anatomic features of disk disease in patients with no previous lumbar disk surgery[ ]56 [ ]68 [ ]90 MR imaging provides a better assessment of disk morphology than CT or CT myelography because sagittal sections are routinely obtained Assessment of foraminal involvement by displaced disk material is more accurate (Fig 27) and anterior disk herniations can be detected more easily than with CT or CT myelography If one is looking specifically for herniated lumbar disks associated with nerve root compression however it has been demonstrated that CT is equally accurate[ ]82 Alterations of the central or peripheral disk signal intensity on T2-weighted images are seen in most disks afflicted with an anular tear[ ]48 and alert the observer to scrutinize the disk contour in search for local modifications indicative of a herniation Because the signal of the displaced disk material is usually very similar to that of the outer anulus PLLC and vertebral body cortical bone small herniations are generally more conspicuous on axial CT sections than on corresponding axial MR imaging sections Gas and calcium deposits within the displaced fragment cannot usually

be detected but associated vertebral body bone marrow changes are typically seen and are helpful in differentiating acute from chronic processes[ ]57 The occasional presence of a high-intensity zone in the herniated material with an occasionally enhancing border after contrast injection is probably caused by a mixture of displaced nuclear material acute and subacute inflammatory tissue and neovascularized reactive tissue[ ]4 [ ]48 [ ]72 Contradictory reports have been published regarding the accuracy of MR imaging to differentiate subligamentous from transligamentous herniations[ ]26 [ ]38 [ ]73 [ ]76 Understanding the anatomy of the PLLC is helpful to make the distinction (Fig 28) (Figure Not Available) Masaryk et al[ ]46 have suggested that MR imaging is accurate to distinguish sequestered disks from other forms of lumbar disk herniations but most observers find this distinction difficult to establish[ ]42

Figure 27 A Left L4-L5 foraminal herniation well seen on an intermediate-weighted left parasagittal MR section (arrow) in a 47-year-old man B The lesion is much less obvious on intermediate-weighted (left) and T2-weighted (right) axial sections and was in fact more conspicuous on the corresponding CT scan section

Figure 28 (Figure Not Available) A Subligamentous disk herniation Left T1-weighted image demonstrating displaced disk material with a smooth outline imposed by the demarcation of the anterior epidural space (AES) by the lateral membrane of the PLLC Right Correlative drawing B Transligamentous disk herniation Left T1-weighted image of a large disk herniation (cervical in this case) which has ruptured through the posterior confines of the AES Penetration of the right lateral membrane can be observed (arrow) and the disk fragment contour is serrated Right Correlative drawing (From Schellinger D Manz HJ Vidic B et al Disk fragment migration Radiology 175831-836 1990 with permission)

Diskography and CT Diskography

During 30 years (1950 to 1980) when myelography was the only available imaging technique to demonstrate lumbar disk herniations diskography was an invasive but efficient way to demonstrate posterior central L5-S1 herniations and other large herniations (other than posterior central and paramedial) that could not be detected by myelography[ ]50 These herniations are now usually well demonstrated by CT and MR imaging Comparing the accuracy of five imaging modalities (excluding MR imaging) for the diagnosis of lumbar disk herniation Jackson et al[ ]31 found that CT diskography (Fig 29) was the most accurate test (87) compared with 77 for CT myelography 74 for CT 70 for myelography 64 for pain reproduction during diskography and 58 for diskography without CT Disk injection reproduced the patients clinical pain pattern in only 36 of herniated disks This clinical test isolated from the images had high specificity (89) but low sensitivity (43) for the diagnosis of disk herniation The reported low sensitivity of diskography images (unassociated with CT) to diagnose disk herniation is to be expected the purpose of the intradiskal injection being primarily the demonstration of an anular tear the contrast leaking through the tear only occasionally delineates an extruded fragment When a disk herniation has been diagnosed by other imaging modalities diskography allows to determine if the herniation is contained or noncontained (Figs 30 and 31) this information may have clinical relevance[ ]62 It also allows to establish if the displaced disk material is communicating or not with the parent disk and establishes the likelihood that it is sequestered or not There always remains a possibility that the contrast injected under pressure may reach a disk fragment that is nevertheless sequestered by leaking through the associated anular tear CT diskography also allows assessment in most cases of the integrity of the PLLC[ ]89 The superior sensitivity of diskography over MR imaging to demonstrate anular tears has been well established[ ]27 [ ]44 [ ]48 [ ]64 [ ]77 [ ]91 [ ]94 The presence of a radial tear and the inflammatory reaction it creates may be symptomatic despite the absence of true disk herniation[ ]29 [ ]48 [ ]49 [ ]69

Figure 29 L4-L5 CT diskogram demonstrating a large left posterolateral radial anular tear associated with

a left foraminal and extraforaminal herniaton (same patient as in Figure 28) (Figure Not Available)

Figure 30 Contained posterior L4-L5 and L5-S1 disk herniations in a 57-year-old man demonstrated by diskography The L3-L4 disk is normal

Figure 31 Noncontained L4-L5 disk herniation in a 23-year-old woman Reflux of injected contrast is seen in the anterior epidural space above and below the disk space The L5-S1 disk also demonstrates incomplete anterior and posterior radial anular tears

SUMMARY

The absence of universal nomenclature standardization with respect to the definition of a disk herniation and its different categories especially regarding type and location is still a major problem that will only be overcome when major national or international scientific societies join efforts to support a particular scheme Meanwhile it is important to realize that the two models that are currently most used are based on a different perspective Trying to straddle the two by opposing for instance bulging disk and herniation is doomed to failure because this exercise defies formal logic MR imaging is currently the most accurate noninvasive imaging modality to diagnose a disk herniation and to determine its exact location The determination of some pathoanatomic characteristics of herniated disks (type and composition) may require the use of CT diskography or CT diskography

References

1 Albeck MJ Hilden J Kjaer L et al A controlled comparison of myelography computed tomography and magnetic resonance imaging in clinically suspected lumbar disc herniation Spine 20443-448 1995 Abstract 2 American Academy of Orthopedic Surgeons Glossary on Spinal Terminology Chicago American Academy of Orthopedic Surgeons 1981 3 Andersson GB Weinstein JN Disc herniation [editorial] Spine 211S 1996 Citation 4 Aprill C Bogduk N High-intensity zone A diagnostic sign of painful lumbar disc on magnetic resonance imaging Br J Radiol 65361-369 1992 Abstract 5 Birney TJ White JJ Jr Berens D et al Comparison of MRI and discography in the diagnosis of lumbar degenerative disc disease J Spinal Disord 5417-423 1992 Abstract 6 Bischoff RJ Rodriguez RP Gupta K et al A comparison of computed tomography-myelography magnetic resonance imaging and myelography in the diagnosis of herniated nucleus pulposus and spinal stenosis J Spinal Disord 6289-295 1993 Abstract 7 Bogduk N The innervation of the lumbar spine Spine 8286-293 1983 Abstract 8 Bogduk N Tynan W Wilson AS The nerve supply to the human lumbar intervertebral discs J Anat 13239-56 1981 Abstract 9 Bonneville JF La carte-image des hernies discales lombaires Rachis 2255-257 1990 10 Bonneville JF La topografia simbolica delle ernie discali lombari Riv Neuroradiol 5427-431 1992 11 Bonneville JF Plaidoyer pour une classification par limage des hernies discales lombaires La carte-image Rev Imag Med 2557-560 1990 12 Brant-Zawadzki M Jensen M Spinal nomenclature Spine 20388-390 1995 Abstract

13 Brant-Zawadzki MN Jensen MC Obuchowski N et al Interobserver and intraobserver variability in interpretation of lumbar disc abnormalities A comparison of two nomenclatures Spine 201257-1263 1995 Abstract 14 Breton G Is that a bulging disk a small herniation or a moderate protrusion [editorial] Can Assoc Radiol J 42318 1991 Citation 15 Czervionke LF Lumbar intervertebral disc disease Neuroimaging Clin North Am 3465-485 1993 16 Deyo RA Nonsurgical care of low back pain Neurosurg Clin North Am 2851-862 1991 17 Deyo RA Loeser JD Bigos SJ Herniated lumbar intervertebral disk Ann Intern Med 112598-603 1990 Abstract 18 Dorlands Illustrated Medical Dictionary ed 28 Philadelphia WB Saunders 1994 19 Fardon D Pinkerton S Balderston R et al Terms used for diagnosis by English speaking spine surgeons Spine 18274-277 1993 Citation 20 Fardon DF Herzog RJ Mink JH et al Nomenclature of Lumbar Disc Disorders Contemporary Concepts in Spine Care Rosemont IL North American Spine Society 1995 21 Fardon DF Herzog RJ Mink JH et al Nomenclature of lumbar disc disorders In Garfin S Vaccaro A (eds) Orthopedic Knowledge Update Spine Rosemont IL American Academy of Orthopedic Surgeons 1997 pp A3-A14 22 Forristall RM Marsh HO Pay NT Magnetic resonance imaging and contrast CT of the lumbar spine Comparison of diagnostic methods and correlation with surgical findings Spine 131049-1054 1988 Abstract 23 Fries JW Abodeely DA Vijungco JG et al Computed tomography of herniated and extruded nucleus pulposus J Comput Assist Tomogr 6874-887 1982 Abstract 24 Frymoyer JW Newberg A Pope MH et al Spine radiographs in patients with low-back pain An epidemiological study in men J Bone Joint Surg Am 661048-1055 1984 Abstract 25 Gospodarowicz M Benedet L Hutter RV et al History and international developments in cancer staging Cancer Prev Control 2262-268 1998 Abstract 26 Grenier N Greselle JF Vital JM et al Normal and disrupted lumbar longitudinal ligaments Correlative MR and anatomic study Radiology 171197-205 1989 Abstract 27 Gunzburg R Parkinson R Moore R et al A cadaveric study comparing discography magnetic resonance imaging histology and mechanical behavior of the human lumbar disc Spine 17417-426 1992 Abstract 28 Haughton VM Eldevik OP Magnaes B et al A prospective comparison of computed tomography and myelography in the diagnosis of herniated lumbar disks Radiology 142103-110 1982 Abstract

29 Haughton VM Lim TH An H Intervertebral disk appearance correlated with stiffness of lumbar spinal motion segments AJNR Am J Neuroradiol 201161-1165 1999 Abstract 30 Herzog RJ The radiologic assessment for a lumbar disc herniation Spine 2119S-38S 1996 Abstract 31 Jackson RP Becker GJ Jacobs RR et al The neuroradiographic diagnosis of lumbar herniated nucleus pulposus I A comparison of computed tomography (CT) myelography CT-myelography discography and CT-discography Spine 141356-1361 1989 Abstract 32 Jackson RP Cain JE Jr Jacobs RR et al The neuroradiographic diagnosis of lumbar herniated nucleus pulposus II A comparison of computed tomography (CT) myelography CT-myelography and magnetic resonance imaging Spine 141362-1367 1989 Abstract 33 Jarvik JG Haynor DR Koepsell TD et al Interreader reliability for a new classification of lumbar disk disease Acad Radiol 3537-544 1996 Abstract 34 Jensen MC Brant-Zawadzki MN Obuchowski N et al Magnetic resonance imaging of the lumbar spine in people without back pain N Engl J Med 33169-73 1994 Abstract 35 Kent DL Haynor DR Larson EB et al Diagnosis of lumbar spinal stenosis in adults A meta-analysis of the accuracy of CT MR and myelography AJR Am J Roentgenol 1581135-1144 1992 Abstract 36 Kieffer SA Sherry RG Wellenstein DE et al Bulging lumbar intervertebral disk Myelographic differentiation from herniated disk with nerve root compression AJR Am J Roentgenol 138709-716 1982 Abstract 37 Kieffer SA Stadlan EM Mohandas A et al Discographic-anatomical correlation of developmental changes with age in the intervertebral disc Acta Radiol 9733-739 1969 38 Kim KY Kim YT Lee CS et al MRI classification of lumbar herniated intervertebral disc Orthopedics 15493-497 1992 Abstract 39 Kornberg M Rechtine GR Dupuy TE Computed tomography in the diagnosis of a herniated disk at the L5-S1 level Spine 9433-436 1984 Abstract 40 Kramer MS Clinical Epidemiology and Biostatistics New York Springer-Verlag 1988 41 Landis JR Koch GG The measurement of observer agreement agreement for categorical data Biometrics 33159-174 1977 Abstract 42 Laredo JD Bossard P Vuillemin-Bodaghi Formes anatomo-radiologiques des hernies discales In Morvan G Deburge A Bard H et al (eds) Le Rachis Lombaire Degeneratif Montpellier Sauramps Medical 1998 pp 37-49 43 Lee SH Coleman PE Hahn FJ Magnetic resonance imaging of degenerative disk disease of the spine Radiol Clin North Am 26949-964 1988 Abstract 44 Linson MA Crowe CH Comparison of magnetic resonance imaging and lumbar discography in the diagnosis of disc degeneration Clin Orthop 160-163 1990

45 Marchand F Ahmed AM Investigation of the laminate structure of lumbar disc anulus fibrosus Spine 15402-410 1990 Abstract 46 Masaryk TJ Ross JS Modic MT et al High-resolution MR imaging of sequestered lumbar intervertebral disks AJR Am J Roentgenol 1501155-1162 1988 Abstract 47 Milette PC The proper terminology for reporting lumbar intervertebral disk disorders AJNR Am J Neuroradiol 181859-1866 1997 Citation 48 Milette PC Fontaine S Lepanto L et al Differentiating lumbar disc protrusions disk bulges and discs with normal contour but abnormal signal intensity Magnetic resonance imaging with discographic correlations Spine 2444-53 1999 Abstract 49 Milette PC Fontaine S Lepanto L et al Radiating pain to the lower extremities caused by lumbar disk rupture without spinal nerve root involvement AJNR Am J Neuroradiol 161605-1613 1995 Abstract 50 Milette PC Melancon D A reappraisal of lumbar discography Can Assoc Radiol J 33176-182 1982 51 Milette PC Melancon D Dupuis PR et al A simplified terminology for abnormalities of the lumbar disk Can Assoc Radiol J 42319-325 1991 Abstract 52 Milette PC Raymond J Fontaine S Comparison of high-resolution computed tomography with discography in the evaluation of lumbar disc herniations Spine 15525-533 1990 Abstract 53 Mink JH Deutsch AL Goldstein TB et al Spinal imaging and intervention 1998 Phys Med Rehabil Clin North Am 9343-380 1998 54 Mixter WJ Barr JS Rupture of the intervertebral disc with involvement of the spinal canal N Engl J Med 211210-234 1934 55 Modic MT Masaryk TJ Ross JS et al Imaging of degenerative disk disease Radiology 168177-186 1988 Citation 56 Modic MT Ross JS Obuchowski NA et al Contrast-enhanced MR imaging in acute lumbar radiculopathy A pilot study of the natural history Radiology 195429-435 1995 Abstract 57 Modic MT Steinberg PM Ross JS et al Degenerative disk disease Assessment of changes in vertebral body marrow with MR imaging Radiology 166193-199 1988 58 Morvan G Mathieu P Les stenoses laterales In Morvan G Deburge A Bard H et al (eds) Le Rachis Lombaire Degeneratif Montpellier Sauramps Medical 1998 pp 315-324 59 Murray RO Skeletal trauma Regional In Sutton D (ed) Textbook of Radiology and Imaging ed 3 New York Churchill Livingstone 1980 pp 210-231 60 Nachemson A Lumbar disc herniation Conclusions Acta Orthop Scand 64(suppl 251)49 1993 Citation

61 Nathan H Osteophytes of the vertebral column An anatomical study of their development according to age race and sex with consideration as to their etiology and significance J Bone Joint Surg Am 44243-268 1962 62 Nygaard OP Mellgren SI Osterud B The inflammatory properties of contained and noncontained lumbar disc herniations Spine 222584-2488 1997 Abstract 63 Ohshima H Hirano N Osada R et al Morphologic variation of lumbar posterior longitudinal ligament and the modality of disc herniation Spine 182408-2411 1993 Abstract 64 Osti OL Fraser RD MRI and discography of annular tears and intervertebral disc degeneration A prospective clinical comparison J Bone Joint Surg Br 74431-435 1992 Abstract 65 Palmgren T Gronblad M Virri J et al Immunohistochemical demonstration of sensory and autonomic nerve terminals in herniated lumbar disc tissue Spine 211301-1306 1996 Abstract 66 Resnick D Niwayama G Degenerative disease of the spine In Resnick D (ed) Diagnosis of Bone and Joint Disorders ed 3 Philadelphia WB Saunders 1995 pp 1372-1462 67 Resnick D Niwayama G Intravertebral disk herniations Cartilaginous (Schmorls) nodes Radiology 12657-65 1978 Abstract 68 Ross JS Modic MT Masaryk TJ Tears of the anulus fibrosus Assessment with Gd-DTPA-enhanced MR imaging AJR Am J Roentgenol 154159-162 1990 Abstract 69 Saal JS The role of inflammation in lumbar pain Spine 201821-1827 1995 Abstract 70 Sachs BL Vanharanta H Spivey MA et al Dallas discogram description A new classification of CTdiscography in low-back disorders Spine 12287-294 1987 Abstract 71 Sauser DD Goldman AB Kaye JJ Discogenic vertebral sclerosis J Can Assoc Radiol 2944-50 1978 Abstract 72 Schellhas KP Pollei SR Gundry CR et al Lumbar disc high-intensity zone Correlation of magnetic resonance imaging and discography Spine 2179-86 1996 Abstract 73 Schellinger D Manz HJ Vidic B et al Disk fragment migration Radiology 175831-836 1990 Abstract 74 Schipper J Kardaun JW Braakman R et al Lumbar disk herniation Diagnosis with CT or myelography Radiology 165227-231 1987 Abstract 75 Schmorl G Junghanns H The Human Spine in Health and Disease ed 2 New York Grune and Stratton 1971 76 Silverman CS Lenchik L Shimkin PM et al The value of MR in differentiating subligamentous from supraligamentous lumbar disk herniations AJNR Am J Neuroradiol 16571-579 1995 Abstract 77 Simmons JW Emery SF McMillin JN et al Awake discography A comparison study with magnetic

resonance imaging Spine 16S216-221 1991 Abstract 78 Smyth MJ Wright V Sciatica and the intervertebral disc J Bone Joint Surg Am 401401-1418 1958 79 Taveras JM Radiologic aspects of low back pain and sciatic syndromes [editorial] AJNR Am J Neuroradiol 9351-358 1989 80 Tehranzadeh J Discography 2000 Radiol Clin North Am 36463-495 1998 Full Text 81 Thelander U Fagerlund M Friberg S et al Describing the size of lumbar disc herniations using computed tomography A comparison of different size index calculations and their relation to sciatica Spine 191979-1984 1994 Abstract 82 Thornbury JR Fryback DG Turski PA et al Disk-caused nerve compression in patients with acute low-back pain Diagnosis with MR CT myelography and plain CT Radiology 186731-738 1993 Abstract 83 Twomey L Taylor J Age changes in lumbar intervertebral discs Acta Orthop Scand 56496-499 1985 Abstract 84 Twomey LT Taylor JR Age changes in lumbar vertebrae and intervertebral discs Clin Orthop 22497-104 1987 85 Williams AL CT diagnosis of degenerative disc disease The bulging annulus Radiol Clin North Am 21289-300 1983 Abstract 86 Williams AL Haughton VM Meyer GA et al Computed tomographic appearance of the bulging annulus Radiology 142403-408 1982 Abstract 87 Williams AL Haughton VM Syvertsen A Computed tomography in the diagnosis of herniated nucleus pulposus Radiology 13595-99 1980 Abstract 88 Wiltse LL Berger PE McCulloch JA A system for reporting the size and location of lesions in the spine Spine 221534-1537 1997 Abstract 89 Wiltse LL Fonseca AS Amster J et al Relationship of the dura Hofmanns ligaments Batsons plexus and a fibrovascular membrane lying on the posterior surface of the vertebral bodies and attaching to the deep layer of the posterior longitudinal ligament An anatomical radiologic and clinical study Spine 181030-1043 1993 Abstract 90 Yamashita K Hiroshima K Kurata A Gadolinium-DTPA-enhanced magnetic resonance imaging of a sequestered lumbar intervertebral disc and its correlation with pathologic findings Spine 19479-482 1994 Abstract 91 Yu SW Haughton VM Sether LA et al Comparison of MR and diskography in detecting radial tears of the anulus A postmortem study AJNR Am J Neuroradiol 101077-1081 1989 Abstract 92 Yu SW Sether LA Ho PS et al Tears of the anulus fibrosus Correlation between MR and pathologic findings in cadavers AJNR Am J Neuroradiol 9367-370 1988 Abstract

93 Yussen PS Swartz JD The acute lumbar disc herniation Imaging diagnosis Semin Ultrasound CT MR 14389-398 1993 Abstract 94 Zucherman J Derby R Hsu K et al Normal magnetic resonance imaging with abnormal discography Spine 131355-1359 1988 Abstract

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  • CLASSIFICATION DIAGNOSTIC IMAGING AND IMAGING CHARACTERIZATION OF A LUMBAR HERNIATED DISK
    • IMAGING OF LOW BACK PAIN I
      • CLASSIFICATION DIAGNOSTIC IMAGING AND IMAGING CHARACTERIZATION OF A LUMBAR HERNIATED DISK
        • DEFINITION OF A DISK HERNIATION
        • CLASSIFICATION OF A HERNIATED LUMBAR DISK
          • Main Categories of Noninfectious Disk Abnormalities
          • Further Qualifying the Displaced Disk Material Beyond the Disk Space
            • DIAGNOSTIC IMAGING AND CHARACTERIZATION OF A HERNIATED LUMBAR DISK
              • Conventional Radiographs
              • Myelography
              • CT
              • CT Myelography
              • MR Imaging
              • Diskography and CT Diskography
                • SUMMARY
                  • References
Page 19: CLASSIFICATION, DIAGNOSTIC IMAGING, AND IMAGING ... · PDF fileclassification, diagnostic imaging, and imaging characterization of a lumbar herniated disk ... classification, diagnostic

Not Available) and 19) (Figure Not Available) Radiologists interpreting axial CT or MR images may find it difficult to use the medial edge of the facets as the landmark that separates the central zone from the subarticular zone because the superior articular facets are generally not included in axial sections at the disk level The alternative is to use the expression posterolateral to designate collectively all posterior herniations that are not midline but do not extend into a foramen as was proposed by Bonneville[ ]9 [ ]10 [ ]11

Figure 15 (Figure Not Available) In the horizontal plane herniations are labeled midline (a) posterolateral (b) foraminal (c) and extra-foraminal (d) (From Bonneville JF Plaidoyer pour une classification par limage des hernies discales lombaires la carte-image Rev Imag Med 2557-560 1990 with permission)

Figure 16 (Figure Not Available) In the craniocaudal direction disk migration is labeled +1 +2 +3 or -1 -2 -3 by referring to the height of a vertebral body divided in thirds (From Bonneville JF Plaidoyer pour une classification par limage des hernies discales lombaires la carte-image Rev Imag Med 2557-560 1990 with permission)

Figure 17 (Figure Not Available) The anatomic zones identified on axial images The anterior zone (not shown) is delineated from the extraforaminal zone by an imaginary coronal line in the center of the vertebral body (From Wiltse LL Berger PE McCulloch JA A system for reporting the size and location of lesions in the spine Spine 221534-1537 1997 with permission)

Figure 18 (Figure Not Available) The anatomical levels identified on craniocaudal images (From Wiltse LL Berger PE McCulloch AJ A system for reporting the size and location of lesions in the spine Spine 221534-1537 1997 with permission)

Figure 19 (Figure Not Available) Coronal view of the main zones and levels (From Wiltse LL Berger PE McCulloch JA A system for reporting the size and location of lesions in the spine Spine 221534-1537 1997 with permission)

Composition of Herniated Material

Displaced disk material may consist of glycosaminoglycans type 1 or 2 collagen end plate cartilage and bone fragments avulsed from the ring epiphysis A reactive inflammatory reaction usually results in edematous tissue followed by granulation tissue which may undergo calcification (Fig 20) Necrotic and partially resorbed displaced disk material sometimes produces a large fluid-filled pouch distinguishable from the common high-intensity zone because of its size (Fig 21) or a gas-filled cavity generally in continuity with gas in the intervertebral space (Fig 22) [ ]42 These characteristics may be meaningful if intradiskal injection therapy is considered In imaging reports herniations exhibiting calcium deposits and those exhibiting replacement of disk material by gas or a relatively large fluid collection can be qualified as chronic herniations

Figure 20 A CT scan demonstration of a small posterior central L4-L5 calcified subligamentous herniation The resistant deep layer of the PLLC restrains displacement of the disk material in the posterior central direction and does not allow a detectable distortion of the disk contour In this particular case the presence of the calcification is actually the only evidence that a posterior midline anular tear and a small subligamentous herniation are present B Posterior right central and sub-articular L5-S1 calcified disk herniation in same patient Posterolateral herniations are generally more conspicuous than posterior midline herniations because the deep layer of the PLLC gets thinner away from the midline

Figure 21 Posterior central midline L4-L5 herniation in a 52-year-old man demonstrated on a T2-weighted midline MR sagittal section There is intervertebral space narrowing with loss of normal central disk signal

intensity while the herniated disk material demonstrates high signal intensity consistent with a predominantly fluid consistency

Figure 22 CT scan demonstration in a 51-year-old woman of a left posterolateral L5-S1 disk hernation consisting essentially in a gas-filled pouch (white arrow) Gas is also present in the central portion of the intervertebral disk space (black arrow)

DIAGNOSTIC IMAGING AND CHARACTERIZATION OF A HERNIATED LUMBAR DISK

Assessing the validity of the currently used imaging procedures to diagnose a herniated lumbar disk is not an easy endeavor The validity of a measurement is the extent to which it corresponds to the true biologic value or some accepted gold standard[ ]40 With the exception of postmortem studies evaluation of the pathoanatomy by the surgeon in the operating room has always been considered the gold standard but this does not constitute an ideal situation Inspection of the disk through a small laminectomy incision to determine for instance if nuclear fragments lie within or outside the anular fibers may not be very reliable Also unbiased intraoperative determination of a normal degenerated or herniated disk in a patient with sciatica may also be difficult[ ]86 Because the validity of diskography has been previously established by postmortem studies and surgical correlations[ ]48 it is sometimes used as a gold standard in situations where no surgery has been performed

Conventional Radiographs

Lumbar disk herniations can exceptionally be diagnosed directly on good quality lateral projections because the x-ray attenuation is slightly greater in displaced disk material than in epidural fat Occasionally a calcified rim outlines the displaced disk fragment

(Fig 23) In most situations however narrowing of an intervertebral disk space in the absence of other evidence of chronic diskopathy is the only detectable sign suggesting the presence of a disk herniation To my knowledge the sensitivity and specificity of this sign has never been assessed The accepted rule of thumb is that the height of a given lumbar intervertebral disk space should always be slightly greater than the height of the above located interspace This rule does not apply to the transition disk immediately above the sacrum (usually L5-S1) The specificity of this sign is probably quite high but a few false-positives are seen especially at the L4-L5 level because of minor congenital hypoplasia The presence of posterior or foraminal vertebral body osteophytes associated or not with disk space narrowing is a definite sign of a chronic disk herniation

Figure 23 A Chronic left L3-L4 extraforaminal disk hernation in a 54-year-old man suspected on an AP radiograph demonstrating a calcified shell on the left side of the intervertebral disk space (white arrow) B Axial CT scan section confirming the diagnosis of a chronic extraforaminal L3-L4 herniation

Myelography

Myelography is essentially an exploration of the subarachnoid space Disk herniations are demonstrated only indirectly because they can cause thecal sac deformity and individual nerve root sleeve filling defects (Fig 24) Of all the special imaging procedures

myelography is the only one that allows upright projections with full weight bearing It is not unusual to demonstrate in this way small posterior central or posterolateral herniations that are undetectable on CT sections Interestingly the overall sensitivity of myelography to detect disk herniations has been found to be higher than that of CT whereas its specificity has been found to be lower[ ]74 In comparison with standard CT examination which usually includes only the three or four lower lumbar disks myelography easily allows coverage of the entire lumbar area and assessment of the intrathecal structures (cauda equina and conus medullaris) Far lateral foraminal herniations extraforaminal herniations and anterior herniations however are not detected The sensitivity for detection of posterior central L5-S1 herniations is also relatively poor because of the greater distance between the thecal sac and the posterior aspect of this particular disk

Figure 24 L5-S1 disk herniation in a 25-year-old man detected by indirect signs using lumbosacral myelography A Upright oblique projections showing a filling defect of the left S1 root sleeve (white arrow) suggesting significant nerve root compression by a left posterolateral disk hernation The right S1 root sleeve fills normally with contrast (black arrow) B Subtle compression of the anterior wall of the dural sac by displaced disk material (small arrows) demonstrated on upright lateral projection This sign is usually absent in the presence of a large amount of fat and venous structures in the anterior epidural compartment

CT

The sensitivity of CT to diagnose a herniation of the nucleus pulposus at the L5-S1 interspace is greater than that of myelography if images in the exact plane of the disk can be obtained[ ]23 [ ]39 Otherwise the superiority of plain CT over myelography to demonstrate disk herniations has not been established but CT has the distinct advantage of being

noninvasive and provides direct anatomic information[ ]23 Large herniations are easily detected but as explained previously the distinction between protrusions and extrusions is often difficult without sagittal reconstructions CT essentially allows an assessment of the contour of the disk The diagnosis of very small herniations in the absence of direct or indirect evidence of a radial tear is hazardous and associated with a high percentage of false-positives and false-negatives[ ]52 The diagnosis of moderate and large size herniations in different directions is usually possible but anterior herniations are rarely diagnosed not because they are not detectable but because observers pay little attention to the anterior contour of the disk (Fig 25) Because the PLLC cannot usually be identified the distinction of subligamentous from transligamentous herniation can only be suggested in most cases by the size of the herniated material A definite diagnosis of sequestration is rarely possible Calcifications within the displaced material are readily seen but may be difficult at times to differentiate from an accompanying osteophyte or an avulsed bone fragment from the vertebral body ring epiphysis (Fig 26) The presence of gas in the herniated material is easily detected

Figure 25 Anterior L4-L5 herniation demonstrated by CT scan in a 51-year-old woman with chronic low back pain Although sometimes quite conspicuous such herniations are rarely reported because observers pay little attention to the anterior contour of the disk

Figure 26 CT scan demonstration of a posterior right central L4-L5 disk herniation in a 38-year-old woman with avulsion of a bone fragment from the ring epiphysis and adjacent part of the superior L5 end plate Reactive osteosclerosis is seen around the vertebral body defect (arrows) suggesting a chronic lesion

CT Myelography

This association combines the advantages of both imaging modalities The fact that its accuracy has been reported as being less[ ]22 [ ]32 higher[ ]1 [ ]6 or equivalent[ ]82 to MR imaging is a reflection of the differences in technologic advancement and pathologic nomenclature that hamper valid comparisons between different studies

MR Imaging

Most reported studies establish MR imaging as the first choice modality to diagnose a herniated lumbar disk[ ]5 [ ]22 [ ]32 [ ]46 The associated intravenous injection of a paramagnetic agent has been found useful to demonstrate some anatomic features of disk disease in patients with no previous lumbar disk surgery[ ]56 [ ]68 [ ]90 MR imaging provides a better assessment of disk morphology than CT or CT myelography because sagittal sections are routinely obtained Assessment of foraminal involvement by displaced disk material is more accurate (Fig 27) and anterior disk herniations can be detected more easily than with CT or CT myelography If one is looking specifically for herniated lumbar disks associated with nerve root compression however it has been demonstrated that CT is equally accurate[ ]82 Alterations of the central or peripheral disk signal intensity on T2-weighted images are seen in most disks afflicted with an anular tear[ ]48 and alert the observer to scrutinize the disk contour in search for local modifications indicative of a herniation Because the signal of the displaced disk material is usually very similar to that of the outer anulus PLLC and vertebral body cortical bone small herniations are generally more conspicuous on axial CT sections than on corresponding axial MR imaging sections Gas and calcium deposits within the displaced fragment cannot usually

be detected but associated vertebral body bone marrow changes are typically seen and are helpful in differentiating acute from chronic processes[ ]57 The occasional presence of a high-intensity zone in the herniated material with an occasionally enhancing border after contrast injection is probably caused by a mixture of displaced nuclear material acute and subacute inflammatory tissue and neovascularized reactive tissue[ ]4 [ ]48 [ ]72 Contradictory reports have been published regarding the accuracy of MR imaging to differentiate subligamentous from transligamentous herniations[ ]26 [ ]38 [ ]73 [ ]76 Understanding the anatomy of the PLLC is helpful to make the distinction (Fig 28) (Figure Not Available) Masaryk et al[ ]46 have suggested that MR imaging is accurate to distinguish sequestered disks from other forms of lumbar disk herniations but most observers find this distinction difficult to establish[ ]42

Figure 27 A Left L4-L5 foraminal herniation well seen on an intermediate-weighted left parasagittal MR section (arrow) in a 47-year-old man B The lesion is much less obvious on intermediate-weighted (left) and T2-weighted (right) axial sections and was in fact more conspicuous on the corresponding CT scan section

Figure 28 (Figure Not Available) A Subligamentous disk herniation Left T1-weighted image demonstrating displaced disk material with a smooth outline imposed by the demarcation of the anterior epidural space (AES) by the lateral membrane of the PLLC Right Correlative drawing B Transligamentous disk herniation Left T1-weighted image of a large disk herniation (cervical in this case) which has ruptured through the posterior confines of the AES Penetration of the right lateral membrane can be observed (arrow) and the disk fragment contour is serrated Right Correlative drawing (From Schellinger D Manz HJ Vidic B et al Disk fragment migration Radiology 175831-836 1990 with permission)

Diskography and CT Diskography

During 30 years (1950 to 1980) when myelography was the only available imaging technique to demonstrate lumbar disk herniations diskography was an invasive but efficient way to demonstrate posterior central L5-S1 herniations and other large herniations (other than posterior central and paramedial) that could not be detected by myelography[ ]50 These herniations are now usually well demonstrated by CT and MR imaging Comparing the accuracy of five imaging modalities (excluding MR imaging) for the diagnosis of lumbar disk herniation Jackson et al[ ]31 found that CT diskography (Fig 29) was the most accurate test (87) compared with 77 for CT myelography 74 for CT 70 for myelography 64 for pain reproduction during diskography and 58 for diskography without CT Disk injection reproduced the patients clinical pain pattern in only 36 of herniated disks This clinical test isolated from the images had high specificity (89) but low sensitivity (43) for the diagnosis of disk herniation The reported low sensitivity of diskography images (unassociated with CT) to diagnose disk herniation is to be expected the purpose of the intradiskal injection being primarily the demonstration of an anular tear the contrast leaking through the tear only occasionally delineates an extruded fragment When a disk herniation has been diagnosed by other imaging modalities diskography allows to determine if the herniation is contained or noncontained (Figs 30 and 31) this information may have clinical relevance[ ]62 It also allows to establish if the displaced disk material is communicating or not with the parent disk and establishes the likelihood that it is sequestered or not There always remains a possibility that the contrast injected under pressure may reach a disk fragment that is nevertheless sequestered by leaking through the associated anular tear CT diskography also allows assessment in most cases of the integrity of the PLLC[ ]89 The superior sensitivity of diskography over MR imaging to demonstrate anular tears has been well established[ ]27 [ ]44 [ ]48 [ ]64 [ ]77 [ ]91 [ ]94 The presence of a radial tear and the inflammatory reaction it creates may be symptomatic despite the absence of true disk herniation[ ]29 [ ]48 [ ]49 [ ]69

Figure 29 L4-L5 CT diskogram demonstrating a large left posterolateral radial anular tear associated with

a left foraminal and extraforaminal herniaton (same patient as in Figure 28) (Figure Not Available)

Figure 30 Contained posterior L4-L5 and L5-S1 disk herniations in a 57-year-old man demonstrated by diskography The L3-L4 disk is normal

Figure 31 Noncontained L4-L5 disk herniation in a 23-year-old woman Reflux of injected contrast is seen in the anterior epidural space above and below the disk space The L5-S1 disk also demonstrates incomplete anterior and posterior radial anular tears

SUMMARY

The absence of universal nomenclature standardization with respect to the definition of a disk herniation and its different categories especially regarding type and location is still a major problem that will only be overcome when major national or international scientific societies join efforts to support a particular scheme Meanwhile it is important to realize that the two models that are currently most used are based on a different perspective Trying to straddle the two by opposing for instance bulging disk and herniation is doomed to failure because this exercise defies formal logic MR imaging is currently the most accurate noninvasive imaging modality to diagnose a disk herniation and to determine its exact location The determination of some pathoanatomic characteristics of herniated disks (type and composition) may require the use of CT diskography or CT diskography

References

1 Albeck MJ Hilden J Kjaer L et al A controlled comparison of myelography computed tomography and magnetic resonance imaging in clinically suspected lumbar disc herniation Spine 20443-448 1995 Abstract 2 American Academy of Orthopedic Surgeons Glossary on Spinal Terminology Chicago American Academy of Orthopedic Surgeons 1981 3 Andersson GB Weinstein JN Disc herniation [editorial] Spine 211S 1996 Citation 4 Aprill C Bogduk N High-intensity zone A diagnostic sign of painful lumbar disc on magnetic resonance imaging Br J Radiol 65361-369 1992 Abstract 5 Birney TJ White JJ Jr Berens D et al Comparison of MRI and discography in the diagnosis of lumbar degenerative disc disease J Spinal Disord 5417-423 1992 Abstract 6 Bischoff RJ Rodriguez RP Gupta K et al A comparison of computed tomography-myelography magnetic resonance imaging and myelography in the diagnosis of herniated nucleus pulposus and spinal stenosis J Spinal Disord 6289-295 1993 Abstract 7 Bogduk N The innervation of the lumbar spine Spine 8286-293 1983 Abstract 8 Bogduk N Tynan W Wilson AS The nerve supply to the human lumbar intervertebral discs J Anat 13239-56 1981 Abstract 9 Bonneville JF La carte-image des hernies discales lombaires Rachis 2255-257 1990 10 Bonneville JF La topografia simbolica delle ernie discali lombari Riv Neuroradiol 5427-431 1992 11 Bonneville JF Plaidoyer pour une classification par limage des hernies discales lombaires La carte-image Rev Imag Med 2557-560 1990 12 Brant-Zawadzki M Jensen M Spinal nomenclature Spine 20388-390 1995 Abstract

13 Brant-Zawadzki MN Jensen MC Obuchowski N et al Interobserver and intraobserver variability in interpretation of lumbar disc abnormalities A comparison of two nomenclatures Spine 201257-1263 1995 Abstract 14 Breton G Is that a bulging disk a small herniation or a moderate protrusion [editorial] Can Assoc Radiol J 42318 1991 Citation 15 Czervionke LF Lumbar intervertebral disc disease Neuroimaging Clin North Am 3465-485 1993 16 Deyo RA Nonsurgical care of low back pain Neurosurg Clin North Am 2851-862 1991 17 Deyo RA Loeser JD Bigos SJ Herniated lumbar intervertebral disk Ann Intern Med 112598-603 1990 Abstract 18 Dorlands Illustrated Medical Dictionary ed 28 Philadelphia WB Saunders 1994 19 Fardon D Pinkerton S Balderston R et al Terms used for diagnosis by English speaking spine surgeons Spine 18274-277 1993 Citation 20 Fardon DF Herzog RJ Mink JH et al Nomenclature of Lumbar Disc Disorders Contemporary Concepts in Spine Care Rosemont IL North American Spine Society 1995 21 Fardon DF Herzog RJ Mink JH et al Nomenclature of lumbar disc disorders In Garfin S Vaccaro A (eds) Orthopedic Knowledge Update Spine Rosemont IL American Academy of Orthopedic Surgeons 1997 pp A3-A14 22 Forristall RM Marsh HO Pay NT Magnetic resonance imaging and contrast CT of the lumbar spine Comparison of diagnostic methods and correlation with surgical findings Spine 131049-1054 1988 Abstract 23 Fries JW Abodeely DA Vijungco JG et al Computed tomography of herniated and extruded nucleus pulposus J Comput Assist Tomogr 6874-887 1982 Abstract 24 Frymoyer JW Newberg A Pope MH et al Spine radiographs in patients with low-back pain An epidemiological study in men J Bone Joint Surg Am 661048-1055 1984 Abstract 25 Gospodarowicz M Benedet L Hutter RV et al History and international developments in cancer staging Cancer Prev Control 2262-268 1998 Abstract 26 Grenier N Greselle JF Vital JM et al Normal and disrupted lumbar longitudinal ligaments Correlative MR and anatomic study Radiology 171197-205 1989 Abstract 27 Gunzburg R Parkinson R Moore R et al A cadaveric study comparing discography magnetic resonance imaging histology and mechanical behavior of the human lumbar disc Spine 17417-426 1992 Abstract 28 Haughton VM Eldevik OP Magnaes B et al A prospective comparison of computed tomography and myelography in the diagnosis of herniated lumbar disks Radiology 142103-110 1982 Abstract

29 Haughton VM Lim TH An H Intervertebral disk appearance correlated with stiffness of lumbar spinal motion segments AJNR Am J Neuroradiol 201161-1165 1999 Abstract 30 Herzog RJ The radiologic assessment for a lumbar disc herniation Spine 2119S-38S 1996 Abstract 31 Jackson RP Becker GJ Jacobs RR et al The neuroradiographic diagnosis of lumbar herniated nucleus pulposus I A comparison of computed tomography (CT) myelography CT-myelography discography and CT-discography Spine 141356-1361 1989 Abstract 32 Jackson RP Cain JE Jr Jacobs RR et al The neuroradiographic diagnosis of lumbar herniated nucleus pulposus II A comparison of computed tomography (CT) myelography CT-myelography and magnetic resonance imaging Spine 141362-1367 1989 Abstract 33 Jarvik JG Haynor DR Koepsell TD et al Interreader reliability for a new classification of lumbar disk disease Acad Radiol 3537-544 1996 Abstract 34 Jensen MC Brant-Zawadzki MN Obuchowski N et al Magnetic resonance imaging of the lumbar spine in people without back pain N Engl J Med 33169-73 1994 Abstract 35 Kent DL Haynor DR Larson EB et al Diagnosis of lumbar spinal stenosis in adults A meta-analysis of the accuracy of CT MR and myelography AJR Am J Roentgenol 1581135-1144 1992 Abstract 36 Kieffer SA Sherry RG Wellenstein DE et al Bulging lumbar intervertebral disk Myelographic differentiation from herniated disk with nerve root compression AJR Am J Roentgenol 138709-716 1982 Abstract 37 Kieffer SA Stadlan EM Mohandas A et al Discographic-anatomical correlation of developmental changes with age in the intervertebral disc Acta Radiol 9733-739 1969 38 Kim KY Kim YT Lee CS et al MRI classification of lumbar herniated intervertebral disc Orthopedics 15493-497 1992 Abstract 39 Kornberg M Rechtine GR Dupuy TE Computed tomography in the diagnosis of a herniated disk at the L5-S1 level Spine 9433-436 1984 Abstract 40 Kramer MS Clinical Epidemiology and Biostatistics New York Springer-Verlag 1988 41 Landis JR Koch GG The measurement of observer agreement agreement for categorical data Biometrics 33159-174 1977 Abstract 42 Laredo JD Bossard P Vuillemin-Bodaghi Formes anatomo-radiologiques des hernies discales In Morvan G Deburge A Bard H et al (eds) Le Rachis Lombaire Degeneratif Montpellier Sauramps Medical 1998 pp 37-49 43 Lee SH Coleman PE Hahn FJ Magnetic resonance imaging of degenerative disk disease of the spine Radiol Clin North Am 26949-964 1988 Abstract 44 Linson MA Crowe CH Comparison of magnetic resonance imaging and lumbar discography in the diagnosis of disc degeneration Clin Orthop 160-163 1990

45 Marchand F Ahmed AM Investigation of the laminate structure of lumbar disc anulus fibrosus Spine 15402-410 1990 Abstract 46 Masaryk TJ Ross JS Modic MT et al High-resolution MR imaging of sequestered lumbar intervertebral disks AJR Am J Roentgenol 1501155-1162 1988 Abstract 47 Milette PC The proper terminology for reporting lumbar intervertebral disk disorders AJNR Am J Neuroradiol 181859-1866 1997 Citation 48 Milette PC Fontaine S Lepanto L et al Differentiating lumbar disc protrusions disk bulges and discs with normal contour but abnormal signal intensity Magnetic resonance imaging with discographic correlations Spine 2444-53 1999 Abstract 49 Milette PC Fontaine S Lepanto L et al Radiating pain to the lower extremities caused by lumbar disk rupture without spinal nerve root involvement AJNR Am J Neuroradiol 161605-1613 1995 Abstract 50 Milette PC Melancon D A reappraisal of lumbar discography Can Assoc Radiol J 33176-182 1982 51 Milette PC Melancon D Dupuis PR et al A simplified terminology for abnormalities of the lumbar disk Can Assoc Radiol J 42319-325 1991 Abstract 52 Milette PC Raymond J Fontaine S Comparison of high-resolution computed tomography with discography in the evaluation of lumbar disc herniations Spine 15525-533 1990 Abstract 53 Mink JH Deutsch AL Goldstein TB et al Spinal imaging and intervention 1998 Phys Med Rehabil Clin North Am 9343-380 1998 54 Mixter WJ Barr JS Rupture of the intervertebral disc with involvement of the spinal canal N Engl J Med 211210-234 1934 55 Modic MT Masaryk TJ Ross JS et al Imaging of degenerative disk disease Radiology 168177-186 1988 Citation 56 Modic MT Ross JS Obuchowski NA et al Contrast-enhanced MR imaging in acute lumbar radiculopathy A pilot study of the natural history Radiology 195429-435 1995 Abstract 57 Modic MT Steinberg PM Ross JS et al Degenerative disk disease Assessment of changes in vertebral body marrow with MR imaging Radiology 166193-199 1988 58 Morvan G Mathieu P Les stenoses laterales In Morvan G Deburge A Bard H et al (eds) Le Rachis Lombaire Degeneratif Montpellier Sauramps Medical 1998 pp 315-324 59 Murray RO Skeletal trauma Regional In Sutton D (ed) Textbook of Radiology and Imaging ed 3 New York Churchill Livingstone 1980 pp 210-231 60 Nachemson A Lumbar disc herniation Conclusions Acta Orthop Scand 64(suppl 251)49 1993 Citation

61 Nathan H Osteophytes of the vertebral column An anatomical study of their development according to age race and sex with consideration as to their etiology and significance J Bone Joint Surg Am 44243-268 1962 62 Nygaard OP Mellgren SI Osterud B The inflammatory properties of contained and noncontained lumbar disc herniations Spine 222584-2488 1997 Abstract 63 Ohshima H Hirano N Osada R et al Morphologic variation of lumbar posterior longitudinal ligament and the modality of disc herniation Spine 182408-2411 1993 Abstract 64 Osti OL Fraser RD MRI and discography of annular tears and intervertebral disc degeneration A prospective clinical comparison J Bone Joint Surg Br 74431-435 1992 Abstract 65 Palmgren T Gronblad M Virri J et al Immunohistochemical demonstration of sensory and autonomic nerve terminals in herniated lumbar disc tissue Spine 211301-1306 1996 Abstract 66 Resnick D Niwayama G Degenerative disease of the spine In Resnick D (ed) Diagnosis of Bone and Joint Disorders ed 3 Philadelphia WB Saunders 1995 pp 1372-1462 67 Resnick D Niwayama G Intravertebral disk herniations Cartilaginous (Schmorls) nodes Radiology 12657-65 1978 Abstract 68 Ross JS Modic MT Masaryk TJ Tears of the anulus fibrosus Assessment with Gd-DTPA-enhanced MR imaging AJR Am J Roentgenol 154159-162 1990 Abstract 69 Saal JS The role of inflammation in lumbar pain Spine 201821-1827 1995 Abstract 70 Sachs BL Vanharanta H Spivey MA et al Dallas discogram description A new classification of CTdiscography in low-back disorders Spine 12287-294 1987 Abstract 71 Sauser DD Goldman AB Kaye JJ Discogenic vertebral sclerosis J Can Assoc Radiol 2944-50 1978 Abstract 72 Schellhas KP Pollei SR Gundry CR et al Lumbar disc high-intensity zone Correlation of magnetic resonance imaging and discography Spine 2179-86 1996 Abstract 73 Schellinger D Manz HJ Vidic B et al Disk fragment migration Radiology 175831-836 1990 Abstract 74 Schipper J Kardaun JW Braakman R et al Lumbar disk herniation Diagnosis with CT or myelography Radiology 165227-231 1987 Abstract 75 Schmorl G Junghanns H The Human Spine in Health and Disease ed 2 New York Grune and Stratton 1971 76 Silverman CS Lenchik L Shimkin PM et al The value of MR in differentiating subligamentous from supraligamentous lumbar disk herniations AJNR Am J Neuroradiol 16571-579 1995 Abstract 77 Simmons JW Emery SF McMillin JN et al Awake discography A comparison study with magnetic

resonance imaging Spine 16S216-221 1991 Abstract 78 Smyth MJ Wright V Sciatica and the intervertebral disc J Bone Joint Surg Am 401401-1418 1958 79 Taveras JM Radiologic aspects of low back pain and sciatic syndromes [editorial] AJNR Am J Neuroradiol 9351-358 1989 80 Tehranzadeh J Discography 2000 Radiol Clin North Am 36463-495 1998 Full Text 81 Thelander U Fagerlund M Friberg S et al Describing the size of lumbar disc herniations using computed tomography A comparison of different size index calculations and their relation to sciatica Spine 191979-1984 1994 Abstract 82 Thornbury JR Fryback DG Turski PA et al Disk-caused nerve compression in patients with acute low-back pain Diagnosis with MR CT myelography and plain CT Radiology 186731-738 1993 Abstract 83 Twomey L Taylor J Age changes in lumbar intervertebral discs Acta Orthop Scand 56496-499 1985 Abstract 84 Twomey LT Taylor JR Age changes in lumbar vertebrae and intervertebral discs Clin Orthop 22497-104 1987 85 Williams AL CT diagnosis of degenerative disc disease The bulging annulus Radiol Clin North Am 21289-300 1983 Abstract 86 Williams AL Haughton VM Meyer GA et al Computed tomographic appearance of the bulging annulus Radiology 142403-408 1982 Abstract 87 Williams AL Haughton VM Syvertsen A Computed tomography in the diagnosis of herniated nucleus pulposus Radiology 13595-99 1980 Abstract 88 Wiltse LL Berger PE McCulloch JA A system for reporting the size and location of lesions in the spine Spine 221534-1537 1997 Abstract 89 Wiltse LL Fonseca AS Amster J et al Relationship of the dura Hofmanns ligaments Batsons plexus and a fibrovascular membrane lying on the posterior surface of the vertebral bodies and attaching to the deep layer of the posterior longitudinal ligament An anatomical radiologic and clinical study Spine 181030-1043 1993 Abstract 90 Yamashita K Hiroshima K Kurata A Gadolinium-DTPA-enhanced magnetic resonance imaging of a sequestered lumbar intervertebral disc and its correlation with pathologic findings Spine 19479-482 1994 Abstract 91 Yu SW Haughton VM Sether LA et al Comparison of MR and diskography in detecting radial tears of the anulus A postmortem study AJNR Am J Neuroradiol 101077-1081 1989 Abstract 92 Yu SW Sether LA Ho PS et al Tears of the anulus fibrosus Correlation between MR and pathologic findings in cadavers AJNR Am J Neuroradiol 9367-370 1988 Abstract

93 Yussen PS Swartz JD The acute lumbar disc herniation Imaging diagnosis Semin Ultrasound CT MR 14389-398 1993 Abstract 94 Zucherman J Derby R Hsu K et al Normal magnetic resonance imaging with abnormal discography Spine 131355-1359 1988 Abstract

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  • CLASSIFICATION DIAGNOSTIC IMAGING AND IMAGING CHARACTERIZATION OF A LUMBAR HERNIATED DISK
    • IMAGING OF LOW BACK PAIN I
      • CLASSIFICATION DIAGNOSTIC IMAGING AND IMAGING CHARACTERIZATION OF A LUMBAR HERNIATED DISK
        • DEFINITION OF A DISK HERNIATION
        • CLASSIFICATION OF A HERNIATED LUMBAR DISK
          • Main Categories of Noninfectious Disk Abnormalities
          • Further Qualifying the Displaced Disk Material Beyond the Disk Space
            • DIAGNOSTIC IMAGING AND CHARACTERIZATION OF A HERNIATED LUMBAR DISK
              • Conventional Radiographs
              • Myelography
              • CT
              • CT Myelography
              • MR Imaging
              • Diskography and CT Diskography
                • SUMMARY
                  • References
Page 20: CLASSIFICATION, DIAGNOSTIC IMAGING, AND IMAGING ... · PDF fileclassification, diagnostic imaging, and imaging characterization of a lumbar herniated disk ... classification, diagnostic

Figure 20 A CT scan demonstration of a small posterior central L4-L5 calcified subligamentous herniation The resistant deep layer of the PLLC restrains displacement of the disk material in the posterior central direction and does not allow a detectable distortion of the disk contour In this particular case the presence of the calcification is actually the only evidence that a posterior midline anular tear and a small subligamentous herniation are present B Posterior right central and sub-articular L5-S1 calcified disk herniation in same patient Posterolateral herniations are generally more conspicuous than posterior midline herniations because the deep layer of the PLLC gets thinner away from the midline

Figure 21 Posterior central midline L4-L5 herniation in a 52-year-old man demonstrated on a T2-weighted midline MR sagittal section There is intervertebral space narrowing with loss of normal central disk signal

intensity while the herniated disk material demonstrates high signal intensity consistent with a predominantly fluid consistency

Figure 22 CT scan demonstration in a 51-year-old woman of a left posterolateral L5-S1 disk hernation consisting essentially in a gas-filled pouch (white arrow) Gas is also present in the central portion of the intervertebral disk space (black arrow)

DIAGNOSTIC IMAGING AND CHARACTERIZATION OF A HERNIATED LUMBAR DISK

Assessing the validity of the currently used imaging procedures to diagnose a herniated lumbar disk is not an easy endeavor The validity of a measurement is the extent to which it corresponds to the true biologic value or some accepted gold standard[ ]40 With the exception of postmortem studies evaluation of the pathoanatomy by the surgeon in the operating room has always been considered the gold standard but this does not constitute an ideal situation Inspection of the disk through a small laminectomy incision to determine for instance if nuclear fragments lie within or outside the anular fibers may not be very reliable Also unbiased intraoperative determination of a normal degenerated or herniated disk in a patient with sciatica may also be difficult[ ]86 Because the validity of diskography has been previously established by postmortem studies and surgical correlations[ ]48 it is sometimes used as a gold standard in situations where no surgery has been performed

Conventional Radiographs

Lumbar disk herniations can exceptionally be diagnosed directly on good quality lateral projections because the x-ray attenuation is slightly greater in displaced disk material than in epidural fat Occasionally a calcified rim outlines the displaced disk fragment

(Fig 23) In most situations however narrowing of an intervertebral disk space in the absence of other evidence of chronic diskopathy is the only detectable sign suggesting the presence of a disk herniation To my knowledge the sensitivity and specificity of this sign has never been assessed The accepted rule of thumb is that the height of a given lumbar intervertebral disk space should always be slightly greater than the height of the above located interspace This rule does not apply to the transition disk immediately above the sacrum (usually L5-S1) The specificity of this sign is probably quite high but a few false-positives are seen especially at the L4-L5 level because of minor congenital hypoplasia The presence of posterior or foraminal vertebral body osteophytes associated or not with disk space narrowing is a definite sign of a chronic disk herniation

Figure 23 A Chronic left L3-L4 extraforaminal disk hernation in a 54-year-old man suspected on an AP radiograph demonstrating a calcified shell on the left side of the intervertebral disk space (white arrow) B Axial CT scan section confirming the diagnosis of a chronic extraforaminal L3-L4 herniation

Myelography

Myelography is essentially an exploration of the subarachnoid space Disk herniations are demonstrated only indirectly because they can cause thecal sac deformity and individual nerve root sleeve filling defects (Fig 24) Of all the special imaging procedures

myelography is the only one that allows upright projections with full weight bearing It is not unusual to demonstrate in this way small posterior central or posterolateral herniations that are undetectable on CT sections Interestingly the overall sensitivity of myelography to detect disk herniations has been found to be higher than that of CT whereas its specificity has been found to be lower[ ]74 In comparison with standard CT examination which usually includes only the three or four lower lumbar disks myelography easily allows coverage of the entire lumbar area and assessment of the intrathecal structures (cauda equina and conus medullaris) Far lateral foraminal herniations extraforaminal herniations and anterior herniations however are not detected The sensitivity for detection of posterior central L5-S1 herniations is also relatively poor because of the greater distance between the thecal sac and the posterior aspect of this particular disk

Figure 24 L5-S1 disk herniation in a 25-year-old man detected by indirect signs using lumbosacral myelography A Upright oblique projections showing a filling defect of the left S1 root sleeve (white arrow) suggesting significant nerve root compression by a left posterolateral disk hernation The right S1 root sleeve fills normally with contrast (black arrow) B Subtle compression of the anterior wall of the dural sac by displaced disk material (small arrows) demonstrated on upright lateral projection This sign is usually absent in the presence of a large amount of fat and venous structures in the anterior epidural compartment

CT

The sensitivity of CT to diagnose a herniation of the nucleus pulposus at the L5-S1 interspace is greater than that of myelography if images in the exact plane of the disk can be obtained[ ]23 [ ]39 Otherwise the superiority of plain CT over myelography to demonstrate disk herniations has not been established but CT has the distinct advantage of being

noninvasive and provides direct anatomic information[ ]23 Large herniations are easily detected but as explained previously the distinction between protrusions and extrusions is often difficult without sagittal reconstructions CT essentially allows an assessment of the contour of the disk The diagnosis of very small herniations in the absence of direct or indirect evidence of a radial tear is hazardous and associated with a high percentage of false-positives and false-negatives[ ]52 The diagnosis of moderate and large size herniations in different directions is usually possible but anterior herniations are rarely diagnosed not because they are not detectable but because observers pay little attention to the anterior contour of the disk (Fig 25) Because the PLLC cannot usually be identified the distinction of subligamentous from transligamentous herniation can only be suggested in most cases by the size of the herniated material A definite diagnosis of sequestration is rarely possible Calcifications within the displaced material are readily seen but may be difficult at times to differentiate from an accompanying osteophyte or an avulsed bone fragment from the vertebral body ring epiphysis (Fig 26) The presence of gas in the herniated material is easily detected

Figure 25 Anterior L4-L5 herniation demonstrated by CT scan in a 51-year-old woman with chronic low back pain Although sometimes quite conspicuous such herniations are rarely reported because observers pay little attention to the anterior contour of the disk

Figure 26 CT scan demonstration of a posterior right central L4-L5 disk herniation in a 38-year-old woman with avulsion of a bone fragment from the ring epiphysis and adjacent part of the superior L5 end plate Reactive osteosclerosis is seen around the vertebral body defect (arrows) suggesting a chronic lesion

CT Myelography

This association combines the advantages of both imaging modalities The fact that its accuracy has been reported as being less[ ]22 [ ]32 higher[ ]1 [ ]6 or equivalent[ ]82 to MR imaging is a reflection of the differences in technologic advancement and pathologic nomenclature that hamper valid comparisons between different studies

MR Imaging

Most reported studies establish MR imaging as the first choice modality to diagnose a herniated lumbar disk[ ]5 [ ]22 [ ]32 [ ]46 The associated intravenous injection of a paramagnetic agent has been found useful to demonstrate some anatomic features of disk disease in patients with no previous lumbar disk surgery[ ]56 [ ]68 [ ]90 MR imaging provides a better assessment of disk morphology than CT or CT myelography because sagittal sections are routinely obtained Assessment of foraminal involvement by displaced disk material is more accurate (Fig 27) and anterior disk herniations can be detected more easily than with CT or CT myelography If one is looking specifically for herniated lumbar disks associated with nerve root compression however it has been demonstrated that CT is equally accurate[ ]82 Alterations of the central or peripheral disk signal intensity on T2-weighted images are seen in most disks afflicted with an anular tear[ ]48 and alert the observer to scrutinize the disk contour in search for local modifications indicative of a herniation Because the signal of the displaced disk material is usually very similar to that of the outer anulus PLLC and vertebral body cortical bone small herniations are generally more conspicuous on axial CT sections than on corresponding axial MR imaging sections Gas and calcium deposits within the displaced fragment cannot usually

be detected but associated vertebral body bone marrow changes are typically seen and are helpful in differentiating acute from chronic processes[ ]57 The occasional presence of a high-intensity zone in the herniated material with an occasionally enhancing border after contrast injection is probably caused by a mixture of displaced nuclear material acute and subacute inflammatory tissue and neovascularized reactive tissue[ ]4 [ ]48 [ ]72 Contradictory reports have been published regarding the accuracy of MR imaging to differentiate subligamentous from transligamentous herniations[ ]26 [ ]38 [ ]73 [ ]76 Understanding the anatomy of the PLLC is helpful to make the distinction (Fig 28) (Figure Not Available) Masaryk et al[ ]46 have suggested that MR imaging is accurate to distinguish sequestered disks from other forms of lumbar disk herniations but most observers find this distinction difficult to establish[ ]42

Figure 27 A Left L4-L5 foraminal herniation well seen on an intermediate-weighted left parasagittal MR section (arrow) in a 47-year-old man B The lesion is much less obvious on intermediate-weighted (left) and T2-weighted (right) axial sections and was in fact more conspicuous on the corresponding CT scan section

Figure 28 (Figure Not Available) A Subligamentous disk herniation Left T1-weighted image demonstrating displaced disk material with a smooth outline imposed by the demarcation of the anterior epidural space (AES) by the lateral membrane of the PLLC Right Correlative drawing B Transligamentous disk herniation Left T1-weighted image of a large disk herniation (cervical in this case) which has ruptured through the posterior confines of the AES Penetration of the right lateral membrane can be observed (arrow) and the disk fragment contour is serrated Right Correlative drawing (From Schellinger D Manz HJ Vidic B et al Disk fragment migration Radiology 175831-836 1990 with permission)

Diskography and CT Diskography

During 30 years (1950 to 1980) when myelography was the only available imaging technique to demonstrate lumbar disk herniations diskography was an invasive but efficient way to demonstrate posterior central L5-S1 herniations and other large herniations (other than posterior central and paramedial) that could not be detected by myelography[ ]50 These herniations are now usually well demonstrated by CT and MR imaging Comparing the accuracy of five imaging modalities (excluding MR imaging) for the diagnosis of lumbar disk herniation Jackson et al[ ]31 found that CT diskography (Fig 29) was the most accurate test (87) compared with 77 for CT myelography 74 for CT 70 for myelography 64 for pain reproduction during diskography and 58 for diskography without CT Disk injection reproduced the patients clinical pain pattern in only 36 of herniated disks This clinical test isolated from the images had high specificity (89) but low sensitivity (43) for the diagnosis of disk herniation The reported low sensitivity of diskography images (unassociated with CT) to diagnose disk herniation is to be expected the purpose of the intradiskal injection being primarily the demonstration of an anular tear the contrast leaking through the tear only occasionally delineates an extruded fragment When a disk herniation has been diagnosed by other imaging modalities diskography allows to determine if the herniation is contained or noncontained (Figs 30 and 31) this information may have clinical relevance[ ]62 It also allows to establish if the displaced disk material is communicating or not with the parent disk and establishes the likelihood that it is sequestered or not There always remains a possibility that the contrast injected under pressure may reach a disk fragment that is nevertheless sequestered by leaking through the associated anular tear CT diskography also allows assessment in most cases of the integrity of the PLLC[ ]89 The superior sensitivity of diskography over MR imaging to demonstrate anular tears has been well established[ ]27 [ ]44 [ ]48 [ ]64 [ ]77 [ ]91 [ ]94 The presence of a radial tear and the inflammatory reaction it creates may be symptomatic despite the absence of true disk herniation[ ]29 [ ]48 [ ]49 [ ]69

Figure 29 L4-L5 CT diskogram demonstrating a large left posterolateral radial anular tear associated with

a left foraminal and extraforaminal herniaton (same patient as in Figure 28) (Figure Not Available)

Figure 30 Contained posterior L4-L5 and L5-S1 disk herniations in a 57-year-old man demonstrated by diskography The L3-L4 disk is normal

Figure 31 Noncontained L4-L5 disk herniation in a 23-year-old woman Reflux of injected contrast is seen in the anterior epidural space above and below the disk space The L5-S1 disk also demonstrates incomplete anterior and posterior radial anular tears

SUMMARY

The absence of universal nomenclature standardization with respect to the definition of a disk herniation and its different categories especially regarding type and location is still a major problem that will only be overcome when major national or international scientific societies join efforts to support a particular scheme Meanwhile it is important to realize that the two models that are currently most used are based on a different perspective Trying to straddle the two by opposing for instance bulging disk and herniation is doomed to failure because this exercise defies formal logic MR imaging is currently the most accurate noninvasive imaging modality to diagnose a disk herniation and to determine its exact location The determination of some pathoanatomic characteristics of herniated disks (type and composition) may require the use of CT diskography or CT diskography

References

1 Albeck MJ Hilden J Kjaer L et al A controlled comparison of myelography computed tomography and magnetic resonance imaging in clinically suspected lumbar disc herniation Spine 20443-448 1995 Abstract 2 American Academy of Orthopedic Surgeons Glossary on Spinal Terminology Chicago American Academy of Orthopedic Surgeons 1981 3 Andersson GB Weinstein JN Disc herniation [editorial] Spine 211S 1996 Citation 4 Aprill C Bogduk N High-intensity zone A diagnostic sign of painful lumbar disc on magnetic resonance imaging Br J Radiol 65361-369 1992 Abstract 5 Birney TJ White JJ Jr Berens D et al Comparison of MRI and discography in the diagnosis of lumbar degenerative disc disease J Spinal Disord 5417-423 1992 Abstract 6 Bischoff RJ Rodriguez RP Gupta K et al A comparison of computed tomography-myelography magnetic resonance imaging and myelography in the diagnosis of herniated nucleus pulposus and spinal stenosis J Spinal Disord 6289-295 1993 Abstract 7 Bogduk N The innervation of the lumbar spine Spine 8286-293 1983 Abstract 8 Bogduk N Tynan W Wilson AS The nerve supply to the human lumbar intervertebral discs J Anat 13239-56 1981 Abstract 9 Bonneville JF La carte-image des hernies discales lombaires Rachis 2255-257 1990 10 Bonneville JF La topografia simbolica delle ernie discali lombari Riv Neuroradiol 5427-431 1992 11 Bonneville JF Plaidoyer pour une classification par limage des hernies discales lombaires La carte-image Rev Imag Med 2557-560 1990 12 Brant-Zawadzki M Jensen M Spinal nomenclature Spine 20388-390 1995 Abstract

13 Brant-Zawadzki MN Jensen MC Obuchowski N et al Interobserver and intraobserver variability in interpretation of lumbar disc abnormalities A comparison of two nomenclatures Spine 201257-1263 1995 Abstract 14 Breton G Is that a bulging disk a small herniation or a moderate protrusion [editorial] Can Assoc Radiol J 42318 1991 Citation 15 Czervionke LF Lumbar intervertebral disc disease Neuroimaging Clin North Am 3465-485 1993 16 Deyo RA Nonsurgical care of low back pain Neurosurg Clin North Am 2851-862 1991 17 Deyo RA Loeser JD Bigos SJ Herniated lumbar intervertebral disk Ann Intern Med 112598-603 1990 Abstract 18 Dorlands Illustrated Medical Dictionary ed 28 Philadelphia WB Saunders 1994 19 Fardon D Pinkerton S Balderston R et al Terms used for diagnosis by English speaking spine surgeons Spine 18274-277 1993 Citation 20 Fardon DF Herzog RJ Mink JH et al Nomenclature of Lumbar Disc Disorders Contemporary Concepts in Spine Care Rosemont IL North American Spine Society 1995 21 Fardon DF Herzog RJ Mink JH et al Nomenclature of lumbar disc disorders In Garfin S Vaccaro A (eds) Orthopedic Knowledge Update Spine Rosemont IL American Academy of Orthopedic Surgeons 1997 pp A3-A14 22 Forristall RM Marsh HO Pay NT Magnetic resonance imaging and contrast CT of the lumbar spine Comparison of diagnostic methods and correlation with surgical findings Spine 131049-1054 1988 Abstract 23 Fries JW Abodeely DA Vijungco JG et al Computed tomography of herniated and extruded nucleus pulposus J Comput Assist Tomogr 6874-887 1982 Abstract 24 Frymoyer JW Newberg A Pope MH et al Spine radiographs in patients with low-back pain An epidemiological study in men J Bone Joint Surg Am 661048-1055 1984 Abstract 25 Gospodarowicz M Benedet L Hutter RV et al History and international developments in cancer staging Cancer Prev Control 2262-268 1998 Abstract 26 Grenier N Greselle JF Vital JM et al Normal and disrupted lumbar longitudinal ligaments Correlative MR and anatomic study Radiology 171197-205 1989 Abstract 27 Gunzburg R Parkinson R Moore R et al A cadaveric study comparing discography magnetic resonance imaging histology and mechanical behavior of the human lumbar disc Spine 17417-426 1992 Abstract 28 Haughton VM Eldevik OP Magnaes B et al A prospective comparison of computed tomography and myelography in the diagnosis of herniated lumbar disks Radiology 142103-110 1982 Abstract

29 Haughton VM Lim TH An H Intervertebral disk appearance correlated with stiffness of lumbar spinal motion segments AJNR Am J Neuroradiol 201161-1165 1999 Abstract 30 Herzog RJ The radiologic assessment for a lumbar disc herniation Spine 2119S-38S 1996 Abstract 31 Jackson RP Becker GJ Jacobs RR et al The neuroradiographic diagnosis of lumbar herniated nucleus pulposus I A comparison of computed tomography (CT) myelography CT-myelography discography and CT-discography Spine 141356-1361 1989 Abstract 32 Jackson RP Cain JE Jr Jacobs RR et al The neuroradiographic diagnosis of lumbar herniated nucleus pulposus II A comparison of computed tomography (CT) myelography CT-myelography and magnetic resonance imaging Spine 141362-1367 1989 Abstract 33 Jarvik JG Haynor DR Koepsell TD et al Interreader reliability for a new classification of lumbar disk disease Acad Radiol 3537-544 1996 Abstract 34 Jensen MC Brant-Zawadzki MN Obuchowski N et al Magnetic resonance imaging of the lumbar spine in people without back pain N Engl J Med 33169-73 1994 Abstract 35 Kent DL Haynor DR Larson EB et al Diagnosis of lumbar spinal stenosis in adults A meta-analysis of the accuracy of CT MR and myelography AJR Am J Roentgenol 1581135-1144 1992 Abstract 36 Kieffer SA Sherry RG Wellenstein DE et al Bulging lumbar intervertebral disk Myelographic differentiation from herniated disk with nerve root compression AJR Am J Roentgenol 138709-716 1982 Abstract 37 Kieffer SA Stadlan EM Mohandas A et al Discographic-anatomical correlation of developmental changes with age in the intervertebral disc Acta Radiol 9733-739 1969 38 Kim KY Kim YT Lee CS et al MRI classification of lumbar herniated intervertebral disc Orthopedics 15493-497 1992 Abstract 39 Kornberg M Rechtine GR Dupuy TE Computed tomography in the diagnosis of a herniated disk at the L5-S1 level Spine 9433-436 1984 Abstract 40 Kramer MS Clinical Epidemiology and Biostatistics New York Springer-Verlag 1988 41 Landis JR Koch GG The measurement of observer agreement agreement for categorical data Biometrics 33159-174 1977 Abstract 42 Laredo JD Bossard P Vuillemin-Bodaghi Formes anatomo-radiologiques des hernies discales In Morvan G Deburge A Bard H et al (eds) Le Rachis Lombaire Degeneratif Montpellier Sauramps Medical 1998 pp 37-49 43 Lee SH Coleman PE Hahn FJ Magnetic resonance imaging of degenerative disk disease of the spine Radiol Clin North Am 26949-964 1988 Abstract 44 Linson MA Crowe CH Comparison of magnetic resonance imaging and lumbar discography in the diagnosis of disc degeneration Clin Orthop 160-163 1990

45 Marchand F Ahmed AM Investigation of the laminate structure of lumbar disc anulus fibrosus Spine 15402-410 1990 Abstract 46 Masaryk TJ Ross JS Modic MT et al High-resolution MR imaging of sequestered lumbar intervertebral disks AJR Am J Roentgenol 1501155-1162 1988 Abstract 47 Milette PC The proper terminology for reporting lumbar intervertebral disk disorders AJNR Am J Neuroradiol 181859-1866 1997 Citation 48 Milette PC Fontaine S Lepanto L et al Differentiating lumbar disc protrusions disk bulges and discs with normal contour but abnormal signal intensity Magnetic resonance imaging with discographic correlations Spine 2444-53 1999 Abstract 49 Milette PC Fontaine S Lepanto L et al Radiating pain to the lower extremities caused by lumbar disk rupture without spinal nerve root involvement AJNR Am J Neuroradiol 161605-1613 1995 Abstract 50 Milette PC Melancon D A reappraisal of lumbar discography Can Assoc Radiol J 33176-182 1982 51 Milette PC Melancon D Dupuis PR et al A simplified terminology for abnormalities of the lumbar disk Can Assoc Radiol J 42319-325 1991 Abstract 52 Milette PC Raymond J Fontaine S Comparison of high-resolution computed tomography with discography in the evaluation of lumbar disc herniations Spine 15525-533 1990 Abstract 53 Mink JH Deutsch AL Goldstein TB et al Spinal imaging and intervention 1998 Phys Med Rehabil Clin North Am 9343-380 1998 54 Mixter WJ Barr JS Rupture of the intervertebral disc with involvement of the spinal canal N Engl J Med 211210-234 1934 55 Modic MT Masaryk TJ Ross JS et al Imaging of degenerative disk disease Radiology 168177-186 1988 Citation 56 Modic MT Ross JS Obuchowski NA et al Contrast-enhanced MR imaging in acute lumbar radiculopathy A pilot study of the natural history Radiology 195429-435 1995 Abstract 57 Modic MT Steinberg PM Ross JS et al Degenerative disk disease Assessment of changes in vertebral body marrow with MR imaging Radiology 166193-199 1988 58 Morvan G Mathieu P Les stenoses laterales In Morvan G Deburge A Bard H et al (eds) Le Rachis Lombaire Degeneratif Montpellier Sauramps Medical 1998 pp 315-324 59 Murray RO Skeletal trauma Regional In Sutton D (ed) Textbook of Radiology and Imaging ed 3 New York Churchill Livingstone 1980 pp 210-231 60 Nachemson A Lumbar disc herniation Conclusions Acta Orthop Scand 64(suppl 251)49 1993 Citation

61 Nathan H Osteophytes of the vertebral column An anatomical study of their development according to age race and sex with consideration as to their etiology and significance J Bone Joint Surg Am 44243-268 1962 62 Nygaard OP Mellgren SI Osterud B The inflammatory properties of contained and noncontained lumbar disc herniations Spine 222584-2488 1997 Abstract 63 Ohshima H Hirano N Osada R et al Morphologic variation of lumbar posterior longitudinal ligament and the modality of disc herniation Spine 182408-2411 1993 Abstract 64 Osti OL Fraser RD MRI and discography of annular tears and intervertebral disc degeneration A prospective clinical comparison J Bone Joint Surg Br 74431-435 1992 Abstract 65 Palmgren T Gronblad M Virri J et al Immunohistochemical demonstration of sensory and autonomic nerve terminals in herniated lumbar disc tissue Spine 211301-1306 1996 Abstract 66 Resnick D Niwayama G Degenerative disease of the spine In Resnick D (ed) Diagnosis of Bone and Joint Disorders ed 3 Philadelphia WB Saunders 1995 pp 1372-1462 67 Resnick D Niwayama G Intravertebral disk herniations Cartilaginous (Schmorls) nodes Radiology 12657-65 1978 Abstract 68 Ross JS Modic MT Masaryk TJ Tears of the anulus fibrosus Assessment with Gd-DTPA-enhanced MR imaging AJR Am J Roentgenol 154159-162 1990 Abstract 69 Saal JS The role of inflammation in lumbar pain Spine 201821-1827 1995 Abstract 70 Sachs BL Vanharanta H Spivey MA et al Dallas discogram description A new classification of CTdiscography in low-back disorders Spine 12287-294 1987 Abstract 71 Sauser DD Goldman AB Kaye JJ Discogenic vertebral sclerosis J Can Assoc Radiol 2944-50 1978 Abstract 72 Schellhas KP Pollei SR Gundry CR et al Lumbar disc high-intensity zone Correlation of magnetic resonance imaging and discography Spine 2179-86 1996 Abstract 73 Schellinger D Manz HJ Vidic B et al Disk fragment migration Radiology 175831-836 1990 Abstract 74 Schipper J Kardaun JW Braakman R et al Lumbar disk herniation Diagnosis with CT or myelography Radiology 165227-231 1987 Abstract 75 Schmorl G Junghanns H The Human Spine in Health and Disease ed 2 New York Grune and Stratton 1971 76 Silverman CS Lenchik L Shimkin PM et al The value of MR in differentiating subligamentous from supraligamentous lumbar disk herniations AJNR Am J Neuroradiol 16571-579 1995 Abstract 77 Simmons JW Emery SF McMillin JN et al Awake discography A comparison study with magnetic

resonance imaging Spine 16S216-221 1991 Abstract 78 Smyth MJ Wright V Sciatica and the intervertebral disc J Bone Joint Surg Am 401401-1418 1958 79 Taveras JM Radiologic aspects of low back pain and sciatic syndromes [editorial] AJNR Am J Neuroradiol 9351-358 1989 80 Tehranzadeh J Discography 2000 Radiol Clin North Am 36463-495 1998 Full Text 81 Thelander U Fagerlund M Friberg S et al Describing the size of lumbar disc herniations using computed tomography A comparison of different size index calculations and their relation to sciatica Spine 191979-1984 1994 Abstract 82 Thornbury JR Fryback DG Turski PA et al Disk-caused nerve compression in patients with acute low-back pain Diagnosis with MR CT myelography and plain CT Radiology 186731-738 1993 Abstract 83 Twomey L Taylor J Age changes in lumbar intervertebral discs Acta Orthop Scand 56496-499 1985 Abstract 84 Twomey LT Taylor JR Age changes in lumbar vertebrae and intervertebral discs Clin Orthop 22497-104 1987 85 Williams AL CT diagnosis of degenerative disc disease The bulging annulus Radiol Clin North Am 21289-300 1983 Abstract 86 Williams AL Haughton VM Meyer GA et al Computed tomographic appearance of the bulging annulus Radiology 142403-408 1982 Abstract 87 Williams AL Haughton VM Syvertsen A Computed tomography in the diagnosis of herniated nucleus pulposus Radiology 13595-99 1980 Abstract 88 Wiltse LL Berger PE McCulloch JA A system for reporting the size and location of lesions in the spine Spine 221534-1537 1997 Abstract 89 Wiltse LL Fonseca AS Amster J et al Relationship of the dura Hofmanns ligaments Batsons plexus and a fibrovascular membrane lying on the posterior surface of the vertebral bodies and attaching to the deep layer of the posterior longitudinal ligament An anatomical radiologic and clinical study Spine 181030-1043 1993 Abstract 90 Yamashita K Hiroshima K Kurata A Gadolinium-DTPA-enhanced magnetic resonance imaging of a sequestered lumbar intervertebral disc and its correlation with pathologic findings Spine 19479-482 1994 Abstract 91 Yu SW Haughton VM Sether LA et al Comparison of MR and diskography in detecting radial tears of the anulus A postmortem study AJNR Am J Neuroradiol 101077-1081 1989 Abstract 92 Yu SW Sether LA Ho PS et al Tears of the anulus fibrosus Correlation between MR and pathologic findings in cadavers AJNR Am J Neuroradiol 9367-370 1988 Abstract

93 Yussen PS Swartz JD The acute lumbar disc herniation Imaging diagnosis Semin Ultrasound CT MR 14389-398 1993 Abstract 94 Zucherman J Derby R Hsu K et al Normal magnetic resonance imaging with abnormal discography Spine 131355-1359 1988 Abstract

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  • CLASSIFICATION DIAGNOSTIC IMAGING AND IMAGING CHARACTERIZATION OF A LUMBAR HERNIATED DISK
    • IMAGING OF LOW BACK PAIN I
      • CLASSIFICATION DIAGNOSTIC IMAGING AND IMAGING CHARACTERIZATION OF A LUMBAR HERNIATED DISK
        • DEFINITION OF A DISK HERNIATION
        • CLASSIFICATION OF A HERNIATED LUMBAR DISK
          • Main Categories of Noninfectious Disk Abnormalities
          • Further Qualifying the Displaced Disk Material Beyond the Disk Space
            • DIAGNOSTIC IMAGING AND CHARACTERIZATION OF A HERNIATED LUMBAR DISK
              • Conventional Radiographs
              • Myelography
              • CT
              • CT Myelography
              • MR Imaging
              • Diskography and CT Diskography
                • SUMMARY
                  • References
Page 21: CLASSIFICATION, DIAGNOSTIC IMAGING, AND IMAGING ... · PDF fileclassification, diagnostic imaging, and imaging characterization of a lumbar herniated disk ... classification, diagnostic

intensity while the herniated disk material demonstrates high signal intensity consistent with a predominantly fluid consistency

Figure 22 CT scan demonstration in a 51-year-old woman of a left posterolateral L5-S1 disk hernation consisting essentially in a gas-filled pouch (white arrow) Gas is also present in the central portion of the intervertebral disk space (black arrow)

DIAGNOSTIC IMAGING AND CHARACTERIZATION OF A HERNIATED LUMBAR DISK

Assessing the validity of the currently used imaging procedures to diagnose a herniated lumbar disk is not an easy endeavor The validity of a measurement is the extent to which it corresponds to the true biologic value or some accepted gold standard[ ]40 With the exception of postmortem studies evaluation of the pathoanatomy by the surgeon in the operating room has always been considered the gold standard but this does not constitute an ideal situation Inspection of the disk through a small laminectomy incision to determine for instance if nuclear fragments lie within or outside the anular fibers may not be very reliable Also unbiased intraoperative determination of a normal degenerated or herniated disk in a patient with sciatica may also be difficult[ ]86 Because the validity of diskography has been previously established by postmortem studies and surgical correlations[ ]48 it is sometimes used as a gold standard in situations where no surgery has been performed

Conventional Radiographs

Lumbar disk herniations can exceptionally be diagnosed directly on good quality lateral projections because the x-ray attenuation is slightly greater in displaced disk material than in epidural fat Occasionally a calcified rim outlines the displaced disk fragment

(Fig 23) In most situations however narrowing of an intervertebral disk space in the absence of other evidence of chronic diskopathy is the only detectable sign suggesting the presence of a disk herniation To my knowledge the sensitivity and specificity of this sign has never been assessed The accepted rule of thumb is that the height of a given lumbar intervertebral disk space should always be slightly greater than the height of the above located interspace This rule does not apply to the transition disk immediately above the sacrum (usually L5-S1) The specificity of this sign is probably quite high but a few false-positives are seen especially at the L4-L5 level because of minor congenital hypoplasia The presence of posterior or foraminal vertebral body osteophytes associated or not with disk space narrowing is a definite sign of a chronic disk herniation

Figure 23 A Chronic left L3-L4 extraforaminal disk hernation in a 54-year-old man suspected on an AP radiograph demonstrating a calcified shell on the left side of the intervertebral disk space (white arrow) B Axial CT scan section confirming the diagnosis of a chronic extraforaminal L3-L4 herniation

Myelography

Myelography is essentially an exploration of the subarachnoid space Disk herniations are demonstrated only indirectly because they can cause thecal sac deformity and individual nerve root sleeve filling defects (Fig 24) Of all the special imaging procedures

myelography is the only one that allows upright projections with full weight bearing It is not unusual to demonstrate in this way small posterior central or posterolateral herniations that are undetectable on CT sections Interestingly the overall sensitivity of myelography to detect disk herniations has been found to be higher than that of CT whereas its specificity has been found to be lower[ ]74 In comparison with standard CT examination which usually includes only the three or four lower lumbar disks myelography easily allows coverage of the entire lumbar area and assessment of the intrathecal structures (cauda equina and conus medullaris) Far lateral foraminal herniations extraforaminal herniations and anterior herniations however are not detected The sensitivity for detection of posterior central L5-S1 herniations is also relatively poor because of the greater distance between the thecal sac and the posterior aspect of this particular disk

Figure 24 L5-S1 disk herniation in a 25-year-old man detected by indirect signs using lumbosacral myelography A Upright oblique projections showing a filling defect of the left S1 root sleeve (white arrow) suggesting significant nerve root compression by a left posterolateral disk hernation The right S1 root sleeve fills normally with contrast (black arrow) B Subtle compression of the anterior wall of the dural sac by displaced disk material (small arrows) demonstrated on upright lateral projection This sign is usually absent in the presence of a large amount of fat and venous structures in the anterior epidural compartment

CT

The sensitivity of CT to diagnose a herniation of the nucleus pulposus at the L5-S1 interspace is greater than that of myelography if images in the exact plane of the disk can be obtained[ ]23 [ ]39 Otherwise the superiority of plain CT over myelography to demonstrate disk herniations has not been established but CT has the distinct advantage of being

noninvasive and provides direct anatomic information[ ]23 Large herniations are easily detected but as explained previously the distinction between protrusions and extrusions is often difficult without sagittal reconstructions CT essentially allows an assessment of the contour of the disk The diagnosis of very small herniations in the absence of direct or indirect evidence of a radial tear is hazardous and associated with a high percentage of false-positives and false-negatives[ ]52 The diagnosis of moderate and large size herniations in different directions is usually possible but anterior herniations are rarely diagnosed not because they are not detectable but because observers pay little attention to the anterior contour of the disk (Fig 25) Because the PLLC cannot usually be identified the distinction of subligamentous from transligamentous herniation can only be suggested in most cases by the size of the herniated material A definite diagnosis of sequestration is rarely possible Calcifications within the displaced material are readily seen but may be difficult at times to differentiate from an accompanying osteophyte or an avulsed bone fragment from the vertebral body ring epiphysis (Fig 26) The presence of gas in the herniated material is easily detected

Figure 25 Anterior L4-L5 herniation demonstrated by CT scan in a 51-year-old woman with chronic low back pain Although sometimes quite conspicuous such herniations are rarely reported because observers pay little attention to the anterior contour of the disk

Figure 26 CT scan demonstration of a posterior right central L4-L5 disk herniation in a 38-year-old woman with avulsion of a bone fragment from the ring epiphysis and adjacent part of the superior L5 end plate Reactive osteosclerosis is seen around the vertebral body defect (arrows) suggesting a chronic lesion

CT Myelography

This association combines the advantages of both imaging modalities The fact that its accuracy has been reported as being less[ ]22 [ ]32 higher[ ]1 [ ]6 or equivalent[ ]82 to MR imaging is a reflection of the differences in technologic advancement and pathologic nomenclature that hamper valid comparisons between different studies

MR Imaging

Most reported studies establish MR imaging as the first choice modality to diagnose a herniated lumbar disk[ ]5 [ ]22 [ ]32 [ ]46 The associated intravenous injection of a paramagnetic agent has been found useful to demonstrate some anatomic features of disk disease in patients with no previous lumbar disk surgery[ ]56 [ ]68 [ ]90 MR imaging provides a better assessment of disk morphology than CT or CT myelography because sagittal sections are routinely obtained Assessment of foraminal involvement by displaced disk material is more accurate (Fig 27) and anterior disk herniations can be detected more easily than with CT or CT myelography If one is looking specifically for herniated lumbar disks associated with nerve root compression however it has been demonstrated that CT is equally accurate[ ]82 Alterations of the central or peripheral disk signal intensity on T2-weighted images are seen in most disks afflicted with an anular tear[ ]48 and alert the observer to scrutinize the disk contour in search for local modifications indicative of a herniation Because the signal of the displaced disk material is usually very similar to that of the outer anulus PLLC and vertebral body cortical bone small herniations are generally more conspicuous on axial CT sections than on corresponding axial MR imaging sections Gas and calcium deposits within the displaced fragment cannot usually

be detected but associated vertebral body bone marrow changes are typically seen and are helpful in differentiating acute from chronic processes[ ]57 The occasional presence of a high-intensity zone in the herniated material with an occasionally enhancing border after contrast injection is probably caused by a mixture of displaced nuclear material acute and subacute inflammatory tissue and neovascularized reactive tissue[ ]4 [ ]48 [ ]72 Contradictory reports have been published regarding the accuracy of MR imaging to differentiate subligamentous from transligamentous herniations[ ]26 [ ]38 [ ]73 [ ]76 Understanding the anatomy of the PLLC is helpful to make the distinction (Fig 28) (Figure Not Available) Masaryk et al[ ]46 have suggested that MR imaging is accurate to distinguish sequestered disks from other forms of lumbar disk herniations but most observers find this distinction difficult to establish[ ]42

Figure 27 A Left L4-L5 foraminal herniation well seen on an intermediate-weighted left parasagittal MR section (arrow) in a 47-year-old man B The lesion is much less obvious on intermediate-weighted (left) and T2-weighted (right) axial sections and was in fact more conspicuous on the corresponding CT scan section

Figure 28 (Figure Not Available) A Subligamentous disk herniation Left T1-weighted image demonstrating displaced disk material with a smooth outline imposed by the demarcation of the anterior epidural space (AES) by the lateral membrane of the PLLC Right Correlative drawing B Transligamentous disk herniation Left T1-weighted image of a large disk herniation (cervical in this case) which has ruptured through the posterior confines of the AES Penetration of the right lateral membrane can be observed (arrow) and the disk fragment contour is serrated Right Correlative drawing (From Schellinger D Manz HJ Vidic B et al Disk fragment migration Radiology 175831-836 1990 with permission)

Diskography and CT Diskography

During 30 years (1950 to 1980) when myelography was the only available imaging technique to demonstrate lumbar disk herniations diskography was an invasive but efficient way to demonstrate posterior central L5-S1 herniations and other large herniations (other than posterior central and paramedial) that could not be detected by myelography[ ]50 These herniations are now usually well demonstrated by CT and MR imaging Comparing the accuracy of five imaging modalities (excluding MR imaging) for the diagnosis of lumbar disk herniation Jackson et al[ ]31 found that CT diskography (Fig 29) was the most accurate test (87) compared with 77 for CT myelography 74 for CT 70 for myelography 64 for pain reproduction during diskography and 58 for diskography without CT Disk injection reproduced the patients clinical pain pattern in only 36 of herniated disks This clinical test isolated from the images had high specificity (89) but low sensitivity (43) for the diagnosis of disk herniation The reported low sensitivity of diskography images (unassociated with CT) to diagnose disk herniation is to be expected the purpose of the intradiskal injection being primarily the demonstration of an anular tear the contrast leaking through the tear only occasionally delineates an extruded fragment When a disk herniation has been diagnosed by other imaging modalities diskography allows to determine if the herniation is contained or noncontained (Figs 30 and 31) this information may have clinical relevance[ ]62 It also allows to establish if the displaced disk material is communicating or not with the parent disk and establishes the likelihood that it is sequestered or not There always remains a possibility that the contrast injected under pressure may reach a disk fragment that is nevertheless sequestered by leaking through the associated anular tear CT diskography also allows assessment in most cases of the integrity of the PLLC[ ]89 The superior sensitivity of diskography over MR imaging to demonstrate anular tears has been well established[ ]27 [ ]44 [ ]48 [ ]64 [ ]77 [ ]91 [ ]94 The presence of a radial tear and the inflammatory reaction it creates may be symptomatic despite the absence of true disk herniation[ ]29 [ ]48 [ ]49 [ ]69

Figure 29 L4-L5 CT diskogram demonstrating a large left posterolateral radial anular tear associated with

a left foraminal and extraforaminal herniaton (same patient as in Figure 28) (Figure Not Available)

Figure 30 Contained posterior L4-L5 and L5-S1 disk herniations in a 57-year-old man demonstrated by diskography The L3-L4 disk is normal

Figure 31 Noncontained L4-L5 disk herniation in a 23-year-old woman Reflux of injected contrast is seen in the anterior epidural space above and below the disk space The L5-S1 disk also demonstrates incomplete anterior and posterior radial anular tears

SUMMARY

The absence of universal nomenclature standardization with respect to the definition of a disk herniation and its different categories especially regarding type and location is still a major problem that will only be overcome when major national or international scientific societies join efforts to support a particular scheme Meanwhile it is important to realize that the two models that are currently most used are based on a different perspective Trying to straddle the two by opposing for instance bulging disk and herniation is doomed to failure because this exercise defies formal logic MR imaging is currently the most accurate noninvasive imaging modality to diagnose a disk herniation and to determine its exact location The determination of some pathoanatomic characteristics of herniated disks (type and composition) may require the use of CT diskography or CT diskography

References

1 Albeck MJ Hilden J Kjaer L et al A controlled comparison of myelography computed tomography and magnetic resonance imaging in clinically suspected lumbar disc herniation Spine 20443-448 1995 Abstract 2 American Academy of Orthopedic Surgeons Glossary on Spinal Terminology Chicago American Academy of Orthopedic Surgeons 1981 3 Andersson GB Weinstein JN Disc herniation [editorial] Spine 211S 1996 Citation 4 Aprill C Bogduk N High-intensity zone A diagnostic sign of painful lumbar disc on magnetic resonance imaging Br J Radiol 65361-369 1992 Abstract 5 Birney TJ White JJ Jr Berens D et al Comparison of MRI and discography in the diagnosis of lumbar degenerative disc disease J Spinal Disord 5417-423 1992 Abstract 6 Bischoff RJ Rodriguez RP Gupta K et al A comparison of computed tomography-myelography magnetic resonance imaging and myelography in the diagnosis of herniated nucleus pulposus and spinal stenosis J Spinal Disord 6289-295 1993 Abstract 7 Bogduk N The innervation of the lumbar spine Spine 8286-293 1983 Abstract 8 Bogduk N Tynan W Wilson AS The nerve supply to the human lumbar intervertebral discs J Anat 13239-56 1981 Abstract 9 Bonneville JF La carte-image des hernies discales lombaires Rachis 2255-257 1990 10 Bonneville JF La topografia simbolica delle ernie discali lombari Riv Neuroradiol 5427-431 1992 11 Bonneville JF Plaidoyer pour une classification par limage des hernies discales lombaires La carte-image Rev Imag Med 2557-560 1990 12 Brant-Zawadzki M Jensen M Spinal nomenclature Spine 20388-390 1995 Abstract

13 Brant-Zawadzki MN Jensen MC Obuchowski N et al Interobserver and intraobserver variability in interpretation of lumbar disc abnormalities A comparison of two nomenclatures Spine 201257-1263 1995 Abstract 14 Breton G Is that a bulging disk a small herniation or a moderate protrusion [editorial] Can Assoc Radiol J 42318 1991 Citation 15 Czervionke LF Lumbar intervertebral disc disease Neuroimaging Clin North Am 3465-485 1993 16 Deyo RA Nonsurgical care of low back pain Neurosurg Clin North Am 2851-862 1991 17 Deyo RA Loeser JD Bigos SJ Herniated lumbar intervertebral disk Ann Intern Med 112598-603 1990 Abstract 18 Dorlands Illustrated Medical Dictionary ed 28 Philadelphia WB Saunders 1994 19 Fardon D Pinkerton S Balderston R et al Terms used for diagnosis by English speaking spine surgeons Spine 18274-277 1993 Citation 20 Fardon DF Herzog RJ Mink JH et al Nomenclature of Lumbar Disc Disorders Contemporary Concepts in Spine Care Rosemont IL North American Spine Society 1995 21 Fardon DF Herzog RJ Mink JH et al Nomenclature of lumbar disc disorders In Garfin S Vaccaro A (eds) Orthopedic Knowledge Update Spine Rosemont IL American Academy of Orthopedic Surgeons 1997 pp A3-A14 22 Forristall RM Marsh HO Pay NT Magnetic resonance imaging and contrast CT of the lumbar spine Comparison of diagnostic methods and correlation with surgical findings Spine 131049-1054 1988 Abstract 23 Fries JW Abodeely DA Vijungco JG et al Computed tomography of herniated and extruded nucleus pulposus J Comput Assist Tomogr 6874-887 1982 Abstract 24 Frymoyer JW Newberg A Pope MH et al Spine radiographs in patients with low-back pain An epidemiological study in men J Bone Joint Surg Am 661048-1055 1984 Abstract 25 Gospodarowicz M Benedet L Hutter RV et al History and international developments in cancer staging Cancer Prev Control 2262-268 1998 Abstract 26 Grenier N Greselle JF Vital JM et al Normal and disrupted lumbar longitudinal ligaments Correlative MR and anatomic study Radiology 171197-205 1989 Abstract 27 Gunzburg R Parkinson R Moore R et al A cadaveric study comparing discography magnetic resonance imaging histology and mechanical behavior of the human lumbar disc Spine 17417-426 1992 Abstract 28 Haughton VM Eldevik OP Magnaes B et al A prospective comparison of computed tomography and myelography in the diagnosis of herniated lumbar disks Radiology 142103-110 1982 Abstract

29 Haughton VM Lim TH An H Intervertebral disk appearance correlated with stiffness of lumbar spinal motion segments AJNR Am J Neuroradiol 201161-1165 1999 Abstract 30 Herzog RJ The radiologic assessment for a lumbar disc herniation Spine 2119S-38S 1996 Abstract 31 Jackson RP Becker GJ Jacobs RR et al The neuroradiographic diagnosis of lumbar herniated nucleus pulposus I A comparison of computed tomography (CT) myelography CT-myelography discography and CT-discography Spine 141356-1361 1989 Abstract 32 Jackson RP Cain JE Jr Jacobs RR et al The neuroradiographic diagnosis of lumbar herniated nucleus pulposus II A comparison of computed tomography (CT) myelography CT-myelography and magnetic resonance imaging Spine 141362-1367 1989 Abstract 33 Jarvik JG Haynor DR Koepsell TD et al Interreader reliability for a new classification of lumbar disk disease Acad Radiol 3537-544 1996 Abstract 34 Jensen MC Brant-Zawadzki MN Obuchowski N et al Magnetic resonance imaging of the lumbar spine in people without back pain N Engl J Med 33169-73 1994 Abstract 35 Kent DL Haynor DR Larson EB et al Diagnosis of lumbar spinal stenosis in adults A meta-analysis of the accuracy of CT MR and myelography AJR Am J Roentgenol 1581135-1144 1992 Abstract 36 Kieffer SA Sherry RG Wellenstein DE et al Bulging lumbar intervertebral disk Myelographic differentiation from herniated disk with nerve root compression AJR Am J Roentgenol 138709-716 1982 Abstract 37 Kieffer SA Stadlan EM Mohandas A et al Discographic-anatomical correlation of developmental changes with age in the intervertebral disc Acta Radiol 9733-739 1969 38 Kim KY Kim YT Lee CS et al MRI classification of lumbar herniated intervertebral disc Orthopedics 15493-497 1992 Abstract 39 Kornberg M Rechtine GR Dupuy TE Computed tomography in the diagnosis of a herniated disk at the L5-S1 level Spine 9433-436 1984 Abstract 40 Kramer MS Clinical Epidemiology and Biostatistics New York Springer-Verlag 1988 41 Landis JR Koch GG The measurement of observer agreement agreement for categorical data Biometrics 33159-174 1977 Abstract 42 Laredo JD Bossard P Vuillemin-Bodaghi Formes anatomo-radiologiques des hernies discales In Morvan G Deburge A Bard H et al (eds) Le Rachis Lombaire Degeneratif Montpellier Sauramps Medical 1998 pp 37-49 43 Lee SH Coleman PE Hahn FJ Magnetic resonance imaging of degenerative disk disease of the spine Radiol Clin North Am 26949-964 1988 Abstract 44 Linson MA Crowe CH Comparison of magnetic resonance imaging and lumbar discography in the diagnosis of disc degeneration Clin Orthop 160-163 1990

45 Marchand F Ahmed AM Investigation of the laminate structure of lumbar disc anulus fibrosus Spine 15402-410 1990 Abstract 46 Masaryk TJ Ross JS Modic MT et al High-resolution MR imaging of sequestered lumbar intervertebral disks AJR Am J Roentgenol 1501155-1162 1988 Abstract 47 Milette PC The proper terminology for reporting lumbar intervertebral disk disorders AJNR Am J Neuroradiol 181859-1866 1997 Citation 48 Milette PC Fontaine S Lepanto L et al Differentiating lumbar disc protrusions disk bulges and discs with normal contour but abnormal signal intensity Magnetic resonance imaging with discographic correlations Spine 2444-53 1999 Abstract 49 Milette PC Fontaine S Lepanto L et al Radiating pain to the lower extremities caused by lumbar disk rupture without spinal nerve root involvement AJNR Am J Neuroradiol 161605-1613 1995 Abstract 50 Milette PC Melancon D A reappraisal of lumbar discography Can Assoc Radiol J 33176-182 1982 51 Milette PC Melancon D Dupuis PR et al A simplified terminology for abnormalities of the lumbar disk Can Assoc Radiol J 42319-325 1991 Abstract 52 Milette PC Raymond J Fontaine S Comparison of high-resolution computed tomography with discography in the evaluation of lumbar disc herniations Spine 15525-533 1990 Abstract 53 Mink JH Deutsch AL Goldstein TB et al Spinal imaging and intervention 1998 Phys Med Rehabil Clin North Am 9343-380 1998 54 Mixter WJ Barr JS Rupture of the intervertebral disc with involvement of the spinal canal N Engl J Med 211210-234 1934 55 Modic MT Masaryk TJ Ross JS et al Imaging of degenerative disk disease Radiology 168177-186 1988 Citation 56 Modic MT Ross JS Obuchowski NA et al Contrast-enhanced MR imaging in acute lumbar radiculopathy A pilot study of the natural history Radiology 195429-435 1995 Abstract 57 Modic MT Steinberg PM Ross JS et al Degenerative disk disease Assessment of changes in vertebral body marrow with MR imaging Radiology 166193-199 1988 58 Morvan G Mathieu P Les stenoses laterales In Morvan G Deburge A Bard H et al (eds) Le Rachis Lombaire Degeneratif Montpellier Sauramps Medical 1998 pp 315-324 59 Murray RO Skeletal trauma Regional In Sutton D (ed) Textbook of Radiology and Imaging ed 3 New York Churchill Livingstone 1980 pp 210-231 60 Nachemson A Lumbar disc herniation Conclusions Acta Orthop Scand 64(suppl 251)49 1993 Citation

61 Nathan H Osteophytes of the vertebral column An anatomical study of their development according to age race and sex with consideration as to their etiology and significance J Bone Joint Surg Am 44243-268 1962 62 Nygaard OP Mellgren SI Osterud B The inflammatory properties of contained and noncontained lumbar disc herniations Spine 222584-2488 1997 Abstract 63 Ohshima H Hirano N Osada R et al Morphologic variation of lumbar posterior longitudinal ligament and the modality of disc herniation Spine 182408-2411 1993 Abstract 64 Osti OL Fraser RD MRI and discography of annular tears and intervertebral disc degeneration A prospective clinical comparison J Bone Joint Surg Br 74431-435 1992 Abstract 65 Palmgren T Gronblad M Virri J et al Immunohistochemical demonstration of sensory and autonomic nerve terminals in herniated lumbar disc tissue Spine 211301-1306 1996 Abstract 66 Resnick D Niwayama G Degenerative disease of the spine In Resnick D (ed) Diagnosis of Bone and Joint Disorders ed 3 Philadelphia WB Saunders 1995 pp 1372-1462 67 Resnick D Niwayama G Intravertebral disk herniations Cartilaginous (Schmorls) nodes Radiology 12657-65 1978 Abstract 68 Ross JS Modic MT Masaryk TJ Tears of the anulus fibrosus Assessment with Gd-DTPA-enhanced MR imaging AJR Am J Roentgenol 154159-162 1990 Abstract 69 Saal JS The role of inflammation in lumbar pain Spine 201821-1827 1995 Abstract 70 Sachs BL Vanharanta H Spivey MA et al Dallas discogram description A new classification of CTdiscography in low-back disorders Spine 12287-294 1987 Abstract 71 Sauser DD Goldman AB Kaye JJ Discogenic vertebral sclerosis J Can Assoc Radiol 2944-50 1978 Abstract 72 Schellhas KP Pollei SR Gundry CR et al Lumbar disc high-intensity zone Correlation of magnetic resonance imaging and discography Spine 2179-86 1996 Abstract 73 Schellinger D Manz HJ Vidic B et al Disk fragment migration Radiology 175831-836 1990 Abstract 74 Schipper J Kardaun JW Braakman R et al Lumbar disk herniation Diagnosis with CT or myelography Radiology 165227-231 1987 Abstract 75 Schmorl G Junghanns H The Human Spine in Health and Disease ed 2 New York Grune and Stratton 1971 76 Silverman CS Lenchik L Shimkin PM et al The value of MR in differentiating subligamentous from supraligamentous lumbar disk herniations AJNR Am J Neuroradiol 16571-579 1995 Abstract 77 Simmons JW Emery SF McMillin JN et al Awake discography A comparison study with magnetic

resonance imaging Spine 16S216-221 1991 Abstract 78 Smyth MJ Wright V Sciatica and the intervertebral disc J Bone Joint Surg Am 401401-1418 1958 79 Taveras JM Radiologic aspects of low back pain and sciatic syndromes [editorial] AJNR Am J Neuroradiol 9351-358 1989 80 Tehranzadeh J Discography 2000 Radiol Clin North Am 36463-495 1998 Full Text 81 Thelander U Fagerlund M Friberg S et al Describing the size of lumbar disc herniations using computed tomography A comparison of different size index calculations and their relation to sciatica Spine 191979-1984 1994 Abstract 82 Thornbury JR Fryback DG Turski PA et al Disk-caused nerve compression in patients with acute low-back pain Diagnosis with MR CT myelography and plain CT Radiology 186731-738 1993 Abstract 83 Twomey L Taylor J Age changes in lumbar intervertebral discs Acta Orthop Scand 56496-499 1985 Abstract 84 Twomey LT Taylor JR Age changes in lumbar vertebrae and intervertebral discs Clin Orthop 22497-104 1987 85 Williams AL CT diagnosis of degenerative disc disease The bulging annulus Radiol Clin North Am 21289-300 1983 Abstract 86 Williams AL Haughton VM Meyer GA et al Computed tomographic appearance of the bulging annulus Radiology 142403-408 1982 Abstract 87 Williams AL Haughton VM Syvertsen A Computed tomography in the diagnosis of herniated nucleus pulposus Radiology 13595-99 1980 Abstract 88 Wiltse LL Berger PE McCulloch JA A system for reporting the size and location of lesions in the spine Spine 221534-1537 1997 Abstract 89 Wiltse LL Fonseca AS Amster J et al Relationship of the dura Hofmanns ligaments Batsons plexus and a fibrovascular membrane lying on the posterior surface of the vertebral bodies and attaching to the deep layer of the posterior longitudinal ligament An anatomical radiologic and clinical study Spine 181030-1043 1993 Abstract 90 Yamashita K Hiroshima K Kurata A Gadolinium-DTPA-enhanced magnetic resonance imaging of a sequestered lumbar intervertebral disc and its correlation with pathologic findings Spine 19479-482 1994 Abstract 91 Yu SW Haughton VM Sether LA et al Comparison of MR and diskography in detecting radial tears of the anulus A postmortem study AJNR Am J Neuroradiol 101077-1081 1989 Abstract 92 Yu SW Sether LA Ho PS et al Tears of the anulus fibrosus Correlation between MR and pathologic findings in cadavers AJNR Am J Neuroradiol 9367-370 1988 Abstract

93 Yussen PS Swartz JD The acute lumbar disc herniation Imaging diagnosis Semin Ultrasound CT MR 14389-398 1993 Abstract 94 Zucherman J Derby R Hsu K et al Normal magnetic resonance imaging with abnormal discography Spine 131355-1359 1988 Abstract

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  • CLASSIFICATION DIAGNOSTIC IMAGING AND IMAGING CHARACTERIZATION OF A LUMBAR HERNIATED DISK
    • IMAGING OF LOW BACK PAIN I
      • CLASSIFICATION DIAGNOSTIC IMAGING AND IMAGING CHARACTERIZATION OF A LUMBAR HERNIATED DISK
        • DEFINITION OF A DISK HERNIATION
        • CLASSIFICATION OF A HERNIATED LUMBAR DISK
          • Main Categories of Noninfectious Disk Abnormalities
          • Further Qualifying the Displaced Disk Material Beyond the Disk Space
            • DIAGNOSTIC IMAGING AND CHARACTERIZATION OF A HERNIATED LUMBAR DISK
              • Conventional Radiographs
              • Myelography
              • CT
              • CT Myelography
              • MR Imaging
              • Diskography and CT Diskography
                • SUMMARY
                  • References
Page 22: CLASSIFICATION, DIAGNOSTIC IMAGING, AND IMAGING ... · PDF fileclassification, diagnostic imaging, and imaging characterization of a lumbar herniated disk ... classification, diagnostic

(Fig 23) In most situations however narrowing of an intervertebral disk space in the absence of other evidence of chronic diskopathy is the only detectable sign suggesting the presence of a disk herniation To my knowledge the sensitivity and specificity of this sign has never been assessed The accepted rule of thumb is that the height of a given lumbar intervertebral disk space should always be slightly greater than the height of the above located interspace This rule does not apply to the transition disk immediately above the sacrum (usually L5-S1) The specificity of this sign is probably quite high but a few false-positives are seen especially at the L4-L5 level because of minor congenital hypoplasia The presence of posterior or foraminal vertebral body osteophytes associated or not with disk space narrowing is a definite sign of a chronic disk herniation

Figure 23 A Chronic left L3-L4 extraforaminal disk hernation in a 54-year-old man suspected on an AP radiograph demonstrating a calcified shell on the left side of the intervertebral disk space (white arrow) B Axial CT scan section confirming the diagnosis of a chronic extraforaminal L3-L4 herniation

Myelography

Myelography is essentially an exploration of the subarachnoid space Disk herniations are demonstrated only indirectly because they can cause thecal sac deformity and individual nerve root sleeve filling defects (Fig 24) Of all the special imaging procedures

myelography is the only one that allows upright projections with full weight bearing It is not unusual to demonstrate in this way small posterior central or posterolateral herniations that are undetectable on CT sections Interestingly the overall sensitivity of myelography to detect disk herniations has been found to be higher than that of CT whereas its specificity has been found to be lower[ ]74 In comparison with standard CT examination which usually includes only the three or four lower lumbar disks myelography easily allows coverage of the entire lumbar area and assessment of the intrathecal structures (cauda equina and conus medullaris) Far lateral foraminal herniations extraforaminal herniations and anterior herniations however are not detected The sensitivity for detection of posterior central L5-S1 herniations is also relatively poor because of the greater distance between the thecal sac and the posterior aspect of this particular disk

Figure 24 L5-S1 disk herniation in a 25-year-old man detected by indirect signs using lumbosacral myelography A Upright oblique projections showing a filling defect of the left S1 root sleeve (white arrow) suggesting significant nerve root compression by a left posterolateral disk hernation The right S1 root sleeve fills normally with contrast (black arrow) B Subtle compression of the anterior wall of the dural sac by displaced disk material (small arrows) demonstrated on upright lateral projection This sign is usually absent in the presence of a large amount of fat and venous structures in the anterior epidural compartment

CT

The sensitivity of CT to diagnose a herniation of the nucleus pulposus at the L5-S1 interspace is greater than that of myelography if images in the exact plane of the disk can be obtained[ ]23 [ ]39 Otherwise the superiority of plain CT over myelography to demonstrate disk herniations has not been established but CT has the distinct advantage of being

noninvasive and provides direct anatomic information[ ]23 Large herniations are easily detected but as explained previously the distinction between protrusions and extrusions is often difficult without sagittal reconstructions CT essentially allows an assessment of the contour of the disk The diagnosis of very small herniations in the absence of direct or indirect evidence of a radial tear is hazardous and associated with a high percentage of false-positives and false-negatives[ ]52 The diagnosis of moderate and large size herniations in different directions is usually possible but anterior herniations are rarely diagnosed not because they are not detectable but because observers pay little attention to the anterior contour of the disk (Fig 25) Because the PLLC cannot usually be identified the distinction of subligamentous from transligamentous herniation can only be suggested in most cases by the size of the herniated material A definite diagnosis of sequestration is rarely possible Calcifications within the displaced material are readily seen but may be difficult at times to differentiate from an accompanying osteophyte or an avulsed bone fragment from the vertebral body ring epiphysis (Fig 26) The presence of gas in the herniated material is easily detected

Figure 25 Anterior L4-L5 herniation demonstrated by CT scan in a 51-year-old woman with chronic low back pain Although sometimes quite conspicuous such herniations are rarely reported because observers pay little attention to the anterior contour of the disk

Figure 26 CT scan demonstration of a posterior right central L4-L5 disk herniation in a 38-year-old woman with avulsion of a bone fragment from the ring epiphysis and adjacent part of the superior L5 end plate Reactive osteosclerosis is seen around the vertebral body defect (arrows) suggesting a chronic lesion

CT Myelography

This association combines the advantages of both imaging modalities The fact that its accuracy has been reported as being less[ ]22 [ ]32 higher[ ]1 [ ]6 or equivalent[ ]82 to MR imaging is a reflection of the differences in technologic advancement and pathologic nomenclature that hamper valid comparisons between different studies

MR Imaging

Most reported studies establish MR imaging as the first choice modality to diagnose a herniated lumbar disk[ ]5 [ ]22 [ ]32 [ ]46 The associated intravenous injection of a paramagnetic agent has been found useful to demonstrate some anatomic features of disk disease in patients with no previous lumbar disk surgery[ ]56 [ ]68 [ ]90 MR imaging provides a better assessment of disk morphology than CT or CT myelography because sagittal sections are routinely obtained Assessment of foraminal involvement by displaced disk material is more accurate (Fig 27) and anterior disk herniations can be detected more easily than with CT or CT myelography If one is looking specifically for herniated lumbar disks associated with nerve root compression however it has been demonstrated that CT is equally accurate[ ]82 Alterations of the central or peripheral disk signal intensity on T2-weighted images are seen in most disks afflicted with an anular tear[ ]48 and alert the observer to scrutinize the disk contour in search for local modifications indicative of a herniation Because the signal of the displaced disk material is usually very similar to that of the outer anulus PLLC and vertebral body cortical bone small herniations are generally more conspicuous on axial CT sections than on corresponding axial MR imaging sections Gas and calcium deposits within the displaced fragment cannot usually

be detected but associated vertebral body bone marrow changes are typically seen and are helpful in differentiating acute from chronic processes[ ]57 The occasional presence of a high-intensity zone in the herniated material with an occasionally enhancing border after contrast injection is probably caused by a mixture of displaced nuclear material acute and subacute inflammatory tissue and neovascularized reactive tissue[ ]4 [ ]48 [ ]72 Contradictory reports have been published regarding the accuracy of MR imaging to differentiate subligamentous from transligamentous herniations[ ]26 [ ]38 [ ]73 [ ]76 Understanding the anatomy of the PLLC is helpful to make the distinction (Fig 28) (Figure Not Available) Masaryk et al[ ]46 have suggested that MR imaging is accurate to distinguish sequestered disks from other forms of lumbar disk herniations but most observers find this distinction difficult to establish[ ]42

Figure 27 A Left L4-L5 foraminal herniation well seen on an intermediate-weighted left parasagittal MR section (arrow) in a 47-year-old man B The lesion is much less obvious on intermediate-weighted (left) and T2-weighted (right) axial sections and was in fact more conspicuous on the corresponding CT scan section

Figure 28 (Figure Not Available) A Subligamentous disk herniation Left T1-weighted image demonstrating displaced disk material with a smooth outline imposed by the demarcation of the anterior epidural space (AES) by the lateral membrane of the PLLC Right Correlative drawing B Transligamentous disk herniation Left T1-weighted image of a large disk herniation (cervical in this case) which has ruptured through the posterior confines of the AES Penetration of the right lateral membrane can be observed (arrow) and the disk fragment contour is serrated Right Correlative drawing (From Schellinger D Manz HJ Vidic B et al Disk fragment migration Radiology 175831-836 1990 with permission)

Diskography and CT Diskography

During 30 years (1950 to 1980) when myelography was the only available imaging technique to demonstrate lumbar disk herniations diskography was an invasive but efficient way to demonstrate posterior central L5-S1 herniations and other large herniations (other than posterior central and paramedial) that could not be detected by myelography[ ]50 These herniations are now usually well demonstrated by CT and MR imaging Comparing the accuracy of five imaging modalities (excluding MR imaging) for the diagnosis of lumbar disk herniation Jackson et al[ ]31 found that CT diskography (Fig 29) was the most accurate test (87) compared with 77 for CT myelography 74 for CT 70 for myelography 64 for pain reproduction during diskography and 58 for diskography without CT Disk injection reproduced the patients clinical pain pattern in only 36 of herniated disks This clinical test isolated from the images had high specificity (89) but low sensitivity (43) for the diagnosis of disk herniation The reported low sensitivity of diskography images (unassociated with CT) to diagnose disk herniation is to be expected the purpose of the intradiskal injection being primarily the demonstration of an anular tear the contrast leaking through the tear only occasionally delineates an extruded fragment When a disk herniation has been diagnosed by other imaging modalities diskography allows to determine if the herniation is contained or noncontained (Figs 30 and 31) this information may have clinical relevance[ ]62 It also allows to establish if the displaced disk material is communicating or not with the parent disk and establishes the likelihood that it is sequestered or not There always remains a possibility that the contrast injected under pressure may reach a disk fragment that is nevertheless sequestered by leaking through the associated anular tear CT diskography also allows assessment in most cases of the integrity of the PLLC[ ]89 The superior sensitivity of diskography over MR imaging to demonstrate anular tears has been well established[ ]27 [ ]44 [ ]48 [ ]64 [ ]77 [ ]91 [ ]94 The presence of a radial tear and the inflammatory reaction it creates may be symptomatic despite the absence of true disk herniation[ ]29 [ ]48 [ ]49 [ ]69

Figure 29 L4-L5 CT diskogram demonstrating a large left posterolateral radial anular tear associated with

a left foraminal and extraforaminal herniaton (same patient as in Figure 28) (Figure Not Available)

Figure 30 Contained posterior L4-L5 and L5-S1 disk herniations in a 57-year-old man demonstrated by diskography The L3-L4 disk is normal

Figure 31 Noncontained L4-L5 disk herniation in a 23-year-old woman Reflux of injected contrast is seen in the anterior epidural space above and below the disk space The L5-S1 disk also demonstrates incomplete anterior and posterior radial anular tears

SUMMARY

The absence of universal nomenclature standardization with respect to the definition of a disk herniation and its different categories especially regarding type and location is still a major problem that will only be overcome when major national or international scientific societies join efforts to support a particular scheme Meanwhile it is important to realize that the two models that are currently most used are based on a different perspective Trying to straddle the two by opposing for instance bulging disk and herniation is doomed to failure because this exercise defies formal logic MR imaging is currently the most accurate noninvasive imaging modality to diagnose a disk herniation and to determine its exact location The determination of some pathoanatomic characteristics of herniated disks (type and composition) may require the use of CT diskography or CT diskography

References

1 Albeck MJ Hilden J Kjaer L et al A controlled comparison of myelography computed tomography and magnetic resonance imaging in clinically suspected lumbar disc herniation Spine 20443-448 1995 Abstract 2 American Academy of Orthopedic Surgeons Glossary on Spinal Terminology Chicago American Academy of Orthopedic Surgeons 1981 3 Andersson GB Weinstein JN Disc herniation [editorial] Spine 211S 1996 Citation 4 Aprill C Bogduk N High-intensity zone A diagnostic sign of painful lumbar disc on magnetic resonance imaging Br J Radiol 65361-369 1992 Abstract 5 Birney TJ White JJ Jr Berens D et al Comparison of MRI and discography in the diagnosis of lumbar degenerative disc disease J Spinal Disord 5417-423 1992 Abstract 6 Bischoff RJ Rodriguez RP Gupta K et al A comparison of computed tomography-myelography magnetic resonance imaging and myelography in the diagnosis of herniated nucleus pulposus and spinal stenosis J Spinal Disord 6289-295 1993 Abstract 7 Bogduk N The innervation of the lumbar spine Spine 8286-293 1983 Abstract 8 Bogduk N Tynan W Wilson AS The nerve supply to the human lumbar intervertebral discs J Anat 13239-56 1981 Abstract 9 Bonneville JF La carte-image des hernies discales lombaires Rachis 2255-257 1990 10 Bonneville JF La topografia simbolica delle ernie discali lombari Riv Neuroradiol 5427-431 1992 11 Bonneville JF Plaidoyer pour une classification par limage des hernies discales lombaires La carte-image Rev Imag Med 2557-560 1990 12 Brant-Zawadzki M Jensen M Spinal nomenclature Spine 20388-390 1995 Abstract

13 Brant-Zawadzki MN Jensen MC Obuchowski N et al Interobserver and intraobserver variability in interpretation of lumbar disc abnormalities A comparison of two nomenclatures Spine 201257-1263 1995 Abstract 14 Breton G Is that a bulging disk a small herniation or a moderate protrusion [editorial] Can Assoc Radiol J 42318 1991 Citation 15 Czervionke LF Lumbar intervertebral disc disease Neuroimaging Clin North Am 3465-485 1993 16 Deyo RA Nonsurgical care of low back pain Neurosurg Clin North Am 2851-862 1991 17 Deyo RA Loeser JD Bigos SJ Herniated lumbar intervertebral disk Ann Intern Med 112598-603 1990 Abstract 18 Dorlands Illustrated Medical Dictionary ed 28 Philadelphia WB Saunders 1994 19 Fardon D Pinkerton S Balderston R et al Terms used for diagnosis by English speaking spine surgeons Spine 18274-277 1993 Citation 20 Fardon DF Herzog RJ Mink JH et al Nomenclature of Lumbar Disc Disorders Contemporary Concepts in Spine Care Rosemont IL North American Spine Society 1995 21 Fardon DF Herzog RJ Mink JH et al Nomenclature of lumbar disc disorders In Garfin S Vaccaro A (eds) Orthopedic Knowledge Update Spine Rosemont IL American Academy of Orthopedic Surgeons 1997 pp A3-A14 22 Forristall RM Marsh HO Pay NT Magnetic resonance imaging and contrast CT of the lumbar spine Comparison of diagnostic methods and correlation with surgical findings Spine 131049-1054 1988 Abstract 23 Fries JW Abodeely DA Vijungco JG et al Computed tomography of herniated and extruded nucleus pulposus J Comput Assist Tomogr 6874-887 1982 Abstract 24 Frymoyer JW Newberg A Pope MH et al Spine radiographs in patients with low-back pain An epidemiological study in men J Bone Joint Surg Am 661048-1055 1984 Abstract 25 Gospodarowicz M Benedet L Hutter RV et al History and international developments in cancer staging Cancer Prev Control 2262-268 1998 Abstract 26 Grenier N Greselle JF Vital JM et al Normal and disrupted lumbar longitudinal ligaments Correlative MR and anatomic study Radiology 171197-205 1989 Abstract 27 Gunzburg R Parkinson R Moore R et al A cadaveric study comparing discography magnetic resonance imaging histology and mechanical behavior of the human lumbar disc Spine 17417-426 1992 Abstract 28 Haughton VM Eldevik OP Magnaes B et al A prospective comparison of computed tomography and myelography in the diagnosis of herniated lumbar disks Radiology 142103-110 1982 Abstract

29 Haughton VM Lim TH An H Intervertebral disk appearance correlated with stiffness of lumbar spinal motion segments AJNR Am J Neuroradiol 201161-1165 1999 Abstract 30 Herzog RJ The radiologic assessment for a lumbar disc herniation Spine 2119S-38S 1996 Abstract 31 Jackson RP Becker GJ Jacobs RR et al The neuroradiographic diagnosis of lumbar herniated nucleus pulposus I A comparison of computed tomography (CT) myelography CT-myelography discography and CT-discography Spine 141356-1361 1989 Abstract 32 Jackson RP Cain JE Jr Jacobs RR et al The neuroradiographic diagnosis of lumbar herniated nucleus pulposus II A comparison of computed tomography (CT) myelography CT-myelography and magnetic resonance imaging Spine 141362-1367 1989 Abstract 33 Jarvik JG Haynor DR Koepsell TD et al Interreader reliability for a new classification of lumbar disk disease Acad Radiol 3537-544 1996 Abstract 34 Jensen MC Brant-Zawadzki MN Obuchowski N et al Magnetic resonance imaging of the lumbar spine in people without back pain N Engl J Med 33169-73 1994 Abstract 35 Kent DL Haynor DR Larson EB et al Diagnosis of lumbar spinal stenosis in adults A meta-analysis of the accuracy of CT MR and myelography AJR Am J Roentgenol 1581135-1144 1992 Abstract 36 Kieffer SA Sherry RG Wellenstein DE et al Bulging lumbar intervertebral disk Myelographic differentiation from herniated disk with nerve root compression AJR Am J Roentgenol 138709-716 1982 Abstract 37 Kieffer SA Stadlan EM Mohandas A et al Discographic-anatomical correlation of developmental changes with age in the intervertebral disc Acta Radiol 9733-739 1969 38 Kim KY Kim YT Lee CS et al MRI classification of lumbar herniated intervertebral disc Orthopedics 15493-497 1992 Abstract 39 Kornberg M Rechtine GR Dupuy TE Computed tomography in the diagnosis of a herniated disk at the L5-S1 level Spine 9433-436 1984 Abstract 40 Kramer MS Clinical Epidemiology and Biostatistics New York Springer-Verlag 1988 41 Landis JR Koch GG The measurement of observer agreement agreement for categorical data Biometrics 33159-174 1977 Abstract 42 Laredo JD Bossard P Vuillemin-Bodaghi Formes anatomo-radiologiques des hernies discales In Morvan G Deburge A Bard H et al (eds) Le Rachis Lombaire Degeneratif Montpellier Sauramps Medical 1998 pp 37-49 43 Lee SH Coleman PE Hahn FJ Magnetic resonance imaging of degenerative disk disease of the spine Radiol Clin North Am 26949-964 1988 Abstract 44 Linson MA Crowe CH Comparison of magnetic resonance imaging and lumbar discography in the diagnosis of disc degeneration Clin Orthop 160-163 1990

45 Marchand F Ahmed AM Investigation of the laminate structure of lumbar disc anulus fibrosus Spine 15402-410 1990 Abstract 46 Masaryk TJ Ross JS Modic MT et al High-resolution MR imaging of sequestered lumbar intervertebral disks AJR Am J Roentgenol 1501155-1162 1988 Abstract 47 Milette PC The proper terminology for reporting lumbar intervertebral disk disorders AJNR Am J Neuroradiol 181859-1866 1997 Citation 48 Milette PC Fontaine S Lepanto L et al Differentiating lumbar disc protrusions disk bulges and discs with normal contour but abnormal signal intensity Magnetic resonance imaging with discographic correlations Spine 2444-53 1999 Abstract 49 Milette PC Fontaine S Lepanto L et al Radiating pain to the lower extremities caused by lumbar disk rupture without spinal nerve root involvement AJNR Am J Neuroradiol 161605-1613 1995 Abstract 50 Milette PC Melancon D A reappraisal of lumbar discography Can Assoc Radiol J 33176-182 1982 51 Milette PC Melancon D Dupuis PR et al A simplified terminology for abnormalities of the lumbar disk Can Assoc Radiol J 42319-325 1991 Abstract 52 Milette PC Raymond J Fontaine S Comparison of high-resolution computed tomography with discography in the evaluation of lumbar disc herniations Spine 15525-533 1990 Abstract 53 Mink JH Deutsch AL Goldstein TB et al Spinal imaging and intervention 1998 Phys Med Rehabil Clin North Am 9343-380 1998 54 Mixter WJ Barr JS Rupture of the intervertebral disc with involvement of the spinal canal N Engl J Med 211210-234 1934 55 Modic MT Masaryk TJ Ross JS et al Imaging of degenerative disk disease Radiology 168177-186 1988 Citation 56 Modic MT Ross JS Obuchowski NA et al Contrast-enhanced MR imaging in acute lumbar radiculopathy A pilot study of the natural history Radiology 195429-435 1995 Abstract 57 Modic MT Steinberg PM Ross JS et al Degenerative disk disease Assessment of changes in vertebral body marrow with MR imaging Radiology 166193-199 1988 58 Morvan G Mathieu P Les stenoses laterales In Morvan G Deburge A Bard H et al (eds) Le Rachis Lombaire Degeneratif Montpellier Sauramps Medical 1998 pp 315-324 59 Murray RO Skeletal trauma Regional In Sutton D (ed) Textbook of Radiology and Imaging ed 3 New York Churchill Livingstone 1980 pp 210-231 60 Nachemson A Lumbar disc herniation Conclusions Acta Orthop Scand 64(suppl 251)49 1993 Citation

61 Nathan H Osteophytes of the vertebral column An anatomical study of their development according to age race and sex with consideration as to their etiology and significance J Bone Joint Surg Am 44243-268 1962 62 Nygaard OP Mellgren SI Osterud B The inflammatory properties of contained and noncontained lumbar disc herniations Spine 222584-2488 1997 Abstract 63 Ohshima H Hirano N Osada R et al Morphologic variation of lumbar posterior longitudinal ligament and the modality of disc herniation Spine 182408-2411 1993 Abstract 64 Osti OL Fraser RD MRI and discography of annular tears and intervertebral disc degeneration A prospective clinical comparison J Bone Joint Surg Br 74431-435 1992 Abstract 65 Palmgren T Gronblad M Virri J et al Immunohistochemical demonstration of sensory and autonomic nerve terminals in herniated lumbar disc tissue Spine 211301-1306 1996 Abstract 66 Resnick D Niwayama G Degenerative disease of the spine In Resnick D (ed) Diagnosis of Bone and Joint Disorders ed 3 Philadelphia WB Saunders 1995 pp 1372-1462 67 Resnick D Niwayama G Intravertebral disk herniations Cartilaginous (Schmorls) nodes Radiology 12657-65 1978 Abstract 68 Ross JS Modic MT Masaryk TJ Tears of the anulus fibrosus Assessment with Gd-DTPA-enhanced MR imaging AJR Am J Roentgenol 154159-162 1990 Abstract 69 Saal JS The role of inflammation in lumbar pain Spine 201821-1827 1995 Abstract 70 Sachs BL Vanharanta H Spivey MA et al Dallas discogram description A new classification of CTdiscography in low-back disorders Spine 12287-294 1987 Abstract 71 Sauser DD Goldman AB Kaye JJ Discogenic vertebral sclerosis J Can Assoc Radiol 2944-50 1978 Abstract 72 Schellhas KP Pollei SR Gundry CR et al Lumbar disc high-intensity zone Correlation of magnetic resonance imaging and discography Spine 2179-86 1996 Abstract 73 Schellinger D Manz HJ Vidic B et al Disk fragment migration Radiology 175831-836 1990 Abstract 74 Schipper J Kardaun JW Braakman R et al Lumbar disk herniation Diagnosis with CT or myelography Radiology 165227-231 1987 Abstract 75 Schmorl G Junghanns H The Human Spine in Health and Disease ed 2 New York Grune and Stratton 1971 76 Silverman CS Lenchik L Shimkin PM et al The value of MR in differentiating subligamentous from supraligamentous lumbar disk herniations AJNR Am J Neuroradiol 16571-579 1995 Abstract 77 Simmons JW Emery SF McMillin JN et al Awake discography A comparison study with magnetic

resonance imaging Spine 16S216-221 1991 Abstract 78 Smyth MJ Wright V Sciatica and the intervertebral disc J Bone Joint Surg Am 401401-1418 1958 79 Taveras JM Radiologic aspects of low back pain and sciatic syndromes [editorial] AJNR Am J Neuroradiol 9351-358 1989 80 Tehranzadeh J Discography 2000 Radiol Clin North Am 36463-495 1998 Full Text 81 Thelander U Fagerlund M Friberg S et al Describing the size of lumbar disc herniations using computed tomography A comparison of different size index calculations and their relation to sciatica Spine 191979-1984 1994 Abstract 82 Thornbury JR Fryback DG Turski PA et al Disk-caused nerve compression in patients with acute low-back pain Diagnosis with MR CT myelography and plain CT Radiology 186731-738 1993 Abstract 83 Twomey L Taylor J Age changes in lumbar intervertebral discs Acta Orthop Scand 56496-499 1985 Abstract 84 Twomey LT Taylor JR Age changes in lumbar vertebrae and intervertebral discs Clin Orthop 22497-104 1987 85 Williams AL CT diagnosis of degenerative disc disease The bulging annulus Radiol Clin North Am 21289-300 1983 Abstract 86 Williams AL Haughton VM Meyer GA et al Computed tomographic appearance of the bulging annulus Radiology 142403-408 1982 Abstract 87 Williams AL Haughton VM Syvertsen A Computed tomography in the diagnosis of herniated nucleus pulposus Radiology 13595-99 1980 Abstract 88 Wiltse LL Berger PE McCulloch JA A system for reporting the size and location of lesions in the spine Spine 221534-1537 1997 Abstract 89 Wiltse LL Fonseca AS Amster J et al Relationship of the dura Hofmanns ligaments Batsons plexus and a fibrovascular membrane lying on the posterior surface of the vertebral bodies and attaching to the deep layer of the posterior longitudinal ligament An anatomical radiologic and clinical study Spine 181030-1043 1993 Abstract 90 Yamashita K Hiroshima K Kurata A Gadolinium-DTPA-enhanced magnetic resonance imaging of a sequestered lumbar intervertebral disc and its correlation with pathologic findings Spine 19479-482 1994 Abstract 91 Yu SW Haughton VM Sether LA et al Comparison of MR and diskography in detecting radial tears of the anulus A postmortem study AJNR Am J Neuroradiol 101077-1081 1989 Abstract 92 Yu SW Sether LA Ho PS et al Tears of the anulus fibrosus Correlation between MR and pathologic findings in cadavers AJNR Am J Neuroradiol 9367-370 1988 Abstract

93 Yussen PS Swartz JD The acute lumbar disc herniation Imaging diagnosis Semin Ultrasound CT MR 14389-398 1993 Abstract 94 Zucherman J Derby R Hsu K et al Normal magnetic resonance imaging with abnormal discography Spine 131355-1359 1988 Abstract

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  • CLASSIFICATION DIAGNOSTIC IMAGING AND IMAGING CHARACTERIZATION OF A LUMBAR HERNIATED DISK
    • IMAGING OF LOW BACK PAIN I
      • CLASSIFICATION DIAGNOSTIC IMAGING AND IMAGING CHARACTERIZATION OF A LUMBAR HERNIATED DISK
        • DEFINITION OF A DISK HERNIATION
        • CLASSIFICATION OF A HERNIATED LUMBAR DISK
          • Main Categories of Noninfectious Disk Abnormalities
          • Further Qualifying the Displaced Disk Material Beyond the Disk Space
            • DIAGNOSTIC IMAGING AND CHARACTERIZATION OF A HERNIATED LUMBAR DISK
              • Conventional Radiographs
              • Myelography
              • CT
              • CT Myelography
              • MR Imaging
              • Diskography and CT Diskography
                • SUMMARY
                  • References
Page 23: CLASSIFICATION, DIAGNOSTIC IMAGING, AND IMAGING ... · PDF fileclassification, diagnostic imaging, and imaging characterization of a lumbar herniated disk ... classification, diagnostic

myelography is the only one that allows upright projections with full weight bearing It is not unusual to demonstrate in this way small posterior central or posterolateral herniations that are undetectable on CT sections Interestingly the overall sensitivity of myelography to detect disk herniations has been found to be higher than that of CT whereas its specificity has been found to be lower[ ]74 In comparison with standard CT examination which usually includes only the three or four lower lumbar disks myelography easily allows coverage of the entire lumbar area and assessment of the intrathecal structures (cauda equina and conus medullaris) Far lateral foraminal herniations extraforaminal herniations and anterior herniations however are not detected The sensitivity for detection of posterior central L5-S1 herniations is also relatively poor because of the greater distance between the thecal sac and the posterior aspect of this particular disk

Figure 24 L5-S1 disk herniation in a 25-year-old man detected by indirect signs using lumbosacral myelography A Upright oblique projections showing a filling defect of the left S1 root sleeve (white arrow) suggesting significant nerve root compression by a left posterolateral disk hernation The right S1 root sleeve fills normally with contrast (black arrow) B Subtle compression of the anterior wall of the dural sac by displaced disk material (small arrows) demonstrated on upright lateral projection This sign is usually absent in the presence of a large amount of fat and venous structures in the anterior epidural compartment

CT

The sensitivity of CT to diagnose a herniation of the nucleus pulposus at the L5-S1 interspace is greater than that of myelography if images in the exact plane of the disk can be obtained[ ]23 [ ]39 Otherwise the superiority of plain CT over myelography to demonstrate disk herniations has not been established but CT has the distinct advantage of being

noninvasive and provides direct anatomic information[ ]23 Large herniations are easily detected but as explained previously the distinction between protrusions and extrusions is often difficult without sagittal reconstructions CT essentially allows an assessment of the contour of the disk The diagnosis of very small herniations in the absence of direct or indirect evidence of a radial tear is hazardous and associated with a high percentage of false-positives and false-negatives[ ]52 The diagnosis of moderate and large size herniations in different directions is usually possible but anterior herniations are rarely diagnosed not because they are not detectable but because observers pay little attention to the anterior contour of the disk (Fig 25) Because the PLLC cannot usually be identified the distinction of subligamentous from transligamentous herniation can only be suggested in most cases by the size of the herniated material A definite diagnosis of sequestration is rarely possible Calcifications within the displaced material are readily seen but may be difficult at times to differentiate from an accompanying osteophyte or an avulsed bone fragment from the vertebral body ring epiphysis (Fig 26) The presence of gas in the herniated material is easily detected

Figure 25 Anterior L4-L5 herniation demonstrated by CT scan in a 51-year-old woman with chronic low back pain Although sometimes quite conspicuous such herniations are rarely reported because observers pay little attention to the anterior contour of the disk

Figure 26 CT scan demonstration of a posterior right central L4-L5 disk herniation in a 38-year-old woman with avulsion of a bone fragment from the ring epiphysis and adjacent part of the superior L5 end plate Reactive osteosclerosis is seen around the vertebral body defect (arrows) suggesting a chronic lesion

CT Myelography

This association combines the advantages of both imaging modalities The fact that its accuracy has been reported as being less[ ]22 [ ]32 higher[ ]1 [ ]6 or equivalent[ ]82 to MR imaging is a reflection of the differences in technologic advancement and pathologic nomenclature that hamper valid comparisons between different studies

MR Imaging

Most reported studies establish MR imaging as the first choice modality to diagnose a herniated lumbar disk[ ]5 [ ]22 [ ]32 [ ]46 The associated intravenous injection of a paramagnetic agent has been found useful to demonstrate some anatomic features of disk disease in patients with no previous lumbar disk surgery[ ]56 [ ]68 [ ]90 MR imaging provides a better assessment of disk morphology than CT or CT myelography because sagittal sections are routinely obtained Assessment of foraminal involvement by displaced disk material is more accurate (Fig 27) and anterior disk herniations can be detected more easily than with CT or CT myelography If one is looking specifically for herniated lumbar disks associated with nerve root compression however it has been demonstrated that CT is equally accurate[ ]82 Alterations of the central or peripheral disk signal intensity on T2-weighted images are seen in most disks afflicted with an anular tear[ ]48 and alert the observer to scrutinize the disk contour in search for local modifications indicative of a herniation Because the signal of the displaced disk material is usually very similar to that of the outer anulus PLLC and vertebral body cortical bone small herniations are generally more conspicuous on axial CT sections than on corresponding axial MR imaging sections Gas and calcium deposits within the displaced fragment cannot usually

be detected but associated vertebral body bone marrow changes are typically seen and are helpful in differentiating acute from chronic processes[ ]57 The occasional presence of a high-intensity zone in the herniated material with an occasionally enhancing border after contrast injection is probably caused by a mixture of displaced nuclear material acute and subacute inflammatory tissue and neovascularized reactive tissue[ ]4 [ ]48 [ ]72 Contradictory reports have been published regarding the accuracy of MR imaging to differentiate subligamentous from transligamentous herniations[ ]26 [ ]38 [ ]73 [ ]76 Understanding the anatomy of the PLLC is helpful to make the distinction (Fig 28) (Figure Not Available) Masaryk et al[ ]46 have suggested that MR imaging is accurate to distinguish sequestered disks from other forms of lumbar disk herniations but most observers find this distinction difficult to establish[ ]42

Figure 27 A Left L4-L5 foraminal herniation well seen on an intermediate-weighted left parasagittal MR section (arrow) in a 47-year-old man B The lesion is much less obvious on intermediate-weighted (left) and T2-weighted (right) axial sections and was in fact more conspicuous on the corresponding CT scan section

Figure 28 (Figure Not Available) A Subligamentous disk herniation Left T1-weighted image demonstrating displaced disk material with a smooth outline imposed by the demarcation of the anterior epidural space (AES) by the lateral membrane of the PLLC Right Correlative drawing B Transligamentous disk herniation Left T1-weighted image of a large disk herniation (cervical in this case) which has ruptured through the posterior confines of the AES Penetration of the right lateral membrane can be observed (arrow) and the disk fragment contour is serrated Right Correlative drawing (From Schellinger D Manz HJ Vidic B et al Disk fragment migration Radiology 175831-836 1990 with permission)

Diskography and CT Diskography

During 30 years (1950 to 1980) when myelography was the only available imaging technique to demonstrate lumbar disk herniations diskography was an invasive but efficient way to demonstrate posterior central L5-S1 herniations and other large herniations (other than posterior central and paramedial) that could not be detected by myelography[ ]50 These herniations are now usually well demonstrated by CT and MR imaging Comparing the accuracy of five imaging modalities (excluding MR imaging) for the diagnosis of lumbar disk herniation Jackson et al[ ]31 found that CT diskography (Fig 29) was the most accurate test (87) compared with 77 for CT myelography 74 for CT 70 for myelography 64 for pain reproduction during diskography and 58 for diskography without CT Disk injection reproduced the patients clinical pain pattern in only 36 of herniated disks This clinical test isolated from the images had high specificity (89) but low sensitivity (43) for the diagnosis of disk herniation The reported low sensitivity of diskography images (unassociated with CT) to diagnose disk herniation is to be expected the purpose of the intradiskal injection being primarily the demonstration of an anular tear the contrast leaking through the tear only occasionally delineates an extruded fragment When a disk herniation has been diagnosed by other imaging modalities diskography allows to determine if the herniation is contained or noncontained (Figs 30 and 31) this information may have clinical relevance[ ]62 It also allows to establish if the displaced disk material is communicating or not with the parent disk and establishes the likelihood that it is sequestered or not There always remains a possibility that the contrast injected under pressure may reach a disk fragment that is nevertheless sequestered by leaking through the associated anular tear CT diskography also allows assessment in most cases of the integrity of the PLLC[ ]89 The superior sensitivity of diskography over MR imaging to demonstrate anular tears has been well established[ ]27 [ ]44 [ ]48 [ ]64 [ ]77 [ ]91 [ ]94 The presence of a radial tear and the inflammatory reaction it creates may be symptomatic despite the absence of true disk herniation[ ]29 [ ]48 [ ]49 [ ]69

Figure 29 L4-L5 CT diskogram demonstrating a large left posterolateral radial anular tear associated with

a left foraminal and extraforaminal herniaton (same patient as in Figure 28) (Figure Not Available)

Figure 30 Contained posterior L4-L5 and L5-S1 disk herniations in a 57-year-old man demonstrated by diskography The L3-L4 disk is normal

Figure 31 Noncontained L4-L5 disk herniation in a 23-year-old woman Reflux of injected contrast is seen in the anterior epidural space above and below the disk space The L5-S1 disk also demonstrates incomplete anterior and posterior radial anular tears

SUMMARY

The absence of universal nomenclature standardization with respect to the definition of a disk herniation and its different categories especially regarding type and location is still a major problem that will only be overcome when major national or international scientific societies join efforts to support a particular scheme Meanwhile it is important to realize that the two models that are currently most used are based on a different perspective Trying to straddle the two by opposing for instance bulging disk and herniation is doomed to failure because this exercise defies formal logic MR imaging is currently the most accurate noninvasive imaging modality to diagnose a disk herniation and to determine its exact location The determination of some pathoanatomic characteristics of herniated disks (type and composition) may require the use of CT diskography or CT diskography

References

1 Albeck MJ Hilden J Kjaer L et al A controlled comparison of myelography computed tomography and magnetic resonance imaging in clinically suspected lumbar disc herniation Spine 20443-448 1995 Abstract 2 American Academy of Orthopedic Surgeons Glossary on Spinal Terminology Chicago American Academy of Orthopedic Surgeons 1981 3 Andersson GB Weinstein JN Disc herniation [editorial] Spine 211S 1996 Citation 4 Aprill C Bogduk N High-intensity zone A diagnostic sign of painful lumbar disc on magnetic resonance imaging Br J Radiol 65361-369 1992 Abstract 5 Birney TJ White JJ Jr Berens D et al Comparison of MRI and discography in the diagnosis of lumbar degenerative disc disease J Spinal Disord 5417-423 1992 Abstract 6 Bischoff RJ Rodriguez RP Gupta K et al A comparison of computed tomography-myelography magnetic resonance imaging and myelography in the diagnosis of herniated nucleus pulposus and spinal stenosis J Spinal Disord 6289-295 1993 Abstract 7 Bogduk N The innervation of the lumbar spine Spine 8286-293 1983 Abstract 8 Bogduk N Tynan W Wilson AS The nerve supply to the human lumbar intervertebral discs J Anat 13239-56 1981 Abstract 9 Bonneville JF La carte-image des hernies discales lombaires Rachis 2255-257 1990 10 Bonneville JF La topografia simbolica delle ernie discali lombari Riv Neuroradiol 5427-431 1992 11 Bonneville JF Plaidoyer pour une classification par limage des hernies discales lombaires La carte-image Rev Imag Med 2557-560 1990 12 Brant-Zawadzki M Jensen M Spinal nomenclature Spine 20388-390 1995 Abstract

13 Brant-Zawadzki MN Jensen MC Obuchowski N et al Interobserver and intraobserver variability in interpretation of lumbar disc abnormalities A comparison of two nomenclatures Spine 201257-1263 1995 Abstract 14 Breton G Is that a bulging disk a small herniation or a moderate protrusion [editorial] Can Assoc Radiol J 42318 1991 Citation 15 Czervionke LF Lumbar intervertebral disc disease Neuroimaging Clin North Am 3465-485 1993 16 Deyo RA Nonsurgical care of low back pain Neurosurg Clin North Am 2851-862 1991 17 Deyo RA Loeser JD Bigos SJ Herniated lumbar intervertebral disk Ann Intern Med 112598-603 1990 Abstract 18 Dorlands Illustrated Medical Dictionary ed 28 Philadelphia WB Saunders 1994 19 Fardon D Pinkerton S Balderston R et al Terms used for diagnosis by English speaking spine surgeons Spine 18274-277 1993 Citation 20 Fardon DF Herzog RJ Mink JH et al Nomenclature of Lumbar Disc Disorders Contemporary Concepts in Spine Care Rosemont IL North American Spine Society 1995 21 Fardon DF Herzog RJ Mink JH et al Nomenclature of lumbar disc disorders In Garfin S Vaccaro A (eds) Orthopedic Knowledge Update Spine Rosemont IL American Academy of Orthopedic Surgeons 1997 pp A3-A14 22 Forristall RM Marsh HO Pay NT Magnetic resonance imaging and contrast CT of the lumbar spine Comparison of diagnostic methods and correlation with surgical findings Spine 131049-1054 1988 Abstract 23 Fries JW Abodeely DA Vijungco JG et al Computed tomography of herniated and extruded nucleus pulposus J Comput Assist Tomogr 6874-887 1982 Abstract 24 Frymoyer JW Newberg A Pope MH et al Spine radiographs in patients with low-back pain An epidemiological study in men J Bone Joint Surg Am 661048-1055 1984 Abstract 25 Gospodarowicz M Benedet L Hutter RV et al History and international developments in cancer staging Cancer Prev Control 2262-268 1998 Abstract 26 Grenier N Greselle JF Vital JM et al Normal and disrupted lumbar longitudinal ligaments Correlative MR and anatomic study Radiology 171197-205 1989 Abstract 27 Gunzburg R Parkinson R Moore R et al A cadaveric study comparing discography magnetic resonance imaging histology and mechanical behavior of the human lumbar disc Spine 17417-426 1992 Abstract 28 Haughton VM Eldevik OP Magnaes B et al A prospective comparison of computed tomography and myelography in the diagnosis of herniated lumbar disks Radiology 142103-110 1982 Abstract

29 Haughton VM Lim TH An H Intervertebral disk appearance correlated with stiffness of lumbar spinal motion segments AJNR Am J Neuroradiol 201161-1165 1999 Abstract 30 Herzog RJ The radiologic assessment for a lumbar disc herniation Spine 2119S-38S 1996 Abstract 31 Jackson RP Becker GJ Jacobs RR et al The neuroradiographic diagnosis of lumbar herniated nucleus pulposus I A comparison of computed tomography (CT) myelography CT-myelography discography and CT-discography Spine 141356-1361 1989 Abstract 32 Jackson RP Cain JE Jr Jacobs RR et al The neuroradiographic diagnosis of lumbar herniated nucleus pulposus II A comparison of computed tomography (CT) myelography CT-myelography and magnetic resonance imaging Spine 141362-1367 1989 Abstract 33 Jarvik JG Haynor DR Koepsell TD et al Interreader reliability for a new classification of lumbar disk disease Acad Radiol 3537-544 1996 Abstract 34 Jensen MC Brant-Zawadzki MN Obuchowski N et al Magnetic resonance imaging of the lumbar spine in people without back pain N Engl J Med 33169-73 1994 Abstract 35 Kent DL Haynor DR Larson EB et al Diagnosis of lumbar spinal stenosis in adults A meta-analysis of the accuracy of CT MR and myelography AJR Am J Roentgenol 1581135-1144 1992 Abstract 36 Kieffer SA Sherry RG Wellenstein DE et al Bulging lumbar intervertebral disk Myelographic differentiation from herniated disk with nerve root compression AJR Am J Roentgenol 138709-716 1982 Abstract 37 Kieffer SA Stadlan EM Mohandas A et al Discographic-anatomical correlation of developmental changes with age in the intervertebral disc Acta Radiol 9733-739 1969 38 Kim KY Kim YT Lee CS et al MRI classification of lumbar herniated intervertebral disc Orthopedics 15493-497 1992 Abstract 39 Kornberg M Rechtine GR Dupuy TE Computed tomography in the diagnosis of a herniated disk at the L5-S1 level Spine 9433-436 1984 Abstract 40 Kramer MS Clinical Epidemiology and Biostatistics New York Springer-Verlag 1988 41 Landis JR Koch GG The measurement of observer agreement agreement for categorical data Biometrics 33159-174 1977 Abstract 42 Laredo JD Bossard P Vuillemin-Bodaghi Formes anatomo-radiologiques des hernies discales In Morvan G Deburge A Bard H et al (eds) Le Rachis Lombaire Degeneratif Montpellier Sauramps Medical 1998 pp 37-49 43 Lee SH Coleman PE Hahn FJ Magnetic resonance imaging of degenerative disk disease of the spine Radiol Clin North Am 26949-964 1988 Abstract 44 Linson MA Crowe CH Comparison of magnetic resonance imaging and lumbar discography in the diagnosis of disc degeneration Clin Orthop 160-163 1990

45 Marchand F Ahmed AM Investigation of the laminate structure of lumbar disc anulus fibrosus Spine 15402-410 1990 Abstract 46 Masaryk TJ Ross JS Modic MT et al High-resolution MR imaging of sequestered lumbar intervertebral disks AJR Am J Roentgenol 1501155-1162 1988 Abstract 47 Milette PC The proper terminology for reporting lumbar intervertebral disk disorders AJNR Am J Neuroradiol 181859-1866 1997 Citation 48 Milette PC Fontaine S Lepanto L et al Differentiating lumbar disc protrusions disk bulges and discs with normal contour but abnormal signal intensity Magnetic resonance imaging with discographic correlations Spine 2444-53 1999 Abstract 49 Milette PC Fontaine S Lepanto L et al Radiating pain to the lower extremities caused by lumbar disk rupture without spinal nerve root involvement AJNR Am J Neuroradiol 161605-1613 1995 Abstract 50 Milette PC Melancon D A reappraisal of lumbar discography Can Assoc Radiol J 33176-182 1982 51 Milette PC Melancon D Dupuis PR et al A simplified terminology for abnormalities of the lumbar disk Can Assoc Radiol J 42319-325 1991 Abstract 52 Milette PC Raymond J Fontaine S Comparison of high-resolution computed tomography with discography in the evaluation of lumbar disc herniations Spine 15525-533 1990 Abstract 53 Mink JH Deutsch AL Goldstein TB et al Spinal imaging and intervention 1998 Phys Med Rehabil Clin North Am 9343-380 1998 54 Mixter WJ Barr JS Rupture of the intervertebral disc with involvement of the spinal canal N Engl J Med 211210-234 1934 55 Modic MT Masaryk TJ Ross JS et al Imaging of degenerative disk disease Radiology 168177-186 1988 Citation 56 Modic MT Ross JS Obuchowski NA et al Contrast-enhanced MR imaging in acute lumbar radiculopathy A pilot study of the natural history Radiology 195429-435 1995 Abstract 57 Modic MT Steinberg PM Ross JS et al Degenerative disk disease Assessment of changes in vertebral body marrow with MR imaging Radiology 166193-199 1988 58 Morvan G Mathieu P Les stenoses laterales In Morvan G Deburge A Bard H et al (eds) Le Rachis Lombaire Degeneratif Montpellier Sauramps Medical 1998 pp 315-324 59 Murray RO Skeletal trauma Regional In Sutton D (ed) Textbook of Radiology and Imaging ed 3 New York Churchill Livingstone 1980 pp 210-231 60 Nachemson A Lumbar disc herniation Conclusions Acta Orthop Scand 64(suppl 251)49 1993 Citation

61 Nathan H Osteophytes of the vertebral column An anatomical study of their development according to age race and sex with consideration as to their etiology and significance J Bone Joint Surg Am 44243-268 1962 62 Nygaard OP Mellgren SI Osterud B The inflammatory properties of contained and noncontained lumbar disc herniations Spine 222584-2488 1997 Abstract 63 Ohshima H Hirano N Osada R et al Morphologic variation of lumbar posterior longitudinal ligament and the modality of disc herniation Spine 182408-2411 1993 Abstract 64 Osti OL Fraser RD MRI and discography of annular tears and intervertebral disc degeneration A prospective clinical comparison J Bone Joint Surg Br 74431-435 1992 Abstract 65 Palmgren T Gronblad M Virri J et al Immunohistochemical demonstration of sensory and autonomic nerve terminals in herniated lumbar disc tissue Spine 211301-1306 1996 Abstract 66 Resnick D Niwayama G Degenerative disease of the spine In Resnick D (ed) Diagnosis of Bone and Joint Disorders ed 3 Philadelphia WB Saunders 1995 pp 1372-1462 67 Resnick D Niwayama G Intravertebral disk herniations Cartilaginous (Schmorls) nodes Radiology 12657-65 1978 Abstract 68 Ross JS Modic MT Masaryk TJ Tears of the anulus fibrosus Assessment with Gd-DTPA-enhanced MR imaging AJR Am J Roentgenol 154159-162 1990 Abstract 69 Saal JS The role of inflammation in lumbar pain Spine 201821-1827 1995 Abstract 70 Sachs BL Vanharanta H Spivey MA et al Dallas discogram description A new classification of CTdiscography in low-back disorders Spine 12287-294 1987 Abstract 71 Sauser DD Goldman AB Kaye JJ Discogenic vertebral sclerosis J Can Assoc Radiol 2944-50 1978 Abstract 72 Schellhas KP Pollei SR Gundry CR et al Lumbar disc high-intensity zone Correlation of magnetic resonance imaging and discography Spine 2179-86 1996 Abstract 73 Schellinger D Manz HJ Vidic B et al Disk fragment migration Radiology 175831-836 1990 Abstract 74 Schipper J Kardaun JW Braakman R et al Lumbar disk herniation Diagnosis with CT or myelography Radiology 165227-231 1987 Abstract 75 Schmorl G Junghanns H The Human Spine in Health and Disease ed 2 New York Grune and Stratton 1971 76 Silverman CS Lenchik L Shimkin PM et al The value of MR in differentiating subligamentous from supraligamentous lumbar disk herniations AJNR Am J Neuroradiol 16571-579 1995 Abstract 77 Simmons JW Emery SF McMillin JN et al Awake discography A comparison study with magnetic

resonance imaging Spine 16S216-221 1991 Abstract 78 Smyth MJ Wright V Sciatica and the intervertebral disc J Bone Joint Surg Am 401401-1418 1958 79 Taveras JM Radiologic aspects of low back pain and sciatic syndromes [editorial] AJNR Am J Neuroradiol 9351-358 1989 80 Tehranzadeh J Discography 2000 Radiol Clin North Am 36463-495 1998 Full Text 81 Thelander U Fagerlund M Friberg S et al Describing the size of lumbar disc herniations using computed tomography A comparison of different size index calculations and their relation to sciatica Spine 191979-1984 1994 Abstract 82 Thornbury JR Fryback DG Turski PA et al Disk-caused nerve compression in patients with acute low-back pain Diagnosis with MR CT myelography and plain CT Radiology 186731-738 1993 Abstract 83 Twomey L Taylor J Age changes in lumbar intervertebral discs Acta Orthop Scand 56496-499 1985 Abstract 84 Twomey LT Taylor JR Age changes in lumbar vertebrae and intervertebral discs Clin Orthop 22497-104 1987 85 Williams AL CT diagnosis of degenerative disc disease The bulging annulus Radiol Clin North Am 21289-300 1983 Abstract 86 Williams AL Haughton VM Meyer GA et al Computed tomographic appearance of the bulging annulus Radiology 142403-408 1982 Abstract 87 Williams AL Haughton VM Syvertsen A Computed tomography in the diagnosis of herniated nucleus pulposus Radiology 13595-99 1980 Abstract 88 Wiltse LL Berger PE McCulloch JA A system for reporting the size and location of lesions in the spine Spine 221534-1537 1997 Abstract 89 Wiltse LL Fonseca AS Amster J et al Relationship of the dura Hofmanns ligaments Batsons plexus and a fibrovascular membrane lying on the posterior surface of the vertebral bodies and attaching to the deep layer of the posterior longitudinal ligament An anatomical radiologic and clinical study Spine 181030-1043 1993 Abstract 90 Yamashita K Hiroshima K Kurata A Gadolinium-DTPA-enhanced magnetic resonance imaging of a sequestered lumbar intervertebral disc and its correlation with pathologic findings Spine 19479-482 1994 Abstract 91 Yu SW Haughton VM Sether LA et al Comparison of MR and diskography in detecting radial tears of the anulus A postmortem study AJNR Am J Neuroradiol 101077-1081 1989 Abstract 92 Yu SW Sether LA Ho PS et al Tears of the anulus fibrosus Correlation between MR and pathologic findings in cadavers AJNR Am J Neuroradiol 9367-370 1988 Abstract

93 Yussen PS Swartz JD The acute lumbar disc herniation Imaging diagnosis Semin Ultrasound CT MR 14389-398 1993 Abstract 94 Zucherman J Derby R Hsu K et al Normal magnetic resonance imaging with abnormal discography Spine 131355-1359 1988 Abstract

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  • CLASSIFICATION DIAGNOSTIC IMAGING AND IMAGING CHARACTERIZATION OF A LUMBAR HERNIATED DISK
    • IMAGING OF LOW BACK PAIN I
      • CLASSIFICATION DIAGNOSTIC IMAGING AND IMAGING CHARACTERIZATION OF A LUMBAR HERNIATED DISK
        • DEFINITION OF A DISK HERNIATION
        • CLASSIFICATION OF A HERNIATED LUMBAR DISK
          • Main Categories of Noninfectious Disk Abnormalities
          • Further Qualifying the Displaced Disk Material Beyond the Disk Space
            • DIAGNOSTIC IMAGING AND CHARACTERIZATION OF A HERNIATED LUMBAR DISK
              • Conventional Radiographs
              • Myelography
              • CT
              • CT Myelography
              • MR Imaging
              • Diskography and CT Diskography
                • SUMMARY
                  • References
Page 24: CLASSIFICATION, DIAGNOSTIC IMAGING, AND IMAGING ... · PDF fileclassification, diagnostic imaging, and imaging characterization of a lumbar herniated disk ... classification, diagnostic

noninvasive and provides direct anatomic information[ ]23 Large herniations are easily detected but as explained previously the distinction between protrusions and extrusions is often difficult without sagittal reconstructions CT essentially allows an assessment of the contour of the disk The diagnosis of very small herniations in the absence of direct or indirect evidence of a radial tear is hazardous and associated with a high percentage of false-positives and false-negatives[ ]52 The diagnosis of moderate and large size herniations in different directions is usually possible but anterior herniations are rarely diagnosed not because they are not detectable but because observers pay little attention to the anterior contour of the disk (Fig 25) Because the PLLC cannot usually be identified the distinction of subligamentous from transligamentous herniation can only be suggested in most cases by the size of the herniated material A definite diagnosis of sequestration is rarely possible Calcifications within the displaced material are readily seen but may be difficult at times to differentiate from an accompanying osteophyte or an avulsed bone fragment from the vertebral body ring epiphysis (Fig 26) The presence of gas in the herniated material is easily detected

Figure 25 Anterior L4-L5 herniation demonstrated by CT scan in a 51-year-old woman with chronic low back pain Although sometimes quite conspicuous such herniations are rarely reported because observers pay little attention to the anterior contour of the disk

Figure 26 CT scan demonstration of a posterior right central L4-L5 disk herniation in a 38-year-old woman with avulsion of a bone fragment from the ring epiphysis and adjacent part of the superior L5 end plate Reactive osteosclerosis is seen around the vertebral body defect (arrows) suggesting a chronic lesion

CT Myelography

This association combines the advantages of both imaging modalities The fact that its accuracy has been reported as being less[ ]22 [ ]32 higher[ ]1 [ ]6 or equivalent[ ]82 to MR imaging is a reflection of the differences in technologic advancement and pathologic nomenclature that hamper valid comparisons between different studies

MR Imaging

Most reported studies establish MR imaging as the first choice modality to diagnose a herniated lumbar disk[ ]5 [ ]22 [ ]32 [ ]46 The associated intravenous injection of a paramagnetic agent has been found useful to demonstrate some anatomic features of disk disease in patients with no previous lumbar disk surgery[ ]56 [ ]68 [ ]90 MR imaging provides a better assessment of disk morphology than CT or CT myelography because sagittal sections are routinely obtained Assessment of foraminal involvement by displaced disk material is more accurate (Fig 27) and anterior disk herniations can be detected more easily than with CT or CT myelography If one is looking specifically for herniated lumbar disks associated with nerve root compression however it has been demonstrated that CT is equally accurate[ ]82 Alterations of the central or peripheral disk signal intensity on T2-weighted images are seen in most disks afflicted with an anular tear[ ]48 and alert the observer to scrutinize the disk contour in search for local modifications indicative of a herniation Because the signal of the displaced disk material is usually very similar to that of the outer anulus PLLC and vertebral body cortical bone small herniations are generally more conspicuous on axial CT sections than on corresponding axial MR imaging sections Gas and calcium deposits within the displaced fragment cannot usually

be detected but associated vertebral body bone marrow changes are typically seen and are helpful in differentiating acute from chronic processes[ ]57 The occasional presence of a high-intensity zone in the herniated material with an occasionally enhancing border after contrast injection is probably caused by a mixture of displaced nuclear material acute and subacute inflammatory tissue and neovascularized reactive tissue[ ]4 [ ]48 [ ]72 Contradictory reports have been published regarding the accuracy of MR imaging to differentiate subligamentous from transligamentous herniations[ ]26 [ ]38 [ ]73 [ ]76 Understanding the anatomy of the PLLC is helpful to make the distinction (Fig 28) (Figure Not Available) Masaryk et al[ ]46 have suggested that MR imaging is accurate to distinguish sequestered disks from other forms of lumbar disk herniations but most observers find this distinction difficult to establish[ ]42

Figure 27 A Left L4-L5 foraminal herniation well seen on an intermediate-weighted left parasagittal MR section (arrow) in a 47-year-old man B The lesion is much less obvious on intermediate-weighted (left) and T2-weighted (right) axial sections and was in fact more conspicuous on the corresponding CT scan section

Figure 28 (Figure Not Available) A Subligamentous disk herniation Left T1-weighted image demonstrating displaced disk material with a smooth outline imposed by the demarcation of the anterior epidural space (AES) by the lateral membrane of the PLLC Right Correlative drawing B Transligamentous disk herniation Left T1-weighted image of a large disk herniation (cervical in this case) which has ruptured through the posterior confines of the AES Penetration of the right lateral membrane can be observed (arrow) and the disk fragment contour is serrated Right Correlative drawing (From Schellinger D Manz HJ Vidic B et al Disk fragment migration Radiology 175831-836 1990 with permission)

Diskography and CT Diskography

During 30 years (1950 to 1980) when myelography was the only available imaging technique to demonstrate lumbar disk herniations diskography was an invasive but efficient way to demonstrate posterior central L5-S1 herniations and other large herniations (other than posterior central and paramedial) that could not be detected by myelography[ ]50 These herniations are now usually well demonstrated by CT and MR imaging Comparing the accuracy of five imaging modalities (excluding MR imaging) for the diagnosis of lumbar disk herniation Jackson et al[ ]31 found that CT diskography (Fig 29) was the most accurate test (87) compared with 77 for CT myelography 74 for CT 70 for myelography 64 for pain reproduction during diskography and 58 for diskography without CT Disk injection reproduced the patients clinical pain pattern in only 36 of herniated disks This clinical test isolated from the images had high specificity (89) but low sensitivity (43) for the diagnosis of disk herniation The reported low sensitivity of diskography images (unassociated with CT) to diagnose disk herniation is to be expected the purpose of the intradiskal injection being primarily the demonstration of an anular tear the contrast leaking through the tear only occasionally delineates an extruded fragment When a disk herniation has been diagnosed by other imaging modalities diskography allows to determine if the herniation is contained or noncontained (Figs 30 and 31) this information may have clinical relevance[ ]62 It also allows to establish if the displaced disk material is communicating or not with the parent disk and establishes the likelihood that it is sequestered or not There always remains a possibility that the contrast injected under pressure may reach a disk fragment that is nevertheless sequestered by leaking through the associated anular tear CT diskography also allows assessment in most cases of the integrity of the PLLC[ ]89 The superior sensitivity of diskography over MR imaging to demonstrate anular tears has been well established[ ]27 [ ]44 [ ]48 [ ]64 [ ]77 [ ]91 [ ]94 The presence of a radial tear and the inflammatory reaction it creates may be symptomatic despite the absence of true disk herniation[ ]29 [ ]48 [ ]49 [ ]69

Figure 29 L4-L5 CT diskogram demonstrating a large left posterolateral radial anular tear associated with

a left foraminal and extraforaminal herniaton (same patient as in Figure 28) (Figure Not Available)

Figure 30 Contained posterior L4-L5 and L5-S1 disk herniations in a 57-year-old man demonstrated by diskography The L3-L4 disk is normal

Figure 31 Noncontained L4-L5 disk herniation in a 23-year-old woman Reflux of injected contrast is seen in the anterior epidural space above and below the disk space The L5-S1 disk also demonstrates incomplete anterior and posterior radial anular tears

SUMMARY

The absence of universal nomenclature standardization with respect to the definition of a disk herniation and its different categories especially regarding type and location is still a major problem that will only be overcome when major national or international scientific societies join efforts to support a particular scheme Meanwhile it is important to realize that the two models that are currently most used are based on a different perspective Trying to straddle the two by opposing for instance bulging disk and herniation is doomed to failure because this exercise defies formal logic MR imaging is currently the most accurate noninvasive imaging modality to diagnose a disk herniation and to determine its exact location The determination of some pathoanatomic characteristics of herniated disks (type and composition) may require the use of CT diskography or CT diskography

References

1 Albeck MJ Hilden J Kjaer L et al A controlled comparison of myelography computed tomography and magnetic resonance imaging in clinically suspected lumbar disc herniation Spine 20443-448 1995 Abstract 2 American Academy of Orthopedic Surgeons Glossary on Spinal Terminology Chicago American Academy of Orthopedic Surgeons 1981 3 Andersson GB Weinstein JN Disc herniation [editorial] Spine 211S 1996 Citation 4 Aprill C Bogduk N High-intensity zone A diagnostic sign of painful lumbar disc on magnetic resonance imaging Br J Radiol 65361-369 1992 Abstract 5 Birney TJ White JJ Jr Berens D et al Comparison of MRI and discography in the diagnosis of lumbar degenerative disc disease J Spinal Disord 5417-423 1992 Abstract 6 Bischoff RJ Rodriguez RP Gupta K et al A comparison of computed tomography-myelography magnetic resonance imaging and myelography in the diagnosis of herniated nucleus pulposus and spinal stenosis J Spinal Disord 6289-295 1993 Abstract 7 Bogduk N The innervation of the lumbar spine Spine 8286-293 1983 Abstract 8 Bogduk N Tynan W Wilson AS The nerve supply to the human lumbar intervertebral discs J Anat 13239-56 1981 Abstract 9 Bonneville JF La carte-image des hernies discales lombaires Rachis 2255-257 1990 10 Bonneville JF La topografia simbolica delle ernie discali lombari Riv Neuroradiol 5427-431 1992 11 Bonneville JF Plaidoyer pour une classification par limage des hernies discales lombaires La carte-image Rev Imag Med 2557-560 1990 12 Brant-Zawadzki M Jensen M Spinal nomenclature Spine 20388-390 1995 Abstract

13 Brant-Zawadzki MN Jensen MC Obuchowski N et al Interobserver and intraobserver variability in interpretation of lumbar disc abnormalities A comparison of two nomenclatures Spine 201257-1263 1995 Abstract 14 Breton G Is that a bulging disk a small herniation or a moderate protrusion [editorial] Can Assoc Radiol J 42318 1991 Citation 15 Czervionke LF Lumbar intervertebral disc disease Neuroimaging Clin North Am 3465-485 1993 16 Deyo RA Nonsurgical care of low back pain Neurosurg Clin North Am 2851-862 1991 17 Deyo RA Loeser JD Bigos SJ Herniated lumbar intervertebral disk Ann Intern Med 112598-603 1990 Abstract 18 Dorlands Illustrated Medical Dictionary ed 28 Philadelphia WB Saunders 1994 19 Fardon D Pinkerton S Balderston R et al Terms used for diagnosis by English speaking spine surgeons Spine 18274-277 1993 Citation 20 Fardon DF Herzog RJ Mink JH et al Nomenclature of Lumbar Disc Disorders Contemporary Concepts in Spine Care Rosemont IL North American Spine Society 1995 21 Fardon DF Herzog RJ Mink JH et al Nomenclature of lumbar disc disorders In Garfin S Vaccaro A (eds) Orthopedic Knowledge Update Spine Rosemont IL American Academy of Orthopedic Surgeons 1997 pp A3-A14 22 Forristall RM Marsh HO Pay NT Magnetic resonance imaging and contrast CT of the lumbar spine Comparison of diagnostic methods and correlation with surgical findings Spine 131049-1054 1988 Abstract 23 Fries JW Abodeely DA Vijungco JG et al Computed tomography of herniated and extruded nucleus pulposus J Comput Assist Tomogr 6874-887 1982 Abstract 24 Frymoyer JW Newberg A Pope MH et al Spine radiographs in patients with low-back pain An epidemiological study in men J Bone Joint Surg Am 661048-1055 1984 Abstract 25 Gospodarowicz M Benedet L Hutter RV et al History and international developments in cancer staging Cancer Prev Control 2262-268 1998 Abstract 26 Grenier N Greselle JF Vital JM et al Normal and disrupted lumbar longitudinal ligaments Correlative MR and anatomic study Radiology 171197-205 1989 Abstract 27 Gunzburg R Parkinson R Moore R et al A cadaveric study comparing discography magnetic resonance imaging histology and mechanical behavior of the human lumbar disc Spine 17417-426 1992 Abstract 28 Haughton VM Eldevik OP Magnaes B et al A prospective comparison of computed tomography and myelography in the diagnosis of herniated lumbar disks Radiology 142103-110 1982 Abstract

29 Haughton VM Lim TH An H Intervertebral disk appearance correlated with stiffness of lumbar spinal motion segments AJNR Am J Neuroradiol 201161-1165 1999 Abstract 30 Herzog RJ The radiologic assessment for a lumbar disc herniation Spine 2119S-38S 1996 Abstract 31 Jackson RP Becker GJ Jacobs RR et al The neuroradiographic diagnosis of lumbar herniated nucleus pulposus I A comparison of computed tomography (CT) myelography CT-myelography discography and CT-discography Spine 141356-1361 1989 Abstract 32 Jackson RP Cain JE Jr Jacobs RR et al The neuroradiographic diagnosis of lumbar herniated nucleus pulposus II A comparison of computed tomography (CT) myelography CT-myelography and magnetic resonance imaging Spine 141362-1367 1989 Abstract 33 Jarvik JG Haynor DR Koepsell TD et al Interreader reliability for a new classification of lumbar disk disease Acad Radiol 3537-544 1996 Abstract 34 Jensen MC Brant-Zawadzki MN Obuchowski N et al Magnetic resonance imaging of the lumbar spine in people without back pain N Engl J Med 33169-73 1994 Abstract 35 Kent DL Haynor DR Larson EB et al Diagnosis of lumbar spinal stenosis in adults A meta-analysis of the accuracy of CT MR and myelography AJR Am J Roentgenol 1581135-1144 1992 Abstract 36 Kieffer SA Sherry RG Wellenstein DE et al Bulging lumbar intervertebral disk Myelographic differentiation from herniated disk with nerve root compression AJR Am J Roentgenol 138709-716 1982 Abstract 37 Kieffer SA Stadlan EM Mohandas A et al Discographic-anatomical correlation of developmental changes with age in the intervertebral disc Acta Radiol 9733-739 1969 38 Kim KY Kim YT Lee CS et al MRI classification of lumbar herniated intervertebral disc Orthopedics 15493-497 1992 Abstract 39 Kornberg M Rechtine GR Dupuy TE Computed tomography in the diagnosis of a herniated disk at the L5-S1 level Spine 9433-436 1984 Abstract 40 Kramer MS Clinical Epidemiology and Biostatistics New York Springer-Verlag 1988 41 Landis JR Koch GG The measurement of observer agreement agreement for categorical data Biometrics 33159-174 1977 Abstract 42 Laredo JD Bossard P Vuillemin-Bodaghi Formes anatomo-radiologiques des hernies discales In Morvan G Deburge A Bard H et al (eds) Le Rachis Lombaire Degeneratif Montpellier Sauramps Medical 1998 pp 37-49 43 Lee SH Coleman PE Hahn FJ Magnetic resonance imaging of degenerative disk disease of the spine Radiol Clin North Am 26949-964 1988 Abstract 44 Linson MA Crowe CH Comparison of magnetic resonance imaging and lumbar discography in the diagnosis of disc degeneration Clin Orthop 160-163 1990

45 Marchand F Ahmed AM Investigation of the laminate structure of lumbar disc anulus fibrosus Spine 15402-410 1990 Abstract 46 Masaryk TJ Ross JS Modic MT et al High-resolution MR imaging of sequestered lumbar intervertebral disks AJR Am J Roentgenol 1501155-1162 1988 Abstract 47 Milette PC The proper terminology for reporting lumbar intervertebral disk disorders AJNR Am J Neuroradiol 181859-1866 1997 Citation 48 Milette PC Fontaine S Lepanto L et al Differentiating lumbar disc protrusions disk bulges and discs with normal contour but abnormal signal intensity Magnetic resonance imaging with discographic correlations Spine 2444-53 1999 Abstract 49 Milette PC Fontaine S Lepanto L et al Radiating pain to the lower extremities caused by lumbar disk rupture without spinal nerve root involvement AJNR Am J Neuroradiol 161605-1613 1995 Abstract 50 Milette PC Melancon D A reappraisal of lumbar discography Can Assoc Radiol J 33176-182 1982 51 Milette PC Melancon D Dupuis PR et al A simplified terminology for abnormalities of the lumbar disk Can Assoc Radiol J 42319-325 1991 Abstract 52 Milette PC Raymond J Fontaine S Comparison of high-resolution computed tomography with discography in the evaluation of lumbar disc herniations Spine 15525-533 1990 Abstract 53 Mink JH Deutsch AL Goldstein TB et al Spinal imaging and intervention 1998 Phys Med Rehabil Clin North Am 9343-380 1998 54 Mixter WJ Barr JS Rupture of the intervertebral disc with involvement of the spinal canal N Engl J Med 211210-234 1934 55 Modic MT Masaryk TJ Ross JS et al Imaging of degenerative disk disease Radiology 168177-186 1988 Citation 56 Modic MT Ross JS Obuchowski NA et al Contrast-enhanced MR imaging in acute lumbar radiculopathy A pilot study of the natural history Radiology 195429-435 1995 Abstract 57 Modic MT Steinberg PM Ross JS et al Degenerative disk disease Assessment of changes in vertebral body marrow with MR imaging Radiology 166193-199 1988 58 Morvan G Mathieu P Les stenoses laterales In Morvan G Deburge A Bard H et al (eds) Le Rachis Lombaire Degeneratif Montpellier Sauramps Medical 1998 pp 315-324 59 Murray RO Skeletal trauma Regional In Sutton D (ed) Textbook of Radiology and Imaging ed 3 New York Churchill Livingstone 1980 pp 210-231 60 Nachemson A Lumbar disc herniation Conclusions Acta Orthop Scand 64(suppl 251)49 1993 Citation

61 Nathan H Osteophytes of the vertebral column An anatomical study of their development according to age race and sex with consideration as to their etiology and significance J Bone Joint Surg Am 44243-268 1962 62 Nygaard OP Mellgren SI Osterud B The inflammatory properties of contained and noncontained lumbar disc herniations Spine 222584-2488 1997 Abstract 63 Ohshima H Hirano N Osada R et al Morphologic variation of lumbar posterior longitudinal ligament and the modality of disc herniation Spine 182408-2411 1993 Abstract 64 Osti OL Fraser RD MRI and discography of annular tears and intervertebral disc degeneration A prospective clinical comparison J Bone Joint Surg Br 74431-435 1992 Abstract 65 Palmgren T Gronblad M Virri J et al Immunohistochemical demonstration of sensory and autonomic nerve terminals in herniated lumbar disc tissue Spine 211301-1306 1996 Abstract 66 Resnick D Niwayama G Degenerative disease of the spine In Resnick D (ed) Diagnosis of Bone and Joint Disorders ed 3 Philadelphia WB Saunders 1995 pp 1372-1462 67 Resnick D Niwayama G Intravertebral disk herniations Cartilaginous (Schmorls) nodes Radiology 12657-65 1978 Abstract 68 Ross JS Modic MT Masaryk TJ Tears of the anulus fibrosus Assessment with Gd-DTPA-enhanced MR imaging AJR Am J Roentgenol 154159-162 1990 Abstract 69 Saal JS The role of inflammation in lumbar pain Spine 201821-1827 1995 Abstract 70 Sachs BL Vanharanta H Spivey MA et al Dallas discogram description A new classification of CTdiscography in low-back disorders Spine 12287-294 1987 Abstract 71 Sauser DD Goldman AB Kaye JJ Discogenic vertebral sclerosis J Can Assoc Radiol 2944-50 1978 Abstract 72 Schellhas KP Pollei SR Gundry CR et al Lumbar disc high-intensity zone Correlation of magnetic resonance imaging and discography Spine 2179-86 1996 Abstract 73 Schellinger D Manz HJ Vidic B et al Disk fragment migration Radiology 175831-836 1990 Abstract 74 Schipper J Kardaun JW Braakman R et al Lumbar disk herniation Diagnosis with CT or myelography Radiology 165227-231 1987 Abstract 75 Schmorl G Junghanns H The Human Spine in Health and Disease ed 2 New York Grune and Stratton 1971 76 Silverman CS Lenchik L Shimkin PM et al The value of MR in differentiating subligamentous from supraligamentous lumbar disk herniations AJNR Am J Neuroradiol 16571-579 1995 Abstract 77 Simmons JW Emery SF McMillin JN et al Awake discography A comparison study with magnetic

resonance imaging Spine 16S216-221 1991 Abstract 78 Smyth MJ Wright V Sciatica and the intervertebral disc J Bone Joint Surg Am 401401-1418 1958 79 Taveras JM Radiologic aspects of low back pain and sciatic syndromes [editorial] AJNR Am J Neuroradiol 9351-358 1989 80 Tehranzadeh J Discography 2000 Radiol Clin North Am 36463-495 1998 Full Text 81 Thelander U Fagerlund M Friberg S et al Describing the size of lumbar disc herniations using computed tomography A comparison of different size index calculations and their relation to sciatica Spine 191979-1984 1994 Abstract 82 Thornbury JR Fryback DG Turski PA et al Disk-caused nerve compression in patients with acute low-back pain Diagnosis with MR CT myelography and plain CT Radiology 186731-738 1993 Abstract 83 Twomey L Taylor J Age changes in lumbar intervertebral discs Acta Orthop Scand 56496-499 1985 Abstract 84 Twomey LT Taylor JR Age changes in lumbar vertebrae and intervertebral discs Clin Orthop 22497-104 1987 85 Williams AL CT diagnosis of degenerative disc disease The bulging annulus Radiol Clin North Am 21289-300 1983 Abstract 86 Williams AL Haughton VM Meyer GA et al Computed tomographic appearance of the bulging annulus Radiology 142403-408 1982 Abstract 87 Williams AL Haughton VM Syvertsen A Computed tomography in the diagnosis of herniated nucleus pulposus Radiology 13595-99 1980 Abstract 88 Wiltse LL Berger PE McCulloch JA A system for reporting the size and location of lesions in the spine Spine 221534-1537 1997 Abstract 89 Wiltse LL Fonseca AS Amster J et al Relationship of the dura Hofmanns ligaments Batsons plexus and a fibrovascular membrane lying on the posterior surface of the vertebral bodies and attaching to the deep layer of the posterior longitudinal ligament An anatomical radiologic and clinical study Spine 181030-1043 1993 Abstract 90 Yamashita K Hiroshima K Kurata A Gadolinium-DTPA-enhanced magnetic resonance imaging of a sequestered lumbar intervertebral disc and its correlation with pathologic findings Spine 19479-482 1994 Abstract 91 Yu SW Haughton VM Sether LA et al Comparison of MR and diskography in detecting radial tears of the anulus A postmortem study AJNR Am J Neuroradiol 101077-1081 1989 Abstract 92 Yu SW Sether LA Ho PS et al Tears of the anulus fibrosus Correlation between MR and pathologic findings in cadavers AJNR Am J Neuroradiol 9367-370 1988 Abstract

93 Yussen PS Swartz JD The acute lumbar disc herniation Imaging diagnosis Semin Ultrasound CT MR 14389-398 1993 Abstract 94 Zucherman J Derby R Hsu K et al Normal magnetic resonance imaging with abnormal discography Spine 131355-1359 1988 Abstract

Copyright copy 2008 Elsevier Inc All rights reserved - wwwmdconsultcom

Bookmark URL dasjournalview0N11535915ja=198094ampPAGE=1htmlampissn=0033-8389ampsource=MI

  • CLASSIFICATION DIAGNOSTIC IMAGING AND IMAGING CHARACTERIZATION OF A LUMBAR HERNIATED DISK
    • IMAGING OF LOW BACK PAIN I
      • CLASSIFICATION DIAGNOSTIC IMAGING AND IMAGING CHARACTERIZATION OF A LUMBAR HERNIATED DISK
        • DEFINITION OF A DISK HERNIATION
        • CLASSIFICATION OF A HERNIATED LUMBAR DISK
          • Main Categories of Noninfectious Disk Abnormalities
          • Further Qualifying the Displaced Disk Material Beyond the Disk Space
            • DIAGNOSTIC IMAGING AND CHARACTERIZATION OF A HERNIATED LUMBAR DISK
              • Conventional Radiographs
              • Myelography
              • CT
              • CT Myelography
              • MR Imaging
              • Diskography and CT Diskography
                • SUMMARY
                  • References
Page 25: CLASSIFICATION, DIAGNOSTIC IMAGING, AND IMAGING ... · PDF fileclassification, diagnostic imaging, and imaging characterization of a lumbar herniated disk ... classification, diagnostic

Figure 26 CT scan demonstration of a posterior right central L4-L5 disk herniation in a 38-year-old woman with avulsion of a bone fragment from the ring epiphysis and adjacent part of the superior L5 end plate Reactive osteosclerosis is seen around the vertebral body defect (arrows) suggesting a chronic lesion

CT Myelography

This association combines the advantages of both imaging modalities The fact that its accuracy has been reported as being less[ ]22 [ ]32 higher[ ]1 [ ]6 or equivalent[ ]82 to MR imaging is a reflection of the differences in technologic advancement and pathologic nomenclature that hamper valid comparisons between different studies

MR Imaging

Most reported studies establish MR imaging as the first choice modality to diagnose a herniated lumbar disk[ ]5 [ ]22 [ ]32 [ ]46 The associated intravenous injection of a paramagnetic agent has been found useful to demonstrate some anatomic features of disk disease in patients with no previous lumbar disk surgery[ ]56 [ ]68 [ ]90 MR imaging provides a better assessment of disk morphology than CT or CT myelography because sagittal sections are routinely obtained Assessment of foraminal involvement by displaced disk material is more accurate (Fig 27) and anterior disk herniations can be detected more easily than with CT or CT myelography If one is looking specifically for herniated lumbar disks associated with nerve root compression however it has been demonstrated that CT is equally accurate[ ]82 Alterations of the central or peripheral disk signal intensity on T2-weighted images are seen in most disks afflicted with an anular tear[ ]48 and alert the observer to scrutinize the disk contour in search for local modifications indicative of a herniation Because the signal of the displaced disk material is usually very similar to that of the outer anulus PLLC and vertebral body cortical bone small herniations are generally more conspicuous on axial CT sections than on corresponding axial MR imaging sections Gas and calcium deposits within the displaced fragment cannot usually

be detected but associated vertebral body bone marrow changes are typically seen and are helpful in differentiating acute from chronic processes[ ]57 The occasional presence of a high-intensity zone in the herniated material with an occasionally enhancing border after contrast injection is probably caused by a mixture of displaced nuclear material acute and subacute inflammatory tissue and neovascularized reactive tissue[ ]4 [ ]48 [ ]72 Contradictory reports have been published regarding the accuracy of MR imaging to differentiate subligamentous from transligamentous herniations[ ]26 [ ]38 [ ]73 [ ]76 Understanding the anatomy of the PLLC is helpful to make the distinction (Fig 28) (Figure Not Available) Masaryk et al[ ]46 have suggested that MR imaging is accurate to distinguish sequestered disks from other forms of lumbar disk herniations but most observers find this distinction difficult to establish[ ]42

Figure 27 A Left L4-L5 foraminal herniation well seen on an intermediate-weighted left parasagittal MR section (arrow) in a 47-year-old man B The lesion is much less obvious on intermediate-weighted (left) and T2-weighted (right) axial sections and was in fact more conspicuous on the corresponding CT scan section

Figure 28 (Figure Not Available) A Subligamentous disk herniation Left T1-weighted image demonstrating displaced disk material with a smooth outline imposed by the demarcation of the anterior epidural space (AES) by the lateral membrane of the PLLC Right Correlative drawing B Transligamentous disk herniation Left T1-weighted image of a large disk herniation (cervical in this case) which has ruptured through the posterior confines of the AES Penetration of the right lateral membrane can be observed (arrow) and the disk fragment contour is serrated Right Correlative drawing (From Schellinger D Manz HJ Vidic B et al Disk fragment migration Radiology 175831-836 1990 with permission)

Diskography and CT Diskography

During 30 years (1950 to 1980) when myelography was the only available imaging technique to demonstrate lumbar disk herniations diskography was an invasive but efficient way to demonstrate posterior central L5-S1 herniations and other large herniations (other than posterior central and paramedial) that could not be detected by myelography[ ]50 These herniations are now usually well demonstrated by CT and MR imaging Comparing the accuracy of five imaging modalities (excluding MR imaging) for the diagnosis of lumbar disk herniation Jackson et al[ ]31 found that CT diskography (Fig 29) was the most accurate test (87) compared with 77 for CT myelography 74 for CT 70 for myelography 64 for pain reproduction during diskography and 58 for diskography without CT Disk injection reproduced the patients clinical pain pattern in only 36 of herniated disks This clinical test isolated from the images had high specificity (89) but low sensitivity (43) for the diagnosis of disk herniation The reported low sensitivity of diskography images (unassociated with CT) to diagnose disk herniation is to be expected the purpose of the intradiskal injection being primarily the demonstration of an anular tear the contrast leaking through the tear only occasionally delineates an extruded fragment When a disk herniation has been diagnosed by other imaging modalities diskography allows to determine if the herniation is contained or noncontained (Figs 30 and 31) this information may have clinical relevance[ ]62 It also allows to establish if the displaced disk material is communicating or not with the parent disk and establishes the likelihood that it is sequestered or not There always remains a possibility that the contrast injected under pressure may reach a disk fragment that is nevertheless sequestered by leaking through the associated anular tear CT diskography also allows assessment in most cases of the integrity of the PLLC[ ]89 The superior sensitivity of diskography over MR imaging to demonstrate anular tears has been well established[ ]27 [ ]44 [ ]48 [ ]64 [ ]77 [ ]91 [ ]94 The presence of a radial tear and the inflammatory reaction it creates may be symptomatic despite the absence of true disk herniation[ ]29 [ ]48 [ ]49 [ ]69

Figure 29 L4-L5 CT diskogram demonstrating a large left posterolateral radial anular tear associated with

a left foraminal and extraforaminal herniaton (same patient as in Figure 28) (Figure Not Available)

Figure 30 Contained posterior L4-L5 and L5-S1 disk herniations in a 57-year-old man demonstrated by diskography The L3-L4 disk is normal

Figure 31 Noncontained L4-L5 disk herniation in a 23-year-old woman Reflux of injected contrast is seen in the anterior epidural space above and below the disk space The L5-S1 disk also demonstrates incomplete anterior and posterior radial anular tears

SUMMARY

The absence of universal nomenclature standardization with respect to the definition of a disk herniation and its different categories especially regarding type and location is still a major problem that will only be overcome when major national or international scientific societies join efforts to support a particular scheme Meanwhile it is important to realize that the two models that are currently most used are based on a different perspective Trying to straddle the two by opposing for instance bulging disk and herniation is doomed to failure because this exercise defies formal logic MR imaging is currently the most accurate noninvasive imaging modality to diagnose a disk herniation and to determine its exact location The determination of some pathoanatomic characteristics of herniated disks (type and composition) may require the use of CT diskography or CT diskography

References

1 Albeck MJ Hilden J Kjaer L et al A controlled comparison of myelography computed tomography and magnetic resonance imaging in clinically suspected lumbar disc herniation Spine 20443-448 1995 Abstract 2 American Academy of Orthopedic Surgeons Glossary on Spinal Terminology Chicago American Academy of Orthopedic Surgeons 1981 3 Andersson GB Weinstein JN Disc herniation [editorial] Spine 211S 1996 Citation 4 Aprill C Bogduk N High-intensity zone A diagnostic sign of painful lumbar disc on magnetic resonance imaging Br J Radiol 65361-369 1992 Abstract 5 Birney TJ White JJ Jr Berens D et al Comparison of MRI and discography in the diagnosis of lumbar degenerative disc disease J Spinal Disord 5417-423 1992 Abstract 6 Bischoff RJ Rodriguez RP Gupta K et al A comparison of computed tomography-myelography magnetic resonance imaging and myelography in the diagnosis of herniated nucleus pulposus and spinal stenosis J Spinal Disord 6289-295 1993 Abstract 7 Bogduk N The innervation of the lumbar spine Spine 8286-293 1983 Abstract 8 Bogduk N Tynan W Wilson AS The nerve supply to the human lumbar intervertebral discs J Anat 13239-56 1981 Abstract 9 Bonneville JF La carte-image des hernies discales lombaires Rachis 2255-257 1990 10 Bonneville JF La topografia simbolica delle ernie discali lombari Riv Neuroradiol 5427-431 1992 11 Bonneville JF Plaidoyer pour une classification par limage des hernies discales lombaires La carte-image Rev Imag Med 2557-560 1990 12 Brant-Zawadzki M Jensen M Spinal nomenclature Spine 20388-390 1995 Abstract

13 Brant-Zawadzki MN Jensen MC Obuchowski N et al Interobserver and intraobserver variability in interpretation of lumbar disc abnormalities A comparison of two nomenclatures Spine 201257-1263 1995 Abstract 14 Breton G Is that a bulging disk a small herniation or a moderate protrusion [editorial] Can Assoc Radiol J 42318 1991 Citation 15 Czervionke LF Lumbar intervertebral disc disease Neuroimaging Clin North Am 3465-485 1993 16 Deyo RA Nonsurgical care of low back pain Neurosurg Clin North Am 2851-862 1991 17 Deyo RA Loeser JD Bigos SJ Herniated lumbar intervertebral disk Ann Intern Med 112598-603 1990 Abstract 18 Dorlands Illustrated Medical Dictionary ed 28 Philadelphia WB Saunders 1994 19 Fardon D Pinkerton S Balderston R et al Terms used for diagnosis by English speaking spine surgeons Spine 18274-277 1993 Citation 20 Fardon DF Herzog RJ Mink JH et al Nomenclature of Lumbar Disc Disorders Contemporary Concepts in Spine Care Rosemont IL North American Spine Society 1995 21 Fardon DF Herzog RJ Mink JH et al Nomenclature of lumbar disc disorders In Garfin S Vaccaro A (eds) Orthopedic Knowledge Update Spine Rosemont IL American Academy of Orthopedic Surgeons 1997 pp A3-A14 22 Forristall RM Marsh HO Pay NT Magnetic resonance imaging and contrast CT of the lumbar spine Comparison of diagnostic methods and correlation with surgical findings Spine 131049-1054 1988 Abstract 23 Fries JW Abodeely DA Vijungco JG et al Computed tomography of herniated and extruded nucleus pulposus J Comput Assist Tomogr 6874-887 1982 Abstract 24 Frymoyer JW Newberg A Pope MH et al Spine radiographs in patients with low-back pain An epidemiological study in men J Bone Joint Surg Am 661048-1055 1984 Abstract 25 Gospodarowicz M Benedet L Hutter RV et al History and international developments in cancer staging Cancer Prev Control 2262-268 1998 Abstract 26 Grenier N Greselle JF Vital JM et al Normal and disrupted lumbar longitudinal ligaments Correlative MR and anatomic study Radiology 171197-205 1989 Abstract 27 Gunzburg R Parkinson R Moore R et al A cadaveric study comparing discography magnetic resonance imaging histology and mechanical behavior of the human lumbar disc Spine 17417-426 1992 Abstract 28 Haughton VM Eldevik OP Magnaes B et al A prospective comparison of computed tomography and myelography in the diagnosis of herniated lumbar disks Radiology 142103-110 1982 Abstract

29 Haughton VM Lim TH An H Intervertebral disk appearance correlated with stiffness of lumbar spinal motion segments AJNR Am J Neuroradiol 201161-1165 1999 Abstract 30 Herzog RJ The radiologic assessment for a lumbar disc herniation Spine 2119S-38S 1996 Abstract 31 Jackson RP Becker GJ Jacobs RR et al The neuroradiographic diagnosis of lumbar herniated nucleus pulposus I A comparison of computed tomography (CT) myelography CT-myelography discography and CT-discography Spine 141356-1361 1989 Abstract 32 Jackson RP Cain JE Jr Jacobs RR et al The neuroradiographic diagnosis of lumbar herniated nucleus pulposus II A comparison of computed tomography (CT) myelography CT-myelography and magnetic resonance imaging Spine 141362-1367 1989 Abstract 33 Jarvik JG Haynor DR Koepsell TD et al Interreader reliability for a new classification of lumbar disk disease Acad Radiol 3537-544 1996 Abstract 34 Jensen MC Brant-Zawadzki MN Obuchowski N et al Magnetic resonance imaging of the lumbar spine in people without back pain N Engl J Med 33169-73 1994 Abstract 35 Kent DL Haynor DR Larson EB et al Diagnosis of lumbar spinal stenosis in adults A meta-analysis of the accuracy of CT MR and myelography AJR Am J Roentgenol 1581135-1144 1992 Abstract 36 Kieffer SA Sherry RG Wellenstein DE et al Bulging lumbar intervertebral disk Myelographic differentiation from herniated disk with nerve root compression AJR Am J Roentgenol 138709-716 1982 Abstract 37 Kieffer SA Stadlan EM Mohandas A et al Discographic-anatomical correlation of developmental changes with age in the intervertebral disc Acta Radiol 9733-739 1969 38 Kim KY Kim YT Lee CS et al MRI classification of lumbar herniated intervertebral disc Orthopedics 15493-497 1992 Abstract 39 Kornberg M Rechtine GR Dupuy TE Computed tomography in the diagnosis of a herniated disk at the L5-S1 level Spine 9433-436 1984 Abstract 40 Kramer MS Clinical Epidemiology and Biostatistics New York Springer-Verlag 1988 41 Landis JR Koch GG The measurement of observer agreement agreement for categorical data Biometrics 33159-174 1977 Abstract 42 Laredo JD Bossard P Vuillemin-Bodaghi Formes anatomo-radiologiques des hernies discales In Morvan G Deburge A Bard H et al (eds) Le Rachis Lombaire Degeneratif Montpellier Sauramps Medical 1998 pp 37-49 43 Lee SH Coleman PE Hahn FJ Magnetic resonance imaging of degenerative disk disease of the spine Radiol Clin North Am 26949-964 1988 Abstract 44 Linson MA Crowe CH Comparison of magnetic resonance imaging and lumbar discography in the diagnosis of disc degeneration Clin Orthop 160-163 1990

45 Marchand F Ahmed AM Investigation of the laminate structure of lumbar disc anulus fibrosus Spine 15402-410 1990 Abstract 46 Masaryk TJ Ross JS Modic MT et al High-resolution MR imaging of sequestered lumbar intervertebral disks AJR Am J Roentgenol 1501155-1162 1988 Abstract 47 Milette PC The proper terminology for reporting lumbar intervertebral disk disorders AJNR Am J Neuroradiol 181859-1866 1997 Citation 48 Milette PC Fontaine S Lepanto L et al Differentiating lumbar disc protrusions disk bulges and discs with normal contour but abnormal signal intensity Magnetic resonance imaging with discographic correlations Spine 2444-53 1999 Abstract 49 Milette PC Fontaine S Lepanto L et al Radiating pain to the lower extremities caused by lumbar disk rupture without spinal nerve root involvement AJNR Am J Neuroradiol 161605-1613 1995 Abstract 50 Milette PC Melancon D A reappraisal of lumbar discography Can Assoc Radiol J 33176-182 1982 51 Milette PC Melancon D Dupuis PR et al A simplified terminology for abnormalities of the lumbar disk Can Assoc Radiol J 42319-325 1991 Abstract 52 Milette PC Raymond J Fontaine S Comparison of high-resolution computed tomography with discography in the evaluation of lumbar disc herniations Spine 15525-533 1990 Abstract 53 Mink JH Deutsch AL Goldstein TB et al Spinal imaging and intervention 1998 Phys Med Rehabil Clin North Am 9343-380 1998 54 Mixter WJ Barr JS Rupture of the intervertebral disc with involvement of the spinal canal N Engl J Med 211210-234 1934 55 Modic MT Masaryk TJ Ross JS et al Imaging of degenerative disk disease Radiology 168177-186 1988 Citation 56 Modic MT Ross JS Obuchowski NA et al Contrast-enhanced MR imaging in acute lumbar radiculopathy A pilot study of the natural history Radiology 195429-435 1995 Abstract 57 Modic MT Steinberg PM Ross JS et al Degenerative disk disease Assessment of changes in vertebral body marrow with MR imaging Radiology 166193-199 1988 58 Morvan G Mathieu P Les stenoses laterales In Morvan G Deburge A Bard H et al (eds) Le Rachis Lombaire Degeneratif Montpellier Sauramps Medical 1998 pp 315-324 59 Murray RO Skeletal trauma Regional In Sutton D (ed) Textbook of Radiology and Imaging ed 3 New York Churchill Livingstone 1980 pp 210-231 60 Nachemson A Lumbar disc herniation Conclusions Acta Orthop Scand 64(suppl 251)49 1993 Citation

61 Nathan H Osteophytes of the vertebral column An anatomical study of their development according to age race and sex with consideration as to their etiology and significance J Bone Joint Surg Am 44243-268 1962 62 Nygaard OP Mellgren SI Osterud B The inflammatory properties of contained and noncontained lumbar disc herniations Spine 222584-2488 1997 Abstract 63 Ohshima H Hirano N Osada R et al Morphologic variation of lumbar posterior longitudinal ligament and the modality of disc herniation Spine 182408-2411 1993 Abstract 64 Osti OL Fraser RD MRI and discography of annular tears and intervertebral disc degeneration A prospective clinical comparison J Bone Joint Surg Br 74431-435 1992 Abstract 65 Palmgren T Gronblad M Virri J et al Immunohistochemical demonstration of sensory and autonomic nerve terminals in herniated lumbar disc tissue Spine 211301-1306 1996 Abstract 66 Resnick D Niwayama G Degenerative disease of the spine In Resnick D (ed) Diagnosis of Bone and Joint Disorders ed 3 Philadelphia WB Saunders 1995 pp 1372-1462 67 Resnick D Niwayama G Intravertebral disk herniations Cartilaginous (Schmorls) nodes Radiology 12657-65 1978 Abstract 68 Ross JS Modic MT Masaryk TJ Tears of the anulus fibrosus Assessment with Gd-DTPA-enhanced MR imaging AJR Am J Roentgenol 154159-162 1990 Abstract 69 Saal JS The role of inflammation in lumbar pain Spine 201821-1827 1995 Abstract 70 Sachs BL Vanharanta H Spivey MA et al Dallas discogram description A new classification of CTdiscography in low-back disorders Spine 12287-294 1987 Abstract 71 Sauser DD Goldman AB Kaye JJ Discogenic vertebral sclerosis J Can Assoc Radiol 2944-50 1978 Abstract 72 Schellhas KP Pollei SR Gundry CR et al Lumbar disc high-intensity zone Correlation of magnetic resonance imaging and discography Spine 2179-86 1996 Abstract 73 Schellinger D Manz HJ Vidic B et al Disk fragment migration Radiology 175831-836 1990 Abstract 74 Schipper J Kardaun JW Braakman R et al Lumbar disk herniation Diagnosis with CT or myelography Radiology 165227-231 1987 Abstract 75 Schmorl G Junghanns H The Human Spine in Health and Disease ed 2 New York Grune and Stratton 1971 76 Silverman CS Lenchik L Shimkin PM et al The value of MR in differentiating subligamentous from supraligamentous lumbar disk herniations AJNR Am J Neuroradiol 16571-579 1995 Abstract 77 Simmons JW Emery SF McMillin JN et al Awake discography A comparison study with magnetic

resonance imaging Spine 16S216-221 1991 Abstract 78 Smyth MJ Wright V Sciatica and the intervertebral disc J Bone Joint Surg Am 401401-1418 1958 79 Taveras JM Radiologic aspects of low back pain and sciatic syndromes [editorial] AJNR Am J Neuroradiol 9351-358 1989 80 Tehranzadeh J Discography 2000 Radiol Clin North Am 36463-495 1998 Full Text 81 Thelander U Fagerlund M Friberg S et al Describing the size of lumbar disc herniations using computed tomography A comparison of different size index calculations and their relation to sciatica Spine 191979-1984 1994 Abstract 82 Thornbury JR Fryback DG Turski PA et al Disk-caused nerve compression in patients with acute low-back pain Diagnosis with MR CT myelography and plain CT Radiology 186731-738 1993 Abstract 83 Twomey L Taylor J Age changes in lumbar intervertebral discs Acta Orthop Scand 56496-499 1985 Abstract 84 Twomey LT Taylor JR Age changes in lumbar vertebrae and intervertebral discs Clin Orthop 22497-104 1987 85 Williams AL CT diagnosis of degenerative disc disease The bulging annulus Radiol Clin North Am 21289-300 1983 Abstract 86 Williams AL Haughton VM Meyer GA et al Computed tomographic appearance of the bulging annulus Radiology 142403-408 1982 Abstract 87 Williams AL Haughton VM Syvertsen A Computed tomography in the diagnosis of herniated nucleus pulposus Radiology 13595-99 1980 Abstract 88 Wiltse LL Berger PE McCulloch JA A system for reporting the size and location of lesions in the spine Spine 221534-1537 1997 Abstract 89 Wiltse LL Fonseca AS Amster J et al Relationship of the dura Hofmanns ligaments Batsons plexus and a fibrovascular membrane lying on the posterior surface of the vertebral bodies and attaching to the deep layer of the posterior longitudinal ligament An anatomical radiologic and clinical study Spine 181030-1043 1993 Abstract 90 Yamashita K Hiroshima K Kurata A Gadolinium-DTPA-enhanced magnetic resonance imaging of a sequestered lumbar intervertebral disc and its correlation with pathologic findings Spine 19479-482 1994 Abstract 91 Yu SW Haughton VM Sether LA et al Comparison of MR and diskography in detecting radial tears of the anulus A postmortem study AJNR Am J Neuroradiol 101077-1081 1989 Abstract 92 Yu SW Sether LA Ho PS et al Tears of the anulus fibrosus Correlation between MR and pathologic findings in cadavers AJNR Am J Neuroradiol 9367-370 1988 Abstract

93 Yussen PS Swartz JD The acute lumbar disc herniation Imaging diagnosis Semin Ultrasound CT MR 14389-398 1993 Abstract 94 Zucherman J Derby R Hsu K et al Normal magnetic resonance imaging with abnormal discography Spine 131355-1359 1988 Abstract

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  • CLASSIFICATION DIAGNOSTIC IMAGING AND IMAGING CHARACTERIZATION OF A LUMBAR HERNIATED DISK
    • IMAGING OF LOW BACK PAIN I
      • CLASSIFICATION DIAGNOSTIC IMAGING AND IMAGING CHARACTERIZATION OF A LUMBAR HERNIATED DISK
        • DEFINITION OF A DISK HERNIATION
        • CLASSIFICATION OF A HERNIATED LUMBAR DISK
          • Main Categories of Noninfectious Disk Abnormalities
          • Further Qualifying the Displaced Disk Material Beyond the Disk Space
            • DIAGNOSTIC IMAGING AND CHARACTERIZATION OF A HERNIATED LUMBAR DISK
              • Conventional Radiographs
              • Myelography
              • CT
              • CT Myelography
              • MR Imaging
              • Diskography and CT Diskography
                • SUMMARY
                  • References
Page 26: CLASSIFICATION, DIAGNOSTIC IMAGING, AND IMAGING ... · PDF fileclassification, diagnostic imaging, and imaging characterization of a lumbar herniated disk ... classification, diagnostic

be detected but associated vertebral body bone marrow changes are typically seen and are helpful in differentiating acute from chronic processes[ ]57 The occasional presence of a high-intensity zone in the herniated material with an occasionally enhancing border after contrast injection is probably caused by a mixture of displaced nuclear material acute and subacute inflammatory tissue and neovascularized reactive tissue[ ]4 [ ]48 [ ]72 Contradictory reports have been published regarding the accuracy of MR imaging to differentiate subligamentous from transligamentous herniations[ ]26 [ ]38 [ ]73 [ ]76 Understanding the anatomy of the PLLC is helpful to make the distinction (Fig 28) (Figure Not Available) Masaryk et al[ ]46 have suggested that MR imaging is accurate to distinguish sequestered disks from other forms of lumbar disk herniations but most observers find this distinction difficult to establish[ ]42

Figure 27 A Left L4-L5 foraminal herniation well seen on an intermediate-weighted left parasagittal MR section (arrow) in a 47-year-old man B The lesion is much less obvious on intermediate-weighted (left) and T2-weighted (right) axial sections and was in fact more conspicuous on the corresponding CT scan section

Figure 28 (Figure Not Available) A Subligamentous disk herniation Left T1-weighted image demonstrating displaced disk material with a smooth outline imposed by the demarcation of the anterior epidural space (AES) by the lateral membrane of the PLLC Right Correlative drawing B Transligamentous disk herniation Left T1-weighted image of a large disk herniation (cervical in this case) which has ruptured through the posterior confines of the AES Penetration of the right lateral membrane can be observed (arrow) and the disk fragment contour is serrated Right Correlative drawing (From Schellinger D Manz HJ Vidic B et al Disk fragment migration Radiology 175831-836 1990 with permission)

Diskography and CT Diskography

During 30 years (1950 to 1980) when myelography was the only available imaging technique to demonstrate lumbar disk herniations diskography was an invasive but efficient way to demonstrate posterior central L5-S1 herniations and other large herniations (other than posterior central and paramedial) that could not be detected by myelography[ ]50 These herniations are now usually well demonstrated by CT and MR imaging Comparing the accuracy of five imaging modalities (excluding MR imaging) for the diagnosis of lumbar disk herniation Jackson et al[ ]31 found that CT diskography (Fig 29) was the most accurate test (87) compared with 77 for CT myelography 74 for CT 70 for myelography 64 for pain reproduction during diskography and 58 for diskography without CT Disk injection reproduced the patients clinical pain pattern in only 36 of herniated disks This clinical test isolated from the images had high specificity (89) but low sensitivity (43) for the diagnosis of disk herniation The reported low sensitivity of diskography images (unassociated with CT) to diagnose disk herniation is to be expected the purpose of the intradiskal injection being primarily the demonstration of an anular tear the contrast leaking through the tear only occasionally delineates an extruded fragment When a disk herniation has been diagnosed by other imaging modalities diskography allows to determine if the herniation is contained or noncontained (Figs 30 and 31) this information may have clinical relevance[ ]62 It also allows to establish if the displaced disk material is communicating or not with the parent disk and establishes the likelihood that it is sequestered or not There always remains a possibility that the contrast injected under pressure may reach a disk fragment that is nevertheless sequestered by leaking through the associated anular tear CT diskography also allows assessment in most cases of the integrity of the PLLC[ ]89 The superior sensitivity of diskography over MR imaging to demonstrate anular tears has been well established[ ]27 [ ]44 [ ]48 [ ]64 [ ]77 [ ]91 [ ]94 The presence of a radial tear and the inflammatory reaction it creates may be symptomatic despite the absence of true disk herniation[ ]29 [ ]48 [ ]49 [ ]69

Figure 29 L4-L5 CT diskogram demonstrating a large left posterolateral radial anular tear associated with

a left foraminal and extraforaminal herniaton (same patient as in Figure 28) (Figure Not Available)

Figure 30 Contained posterior L4-L5 and L5-S1 disk herniations in a 57-year-old man demonstrated by diskography The L3-L4 disk is normal

Figure 31 Noncontained L4-L5 disk herniation in a 23-year-old woman Reflux of injected contrast is seen in the anterior epidural space above and below the disk space The L5-S1 disk also demonstrates incomplete anterior and posterior radial anular tears

SUMMARY

The absence of universal nomenclature standardization with respect to the definition of a disk herniation and its different categories especially regarding type and location is still a major problem that will only be overcome when major national or international scientific societies join efforts to support a particular scheme Meanwhile it is important to realize that the two models that are currently most used are based on a different perspective Trying to straddle the two by opposing for instance bulging disk and herniation is doomed to failure because this exercise defies formal logic MR imaging is currently the most accurate noninvasive imaging modality to diagnose a disk herniation and to determine its exact location The determination of some pathoanatomic characteristics of herniated disks (type and composition) may require the use of CT diskography or CT diskography

References

1 Albeck MJ Hilden J Kjaer L et al A controlled comparison of myelography computed tomography and magnetic resonance imaging in clinically suspected lumbar disc herniation Spine 20443-448 1995 Abstract 2 American Academy of Orthopedic Surgeons Glossary on Spinal Terminology Chicago American Academy of Orthopedic Surgeons 1981 3 Andersson GB Weinstein JN Disc herniation [editorial] Spine 211S 1996 Citation 4 Aprill C Bogduk N High-intensity zone A diagnostic sign of painful lumbar disc on magnetic resonance imaging Br J Radiol 65361-369 1992 Abstract 5 Birney TJ White JJ Jr Berens D et al Comparison of MRI and discography in the diagnosis of lumbar degenerative disc disease J Spinal Disord 5417-423 1992 Abstract 6 Bischoff RJ Rodriguez RP Gupta K et al A comparison of computed tomography-myelography magnetic resonance imaging and myelography in the diagnosis of herniated nucleus pulposus and spinal stenosis J Spinal Disord 6289-295 1993 Abstract 7 Bogduk N The innervation of the lumbar spine Spine 8286-293 1983 Abstract 8 Bogduk N Tynan W Wilson AS The nerve supply to the human lumbar intervertebral discs J Anat 13239-56 1981 Abstract 9 Bonneville JF La carte-image des hernies discales lombaires Rachis 2255-257 1990 10 Bonneville JF La topografia simbolica delle ernie discali lombari Riv Neuroradiol 5427-431 1992 11 Bonneville JF Plaidoyer pour une classification par limage des hernies discales lombaires La carte-image Rev Imag Med 2557-560 1990 12 Brant-Zawadzki M Jensen M Spinal nomenclature Spine 20388-390 1995 Abstract

13 Brant-Zawadzki MN Jensen MC Obuchowski N et al Interobserver and intraobserver variability in interpretation of lumbar disc abnormalities A comparison of two nomenclatures Spine 201257-1263 1995 Abstract 14 Breton G Is that a bulging disk a small herniation or a moderate protrusion [editorial] Can Assoc Radiol J 42318 1991 Citation 15 Czervionke LF Lumbar intervertebral disc disease Neuroimaging Clin North Am 3465-485 1993 16 Deyo RA Nonsurgical care of low back pain Neurosurg Clin North Am 2851-862 1991 17 Deyo RA Loeser JD Bigos SJ Herniated lumbar intervertebral disk Ann Intern Med 112598-603 1990 Abstract 18 Dorlands Illustrated Medical Dictionary ed 28 Philadelphia WB Saunders 1994 19 Fardon D Pinkerton S Balderston R et al Terms used for diagnosis by English speaking spine surgeons Spine 18274-277 1993 Citation 20 Fardon DF Herzog RJ Mink JH et al Nomenclature of Lumbar Disc Disorders Contemporary Concepts in Spine Care Rosemont IL North American Spine Society 1995 21 Fardon DF Herzog RJ Mink JH et al Nomenclature of lumbar disc disorders In Garfin S Vaccaro A (eds) Orthopedic Knowledge Update Spine Rosemont IL American Academy of Orthopedic Surgeons 1997 pp A3-A14 22 Forristall RM Marsh HO Pay NT Magnetic resonance imaging and contrast CT of the lumbar spine Comparison of diagnostic methods and correlation with surgical findings Spine 131049-1054 1988 Abstract 23 Fries JW Abodeely DA Vijungco JG et al Computed tomography of herniated and extruded nucleus pulposus J Comput Assist Tomogr 6874-887 1982 Abstract 24 Frymoyer JW Newberg A Pope MH et al Spine radiographs in patients with low-back pain An epidemiological study in men J Bone Joint Surg Am 661048-1055 1984 Abstract 25 Gospodarowicz M Benedet L Hutter RV et al History and international developments in cancer staging Cancer Prev Control 2262-268 1998 Abstract 26 Grenier N Greselle JF Vital JM et al Normal and disrupted lumbar longitudinal ligaments Correlative MR and anatomic study Radiology 171197-205 1989 Abstract 27 Gunzburg R Parkinson R Moore R et al A cadaveric study comparing discography magnetic resonance imaging histology and mechanical behavior of the human lumbar disc Spine 17417-426 1992 Abstract 28 Haughton VM Eldevik OP Magnaes B et al A prospective comparison of computed tomography and myelography in the diagnosis of herniated lumbar disks Radiology 142103-110 1982 Abstract

29 Haughton VM Lim TH An H Intervertebral disk appearance correlated with stiffness of lumbar spinal motion segments AJNR Am J Neuroradiol 201161-1165 1999 Abstract 30 Herzog RJ The radiologic assessment for a lumbar disc herniation Spine 2119S-38S 1996 Abstract 31 Jackson RP Becker GJ Jacobs RR et al The neuroradiographic diagnosis of lumbar herniated nucleus pulposus I A comparison of computed tomography (CT) myelography CT-myelography discography and CT-discography Spine 141356-1361 1989 Abstract 32 Jackson RP Cain JE Jr Jacobs RR et al The neuroradiographic diagnosis of lumbar herniated nucleus pulposus II A comparison of computed tomography (CT) myelography CT-myelography and magnetic resonance imaging Spine 141362-1367 1989 Abstract 33 Jarvik JG Haynor DR Koepsell TD et al Interreader reliability for a new classification of lumbar disk disease Acad Radiol 3537-544 1996 Abstract 34 Jensen MC Brant-Zawadzki MN Obuchowski N et al Magnetic resonance imaging of the lumbar spine in people without back pain N Engl J Med 33169-73 1994 Abstract 35 Kent DL Haynor DR Larson EB et al Diagnosis of lumbar spinal stenosis in adults A meta-analysis of the accuracy of CT MR and myelography AJR Am J Roentgenol 1581135-1144 1992 Abstract 36 Kieffer SA Sherry RG Wellenstein DE et al Bulging lumbar intervertebral disk Myelographic differentiation from herniated disk with nerve root compression AJR Am J Roentgenol 138709-716 1982 Abstract 37 Kieffer SA Stadlan EM Mohandas A et al Discographic-anatomical correlation of developmental changes with age in the intervertebral disc Acta Radiol 9733-739 1969 38 Kim KY Kim YT Lee CS et al MRI classification of lumbar herniated intervertebral disc Orthopedics 15493-497 1992 Abstract 39 Kornberg M Rechtine GR Dupuy TE Computed tomography in the diagnosis of a herniated disk at the L5-S1 level Spine 9433-436 1984 Abstract 40 Kramer MS Clinical Epidemiology and Biostatistics New York Springer-Verlag 1988 41 Landis JR Koch GG The measurement of observer agreement agreement for categorical data Biometrics 33159-174 1977 Abstract 42 Laredo JD Bossard P Vuillemin-Bodaghi Formes anatomo-radiologiques des hernies discales In Morvan G Deburge A Bard H et al (eds) Le Rachis Lombaire Degeneratif Montpellier Sauramps Medical 1998 pp 37-49 43 Lee SH Coleman PE Hahn FJ Magnetic resonance imaging of degenerative disk disease of the spine Radiol Clin North Am 26949-964 1988 Abstract 44 Linson MA Crowe CH Comparison of magnetic resonance imaging and lumbar discography in the diagnosis of disc degeneration Clin Orthop 160-163 1990

45 Marchand F Ahmed AM Investigation of the laminate structure of lumbar disc anulus fibrosus Spine 15402-410 1990 Abstract 46 Masaryk TJ Ross JS Modic MT et al High-resolution MR imaging of sequestered lumbar intervertebral disks AJR Am J Roentgenol 1501155-1162 1988 Abstract 47 Milette PC The proper terminology for reporting lumbar intervertebral disk disorders AJNR Am J Neuroradiol 181859-1866 1997 Citation 48 Milette PC Fontaine S Lepanto L et al Differentiating lumbar disc protrusions disk bulges and discs with normal contour but abnormal signal intensity Magnetic resonance imaging with discographic correlations Spine 2444-53 1999 Abstract 49 Milette PC Fontaine S Lepanto L et al Radiating pain to the lower extremities caused by lumbar disk rupture without spinal nerve root involvement AJNR Am J Neuroradiol 161605-1613 1995 Abstract 50 Milette PC Melancon D A reappraisal of lumbar discography Can Assoc Radiol J 33176-182 1982 51 Milette PC Melancon D Dupuis PR et al A simplified terminology for abnormalities of the lumbar disk Can Assoc Radiol J 42319-325 1991 Abstract 52 Milette PC Raymond J Fontaine S Comparison of high-resolution computed tomography with discography in the evaluation of lumbar disc herniations Spine 15525-533 1990 Abstract 53 Mink JH Deutsch AL Goldstein TB et al Spinal imaging and intervention 1998 Phys Med Rehabil Clin North Am 9343-380 1998 54 Mixter WJ Barr JS Rupture of the intervertebral disc with involvement of the spinal canal N Engl J Med 211210-234 1934 55 Modic MT Masaryk TJ Ross JS et al Imaging of degenerative disk disease Radiology 168177-186 1988 Citation 56 Modic MT Ross JS Obuchowski NA et al Contrast-enhanced MR imaging in acute lumbar radiculopathy A pilot study of the natural history Radiology 195429-435 1995 Abstract 57 Modic MT Steinberg PM Ross JS et al Degenerative disk disease Assessment of changes in vertebral body marrow with MR imaging Radiology 166193-199 1988 58 Morvan G Mathieu P Les stenoses laterales In Morvan G Deburge A Bard H et al (eds) Le Rachis Lombaire Degeneratif Montpellier Sauramps Medical 1998 pp 315-324 59 Murray RO Skeletal trauma Regional In Sutton D (ed) Textbook of Radiology and Imaging ed 3 New York Churchill Livingstone 1980 pp 210-231 60 Nachemson A Lumbar disc herniation Conclusions Acta Orthop Scand 64(suppl 251)49 1993 Citation

61 Nathan H Osteophytes of the vertebral column An anatomical study of their development according to age race and sex with consideration as to their etiology and significance J Bone Joint Surg Am 44243-268 1962 62 Nygaard OP Mellgren SI Osterud B The inflammatory properties of contained and noncontained lumbar disc herniations Spine 222584-2488 1997 Abstract 63 Ohshima H Hirano N Osada R et al Morphologic variation of lumbar posterior longitudinal ligament and the modality of disc herniation Spine 182408-2411 1993 Abstract 64 Osti OL Fraser RD MRI and discography of annular tears and intervertebral disc degeneration A prospective clinical comparison J Bone Joint Surg Br 74431-435 1992 Abstract 65 Palmgren T Gronblad M Virri J et al Immunohistochemical demonstration of sensory and autonomic nerve terminals in herniated lumbar disc tissue Spine 211301-1306 1996 Abstract 66 Resnick D Niwayama G Degenerative disease of the spine In Resnick D (ed) Diagnosis of Bone and Joint Disorders ed 3 Philadelphia WB Saunders 1995 pp 1372-1462 67 Resnick D Niwayama G Intravertebral disk herniations Cartilaginous (Schmorls) nodes Radiology 12657-65 1978 Abstract 68 Ross JS Modic MT Masaryk TJ Tears of the anulus fibrosus Assessment with Gd-DTPA-enhanced MR imaging AJR Am J Roentgenol 154159-162 1990 Abstract 69 Saal JS The role of inflammation in lumbar pain Spine 201821-1827 1995 Abstract 70 Sachs BL Vanharanta H Spivey MA et al Dallas discogram description A new classification of CTdiscography in low-back disorders Spine 12287-294 1987 Abstract 71 Sauser DD Goldman AB Kaye JJ Discogenic vertebral sclerosis J Can Assoc Radiol 2944-50 1978 Abstract 72 Schellhas KP Pollei SR Gundry CR et al Lumbar disc high-intensity zone Correlation of magnetic resonance imaging and discography Spine 2179-86 1996 Abstract 73 Schellinger D Manz HJ Vidic B et al Disk fragment migration Radiology 175831-836 1990 Abstract 74 Schipper J Kardaun JW Braakman R et al Lumbar disk herniation Diagnosis with CT or myelography Radiology 165227-231 1987 Abstract 75 Schmorl G Junghanns H The Human Spine in Health and Disease ed 2 New York Grune and Stratton 1971 76 Silverman CS Lenchik L Shimkin PM et al The value of MR in differentiating subligamentous from supraligamentous lumbar disk herniations AJNR Am J Neuroradiol 16571-579 1995 Abstract 77 Simmons JW Emery SF McMillin JN et al Awake discography A comparison study with magnetic

resonance imaging Spine 16S216-221 1991 Abstract 78 Smyth MJ Wright V Sciatica and the intervertebral disc J Bone Joint Surg Am 401401-1418 1958 79 Taveras JM Radiologic aspects of low back pain and sciatic syndromes [editorial] AJNR Am J Neuroradiol 9351-358 1989 80 Tehranzadeh J Discography 2000 Radiol Clin North Am 36463-495 1998 Full Text 81 Thelander U Fagerlund M Friberg S et al Describing the size of lumbar disc herniations using computed tomography A comparison of different size index calculations and their relation to sciatica Spine 191979-1984 1994 Abstract 82 Thornbury JR Fryback DG Turski PA et al Disk-caused nerve compression in patients with acute low-back pain Diagnosis with MR CT myelography and plain CT Radiology 186731-738 1993 Abstract 83 Twomey L Taylor J Age changes in lumbar intervertebral discs Acta Orthop Scand 56496-499 1985 Abstract 84 Twomey LT Taylor JR Age changes in lumbar vertebrae and intervertebral discs Clin Orthop 22497-104 1987 85 Williams AL CT diagnosis of degenerative disc disease The bulging annulus Radiol Clin North Am 21289-300 1983 Abstract 86 Williams AL Haughton VM Meyer GA et al Computed tomographic appearance of the bulging annulus Radiology 142403-408 1982 Abstract 87 Williams AL Haughton VM Syvertsen A Computed tomography in the diagnosis of herniated nucleus pulposus Radiology 13595-99 1980 Abstract 88 Wiltse LL Berger PE McCulloch JA A system for reporting the size and location of lesions in the spine Spine 221534-1537 1997 Abstract 89 Wiltse LL Fonseca AS Amster J et al Relationship of the dura Hofmanns ligaments Batsons plexus and a fibrovascular membrane lying on the posterior surface of the vertebral bodies and attaching to the deep layer of the posterior longitudinal ligament An anatomical radiologic and clinical study Spine 181030-1043 1993 Abstract 90 Yamashita K Hiroshima K Kurata A Gadolinium-DTPA-enhanced magnetic resonance imaging of a sequestered lumbar intervertebral disc and its correlation with pathologic findings Spine 19479-482 1994 Abstract 91 Yu SW Haughton VM Sether LA et al Comparison of MR and diskography in detecting radial tears of the anulus A postmortem study AJNR Am J Neuroradiol 101077-1081 1989 Abstract 92 Yu SW Sether LA Ho PS et al Tears of the anulus fibrosus Correlation between MR and pathologic findings in cadavers AJNR Am J Neuroradiol 9367-370 1988 Abstract

93 Yussen PS Swartz JD The acute lumbar disc herniation Imaging diagnosis Semin Ultrasound CT MR 14389-398 1993 Abstract 94 Zucherman J Derby R Hsu K et al Normal magnetic resonance imaging with abnormal discography Spine 131355-1359 1988 Abstract

Copyright copy 2008 Elsevier Inc All rights reserved - wwwmdconsultcom

Bookmark URL dasjournalview0N11535915ja=198094ampPAGE=1htmlampissn=0033-8389ampsource=MI

  • CLASSIFICATION DIAGNOSTIC IMAGING AND IMAGING CHARACTERIZATION OF A LUMBAR HERNIATED DISK
    • IMAGING OF LOW BACK PAIN I
      • CLASSIFICATION DIAGNOSTIC IMAGING AND IMAGING CHARACTERIZATION OF A LUMBAR HERNIATED DISK
        • DEFINITION OF A DISK HERNIATION
        • CLASSIFICATION OF A HERNIATED LUMBAR DISK
          • Main Categories of Noninfectious Disk Abnormalities
          • Further Qualifying the Displaced Disk Material Beyond the Disk Space
            • DIAGNOSTIC IMAGING AND CHARACTERIZATION OF A HERNIATED LUMBAR DISK
              • Conventional Radiographs
              • Myelography
              • CT
              • CT Myelography
              • MR Imaging
              • Diskography and CT Diskography
                • SUMMARY
                  • References
Page 27: CLASSIFICATION, DIAGNOSTIC IMAGING, AND IMAGING ... · PDF fileclassification, diagnostic imaging, and imaging characterization of a lumbar herniated disk ... classification, diagnostic

Diskography and CT Diskography

During 30 years (1950 to 1980) when myelography was the only available imaging technique to demonstrate lumbar disk herniations diskography was an invasive but efficient way to demonstrate posterior central L5-S1 herniations and other large herniations (other than posterior central and paramedial) that could not be detected by myelography[ ]50 These herniations are now usually well demonstrated by CT and MR imaging Comparing the accuracy of five imaging modalities (excluding MR imaging) for the diagnosis of lumbar disk herniation Jackson et al[ ]31 found that CT diskography (Fig 29) was the most accurate test (87) compared with 77 for CT myelography 74 for CT 70 for myelography 64 for pain reproduction during diskography and 58 for diskography without CT Disk injection reproduced the patients clinical pain pattern in only 36 of herniated disks This clinical test isolated from the images had high specificity (89) but low sensitivity (43) for the diagnosis of disk herniation The reported low sensitivity of diskography images (unassociated with CT) to diagnose disk herniation is to be expected the purpose of the intradiskal injection being primarily the demonstration of an anular tear the contrast leaking through the tear only occasionally delineates an extruded fragment When a disk herniation has been diagnosed by other imaging modalities diskography allows to determine if the herniation is contained or noncontained (Figs 30 and 31) this information may have clinical relevance[ ]62 It also allows to establish if the displaced disk material is communicating or not with the parent disk and establishes the likelihood that it is sequestered or not There always remains a possibility that the contrast injected under pressure may reach a disk fragment that is nevertheless sequestered by leaking through the associated anular tear CT diskography also allows assessment in most cases of the integrity of the PLLC[ ]89 The superior sensitivity of diskography over MR imaging to demonstrate anular tears has been well established[ ]27 [ ]44 [ ]48 [ ]64 [ ]77 [ ]91 [ ]94 The presence of a radial tear and the inflammatory reaction it creates may be symptomatic despite the absence of true disk herniation[ ]29 [ ]48 [ ]49 [ ]69

Figure 29 L4-L5 CT diskogram demonstrating a large left posterolateral radial anular tear associated with

a left foraminal and extraforaminal herniaton (same patient as in Figure 28) (Figure Not Available)

Figure 30 Contained posterior L4-L5 and L5-S1 disk herniations in a 57-year-old man demonstrated by diskography The L3-L4 disk is normal

Figure 31 Noncontained L4-L5 disk herniation in a 23-year-old woman Reflux of injected contrast is seen in the anterior epidural space above and below the disk space The L5-S1 disk also demonstrates incomplete anterior and posterior radial anular tears

SUMMARY

The absence of universal nomenclature standardization with respect to the definition of a disk herniation and its different categories especially regarding type and location is still a major problem that will only be overcome when major national or international scientific societies join efforts to support a particular scheme Meanwhile it is important to realize that the two models that are currently most used are based on a different perspective Trying to straddle the two by opposing for instance bulging disk and herniation is doomed to failure because this exercise defies formal logic MR imaging is currently the most accurate noninvasive imaging modality to diagnose a disk herniation and to determine its exact location The determination of some pathoanatomic characteristics of herniated disks (type and composition) may require the use of CT diskography or CT diskography

References

1 Albeck MJ Hilden J Kjaer L et al A controlled comparison of myelography computed tomography and magnetic resonance imaging in clinically suspected lumbar disc herniation Spine 20443-448 1995 Abstract 2 American Academy of Orthopedic Surgeons Glossary on Spinal Terminology Chicago American Academy of Orthopedic Surgeons 1981 3 Andersson GB Weinstein JN Disc herniation [editorial] Spine 211S 1996 Citation 4 Aprill C Bogduk N High-intensity zone A diagnostic sign of painful lumbar disc on magnetic resonance imaging Br J Radiol 65361-369 1992 Abstract 5 Birney TJ White JJ Jr Berens D et al Comparison of MRI and discography in the diagnosis of lumbar degenerative disc disease J Spinal Disord 5417-423 1992 Abstract 6 Bischoff RJ Rodriguez RP Gupta K et al A comparison of computed tomography-myelography magnetic resonance imaging and myelography in the diagnosis of herniated nucleus pulposus and spinal stenosis J Spinal Disord 6289-295 1993 Abstract 7 Bogduk N The innervation of the lumbar spine Spine 8286-293 1983 Abstract 8 Bogduk N Tynan W Wilson AS The nerve supply to the human lumbar intervertebral discs J Anat 13239-56 1981 Abstract 9 Bonneville JF La carte-image des hernies discales lombaires Rachis 2255-257 1990 10 Bonneville JF La topografia simbolica delle ernie discali lombari Riv Neuroradiol 5427-431 1992 11 Bonneville JF Plaidoyer pour une classification par limage des hernies discales lombaires La carte-image Rev Imag Med 2557-560 1990 12 Brant-Zawadzki M Jensen M Spinal nomenclature Spine 20388-390 1995 Abstract

13 Brant-Zawadzki MN Jensen MC Obuchowski N et al Interobserver and intraobserver variability in interpretation of lumbar disc abnormalities A comparison of two nomenclatures Spine 201257-1263 1995 Abstract 14 Breton G Is that a bulging disk a small herniation or a moderate protrusion [editorial] Can Assoc Radiol J 42318 1991 Citation 15 Czervionke LF Lumbar intervertebral disc disease Neuroimaging Clin North Am 3465-485 1993 16 Deyo RA Nonsurgical care of low back pain Neurosurg Clin North Am 2851-862 1991 17 Deyo RA Loeser JD Bigos SJ Herniated lumbar intervertebral disk Ann Intern Med 112598-603 1990 Abstract 18 Dorlands Illustrated Medical Dictionary ed 28 Philadelphia WB Saunders 1994 19 Fardon D Pinkerton S Balderston R et al Terms used for diagnosis by English speaking spine surgeons Spine 18274-277 1993 Citation 20 Fardon DF Herzog RJ Mink JH et al Nomenclature of Lumbar Disc Disorders Contemporary Concepts in Spine Care Rosemont IL North American Spine Society 1995 21 Fardon DF Herzog RJ Mink JH et al Nomenclature of lumbar disc disorders In Garfin S Vaccaro A (eds) Orthopedic Knowledge Update Spine Rosemont IL American Academy of Orthopedic Surgeons 1997 pp A3-A14 22 Forristall RM Marsh HO Pay NT Magnetic resonance imaging and contrast CT of the lumbar spine Comparison of diagnostic methods and correlation with surgical findings Spine 131049-1054 1988 Abstract 23 Fries JW Abodeely DA Vijungco JG et al Computed tomography of herniated and extruded nucleus pulposus J Comput Assist Tomogr 6874-887 1982 Abstract 24 Frymoyer JW Newberg A Pope MH et al Spine radiographs in patients with low-back pain An epidemiological study in men J Bone Joint Surg Am 661048-1055 1984 Abstract 25 Gospodarowicz M Benedet L Hutter RV et al History and international developments in cancer staging Cancer Prev Control 2262-268 1998 Abstract 26 Grenier N Greselle JF Vital JM et al Normal and disrupted lumbar longitudinal ligaments Correlative MR and anatomic study Radiology 171197-205 1989 Abstract 27 Gunzburg R Parkinson R Moore R et al A cadaveric study comparing discography magnetic resonance imaging histology and mechanical behavior of the human lumbar disc Spine 17417-426 1992 Abstract 28 Haughton VM Eldevik OP Magnaes B et al A prospective comparison of computed tomography and myelography in the diagnosis of herniated lumbar disks Radiology 142103-110 1982 Abstract

29 Haughton VM Lim TH An H Intervertebral disk appearance correlated with stiffness of lumbar spinal motion segments AJNR Am J Neuroradiol 201161-1165 1999 Abstract 30 Herzog RJ The radiologic assessment for a lumbar disc herniation Spine 2119S-38S 1996 Abstract 31 Jackson RP Becker GJ Jacobs RR et al The neuroradiographic diagnosis of lumbar herniated nucleus pulposus I A comparison of computed tomography (CT) myelography CT-myelography discography and CT-discography Spine 141356-1361 1989 Abstract 32 Jackson RP Cain JE Jr Jacobs RR et al The neuroradiographic diagnosis of lumbar herniated nucleus pulposus II A comparison of computed tomography (CT) myelography CT-myelography and magnetic resonance imaging Spine 141362-1367 1989 Abstract 33 Jarvik JG Haynor DR Koepsell TD et al Interreader reliability for a new classification of lumbar disk disease Acad Radiol 3537-544 1996 Abstract 34 Jensen MC Brant-Zawadzki MN Obuchowski N et al Magnetic resonance imaging of the lumbar spine in people without back pain N Engl J Med 33169-73 1994 Abstract 35 Kent DL Haynor DR Larson EB et al Diagnosis of lumbar spinal stenosis in adults A meta-analysis of the accuracy of CT MR and myelography AJR Am J Roentgenol 1581135-1144 1992 Abstract 36 Kieffer SA Sherry RG Wellenstein DE et al Bulging lumbar intervertebral disk Myelographic differentiation from herniated disk with nerve root compression AJR Am J Roentgenol 138709-716 1982 Abstract 37 Kieffer SA Stadlan EM Mohandas A et al Discographic-anatomical correlation of developmental changes with age in the intervertebral disc Acta Radiol 9733-739 1969 38 Kim KY Kim YT Lee CS et al MRI classification of lumbar herniated intervertebral disc Orthopedics 15493-497 1992 Abstract 39 Kornberg M Rechtine GR Dupuy TE Computed tomography in the diagnosis of a herniated disk at the L5-S1 level Spine 9433-436 1984 Abstract 40 Kramer MS Clinical Epidemiology and Biostatistics New York Springer-Verlag 1988 41 Landis JR Koch GG The measurement of observer agreement agreement for categorical data Biometrics 33159-174 1977 Abstract 42 Laredo JD Bossard P Vuillemin-Bodaghi Formes anatomo-radiologiques des hernies discales In Morvan G Deburge A Bard H et al (eds) Le Rachis Lombaire Degeneratif Montpellier Sauramps Medical 1998 pp 37-49 43 Lee SH Coleman PE Hahn FJ Magnetic resonance imaging of degenerative disk disease of the spine Radiol Clin North Am 26949-964 1988 Abstract 44 Linson MA Crowe CH Comparison of magnetic resonance imaging and lumbar discography in the diagnosis of disc degeneration Clin Orthop 160-163 1990

45 Marchand F Ahmed AM Investigation of the laminate structure of lumbar disc anulus fibrosus Spine 15402-410 1990 Abstract 46 Masaryk TJ Ross JS Modic MT et al High-resolution MR imaging of sequestered lumbar intervertebral disks AJR Am J Roentgenol 1501155-1162 1988 Abstract 47 Milette PC The proper terminology for reporting lumbar intervertebral disk disorders AJNR Am J Neuroradiol 181859-1866 1997 Citation 48 Milette PC Fontaine S Lepanto L et al Differentiating lumbar disc protrusions disk bulges and discs with normal contour but abnormal signal intensity Magnetic resonance imaging with discographic correlations Spine 2444-53 1999 Abstract 49 Milette PC Fontaine S Lepanto L et al Radiating pain to the lower extremities caused by lumbar disk rupture without spinal nerve root involvement AJNR Am J Neuroradiol 161605-1613 1995 Abstract 50 Milette PC Melancon D A reappraisal of lumbar discography Can Assoc Radiol J 33176-182 1982 51 Milette PC Melancon D Dupuis PR et al A simplified terminology for abnormalities of the lumbar disk Can Assoc Radiol J 42319-325 1991 Abstract 52 Milette PC Raymond J Fontaine S Comparison of high-resolution computed tomography with discography in the evaluation of lumbar disc herniations Spine 15525-533 1990 Abstract 53 Mink JH Deutsch AL Goldstein TB et al Spinal imaging and intervention 1998 Phys Med Rehabil Clin North Am 9343-380 1998 54 Mixter WJ Barr JS Rupture of the intervertebral disc with involvement of the spinal canal N Engl J Med 211210-234 1934 55 Modic MT Masaryk TJ Ross JS et al Imaging of degenerative disk disease Radiology 168177-186 1988 Citation 56 Modic MT Ross JS Obuchowski NA et al Contrast-enhanced MR imaging in acute lumbar radiculopathy A pilot study of the natural history Radiology 195429-435 1995 Abstract 57 Modic MT Steinberg PM Ross JS et al Degenerative disk disease Assessment of changes in vertebral body marrow with MR imaging Radiology 166193-199 1988 58 Morvan G Mathieu P Les stenoses laterales In Morvan G Deburge A Bard H et al (eds) Le Rachis Lombaire Degeneratif Montpellier Sauramps Medical 1998 pp 315-324 59 Murray RO Skeletal trauma Regional In Sutton D (ed) Textbook of Radiology and Imaging ed 3 New York Churchill Livingstone 1980 pp 210-231 60 Nachemson A Lumbar disc herniation Conclusions Acta Orthop Scand 64(suppl 251)49 1993 Citation

61 Nathan H Osteophytes of the vertebral column An anatomical study of their development according to age race and sex with consideration as to their etiology and significance J Bone Joint Surg Am 44243-268 1962 62 Nygaard OP Mellgren SI Osterud B The inflammatory properties of contained and noncontained lumbar disc herniations Spine 222584-2488 1997 Abstract 63 Ohshima H Hirano N Osada R et al Morphologic variation of lumbar posterior longitudinal ligament and the modality of disc herniation Spine 182408-2411 1993 Abstract 64 Osti OL Fraser RD MRI and discography of annular tears and intervertebral disc degeneration A prospective clinical comparison J Bone Joint Surg Br 74431-435 1992 Abstract 65 Palmgren T Gronblad M Virri J et al Immunohistochemical demonstration of sensory and autonomic nerve terminals in herniated lumbar disc tissue Spine 211301-1306 1996 Abstract 66 Resnick D Niwayama G Degenerative disease of the spine In Resnick D (ed) Diagnosis of Bone and Joint Disorders ed 3 Philadelphia WB Saunders 1995 pp 1372-1462 67 Resnick D Niwayama G Intravertebral disk herniations Cartilaginous (Schmorls) nodes Radiology 12657-65 1978 Abstract 68 Ross JS Modic MT Masaryk TJ Tears of the anulus fibrosus Assessment with Gd-DTPA-enhanced MR imaging AJR Am J Roentgenol 154159-162 1990 Abstract 69 Saal JS The role of inflammation in lumbar pain Spine 201821-1827 1995 Abstract 70 Sachs BL Vanharanta H Spivey MA et al Dallas discogram description A new classification of CTdiscography in low-back disorders Spine 12287-294 1987 Abstract 71 Sauser DD Goldman AB Kaye JJ Discogenic vertebral sclerosis J Can Assoc Radiol 2944-50 1978 Abstract 72 Schellhas KP Pollei SR Gundry CR et al Lumbar disc high-intensity zone Correlation of magnetic resonance imaging and discography Spine 2179-86 1996 Abstract 73 Schellinger D Manz HJ Vidic B et al Disk fragment migration Radiology 175831-836 1990 Abstract 74 Schipper J Kardaun JW Braakman R et al Lumbar disk herniation Diagnosis with CT or myelography Radiology 165227-231 1987 Abstract 75 Schmorl G Junghanns H The Human Spine in Health and Disease ed 2 New York Grune and Stratton 1971 76 Silverman CS Lenchik L Shimkin PM et al The value of MR in differentiating subligamentous from supraligamentous lumbar disk herniations AJNR Am J Neuroradiol 16571-579 1995 Abstract 77 Simmons JW Emery SF McMillin JN et al Awake discography A comparison study with magnetic

resonance imaging Spine 16S216-221 1991 Abstract 78 Smyth MJ Wright V Sciatica and the intervertebral disc J Bone Joint Surg Am 401401-1418 1958 79 Taveras JM Radiologic aspects of low back pain and sciatic syndromes [editorial] AJNR Am J Neuroradiol 9351-358 1989 80 Tehranzadeh J Discography 2000 Radiol Clin North Am 36463-495 1998 Full Text 81 Thelander U Fagerlund M Friberg S et al Describing the size of lumbar disc herniations using computed tomography A comparison of different size index calculations and their relation to sciatica Spine 191979-1984 1994 Abstract 82 Thornbury JR Fryback DG Turski PA et al Disk-caused nerve compression in patients with acute low-back pain Diagnosis with MR CT myelography and plain CT Radiology 186731-738 1993 Abstract 83 Twomey L Taylor J Age changes in lumbar intervertebral discs Acta Orthop Scand 56496-499 1985 Abstract 84 Twomey LT Taylor JR Age changes in lumbar vertebrae and intervertebral discs Clin Orthop 22497-104 1987 85 Williams AL CT diagnosis of degenerative disc disease The bulging annulus Radiol Clin North Am 21289-300 1983 Abstract 86 Williams AL Haughton VM Meyer GA et al Computed tomographic appearance of the bulging annulus Radiology 142403-408 1982 Abstract 87 Williams AL Haughton VM Syvertsen A Computed tomography in the diagnosis of herniated nucleus pulposus Radiology 13595-99 1980 Abstract 88 Wiltse LL Berger PE McCulloch JA A system for reporting the size and location of lesions in the spine Spine 221534-1537 1997 Abstract 89 Wiltse LL Fonseca AS Amster J et al Relationship of the dura Hofmanns ligaments Batsons plexus and a fibrovascular membrane lying on the posterior surface of the vertebral bodies and attaching to the deep layer of the posterior longitudinal ligament An anatomical radiologic and clinical study Spine 181030-1043 1993 Abstract 90 Yamashita K Hiroshima K Kurata A Gadolinium-DTPA-enhanced magnetic resonance imaging of a sequestered lumbar intervertebral disc and its correlation with pathologic findings Spine 19479-482 1994 Abstract 91 Yu SW Haughton VM Sether LA et al Comparison of MR and diskography in detecting radial tears of the anulus A postmortem study AJNR Am J Neuroradiol 101077-1081 1989 Abstract 92 Yu SW Sether LA Ho PS et al Tears of the anulus fibrosus Correlation between MR and pathologic findings in cadavers AJNR Am J Neuroradiol 9367-370 1988 Abstract

93 Yussen PS Swartz JD The acute lumbar disc herniation Imaging diagnosis Semin Ultrasound CT MR 14389-398 1993 Abstract 94 Zucherman J Derby R Hsu K et al Normal magnetic resonance imaging with abnormal discography Spine 131355-1359 1988 Abstract

Copyright copy 2008 Elsevier Inc All rights reserved - wwwmdconsultcom

Bookmark URL dasjournalview0N11535915ja=198094ampPAGE=1htmlampissn=0033-8389ampsource=MI

  • CLASSIFICATION DIAGNOSTIC IMAGING AND IMAGING CHARACTERIZATION OF A LUMBAR HERNIATED DISK
    • IMAGING OF LOW BACK PAIN I
      • CLASSIFICATION DIAGNOSTIC IMAGING AND IMAGING CHARACTERIZATION OF A LUMBAR HERNIATED DISK
        • DEFINITION OF A DISK HERNIATION
        • CLASSIFICATION OF A HERNIATED LUMBAR DISK
          • Main Categories of Noninfectious Disk Abnormalities
          • Further Qualifying the Displaced Disk Material Beyond the Disk Space
            • DIAGNOSTIC IMAGING AND CHARACTERIZATION OF A HERNIATED LUMBAR DISK
              • Conventional Radiographs
              • Myelography
              • CT
              • CT Myelography
              • MR Imaging
              • Diskography and CT Diskography
                • SUMMARY
                  • References
Page 28: CLASSIFICATION, DIAGNOSTIC IMAGING, AND IMAGING ... · PDF fileclassification, diagnostic imaging, and imaging characterization of a lumbar herniated disk ... classification, diagnostic

a left foraminal and extraforaminal herniaton (same patient as in Figure 28) (Figure Not Available)

Figure 30 Contained posterior L4-L5 and L5-S1 disk herniations in a 57-year-old man demonstrated by diskography The L3-L4 disk is normal

Figure 31 Noncontained L4-L5 disk herniation in a 23-year-old woman Reflux of injected contrast is seen in the anterior epidural space above and below the disk space The L5-S1 disk also demonstrates incomplete anterior and posterior radial anular tears

SUMMARY

The absence of universal nomenclature standardization with respect to the definition of a disk herniation and its different categories especially regarding type and location is still a major problem that will only be overcome when major national or international scientific societies join efforts to support a particular scheme Meanwhile it is important to realize that the two models that are currently most used are based on a different perspective Trying to straddle the two by opposing for instance bulging disk and herniation is doomed to failure because this exercise defies formal logic MR imaging is currently the most accurate noninvasive imaging modality to diagnose a disk herniation and to determine its exact location The determination of some pathoanatomic characteristics of herniated disks (type and composition) may require the use of CT diskography or CT diskography

References

1 Albeck MJ Hilden J Kjaer L et al A controlled comparison of myelography computed tomography and magnetic resonance imaging in clinically suspected lumbar disc herniation Spine 20443-448 1995 Abstract 2 American Academy of Orthopedic Surgeons Glossary on Spinal Terminology Chicago American Academy of Orthopedic Surgeons 1981 3 Andersson GB Weinstein JN Disc herniation [editorial] Spine 211S 1996 Citation 4 Aprill C Bogduk N High-intensity zone A diagnostic sign of painful lumbar disc on magnetic resonance imaging Br J Radiol 65361-369 1992 Abstract 5 Birney TJ White JJ Jr Berens D et al Comparison of MRI and discography in the diagnosis of lumbar degenerative disc disease J Spinal Disord 5417-423 1992 Abstract 6 Bischoff RJ Rodriguez RP Gupta K et al A comparison of computed tomography-myelography magnetic resonance imaging and myelography in the diagnosis of herniated nucleus pulposus and spinal stenosis J Spinal Disord 6289-295 1993 Abstract 7 Bogduk N The innervation of the lumbar spine Spine 8286-293 1983 Abstract 8 Bogduk N Tynan W Wilson AS The nerve supply to the human lumbar intervertebral discs J Anat 13239-56 1981 Abstract 9 Bonneville JF La carte-image des hernies discales lombaires Rachis 2255-257 1990 10 Bonneville JF La topografia simbolica delle ernie discali lombari Riv Neuroradiol 5427-431 1992 11 Bonneville JF Plaidoyer pour une classification par limage des hernies discales lombaires La carte-image Rev Imag Med 2557-560 1990 12 Brant-Zawadzki M Jensen M Spinal nomenclature Spine 20388-390 1995 Abstract

13 Brant-Zawadzki MN Jensen MC Obuchowski N et al Interobserver and intraobserver variability in interpretation of lumbar disc abnormalities A comparison of two nomenclatures Spine 201257-1263 1995 Abstract 14 Breton G Is that a bulging disk a small herniation or a moderate protrusion [editorial] Can Assoc Radiol J 42318 1991 Citation 15 Czervionke LF Lumbar intervertebral disc disease Neuroimaging Clin North Am 3465-485 1993 16 Deyo RA Nonsurgical care of low back pain Neurosurg Clin North Am 2851-862 1991 17 Deyo RA Loeser JD Bigos SJ Herniated lumbar intervertebral disk Ann Intern Med 112598-603 1990 Abstract 18 Dorlands Illustrated Medical Dictionary ed 28 Philadelphia WB Saunders 1994 19 Fardon D Pinkerton S Balderston R et al Terms used for diagnosis by English speaking spine surgeons Spine 18274-277 1993 Citation 20 Fardon DF Herzog RJ Mink JH et al Nomenclature of Lumbar Disc Disorders Contemporary Concepts in Spine Care Rosemont IL North American Spine Society 1995 21 Fardon DF Herzog RJ Mink JH et al Nomenclature of lumbar disc disorders In Garfin S Vaccaro A (eds) Orthopedic Knowledge Update Spine Rosemont IL American Academy of Orthopedic Surgeons 1997 pp A3-A14 22 Forristall RM Marsh HO Pay NT Magnetic resonance imaging and contrast CT of the lumbar spine Comparison of diagnostic methods and correlation with surgical findings Spine 131049-1054 1988 Abstract 23 Fries JW Abodeely DA Vijungco JG et al Computed tomography of herniated and extruded nucleus pulposus J Comput Assist Tomogr 6874-887 1982 Abstract 24 Frymoyer JW Newberg A Pope MH et al Spine radiographs in patients with low-back pain An epidemiological study in men J Bone Joint Surg Am 661048-1055 1984 Abstract 25 Gospodarowicz M Benedet L Hutter RV et al History and international developments in cancer staging Cancer Prev Control 2262-268 1998 Abstract 26 Grenier N Greselle JF Vital JM et al Normal and disrupted lumbar longitudinal ligaments Correlative MR and anatomic study Radiology 171197-205 1989 Abstract 27 Gunzburg R Parkinson R Moore R et al A cadaveric study comparing discography magnetic resonance imaging histology and mechanical behavior of the human lumbar disc Spine 17417-426 1992 Abstract 28 Haughton VM Eldevik OP Magnaes B et al A prospective comparison of computed tomography and myelography in the diagnosis of herniated lumbar disks Radiology 142103-110 1982 Abstract

29 Haughton VM Lim TH An H Intervertebral disk appearance correlated with stiffness of lumbar spinal motion segments AJNR Am J Neuroradiol 201161-1165 1999 Abstract 30 Herzog RJ The radiologic assessment for a lumbar disc herniation Spine 2119S-38S 1996 Abstract 31 Jackson RP Becker GJ Jacobs RR et al The neuroradiographic diagnosis of lumbar herniated nucleus pulposus I A comparison of computed tomography (CT) myelography CT-myelography discography and CT-discography Spine 141356-1361 1989 Abstract 32 Jackson RP Cain JE Jr Jacobs RR et al The neuroradiographic diagnosis of lumbar herniated nucleus pulposus II A comparison of computed tomography (CT) myelography CT-myelography and magnetic resonance imaging Spine 141362-1367 1989 Abstract 33 Jarvik JG Haynor DR Koepsell TD et al Interreader reliability for a new classification of lumbar disk disease Acad Radiol 3537-544 1996 Abstract 34 Jensen MC Brant-Zawadzki MN Obuchowski N et al Magnetic resonance imaging of the lumbar spine in people without back pain N Engl J Med 33169-73 1994 Abstract 35 Kent DL Haynor DR Larson EB et al Diagnosis of lumbar spinal stenosis in adults A meta-analysis of the accuracy of CT MR and myelography AJR Am J Roentgenol 1581135-1144 1992 Abstract 36 Kieffer SA Sherry RG Wellenstein DE et al Bulging lumbar intervertebral disk Myelographic differentiation from herniated disk with nerve root compression AJR Am J Roentgenol 138709-716 1982 Abstract 37 Kieffer SA Stadlan EM Mohandas A et al Discographic-anatomical correlation of developmental changes with age in the intervertebral disc Acta Radiol 9733-739 1969 38 Kim KY Kim YT Lee CS et al MRI classification of lumbar herniated intervertebral disc Orthopedics 15493-497 1992 Abstract 39 Kornberg M Rechtine GR Dupuy TE Computed tomography in the diagnosis of a herniated disk at the L5-S1 level Spine 9433-436 1984 Abstract 40 Kramer MS Clinical Epidemiology and Biostatistics New York Springer-Verlag 1988 41 Landis JR Koch GG The measurement of observer agreement agreement for categorical data Biometrics 33159-174 1977 Abstract 42 Laredo JD Bossard P Vuillemin-Bodaghi Formes anatomo-radiologiques des hernies discales In Morvan G Deburge A Bard H et al (eds) Le Rachis Lombaire Degeneratif Montpellier Sauramps Medical 1998 pp 37-49 43 Lee SH Coleman PE Hahn FJ Magnetic resonance imaging of degenerative disk disease of the spine Radiol Clin North Am 26949-964 1988 Abstract 44 Linson MA Crowe CH Comparison of magnetic resonance imaging and lumbar discography in the diagnosis of disc degeneration Clin Orthop 160-163 1990

45 Marchand F Ahmed AM Investigation of the laminate structure of lumbar disc anulus fibrosus Spine 15402-410 1990 Abstract 46 Masaryk TJ Ross JS Modic MT et al High-resolution MR imaging of sequestered lumbar intervertebral disks AJR Am J Roentgenol 1501155-1162 1988 Abstract 47 Milette PC The proper terminology for reporting lumbar intervertebral disk disorders AJNR Am J Neuroradiol 181859-1866 1997 Citation 48 Milette PC Fontaine S Lepanto L et al Differentiating lumbar disc protrusions disk bulges and discs with normal contour but abnormal signal intensity Magnetic resonance imaging with discographic correlations Spine 2444-53 1999 Abstract 49 Milette PC Fontaine S Lepanto L et al Radiating pain to the lower extremities caused by lumbar disk rupture without spinal nerve root involvement AJNR Am J Neuroradiol 161605-1613 1995 Abstract 50 Milette PC Melancon D A reappraisal of lumbar discography Can Assoc Radiol J 33176-182 1982 51 Milette PC Melancon D Dupuis PR et al A simplified terminology for abnormalities of the lumbar disk Can Assoc Radiol J 42319-325 1991 Abstract 52 Milette PC Raymond J Fontaine S Comparison of high-resolution computed tomography with discography in the evaluation of lumbar disc herniations Spine 15525-533 1990 Abstract 53 Mink JH Deutsch AL Goldstein TB et al Spinal imaging and intervention 1998 Phys Med Rehabil Clin North Am 9343-380 1998 54 Mixter WJ Barr JS Rupture of the intervertebral disc with involvement of the spinal canal N Engl J Med 211210-234 1934 55 Modic MT Masaryk TJ Ross JS et al Imaging of degenerative disk disease Radiology 168177-186 1988 Citation 56 Modic MT Ross JS Obuchowski NA et al Contrast-enhanced MR imaging in acute lumbar radiculopathy A pilot study of the natural history Radiology 195429-435 1995 Abstract 57 Modic MT Steinberg PM Ross JS et al Degenerative disk disease Assessment of changes in vertebral body marrow with MR imaging Radiology 166193-199 1988 58 Morvan G Mathieu P Les stenoses laterales In Morvan G Deburge A Bard H et al (eds) Le Rachis Lombaire Degeneratif Montpellier Sauramps Medical 1998 pp 315-324 59 Murray RO Skeletal trauma Regional In Sutton D (ed) Textbook of Radiology and Imaging ed 3 New York Churchill Livingstone 1980 pp 210-231 60 Nachemson A Lumbar disc herniation Conclusions Acta Orthop Scand 64(suppl 251)49 1993 Citation

61 Nathan H Osteophytes of the vertebral column An anatomical study of their development according to age race and sex with consideration as to their etiology and significance J Bone Joint Surg Am 44243-268 1962 62 Nygaard OP Mellgren SI Osterud B The inflammatory properties of contained and noncontained lumbar disc herniations Spine 222584-2488 1997 Abstract 63 Ohshima H Hirano N Osada R et al Morphologic variation of lumbar posterior longitudinal ligament and the modality of disc herniation Spine 182408-2411 1993 Abstract 64 Osti OL Fraser RD MRI and discography of annular tears and intervertebral disc degeneration A prospective clinical comparison J Bone Joint Surg Br 74431-435 1992 Abstract 65 Palmgren T Gronblad M Virri J et al Immunohistochemical demonstration of sensory and autonomic nerve terminals in herniated lumbar disc tissue Spine 211301-1306 1996 Abstract 66 Resnick D Niwayama G Degenerative disease of the spine In Resnick D (ed) Diagnosis of Bone and Joint Disorders ed 3 Philadelphia WB Saunders 1995 pp 1372-1462 67 Resnick D Niwayama G Intravertebral disk herniations Cartilaginous (Schmorls) nodes Radiology 12657-65 1978 Abstract 68 Ross JS Modic MT Masaryk TJ Tears of the anulus fibrosus Assessment with Gd-DTPA-enhanced MR imaging AJR Am J Roentgenol 154159-162 1990 Abstract 69 Saal JS The role of inflammation in lumbar pain Spine 201821-1827 1995 Abstract 70 Sachs BL Vanharanta H Spivey MA et al Dallas discogram description A new classification of CTdiscography in low-back disorders Spine 12287-294 1987 Abstract 71 Sauser DD Goldman AB Kaye JJ Discogenic vertebral sclerosis J Can Assoc Radiol 2944-50 1978 Abstract 72 Schellhas KP Pollei SR Gundry CR et al Lumbar disc high-intensity zone Correlation of magnetic resonance imaging and discography Spine 2179-86 1996 Abstract 73 Schellinger D Manz HJ Vidic B et al Disk fragment migration Radiology 175831-836 1990 Abstract 74 Schipper J Kardaun JW Braakman R et al Lumbar disk herniation Diagnosis with CT or myelography Radiology 165227-231 1987 Abstract 75 Schmorl G Junghanns H The Human Spine in Health and Disease ed 2 New York Grune and Stratton 1971 76 Silverman CS Lenchik L Shimkin PM et al The value of MR in differentiating subligamentous from supraligamentous lumbar disk herniations AJNR Am J Neuroradiol 16571-579 1995 Abstract 77 Simmons JW Emery SF McMillin JN et al Awake discography A comparison study with magnetic

resonance imaging Spine 16S216-221 1991 Abstract 78 Smyth MJ Wright V Sciatica and the intervertebral disc J Bone Joint Surg Am 401401-1418 1958 79 Taveras JM Radiologic aspects of low back pain and sciatic syndromes [editorial] AJNR Am J Neuroradiol 9351-358 1989 80 Tehranzadeh J Discography 2000 Radiol Clin North Am 36463-495 1998 Full Text 81 Thelander U Fagerlund M Friberg S et al Describing the size of lumbar disc herniations using computed tomography A comparison of different size index calculations and their relation to sciatica Spine 191979-1984 1994 Abstract 82 Thornbury JR Fryback DG Turski PA et al Disk-caused nerve compression in patients with acute low-back pain Diagnosis with MR CT myelography and plain CT Radiology 186731-738 1993 Abstract 83 Twomey L Taylor J Age changes in lumbar intervertebral discs Acta Orthop Scand 56496-499 1985 Abstract 84 Twomey LT Taylor JR Age changes in lumbar vertebrae and intervertebral discs Clin Orthop 22497-104 1987 85 Williams AL CT diagnosis of degenerative disc disease The bulging annulus Radiol Clin North Am 21289-300 1983 Abstract 86 Williams AL Haughton VM Meyer GA et al Computed tomographic appearance of the bulging annulus Radiology 142403-408 1982 Abstract 87 Williams AL Haughton VM Syvertsen A Computed tomography in the diagnosis of herniated nucleus pulposus Radiology 13595-99 1980 Abstract 88 Wiltse LL Berger PE McCulloch JA A system for reporting the size and location of lesions in the spine Spine 221534-1537 1997 Abstract 89 Wiltse LL Fonseca AS Amster J et al Relationship of the dura Hofmanns ligaments Batsons plexus and a fibrovascular membrane lying on the posterior surface of the vertebral bodies and attaching to the deep layer of the posterior longitudinal ligament An anatomical radiologic and clinical study Spine 181030-1043 1993 Abstract 90 Yamashita K Hiroshima K Kurata A Gadolinium-DTPA-enhanced magnetic resonance imaging of a sequestered lumbar intervertebral disc and its correlation with pathologic findings Spine 19479-482 1994 Abstract 91 Yu SW Haughton VM Sether LA et al Comparison of MR and diskography in detecting radial tears of the anulus A postmortem study AJNR Am J Neuroradiol 101077-1081 1989 Abstract 92 Yu SW Sether LA Ho PS et al Tears of the anulus fibrosus Correlation between MR and pathologic findings in cadavers AJNR Am J Neuroradiol 9367-370 1988 Abstract

93 Yussen PS Swartz JD The acute lumbar disc herniation Imaging diagnosis Semin Ultrasound CT MR 14389-398 1993 Abstract 94 Zucherman J Derby R Hsu K et al Normal magnetic resonance imaging with abnormal discography Spine 131355-1359 1988 Abstract

Copyright copy 2008 Elsevier Inc All rights reserved - wwwmdconsultcom

Bookmark URL dasjournalview0N11535915ja=198094ampPAGE=1htmlampissn=0033-8389ampsource=MI

  • CLASSIFICATION DIAGNOSTIC IMAGING AND IMAGING CHARACTERIZATION OF A LUMBAR HERNIATED DISK
    • IMAGING OF LOW BACK PAIN I
      • CLASSIFICATION DIAGNOSTIC IMAGING AND IMAGING CHARACTERIZATION OF A LUMBAR HERNIATED DISK
        • DEFINITION OF A DISK HERNIATION
        • CLASSIFICATION OF A HERNIATED LUMBAR DISK
          • Main Categories of Noninfectious Disk Abnormalities
          • Further Qualifying the Displaced Disk Material Beyond the Disk Space
            • DIAGNOSTIC IMAGING AND CHARACTERIZATION OF A HERNIATED LUMBAR DISK
              • Conventional Radiographs
              • Myelography
              • CT
              • CT Myelography
              • MR Imaging
              • Diskography and CT Diskography
                • SUMMARY
                  • References
Page 29: CLASSIFICATION, DIAGNOSTIC IMAGING, AND IMAGING ... · PDF fileclassification, diagnostic imaging, and imaging characterization of a lumbar herniated disk ... classification, diagnostic

The absence of universal nomenclature standardization with respect to the definition of a disk herniation and its different categories especially regarding type and location is still a major problem that will only be overcome when major national or international scientific societies join efforts to support a particular scheme Meanwhile it is important to realize that the two models that are currently most used are based on a different perspective Trying to straddle the two by opposing for instance bulging disk and herniation is doomed to failure because this exercise defies formal logic MR imaging is currently the most accurate noninvasive imaging modality to diagnose a disk herniation and to determine its exact location The determination of some pathoanatomic characteristics of herniated disks (type and composition) may require the use of CT diskography or CT diskography

References

1 Albeck MJ Hilden J Kjaer L et al A controlled comparison of myelography computed tomography and magnetic resonance imaging in clinically suspected lumbar disc herniation Spine 20443-448 1995 Abstract 2 American Academy of Orthopedic Surgeons Glossary on Spinal Terminology Chicago American Academy of Orthopedic Surgeons 1981 3 Andersson GB Weinstein JN Disc herniation [editorial] Spine 211S 1996 Citation 4 Aprill C Bogduk N High-intensity zone A diagnostic sign of painful lumbar disc on magnetic resonance imaging Br J Radiol 65361-369 1992 Abstract 5 Birney TJ White JJ Jr Berens D et al Comparison of MRI and discography in the diagnosis of lumbar degenerative disc disease J Spinal Disord 5417-423 1992 Abstract 6 Bischoff RJ Rodriguez RP Gupta K et al A comparison of computed tomography-myelography magnetic resonance imaging and myelography in the diagnosis of herniated nucleus pulposus and spinal stenosis J Spinal Disord 6289-295 1993 Abstract 7 Bogduk N The innervation of the lumbar spine Spine 8286-293 1983 Abstract 8 Bogduk N Tynan W Wilson AS The nerve supply to the human lumbar intervertebral discs J Anat 13239-56 1981 Abstract 9 Bonneville JF La carte-image des hernies discales lombaires Rachis 2255-257 1990 10 Bonneville JF La topografia simbolica delle ernie discali lombari Riv Neuroradiol 5427-431 1992 11 Bonneville JF Plaidoyer pour une classification par limage des hernies discales lombaires La carte-image Rev Imag Med 2557-560 1990 12 Brant-Zawadzki M Jensen M Spinal nomenclature Spine 20388-390 1995 Abstract

13 Brant-Zawadzki MN Jensen MC Obuchowski N et al Interobserver and intraobserver variability in interpretation of lumbar disc abnormalities A comparison of two nomenclatures Spine 201257-1263 1995 Abstract 14 Breton G Is that a bulging disk a small herniation or a moderate protrusion [editorial] Can Assoc Radiol J 42318 1991 Citation 15 Czervionke LF Lumbar intervertebral disc disease Neuroimaging Clin North Am 3465-485 1993 16 Deyo RA Nonsurgical care of low back pain Neurosurg Clin North Am 2851-862 1991 17 Deyo RA Loeser JD Bigos SJ Herniated lumbar intervertebral disk Ann Intern Med 112598-603 1990 Abstract 18 Dorlands Illustrated Medical Dictionary ed 28 Philadelphia WB Saunders 1994 19 Fardon D Pinkerton S Balderston R et al Terms used for diagnosis by English speaking spine surgeons Spine 18274-277 1993 Citation 20 Fardon DF Herzog RJ Mink JH et al Nomenclature of Lumbar Disc Disorders Contemporary Concepts in Spine Care Rosemont IL North American Spine Society 1995 21 Fardon DF Herzog RJ Mink JH et al Nomenclature of lumbar disc disorders In Garfin S Vaccaro A (eds) Orthopedic Knowledge Update Spine Rosemont IL American Academy of Orthopedic Surgeons 1997 pp A3-A14 22 Forristall RM Marsh HO Pay NT Magnetic resonance imaging and contrast CT of the lumbar spine Comparison of diagnostic methods and correlation with surgical findings Spine 131049-1054 1988 Abstract 23 Fries JW Abodeely DA Vijungco JG et al Computed tomography of herniated and extruded nucleus pulposus J Comput Assist Tomogr 6874-887 1982 Abstract 24 Frymoyer JW Newberg A Pope MH et al Spine radiographs in patients with low-back pain An epidemiological study in men J Bone Joint Surg Am 661048-1055 1984 Abstract 25 Gospodarowicz M Benedet L Hutter RV et al History and international developments in cancer staging Cancer Prev Control 2262-268 1998 Abstract 26 Grenier N Greselle JF Vital JM et al Normal and disrupted lumbar longitudinal ligaments Correlative MR and anatomic study Radiology 171197-205 1989 Abstract 27 Gunzburg R Parkinson R Moore R et al A cadaveric study comparing discography magnetic resonance imaging histology and mechanical behavior of the human lumbar disc Spine 17417-426 1992 Abstract 28 Haughton VM Eldevik OP Magnaes B et al A prospective comparison of computed tomography and myelography in the diagnosis of herniated lumbar disks Radiology 142103-110 1982 Abstract

29 Haughton VM Lim TH An H Intervertebral disk appearance correlated with stiffness of lumbar spinal motion segments AJNR Am J Neuroradiol 201161-1165 1999 Abstract 30 Herzog RJ The radiologic assessment for a lumbar disc herniation Spine 2119S-38S 1996 Abstract 31 Jackson RP Becker GJ Jacobs RR et al The neuroradiographic diagnosis of lumbar herniated nucleus pulposus I A comparison of computed tomography (CT) myelography CT-myelography discography and CT-discography Spine 141356-1361 1989 Abstract 32 Jackson RP Cain JE Jr Jacobs RR et al The neuroradiographic diagnosis of lumbar herniated nucleus pulposus II A comparison of computed tomography (CT) myelography CT-myelography and magnetic resonance imaging Spine 141362-1367 1989 Abstract 33 Jarvik JG Haynor DR Koepsell TD et al Interreader reliability for a new classification of lumbar disk disease Acad Radiol 3537-544 1996 Abstract 34 Jensen MC Brant-Zawadzki MN Obuchowski N et al Magnetic resonance imaging of the lumbar spine in people without back pain N Engl J Med 33169-73 1994 Abstract 35 Kent DL Haynor DR Larson EB et al Diagnosis of lumbar spinal stenosis in adults A meta-analysis of the accuracy of CT MR and myelography AJR Am J Roentgenol 1581135-1144 1992 Abstract 36 Kieffer SA Sherry RG Wellenstein DE et al Bulging lumbar intervertebral disk Myelographic differentiation from herniated disk with nerve root compression AJR Am J Roentgenol 138709-716 1982 Abstract 37 Kieffer SA Stadlan EM Mohandas A et al Discographic-anatomical correlation of developmental changes with age in the intervertebral disc Acta Radiol 9733-739 1969 38 Kim KY Kim YT Lee CS et al MRI classification of lumbar herniated intervertebral disc Orthopedics 15493-497 1992 Abstract 39 Kornberg M Rechtine GR Dupuy TE Computed tomography in the diagnosis of a herniated disk at the L5-S1 level Spine 9433-436 1984 Abstract 40 Kramer MS Clinical Epidemiology and Biostatistics New York Springer-Verlag 1988 41 Landis JR Koch GG The measurement of observer agreement agreement for categorical data Biometrics 33159-174 1977 Abstract 42 Laredo JD Bossard P Vuillemin-Bodaghi Formes anatomo-radiologiques des hernies discales In Morvan G Deburge A Bard H et al (eds) Le Rachis Lombaire Degeneratif Montpellier Sauramps Medical 1998 pp 37-49 43 Lee SH Coleman PE Hahn FJ Magnetic resonance imaging of degenerative disk disease of the spine Radiol Clin North Am 26949-964 1988 Abstract 44 Linson MA Crowe CH Comparison of magnetic resonance imaging and lumbar discography in the diagnosis of disc degeneration Clin Orthop 160-163 1990

45 Marchand F Ahmed AM Investigation of the laminate structure of lumbar disc anulus fibrosus Spine 15402-410 1990 Abstract 46 Masaryk TJ Ross JS Modic MT et al High-resolution MR imaging of sequestered lumbar intervertebral disks AJR Am J Roentgenol 1501155-1162 1988 Abstract 47 Milette PC The proper terminology for reporting lumbar intervertebral disk disorders AJNR Am J Neuroradiol 181859-1866 1997 Citation 48 Milette PC Fontaine S Lepanto L et al Differentiating lumbar disc protrusions disk bulges and discs with normal contour but abnormal signal intensity Magnetic resonance imaging with discographic correlations Spine 2444-53 1999 Abstract 49 Milette PC Fontaine S Lepanto L et al Radiating pain to the lower extremities caused by lumbar disk rupture without spinal nerve root involvement AJNR Am J Neuroradiol 161605-1613 1995 Abstract 50 Milette PC Melancon D A reappraisal of lumbar discography Can Assoc Radiol J 33176-182 1982 51 Milette PC Melancon D Dupuis PR et al A simplified terminology for abnormalities of the lumbar disk Can Assoc Radiol J 42319-325 1991 Abstract 52 Milette PC Raymond J Fontaine S Comparison of high-resolution computed tomography with discography in the evaluation of lumbar disc herniations Spine 15525-533 1990 Abstract 53 Mink JH Deutsch AL Goldstein TB et al Spinal imaging and intervention 1998 Phys Med Rehabil Clin North Am 9343-380 1998 54 Mixter WJ Barr JS Rupture of the intervertebral disc with involvement of the spinal canal N Engl J Med 211210-234 1934 55 Modic MT Masaryk TJ Ross JS et al Imaging of degenerative disk disease Radiology 168177-186 1988 Citation 56 Modic MT Ross JS Obuchowski NA et al Contrast-enhanced MR imaging in acute lumbar radiculopathy A pilot study of the natural history Radiology 195429-435 1995 Abstract 57 Modic MT Steinberg PM Ross JS et al Degenerative disk disease Assessment of changes in vertebral body marrow with MR imaging Radiology 166193-199 1988 58 Morvan G Mathieu P Les stenoses laterales In Morvan G Deburge A Bard H et al (eds) Le Rachis Lombaire Degeneratif Montpellier Sauramps Medical 1998 pp 315-324 59 Murray RO Skeletal trauma Regional In Sutton D (ed) Textbook of Radiology and Imaging ed 3 New York Churchill Livingstone 1980 pp 210-231 60 Nachemson A Lumbar disc herniation Conclusions Acta Orthop Scand 64(suppl 251)49 1993 Citation

61 Nathan H Osteophytes of the vertebral column An anatomical study of their development according to age race and sex with consideration as to their etiology and significance J Bone Joint Surg Am 44243-268 1962 62 Nygaard OP Mellgren SI Osterud B The inflammatory properties of contained and noncontained lumbar disc herniations Spine 222584-2488 1997 Abstract 63 Ohshima H Hirano N Osada R et al Morphologic variation of lumbar posterior longitudinal ligament and the modality of disc herniation Spine 182408-2411 1993 Abstract 64 Osti OL Fraser RD MRI and discography of annular tears and intervertebral disc degeneration A prospective clinical comparison J Bone Joint Surg Br 74431-435 1992 Abstract 65 Palmgren T Gronblad M Virri J et al Immunohistochemical demonstration of sensory and autonomic nerve terminals in herniated lumbar disc tissue Spine 211301-1306 1996 Abstract 66 Resnick D Niwayama G Degenerative disease of the spine In Resnick D (ed) Diagnosis of Bone and Joint Disorders ed 3 Philadelphia WB Saunders 1995 pp 1372-1462 67 Resnick D Niwayama G Intravertebral disk herniations Cartilaginous (Schmorls) nodes Radiology 12657-65 1978 Abstract 68 Ross JS Modic MT Masaryk TJ Tears of the anulus fibrosus Assessment with Gd-DTPA-enhanced MR imaging AJR Am J Roentgenol 154159-162 1990 Abstract 69 Saal JS The role of inflammation in lumbar pain Spine 201821-1827 1995 Abstract 70 Sachs BL Vanharanta H Spivey MA et al Dallas discogram description A new classification of CTdiscography in low-back disorders Spine 12287-294 1987 Abstract 71 Sauser DD Goldman AB Kaye JJ Discogenic vertebral sclerosis J Can Assoc Radiol 2944-50 1978 Abstract 72 Schellhas KP Pollei SR Gundry CR et al Lumbar disc high-intensity zone Correlation of magnetic resonance imaging and discography Spine 2179-86 1996 Abstract 73 Schellinger D Manz HJ Vidic B et al Disk fragment migration Radiology 175831-836 1990 Abstract 74 Schipper J Kardaun JW Braakman R et al Lumbar disk herniation Diagnosis with CT or myelography Radiology 165227-231 1987 Abstract 75 Schmorl G Junghanns H The Human Spine in Health and Disease ed 2 New York Grune and Stratton 1971 76 Silverman CS Lenchik L Shimkin PM et al The value of MR in differentiating subligamentous from supraligamentous lumbar disk herniations AJNR Am J Neuroradiol 16571-579 1995 Abstract 77 Simmons JW Emery SF McMillin JN et al Awake discography A comparison study with magnetic

resonance imaging Spine 16S216-221 1991 Abstract 78 Smyth MJ Wright V Sciatica and the intervertebral disc J Bone Joint Surg Am 401401-1418 1958 79 Taveras JM Radiologic aspects of low back pain and sciatic syndromes [editorial] AJNR Am J Neuroradiol 9351-358 1989 80 Tehranzadeh J Discography 2000 Radiol Clin North Am 36463-495 1998 Full Text 81 Thelander U Fagerlund M Friberg S et al Describing the size of lumbar disc herniations using computed tomography A comparison of different size index calculations and their relation to sciatica Spine 191979-1984 1994 Abstract 82 Thornbury JR Fryback DG Turski PA et al Disk-caused nerve compression in patients with acute low-back pain Diagnosis with MR CT myelography and plain CT Radiology 186731-738 1993 Abstract 83 Twomey L Taylor J Age changes in lumbar intervertebral discs Acta Orthop Scand 56496-499 1985 Abstract 84 Twomey LT Taylor JR Age changes in lumbar vertebrae and intervertebral discs Clin Orthop 22497-104 1987 85 Williams AL CT diagnosis of degenerative disc disease The bulging annulus Radiol Clin North Am 21289-300 1983 Abstract 86 Williams AL Haughton VM Meyer GA et al Computed tomographic appearance of the bulging annulus Radiology 142403-408 1982 Abstract 87 Williams AL Haughton VM Syvertsen A Computed tomography in the diagnosis of herniated nucleus pulposus Radiology 13595-99 1980 Abstract 88 Wiltse LL Berger PE McCulloch JA A system for reporting the size and location of lesions in the spine Spine 221534-1537 1997 Abstract 89 Wiltse LL Fonseca AS Amster J et al Relationship of the dura Hofmanns ligaments Batsons plexus and a fibrovascular membrane lying on the posterior surface of the vertebral bodies and attaching to the deep layer of the posterior longitudinal ligament An anatomical radiologic and clinical study Spine 181030-1043 1993 Abstract 90 Yamashita K Hiroshima K Kurata A Gadolinium-DTPA-enhanced magnetic resonance imaging of a sequestered lumbar intervertebral disc and its correlation with pathologic findings Spine 19479-482 1994 Abstract 91 Yu SW Haughton VM Sether LA et al Comparison of MR and diskography in detecting radial tears of the anulus A postmortem study AJNR Am J Neuroradiol 101077-1081 1989 Abstract 92 Yu SW Sether LA Ho PS et al Tears of the anulus fibrosus Correlation between MR and pathologic findings in cadavers AJNR Am J Neuroradiol 9367-370 1988 Abstract

93 Yussen PS Swartz JD The acute lumbar disc herniation Imaging diagnosis Semin Ultrasound CT MR 14389-398 1993 Abstract 94 Zucherman J Derby R Hsu K et al Normal magnetic resonance imaging with abnormal discography Spine 131355-1359 1988 Abstract

Copyright copy 2008 Elsevier Inc All rights reserved - wwwmdconsultcom

Bookmark URL dasjournalview0N11535915ja=198094ampPAGE=1htmlampissn=0033-8389ampsource=MI

  • CLASSIFICATION DIAGNOSTIC IMAGING AND IMAGING CHARACTERIZATION OF A LUMBAR HERNIATED DISK
    • IMAGING OF LOW BACK PAIN I
      • CLASSIFICATION DIAGNOSTIC IMAGING AND IMAGING CHARACTERIZATION OF A LUMBAR HERNIATED DISK
        • DEFINITION OF A DISK HERNIATION
        • CLASSIFICATION OF A HERNIATED LUMBAR DISK
          • Main Categories of Noninfectious Disk Abnormalities
          • Further Qualifying the Displaced Disk Material Beyond the Disk Space
            • DIAGNOSTIC IMAGING AND CHARACTERIZATION OF A HERNIATED LUMBAR DISK
              • Conventional Radiographs
              • Myelography
              • CT
              • CT Myelography
              • MR Imaging
              • Diskography and CT Diskography
                • SUMMARY
                  • References
Page 30: CLASSIFICATION, DIAGNOSTIC IMAGING, AND IMAGING ... · PDF fileclassification, diagnostic imaging, and imaging characterization of a lumbar herniated disk ... classification, diagnostic

13 Brant-Zawadzki MN Jensen MC Obuchowski N et al Interobserver and intraobserver variability in interpretation of lumbar disc abnormalities A comparison of two nomenclatures Spine 201257-1263 1995 Abstract 14 Breton G Is that a bulging disk a small herniation or a moderate protrusion [editorial] Can Assoc Radiol J 42318 1991 Citation 15 Czervionke LF Lumbar intervertebral disc disease Neuroimaging Clin North Am 3465-485 1993 16 Deyo RA Nonsurgical care of low back pain Neurosurg Clin North Am 2851-862 1991 17 Deyo RA Loeser JD Bigos SJ Herniated lumbar intervertebral disk Ann Intern Med 112598-603 1990 Abstract 18 Dorlands Illustrated Medical Dictionary ed 28 Philadelphia WB Saunders 1994 19 Fardon D Pinkerton S Balderston R et al Terms used for diagnosis by English speaking spine surgeons Spine 18274-277 1993 Citation 20 Fardon DF Herzog RJ Mink JH et al Nomenclature of Lumbar Disc Disorders Contemporary Concepts in Spine Care Rosemont IL North American Spine Society 1995 21 Fardon DF Herzog RJ Mink JH et al Nomenclature of lumbar disc disorders In Garfin S Vaccaro A (eds) Orthopedic Knowledge Update Spine Rosemont IL American Academy of Orthopedic Surgeons 1997 pp A3-A14 22 Forristall RM Marsh HO Pay NT Magnetic resonance imaging and contrast CT of the lumbar spine Comparison of diagnostic methods and correlation with surgical findings Spine 131049-1054 1988 Abstract 23 Fries JW Abodeely DA Vijungco JG et al Computed tomography of herniated and extruded nucleus pulposus J Comput Assist Tomogr 6874-887 1982 Abstract 24 Frymoyer JW Newberg A Pope MH et al Spine radiographs in patients with low-back pain An epidemiological study in men J Bone Joint Surg Am 661048-1055 1984 Abstract 25 Gospodarowicz M Benedet L Hutter RV et al History and international developments in cancer staging Cancer Prev Control 2262-268 1998 Abstract 26 Grenier N Greselle JF Vital JM et al Normal and disrupted lumbar longitudinal ligaments Correlative MR and anatomic study Radiology 171197-205 1989 Abstract 27 Gunzburg R Parkinson R Moore R et al A cadaveric study comparing discography magnetic resonance imaging histology and mechanical behavior of the human lumbar disc Spine 17417-426 1992 Abstract 28 Haughton VM Eldevik OP Magnaes B et al A prospective comparison of computed tomography and myelography in the diagnosis of herniated lumbar disks Radiology 142103-110 1982 Abstract

29 Haughton VM Lim TH An H Intervertebral disk appearance correlated with stiffness of lumbar spinal motion segments AJNR Am J Neuroradiol 201161-1165 1999 Abstract 30 Herzog RJ The radiologic assessment for a lumbar disc herniation Spine 2119S-38S 1996 Abstract 31 Jackson RP Becker GJ Jacobs RR et al The neuroradiographic diagnosis of lumbar herniated nucleus pulposus I A comparison of computed tomography (CT) myelography CT-myelography discography and CT-discography Spine 141356-1361 1989 Abstract 32 Jackson RP Cain JE Jr Jacobs RR et al The neuroradiographic diagnosis of lumbar herniated nucleus pulposus II A comparison of computed tomography (CT) myelography CT-myelography and magnetic resonance imaging Spine 141362-1367 1989 Abstract 33 Jarvik JG Haynor DR Koepsell TD et al Interreader reliability for a new classification of lumbar disk disease Acad Radiol 3537-544 1996 Abstract 34 Jensen MC Brant-Zawadzki MN Obuchowski N et al Magnetic resonance imaging of the lumbar spine in people without back pain N Engl J Med 33169-73 1994 Abstract 35 Kent DL Haynor DR Larson EB et al Diagnosis of lumbar spinal stenosis in adults A meta-analysis of the accuracy of CT MR and myelography AJR Am J Roentgenol 1581135-1144 1992 Abstract 36 Kieffer SA Sherry RG Wellenstein DE et al Bulging lumbar intervertebral disk Myelographic differentiation from herniated disk with nerve root compression AJR Am J Roentgenol 138709-716 1982 Abstract 37 Kieffer SA Stadlan EM Mohandas A et al Discographic-anatomical correlation of developmental changes with age in the intervertebral disc Acta Radiol 9733-739 1969 38 Kim KY Kim YT Lee CS et al MRI classification of lumbar herniated intervertebral disc Orthopedics 15493-497 1992 Abstract 39 Kornberg M Rechtine GR Dupuy TE Computed tomography in the diagnosis of a herniated disk at the L5-S1 level Spine 9433-436 1984 Abstract 40 Kramer MS Clinical Epidemiology and Biostatistics New York Springer-Verlag 1988 41 Landis JR Koch GG The measurement of observer agreement agreement for categorical data Biometrics 33159-174 1977 Abstract 42 Laredo JD Bossard P Vuillemin-Bodaghi Formes anatomo-radiologiques des hernies discales In Morvan G Deburge A Bard H et al (eds) Le Rachis Lombaire Degeneratif Montpellier Sauramps Medical 1998 pp 37-49 43 Lee SH Coleman PE Hahn FJ Magnetic resonance imaging of degenerative disk disease of the spine Radiol Clin North Am 26949-964 1988 Abstract 44 Linson MA Crowe CH Comparison of magnetic resonance imaging and lumbar discography in the diagnosis of disc degeneration Clin Orthop 160-163 1990

45 Marchand F Ahmed AM Investigation of the laminate structure of lumbar disc anulus fibrosus Spine 15402-410 1990 Abstract 46 Masaryk TJ Ross JS Modic MT et al High-resolution MR imaging of sequestered lumbar intervertebral disks AJR Am J Roentgenol 1501155-1162 1988 Abstract 47 Milette PC The proper terminology for reporting lumbar intervertebral disk disorders AJNR Am J Neuroradiol 181859-1866 1997 Citation 48 Milette PC Fontaine S Lepanto L et al Differentiating lumbar disc protrusions disk bulges and discs with normal contour but abnormal signal intensity Magnetic resonance imaging with discographic correlations Spine 2444-53 1999 Abstract 49 Milette PC Fontaine S Lepanto L et al Radiating pain to the lower extremities caused by lumbar disk rupture without spinal nerve root involvement AJNR Am J Neuroradiol 161605-1613 1995 Abstract 50 Milette PC Melancon D A reappraisal of lumbar discography Can Assoc Radiol J 33176-182 1982 51 Milette PC Melancon D Dupuis PR et al A simplified terminology for abnormalities of the lumbar disk Can Assoc Radiol J 42319-325 1991 Abstract 52 Milette PC Raymond J Fontaine S Comparison of high-resolution computed tomography with discography in the evaluation of lumbar disc herniations Spine 15525-533 1990 Abstract 53 Mink JH Deutsch AL Goldstein TB et al Spinal imaging and intervention 1998 Phys Med Rehabil Clin North Am 9343-380 1998 54 Mixter WJ Barr JS Rupture of the intervertebral disc with involvement of the spinal canal N Engl J Med 211210-234 1934 55 Modic MT Masaryk TJ Ross JS et al Imaging of degenerative disk disease Radiology 168177-186 1988 Citation 56 Modic MT Ross JS Obuchowski NA et al Contrast-enhanced MR imaging in acute lumbar radiculopathy A pilot study of the natural history Radiology 195429-435 1995 Abstract 57 Modic MT Steinberg PM Ross JS et al Degenerative disk disease Assessment of changes in vertebral body marrow with MR imaging Radiology 166193-199 1988 58 Morvan G Mathieu P Les stenoses laterales In Morvan G Deburge A Bard H et al (eds) Le Rachis Lombaire Degeneratif Montpellier Sauramps Medical 1998 pp 315-324 59 Murray RO Skeletal trauma Regional In Sutton D (ed) Textbook of Radiology and Imaging ed 3 New York Churchill Livingstone 1980 pp 210-231 60 Nachemson A Lumbar disc herniation Conclusions Acta Orthop Scand 64(suppl 251)49 1993 Citation

61 Nathan H Osteophytes of the vertebral column An anatomical study of their development according to age race and sex with consideration as to their etiology and significance J Bone Joint Surg Am 44243-268 1962 62 Nygaard OP Mellgren SI Osterud B The inflammatory properties of contained and noncontained lumbar disc herniations Spine 222584-2488 1997 Abstract 63 Ohshima H Hirano N Osada R et al Morphologic variation of lumbar posterior longitudinal ligament and the modality of disc herniation Spine 182408-2411 1993 Abstract 64 Osti OL Fraser RD MRI and discography of annular tears and intervertebral disc degeneration A prospective clinical comparison J Bone Joint Surg Br 74431-435 1992 Abstract 65 Palmgren T Gronblad M Virri J et al Immunohistochemical demonstration of sensory and autonomic nerve terminals in herniated lumbar disc tissue Spine 211301-1306 1996 Abstract 66 Resnick D Niwayama G Degenerative disease of the spine In Resnick D (ed) Diagnosis of Bone and Joint Disorders ed 3 Philadelphia WB Saunders 1995 pp 1372-1462 67 Resnick D Niwayama G Intravertebral disk herniations Cartilaginous (Schmorls) nodes Radiology 12657-65 1978 Abstract 68 Ross JS Modic MT Masaryk TJ Tears of the anulus fibrosus Assessment with Gd-DTPA-enhanced MR imaging AJR Am J Roentgenol 154159-162 1990 Abstract 69 Saal JS The role of inflammation in lumbar pain Spine 201821-1827 1995 Abstract 70 Sachs BL Vanharanta H Spivey MA et al Dallas discogram description A new classification of CTdiscography in low-back disorders Spine 12287-294 1987 Abstract 71 Sauser DD Goldman AB Kaye JJ Discogenic vertebral sclerosis J Can Assoc Radiol 2944-50 1978 Abstract 72 Schellhas KP Pollei SR Gundry CR et al Lumbar disc high-intensity zone Correlation of magnetic resonance imaging and discography Spine 2179-86 1996 Abstract 73 Schellinger D Manz HJ Vidic B et al Disk fragment migration Radiology 175831-836 1990 Abstract 74 Schipper J Kardaun JW Braakman R et al Lumbar disk herniation Diagnosis with CT or myelography Radiology 165227-231 1987 Abstract 75 Schmorl G Junghanns H The Human Spine in Health and Disease ed 2 New York Grune and Stratton 1971 76 Silverman CS Lenchik L Shimkin PM et al The value of MR in differentiating subligamentous from supraligamentous lumbar disk herniations AJNR Am J Neuroradiol 16571-579 1995 Abstract 77 Simmons JW Emery SF McMillin JN et al Awake discography A comparison study with magnetic

resonance imaging Spine 16S216-221 1991 Abstract 78 Smyth MJ Wright V Sciatica and the intervertebral disc J Bone Joint Surg Am 401401-1418 1958 79 Taveras JM Radiologic aspects of low back pain and sciatic syndromes [editorial] AJNR Am J Neuroradiol 9351-358 1989 80 Tehranzadeh J Discography 2000 Radiol Clin North Am 36463-495 1998 Full Text 81 Thelander U Fagerlund M Friberg S et al Describing the size of lumbar disc herniations using computed tomography A comparison of different size index calculations and their relation to sciatica Spine 191979-1984 1994 Abstract 82 Thornbury JR Fryback DG Turski PA et al Disk-caused nerve compression in patients with acute low-back pain Diagnosis with MR CT myelography and plain CT Radiology 186731-738 1993 Abstract 83 Twomey L Taylor J Age changes in lumbar intervertebral discs Acta Orthop Scand 56496-499 1985 Abstract 84 Twomey LT Taylor JR Age changes in lumbar vertebrae and intervertebral discs Clin Orthop 22497-104 1987 85 Williams AL CT diagnosis of degenerative disc disease The bulging annulus Radiol Clin North Am 21289-300 1983 Abstract 86 Williams AL Haughton VM Meyer GA et al Computed tomographic appearance of the bulging annulus Radiology 142403-408 1982 Abstract 87 Williams AL Haughton VM Syvertsen A Computed tomography in the diagnosis of herniated nucleus pulposus Radiology 13595-99 1980 Abstract 88 Wiltse LL Berger PE McCulloch JA A system for reporting the size and location of lesions in the spine Spine 221534-1537 1997 Abstract 89 Wiltse LL Fonseca AS Amster J et al Relationship of the dura Hofmanns ligaments Batsons plexus and a fibrovascular membrane lying on the posterior surface of the vertebral bodies and attaching to the deep layer of the posterior longitudinal ligament An anatomical radiologic and clinical study Spine 181030-1043 1993 Abstract 90 Yamashita K Hiroshima K Kurata A Gadolinium-DTPA-enhanced magnetic resonance imaging of a sequestered lumbar intervertebral disc and its correlation with pathologic findings Spine 19479-482 1994 Abstract 91 Yu SW Haughton VM Sether LA et al Comparison of MR and diskography in detecting radial tears of the anulus A postmortem study AJNR Am J Neuroradiol 101077-1081 1989 Abstract 92 Yu SW Sether LA Ho PS et al Tears of the anulus fibrosus Correlation between MR and pathologic findings in cadavers AJNR Am J Neuroradiol 9367-370 1988 Abstract

93 Yussen PS Swartz JD The acute lumbar disc herniation Imaging diagnosis Semin Ultrasound CT MR 14389-398 1993 Abstract 94 Zucherman J Derby R Hsu K et al Normal magnetic resonance imaging with abnormal discography Spine 131355-1359 1988 Abstract

Copyright copy 2008 Elsevier Inc All rights reserved - wwwmdconsultcom

Bookmark URL dasjournalview0N11535915ja=198094ampPAGE=1htmlampissn=0033-8389ampsource=MI

  • CLASSIFICATION DIAGNOSTIC IMAGING AND IMAGING CHARACTERIZATION OF A LUMBAR HERNIATED DISK
    • IMAGING OF LOW BACK PAIN I
      • CLASSIFICATION DIAGNOSTIC IMAGING AND IMAGING CHARACTERIZATION OF A LUMBAR HERNIATED DISK
        • DEFINITION OF A DISK HERNIATION
        • CLASSIFICATION OF A HERNIATED LUMBAR DISK
          • Main Categories of Noninfectious Disk Abnormalities
          • Further Qualifying the Displaced Disk Material Beyond the Disk Space
            • DIAGNOSTIC IMAGING AND CHARACTERIZATION OF A HERNIATED LUMBAR DISK
              • Conventional Radiographs
              • Myelography
              • CT
              • CT Myelography
              • MR Imaging
              • Diskography and CT Diskography
                • SUMMARY
                  • References
Page 31: CLASSIFICATION, DIAGNOSTIC IMAGING, AND IMAGING ... · PDF fileclassification, diagnostic imaging, and imaging characterization of a lumbar herniated disk ... classification, diagnostic

29 Haughton VM Lim TH An H Intervertebral disk appearance correlated with stiffness of lumbar spinal motion segments AJNR Am J Neuroradiol 201161-1165 1999 Abstract 30 Herzog RJ The radiologic assessment for a lumbar disc herniation Spine 2119S-38S 1996 Abstract 31 Jackson RP Becker GJ Jacobs RR et al The neuroradiographic diagnosis of lumbar herniated nucleus pulposus I A comparison of computed tomography (CT) myelography CT-myelography discography and CT-discography Spine 141356-1361 1989 Abstract 32 Jackson RP Cain JE Jr Jacobs RR et al The neuroradiographic diagnosis of lumbar herniated nucleus pulposus II A comparison of computed tomography (CT) myelography CT-myelography and magnetic resonance imaging Spine 141362-1367 1989 Abstract 33 Jarvik JG Haynor DR Koepsell TD et al Interreader reliability for a new classification of lumbar disk disease Acad Radiol 3537-544 1996 Abstract 34 Jensen MC Brant-Zawadzki MN Obuchowski N et al Magnetic resonance imaging of the lumbar spine in people without back pain N Engl J Med 33169-73 1994 Abstract 35 Kent DL Haynor DR Larson EB et al Diagnosis of lumbar spinal stenosis in adults A meta-analysis of the accuracy of CT MR and myelography AJR Am J Roentgenol 1581135-1144 1992 Abstract 36 Kieffer SA Sherry RG Wellenstein DE et al Bulging lumbar intervertebral disk Myelographic differentiation from herniated disk with nerve root compression AJR Am J Roentgenol 138709-716 1982 Abstract 37 Kieffer SA Stadlan EM Mohandas A et al Discographic-anatomical correlation of developmental changes with age in the intervertebral disc Acta Radiol 9733-739 1969 38 Kim KY Kim YT Lee CS et al MRI classification of lumbar herniated intervertebral disc Orthopedics 15493-497 1992 Abstract 39 Kornberg M Rechtine GR Dupuy TE Computed tomography in the diagnosis of a herniated disk at the L5-S1 level Spine 9433-436 1984 Abstract 40 Kramer MS Clinical Epidemiology and Biostatistics New York Springer-Verlag 1988 41 Landis JR Koch GG The measurement of observer agreement agreement for categorical data Biometrics 33159-174 1977 Abstract 42 Laredo JD Bossard P Vuillemin-Bodaghi Formes anatomo-radiologiques des hernies discales In Morvan G Deburge A Bard H et al (eds) Le Rachis Lombaire Degeneratif Montpellier Sauramps Medical 1998 pp 37-49 43 Lee SH Coleman PE Hahn FJ Magnetic resonance imaging of degenerative disk disease of the spine Radiol Clin North Am 26949-964 1988 Abstract 44 Linson MA Crowe CH Comparison of magnetic resonance imaging and lumbar discography in the diagnosis of disc degeneration Clin Orthop 160-163 1990

45 Marchand F Ahmed AM Investigation of the laminate structure of lumbar disc anulus fibrosus Spine 15402-410 1990 Abstract 46 Masaryk TJ Ross JS Modic MT et al High-resolution MR imaging of sequestered lumbar intervertebral disks AJR Am J Roentgenol 1501155-1162 1988 Abstract 47 Milette PC The proper terminology for reporting lumbar intervertebral disk disorders AJNR Am J Neuroradiol 181859-1866 1997 Citation 48 Milette PC Fontaine S Lepanto L et al Differentiating lumbar disc protrusions disk bulges and discs with normal contour but abnormal signal intensity Magnetic resonance imaging with discographic correlations Spine 2444-53 1999 Abstract 49 Milette PC Fontaine S Lepanto L et al Radiating pain to the lower extremities caused by lumbar disk rupture without spinal nerve root involvement AJNR Am J Neuroradiol 161605-1613 1995 Abstract 50 Milette PC Melancon D A reappraisal of lumbar discography Can Assoc Radiol J 33176-182 1982 51 Milette PC Melancon D Dupuis PR et al A simplified terminology for abnormalities of the lumbar disk Can Assoc Radiol J 42319-325 1991 Abstract 52 Milette PC Raymond J Fontaine S Comparison of high-resolution computed tomography with discography in the evaluation of lumbar disc herniations Spine 15525-533 1990 Abstract 53 Mink JH Deutsch AL Goldstein TB et al Spinal imaging and intervention 1998 Phys Med Rehabil Clin North Am 9343-380 1998 54 Mixter WJ Barr JS Rupture of the intervertebral disc with involvement of the spinal canal N Engl J Med 211210-234 1934 55 Modic MT Masaryk TJ Ross JS et al Imaging of degenerative disk disease Radiology 168177-186 1988 Citation 56 Modic MT Ross JS Obuchowski NA et al Contrast-enhanced MR imaging in acute lumbar radiculopathy A pilot study of the natural history Radiology 195429-435 1995 Abstract 57 Modic MT Steinberg PM Ross JS et al Degenerative disk disease Assessment of changes in vertebral body marrow with MR imaging Radiology 166193-199 1988 58 Morvan G Mathieu P Les stenoses laterales In Morvan G Deburge A Bard H et al (eds) Le Rachis Lombaire Degeneratif Montpellier Sauramps Medical 1998 pp 315-324 59 Murray RO Skeletal trauma Regional In Sutton D (ed) Textbook of Radiology and Imaging ed 3 New York Churchill Livingstone 1980 pp 210-231 60 Nachemson A Lumbar disc herniation Conclusions Acta Orthop Scand 64(suppl 251)49 1993 Citation

61 Nathan H Osteophytes of the vertebral column An anatomical study of their development according to age race and sex with consideration as to their etiology and significance J Bone Joint Surg Am 44243-268 1962 62 Nygaard OP Mellgren SI Osterud B The inflammatory properties of contained and noncontained lumbar disc herniations Spine 222584-2488 1997 Abstract 63 Ohshima H Hirano N Osada R et al Morphologic variation of lumbar posterior longitudinal ligament and the modality of disc herniation Spine 182408-2411 1993 Abstract 64 Osti OL Fraser RD MRI and discography of annular tears and intervertebral disc degeneration A prospective clinical comparison J Bone Joint Surg Br 74431-435 1992 Abstract 65 Palmgren T Gronblad M Virri J et al Immunohistochemical demonstration of sensory and autonomic nerve terminals in herniated lumbar disc tissue Spine 211301-1306 1996 Abstract 66 Resnick D Niwayama G Degenerative disease of the spine In Resnick D (ed) Diagnosis of Bone and Joint Disorders ed 3 Philadelphia WB Saunders 1995 pp 1372-1462 67 Resnick D Niwayama G Intravertebral disk herniations Cartilaginous (Schmorls) nodes Radiology 12657-65 1978 Abstract 68 Ross JS Modic MT Masaryk TJ Tears of the anulus fibrosus Assessment with Gd-DTPA-enhanced MR imaging AJR Am J Roentgenol 154159-162 1990 Abstract 69 Saal JS The role of inflammation in lumbar pain Spine 201821-1827 1995 Abstract 70 Sachs BL Vanharanta H Spivey MA et al Dallas discogram description A new classification of CTdiscography in low-back disorders Spine 12287-294 1987 Abstract 71 Sauser DD Goldman AB Kaye JJ Discogenic vertebral sclerosis J Can Assoc Radiol 2944-50 1978 Abstract 72 Schellhas KP Pollei SR Gundry CR et al Lumbar disc high-intensity zone Correlation of magnetic resonance imaging and discography Spine 2179-86 1996 Abstract 73 Schellinger D Manz HJ Vidic B et al Disk fragment migration Radiology 175831-836 1990 Abstract 74 Schipper J Kardaun JW Braakman R et al Lumbar disk herniation Diagnosis with CT or myelography Radiology 165227-231 1987 Abstract 75 Schmorl G Junghanns H The Human Spine in Health and Disease ed 2 New York Grune and Stratton 1971 76 Silverman CS Lenchik L Shimkin PM et al The value of MR in differentiating subligamentous from supraligamentous lumbar disk herniations AJNR Am J Neuroradiol 16571-579 1995 Abstract 77 Simmons JW Emery SF McMillin JN et al Awake discography A comparison study with magnetic

resonance imaging Spine 16S216-221 1991 Abstract 78 Smyth MJ Wright V Sciatica and the intervertebral disc J Bone Joint Surg Am 401401-1418 1958 79 Taveras JM Radiologic aspects of low back pain and sciatic syndromes [editorial] AJNR Am J Neuroradiol 9351-358 1989 80 Tehranzadeh J Discography 2000 Radiol Clin North Am 36463-495 1998 Full Text 81 Thelander U Fagerlund M Friberg S et al Describing the size of lumbar disc herniations using computed tomography A comparison of different size index calculations and their relation to sciatica Spine 191979-1984 1994 Abstract 82 Thornbury JR Fryback DG Turski PA et al Disk-caused nerve compression in patients with acute low-back pain Diagnosis with MR CT myelography and plain CT Radiology 186731-738 1993 Abstract 83 Twomey L Taylor J Age changes in lumbar intervertebral discs Acta Orthop Scand 56496-499 1985 Abstract 84 Twomey LT Taylor JR Age changes in lumbar vertebrae and intervertebral discs Clin Orthop 22497-104 1987 85 Williams AL CT diagnosis of degenerative disc disease The bulging annulus Radiol Clin North Am 21289-300 1983 Abstract 86 Williams AL Haughton VM Meyer GA et al Computed tomographic appearance of the bulging annulus Radiology 142403-408 1982 Abstract 87 Williams AL Haughton VM Syvertsen A Computed tomography in the diagnosis of herniated nucleus pulposus Radiology 13595-99 1980 Abstract 88 Wiltse LL Berger PE McCulloch JA A system for reporting the size and location of lesions in the spine Spine 221534-1537 1997 Abstract 89 Wiltse LL Fonseca AS Amster J et al Relationship of the dura Hofmanns ligaments Batsons plexus and a fibrovascular membrane lying on the posterior surface of the vertebral bodies and attaching to the deep layer of the posterior longitudinal ligament An anatomical radiologic and clinical study Spine 181030-1043 1993 Abstract 90 Yamashita K Hiroshima K Kurata A Gadolinium-DTPA-enhanced magnetic resonance imaging of a sequestered lumbar intervertebral disc and its correlation with pathologic findings Spine 19479-482 1994 Abstract 91 Yu SW Haughton VM Sether LA et al Comparison of MR and diskography in detecting radial tears of the anulus A postmortem study AJNR Am J Neuroradiol 101077-1081 1989 Abstract 92 Yu SW Sether LA Ho PS et al Tears of the anulus fibrosus Correlation between MR and pathologic findings in cadavers AJNR Am J Neuroradiol 9367-370 1988 Abstract

93 Yussen PS Swartz JD The acute lumbar disc herniation Imaging diagnosis Semin Ultrasound CT MR 14389-398 1993 Abstract 94 Zucherman J Derby R Hsu K et al Normal magnetic resonance imaging with abnormal discography Spine 131355-1359 1988 Abstract

Copyright copy 2008 Elsevier Inc All rights reserved - wwwmdconsultcom

Bookmark URL dasjournalview0N11535915ja=198094ampPAGE=1htmlampissn=0033-8389ampsource=MI

  • CLASSIFICATION DIAGNOSTIC IMAGING AND IMAGING CHARACTERIZATION OF A LUMBAR HERNIATED DISK
    • IMAGING OF LOW BACK PAIN I
      • CLASSIFICATION DIAGNOSTIC IMAGING AND IMAGING CHARACTERIZATION OF A LUMBAR HERNIATED DISK
        • DEFINITION OF A DISK HERNIATION
        • CLASSIFICATION OF A HERNIATED LUMBAR DISK
          • Main Categories of Noninfectious Disk Abnormalities
          • Further Qualifying the Displaced Disk Material Beyond the Disk Space
            • DIAGNOSTIC IMAGING AND CHARACTERIZATION OF A HERNIATED LUMBAR DISK
              • Conventional Radiographs
              • Myelography
              • CT
              • CT Myelography
              • MR Imaging
              • Diskography and CT Diskography
                • SUMMARY
                  • References
Page 32: CLASSIFICATION, DIAGNOSTIC IMAGING, AND IMAGING ... · PDF fileclassification, diagnostic imaging, and imaging characterization of a lumbar herniated disk ... classification, diagnostic

45 Marchand F Ahmed AM Investigation of the laminate structure of lumbar disc anulus fibrosus Spine 15402-410 1990 Abstract 46 Masaryk TJ Ross JS Modic MT et al High-resolution MR imaging of sequestered lumbar intervertebral disks AJR Am J Roentgenol 1501155-1162 1988 Abstract 47 Milette PC The proper terminology for reporting lumbar intervertebral disk disorders AJNR Am J Neuroradiol 181859-1866 1997 Citation 48 Milette PC Fontaine S Lepanto L et al Differentiating lumbar disc protrusions disk bulges and discs with normal contour but abnormal signal intensity Magnetic resonance imaging with discographic correlations Spine 2444-53 1999 Abstract 49 Milette PC Fontaine S Lepanto L et al Radiating pain to the lower extremities caused by lumbar disk rupture without spinal nerve root involvement AJNR Am J Neuroradiol 161605-1613 1995 Abstract 50 Milette PC Melancon D A reappraisal of lumbar discography Can Assoc Radiol J 33176-182 1982 51 Milette PC Melancon D Dupuis PR et al A simplified terminology for abnormalities of the lumbar disk Can Assoc Radiol J 42319-325 1991 Abstract 52 Milette PC Raymond J Fontaine S Comparison of high-resolution computed tomography with discography in the evaluation of lumbar disc herniations Spine 15525-533 1990 Abstract 53 Mink JH Deutsch AL Goldstein TB et al Spinal imaging and intervention 1998 Phys Med Rehabil Clin North Am 9343-380 1998 54 Mixter WJ Barr JS Rupture of the intervertebral disc with involvement of the spinal canal N Engl J Med 211210-234 1934 55 Modic MT Masaryk TJ Ross JS et al Imaging of degenerative disk disease Radiology 168177-186 1988 Citation 56 Modic MT Ross JS Obuchowski NA et al Contrast-enhanced MR imaging in acute lumbar radiculopathy A pilot study of the natural history Radiology 195429-435 1995 Abstract 57 Modic MT Steinberg PM Ross JS et al Degenerative disk disease Assessment of changes in vertebral body marrow with MR imaging Radiology 166193-199 1988 58 Morvan G Mathieu P Les stenoses laterales In Morvan G Deburge A Bard H et al (eds) Le Rachis Lombaire Degeneratif Montpellier Sauramps Medical 1998 pp 315-324 59 Murray RO Skeletal trauma Regional In Sutton D (ed) Textbook of Radiology and Imaging ed 3 New York Churchill Livingstone 1980 pp 210-231 60 Nachemson A Lumbar disc herniation Conclusions Acta Orthop Scand 64(suppl 251)49 1993 Citation

61 Nathan H Osteophytes of the vertebral column An anatomical study of their development according to age race and sex with consideration as to their etiology and significance J Bone Joint Surg Am 44243-268 1962 62 Nygaard OP Mellgren SI Osterud B The inflammatory properties of contained and noncontained lumbar disc herniations Spine 222584-2488 1997 Abstract 63 Ohshima H Hirano N Osada R et al Morphologic variation of lumbar posterior longitudinal ligament and the modality of disc herniation Spine 182408-2411 1993 Abstract 64 Osti OL Fraser RD MRI and discography of annular tears and intervertebral disc degeneration A prospective clinical comparison J Bone Joint Surg Br 74431-435 1992 Abstract 65 Palmgren T Gronblad M Virri J et al Immunohistochemical demonstration of sensory and autonomic nerve terminals in herniated lumbar disc tissue Spine 211301-1306 1996 Abstract 66 Resnick D Niwayama G Degenerative disease of the spine In Resnick D (ed) Diagnosis of Bone and Joint Disorders ed 3 Philadelphia WB Saunders 1995 pp 1372-1462 67 Resnick D Niwayama G Intravertebral disk herniations Cartilaginous (Schmorls) nodes Radiology 12657-65 1978 Abstract 68 Ross JS Modic MT Masaryk TJ Tears of the anulus fibrosus Assessment with Gd-DTPA-enhanced MR imaging AJR Am J Roentgenol 154159-162 1990 Abstract 69 Saal JS The role of inflammation in lumbar pain Spine 201821-1827 1995 Abstract 70 Sachs BL Vanharanta H Spivey MA et al Dallas discogram description A new classification of CTdiscography in low-back disorders Spine 12287-294 1987 Abstract 71 Sauser DD Goldman AB Kaye JJ Discogenic vertebral sclerosis J Can Assoc Radiol 2944-50 1978 Abstract 72 Schellhas KP Pollei SR Gundry CR et al Lumbar disc high-intensity zone Correlation of magnetic resonance imaging and discography Spine 2179-86 1996 Abstract 73 Schellinger D Manz HJ Vidic B et al Disk fragment migration Radiology 175831-836 1990 Abstract 74 Schipper J Kardaun JW Braakman R et al Lumbar disk herniation Diagnosis with CT or myelography Radiology 165227-231 1987 Abstract 75 Schmorl G Junghanns H The Human Spine in Health and Disease ed 2 New York Grune and Stratton 1971 76 Silverman CS Lenchik L Shimkin PM et al The value of MR in differentiating subligamentous from supraligamentous lumbar disk herniations AJNR Am J Neuroradiol 16571-579 1995 Abstract 77 Simmons JW Emery SF McMillin JN et al Awake discography A comparison study with magnetic

resonance imaging Spine 16S216-221 1991 Abstract 78 Smyth MJ Wright V Sciatica and the intervertebral disc J Bone Joint Surg Am 401401-1418 1958 79 Taveras JM Radiologic aspects of low back pain and sciatic syndromes [editorial] AJNR Am J Neuroradiol 9351-358 1989 80 Tehranzadeh J Discography 2000 Radiol Clin North Am 36463-495 1998 Full Text 81 Thelander U Fagerlund M Friberg S et al Describing the size of lumbar disc herniations using computed tomography A comparison of different size index calculations and their relation to sciatica Spine 191979-1984 1994 Abstract 82 Thornbury JR Fryback DG Turski PA et al Disk-caused nerve compression in patients with acute low-back pain Diagnosis with MR CT myelography and plain CT Radiology 186731-738 1993 Abstract 83 Twomey L Taylor J Age changes in lumbar intervertebral discs Acta Orthop Scand 56496-499 1985 Abstract 84 Twomey LT Taylor JR Age changes in lumbar vertebrae and intervertebral discs Clin Orthop 22497-104 1987 85 Williams AL CT diagnosis of degenerative disc disease The bulging annulus Radiol Clin North Am 21289-300 1983 Abstract 86 Williams AL Haughton VM Meyer GA et al Computed tomographic appearance of the bulging annulus Radiology 142403-408 1982 Abstract 87 Williams AL Haughton VM Syvertsen A Computed tomography in the diagnosis of herniated nucleus pulposus Radiology 13595-99 1980 Abstract 88 Wiltse LL Berger PE McCulloch JA A system for reporting the size and location of lesions in the spine Spine 221534-1537 1997 Abstract 89 Wiltse LL Fonseca AS Amster J et al Relationship of the dura Hofmanns ligaments Batsons plexus and a fibrovascular membrane lying on the posterior surface of the vertebral bodies and attaching to the deep layer of the posterior longitudinal ligament An anatomical radiologic and clinical study Spine 181030-1043 1993 Abstract 90 Yamashita K Hiroshima K Kurata A Gadolinium-DTPA-enhanced magnetic resonance imaging of a sequestered lumbar intervertebral disc and its correlation with pathologic findings Spine 19479-482 1994 Abstract 91 Yu SW Haughton VM Sether LA et al Comparison of MR and diskography in detecting radial tears of the anulus A postmortem study AJNR Am J Neuroradiol 101077-1081 1989 Abstract 92 Yu SW Sether LA Ho PS et al Tears of the anulus fibrosus Correlation between MR and pathologic findings in cadavers AJNR Am J Neuroradiol 9367-370 1988 Abstract

93 Yussen PS Swartz JD The acute lumbar disc herniation Imaging diagnosis Semin Ultrasound CT MR 14389-398 1993 Abstract 94 Zucherman J Derby R Hsu K et al Normal magnetic resonance imaging with abnormal discography Spine 131355-1359 1988 Abstract

Copyright copy 2008 Elsevier Inc All rights reserved - wwwmdconsultcom

Bookmark URL dasjournalview0N11535915ja=198094ampPAGE=1htmlampissn=0033-8389ampsource=MI

  • CLASSIFICATION DIAGNOSTIC IMAGING AND IMAGING CHARACTERIZATION OF A LUMBAR HERNIATED DISK
    • IMAGING OF LOW BACK PAIN I
      • CLASSIFICATION DIAGNOSTIC IMAGING AND IMAGING CHARACTERIZATION OF A LUMBAR HERNIATED DISK
        • DEFINITION OF A DISK HERNIATION
        • CLASSIFICATION OF A HERNIATED LUMBAR DISK
          • Main Categories of Noninfectious Disk Abnormalities
          • Further Qualifying the Displaced Disk Material Beyond the Disk Space
            • DIAGNOSTIC IMAGING AND CHARACTERIZATION OF A HERNIATED LUMBAR DISK
              • Conventional Radiographs
              • Myelography
              • CT
              • CT Myelography
              • MR Imaging
              • Diskography and CT Diskography
                • SUMMARY
                  • References
Page 33: CLASSIFICATION, DIAGNOSTIC IMAGING, AND IMAGING ... · PDF fileclassification, diagnostic imaging, and imaging characterization of a lumbar herniated disk ... classification, diagnostic

61 Nathan H Osteophytes of the vertebral column An anatomical study of their development according to age race and sex with consideration as to their etiology and significance J Bone Joint Surg Am 44243-268 1962 62 Nygaard OP Mellgren SI Osterud B The inflammatory properties of contained and noncontained lumbar disc herniations Spine 222584-2488 1997 Abstract 63 Ohshima H Hirano N Osada R et al Morphologic variation of lumbar posterior longitudinal ligament and the modality of disc herniation Spine 182408-2411 1993 Abstract 64 Osti OL Fraser RD MRI and discography of annular tears and intervertebral disc degeneration A prospective clinical comparison J Bone Joint Surg Br 74431-435 1992 Abstract 65 Palmgren T Gronblad M Virri J et al Immunohistochemical demonstration of sensory and autonomic nerve terminals in herniated lumbar disc tissue Spine 211301-1306 1996 Abstract 66 Resnick D Niwayama G Degenerative disease of the spine In Resnick D (ed) Diagnosis of Bone and Joint Disorders ed 3 Philadelphia WB Saunders 1995 pp 1372-1462 67 Resnick D Niwayama G Intravertebral disk herniations Cartilaginous (Schmorls) nodes Radiology 12657-65 1978 Abstract 68 Ross JS Modic MT Masaryk TJ Tears of the anulus fibrosus Assessment with Gd-DTPA-enhanced MR imaging AJR Am J Roentgenol 154159-162 1990 Abstract 69 Saal JS The role of inflammation in lumbar pain Spine 201821-1827 1995 Abstract 70 Sachs BL Vanharanta H Spivey MA et al Dallas discogram description A new classification of CTdiscography in low-back disorders Spine 12287-294 1987 Abstract 71 Sauser DD Goldman AB Kaye JJ Discogenic vertebral sclerosis J Can Assoc Radiol 2944-50 1978 Abstract 72 Schellhas KP Pollei SR Gundry CR et al Lumbar disc high-intensity zone Correlation of magnetic resonance imaging and discography Spine 2179-86 1996 Abstract 73 Schellinger D Manz HJ Vidic B et al Disk fragment migration Radiology 175831-836 1990 Abstract 74 Schipper J Kardaun JW Braakman R et al Lumbar disk herniation Diagnosis with CT or myelography Radiology 165227-231 1987 Abstract 75 Schmorl G Junghanns H The Human Spine in Health and Disease ed 2 New York Grune and Stratton 1971 76 Silverman CS Lenchik L Shimkin PM et al The value of MR in differentiating subligamentous from supraligamentous lumbar disk herniations AJNR Am J Neuroradiol 16571-579 1995 Abstract 77 Simmons JW Emery SF McMillin JN et al Awake discography A comparison study with magnetic

resonance imaging Spine 16S216-221 1991 Abstract 78 Smyth MJ Wright V Sciatica and the intervertebral disc J Bone Joint Surg Am 401401-1418 1958 79 Taveras JM Radiologic aspects of low back pain and sciatic syndromes [editorial] AJNR Am J Neuroradiol 9351-358 1989 80 Tehranzadeh J Discography 2000 Radiol Clin North Am 36463-495 1998 Full Text 81 Thelander U Fagerlund M Friberg S et al Describing the size of lumbar disc herniations using computed tomography A comparison of different size index calculations and their relation to sciatica Spine 191979-1984 1994 Abstract 82 Thornbury JR Fryback DG Turski PA et al Disk-caused nerve compression in patients with acute low-back pain Diagnosis with MR CT myelography and plain CT Radiology 186731-738 1993 Abstract 83 Twomey L Taylor J Age changes in lumbar intervertebral discs Acta Orthop Scand 56496-499 1985 Abstract 84 Twomey LT Taylor JR Age changes in lumbar vertebrae and intervertebral discs Clin Orthop 22497-104 1987 85 Williams AL CT diagnosis of degenerative disc disease The bulging annulus Radiol Clin North Am 21289-300 1983 Abstract 86 Williams AL Haughton VM Meyer GA et al Computed tomographic appearance of the bulging annulus Radiology 142403-408 1982 Abstract 87 Williams AL Haughton VM Syvertsen A Computed tomography in the diagnosis of herniated nucleus pulposus Radiology 13595-99 1980 Abstract 88 Wiltse LL Berger PE McCulloch JA A system for reporting the size and location of lesions in the spine Spine 221534-1537 1997 Abstract 89 Wiltse LL Fonseca AS Amster J et al Relationship of the dura Hofmanns ligaments Batsons plexus and a fibrovascular membrane lying on the posterior surface of the vertebral bodies and attaching to the deep layer of the posterior longitudinal ligament An anatomical radiologic and clinical study Spine 181030-1043 1993 Abstract 90 Yamashita K Hiroshima K Kurata A Gadolinium-DTPA-enhanced magnetic resonance imaging of a sequestered lumbar intervertebral disc and its correlation with pathologic findings Spine 19479-482 1994 Abstract 91 Yu SW Haughton VM Sether LA et al Comparison of MR and diskography in detecting radial tears of the anulus A postmortem study AJNR Am J Neuroradiol 101077-1081 1989 Abstract 92 Yu SW Sether LA Ho PS et al Tears of the anulus fibrosus Correlation between MR and pathologic findings in cadavers AJNR Am J Neuroradiol 9367-370 1988 Abstract

93 Yussen PS Swartz JD The acute lumbar disc herniation Imaging diagnosis Semin Ultrasound CT MR 14389-398 1993 Abstract 94 Zucherman J Derby R Hsu K et al Normal magnetic resonance imaging with abnormal discography Spine 131355-1359 1988 Abstract

Copyright copy 2008 Elsevier Inc All rights reserved - wwwmdconsultcom

Bookmark URL dasjournalview0N11535915ja=198094ampPAGE=1htmlampissn=0033-8389ampsource=MI

  • CLASSIFICATION DIAGNOSTIC IMAGING AND IMAGING CHARACTERIZATION OF A LUMBAR HERNIATED DISK
    • IMAGING OF LOW BACK PAIN I
      • CLASSIFICATION DIAGNOSTIC IMAGING AND IMAGING CHARACTERIZATION OF A LUMBAR HERNIATED DISK
        • DEFINITION OF A DISK HERNIATION
        • CLASSIFICATION OF A HERNIATED LUMBAR DISK
          • Main Categories of Noninfectious Disk Abnormalities
          • Further Qualifying the Displaced Disk Material Beyond the Disk Space
            • DIAGNOSTIC IMAGING AND CHARACTERIZATION OF A HERNIATED LUMBAR DISK
              • Conventional Radiographs
              • Myelography
              • CT
              • CT Myelography
              • MR Imaging
              • Diskography and CT Diskography
                • SUMMARY
                  • References
Page 34: CLASSIFICATION, DIAGNOSTIC IMAGING, AND IMAGING ... · PDF fileclassification, diagnostic imaging, and imaging characterization of a lumbar herniated disk ... classification, diagnostic

resonance imaging Spine 16S216-221 1991 Abstract 78 Smyth MJ Wright V Sciatica and the intervertebral disc J Bone Joint Surg Am 401401-1418 1958 79 Taveras JM Radiologic aspects of low back pain and sciatic syndromes [editorial] AJNR Am J Neuroradiol 9351-358 1989 80 Tehranzadeh J Discography 2000 Radiol Clin North Am 36463-495 1998 Full Text 81 Thelander U Fagerlund M Friberg S et al Describing the size of lumbar disc herniations using computed tomography A comparison of different size index calculations and their relation to sciatica Spine 191979-1984 1994 Abstract 82 Thornbury JR Fryback DG Turski PA et al Disk-caused nerve compression in patients with acute low-back pain Diagnosis with MR CT myelography and plain CT Radiology 186731-738 1993 Abstract 83 Twomey L Taylor J Age changes in lumbar intervertebral discs Acta Orthop Scand 56496-499 1985 Abstract 84 Twomey LT Taylor JR Age changes in lumbar vertebrae and intervertebral discs Clin Orthop 22497-104 1987 85 Williams AL CT diagnosis of degenerative disc disease The bulging annulus Radiol Clin North Am 21289-300 1983 Abstract 86 Williams AL Haughton VM Meyer GA et al Computed tomographic appearance of the bulging annulus Radiology 142403-408 1982 Abstract 87 Williams AL Haughton VM Syvertsen A Computed tomography in the diagnosis of herniated nucleus pulposus Radiology 13595-99 1980 Abstract 88 Wiltse LL Berger PE McCulloch JA A system for reporting the size and location of lesions in the spine Spine 221534-1537 1997 Abstract 89 Wiltse LL Fonseca AS Amster J et al Relationship of the dura Hofmanns ligaments Batsons plexus and a fibrovascular membrane lying on the posterior surface of the vertebral bodies and attaching to the deep layer of the posterior longitudinal ligament An anatomical radiologic and clinical study Spine 181030-1043 1993 Abstract 90 Yamashita K Hiroshima K Kurata A Gadolinium-DTPA-enhanced magnetic resonance imaging of a sequestered lumbar intervertebral disc and its correlation with pathologic findings Spine 19479-482 1994 Abstract 91 Yu SW Haughton VM Sether LA et al Comparison of MR and diskography in detecting radial tears of the anulus A postmortem study AJNR Am J Neuroradiol 101077-1081 1989 Abstract 92 Yu SW Sether LA Ho PS et al Tears of the anulus fibrosus Correlation between MR and pathologic findings in cadavers AJNR Am J Neuroradiol 9367-370 1988 Abstract

93 Yussen PS Swartz JD The acute lumbar disc herniation Imaging diagnosis Semin Ultrasound CT MR 14389-398 1993 Abstract 94 Zucherman J Derby R Hsu K et al Normal magnetic resonance imaging with abnormal discography Spine 131355-1359 1988 Abstract

Copyright copy 2008 Elsevier Inc All rights reserved - wwwmdconsultcom

Bookmark URL dasjournalview0N11535915ja=198094ampPAGE=1htmlampissn=0033-8389ampsource=MI

  • CLASSIFICATION DIAGNOSTIC IMAGING AND IMAGING CHARACTERIZATION OF A LUMBAR HERNIATED DISK
    • IMAGING OF LOW BACK PAIN I
      • CLASSIFICATION DIAGNOSTIC IMAGING AND IMAGING CHARACTERIZATION OF A LUMBAR HERNIATED DISK
        • DEFINITION OF A DISK HERNIATION
        • CLASSIFICATION OF A HERNIATED LUMBAR DISK
          • Main Categories of Noninfectious Disk Abnormalities
          • Further Qualifying the Displaced Disk Material Beyond the Disk Space
            • DIAGNOSTIC IMAGING AND CHARACTERIZATION OF A HERNIATED LUMBAR DISK
              • Conventional Radiographs
              • Myelography
              • CT
              • CT Myelography
              • MR Imaging
              • Diskography and CT Diskography
                • SUMMARY
                  • References
Page 35: CLASSIFICATION, DIAGNOSTIC IMAGING, AND IMAGING ... · PDF fileclassification, diagnostic imaging, and imaging characterization of a lumbar herniated disk ... classification, diagnostic

93 Yussen PS Swartz JD The acute lumbar disc herniation Imaging diagnosis Semin Ultrasound CT MR 14389-398 1993 Abstract 94 Zucherman J Derby R Hsu K et al Normal magnetic resonance imaging with abnormal discography Spine 131355-1359 1988 Abstract

Copyright copy 2008 Elsevier Inc All rights reserved - wwwmdconsultcom

Bookmark URL dasjournalview0N11535915ja=198094ampPAGE=1htmlampissn=0033-8389ampsource=MI

  • CLASSIFICATION DIAGNOSTIC IMAGING AND IMAGING CHARACTERIZATION OF A LUMBAR HERNIATED DISK
    • IMAGING OF LOW BACK PAIN I
      • CLASSIFICATION DIAGNOSTIC IMAGING AND IMAGING CHARACTERIZATION OF A LUMBAR HERNIATED DISK
        • DEFINITION OF A DISK HERNIATION
        • CLASSIFICATION OF A HERNIATED LUMBAR DISK
          • Main Categories of Noninfectious Disk Abnormalities
          • Further Qualifying the Displaced Disk Material Beyond the Disk Space
            • DIAGNOSTIC IMAGING AND CHARACTERIZATION OF A HERNIATED LUMBAR DISK
              • Conventional Radiographs
              • Myelography
              • CT
              • CT Myelography
              • MR Imaging
              • Diskography and CT Diskography
                • SUMMARY
                  • References