Available online at

www.sciencedirect.com

Joint Bone Spine 75 (2008) 643e649

Clinical-state-of-the-art

Ultrasound of the peripheral nerves

Stefano Bianchi*

Institut de Radiologie, Clinique et Fondation des Grangettes, Geneve, Suisse

Accepted 17 July 2008

Available online 26 September 2008

Abstract

Peripheral nerves disorders are common in the rheumatologic practice and can mimic a variety of musculoskeletal diseases. Clinicalevaluation remains the mainstay for diagnosing nerve disorders of the extremities. A careful history and an accurate physical examination lead inmost patients to a high diagnostic suspicion. Nevertheless several imaging techniques are usually obtained to confirm the clinical data and in thepreoperative workup. Although standard radiographs and computed tomography do not visualize the nerves directly, they can reveal the adjacentanatomic structures such as bones and joints and can add additional information that frequently is essential in the choice of adequate treatment.Magnetic resonance imaging and ultrasound show peripheral nerves directly and can reveal their size and internal structure. With the newdevelopments in high resolution, electronic broadband transducers, ultrasound (US) is now considered an optimal imaging technique to evaluatethe normal anatomy and disorders of peripheral nerves. Well recognized advantages of this technique in this field are: the possibility of realizinga dynamic examination and assessing long nerves segments in a short time; it is non-invasive and low cost. In addition US is better accepted bythe patients. In this article we present a brief description of the normal and US anatomy of the peripheral nerves followed by a description of theUS appearance of the most frequent disorders: entrapment neuropathies (EN), tumor and cystic lesions.� 2008 Elsevier Masson SAS. All rights reserved.

Keywords: Ultrasound; Nerves; Entrapment neuropathies; Tumors

1. Introduction

Peripheral nerve (PN) disorders are common in the routinerheumatologic practice and can mimic a variety of musculo-skeletal diseases [1e3]. Most PN disorders, in particularlynerve entrapments, are probably diagnosed with considerablydelay because of suboptimal knowledge of the anatomy andspecific disorders [3].

Clinical evaluation remains the mainstay of the diagnosis ofdisorders of the PN [4] and in most patients a careful historyand an accurate physical examination can lead to a highdiagnostic suspicion. Imaging techniques such as magneticresonance imaging (MRI) and ultrasound (US) can help theclinician with nerve assessment since they directly show thenerve involved and can reveal its size, internal structure and

* Corresponding author. Route de Florissant 70, 1206, Geneve, Suisse.

E-mail address: stefanobianchi@bluewin.ch

1297-319X/$ - see front matter � 2008 Elsevier Masson SAS. All rights reserved

doi:10.1016/j.jbspin.2008.07.002

vascularity. Due to its dynamic nature, US also allows realtime evaluation of nerve displacement during movements ofadjacent joints. Standard radiographs and computed tomog-raphy (CT) do not visualize the PN but can reveal thesurrounding anatomic structures, particularly bones and joints,and can be an essential source of information in choosing themost suitable treatment.

In the recent years US has gained wide acceptance in theevaluation of the musculoskeletal system [5e7]. With the newdevelopments of high resolution, electronic broadband trans-ducers, US is now considered an optimal imaging technique toevaluate the normal anatomy and disorders of PN [7,8]. Well-recognized advantages of US in this field are: the possibility ofrealizing a dynamic examination; it is non-invasive and lowcost [10e20]. In addition US allows a quick, detailed imagingof the entire length of the major peripheral nerves of bothlimbs [21]. In this article we present a brief description of thenormal and US anatomy of the PN followed by a descriptionof the US appearance the most frequent disorders.

.

Fig. 1. Normal US of a peripheral nerve. Axial (a) and longitudinal (b)

sonograms obtained over the median nerve (white arrow) at the carpal tunnel.

The transverse scan shows the nerve with a background of hyperechoic

connective tissue containing oval-to-round hypoechoic areas corresponding to

the nerve’s fascicles. In the longitudinal image the nerve appears as a tubular

structure including hypo-anechoic discontinuous segments, the so-called

fascicular pattern. Note that the adjacent tendons (black arrows) show

a different pattern (fibrillar pattern) made by hyperechoic fibrils packed

together.

644 S. Bianchi / Joint Bone Spine 75 (2008) 643e649

2. Normal anatomy and US anatomy

PN are made by nerve fibers (made by axon, surrounded bySchwann cells and myelin sheaths) that form the nervesfascicles and by connective tissue that has a supportive action[8,9,22]. While the fibers are surrounded by the endoneurium,the nerves fascicles are surrounded by the perineurium, a thickstructure that houses elastic fibers and vessels, which alsosurrounds the nerve. The perineurium is thicker in theanatomic areas in which PN are more subject to physiologicalcompression or stretching such as when they run insideinextensible fibro-osseus tunnels or superficially, close to boneprotuberances. The size and number of fascicles containedinside a nerve is highly variable and depends on the size of thenerve, its location, and its type [8].

The basic US anatomy of peripheral nerves has been welldescribed in textbooks on musculoskeletal ultrasound [7,8] aswell as in several articles [12,18,22]. The US appearanceclosely correlates to the histologic findings both in transversethen in longitudinal images [22]. Normal nerves appear asmarkedly echogenic tubular structures (corresponding to thesupportive connective tissue) containing hypo-anechoicdiscontinuous segments that correspond to the fascicles orgroup of fascicles. On transverse scans PN appear as hyper-echoic structures including oval-to-round hypoechoic areas(Fig. 1). The size of a single nerve decreases when examinedfrom proximal to distal due to the presence of branchesleaving the main nerve trunk. Usually no normal internalblood flow can be detected with color Doppler and, asa general rule, detectable internal flow signals must beconsidered as pathologic hypervascular changes.

When examining at US PN, as a general rule, axial imagesare best suited for detection and assessment of their rela-tionship with the surrounding structures. PN can be easilydetected both on the basis of their peculiar internal echos-tructure and on their anatomic location and relationship withadjacent vessels, muscles and tendons. In particular adjacentvessels, when present, are very useful landmarks since theycan be very rapidly detected because of their pulsatility andtypical appearance with color Doppler. Once identified thenerves can be easily followed by axial images obtained duringcranial and caudal displacement of the transducer, the so-called ‘‘elevator technique’’ [18,19]. This technique USexamination works well in routine practice and also allowsaccurate assessment of the nerves in anatomic areas that arenot familiar to the sonologist. Longitudinal images are moredifficult to obtain due to the curvilinear course of most nervesof the extremities, but can be valuable in cases with focalnerve compression. In this situation US can demonstrate, inthe same image, the compressed pathologic portion of thenerve together with its normal proximal and distal parts thusallowing a clear diagnosis. The peculiar dynamic nature of USallows exquisite assessment of nerve movements in normal[23,24] and in pathologic conditions [10,12]. Dynamic USexamination realized either in vitro or in vivo shows how PNcan change their shape according to stretching and externalpressure. This is due to changes in the relationship among

internal fascicles that are made possible by the presence of theloose connective tissue of the epineurium and the presence ofelastic fibers.

Several anatomic variations of PN can be easily detected byUS and are frequently found at routine examination. Somevariations are well tolerated but can be interpreted as patho-logic by inexperienced sonologists while others can predisposeto nerve compression. The most relevant anatomic variationscan affect the nerve size and shape, its position or otheradjacent structures. One of the most frequent variations (2.4%of normal individuals) is the presence of a high division of themedian nerve that may or may not be associated witha persistent median artery (Fig. 2) [25e27]. Such a congenitalanomaly must be known if an arthroscopic approach to carpaltunnel release is planned in order to avoid accidental nerveinjury. Bifid median nerves can be associated with a persistentmedian artery. This artery normally envolutes after birth butcan sometimes persist and cause carpal tunnel syndrome iflarger than 3 mm or when thrombosed. The diameter of thepersistent vessel and the presence of internal thrombosis caneasily be demonstrated by US [28]. Anomalies of nerveposition are less frequent. Rarely the median nerve can showa vertical tilt at the level of the proximal carpal tunnel. Theabsence of the superficial retinaculum found at the proximalcubital tunnel of the elbow can predispose to fixed or inter-mittent anterior instability of the ulnar nerve during elbow

Fig. 3. Entrapment neuropathy. Role of dynamic ultrasound. Axial sonograms

obtained over the cubital tunnel of the elbow in extension (a) and flexion (b) of

the joint in a patient suffering from ulnar nerve neuropathy. Images show

a swollen hypoechoic nerve (white arrows). At elbow extension the nerve lies

posteriorly to the medial epycondile, inside the cubital tunnel. During elbow

flexion the nerve displaces anteriorly. Dynamic US can reveal intermittent

instability causing frictional neuritis.

Fig. 2. Bifid median nerve and median artery. Axial (a) and axial color Doppler

(b) sonograms obtained over the carpal tunnel in an asymptomatic subject.

Images show the presence of two distinct nerves (white arrows) running inside

the tunnel, the so-called bifid median nerve. Between the two nerves

a persistent median artery can be seen as a hypoechoic tubular pulsatile

structure showing internal flow signals at color Doppler.

645S. Bianchi / Joint Bone Spine 75 (2008) 643e649

flexion [10,12] (Fig. 3). Anatomic variations can also affectstructures found along the course of the PN and can affect thenerve itself. The most frequent is the presence of a supra-condilar process of the humerus that together with the liga-ment of Struthers, joining it to the distal humeral epiphysis,can cause median or ulnar nerve compression [29].

3. Entrapment neuropathies

The term entrapment neuropathies (EN) refers to a hetero-geneous group of conditions in which PN are compressed orstretched [30]. EN may result from congenital abnormalities,acquired disorders or a combination of both. In entrapmentneuropathies nerve changes and clinical symptoms aredependent both on the degree of compression and on itsduration. Low pressure applied for short time is relatively welltolerated and complete recovery can be expected after with-drawal of external compression. On the other hand high pres-sure for long periods of time can severely alter the morphologyand function of nerves and can eventually can result inirreversible damage.

3.1. Congenital abnormalities

PN can be prone to damage from microtrauma in hereditaryneuropathy with liability to pressure palsies (HNPP), anautosomal dominant inherited demyelinating disorderaffecting peripheral nerves and presenting as recurrent sensoryand motor mononeuropathy [31]. HNPP is due to a deletion on

the chromosome 17p11.2-12. which contains the peripheralmyelin protein-22 gene (PMP22). Ultrasound is able todemonstrate the pathologic appearance of nerves in HNPP asa diffuse enlargement and hypoechogenicity of several PNrunning also outside osteofibrous tunnels. PN that are clini-cally unaffected can show an abnormal appearance [32,33].

Congenital variations in the size of osteofibrous tunnels(such as carpal or cubital tunnel) derived from skeletaldysplasia can lead to local EN due to the chronic microtraumaof the nerve inside a narrowed canal. Accessory congenitalmuscles are common anatomic variants that can mimic tumorsor lead to compression on the adjacent structures [34,35].Accessory muscles running within the cubital tunnel at theelbow, Guyon and carpal tunnel as well as tarsal tunnel canincrease intracanal pressure during contraction or jointmovement and can lead to nerve compression [34-36]. Thesignificance of bifid median nerve and of persistent medianartery has been already discussed.

3.2. Acquired disorders

A variety of systemic disorders including diabetes mellitus,hemodialysis, thyroid disorders, amyloid and acromegaly canfacilitate EN. In several conditions such as diabetes mellitus,the pathomechanism probably relates to a pathologic increasesusceptibility to local compression of PN. In others such ashemodialysis and amyloidosis, narrowing of osteofibrous

646 S. Bianchi / Joint Bone Spine 75 (2008) 643e649

tunnels secondary to accumulation of amyloid is the mainfinding.

Nevertheless most EN found in routine clinical practice aresecondary to microtrauma to PN running inside inextensibleosteofibrous tunnels in patients without congenital or systemicdisorders. In these patients US is useful in the assessment ofthe pathologic appearance of the compressive lesions as wellas of the compressed nerve [30].

When prolonged, external compression on a PN results instructural changes to nerves. First, impaired vein flow leads toincreased intraneural interstitial pressure, which results inreversible intraneural edema, mainly found at the level ofconnective tissue. In more prolonged compressions, ischemiadue to damage of the vasa nervorum, the small vessels that areresponsible for vascularization of the nerve trunk, leads toirreversible internal fibrosis. This results finally in myelinsheath and axonal degeneration. Such morphological changesalter the function of nerve conduction with subsequent sensitiveor motor impairment depending on the type of nerve affected.

The chronic compressed PN presents the same appearanceat US regardless of the cause of the compression. Changes innerve size are most useful in diagnosing EN. The nervetypically presents a focal thinning at the site of the compres-sion and fusiform swelling proximal to it (Fig. 4). Several cut-off values have been proposed in the literature in an effort todistinguish between normal and pathologic size of the PN inEN [7,8]. Sometimes there is an abrupt passage from the two

Fig. 4. Entrapment neuropathy. Cubital tunnel syndrome. Axial sonogram (a)

and corresponding T2-weighted axial magnetic resonance image (b) as well as

a longitudinal image obtained over the cubital tunnel of the elbow in a patient

suffering from ulnar nerve neuropathy. The sonograms show a swollen and

irregularly hypoechoic ulnar nerve (white arrows). In (c) note the normal

internal pattern of the nerve portion located proximal to the tunnel (and the

irregular pattern of the nerve inside the tunnel, at the level of the medial

epycondile (asterisk). MR image obtained at the level of the cubital tunnel

shows an enlarged and hyperintense nerve (white arrowhead) as a result of

internal edema due to chronic impingement.

zones with evidence of the so-called ‘‘notch sign’’ (Fig. 5).This sign is of utmost utility in focusing the attention of thesonologist when the nerve is compressed by a fibrous band thatcan be difficult to detect at US. More rarely enlargement of thenerve can be also observed distal to the compression site. Thisis particularly seen in carpal tunnel syndrome where the distalportion of the nerve located inside the palm of the handdistally to the transverse carpal ligament can assume a ‘‘Cobrasnake head’’ appearance in longitudinal sonograms.

Changes inside the nerve are almost always observed inchronic compression. These are due to alterations in theintranervous connective tissue and correspond first to edemaand alterations of the inner vascularity followed by fibrosis.Unfortunately these changes cannot be differentiated at USand we are unable to differentiate between the two stages withthe current transducers. The nerve involved appears hypo-echoic because of hypoechogenicity of the endoneurium andinterfascicular perineurium, which results in the disappearanceof the typical fascicular pattern (related to the contrastbetween the hypoanechoic fascicles and the hyperechoicconnective tissue). Increased vascular signals can be seeninside the affected nerve at color Doppler.

In addition to assessing nerve changes, US helps in detectingand assessing a variety of causes of EN. Compressing massesare easily detected at the level of the extremities. US can assessthe size of the mass, borders, internal structure and vascularity.In a variety of cases it allows a specific diagnosis on the basis ofmass appearance (accessory muscles, mucoid cysts, lipoma .)

Fig. 5. Entrapment neuropathy. Carpal tunnel syndrome. Axial (a) and

longitudinal (b) sonograms obtained over the median nerve (white arrowheads)

at the carpal tunnel. The transverse scan shows an enlarged nerve compressed

by a hypertrophied synovial tendon sheath (asterisks). In the longitudinal

image the nerve appears swollen proximally to the tunnel (large arrowheads)

while it appears thinned and more hypoechoic (small arrowheads) inside the

osteofibrous canal. Note also significant thickening of the transverse carpal

ligament (black arrowhead). The flexor tendons are normal.

647S. Bianchi / Joint Bone Spine 75 (2008) 643e649

obviating the need for other expensive imaging techniques suchas MRI. Often integration of clinical data with the US findingsallows a higher degree of diagnostic suspicion, as for amyloiddeposits in carpal tunnel syndrome. When the mass presents anaspecific appearance at US, this can efficiently guide a needlebiopsy allowing accurate positioning of the needle. Since theaffected nerve always lies close to the mass, when performinga biopsy, real time US monitoring of the needle advance canavoid inadvertent nerve damage during the procedure. The mostcommon neuropathies affect the median [10e12,14], ulnar[10,11] and radial [15,17,37,38] nerve.

4. Tumors and other masses

Peripheral nerve tumors are mostly benign and include twomajor benign histotypes: schwannomas (also called neu-rilemomas) and neurofibromas [2,8]. Malignant peripheralnerve sheath tumors are rare and usually derive from thesarcomatous transformation of a neurofibroma. The differen-tiation between schwannomas and neurofibromas is importantclinically since the latter infiltrate the nerve trunk and requireresection and grafting. Schwannomas usually dislocate thenerve fascicle and can be shelled out while preserving nervecontiguity [39,40]. At US benign nerve tumors present asround, oval or fusiform hypoechoic masses with well-definedmargins. Internal cystic changes as well as posteriorenhancement can be observed. The most important criterionfor the US diagnosis is the relation of the mass with a nerve[41,42] (Fig. 6). This can be easily accomplished if the nerveis 2 mm or more in size and if the nerve lies in the superficialtissues. Assessment of the relationship with the nerve can bevery difficult in deep masses or when the nerve is small (e.g.nerves running in the subcutaneous tissues). In a recent study

Fig. 6. Schwannoma of the tibial nerve. Axial color Doppler sonogram (a),

longitudinal sonogram (b) and proton density coronal magnetic resonance

image (c) obtained posteriorly to the medial malleolus of the tibia. Sonograms

show a hypoechoic mass (S) located inside the nerve. In (a) note the close

relation of the tumor with the adjacent tibialis posterior artery and veins. In (b)

the tumor appears clearly located inside the nerve (arrowheads). The MR

image confirms the US findings.

on 76 peripheral nerve tumors, the relationship with the nervewas undetermined at US in 40% of the schwannomas and53.8% of the neurofibromas [39]. Axial images are usuallymore efficient in assessing the nerve/tumor relationship. Thenerve is first detected proximally and then followed distally tothe level of the mass. Longitudinal images can also be usefulbut visualization of the nerve entering and leaving the mass inthe same image can be difficult to achieve. As previouslystated differentiation between schwannomas and neurofi-bromas by imaging is of clinical importance since both historyand physical examination are ineffective in this regard.Distinction between the two hystotypes is difficult at US andno ultrasonographic findings currently allow a definite differ-entiation between schwannomas and neurofibromas of theextremities [2,39]. A nerve eccentrically entering the massstrongly suggests a diagnosis of schwannomas. Schwannomasmore often than neurofibromas show intratumor cystic changesand hypervascular pattern at color Doppler.

The majority of cysts (mucoid cysts, ganglia) responsiblefor compression on PN arise from the superior tibiofibularjoint (STFJ) [43,44]. There are two types of such cysts:intramuscular and intranervous ganglia. Both are mucoidcysts, with a fibrous external capsule and no synovial lining,that contain viscid fluid. In intramuscular cysts the compres-sion on the nerve is external while in intranervous cysts thefascicles are compressed by the mucoid ganglion that developsinside the nerve perineurium.

Intramuscular ganglia arising from the STFJ usuallydevelop inside the muscles of the anterolateral compartment ofthe leg and can compress the peroneal nerves and cause motordeficit and ill-defined pain in the anterolateral aspect of theleg. Intranervous ganglia enter the articular nerve branch andthen dissect cranially inside the peroneal nerve until reachingthe sciatic nerve. US demonstrates intramuscular ganglia aspear-shaped, anechoic expansible lesions with the proximalpointed portion closely related to the STFJ and a distalrounded portion extruding inside the muscles [44]. Septationsarising from the internal side of the fibrous wall are usuallyevident in larger ganglia. The relationship between the cystand the peroneal nerves and anterior tibial artery can beassessed by US. Needle aspiration can be efficiently guided byreal-time US and although not curative can ameliorate thepatients’ symptoms by lowering the intracystic pressure andthe pressure on the adjacent nerve.

Intranervous cysts are smaller than intramuscular gangliaand appear as tubuliform anechoic structures developinginside the nerve. US can depict hypoechoic enlargement of thearticular nervous branch and subsequent cranial extension ofthe cyst. If realized with a high-resolution probe, US can showthe compressed nerve fascicles displaced by the cyst thatappears surrounded by the epineurium.

5. Miscellaneous disorders

Due to its high resolution US can also be used to assessother disorders of the PN. These include traumatic nervedisorders either by external open wound such as in knife or

648 S. Bianchi / Joint Bone Spine 75 (2008) 643e649

pistol ball wounds, or nerve incarceration inside fractures suchas radial nerve trauma in humeral fractures [45,46]. In traumaUS can be used to assess the degree of nerve tears anddistinguish between partial and complete section, the distancebetween stumps and to detect eventual interposition of adja-cent structures, such as adipose tissue, between the nervestumps, which can limit correct nerve healing. US can assesspathologic nerve changes in CharcoteMarieeTooth disease[47], leprosy [48] and fibrolipomatous hamartoma [49].Recently because of its dynamic nature and possibility offollowing needle advancement, US is being more and more toguide local anesthesia [50,51].

References

[1] Bard H. Les syndromes canalaires vus en rhumatologie. Numero ped-

agogique. Rev Rhum 2007;74:315e433.

[2] Valle M, Zamorani MP. Nerve and vessels. In: Bianchi S, Martinoli C,

editors. Ultrasound of the musculoskeletal system. Springer-Verlag;

2007. p. 97e136.

[3] Bard H. Les syndromes canalaires. Rev Rhum 2007;74:315e8.

[4] Kim S, Choi JY, Huh YM, et al. Role of magnetic resonance imaging in

entrapment and compressive neuropathy e what, where, and how to see

the peripheral nerves on the musculoskeletal magnetic resonance image:

part 1. Overview and lower extremity. Eur Radiol 2007;17:139e49.

[5] Tardieu M, Brasseur J-L, editors. Echographie de l’appareil locomoteur.

Paris: Masson; 2006.

[6] van Holsbeeck M, Introcaso JH, editors. Musculoskeletal ultrasound. St.

Louis, MO: Mosby; 2001.

[7] Bianchi S, Martinoli C, editors. Ultrasound of the musculoskeletal

system. Berlin: Springer-Verlag; 2007.

[8] Peer S, Bodner G, editors. High-resolution sonography of the peripheral

nervous system. 2nd ed. Berlin: Springer-Verlag; 2008.

[9] Blancher A, Kubis N. Physiopathogenie des syndromes canalaires. In:

Les syndromes canalaires vus en rhumatologie. Rev Rhum, 74; 2007. p.

319e26.

[10] Martinoli C, Bianchi S, Gandolfo N, et al. Ultrasound of nerve entrap-

ments in osteofibrous tunnels. Radiographics 2000;20:S199e213.

[11] Bianchi S, Montet X, Martinoli C, et al. High-resolution sonography

of compressive neuropathies of the wrist. J Clin Ultrasound 2004;32:

451e61.

[12] Martinoli C, Bianchi S, Cohen M, et al. Echographie des nerfs periph-

eriques. J Radiol 2005;86:1869e78.

[13] Bianchi S, Montet X, Martinoli C, et al. Echographie des nerfs des

membres inferieurs. Rev Rhum 2007;74:415e23.

[14] Bianchi S, Demondion X, Bard H, et al. Ultrasound of the median nerve,

Echographie du nerf median. Rev Rhum 2007;74:376e83.

[15] Bodner G, Huber B, Schwabegger A, et al. Sonographic detection of

radial nerve entrapment within a humerus fracture. J Ultrasound Med

1999;18:703e6.

[16] Peer S, Bodner G, Meirer R, et al. Examination of postoperative

peripheral nerve lesions with high-resolution sonography. AJR Am J

Roentgenol 2001;177:415e9.

[17] Bodner G, Harpf C, Meirer R, et al. Ultrasonographic appearance of

supinator syndrome. J Ultrasound Med 2002;21:1289e93.

[18] Creteur V, Bacq C, Fumiere E, et al. [Sonography of peripheral nerves.

Part II: lower limbs]. J Radiol 2007;88:349e60.

[19] Creteur V, Bacq C, Widelec J. [Sonography of peripheral nerves. Part I:

upper limbs]. J Radiol 2004;85:1887e99.

[20] Beekman R, Visser LH. High-resolution sonography of the peripheral

nervous system ea review of the literature. Eur J Neurol 2004;11:

305e14.

[21] Stuart RM, Koh ES, Breidahl WH. Sonography of peripheral nerve

pathology. AJR Am J Roentgenol 2004;182:123e9.

[22] Silvestri E, Martinoli C, Derchi LE, et al. Echotexture of peripheral

nerves: correlation between US and histologic findings and criteria to

differentiate tendons. Radiology 1995;197:291e6.

[23] Dilley A, Summerhayes C, Lynn B. An in vivo investigation of ulnar

nerve sliding during upper limb movements. Clin Biomech (Bristol,

Avon) 2007;22:774e9.

[24] Julius A, Lees R, Dilley A, et al. Shoulder posture and median nerve

sliding. BMC Musculoskelet Disord 2004;5:23.

[25] Propeck T, Quinn TJ, Jacobson JA, et al. Sonography and MR imaging of

bifid median nerve with anatomic and histologic correlation. AJR Am J

Roentgenol 2000;175:1721e5.

[26] Iannicelli E, Chianta GA, Salvini V, et al. Evaluation of bifid median

nerve with sonography and MR imaging. J Ultrasound Med 2000;19:

481e5.

[27] Gassner EM, Schocke M, Peer S, et al. Persistent median artery in the

carpal tunnel: color Doppler ultrasonographic findings. J Ultrasound Med

2002;21:455e61.

[28] Kele H, Verheggen R, Reimers CD. Carpal tunnel syndrome caused

by thrombosis of the median artery: the importance of high-

resolution ultrasonography for diagnosis. Case report. J Neurosurg

2002;97:471e3.

[29] Sener E, Takka S, Cila E. Supracondylar process syndrome. Arch Orthop

Trauma Surg 1998;117:418e9.

[30] Spratt JD, Stanley AJ, Grainger AJ, et al. The role of diagnostic radi-

ology in compressive and entrapment neuropathies. Eur Radiol 2002;12:

2352e64.

[31] Li J, Krajewski K, Shy ME, et al. Hereditary neuropathy with liability to

pressure palsy: the electrophysiology fits the name. Neurology 2002;58:

1769e73.

[32] Beekman R, Visser LH. Sonographic detection of diffuse peripheral

nerve enlargement in hereditary neuropathy with liability to pressure

palsies. J Clin Ultrasound 2002;30:433e6.

[33] Tekin L, Ozgul A. Ultrasound aids in the diagnosis of hereditary

neuropathy with liability to pressure palsies. Surg Neurol 2008 Apr 24

[Epub ahead of print].

[34] Touborg-Jensen A. Carpal-tunnel syndrome caused by an abnormal

distribution of the lumbrical muscles. Case report. Scand J Plast Reconstr

Surg 1970;4:72e4.

[35] Sammarco GJ, Stephens MM. Tarsal tunnel syndrome caused by flexor

digitorum accessorius longus. A case report. J Bone Joint Surg Am 1990;

72:453e4.

[36] Stewart JD. Compression and entrapment neuropathies. In: Dyck PJ,

Thomas PK, editors. Peripheral neuropathy. 3rd ed. Philadelphia, PA:

WB Saunders; 1993. p. 1354e79.

[37] Barnum M, Mastey RD, Weiss AP, et al. Radial tunnel syndrome. Hand

Clin 1996;12:679e89.

[38] Lanzetta M, Foucher G. Entrapment of the superficial branch of the

radial nerve (Wartenberg’s syndrome). A report of 52 cases. Int Orthop

1993;17:342e5.

[39] Tsai WC, Chiou HJ, Chou YH, et al. Differentiation between schwan-

nomas and neurofibromas in the extremities and superficial body: the role

of high-resolution and color Doppler ultrasonography. J Ultrasound Med

2008;27:161e6.

[40] Beaman FD, Kransdorf MJ, Menke DM. Schwannoma: radiologic-

pathologic correlation. Radiographics 2004;24:1477e81.

[41] Reynolds Jr DL, Jacobson JA, Inampudi P, et al. Sonographic charac-

teristics of peripheral nerve sheath tumors. AJR Am J Roentgenol 2004;

182:741e4.

[42] Gruber H, Glodny B, Bendix N, et al. High-resolution ultrasound of

peripheral neurogenic tumors. Eur Radiol 2007;17:2880e8.

[43] Bianchi S, Abdelwahab IF, Kenan S, et al. Intramuscular ganglia arising

from the superior tibio-fibular joint: CT and MR evaluation. Skeletal

Radiol 1995;24:253e6.

[44] Bianchi S, Zwass A, Abdelwahab IF, et al. Sonographic evaluation of

intramuscular ganglia. Clin Radiol 1995;50:235e6.

[45] Shao YC, Harwood P, Grotz MR, et al. Radial nerve palsy associated

with fractures of the shaft of the humerus: a systematic review. J Bone

Joint Surg Br 2005;87:1647e52.

649S. Bianchi / Joint Bone Spine 75 (2008) 643e649

[46] Bodner G, Buchberger W, Schocke M, et al. Radial nerve palsy associ-

ated with humeral shaft fracture: evaluation with US e initial experience.

Radiology 2001;219:811e6.

[47] Martinoli C, Schenone A, Bianchi S, et al. Sonography of the median

nerve in CharcoteMarieeTooth disease. AJR Am J Roentgenol 2002;

178:1553e6.

[48] Martinoli C, Derchi LE, Bertolotto M, et al. US and MR imaging of

peripheral nerves in leprosy. Skeletal Radiol 2000;29:142e50.

[49] Toms AP, Anastakis D, Bleakney RR, et al. Lipofibromatous hamartoma

of the upper extremity: a review of the radiologic findings for 15 patients.

AJR Am J Roentgenol 2006;186:805e11.

[50] Marhofer P, Chan VW. Ultrasound-guided regional anesthesia:

current concepts and future trends. Anesth Analg 2007;104:

1265e9.

[51] Gray AT. Ultrasound-guided regional anesthesia: current state of the art.

Anesthesiology 2006;104:368e73.