imaging the cv junction.part 1. himadri s das

Imaging of the Cranio-Vertebral Junction

Dr Himadri Sikhor Das, MD Dr.P.Hatimota, Dr.P.Hazarika, Dr.C.D.Choudhury.

MATRIX Guwahati, Assam

CV JUNCTION

Parts of CV Junction include:-

The Occiput First Cervical Vertebra (Atlas) Second Cervical Vertebra (Axis) Their articulations and Connecting ligaments

“The C-V junction is a transition site between mobile cranium and relatively rigid spinal column. It is also the site of the medullo spinal junction”.

Embryology of the CV junction

AXIS develops from five primary and two secondary centers.

Body and arches – II cervical sclerotome

Base of Dens – I cervical sclerotome

Apical segment of Dens – IV occipital sclerotome.

Embryology of the CV junction The apical segment is not ossified until 3

years of age. At 12 years it fuses with odontoid to form

normal odontoid; failure leads to Os Terminale

Tip of dens12 3

4 5

6

Body of dens

Dens

Anatomy of the CV junction

ATLANTO-AXIAL JOINT:

Most active joint in the body, moving approximately 600

times per hour.

Normal range of cervical motion is 900 on each side, range of rotation of atlas on axis being 25-530

Rotation of >560 on one side or a R-L diff >80 implies hyper mobility

Rotation of <280 implies hypo mobility

CV Junction

Anatomy of the CV junction

Occipital condyles

Atlantoaxial joint

Tectorial Membrane

Lateral mass of atlas

Transverse lig

Cruciate Ligament

vertical band

Apical Lig

Alar Lig

Imaging of the CV junction

Plain radiographs (standard FFD) Lateral Open mouth Dynamic Flexion & Extension (to r/o

atlantoaxial subluxation / occipitalization of atlas)

Tomograms –AP and LateralVertebral angiogram

may be necessary in select cases, especially BI

Imaging of the CV junction-CT

Spiral CT 1-3 mm collimation Pitch =1 Overlapping reconstruction

In neutral position With head rotated (Torticollis )Flexion (? Transverse ligament

abnormality )2-D axial and multiplanar 3DDynamic CT (AARF)

Imaging of the CV junction- MRITechnique

Surface / Head coil Contiguous thin sections (2-3mm with 3D

acquisitions) Sagittal sections in flexion if C1-C2 Dislocation

to be ruled out Sequences

SE- Sagittal 3D T1W FSE Sagittal T2WCEMR (Gd )Only if intra/extramedullary

lesion is suspectedKinematic MRI – cord compression in AAD,

AARFGRE – to delineate bony cortical outline

Disorders of the CV junction Congenital bony malformations OCCIPUT ANOMALIES

Basilar invagination Anomalies of atlas Odontoid abnormality Atlanto-axial instability Others

Disorders of the CV junction

ACQUIRED MALFORMATIONS

Trauma Arthritides Infection Degeneration Tumours

Lines and Angles The important lines are

Chamberlain’s line Wackenheim’s clivus canal line Mc Gregor’s line (basal line)

Lines and Angles

The important angles are

Basal angle Bull’s angle Height index of Klaus

Chamberlain’s line Synonym Definition Chamberlain's Joins posterior(Palato-occipital Line) tip of hard palate to posterior tip of Foramen Magnum (opisthion) Tip of dens below this line ±3 mm >7mm or >1/2 of odontoid def basilar Invagination DRAWBACK – posterior rim anatomical variations.

Mc Gregor’s line Synonym Definition McGregor’s Line Line drawn from

posterior

tip of Hard palate to

lowest part of Occiput

Odontoid tip >4.5mm above = Basilar InvaginationShould be used when lowest part of occipital bone is not

Foramen Magnum.

Wackenheim’s Line

Synonym Definition Wackenheim's Line drawn along

(Clivus canal) line clivus into cervical spinal

canalOdontoid is ventral and tangential to this line

McRae’s Line

Synonym Definition McRae's (Foramen Joins anterior and Magnum) line posterior edges of

Foramen magnum * Tip of odontoid is below this line.** When sagittal diameter of canal <20mm, neurological symptoms

occur – Foramen Magnum Stenosis

Welcher’s Basal Angle Synonym Definition BASAL ANGLE Angle between two lines drawn from

Nasion to tuberculum sella Tuberculum sellae to the basion along plane of the clivus Normal – 1240 - 142 > 1450 = platybasia < 1300 is seen in achondroplasia

BULL’S ANGLE Line representing prolongation of hard

palate and line joining the midpoints of the ant & post arches of C1.

Normal : <100

Basilar invagination - >130

Platybasia – refers only to an abnormally obtuse basal angle, may be asymptomatic, and is not a measure of basilar invagination.

Basilar impression vs. Basilar invagination

• Basilar impression is defined as upward displacement of vertebral column elements into the foramen magnum.

Specific Anomalies- Basilar Invagination

• primary developmental defect implying prolapse of vertebral column into the

skull at the base due to softening of the bones at the base of the skull.

Causes Hyperparathyroidism Hurler's syndrome Rickets/OM/Scurvy Hajdu-Cheney Syndrome. Paget's disease. Cleidocranial dysostosis Osteogenesis Imperfecta

“ As can be seen from the causes almost all of the causes are associated with bone softening conditions due to which the CV junction is invaginated like a sleeve”

Classification of Basilar Invagination

Morphological classificationAnterior ParamedianClivus short Clivus Normal/longAss. with Platybasia Not ass. with Platybasia

Etiological classification (synonyms )1.Basilar Coarctation ( congenital-Foramen Magnum syndrome)2.Basilar Erosion

(Inflammatory/Neoplastic/Infective) (RA/Tuberculosis/Nasopharyngeal CA)

3.Basilar Impression (Bone softening conditions) (OI/Paget’s/Osteomalacia)

BASILAR INVAGINATION : CT

Thin sections 1-3 mm Overlapping recon Multiplanar recon : Sag & Coronal

BASILAR INVAGINATION

KINEMATIC MRI IN BI

ATLANTO-AXIAL SUBLUXATION (AAS) : anterior type

Anterior Atlanto-Dental Interval (AADI) : AAS is present when it is >3mm in adults &

>5mm in children Measured from posteroinferior margin of ant

arch of C1 to the ant surface of odontoid AADI 3-6 mm trans lig. damage AADI >6mm alar lig. damage also AADI >9mm surgical stabilization

ATLANTO-AXIAL SUBLUXATION (AAS) : anterior typePosterior Atlanto-Dental

Interval (PADI) : ** Distance b/w posterior

surface of odontoid & anterior margin of post ring of C1

Considered better method as it directly measures the spinal canal

Normal : 17-29 mm at C1 PADI <14mm : predicts

cord compression


X-rays in neutral position will miss AAS in 48%. Controlled flexion views always to be done

AAD with cord compression

Pseudosubluxation

In children, C2-3 space & sometimes C3-4 space have normal physiologic displacement

Line drawn from ant. aspect of spinous process of C1-3 should not be >1mm far from any spines

RISK FACTORS FOR CORD COMPRESSION IN AAS

AADI > 9 mm PADI < 14 mm Basilar Invagination,

especially if associated with AAS of any degree

Sub axial canal diameter < 14 mm

CHI <2

ATLANTO-AXIAL SUBLUXATION (AAS) : rare types

Posterior AAS – rare, associated with deficient odontoid process.

Rotatory AAS - (later) Lateral AAS - >2 mm offset of the lateral mass of

C1 on C2 on coronal images. It is usually associated with a rotational deformity.

Specific Anomalies – Occiput anomaliesCondylus Tertius (IIIrd

occipital condyle) : when proatlas persists or fails

to migrate, an ossified remnant is seen at distal end of clivus

May form pseudo joint with odontoid or ant arch of C1 and limit mobility of CVJ

Increased prevalence of Os Odontoideum seen

ATLAS ASSIMILATION

Represents most cephalic ‘blocked vertebra’

0.25% of population Usually occurs in

association with other anomalies such as BI and Klippel Feil syndrome.

Associated with segmentation failures b/w C2-3 : atlanto-axial subluxation in 50%.

Atlas assimilation with CVJ anomaly

ATLAS ASSIMILATION

classic triad consists of low posterior hairline, short neck and limitation of neck movements.

KLIPPEL-FEIL SYNDROME :

KLIPPEL-FEIL SYNDROME

Fused vertebrae (usually C2-3 and C5-6 interfaces)

Hemivertebrae Atlas occipitalization Spina bifida occulta Scoliosis Urogenital, otological

anomalies, Chiari, syndactyly, Sprengel’s etc.

Atlas rachischisis: posterior >> anterior Both together – ‘split atlas’

ATLANTO-AXIAL ROTATORY FIXATION Less common cause of Torticollis in children. Fixation usually occurs within normal

range of rotation of A-A joint.

Fielding types:

Type I : fixn without anterior displ of atlas (trans & alar lig intact, MC type) Type II : fixn with ant displ 3-5mm (trans lig deficient) Type III : fixn with ant displ >5mm (trans & alar lig deficient) Type IV : fixn with posterior displacement of atlas (rarest, odontoid is deficient) Type V : AARF with AORF (atlanto-occipital rotatory fixation) combined

DIAGNOSIS:

X-Ray : asymmetry of lateral masses on open mouth odontoid view. Lateral mass that has rotated forwards appear wider and closer to midline. Asymmetry also on skull lateral.

ATLANTO-AXIAL ROTATORY FIXATION

CT: essential d/t difficulty in obtaining & interpreting X-rays rotated atlas + displacement, fractures, AORF

ATLANTO-AXIAL ROTATORY FIXATION

Dynamic CT: type I AARF vs.

other c/o torticollis : Pt. with fixn demonstrate little or no motion of atlas on the axis. Normal pts or with transient torticollis show a reduction or reversal of the rotation.

Dynamic MRI also

ODONTOID ABNORMALITIES

Persistent Ossiculum Terminale : Also called Bergman Ossicle. Results from failure of fusion of the terminal

ossicle to the rest of odontoid Normally fusion occurs by 12 yrs of age Stable anomaly when isolated with normal

height of dens

Persistent Ossiculum Terminale

May mimic type I odontoid # (avulsion of terminal ossicle) :

difficult to differentiate at times.

imaging the cv junction.part 1. himadri s das

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