Imaging of the Craniovertebral Junction

Dr Taraprasad TripathyResident doctor,Department of radiology,NEIGRIHMS, Shillong

CV JUNCTION

The craniovertebral junction (CVJ) refers anatomically to the occiput, the first (atlas) and second cervical (axis) vertebral segmentsarticulations and connecting ligaments.

complex transition between the skull and the upper cervical spine,and the brain and spinal cord respectively

OCCIPUT

Surrounds the foramen magnum and consist of three parts-

1.The squamosal portion (supra-occiput) 2.The basiocciput or clival portion 3.The condylar part (exoocciput)

ANATOMY ATLAS (C1)

The Axis (C2)

OCCIPITAL BONE

LIGAMENTOUS ANATOMY

Occipitoatlantoaxial ligaments are arranged in 4 layers -Ligaments connecting axis with occipital bone-

Atlanto-occipital membranePaired alar and apical ligamentCruciate ligament along with transverse

ligament tectorial membrane

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LIGAMENTOUS ANATOMY

Ligaments of CVJ

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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

EMBRYOLOGY The bones are developed from 4

Occipital sclerotomes- 1ST & 2nd- Bassiocciput. 3rd- Exoccipital bone that forms jugular tubercle.4th-Proatlas - Anterior tubercle of clivus, -Apical cap of dens, -anterior margin of foramen magnum, - occipital bone - Lateral atlantal masses and -superior portion of posterior arch of atlas2 Cervical sclerotomes-1st-Anterior arch of atlas, posterior & inferior portion of arch of atlas, Odontoid process.2nd-Body of axis, Posterior arch of axis.

Axis C2 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

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

BIOMECHANICSAtlanto-occipital joints- Nodding (yes) -Flexion/extension = 13-15° -Lateral bending = 8°

Atlanto-axial joints- Rotatory (no) -Axial rotation = 37-42° -Flexion/ extension = 10°

Axial rotation > 42 °- Dislocation at opposite facet jointAxial rotation > 45 °- Angulation & occlusion of I/L

vertebral artery

Clinical presentation

Compression of neural and vascular structures Begin insidiously and arise fairly late, progress

slowly, remain stationary and rarely relapse Myelopathy : m/c neurologic deficit Sensory abnormalities : post column involvement Lower CN palsy(20% in B.I.) Vascular symptoms:15% Neck pain: 85%,suboccipital areas radiating to

vertex

Role of Radiology in CVJ

• To determine presence of bony & soft tissue anomalies

• To determine if there is associated instability• To determine if spinal canal compromise has

occurred and whether or not there is existing or potential cord compression

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IMAGING MODALITIES

1. Conventional radiograph

Translateral view-Including upper cervical spine. AP-Open mouth view

2. Conventional tomography (Rarely done)

3. Cervical myelogram ( Rarely done )

5. Non contrast 3D CT with reconstruction images

6. Conventional MRI

7. Dynamic MRI Dynamic nature of cord compression

CONVENTIONAL

TRANSLATERAL VIEW

Cervical spine: lateral view

CRANIOMETRY:

• Uses a series of lines, planes & angles to define the normal anatomic relationships of the CVJ.

• Plain Xrays,3DCT or on MRI.

• No single measurement is helpful.

• Disadvantages : anatomic structures and planes vary within a normal range.

CRANIOMETRIC LINES AND ANGLES IN LATERAL VIEW

Chamberlain’s line (Palato-occipital line)

Posterior pole of hard palate to opisthon Tip of dens 1mm below this line.

Significance: Basilar invagination.

Precipitating causes: Platybasia, atlas occipitalisation, bone softening diseases

McRAE’S LINE (foramen magnum line)

From basion to opisthion Tip of dense doesn’t cross this lineSignificance: • Basilar invagination• Effective sagittal diameter is <20mm

neurological symptoms occur (foramen magnum stenosis)

McGREGOR’S LINE (BASAL LINE)

upper surface of the posterior edge of the hard palate to the most caudal point of the occipital curve

Odontoid apex should not exceed 5mm above this line

Significance: Basilar invagination

HEIGHT INDEX OF KLAUSS

• Distance between tip of dens and tuberculum torcula line

• Normal Value Average: 40-41 mm Minimum: 30 mm

• Significance: Basilar invagination(<30 mm)30-36 mm: Tendency towards BI

BOOGARD’S LINE

• Join nasion to opisthion• The basion should be below this line

Significance: Basilar invagination

BOOGARD’S ANGLE

Angle between McRae’s line and clivus canal line

Normal value: 1220 degree Significance: Basilar invagination (>1350)

BASAL ANGLE

• Angle between the line formed by nasion to tuberculum sellae & tuberculum sellae to basion

• Normal value Average: 124-1420

• Significance: Platybasia-(>1420)

Base is elevated in relation to rest of skull.

BULL’S ANGLE (ATLANTO PALATINE ANGLE)

Angle formed by joining the chamberlain’s line & line joinining midpoints of anterior & posterior arch of atlas

The posterior angle formed by these two lines should be less than 10 degree.

Significance: Angle >130 in BI 10-130 –tendency BI

SPINOLAMELLAR LINE(SPINOUS INTERLAMINAR LINE)

• Line drawn from interoccipital ridge above & down along the fused spinous process of C2-C3

• Should intersect posterior arch of atlas, if atlas is fused, posterior arch is anterior to the line, posterior compression of spinal cord occurs

• When each spinolaminar junction point is joined, a smooth arc like curve results

• Significance: Anterior or posterior dislocation• Especially useful for: Subtle odontoid fracture and

atlantoaxial dislocation(anterior)

WACKENHEIM’S LINE (CLIVUS CANAL LINE)

• Line drawn along clivus into cervical canal. Odontoid process transects the line in basilar invagination in forward position of skull.

• Odontoid tip is ventral and tangential to this line

• Significance: Basilar invagination

CRANIOMETRIC LINES AND ANGLES IN AP VIEW

Fishgold Digastric Line (Biventer Line)

• Joins fossa of digastric muscle on under surface of skull

• The odontoid should not project beyond this line.

• Central axis of dens should be perpendicular to the line

• Significance: may be oblique in unilateral condylar hypoplasia; oblique odontoid s/o paramedian abnormality

FISHGOLD BIMASTOID LINE

• Line connecting tip of the mastoid tips

• Runs across atlanto-occipital joints, line 10mm below digastric line

• Significance: Basilar invagination

SCHMIDT-FISCHER ANGLE

• Angle of axes of atlanto-occipital joints , angle is wider in case of hypoplasia

• Normal value: 124-1250

• Significance: Condylar hypoplasia

AADI

5mm ,<8years 3mm,adults 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 3-6mm trans ligament damage AADI >6mm alar ligament damage also AADI >9mm surgical stabilization

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

Normal diameter of Foramen magnum= 35±4mm (stenosis if <19mm)

Max. prevertebral soft tissue at C1=10mm, C2=5mm, C3-4=7mm, C5-7= 20mm

Normal sagittal diameter of spinal canal

***Rojas et al,Reassessment of the Craniocervical Junction: Normal Values on CT, ajnr, 2007.

Contnd.

CLASSIFICATION OF CVJ ANOMALIES:(congenital)

(A) Malformation of occipital sclerotome including proatlas1.Clivus segmentation anomalies2.Proatlas remnants around foramen magnum3.Condylar hypoplasia4.Assimilation of atlas(B)Malformations of atlas

Assimilation of atlas Atlantoaxial fusion Aplasia of atlas arches

(C) Malformations of axis Irregular atlantoaxial

segmentation Dens dysplasias

Ossiculum terminale persistans

Os odontoideum Hypoplasia-aplasia

Segmentation failure of C2-C3

Developmental and acquired abn. of CVJ

Abnormalities of foramen magnum

Foraminal stenosis (eg. Achondroplasia)

Secondary basilar invagination (eg. Osteomalacia, Pagets disease, rickets etc.)

Atlantoaxial instability Traumatic occipito-atlanto

and atlantoaxial dislocations

Down’s syndrome Infection eg. Tuberculosis Inflammatory eg. RA Tumour eg.

Osteoblastoma, Eosinophilic granuloma, Chordoma,Neurofibromatosis

Errors of metabolism eg. Morquios syndrome

Spontaneous atlantoaxial rotatory subluxation:

Grisel syndrome

INCIDENCE

• Any patient with high cervical cord compression CVJ anomalies to be ruled out

• Age:11-40years• m/c is congenital AAD• 2nd common are combination vizAAD with occipitalisation of C1B.I. with chiari malformationB.I with occipitalization of C1

Basilar invagination vs basilar impression vs platybasia

BASILAR INVAGINATION

Relative cephalad position of the upper cervical vertebra to the base of skull

Developmental defect. Associated with- Occipitalisation of

atlas, Klipple-Feil syndrome , spina bifida occulta of the atlas, odontoid anomalies, agenesis or hypoplasia of atlas and Arnold-Chiari malformation

Two types of deformity present

Anterior variety- Basiocciput-Short Clivus-Short & Horizontally orientedParamedian variety- Hypoplasia of exoccipital bone and dorsal displacement of the clivus (normal length)

Lateral cervical X-ray in extension and flexion shows high placed odontoid with narrowed spinal canal. Also note the assimilation of atlas.

NCCT mid sagittal MIP confirms the high placed odontoid and complete assimilation of atlas

T2W sagittal images show the compression at the cervicomedullary junction

Basilar impression

Secondary: Acquired Bone softening disorders-

Hyperparathyroidism, Rickets, Osteomalacia, Paget’s disease, fibrous dysplasia and osteogenesis imperfecta

Inflammation & infection producing bone destruction with or without ligamentous instability may also cause basilar impression, e.g rheumatoid arthritis, tuberculosis

In this anomaly, all the three parts of the occipital bone (basiocciput, exooccipital bone and supraoccipital bone) are deformated

Platybasia

Anthropometric term Flattening of the angle between the clivus and

body of the sphenoid i.e. basal angle >142 0 (124-1420) No symptoms or sign a/w platybasia alone

Associated: Basilar invagination, occipitalisation of atlas, block vertebra, Klipple-Feil syndrome

Sagittal MRI patient with platybasia and basilar invagination with basilar artery compression (arrow)

B.I.(diagnosis)

Radiological diagnosis :A-P projection : Bimastoid line : if tip of dens >10mm Bidigastric line : If tip of dens cross

Chamberlain’s line-tip of dense 1mm below this line

Height index of klauss <30mm McGregor’s line (basal line)-tip of dense exceed

this line Boogard’s line-join nasion to opisthion- basion

above this line

Arnold-Chiari Malformation Chiari I-

Downward displacement of elongated pointed peg-like cerebellar tonsil through the foramen magnum into the upper cervical spinal canal

Syrinx: 20-40% of case in asymptomatic 60-90% in symptomatic patient. Mild to moderate hydrocephalus is presentAssociated skeletal abnormalities: Basilar invagination, Klippel-Feil anomaly, atlanto-occipital assimilation, widened spinal canal

Plain x-ray

Osseous anomalies(25%):Basilar invaginations(25-50%)Klippel-feil anomaly(5-10%)Atlanto-occipital assimilation(1-5%)

Chiari 1 malformation with the basion-opisthion line shown in green. Note the low-lying, pointed tonsil with vertically oriented folia . The nucleus gracilis is inferiorly displaced.

• Sagittal T2WI in a 23-year-old man with classic Chiari 1 malformation shows a low-lying, pointed tonsil, normal sized posterior fossa. “presyrinx” state

Axial T2WI : “crowded” foramen magnum with obliterated retro cerebellar CSF spaces

Chiari II

Herniation of the inferior portion of the vermis, fourth ventricle and medulla into spinal canal

a/w: Small posterior fossa, Low lying transverse sutures, concave clivus, petrous ridges and fenestrate falx

Others: Myelomeningocele (95-100%), Hydrocephalus (90%), syringohydromyelia (50-90%) and segmentation anomalies (70%)

Graphic depicts a fetus with Chiari 2 malformation , spinal cord tethered into a myelomeningocele.Graphic depicts CM2 with small posterior fossa , large massa intermedia , “beaked” tectum , callosal dysgenesis, elongated fourth ventricle with “cascade” of inferiorly displaced nodulus and choroid plexus, medullary spur

Chiari II

Concave clivus

Chiari III

Herniation of hindbrain a/w occipital encephalocele in combination with many of features of the Chiari Malformation II

Pathology-small posterior fossa, caudal displaced brain stem, low occipital or upper cervical bony defect, cephalocele with herniation of meninges, dysplastic brain ventricle

Sagittal T1-weighted MR scan in a patient with chiari III malformation. Note features of 1. larges massa intermedia 2. cervical syrinx, and 3. cerbellar tissue herniated inferiorly through the foramen magnum into the upper cervical canal. A low occipital encephalocele (open arrows) contains herniated dysplastic-appearing cerebellar tissue

ANOMALIES OF THE ATLAS

Atlas Assimilation Failure of segmentation between atlas and skull Most common CVJ anomaly can be bilateral, unilateral, segmental or focal Associations: Basilar invagination, Klipple-Fiel

syndrome Associated congenital anomalies: Cleft nasal

cartilage, cleft palate, congenital external ear deformities, cervical rib hypospadiasis and urinary tract anomalies

TOPOGRAPHIC FORMS (WACKENHEIM):

Type I: Occipitalization (generally subtotal) associated with BI.

Type II: Occipitalization (generally subtotal) associated with BI & fusion of axis & 3rd cervical vertebrae.

Type III: Total or subtotal Occipitalization with BI & maldevelopment of the transverse ligament.

Type III may be associated with various malformations like C2-C3 fusion, hemivertebra, dens aplasia, tertiary condyle

The neurological symptoms are not caused by occipitalization proper but rather by the fact that in the absence of a free atlas, TL fails to develop which causes posterior displacement of axis & compression of the spinal cord

Plain film

Space between Posterior arch of C1 and base of occiput – Absent or greatly reduced

Thin section CT with multiplanar and 3-D reconstruction

Bony abnormalities

MRI

Infarction, cerebellar tonsil herniation, Syrinx formation, hydrocephalus & for isolating the source of craniocervical cord compression

MRA Vertebrobasilar anomalies - Hypoplasia, occlusion of PICA

C1 assimilation or occipitalization. a Assimilation of the anterior atlantal arch (zone 1 assimilation). b Assimilation of the lateral masses (zone 2 assimilation). c Posterior arch (zone 3) assimilation

Lateral cervical spine x-rays- the posterior arch of the atlas is fused to the base of the occiput (arrow) .The anterior arch is not discernible because it is fused to the anterior foramen magnum (basion).

The space between posterior arch of atlas and the base of the occiput will be absent or greatly reduced, often the site where the vertebral artery, accompanying veins and the first occipital nerve pass over the atlas posterior arch will be come more apparent as a circular bony foramen

Vertebralisation of Atlas

An embryologic tendency for a part of the proatlas to not incorporate into the occiput results in duplication of all or part of the atlas vertebra at the C0-C1 interspace

Duplication of all or part of atlas

On CT and multiplanar reconstructions- Supernumerary atlas, elongated or malformed odontoid

Lateral cervical spine-observe the duplication of the atlas with a posterior and anterior arch (arrows). The inferior normal atlas is well formed with all elements present. The odontoid process is elongated & forms a normal atlantodental articulation at both levels (arrowheads)

AP (OMV):The normal atlas (C1) is completely formed. The superior duplicated atlas has lateral mass (arrows) with non-union of the posterior arch (crossed arrows). Extending superiorly. The elongated dens articulates with both atlas vertebrae (arrowheads)

Agenesis of the Atlas Posterior Arch

• Lack of ossification of posterior arch and may manifest as a small clefts (spina bifida)

• Ossification of posterior arch of atlas is normally present at birth with union visible by the 6 years of age

• Dense fibrous connective tissue remains at the site devoid of ossification

Nonunion of Atlas Anterior Arch

• Synonyms: Anterior spina bifida

• Cleft through the ant arch is vertically oriented and usually in midline

• It may occur as an isolated anomaly or in association with cleft of the posterior arch or lateral cleft through the vertebral artery sulcus

X-ray

• AP (open mouth view): Defect may be superimposed over dens, resembles bipartite dens

• Lateral view: Half moon shaped anterior tubercle, absence of posterior arch spinolaminar junction line.

1.Anterior arch is seen Superimposed over the apex of the odontoid Process, Posterior arch cleft is projected inferiorly.

CT (thin section): Anterior midline cleft with sclerotic, mildly irregular margin

The opposing ends of the non-union are typically beaked anteriorly

MRI: Differentiates # (hematoma and bone marrow edema)

Posterior spina bifida occulta of the atlas

Embryological failure in midline ossification of the vertebral neural arch

X-ray :Lateral view: Absence of the spinolaminar

junction line and the posterior arch is thin and attenuated with clubbed shaped tapered or beaked end

AP(OMV): Midline hiatus

D/D: Jefferson’s #

Posterior spina bifida occulta

Ponticle of Atlas

• Calcification or ossification along the margins of normally occurring foramina on the atlanto-occipital ligament

• 2 typesPosterior ponticleLateral ponticle

Posterior ponticle

Ossification/calcification of the oblique portion of the atlanto-occipital membrane that bridges the posterior lateral mass and the posterior arch

Associated with:

1.Vertebrobasilar insufficiency 2. Chronic upper cervical syndrome

Complete posterior ponticle of the Atlas forming arcuate foramen

Posterior Ponticle

Lateral Ponticle

• Ossification in the oblique occipital membrane

• AP (OMV): Curvilinear ossification between the transverse process and the lateral mass of the atlas

Lateral Ponticle

ANOMALIES OF AXIS

Os Terminale(Bergman ossicle)

Failure of fusion of the tip of dens to the dens

Appears at 2 yrs. of age and fuses to the dens at 12-13 yrs.

IVth occipital sclerotome Association: Down’s syndrome Cx: disruption of interface and AAD,

remaining part of odontoid may compress cervicomedullary junction.

Os Odontoideum Independent bone located rostral to the axis body in

the position of the odontoid process

The gap between os odontoideum and the axis usually extends above the level of the axis superior facet

Usually located in the position of the normal odontoid tip or near the base of the occiput in the area of foramen magnum, where it may fuse with the clivus.

Usually associated with incompetent cruciate ligament and atlanto axial instability

• Etiology: Embryologic, traumatic.

• Types :

• Orthotopic - ossicle lies in the position of normal dens and moves with the axis body and atlas anterior arch. Transverse ligament is intact

• Dystopic : os lies near the basion and is often fused to clivus. Anterior arch of the atlas is hypertrophied & posterior arch is often hypoplastic. The clivus, occiput, atlas and os moves in unison.

• Increased incidence seen in Down’s syndrome, spondylo-epiphyseal dysplasia, morquio’s syndrome , after URI.

Radiological : smooth, rounded cortical borders.

D/D: non union of odontoid fracture: gap between the fractured segments is characteristically narrow and irregular and fracture line may extend into the body of the axis caudal to superior facet of axis.

Wide radiolucent defect above base separated ossicle in normal place

Failure of union of the odontoid process to the base of the body of the axis, as demonstrated by a radiolucent band (arrow). Cortical thickening of the anterior tubercle of the atlas, as well as an angular deformity of the posterior surface of the anterior tubercle, suggests a congenital origin

Differential features

Os odontoideum

1. Wide zone of separation2. Round, smooth, sclerotic

margins3. Odontoid orientation vertical4. Anterior arch hypertrophied5. Located above superior

articular facet

Fracture

1. Narrow zone of separation2. Irregular, non sclerotic3. Odontoid orientation tilted4. Anterior arch normal5. Usually below superior

articular facet

Hypoplastic and Agenetic Odontoid Process

Failure of dens to form and ossify Normally, odontoid tip lies at level of superior

margin of anterior arch of atlas in adults

Associations: Down’s syndrome, occipitalisation, Klippel-Feil syndrome and skeletal dysplasia's

Hypoplasia predisposes to AAI & trauma

A hypertrophic odontoid may be viewed as manifestation of the occipital vertebra

Significant vascular compromise on stretching and distortion of the vertebral artery may occur with odontoid dysplasia

Agenesis of odontoid

Atlanto-Axial Instability

• Depends on the integrity of osseous, ligament and muscle complex

• osseous-integrity of odontoid process, anterior arch of atlas. Ligament-transverse ligament, alar ligament and accessory ligament

• Lateral view: Rupture of transverse ligament and AA dislocation is diagnostic

Atlantodental Interspace (ADI)

Normal value Adults Children

Min: 1mm Min: 1mm,Max:3mm Max: 5mm

Widened: Trauma, Occipitalization, Down’s syndrome (18%) ,pharyngeal infections, mastoiditis, tuberculosis, inflammatory arthropathies ( RA and Reiter’s syndrome).

Dynamic study (flexion & extension) are important not only for the diagnosis but also for the management. i.e. whether the instability is fixed or mobile

Classification: Group I: AAI in combination with occipitalisation of

atlas, fusion of C2 and C3. Odontoid is displaced posteriorly.

Group II: AAI due to incompetence of odontoid processType I: Os odontoideumType II: Ossiculum terminaleType III: Agenesis of odontoid baseType IV: Agenesis of apical segmentType V: Agenesis of odontoid

Group III: Odontoid is seen dislocated posteriorly. No abnormality of C1 or odontoid

KLIPPEL-FEIL SYNDROME

Classical triadLow posterior hairlineShort webbed neckLimitation of neck movements

Associated withFused vertebrae (usually C2-3 & C5-6 interfaces)HemivertebraOccipitalisation of axisSpina bifida occultaScoliosisB.IOdontoid hypoplasiaPlatybasiaChiari I

Associated congenital anomalies

Urogenital anomalies Otological anomalies Cleft palate Chiari malformationAlso a/w Syndactyly Sprengel’s shoulder Absence of ulna

TYPES:

Type 1:Cervical spine fusion in which elements of many vertebrae are incorporated into a single block.

Type 2:Cervical spine fusion in which there is failure of complete segmentation at only one or two cervical levels and may include an occipito-atlantal fusion.

Type 3:Type 1 or type 2 fusion with co-existing segmentation errors in the lower dorsal or lumbar spine.

Lateral cervical radiograph shows fusion of C3 and C4 vertebral bodies, confirming Klippel-Feil syndrome, type 2

Klippel-Fiel syndrome with AAD with C2-4 & lower cervical block vertebrae

Down’s Syndrome

Characterized by increased ligamentous laxity and abnormal joint and bony anatomy

a/w: AOI(61%) AAI(9-30%) Persistent synchondroses Posterior C1 rachischisis Os odontoideum

Achondroplasia-

Most common short limb dwarfism

Foramen magnum is constricted & has characteristic tear drop constriction with obliteration of surrounding sub arachnoid space

Other CVJ anomaly – Odontoid dysplasia bassiociput hypoplasia decrease in basal angle & thickening of posterior rim of the foramen magnum

Mucopolysaccharidoses:

Features are: Hypoplastic or dysplastic dens, ligamentous

instability, soft tissue thickening around the dens and compression of cord by the posterior arch of atlas

Morquio’s (IV) & Hurler (I): Foramen magnum stenosis ± Anterior subluxation of C1 on C2, most

common cause of death

Osteogenesis imperfecta-

Hereditary disorder Associated with defect in collagen production Type IV OI a/w CVJ anomalies Osteoporotic bones result in repetitive micro

fractures causing infolding of the occipital condyles with elevation of clivus and the posterior cranial fossa results in Basilar impression

Inflammatory and Arthritic Disorders

MC Rheumatoid arthritis Others: Psoriatic arthritis, osteoarthritis

3 types of abnormalities AAI(25%) Basilar invagination i.e. upward migration of

odontoid process or cranial settling(8-16%) Rheumatoid granulation tissue or pannus

formation around odontoid process(10-30%)

Rheumatoid arthritis

Cervical spine is clinically affected in 44-88% of patients with RA.

Abnormal separation between odontoid process and anterior arch of atlas causing compression.

Abnormal vertical relationship between tip of the odontoid and base of skull -vertical subluxation of odontoid into foramen magnum (cranial settling)

AAD is the most common abnormality

Initiated by loss of tensile strength and stretching of transverse ligament destructive inflammatory changes from RA secondary degenerative changes in the tissue from

vasculitis

Results in erosive changes in the adjacent bone and formation of the granulation tissue in these synovial joints

Incompetent transverse ligament give rise to dislocation of 3-5mm

Incompetent transverse +alar ligament give rise to dislocation > 5mm

AAD occurs in transverse- rotatory direction as well as anterior- posterior direction

Pannus

Pannus formation-MRI is the modality of choice.Three types-

1.Hypervascular-hyperintense (early enhancement).

2.Hypovascular-intermediate(Delayed enhancement).

3.Fibrous type-low signal intensity (No enhancement)

Rheumatoid arthritis of CVJ (A and B) lateral cervical X-ray shows minimally increased pre-dental interval in extension position which is more marked in flexion position.

CT axial images showing the increased anterior atlantoaxial distance and erosion of odontoid process

Sagittal spin echoes pre contrast and post contrast T1W images showing presence of predental hypointense soft tissue that is showing intense post contrast enhancement

Infectious Disorders:

Tuberculosis (1%)

3 stages Stage I: Retropharyngeal abscess

AAD/AAI Normal bony architexture

Stage II: Retropharyngeal abscess +/- AAD Mild bony destruction

Stage III: Retropharyngeal abscess +/- AAD Gross bony destruction

Confirmed by CT and MRI- Bony destruction Increased prevertebral soft tissue

Sagittal MRI showing destruction of the C1-C2 vertebrae with large pre-vertebral abscess extending into spinal cord with cord compression.

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