The craniovertebral junction (CVJ) refers anatomically to the occiput, atlas, axis, and their articulations and ligaments. It is a complex region forming the transition between the skull and upper cervical spine. The document describes the normal anatomy of the CVJ bones including the occiput, atlas, and axis. It discusses the important ligaments including the occipitoatlantoaxial ligaments. Key radiological measurements and lines used to evaluate the CVJ are presented, along with classification of various congenital and acquired CVJ anomalies and their imaging appearance. Basilar invagination, basilar impression, and platybasia are distinguished.

1. ANATOMY of the
CRANIOVERTEBRAL JUNCTION
Dr SUMIT KUMAR
RADIOLOGY PG
SLIMS

2. CV JUNCTION
 The craniovertebral junction (CVJ) refers
anatomically to the
 occiput,
 the first (atlas) and
 second cervical (axis) vertebral
segments
 articulations and connecting ligaments.
 complex transition between the skull and
the upper cervical spine , and the brain
and spinal cord respectively

4. OCCIPUT
 Surrounds the foramen magnum and consist of
three parts-
1.The squamosal portion (supra-occiput)
2.The basi-occiput or clival portion
3.The condylar part (exo-occiput)

7. ANATOMY ATLAS (C1)

8. The Axis (C2)

10. OCCIPITAL BONE

11. LIGAMENTOUS ANATOMY
 Occipitoatlantoaxial ligaments are
arranged in 4 layers -Ligaments
connecting axis with occipital
bone-
 Atlanto-occipital membrane
 Paired alar and apical ligament
 Cruciate ligament along with
transverse ligament
 tectorial membrane

12. 12
LIGAMENTOUS ANATOMY

13. Ligaments of CVJ
13

14. CV Junction

15. 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

16. 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 atlas
2 Cervical sclerotomes-
1st-Anterior arch of atlas, posterior & inferior
portion of arch of atlas, Odontoid process.
2nd-Body of axis, Posterior arch of axis.

17. 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

18.  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 dens1
2 3
4 5
6
Body of
dens
Dens

19. BIOMECHANICS
 Atlanto-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 joint
 Axial rotation > 45 °- Angulation & occlusion of I/L vertebral
artery

20. 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
21

21. IMAGING
MODALITIES

22. 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

23. Conventional

24. TRANSLATERAL
VIEW

27. Cervical spine: lateral view

28. 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.

29. CRANIOMETRIC
LINES AND
ANGLES IN
LATERAL VIEW

30. 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

33. McRAE’S LINE
(foramen magnum line)
 From basion to opisthion
 Tip of dense doesn’t cross this line
Significance:
• Basilar invagination
• Effective sagittal diameter is <20mm neurological
symptoms occur (foramen magnum stenosis)

35. 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

38. 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

41. BOOGARD’S LINE
• Join nasion to opisthion
• The basion should be below this line
Significance: Basilar invagination

43. BOOGARD’S ANGLE
 Angle between McRae’s line and clivus canal line
 Normal value: 122
0
degree
Significance: Basilar invagination (>135
0
)

46. BASAL ANGLE
• Angle between the line formed by
nasion to tuberculum sellae &
tuberculum sellae to basion
• Normal value
Average: 124-1420
• Significance:
Platybasia-(>1420)

48. 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

50. 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)

52. 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

54. CRANIOMETRIC LINES AND
ANGLES IN AP VIEW

55. 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

58. FISHGOLD BIMASTOID LINE
• Line connecting tip of the mastoid tips
• Runs across atlanto-occipital joints, line 10mm below
digastric line
• Significance: Basilar invagination

60. SCHMIDT-FISCHER ANGLE
• Angle of axes of atlanto-occipital joints , angle is wider
in case of hypoplasia
• Normal value: 124-1250
• Significance: Condylar hypoplasia

62. 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

63. 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

64.  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

65. THANK YOU

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

73. Contnd.

74. CLASSIFICATION OF CVJ ANOMALIES:
(congenital)
(A) Malformation of occipital
sclerotome including
proatlas
1.Clivus segmentation
anomalies
2.Proatlas remnants around
foramen magnum
3.Condylar hypoplasia
4.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

75. 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

76. 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 viz
 AAD with occipitalisation of C1
 B.I. with chiari malformation
 B.I with occipitalization of C1

77. Basilar invagination
vs
basilar impression
vs
 platybasia

78. 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

79.  Two types of deformity present
 Anterior variety-
Basiocciput-Short
Clivus-Short & Horizontally oriented
 Paramedian variety-
Hypoplasia of exoccipital bone and
dorsal displacement of the clivus (normal
length)

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

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

82. T2W sagittal images show the compression at the
cervicomedullary junction

83. Basilar impression
 Secondary: Acquired
 Bone softening disorders-
Hyperparathyroidism, Rickets,
Osteomalacia, Paget’s disease, fibrous
dysplasia and osteogenesis imperfecta

84.  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

85. 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

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

89. 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

90. 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 present
 Associated skeletal abnormalities:
Basilar invagination, Klippel-Feil anomaly, atlanto-occipital
assimilation, widened spinal canal

91. Plain x-ray
 Osseous anomalies(25%):
 Basilar invaginations(25-50%)
 Klippel-feil anomaly(5-10%)
 Atlanto-occipital assimilation(1-5%)

92. 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.

93. • 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

94. 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%)

95. 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

96. Chiari II
Concave clivus

97. 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

98. 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

99. Anomalies of the
atlas

100. 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

101. 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

102.  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

103.  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

104. 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

105. 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).

106. 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

107. 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

108. 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)

109. 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)

110. 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

111. 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

112.  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.

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

115.  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)

116. 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 #

118. Posterior spina bifida occulta

119. Ponticle of Atlas
• Calcification or ossification along the margins of
normally occurring foramina on the atlanto-occipital
ligament
• 2 types
Posterior ponticle
Lateral ponticle

120. 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

121. Complete posterior
ponticle of the
Atlas forming arcuate
foramen
Posterior
Ponticle

122. Lateral Ponticle
• Ossification in the oblique occipital membrane
• AP (OMV): Curvilinear ossification between the
transverse process and the lateral mass of the atlas

123. Lateral Ponticle

124. Anomalies of axis

125. 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.

128. 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

129. • 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.

130.  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.

131. Wide radiolucent defect above base separated
ossicle in normal place

132. 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

134. Differential features
 Os odontoideum
1. Wide zone of separation
2. Round, smooth, sclerotic
margins
3. Odontoid orientation vertical
4. Anterior arch hypertrophied
5. Located above superior articular
facet
 Fracture
1. Narrow zone of separation
2. Irregular, non sclerotic
3. Odontoid orientation tilted
4. Anterior arch normal
5. Usually below superior
articular facet

135. 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

136.  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

137. Agenesis of odontoid

138. 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

139. 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).

140. 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

141. 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
process
 Type I: Os odontoideum
 Type II: Ossiculum terminale
 Type III: Agenesis of odontoid base
 Type IV: Agenesis of apical segment
 Type V: Agenesis of odontoid
 Group III: Odontoid is seen dislocated posteriorly.
No abnormality of C1 or odontoid

142. KLIPPEL-FEIL SYNDROME
 Classical triad
 Low posterior hairline
 Short webbed neck
 Limitation of neck movements

143.  Associated with
 Fused vertebrae (usually C2-3 & C5-6 interfaces)
 Hemivertebra
 Occipitalisation of axis
 Spina bifida occulta
 Scoliosis
 B.I
 Odontoid hypoplasia
 Platybasia
 Chiari I

144.  Associated congenital anomalies
 Urogenital anomalies
 Otological anomalies
 Cleft palate
 Chiari malformation
Also a/w
 Syndactyly
 Sprengel’s shoulder
 Absence of ulna

145. 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.

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

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

148. 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

149. 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

150. 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

151. 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