Abstract ID: IRIA -1251

Knowledge of CVJ anomalies is important as it contains
vital structures including cervicomedullary junction
Aims and objectives
 To illustrate the various methods of craniometry
used in diagnosing CVJ anomalies
Materials and methods
 Multimodality radiological assessment of CVJ
anomalies along with radiological findings in
commonly encountered congenital CVJ anomalies
is illustrated
H
A
G
CD
B
A
B
C
D
E
F
E
A- nasion
B-posterior pole of
hard palate
C-anterior arch C1
D-odontoid process
E-posterior arch C1
F- opisthion
G- basion
H- tuberculum sellae
A- tip of mastoid
process
B-occipital condyle
C-odontoid process
D-axis body
E-lateral mass of atlas
CHAMBERLAIN’S LINE



Posterior margin of hard palate
to opisthion(
)
Normal- tip of dens less than
5mm below this line
Abnormal- in basilar
invagination
MCRAE’S LINE



Line from basion to opisthion
(
)
Normal – tip of dens below this
line
Abnormal-in basilar
invagination
MCGREGOR’S LINE



Posterior margin of hard palate
to lowest part of occipital bone
Normal- tip of dens less than
7mm below this line
Abnormal- in basilar
invagination
WACKENHEIM’S LINE



Line extrapolated along dorsal
surface of clivus
Normal – dens should be
tangential or anterior to this
line
Abnormal-in basilar
invagination
DIGASTRIC LINE


Line between incisurae
mastoidae ( )
Normal- 10mm above atlantooccipital joint
BIMASTOID LINE


Line between tips of mastoid
processes (
)
Normal – intersects atlantooccipital joint
WELCHER BASAL ANGLE



Angle at junction of nasiontuberculum and tuberculumbasion lines
Normal- 132-140 degree
Abnormal->143 degree in
platybasia
CLIVUS CANAL ANGLE



Angle at junction of
Wackenheim’s line and posterior
vertebral body line
Normal – 150-180degree
Abnormal-<150 degree in
platybasia
ATLANTOOCCIPITAL JOINT AXIS
ANGLE



Angle formed at junction of
lines along atlanto-occipital
joints (
)
Normal -124-127 degree
Obtuse in condyle hypoplasia
KLAUS INDEX



Distance between dens and
tuberculum cruciate line ( )
Normal-40-41mm
Basilar invagination-<30mm







Chamberlain’s line (palatooccipital line)
Palato–suboccipital line
(McGregor line)
Foramen magnum line (McRae
line)
Height of the posterior cranial
fossa(Klaus Index)
Wackenhein’s clival canal line
Bull’s angle (Atlanto-palatal
angle)
Atlanto-temporomandibularindex (Fischgold)
• Bimastoid line (Fischgold&
Metzer)
• Bidigastric line (Fischgold&
Metzer)
• Condylar angle (Schmidt &
Fischer)
• Basal angle (Welcher)
• Boogard’s angle
CONGENITAL CVJ ANOMALIES-CLASSIFICATION
Atlanto-occipital
junction

Atlanto-occipital
assimilation

Platybasia

Basilar invagination
Occipital
• Basiocciput hypoplasia
• Occipital condyle
hypoplasia
• Condylus tertius
Atlas
• Posterior arch
anomalies
• Anterior arch
anomalies
Axis
• Ossiculum terminale
• Os odontoideum
• Odontoid aplasia
Associated conditions
• Chiari malformation
• Osteogenesis imperfecta
• Klippel Fiel syndrome
• Achondroplasia
CONGENITAL ANOMALIES-ATLANTO-OCCIPITAL
ATLANTOOCCIPITAL
ASSIMILATION


Failure of segmentation of
C1 and skull base
Association – C2-C3
fusion, atlantoaxial
subluxation
CT coronal section showing complete atlantooccipital assimilation on right side and incomplete
atlanto-occipital assimilation on left side(
)
CT sagittal section showing complete atlanto-occipital
assimilation( ),short clivus( ),violation of Chamberlain’s
line( )-basilar invagination and atlantoaxial dislocation( )
PLATYBASIA






Skull base flattening
Primary and secondary
Bow string deformity
Increased basal angle
Decreased clivus canal
angle ( )
Association – basilar
invagination
32 year old gentleman with decreased
clivus canal angle(
) , violation of Chamberlain’s
line( , ) acute angulation, compression of
cervicomedullary juncion (
)
BASILAR INVAGINATION






Abnormally high vertebral
column
Prolapse into skull base
Secondary- basilar
impression
Chamberlain’s line
Mc Gregor’s line
Digastric line
24 year old gentleman with violation of Chamberlain’s
line( ) and digastric line( ), atlantoaxial
dislocation(atlantodens interval-3.8mm)
BASIOCCIPUT HYPOPLASIA



Shortening of clivus
Violation of Chamberlain’s line
Decreased clivus canal angle
CLIVUS CANAL ANGLE



CT sagittal section showing short clivus ( ),
atlantooccipital assimilation (
) and
violation of Chamberlain’s line ( )
Flattened condyles
Widening of atlanto-occipital
joint axis angle (
)
Causes basilar invagination
CT coronal section showing flattened
occipital condyles( ) and widening of
atlanto-occipital joint axis angle (
)
CONGENITAL ANOMALIES – OCCIPTAL
CONDYLUS TERTIUS



Third condyle
Ossification remnant
at distal end of clivus
Association – os
odontoideum
CT coronal section showing remnant
ossification centre at distal end of clivus( )
CONGENITAL ANOMALIES-ATLAS




Anterior and posterior arch anomalies
Total or partial aplasia
Isolated anterior arch anomalies –rare
Split atlas
CT axial section showing posterior atlas arch
rachischisis
CT axial section showing partial anterior arch
rachischisis( ) and os odontoideum( )
Hypertrophic anterior arch( ); corticated margins
Jefferson’s fracture
Irregular margins ; normal anterior arch
CONGENITAL ANOMALIES-AXIS
OS ODONTOIDEUM


Separate odontoid process
Failure of fusion of base with
body of axis
T1W MRI sagittal section showing os odnotoideum(
OSSICULUM TERMINALE


Bergmann ossicle
Failure of fusion of apical
segment with base of dens
CT sagittal section showing os odnotoideum( )
with ossiculum terminale( )
CONGENITAL SYNDROMES
KLIPPEL FIEL SYNDROME


Complex entity causing
cervicovertebral fusion
Associations- occipito-atlantoid
fusion
CT sagittal section showing violation of
Chamberlain’s line ( ), atlantooccipital fusion( ),
atlantodens interval of 3.9mm( ),fused C5-C8( )
CHIARI MALFORMATION


Low lying tonsils
Associations- basiocciput
hypoplasia, atlanto-occipital
assimilation, platybasia
16 year old lady with herniated tonsils(
Acute clivocanal angle( ),short clivus(
cervical cord compression
)
) and
ATLANTOAXIAL DISLOCATION




Congenital
Acquired
Traumatic
Atlantodens interval
3mm - adults
5mm - children
TRAUMA
20 year old man with type 2 dens
fracture(irregular margins( ) and
atlantoaxial dislocation( )
SPONTANEOUS
38 year old lady with increased
atlantodens interval( )
RHEUMATOID ARTHRITIS
47 year old lady with rheumatoid
arthritis with basilar impression,
sclerosis of atlantoaxial joint( )
and atlantoaxial dislocation( )
INFECTIVE
18 year old lady with TB,
retropharyngeal collection( ),
lytic area in dens( ) and
atlantoaxial dislocation( )
CONCLUSION

Understanding of the important land marks and
accurate assessment of the lines and angles is
crucial in the evaluation of craniovertebral
junction anomalies
REFERENCES
• Wendy etal, Craniovertebral junction:Normal craniometry and
congenital anomalies; Radiographics:1994:14:225-277
• Goel A,Basilar invagination,Chiari malformation,syringomyelia:a
review,Neurology India, 2009(3):235-246
• Tassanawipas etal, magnetic resonance imaging study of the
craniocervical junction, J Orth surg, 2005:13(3):228-231
• Harris J, The cervicocranium:its radiographic assessment,
Radiology 2001;218:337-351