This document discusses various methods of craniometry used to diagnose craniovertebral junction (CVJ) anomalies through multimodality radiological assessment. It describes several important cranial landmarks and reference lines used to evaluate the CVJ, including Chamberlain's line, McRae's line, McGregor's line, and Wackenheim's line. It then classifies common congenital CVJ anomalies such as atlanto-occipital assimilation, platybasia, basilar invagination, occipital condyle hypoplasia, atlas anomalies, axis anomalies, and discusses associated conditions like Chiari malformation.

1. Abstract ID: IRIA -1251

2.  Knowledge of CVJ anomalies is important as it contains
vital structures including cervicomedullary junction
 To illustrate the various methods of craniometry
used in diagnosing CVJ anomalies
Aims and objectives
Materials and methods
 Multimodality radiological assessment of CVJ
anomalies along with radiological findings in
commonly encountered congenital CVJ anomalies
is illustrated

3. 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
B
C D E
F
G
H
A
B
C
D
E
A- tip of mastoid
process
B-occipital condyle
C-odontoid process
D-axis body
E-lateral mass of atlas

4. CHAMBERLAIN’S LINE MCRAE’S LINE
 Posterior margin of hard palate
to opisthion( )
 Normal- tip of dens less than
5mm below this line
 Abnormal- in basilar
invagination
 Line from basion to opisthion
( )
 Normal – tip of dens below this
line
 Abnormal-in basilar
invagination

5. MCGREGOR’S LINE WACKENHEIM’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
 Line extrapolated along dorsal
surface of clivus
 Normal – dens should be
tangential or anterior to this
line
 Abnormal-in basilar
invagination

6. DIGASTRIC LINE BIMASTOID LINE
 Line between incisurae
mastoidae ( )
 Normal- 10mm above atlanto-
occipital joint
 Line between tips of mastoid
processes ( )
 Normal – intersects atlanto-
occipital joint

7. WELCHER BASAL ANGLE CLIVUS CANAL ANGLE
 Angle at junction of nasion-
tuberculum and tuberculum-
basion lines
 Normal- 132-140 degree
 Abnormal->143 degree in
platybasia
 Angle at junction of
Wackenheim’s line and posterior
vertebral body line
 Normal – 150-180degree
 Abnormal-<150 degree in
platybasia

8. ATLANTOOCCIPITAL JOINT AXIS
ANGLE KLAUS INDEX
 Angle formed at junction of
lines along atlanto-occipital
joints ( )
 Normal -124-127 degree
 Obtuse in condyle hypoplasia
 Distance between dens and
tuberculum cruciate line ( )
 Normal-40-41mm
 Basilar invagination-<30mm

9.  Chamberlain’s line (palato-
occipital 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-temporo-
mandibularindex (Fischgold)
• Bimastoid line (Fischgold&
Metzer)
• Bidigastric line (Fischgold&
Metzer)
• Condylar angle (Schmidt &
Fischer)
• Basal angle (Welcher)
• Boogard’s angle

10. 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
• Klippel Fiel syndrome
• Osteogenesis imperfecta
• Achondroplasia
CONGENITAL CVJ ANOMALIES-CLASSIFICATION

11.  Failure of segmentation of
C1 and skull base
 Association – C2-C3
fusion, atlantoaxial
subluxation
CT coronal section showing complete atlanto-
occipital assimilation on right side and incomplete
atlanto-occipital assimilation on left side( )
CONGENITAL ANOMALIES-ATLANTO-OCCIPITAL
ATLANTOOCCIPITAL
ASSIMILATION
CT sagittal section showing complete atlanto-occipital
assimilation( ),short clivus( ),violation of Chamberlain’s
line( )-basilar invagination and atlantoaxial dislocation( )

12.  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 ( )
PLATYBASIA

13.  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)
BASILAR INVAGINATION

14. BASIOCCIPUT HYPOPLASIA CLIVUS CANAL ANGLE
 Shortening of clivus
 Violation of Chamberlain’s line
 Decreased clivus canal angle
 Flattened condyles
 Widening of atlanto-occipital
joint axis angle ( )
 Causes basilar invagination
CT sagittal section showing short clivus ( ),
atlantooccipital assimilation ( ) and
violation of Chamberlain’s line ( )
CT coronal section showing flattened
occipital condyles( ) and widening of
atlanto-occipital joint axis angle ( )

15.  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 – OCCIPTAL
CONDYLUS TERTIUS

16.  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-ATLAS

17. OS ODONTOIDEUM OSSICULUM TERMINALE
 Separate odontoid process
 Failure of fusion of base with
body of axis
 Bergmann ossicle
 Failure of fusion of apical
segment with base of dens
CONGENITAL ANOMALIES-AXIS
T1W MRI sagittal section showing os odnotoideum(
CT sagittal section showing os odnotoideum( )
with ossiculum terminale( )

18. KLIPPEL FIEL SYNDROME CHIARI MALFORMATION
 Complex entity causing
cervicovertebral fusion
 Associations- occipito-atlantoid
fusion
 Low lying tonsils
 Associations- basiocciput
hypoplasia, atlanto-occipital
assimilation, platybasia
CONGENITAL SYNDROMES
16 year old lady with herniated tonsils( )
Acute clivocanal angle( ),short clivus( ) and
cervical cord compression
CT sagittal section showing violation of
Chamberlain’s line ( ), atlantooccipital fusion( ),
atlantodens interval of 3.9mm( ),fused C5-C8( )

19.  Congenital
 Acquired
 Traumatic
 Atlantodens interval
3mm - adults
5mm - children
ATLANTOAXIAL DISLOCATION
20 year old man with type 2 dens
fracture(irregular margins( ) and
atlantoaxial dislocation( )
47 year old lady with rheumatoid
arthritis with basilar impression,
sclerosis of atlantoaxial joint( )
and atlantoaxial dislocation( )
18 year old lady with TB,
retropharyngeal collection( ),
lytic area in dens( ) and
atlantoaxial dislocation( )
38 year old lady with increased
atlantodens interval( )
SPONTANEOUS
INFECTIVE
RHEUMATOID ARTHRITIS
TRAUMA

20.  Understanding of the important land marks and
accurate assessment of the lines and angles is
crucial in the evaluation of craniovertebral
junction anomalies
CONCLUSION
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