Abstract ID: IRIA -1251

 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

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 CD 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

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

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

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

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

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

 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

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

 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( )

 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

 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

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 ( )

 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

 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 a xial 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

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( )

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( )

 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

 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: Goel A,Basilar invagination,Chiari malformation,syringomyelia:a review,Neurology India, 2009(3): Tassanawipas etal, magnetic resonance imaging study of the craniocervical junction, J Orth surg, 2005:13(3): Harris J, The cervicocranium:its radiographic assessment, Radiology 2001;218: