The craniovertebral junction (CVJ) refers to the occiput, atlas, axis, and supporting ligaments. It is a transition zone between the mobile cranium and spinal column. The CVJ encloses important neural and vascular structures. Anomalies of the CVJ can be congenital due to malformations during embryological development, or acquired through conditions like trauma, infection, or tumors. Common congenital anomalies include occipitalization, basilar invagination, dens dysplasia, and atlantoaxial dislocation. Radiological evaluation is important for assessing abnormalities. Measurements of angles and distances between anatomical structures help characterize anomalies.

1. CRANIOVERTEBRAL
JUNCTION

2.  The craniovertebral (CVJ) is a collective term that
refers to the occiput (posterior skull base), atlas, axis,
and supporting ligaments.
 It is a transition zone b/w a mobile cranium & spinal
column.
 It encloses the soft tissue structures of the cervico
medullary junction (medulla, spinal cord, and lower
cranial nerves

3. Contents
 Anatomy of CV junction
 Embryology
 Classification of CV Anomalies
 Clinical features
 Anatomical and radiological aspects
 Specific anomalies – AA dislocation, Dens dysplasia,
 KFS,ACM,

4. Parts of CV Junction include:-
 The Occiput
 First Cervical Vertebra (Atlas)
 Second Cervical Vertebra (Axis)
 Their articulations and
 Connecting ligaments

6. ANATOMY OF CVJ (ARTICULAR)
b/w occiput & atlas
 Upper surfaces of C1 lateral masses is cup-like or concave which fit into
the ball & socket configuration with occipital condyle, united by articular
capsules surr. the AO joint & by the ant. & post. AO membranes.
 ( flexion 10o, extension 25o).
4 synovial joints b/w atlas & axis –
 2 median –front & back of dens (Pivot variety)
 2 lateral –b/w opposing articular facets (Plane variety)
 Each joint has its own capsule & synovial cavity.
 rotation is upto90o & approx ½ occurs at the A-A joint.

7. ANATOMY OF CVJ(LIGAMENTOUS)
Principal stabilizing ligaments of C1 -
 -Transverse atlantal ligament
 -Alar ligaments
Secondary stabilizing ligaments of CVJ are more elastic &
weaker than the primary ligaments.
 -Apical ligament
 -Anterior & posterior A-O membranes
 -Tectorial membrane
 -Ligamentum flavum
 -Capsular ligaments

10. ANATOMY OF CVJ (MUSCLES)
 Muscles have only a minor role related to CVJ
stabilization & do not limit the movements of the joints.
 Their principal function is one of initiating & maintaining
movement at the CVJ.

11. NEURAL
 structures related are –
 Caudal brainstem (Medulla)
 Fourth ventricle
 Rostral part of spinal cord
 Lower cranial (9,10,11 {only N that passes through the
FM},12) & upper cervical nerves (The
C1(SUBOCCIPITAL NERVE) , C2, and C3 nerves with
both rami).
 In cerebellum, only the tonsils, biventral lobules & the
lower part of the vermis (nodule, uvula & pyramid) ,

12. LYMPHATICS
 primarily into the retropharyngeal LN & then into the
deep cervical chain.
 These LN’s also drain the nasopharynx & hence
retrograde infection may affect the synovial lining of the
CVJ complex with resultant neck stiffness & instability.

13. ARTERIAL
The major arteries related to CVJ are :-
 Vertebral arteries (m/c)
 Postero-inferior cerebellar arteries (PICA)
 Meningeal branches of the vertebral
 External and internal carotid arteries.

14. VENOUS
divided into three groups at FM :
 Extradural veins(extraspinal& intraspinalpart)
 Intradural (neural) veins, &
 Dural venous sinuses( superior petrosal, marginal &
occipital)
The three groups anastomose through bridging and
emissary veins.

15. EMBRYOLOGY & DEVELOPMENT
Between 3rd& 5thweek:
 -The first four sclerotomes (which forms the vertebral
bodies ) do not forms the vertebral bodies and fuse to
form the occipital bone.
 CV junction is developed from 4 these and first 2
cervical sclerotome.

16. occipital sclerotomes
1, 2 – basiocciput
3- Jugular tubercles
4 (Proatlas)-ant. Tubercle of clivus,apical cap of
dens,ant.margin of FM,occipital condyles,lateral atlantal
mass,sup.portion of post.arch of atlas.
cervical sclerotome.
1-ant.arch of atlas post.inf,portion of c1,odontoid
process.
2-rest of axis vertebra

17. APPLICATIONS
 Dysgenesis of the occipital sclerotome-may flatten the
clivus-platybasia.
 basiocciput and rim of foramen magnum are
underdeveloped, the odontoid and arch of atlas may
invaginate - Basilar invagination.
 The proatlas may develop into separate vertebrae -
Occipital vertebra
 proatlas fails to fuse with the atlas (cervical
sclerotome), a rare anomaly termed bipartite articular
facets.
 dens body may fail to fuse with apical part (occipital
sclerotome)- Bicornuate dens
 Failure of segmentation b/w the axis & the 3rd cervical
vertebra-Klippel–Feil syndrome.

18. Classification of CV Anomalies
Congenital
 Malformation of occipital sclerotomes
Clivus segmentation anomalies
Condylar hypoplasia
Assimilation of atlas
 Malformation of atlas
Assimilation of atlas
Atlantoaxial fusion.
Aplasia of atlas arches.
 Malformation of axis.
Irregular Atlantoaxial segmentations.
Dens dysplasia
 Segmentations failure of c2-c3

19. Developmental and acquired
 At foraman magnum-stenosis
 Sec.basilar invagination-OI,Pagets ds,o
malacia,rickets,RA.
 Atlantoaxial instability
1. down syndrome
2. Ehlers danlos syndrome
3. MPS
4. Trauma
5. Infection –TB
6. Tumors-mets,FD,EG,chordoma ,osteoblastoma,NF
 Spontaneous rotatory subluxation-grisel syndrome

20. Other classification
 Bony Anomalies
Major Anomalies
1. Platybasia
2. Occipitalization
3. Basilar Invagination
4. Dens Dysplasia
5. Atlanto- axial dis.
Minor Anomalies
Dysplasia of Atlas
Dysplasia of occipital condyles, clivus, etc.
 Soft Tissue anomalies
Arnold-Chiari Malformation
Syringomyelia/ Syringobulbia

21. Clinical features
A. Cervical symptoms and signs- pain suboccipital
region rediating vertex,stifness in 85%
B. Myelopathic Features- long tract involvement and
wasting
C. CN involvement- IX, X,XI,XI inI 20%
D. Vascular in 15% Transient Attack of V-B insufficiency
E. Sensory symptom of post.column involvement.
F. Cerebellar symptoms/signs- Nystagmus, Ataxia,
intention tremor, dysarthria
G. Features of Raised ICT- usually seen in Pts. Having
basilar impresssion and/or ACM

22. Anatomical and radiological
aspects

23. INVESTIGATIONS
 1) X Rays
Antero-posterior view
Lateral view
Open mouth view for dens
 Stress X-Rays (neutral,flexion,extention)
 Tomogram (rare) hypoplastic odontoid,
occipitalisation of atlas are clearly visualised.
 CT Scan and 3d recon
 MRI conventional and dynamic
 Myelogram & Ventriculogram
(used before the advent of CT)
 Angiography

24. X Ray

26. CRANIOMETRY:
 Craniometry of the CVJ uses a series of lines, planes &
angles to define the normal anatomic relationships of
the CVJ.
 These measurements can be taken on plain X rays,
3D CT or on MRI.
 No single measurement is helpful.
 disadvantage --anatomic structures and planes vary
within a normal range.

27. The important lines are
1. Chamberlain’s line
2. Wackenheim’s clivus
canal line
3. Mc Gregor’s line (basal
line)
4. Mc rae’s line ( foramen
magnum line)
5. Height index of Klaus
6. Boogard,s line
7. FISHGOLD’S DIGASTRIC
LINE
8. FISHGOLD’S BIMASTOID
LINE
The important angles are
1. Basal angle
2. Bull’s angle
3. Boogard,s angle

28. Normal landmark

29. Chamberlain’s line
 From tip of hard palate to posterior
tip of
Foramen Magnum (opisthion).
If Tip of dens below this line ±3 mm
Or >1/3 of odontoid above the line
 Defined basilar Invagination

30. Mc Gregor’s line (basal line)
 Line drawn from posterior tip of
Hard palate to lowest part of
Occiput
 Odontoid tip >5mm above =
Basilar Invagination
 Position changed with flexion and
extension so not used.
 Should be used when lowest part
of occipital bone is not Foramen
Magnum.

31. Wackenheim’s clivus canal line
 Line drawn along clivus
into cervical spinal canal
 Odontoid is ventral and
tangential to this line
 AAD and BI

32. Mc rae’s line ( foramen magnum line)
 Joins anterior and posterior edges of Foramen
magnum
 Tip of odontoid is below this line.
 When sagittal diameter of canal <20mm, in patient of
>8 yr of age neurological symptoms occur – Foramen
Magnum Stenosis

33. Boogard ‘s Line
 Nasion to Opisthion
 Basion should lie below this
line
 Altered in basilar impression

34. FISHGOLD’S DIGASTRIC LINE Biventer
line
Connects the digastric grooves ( fossae for digastric muscles on
undersurface of skull just medial to mastoid process)
Line is normally 10mm above the atlanto-occipital junction.
 Upper limit of dens.
 Central axis of dens should perpendicular to this line.
 Corresponds to McRae’s line on lateral view
 For unilateral condylar hypoplasia.

35. FISHGOLD’S BIMASTOID LINE
 Line connecting tip of mastoid process.
 At level of atlanto-occipital junction
 Odontoid process should be less than 10 mm above
this line

36. HEIGHT INDEX OF KLAUS
 Distance between tip of dens and
tuberculum cruciate line( line
drawn from tuberculum sella to
internal occipital protruberence)
 40-41mm normal
 In basilar invagination <30 mm

37. Spinolamellar line

38. Boogard ‘s Angle
 1st line between Dorsum sellae to Basion & Mc Rae’s
line.
 Average - 1220
 > 1350
 Basillar impression

39. Welcher’s Basal Angle
 Nasion to tuberculum sella
 Tuberculum sellae to the basion
along plane of the clivus
 Normal – 1240 - 142
 > 1450 = platybasia
 < 1300 is seen in achondroplasia

40. BULL’S ANGLE
 Line representing prolongation of
hard palate and line joining the
midpoints of the ant & post arches
of C1.
 Normal : <100
 Basilar invagination - >130

41. Schmidt – Fischer angle
 Angle of axis of Atlanto-
Occipital joint
 125 +/- 2 degrees
 Angle is wider in condylar
hypoplasia
O
C2
AA JT
AO JT
C1 C1

42. Lines and angles used in radiologic diagnosis of C.V
anomalies.
Parameter Normal range limits
A. PLATYBASIA
B. BASILAR INVAGINATION
C. ATLANTO-AXIAL DISLOCATION *
• Basal angle < 150
degree
• Boogard’s angle < 136
degree
• Bull’s angle < 13
degree
• Chamberlain’s line < one third of odontoid above this
line
• Mcgregor’s line < 5 mm
• Mcrae line odontoid lies below this
• Klaus height index > 35 mm
• Atlanto-temporo > 22mm.
mandibular index
• Atlanto-odontoid space upto 3 mm in adults
upto 5 mm in children
• EDFM > 19mm
*

45. Ranawat method
 Line joining center of the anterior
arch of C1 to post ring & another
line along the axis of the odontoid
from the centre of the pedicle of C2
to 1st line
 Normal distance between C-1 and
C-2 in
 M 17 mm (±2 SD)
 F 15 mm (± 2 SD).
 A decrease in this distance
indicates cephalad migration of C-
2.
C2
C1

46. Some anomalies

47. Occipitalization of atlas/assimilation
 50%
 Failure of segmentation btw last occipital
and first spinal sclerotome.
 S/S gradual or sudden onset by trauma
 No movement btw OA –leads increases
stress at AA joint –get instability
 Associated –with basilar
invagination,occipital vertebra,KF
syndrome
 When incompletely assimilated, the atlas
arches appear too high on the lateral
plain radiograph or, when completely
assimilated, are not visible at all .

49. TOPOGRAPHIC FORMS (WACKENHEIM):
 Type I: Occipitalization(generally subtotal) associated with BI.
 Type II: Occipitalization(generally subtotal) associated with BI &
fusion of axis & 3rdcervical vertebrae.
 Type III: Total or subtotal occipitalizationwith
BI & mal developmentof the transverse ligament.
 symptoms are due to-
absence of a free atlas- TL fails to develop which causes posterior
displacement of axis & compression of the spinal cord

50. Platybasia
 refers only to an abnormally obtuse basal angle, may be
asymptomatic, and is not a measure of basilar invagination.
 >145 basal angle.

51. BASILAR INVAGINATION
 Floor of the skull is indented by the
upper cervical spine, & hence the tip of
odontoid is more cephalad protruding
into the FM.
 high incidence of vertebral artery
anomalies.
 Two types -primary and secondary
 S/s 2nd or 3rd decade
 Primary invagination
 associated with occipito atlantal fusion,
hypoplasia of the atlas, a bifid posterior
arch of the atlas, odontoid anomalies.

52. Another
 osteogenesis imperfecta
 Klippel-Feil syndrome
 achondroplasia
 Chiari I malformation/Chiari II malformation
 cleidocranial dysostosis
 Schwartz-Jampel syndrome

53. BASILAR IMPRESSION (SECONDARY BASILAR
INVAGINATION
 Due to softening of the bone or
fibrous bands & duraladhesions
 Seen in conditions such as
1. rickets,
2. hyperparathyroidism,
3. osteogenesis imperfecta,
4. Paget disease,
5. neurofibromatosis,
6. skeletal dysplasias, and
7. RA & infection producing
bone destruction.

54. Pseudosubluxation
 In children, C2-3
space & sometimes
C3-4 space have
normal physiologic
displacement
 Line drawn from ant.
aspect of spinous
process of C1-3
should not be >1mm
far from any spines

55. Atlanto-Axial Dislocation
57% of all CVJ anomalies.
– Traumatic
– Spontaneous (Hyperemic)
– Congenital
Wadia Classification
 Group 1- associated with occipitalization & frequent
fusion of C2,C3
 Group 2- Associated with Dens Dysplasia- frequently
totally reducible
 Group 3- No Congenital Bony abnormality but odontoid
dislocation

56. Anterior Atlanto-Dental Interval (AADI)
 AAS is + when >3mm in adults & >5mm in children
 Measured from posteroinferior margin of ant arch of C1 to
the ant surface of odontoid
 AADI 3-6 mm  trans lig. damage
 AADI >6mm  alar lig. damage also
 AADI >9mm  surgical stabilization

57. Posterior Atlanto-Dental Interval (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

58. RISK FACTORS FOR CORD COMPRESSION IN
AAS
 AADI > 9 mm
 PADI < 14 mm
 Basilar Invagination, especially if associated with AAS
of any degree
Associated syndrome-
 Down syndrome -Due to laxity of the transverse
ligament
 Grisel syndrome-Atlantoaxialsubluxationassociated
with inflammation of adjacent soft tissues of the neck

59. Condylar Hypoplasia:
 The occipital condylesare
underdeveloped and have a
flattened -- and widening of the
atlantooccipitaljoint axis angle -
-leading to BI.
 The lateral masses of the atlas
may be fused to the hypo
plasticcondyles, further
accentuating the BI.
 limits, or may even abolish,
movements at the A-O joint.

60. Basiocciput Hypoplasia:
 Hypoplasia of the basiocciput may
be mild or severe, depending on
the number of occipital vertebrae
affected.
 Lead-basilar invagination.
 clivus-canal angle is typically
decreased

61. Third occipital condyle or condylus Tertius:
 When fourth occipital
sclerotome(proatlas) persists or
fails to integrate, an
ossifledremnant may be present at
the distal end of the clivus, called
the condylus tertius.
 This may form pseudojoint with the
odontoid process or with the
anterior arch of the atlas and may
lead to limitation in the range of
motion of the CVJ.
 There is an increased prevalence
of os-odontoideum associated .

62. Posterior Arch Anomalies
 (MC atlas anomaly) :
 Posterior rachischisis > aplasias and, hypoplasia
 Total or partial aplasiaof the posterior atlas arch.
 isolated, is usually asymptomatic, but may be associated with
anterior AA subluxation.
 simulating the Jefferson fracture.

63. Split Atlas
 anterior arch rachischisisis +posterior
rachischisis=“split atlas”.
 Normal -anterior arch of the atlas appears
crescenticor half-moon-shaped, with dense cortical
,and a well-defined predentalspace.
 But in this the anterior arch appears fat or plump and
rounded in configuration, appearing to ‘‘overlap’‘the
odontoidprocess -predentalspace not seen

64. PONTICULUS POSTICUS / KIMMERLE’S DEFORMITY :
 It is a bony ridge projecting posteriorly
from the articular edge of the atlas
superior articular facet.
 The bony projection may be only a few
mm long or may elongate to unite with
the adjacent neural arch of the atlas to
produce an “ARCUATE CANAL”through
which the vertebral artery passes.
 This is due to ossification of a portion of
the oblique A-O ligament.

65. Dens dysplasia
 Type 1 (Os odontoideum) separate
odontoid process
 Type 2 (Ossiculum terminale) failure of
fusion of apical segment with its base
 Type 3 – Agenesis of odontoid base &
apical segment lies separately.
 Type 4 – Agenesis of odontoid apical
segment
 Type 5 –Total agenesis of odontoid
process.

66. OS ODONTOIDEUM
 At birth odontoid base is separate from
the body of axis by a cartilage which
persists until the age of 8, later the
center gets ossified.,or may remain
separate as Os-odontoidium.
 independent osseous structure lying
cephalad to the axis body in the
location of the odontoid process.
 The anterior arch of the atlas is
rounded and hypertrophic but the
posterior arch is hypoplastic.
 cruciateligament incompetence and A-
A instability are common

67.  Confused with Type 2 odontoid fracture –but in os the
margins of the axis body, the os, and anterior arch are all
well corticated and normal halfmoon-shaped appearance
of anterior atlas arch is not seen.
 In fracture- flattened, sharp, uncorticated margin to the
upper axis body and a normal anterior atlas arch with a
narrow gap in b/w # segments.
 Types –Orthotopic& Dystopic.
 Instability is more common with dystopictype.

68. Persistent ossiculum terminale: Bergman ossicle
 Failure of fusion of the terminal
ossicle to the remainder of the
odontoid-normally by 12 years
of age.
 confused with a type 1
odontoid fracture.
 stable when isolated and of
relatively little clinical
significance.
 The odontoid process is
usually normal in height.

69. Klippel- Feil Syndrome
triad
 decreased range of motion in the
cervical spine m/c
 short, webbed neck
 and a low hairline.
 Type
1- Massive fusion of cervical and
upper thoracic vertebra
2 –fusion of 2 cervical vertebra
,hemivertebra,scoliosis,OA fusion
3-lower thoracic and upper lumber
spine anomaly.
4-sacral agenesis

70. ASSOCIATED CONDITIONS:
 Scoliosis- 60%.
 Genito-urinary- 65%. m/c is absence of kidney.
 Sprengel'sdeformity- 35%
 Cardio-pulmonary-5-15%, m/c V.S.D.
 Deafness-30%, all types, MC mixed.
 Sykinesis-Mirror motions 20%.
 Cranio-cervical abnormalities- (25%)-Includes C1-C2
hypermobility and instability, BI,ChiariI malformation,
diastematomyelia, & syringomyelia.

71. Arnold-Chiari Malformation
 Type 1- m/c -caudal displacement of peglike cerebellar
tonsils below the level of the foramen magnum, -
congenital tonsillar herniation, tonsillar ectopia, or
tonsillar descent. syringomyeliain 50 to 70%.
 type II -less common and more severe, almost
invariably associated with
myelomeningocele.symptomatic in infancy or early
childhood. -caudal displacement of lower brainstem
(vermis,medulla, pons, 4th ventricle) through the
foramen magnum.
 type III -herniation of cerebellum into a high cervical
myelomeningocele.
 type IV -cerebellar agenesis.
type III and IV -exceedingly rare and incompatible with life
.

72.  Chiari type I malformation.
 (white line) down to the level of C1 posterior arch.

73. TUBERCULOUS AAD
 <1% of all cases of spinal TB.
 Local pain, restriction of neck movements & acute
tenderness of upper C-spine –Cardinal features.
 Compression of CMJ could be due to granulation
tissue, cold abscess or bony instability & displacement.
 Waxing & waning picture .
 􀂄Ligaments are extensively infiltrated .
 􀂄Hyperaemic decalcification occurs.

74. RHEUMATOID ARTHRITIS & CVJ
 20% of RA have AAD.
 Osteophyte formation (stabilizing effect) does not
occur secondary to deficient
osteogenesis(characteristic of RA).
 loss of tensile strength & stretching of TL due to
destructive inflammatory changes as well as secondary
degenerative changes in tissues from vasculitis--AAD.
 granulation tissue in the synovialjoints.
 􀂄Odontoid process –osteoporosis, angulation/ #.

75. TRAUMATIC LESIONS OF CVJ
OCCIPITAL CONDYLE #:
 Type I : impacted –due to axial loading.
 Type II : Basilar skull # -due to direct blow to skull.
 Type III : Avulsion #.
Type I & II are stable type III is unstable.
OCCIPITO-ATLANTAL INSTABILITY:
 Type I : anterior displacement of occiputon atlas.
 Type II : vertical displacement b/w occiput& cervical
spine
 Type III : posterior displacement of occiputon atlas.

76. # OF ATLAS:
 Posterior arch #: 66%#, occur at the junction of
posterior arch & lateral mass (hyperextension injury).
 Anterior arch #: rare
 Jefferson s # : burst # of atlas,
 Axial loading –downward displacement of condyles
with separation of lateral mass of C1.
 Classically 4 part # -2 # each in ant & post arch.
 Non union –occiputto C2 fusion

77. # Of C2 HANGMAN’S #
 Judicial Hanging”-submental
knots causes # dislocation of
neural arch of axis.
 Today majority due to RTA.
 B/l # passing downward through
the neural arch of axis with
resultant anterior displacement of
C2 on C3.

78. ODONTOID #:
 7 –14 % of cervical spine #.
 Flexion is the MC mechanism
Anderson & D’Alonzo classification–
 􀂄Type I: oblique avulsion # through the upper part
at the point of alar ligament attachment.
 􀂄Type II: # occur at the junction of the odontoid
process & the body of axis ,prone to non union,
 􀂄Type III: # extend in to the body of axis.
T/T
Odontoid compression screws (acute type II #) / C1-
2 arthrodesis

79. Treatment of CV anomalies
Treatment of A-A dislocation
 Conservative treatment- For patients having only cervical
symptoms or transient VB insufficiency with or without mild
neurological deficit conservatively using –
Cervical Collar
Head- Halter Traction- if there is associated myelopathic
features
 Surgical Management
Treatment of Basilar Invagination
 Conservative management
 Surgical treatment- Upper cervical laminectomy and
enlargement of Foramen Magnum