The craniovertebral junction consists of the occiput, atlas, axis, and connecting ligaments. It is a transition zone between the mobile cranium and spinal column. Common anomalies include occipitalization of the atlas, basilar invagination, atlantoaxial dislocation, and platybasia. Radiological assessment involves measurements of angles and distances on plain radiographs and CT/MRI to evaluate for abnormalities. Key measurements include the Chamberlain's line, McGregor's line, and posterior atlantodental interval.

1. CRANIOVERTEBRAL
JUNCTION
 Dr Kanhaiya lal Dr Jai Prakash Sharma

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

5. 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 10*, extension 25*).
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 upto90* & approx ½ occurs at the A-A joint.

6. 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. 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) ,

11. 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.

12. 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.

13. 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.

14. 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

15. 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.

16. 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

17. 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,chordom,osteoblastoma,NF
 Spontaneous rotatory subluxation-Grisel syndrome

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

19. 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
ATAXIA,ATROPHY,SRYNX –POOR PROGNOSIS

20. Anatomical and radiological
aspects

21. 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 CT)
 Angiography

22. X Ray

24. 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.

25. The important lines are
1. Chamberlain’s line
2. Wackenheim’s clivus
canal line
3. Mc Gregor’s line
(basal line)
4. Height index of Klaus
5. Mc rae’s line (
foramen magnum
line)
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

26. Normal landmark

27. 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
 If not defined basilar Invagination

28. 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.

29. Wackenheim’s clivus canal line
 Line drawn along
clivus into cervical
spinal canal
 Odontoid is ventral and
tangential to this line
 If not –suggest AAD or BI

30. Welcher’s Basal Angle
 Nasion to tuberculum sella
 Tuberculum sellae to the basion
along plane of the clivus
 Normal – 1240 - 142
 > 1400 = platybasia
 < 1300 is seen in achondroplasia

31. 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

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
 If not suggest 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. 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

40. Lines and angles used in radiologic diagnosis of C.V
anomalies.
Parameter Normal range limits
• Basal angle < 140
degree
• Boogard’s angle < 135
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 =40 mm
• Atlanto-odontoid space upto 3 mm in adults
upto 5 mm in children
• EDFM = 19mm
*

43. 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

44. Anomalies

45. Occipitalization of atlas/assimilation
 50% of all cvj anomaly
 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 .

47. TOPOGRAPHIC FORMS (WACKENHEIM):
 Type I: Occipitalization(subtotal) with BI.
 Type II: Occipitalization(subtotal) with BI & fusion of 2nd &
3rd cervical vertebrae.
 Type III: occipitalization (Total or subtotal) with
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

48. Platybasia
 refers only to an abnormally obtuse basal angle, may
be asymptomatic, and is not a measure of basilar
invagination.
 >140 basal angle.

49. 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.

50. 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.

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

52. 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

53. 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

54. 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-Atlantoaxial subluxation
associated with inflammation of adjacent soft
tissues of the neck

55. Condylar Hypoplasia:
 The occipital condyles are
underdeveloped and have
a flattened -- and widening
of the AO joint axis angle --
leading to BI.
 The lateral masses of the
atlas may be fused to the
hypoplastic condyles, further
accentuating the BI.
 limits, or may even abolish,
movements at the A-O joint.

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

57. Third occipital condyle or condylus Tertius:
 When proatlas persists or fails to
integrate, an ossicledremnant
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 .

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

59. Split Atlas
 Anterior +posterior arch rachischisisis =“split atlas”.
 Normal -anterior arch of the atlas appears crescent shape
or half-moon-shaped, with dense cortical ,and a well-
defined predental space.
 But in this the anterior arch appears fat or plump and
rounded in configuration, appearing to ‘‘overlap’‘ the
odontoid process –predental space not seen

60. Ponticulus posticus/ kimmerle,s foraman/arcuate
foramen :
 normal variant of the atlas.
 It develops by calcification of the
oblique atlanto-occipital
ligaments.
 The bony projection may be few
mm long or may elongate to
unite with the adjacent neural
arch
 The vertebral arteries pass
through this foramina.

61. 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.

62. OS ODONTOIDEUM
 At birth odontoid base is separate
from the body of axis by a cartilage
which persists until the age of 8,
later -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

63.  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 dystopic type.

64. 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.

65. 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

66. 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.

67. 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 .

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

69. 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.

70. 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 synovial joints.
 Odontoid process –osteoporosis, angulation/ #.

71. TRAUMATIC LESIONS OF CVJ
OCCIPITAL CONDYLE #:
 Type I : impacted –due to axial
loading.
 Type II : with basilar or 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
occiput on atlas.
 Type II : vertical displacement b/w
occiput& cervical spine
 Type III : posterior displacement of
occiputon atlas.

72. # 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 –occiput to C2 fusion

73. # 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.

74. 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

75. 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

76. QUIZ

81. Medanta case

85. THANKS