This document discusses cranio-vertebral anomalies and their classification. It begins by classifying bony and soft tissue anomalies. It then discusses the ossification centers of various bones including the occiput, atlas, and axis. Next, it covers the anatomical landmarks and radiological lines used to evaluate the cranio-vertebral junction, such as Chamberlain's line, McGregor's line, and the basilar angle. It provides the normal measurements for these lines. The document concludes by discussing radiological evaluation techniques including CT and MRI measurements.

1. Cranio-VertebralCranio-Vertebral
AnomaliesAnomalies
DR. AMOL GULHANEDR. AMOL GULHANE

2. ClassificationClassification
I.I. Bony AnomaliesBony Anomalies
A.A. Major AnomaliesMajor Anomalies
1. Platybasia1. Platybasia
2. Occipitalization2. Occipitalization
3. Basilar Invagination3. Basilar Invagination
4. Dens Dysplasia4. Dens Dysplasia
5. Atlanto- axial dis.5. Atlanto- axial dis.
B. Minor Anomalies
1.Dysplasia of Atlas
2.Dysplasia of occipital
condyles, clivus, etc.
II. Soft Tissue anomalies
1. Arnold-Chiari Malformation
2. Syringomyelia/ Syringobulbia

3. OSSIFICATION CENTRES
OCCIPUT & BASIOCCIPUT:
2 occipital squamous portions –2 centres
Basiocciput(clivus) -1 centre
2 Jugular tubercles –2 centres
2 Occipital condyles–2 centres
ATLAS: ossifies from 3 centres
Each half of post. Arch with lateral mass unites at 3 –4 years.
Anterior arch unites with lateral mass at 6 –8 years.
AXIS: ossifies from 5 primary & 2 secondary centres.
2 Neural arches –2 centres appear at 7 –8 wk
Body of axis –1 centre appear at 4 –5 months
Body of dens –2 centres appear at 6 –7 months
4 pieces (at birth) unite at 3 –6 years
Tip of odontoid appears at 3 –6 years, unites with the body of odontoid at 12
years.

4. Cerebellar tonsils
medulla
Vertebral artery
basion

5. Medulla oblongata
basion
Anterior arch of atlas

6. Atlas (anterior arch)
Transverse lig. atlas
Dens of axis
Medulla oblongata
Vertebral artery
Atlas, posterior arch

7. Atlas, lateral mass
Transverse ligament
atlas
Transverse process and
foramen transversarium

8. Anterior longitudinal ligament
Apical ligament of dens
Tectorial membrane
Transverse ligament of atlas
Anterior arch of atlas
Dens of axis (C2)

9. Clivus
Anterior atlanto-
occipital membrane
Atlas (lateral
mass)
Axis
Int carotid artery

10. Alar ligaments
Atlanto-axial jointAtlanto-occipital joint

11. Anatomical and Radiological AspectsAnatomical and Radiological Aspects
• Anatomical LandmarksAnatomical Landmarks
• Nasion,Nasion,
-the middle point of the junction of the frontal and the two nasal bones (fron-the middle point of the junction of the frontal and the two nasal bones (fron
tonasal suturetonasal suture
• ClivusClivus
• Basion,Basion, --the midpoint of the anterior border of the foramen magnum.the midpoint of the anterior border of the foramen magnum.
• OpisthionOpisthion-- posterior margin of the foramen magnumposterior margin of the foramen magnum
•
• Lines , angles and indexesLines , angles and indexes
• Chamberlain’s LineChamberlain’s Line
• McGregor’s LineMcGregor’s Line
• McRae’s LineMcRae’s Line
• Klaus Height IndexKlaus Height Index
• AT IndexAT Index
•Basal Angle
•Boogard’s angle
•Bull’s angle
•A-O interval
•EDFM

14. 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.

15. The Chamberlain’s lineThe Chamberlain’s line
NAME & SYNONYMS OF
LINES
DEFINITION NORMAL MEASUREMENT IMPLICATIONS
Chamberlain ‘s line
Palato-occipital line
Posterior pole of hard
palate to the Opisthion.
Tip of the dens usually
below and upto 3 mm
above this line.
Dens > 6mm in basilar
impression.
H O

17. Significance
An abnormal superior position of the odontoid indicates
basilar impression.
Common precipitating causes include platybasia, atlas
occipitalization, and bone-softening diseases of the skull
base (e.g., Paget’s disease, osteomalacia, and fibrous
dysplasia).
Occasionally, rheumatoid arthritis may also precipitate this
deformity.

18. A drawn from the posterosuperior margin of the
hard palate to the most inferior surface of the
occipital bone.
The McGregor’s line

19. The McGregor’s lineThe McGregor’s line
H
Low occiput
NAME & SYNONYMS OF
LINES
DEFINITION NORMAL MEASUREMENT IMPLICATIONS
Mc Gregor’s line
Basal line
MOST ACCURATE
Postero-superior margin
of Hard palate – most
inferior surface of
occipital bone.
Odontoid apex shouldn’t
lie above.
< 5mm
Superior lie of odontoid
indicates basilar
impression.(>5mm)
Low occiput

20. The McRae’s lineThe McRae’s line
B O
Mc Rae’s line
Formen magnum line
Anterior and posterior
ends of formen
magnum.
(Basion and Opisthion)
Inf margin of occiput
should lie at / below this
line. Tip of dens does
not exceed this line.
Perpendicular line along
odontoid intersects 1st
line in its anterior
quadrant.
Inf margin of occiput lies
superior – Basilar imp.
If sagittal diameter
< 20mm neurological
symptoms (+) (foramen
magnum stenosis)

21. Significance
If the inferior margin of the occipital bone is convex in a
superior direction and/or lies above this line, then basilar
impression is present.
Predisposing causes include platybasia, occipitalization,
rheumatoid arthritis, and bone-softening diseases (e.g.,
Paget’s disease, osteomalacia, and fibrous dysplasia).
If the odontoid apex does not lie in the ventral quarter of this
line, a dislocation of the atlanto-occipital joint or a fracture
or dysplasia of the dens may be present.

22. Clivus-Canal lineClivus-Canal line
C
B
OC2
H
N
NAME & SYNONYMS OF
LINES
DEFINITION NORMAL MEASUREMENT IMPLICATIONS
Wackenhie’s line
Clivus canal line
Drawn along clivus into
cervical canal
Odontoid tip is ventral
and tangential to line
Odontoid transects the
line in basilar imp

23. Basilar Angle/Welcker’s basilar angle/ Martin’s
basilar angle/ sphenobasilar angle.
Landmarks
Three points are located and joined together by two
lines; the subsequent angle is measured.
The three points are the nasion (frontal-nasal junction),
the center of the sella turcica (midpoint between the
clinoid processes), and the basion (anterior margin of the
foramen magnum).
The average normal angle subtended by these two lines
is 137°, with a normal variation of 123-152°

24. Significance
The measurement is an index of the relationship between
the anterior skull and its base.
The angle will increase beyond 152° in platybasia, in
which the base is elevated in relation to the rest of the
skull.
This may or may not be associated with basilar
impression.
The deformity may be congenital (isolated impression,
occipitalization) or acquired (Paget’s disease, rheumatoid
arthritis, fibrous dysplasia).

25. Basilar AngleBasilar Angle
Mid sella
B
N
S
B
N
NAME & SYNONYMS OF
LINES
DEFINITION NORMAL MEASUREMENT IMPLICATIONS
Basilar angle
Welcker’s / Martin’s /
Spheno-BA
Nasion – Centre of the
sella – Basion.
Angle 1370
(123-1520
)
>1520
Platybasia
(Base is elevated)
+/- Basilar impression

26. Modified MRI technique
This technique described by Koenigsbert et al yields a normal value range (95% C.I)
116° - 118° for adults and 113° - 115° for children.
Angle formed by :
line extending across the anterior cranial fossa to the tip to the dorsum sellae
line drawn along the posterior margin of the clivus

27. The Boogard’s lineThe Boogard’s line
N
O
NAME & SYNONYMS OF
LINES
DEFINITION NORMAL MEASUREMENT IMPLICATIONS
Boogard ‘s Line Nasion to Opisthion Basion should lie below
this line
Altered in basilar
impression

28. Boogard’s angleBoogard’s angle
Tuberculum sellaTuberculum sella
B o
N
Mc Ray
s
C
NAME & SYNONYMS OF
LINES
DEFINITION NORMAL MEASUREMENT IMPLICATIONS
Boogard ‘s Angle Angle intersected by
1st
line between Dorsum
sellae to Basion &
Mc Rae’s line.
119-1350
Average - 1220
> 1350
Basillar impression

29. Boogard’s angle

30. MethodMethod of Bullof Bull
C2
Atlas plane
Chamberlain
Bull ‘s angle
Atlanto-palatine angle
Posterior Angle betn
1st
line from Post tip of
hard palate to post
margin of foramen
magnum
2nd
line betn ant & post
tubercles of atlas
Post angle <130
If odontoid is tilted
posteriorly or in case of
change of atlas position
The angle > 130

31. Ranawat methodRanawat method
C2
C1
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
Men averages 17 mm (±2
mm SD)
Women, 15 mm
(± 2 mm SD).
A decrease in this
distance indicates
cephalad migration of
C-2.
C2
C1
C2
C1
PEDICLE

32. Schmidt – Fischer AngleSchmidt – Fischer Angle
(ATLANTO-OCCIPITAL JT AXIS ANGLE)(ATLANTO-OCCIPITAL JT AXIS ANGLE)
O
C2
AA JT
AO JT
C1 C1
NAME & SYNONYMS OF
LINES
DEFINITION NORMAL MEASUREMENT IMPLICATIONS
Schmidt – Fischer
Angle
Angle of axis of Atlanto-
Occipital joint
125 +/- 2 degrees Angle is wider in condylar
hypoplasia

33. CRANIO-VERTEBRAL ANGLECRANIO-VERTEBRAL ANGLE
ax
C
NAME & SYNONYMS OF
LINES
DEFINITION NORMAL MEASUREMENT IMPLICATIONS
Cranio vertebral angle Between clivus line and
post axial line
Flexion – 1500
Extension - 1800
<1500
Platybasia
cord compression
Basilar impression

34. •BDI less than 8.5 mm compared
with 12 mm on data from plain
radiographs.
•An ADI less than 2 mm, compared
with 3 mm previously accepted.
Midsagittal MDCT image of the
craniocervical junction demonstrates
the BDI(basion-dental interval) as
the distance from the most inferior
portion of the basion to the closest
point of the superior aspect of the
dens.
MDCT VS PLAIN RADIOGRAPHY
IN CRANIOMETRY…..

35. MDCT image of the craniocervical junction
demonstrates the ADI, which is calculated
by drawing a line from the posterior aspect
of the anterior arch of C1 to the most
anterior aspect of the dens at the midpoint
of the thickness of the arch in
craniocaudal dimension
Atlantodental Interspace (ADI)
Synonyms.
Atlas-odontoid space, predental interspace,
atlas-dens interval
Flexion is the optimum view to assess the
interspace, because in this position the
most stress is placed on the transverse
ligament of the atlas

36. Normal Values for Atlantodental Interspace
Adults: 1 to 3 mm
Children:1 to 5 mm
Significance.
A decreased space is to be expected with advancing age because of
degenerative joint disease of the atlantodental joint.
A more significant change is an abnormally widened space with
reduction in the neural canal size.
The most frequent causes include trauma, occipitalization, Down’s
syndrome, pharyngeal infections, and inflammatory arthropathies
(e.g., ankylosing spondylitis, rheumatoid arthritis, psoriatic arthritis,
and Reiter’s syndrome).

37. Sagittal CT images: right measures the basion-posterior axial line interval which is
denoted by the small horizontal red line.
The left image demonstrates measurement of the basion-dental interval which is
denoted by the vertical red line.
If either of these distances are greater than 12 mm then the diagnosis of
occipitocervical dissocation is fairly certain.
The basion-posterior axial line interval
(BAI) is drawn along the posterior aspect
of the dens (the posterior axial line) and a
measurement between this line and the tip
of the basion is performed.
Harris Lines or the Rule of Twelve

38. The Powers ratio can be measured to
determine if there is anterior
occipitoatlantal dissociation. The Powers
ratio is the distance between the basion
and the posterior spinolaminar line of C1
(BC) divided by the distance between the
anterior arch of C1 and the opisthion (AO).
If the Power's Rule (BC)/(AO) is greater
than 1 then anterior occipitoatlantal
dissocation has likely occurred.
The accuracy of the Powers ratio is
controversial since it can be difficult to
locate the position of the basion and the
opisthion on the lateral skull radiograph. It
is easier to obtain on sagittal CT..

39. Sagittal MDCT image of the craniocervical
junction demonstrates the AOI, which is
calculated by drawing a line perpendicular
to the articular surfaces of the occipital
condyle and the lateral mass of C1. This
line is drawn at the center of the
articulation by correlating the sagittal and
coronal images.
•The AOI demonstrated 95% of the population
ranged between 0.5 mm and 1.4 mm.

40. AP open mouth
If the lateral margin of the atlas lateral mass lies
lateral to the lateral axis margin, this may be a
radiologic sign of Jefferson’s fracture, odontoid
fracture, alar ligament instability, or rotatory
atlantoaxial subluxation
Atlantoaxial Alignment

41. ATLANTOAXIAL ALIGNMENT.
A. Normal Alignment.
B. Abnormal Alignment. The
abnormality (arrow) is the result of
a Jefferson’s fracture of the atlas.

45. Table : 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

46. RADIOLOGY OF CVJ
(NORMAL VARIANTS
& ANOMALIES)
THE OCCIPUT :
�The basiocciput forms the lower portion
of the clivus.
�The upper portion of the clivusis formed by the basisphenoid, separated
from the basiocciput by the sphenooccipital synchondrosis
�The age at which this synchondrosis fuses, ranges from “after the twelvth
year”to 14-16 years for girls and 16-18.5 years for boys.
�Most occipital anomalies are associated with decreased skull base height
and basilar invagination.

47. Condylus Tertius
Anomalies and malformations of the most caudal of the occipital
sclerotomes are collectively termed ‘ ‘manifestations of occipital vertebrae”
When the hypochordal bow of the fourth occipital sclerotome (proatlas)
persists or when the proatlas fails to integrate, an ossifled
remnant may be present at the distal end of the clivus, called the condylus
tertius or third occipital condyle .
This third condyle may form a joint or 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
with this abnormality
The occipital bone is composed of asioccipital, exoccipital, and
supraoccipital portions enclosing the foramen magnum

48. Condylus tertius and platybasia. Midsagittal Ti-weighted MR image reveals
marked skull base flattening, with a Welcher basal angle of 150 dotted line). Note the
marked bowstring deformity of the cervicomedullary junction.
The C-1 arch (A) lies directly above the tip of the odontoid process (0). Marrow within
accessory ossification centers (condylus tertius)

50. Condylar Hypoplasia
In condylar hypoplasia, the occipital condyles are
underdeveloped and have a flattened appearance, leading to
basilar invagination (violation of the Chamberlain line) and
widening of the atlantooccipital joint axis angle
The tip of the odontoid process and the lateral masses of the
atlas typically lie below a line connecting the mastoid tips
(bimastoid line), this relationship is violated in condylar
hypoplasia.

51. The lateral masses of the atlas may be fused to the hypoplastic
condyles,
further accentuating the basilar invagination.
Clinically, condylar hypoplasia limits, or may even abolish,
movements at the atlantooccipital joint and may occasionally lead to
compression of the vertebral artery secondary
to excessive posterior gliding of the occiput in
relation to the atlas

52. image

53. PLATYBASIA
BASILAR IMPRESSION
BASILAR INVAGINATION
These terms are not synonymous.

54. PLATYBASIA/Martin’s anamoly
Flattening of angle between the clivus and
the body of the sphenoid
C/F
PRIMARY
- Isolated or in conjunction with other
dysplasias like Achondroplasia,
Osteogenesis imperfecta
SECONDARY - Paget’s disease / bone
softening / degenerative disease
Basilar angle > 152°(N=123-1520)
Craniovertebral = clivus-canal angle
becomes acute (<150°)
MC associated changes - Basilar
invagination, anomalies of
C1(occipitalisation)block vertebra,
Klippel-Feil syndrome.

55. BASILAR INVAGINATION
�Basilar invagination implies that the floor of the skull is
indented by the upper cervical spine, & hence the tip of
odontoid is more cephalad protruding into the FM.
�There are two types of basilar invagination: primary
invagination, which is developmental and more common
secondary invagination, which is acquired.
�Primary invagination can be associated with
occipitoatlantal fusion, hypoplasia of the atlas, a bifid
posterior arch of the atlas, odontoid anomalies.

56. In BI, all three parts of the occipital bone (basiocciput,
exoccipital& squamous occipital bone) are deformed.
Topographic types of BI :
�Anterior BI : hypoplasia of the basilar process of the
occipital bone.
�BI of the occipital condyles(ParamedianBI)–Condylar
hypoplasia
�BI in the lateral condylar area.
�Posterior BI: posterior margin of the FM is invaginated.
�Unilateral BI.
�Generalised BI

57. �BI is associated with high incidence of vertebral artery
anomalies.
�Abnormal curvature of VA is due to the fact that they are of
normal length & course through a reduced bone space (wide
angle b/w 3rd
& 4th
part of VA).
�SIGNS / SYMPTOMS: usually occur in 2nd
or 3rd
decade.
�Short neck(78%),torticollis (68%)
�s/s of associated ACM (cerebellar& vestibular disturbances)
& syringomyelia(25 to 35%).

58. �Motor & sensory disturbances (85%).
�Lower cranial nerves involvement
�Headache & pain in the nape of neck (greater occipital N)
�s/s of raised ICP (HCP) due to posterior encroachment which causes
blockage of aqueduct of sylvius.
�Compression of cerebellum & vestibular apparatus leading to vertical
or lateral nystagmus(65%) (not due to direct pressure from post rim of
FM but rather due to a thickened band of dura).
�Vertebral artery insufficiency s/s.

59. •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.
•Primary invagination can be associated
with occipito atlantal fusion, hypoplasia of
the atlas, a bifid posterior arch of the atlas,
odontoid anomalies.
•BI is associated with high incidence of
vertebral artery anomalies.
Chamberlain’s line- tip of dens is >6mm above this line
Mc Gregor’s line- tip of dens is > 5mm above this line
Mc Rae’s line- tip of dens is above this line
Boogard’s line- basion is above this line

60. BASILAR IMPRESSION (SECONDARY BASILAR
INVAGINATION
• Basilar impression refers to secondary or acquired forms of
BI
• due to softening of the bone & is seen in conditions such as
rickets, hyperparathyroidism, osteogenesis imperfecta, Pagets
disease, neurofibromatosis, skeletal dysplasias, and RA &
infection producing bone destruction with or without
ligamentous laxity.
•May be associated with developmental cervical canal stenosis
& also fibrous bands & dural adhesions at the dorsal
cervicomedullary junction.

61. BASILAR IMPRESSION (SECONDARY BASILAR
INVAGINATION
Paget’sdisease :
�Usually symptomatic after
40 years of age.
�CT shows irregular thick
bones with a “moth eaten”
appearance of the calvaria.

62. Achondroplasia:
�Genetically dominant disorder characterized by inhibition of
endochondral bone formation.
�The base of the skull is affected but the membraneous
convexity skull bone grows normally.
�This differential bone growth results in large calvarium on a
small base.
�The mortality is high in the 1st
year of life due to
cervicomedullary dysfunction at the FM.
�A small FM with hypertrophic bone & a posterior dural shelf
results in compression of neural structures.

64. Atlantooccipital Assimilation
failure of segmentation between the skull and first cervical
vertebra results in assimilation of the atlas.
The assimilation may be cornplete or partial.
It invariably results in basilar invagination.
Although the Wackenheim clivus baseline may be normal,
the clivus-canal angle may be decreased.

65. When incompletely assimilated, the atlas arches appear
too high on the lateral plain radiograph
or, when completely assimilated, are not visible
at all
There is an increased prevalence of associated fusion of the axis
and third cervical vertebra in association with atlantooccipital
Assimilation .
When this is present, gradual loosening of the atlantodental joint
with progressive atlantoaxial subluxation may
occur, reported in approximately 50% of cases

66. 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 &
maldevelopment of the transverse ligament.
�Type III may be associated with various malformations like
C2-C3 fusion, hemivertebra, dens aplasia, tertiary condyle, etc.

67. The neurological symptoms are not caused by occipitalization proper
but rather by the fact that in the absence of a free atlas, TL fails to
develop which causes posterior displacement of axis & compression
of the spinal cord.
�Instability b/w atlas & axis is reducible in patients <15 yr’s but after
that irreducible state occurs.

70. ATLAS :
�With the exception of the various atlantooccipital
assimilations, most atlas anomalies, when isolated,
produce no abnormal CVJ relationships and are not
associated with basilar invagination.
�The vast majority of anomalies consist of various arch
clefts, aplasias, and hypoplasias.
�Arch anomalies are frequently mistaken for fractures in
the evaluation of plain radiographs of patients with a
history of cervical spine trauma.

71. The irregular fragments located inferior to
the Anterior arch of the atlas may be
mistaken for fracture fragments . The clear
cortical margins and characteristic location
help to differentiate this variant from a
fracture.
Accessory ossification centre for the anterior arch of
the atlas……

72. 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.

75. Posterior Arch Anomalies (MC atlas anomaly) :
�Total or partial aplasia of the posterior atlas arch
is rare.
�Although absence of the posterior arch, when
isolated, is usually asymptomatic, but may be
associated with anterior atlantoaxial subluxation.
�Bilateral atlantoaxial subluxation may be
associated with both total and partial aplasias,
simulating the Jefferson fracture.

76. In contrast to the aplasias and hypoplasias, clefts of the
atlas arches are much more common.
�Posterior rachischisis, most common, is observed in 4%
of adults.
�The majority of posterior atlas clefts (97%) are midline,
whereas lateral clefts, through the sulcus of the vertebral
artery, account for the remaining 3%.
�Posterior arch rachischisis may be superimposed on the
odontoid process or the axis body on the open-mouth
odontoid view, simulating a fracture.

77. Posterior arch hemiplasia

78. Split Atlas :
�In contrast to posterior arch rachischisis, anterior arch
rachischisisis quite rare (0. 1 %).
�It is typically encountered in association with posterior
rachischisis-“split atlas”.
�Normally, on a lateral radiograph, the anterior arch of the
atlas appears crescentic or half-moon-shaped, with dense
cortical bone surrounding the medullary cavity and a well-
defined predental space.

79. In anterior arch rachischisis, the anterior arch appears fat or
plump and rounded in configuration, appearing to ‘‘overlap’‘
the odontoid process
(making identification of
the predental space impossible);
the arch may have unsharp,
duplicated anterior margins

80. CONGENITAL ODONTOID ANOMALIES OR DYSPLASIA
Types of 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.

81. Persistent OssiculumTerminale:
�Also called Bergman ossicle,
results from failure of fusion of the
terminal ossicle to the remainder of
the odontoid process.
�The fusion typically is
accomplished by 12 years of age.
� Bergman ossicle may be confused with a type 1 odontoid fracture
(avulsion of the terminal ossicle), and absolute differentiation between
the two diagnoses may be difficult.
�Whether traumatic or congenital in origin, this anomaly is stable
when isolated and of relatively little clinical significance.
�The odontoid process is usually normal in height.

82. the normal dense secondary ossification center for the odontoid process tip,
which exhibits a characteristic symmetrical V-shaped lucent zone of separation
from the body of the dens. COMMENT: This is a normal finding of the odontoid
seen in 25% of patients < 12 years of age; but it is usually not seen after this
age, at which time it constitutes non-union (ossiculum terminale of Bergmann).

83. OdontoidAplasia:
�Total aplasia of the odontoid process is extremely rare.
�A true aplasia is associated with an excavation defect into
the body of axis.
�may simulate os odontoideum, as the os fragment may be
perfectly projected over the atlas arch on the open mouth
odontoid view.

84. AP Open Mouth. Here the odontoid
process exists as an abbreviated remnant
stump; therefore, it is not true agenesis.
The lateral shift of the atlas relative to the
axis, C1 on C2, indicates instability

85. OS ODONTOIDEUM
�This term first introduced by Giacominiin 1886, refers to an
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.
�As the gap between the os odontoideum and the axis body
usually extends above the level of the superior articular facet
of the axis, cruciate ligament incompetence and A-A
instability are common.

86. The margins of the axis body, the os, and anterior arch are
all well corticated.
�Type 2 odontoid fracture is typically associated with a
flattened, sharp, uncorticated margin to the upper axis body
and a normal, half moon-shaped appearance to the anterior
atlas arch with a narrow gap in b/w # segments.
�Etiology –Embryologic, Traumatic &/or Vascular.
�Types –Orthotopic& Dystopic.
�Instability is more common with dystopic type.

87. � Reducible–on flexion, dorsal compression of the cord
occurs
on extension ventral compression occurs secondary to
increased angulation anteriorly.
�Irreducible–due to displacement of TL ventral to the
ossicle.
Treatment:
Reducible –Occipitocervical PF in neutral position.
Irreducible –Transoral resection of the os, odontoid
remnant & surrounding granulation tissue.

88. Os odontoideum is defined as
non-union of the dens with the
axis body. A transverse,
radiolucent cleft separates an
ossicle of variable size from
the axis body

89. Os odontoideumOs odontoideum
OS ODONTOIDEUMOS ODONTOIDEUM
 Dens hypoplastic &Dens hypoplastic &
separate from ossicle byseparate from ossicle by
variable distancevariable distance
 Incompetent cruciateIncompetent cruciate
ligmt :ligmt : Unstable
 Corticated, smooth,Corticated, smooth,
roundround
FRACTUREFRACTURE
 Narrow gap betweenNarrow gap between
fractured fragmentsfractured fragments
 Fracture may lie caudalFracture may lie caudal
to superior facetto superior facet
 Jagged edge, no cortexJagged edge, no cortex

90. Subluxation
Os
odontoideum
Fracture

91. Atlanto-Axial Instability
•A: Rotational
–Around the dens
•B: Translational
–Translation between C1–C2, where transverse lig is disrupted
•C: Distraction:
–Indicating craniocervical dissociation

92. Non-traumatic conditions associated with increase in the atlanto axial
distance:
�Down syndrome
�Due to laxity of the transverse ligament
�Grisel syndrome
�Atlantoaxial subluxation associated with inflammation of adjacent soft
tissues of the neck
�Rheumatoid arthritis
�From laxity of the ligaments and destruction of the articular cartilage
�Osteogenesis imperfecta
�Neurofibromatosis
�Morquio syndrome
�Secondary to odontoid hypoplasia or aplasia
�Other arthridities (Psoriasis,Lupus)

93. On the open mouth odontoid view, the combined spread of the lateral
masses of C1 greater than 6.9 mm would indicate rupture of the
transverse ligament.
An atlantoaxial distance greater than 4-5 mm by lateral radiographs,
is indicative of AAI.
Posterior atlanto dental interval (PADI):
Normal range is 19 –32 mm in male & 19 –30mm in females.
Below 19mm, neurological manifestations occur.

94. WADIA CLASSIFICATION :
�Group I: AAD with occipitalization of atlas & fusion of C2
& C3.
�Group II: odontoid incompetence due to its maldevelopment
with no occipitalization of atlas.
�Group III: odontoid dislocation but no maldevelopment of
dens or occipitalization of atlas.
�Incidence of AAD –
57% of all CVJ anomalies.
8.3% of all causes of cervical compression
ATLANTO-AXIAL DISLOCATION OR INSTABILITY

95. Posterior atlanto dental interval (PADI) measured from the
posterior border of the dens to the anterior border of the
posterior tubercle.
�This index may be more important because it more directly
assesses the space available to the spinal cord.
�Normal range for the distance behind the dens is 19 –32 mm
in male & 19 –30mm in females.
�Below 19mm, neurological manifestations occur.

96. Rotatory displacement
(Fielding and Hawkins
classification):
�Type I is simple rotatory
displacement with an intact
transverse ligament.
�Type II injuries involve
anterior displacement of C1
on C2 of 3-5 mm with one
lateral mass serving as a pivot
point and a deficiency of the
transverse ligament.
�Type III injuries involve
greater than 5 mm of anterior
displacement.
�Type IV injuries involve
the posterior displacement of
C1 on C2.

97. Type I injuries (stable subluxations) –Collar.
�Type II injuries may be potentially unstable.
�Type III and IV rotatory displacements that are
unstable are treated surgically with a reduction
and C1-2 fusion.

98. Non-traumatic conditions associated with increase in the atlantoaxial distance:
� Down syndrome
�Due to laxity of the transverse ligament
�Grisel syndrome
�Atlantoaxial subluxation associated with inflammation of
adjacent soft tissues of the neck
�Rheumatoid arthritis
�From laxity of the ligaments and destruction of the articular
cartilage
�Osteogenesis imperfecta
�Neurofibromatosis
�Morquio syndrome
�Secondary to odontoid hypoplasia or aplasia
�Other arthridities(Psoriasis,Lupus)

99. RHEUMATOID ARTHRITIS & CVJ
�First described by Garrodin 1890.
�20% of the patients with RA have AAD.
�AAD is due to loss of tensile strength & stretching of TL
due to destructive inflammatory changes as well as secondary
degenerative changes in tissues from vasculitis.
�Similar changes occur in the median & lateral joints which
result in erosive changes in adjacent bone & formation of
granulation tissue in the synovial joints.
�Odontoid process –osteoporosis, angulation/ #.

100. OCCIPITO-ATLANTAL
INSTABILITY:􀂄Traumatic / non
traumatic
􀂄Traumatic usually fatal, 8%
incidence in RTA.
􀂄Seen with cardiorespiratory
arrest, quadriplegia, loss of
autonomic function, VA
insufficiency, etc
􀂄Traynelis classification:
􀂄Type I : anterior displacement of occiput on atlas.
􀂄 Type II : vertical displacement b/w occiput & cervical spine
􀂄Type III : posterior displacement of occiput on atlas.

101. TRAUMATIC LESIONS OF CVJ
�# OF ATLAS:
�Posterior arch #: 2/3rdof all #, occur at the junction of
posterior arch & lateral mass (hyperextension injury).
�Anterior arch #: rare
�Jefferson s # : burst # of atlas,
1st
described by Geoffrey jefferson in 1920.
Axial loading –downward displacement of condyles with
separation of lateral mass of C1.
Classically 4 part # -2 # each in ant & post arch.
neck pain & stiffness
Cervical collar / Halo immobilization
Non union –occiputto C2 fusion

103. open-mouth show lateral spine
dispalcement of lateral masses of C1
CT scan of C1 shows fratures
through anterior and
posterior rings of C1

104. HANGMAN’S # ( TRAUMATIC SPONDYLOLISTHESIS
OF AXIS ):
�“Judicial Hanging”-submental knots causes # dislocation of
neural arch of axis.
�Today majority due to RTA.
�Two basic mechanisms :
Hyperextension & distraction
Hyperextension & compression

105. Type I: # are either non-displaced or have no angulation&
<3mm of displacement (stable injury with uncommon
neurological deficits).
�Type II: # with significant angulation& translation of
anterior fragment.
�Type III: # with severe angulation& displacement along
with concomitant U/L or B/L facet dislocation.
�Neck pain but neurological deficits less.
�Surgical Rx seldom required due to high chances of
spontaneous interbody fusion & # healing.
�Most # managed by reduction & external immobilization.

106. Radiographic features: (best seen on lateral view)
1. Prevertebral soft tissue swelling.
2. Avulsion of anterior inferior corner of C2 associated with rupture of the anterior
longitudinal ligament.
3. Anterior dislocation of the C2 vertebral body.
4. Bilateral C2 pars interarticularis fractures.
Hangman's Fracture- # through pars of c2

107. Hangman's Fracture
* Traumatic spondylolisthesis of C2
* Fractures of the lamina, articular facets,
pedicles or pars interarticulares of C2 with
disruption of C2-C3 junction

108. Axial CT image of the cervical spin
at C2 level shows fractures of
bilateral C2 pars interarticulares.
The fracture on the right extends to
the transverse foramen where the
right vertebral artery is located.

109. ODONTOID #:
�Constitute about 7 –14 % of cervical spine #.
�Flexion is the MC mechanism of injury causing anterior
displacement of C1 on C2.
Anderson & D’Alonzo classification–
�Type I: oblique avulsion # through the upper part of the
odontoid process at the point of alar ligament attachment.
�Type II: # occur at the junction of the odontoid process &
the body of axis.
�Type III: # extend down in to the body of axis.

110. ODONTOID #
�Type I # are stable & heal well if immobilised in a collar or
brace.
�Type III are usually stable #, skull traction f/b halo or
brace for 3 –4 months results in fusion.
�Type II # are prone to non union, with a failure rate of 30
-60 % with conservative measures.
�Indications for Sx–displacement >= 5mm, nonunion, age
>7 years / disruption of the TL.
�Odontoid compression screws (acute type II #) / C1-2
arthrodesis(wiring / fusion, transarticular screws)

111. CHIARI MALFORMATION
�The Chiari malformations are a group of hindbrain
herniation syndromes initially described by Austrian
pathologist Hans Chiari in 1891.
�Types of Chiari malformations :
�Type I: Caudal descent of cerebellar tonsils in cervical
spine. Osseous anomalies of posterior skull base and spine.
It presents in early adulthood rather than at birth.
Associated with syringomyelia in 50 to 70%.

112. Type II: Caudal descent of cerebellar vermis and brain stem
into cervical spine.
Open spinal dysraphism
Hydrocephalus
Multiple neuroaxis anomalies
�Type III: Craniocervical encephalocele containing
portions of cerebellum and brain stem.
Hydrocephalus
�Type IV: (Controversial: not commonly accepted as a
Chiarimalformation)
Aplasia/hypoplasia cerebellum

113. ARNOLD-CHIARI
MALFORMATION I
Present in adulthood ="cerebellar
tonsillar ectopia"
Herniation of cerebellar tonsils > 5mm
below a line connecting Basion with
Opisthion (= foramen magnum)
Causes:
• small posterior fossa,
•cerebellar overgrowth,
•disproportionate CSF absorption
Associated with:
1. Syringohydromyelia (30-56%)
2. Hydrocephalus (25-44%)
3. Malformation of skull base
NECT:
Effaced Posterior Fossa cisterns
"Crowded" Foramen Magnum
Lateral/3rd ventricles usually normal

114. ARNOLD-CHIARI
MALFORMATION II
Radiography
Lucken shadel -Craniolacunia = Lacunar Skull
= mesenchymal dysplasia of calvarial
ossification
Absent / Hypoplastic posterior arch of C1
Myelography
Tethered cord
NECT
Small posterior fossa
Large, funnel-shaped foramen magnum
"Scalloped" petrous pyramid,
"notched" clivus
Absent falx cerebelli

115. ARNOLD-CHIARI
MALFORMATION III
• High cervical / occipital
meningoencephalocele + intracranial
Chiari 2
malformation
NECT
o Occipital squamo defect
Posterior spina bifida at the P1–P2 level
o Bony features of Chiari 2
Small posterior cranial fossa, scalloped
clivus, lacunar skull
MR Findings
TIWI
Sac contents
• Meninges, cerebellum, ± brain stem
• Cisterns, 4th ventricle, dural sinuses
o Hydrocephalus
T2WI: Tissues in sac may be bright (gliosis)
MRV: ± Veins in cephalocele

116. NEOPLASMS OF CVJ
�Unusual
�Metastatic malignancies, such as carcinoma of the breast,
lung, prostate, kidney and thyroid in adults;
and neuroblastoma, Ewing’s tumor, leukemia, hepatoma and
retinoblastoma in children, are most common.
�Primary malignancies involving the craniocervical junction
are rare(multiple myeloma).
�Benign tumors are very rare.

117. THANK YOUTHANK YOU