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1. Imaging of the Cranio-Vertebral Junction
Dr Himadri Sikhor Das, MD
Dr.P.Hatimota, Dr.P.Hazarika, Dr.C.D.Choudhury.
MATRIX
Guwahati, Assam

2. CV JUNCTION
Parts of CV Junction include:-
 The Occiput
 First Cervical Vertebra (Atlas)
 Second Cervical Vertebra (Axis)
 Their articulations and
 Connecting ligaments
“The C-V junction is a transition site between mobile cranium and
relatively rigid spinal column.
It is also the site of the medullo spinal junction”.

3. • Central skull base
•Atlas ( C1 )
•Axis ( C2 )
Postr arch atlas
Hard palate
Tuberculum Sella
Nasion
Basion
Opisthion
Antr arch atlas
Torcular Herophilii
(Internal Occipital
Protuberance
Clivus
Dens

4. Embryology of the CV junction
Out of 4 occipital sclerotomes
 the first 2 form basiocciput,
 the 3rd Jugular tubercles and
 the 4th (Proatlas) form parts of foramen magnum,
atlas and axis.
ATLAS develops from two primary centers for each
half, and a secondary centre for the cartilage between
them.

5. Embryology of the CV junction
 AXIS develops from five
primary and two
secondary centers.
 Body and arches – II
cervical sclerotome
 Base of Dens – I cervical
sclerotome
 Apical segment of Dens –
IV occipital sclerotome.

6. Embryology of the CV junction
 The apical segment is not ossified until 3 years of
age.
 At 12 years it fuses with odontoid to form normal
odontoid; failure leads to Os Terminale
Tip of dens
1
2 3
4 5
6
Body of
dens
Dens

7. Anatomy of the CV junction
ATLANTO-AXIAL JOINT:
 Most active joint in the body, moving approximately 600
times per hour.
 Normal range of cervical motion is 900 on each side,
range of rotation of atlas on axis being 25-530
 Rotation of >560 on one side or a R-L diff >80 implies
hyper mobility
 Rotation of <280 implies hypo mobility

8. CV Junction

9. Anatomy of the CV junction
Occipital condyles
Atlantoaxial joint
Tectorial Membrane
Lateral mass of
atlas
Transverse lig
Cruciate Ligament
vertical band
Apical Lig
Alar Lig

10. Imaging of the CV junction
Plain radiographs (standard FFD)
 Lateral
 Open mouth
 Dynamic Flexion & Extension (to r/o atlantoaxial
subluxation / occipitalization of atlas)
 Tomograms –AP and Lateral
Vertebral angiogram
 may be necessary in select cases, especially BI

11. Imaging of the CV junction-CT
Spiral CT
 1-3 mm collimation
 Pitch =1
 Overlapping reconstruction
 In neutral position
 With head rotated (Torticollis )
 Flexion (? Transverse ligament abnormality )
 2-D axial and multiplanar
 3D
 Dynamic CT (AARF)

12. Imaging of the CV junction- MRI
Technique
 Surface / Head coil
 Contiguous thin sections (2-3mm with 3D
acquisitions)
 Sagittal sections in flexion if C1-C2 Dislocation to be
ruled out
 Sequences
 SE- Sagittal 3D T1W
 FSE Sagittal T2W
 CEMR (Gd )Only if intra/extramedullary
lesion is suspected
 Kinematic MRI – cord compression in AAD, AARF
 GRE – to delineate bony cortical outline

13. X-ray

14. X-ray

15. X-ray

16. Disorders of the CV junction
Congenital bony malformations
OCCIPUT ANOMALIES
Basilar invagination
Anomalies of atlas
Odontoid abnormality
Atlanto-axial instability
Others

17. Disorders of the CV junction
ACQUIRED MALFORMATIONS
 Trauma
 Arthritides
 Infection
 Degeneration
 Tumours

18. Lines and Angles
The important lines are
 Chamberlain’s line
 Wackenheim’s clivus canal line
 Mc Gregor’s line (basal line)

19. Lines and Angles
The important angles are
 Basal angle
 Bull’s angle
 Height index of Klaus

20. Chamberlain’s line
Synonym Definition
Chamberlain's Joins posterior
(Palato-occipital Line) tip of hard palate to posterior tip of
Foramen Magnum (opisthion)
Tip of dens below this line ±3 mm
>7mm or >1/2 of odontoid def basilar Invagination
DRAWBACK – posterior rim anatomical variations.

21. Mc Gregor’s line
Synonym Definition
McGregor’s Line Line drawn from posterior
tip of Hard palate to
lowest part of Occiput
Odontoid tip >4.5mm above = Basilar Invagination
Should be used when lowest part of occipital bone is not Foramen Magnum.

22. Wackenheim’s Line
Synonym Definition
Wackenheim's Line drawn along
(Clivus canal) line clivus into cervical spinal
canal
Odontoid is ventral and tangential to this line

23. McRae’s Line
Synonym Definition
McRae's (Foramen Joins anterior and
Magnum) line posterior edges of
Foramen magnum
* Tip of odontoid is below this line.
** When sagittal diameter of canal <20mm, neurological symptoms occur – Foramen
Magnum Stenosis

24. Welcher’s Basal Angle
Synonym Definition
BASAL ANGLE Angle between two lines
drawn from
 Nasion to tuberculum sella
 Tuberculum sellae to the basion along plane of the clivus
 Normal – 1240 - 142
 > 1450 = platybasia
 < 1300 is seen in achondroplasia

25. 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

26. Platybasia – refers only to an abnormally obtuse
basal angle, may be asymptomatic, and is not a
measure of basilar invagination.

27. Basilar impression vs. Basilar invagination
• Basilar impression is defined as upward displacement of
vertebral column elements into the foramen magnum.

28. Specific Anomalies- Basilar Invagination
• primary developmental defect implying
prolapse of vertebral column into the skull at the
base due to softening of the bones at the base
of the skull.
Causes
 Hyperparathyroidism
 Hurler's syndrome
 Rickets/OM/Scurvy
 Hajdu-Cheney Syndrome.
 Paget's disease.
 Cleidocranial dysostosis
 Osteogenesis Imperfecta
“ As can be seen from the causes  almost
all of the causes are associated with bone
softening conditions due to which the CV
junction is invaginated like a sleeve”

29. Classification of Basilar Invagination
Morphological classification
Anterior Paramedian
Clivus short Clivus Normal/long
Ass. with Platybasia Not ass. with
Platybasia
Etiological classification (synonyms )
1.Basilar Coarctation ( congenital-Foramen Magnum
syndrome)
2.Basilar Erosion (Inflammatory/Neoplastic/Infective)
(RA/Tuberculosis/Nasopharyngeal CA)
3.Basilar Impression (Bone softening conditions)
(OI/Paget’s/Osteomalacia)

30. BASILAR INVAGINATION : CT
 Thin sections 1-3 mm
 Overlapping recon
 Multiplanar recon : Sag & Coronal

31. BASILAR INVAGINATION

32. BASILAR INVAGINATION

33. KINEMATIC MRI IN BI

34. ATLANTO-AXIAL SUBLUXATION (AAS) : anterior type
Anterior Atlanto-Dental Interval (AADI) :
 AAS is present when it is >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

35. ATLANTO-AXIAL SUBLUXATION (AAS) : anterior
type
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

36. ATLANTO-AXIAL SUBLUXATION (AAS) : anterior type
 X-rays in neutral position will miss AAS in 48%.
 Controlled flexion views always to be done

37. ATLANTO-AXIAL SUBLUXATION (AAS) : anterior type

38. ATLANTO-AXIAL SUBLUXATION (AAS) : anterior type

39. ATLANTO-AXIAL SUBLUXATION (AAS) : anterior type

40. AAD

41. ATLANTO-AXIAL SUBLUXATION (AAS) : anterior type

42. AAD with cord compression

43. 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

44. RISK FACTORS FOR CORD COMPRESSION IN AAS
 AADI > 9 mm
 PADI < 14 mm
 Basilar Invagination,
especially if associated
with AAS of any degree
 Sub axial canal diameter
< 14 mm
 CHI <2

45. ATLANTO-AXIAL SUBLUXATION (AAS) : rare types
 Posterior AAS – rare, associated with deficient odontoid
process.
 Rotatory AAS - (later)
 Lateral AAS - >2 mm offset of the lateral mass of C1 on
C2 on coronal images. It is usually associated with a
rotational deformity.

46. Specific Anomalies – Occiput anomalies
Condylus Tertius (IIIrd
occipital condyle) :
 when proatlas persists or fails to
migrate, an ossified remnant is
seen at distal end of clivus
 May form pseudo joint with
odontoid or ant arch of C1 and
limit mobility of CVJ
 Increased prevalence of Os
Odontoideum seen

47. ATLAS ASSIMILATION
 Represents most cephalic
‘blocked vertebra’
 0.25% of population
 Usually occurs in
association with other
anomalies such as BI and
Klippel Feil syndrome.
 Associated with
segmentation failures
b/w C2-3 : atlanto-axial
subluxation in 50%.

48. Atlas assimilation with CVJ anomaly

49. ATLAS ASSIMILATION

50. classic triad consists of low posterior hairline, short neck and
limitation of neck movements.
KLIPPEL-FEIL SYNDROME :

51. KLIPPEL-FEIL SYNDROME
 Fused vertebrae (usually
C2-3 and C5-6
interfaces)
 Hemivertebrae
 Atlas occipitalization
 Spina bifida occulta
 Scoliosis
 Urogenital, otological
anomalies, Chiari,
syndactyly, Sprengel’s
etc.

52. Atlas rachischisis: posterior >> anterior Both
together – ‘split atlas’

53. ATLANTO-AXIAL ROTATORY FIXATION
Less common cause of Torticollis in children. Fixation usually occurs within
normal range of rotation of A-A joint.
Fielding types:
 Type I : fixn without anterior displ of atlas (trans & alar lig intact, MC
type)
 Type II : fixn with ant displ 3-5mm (trans lig deficient)
 Type III : fixn with ant displ >5mm (trans & alar lig deficient)
 Type IV : fixn with posterior displacement of atlas (rarest, odontoid is
deficient)
 Type V : AARF with AORF (atlanto-occipital rotatory fixation) combined
DIAGNOSIS:
X-Ray : asymmetry of lateral masses on open mouth odontoid view. Lateral
mass that has rotated forwards appear wider and closer to midline.
Asymmetry also on skull lateral.

54. ATLANTO-AXIAL ROTATORY FIXATION
CT: essential d/t difficulty in
obtaining & interpreting
X-rays  rotated atlas +
displacement, fractures,
AORF

55. ATLANTO-AXIAL ROTATORY FIXATION
Dynamic CT:
type I AARF vs. other
c/o torticollis : Pt. with
fixn demonstrate little
or no motion of atlas on
the axis. Normal pts or
with transient torticollis
show a reduction or
reversal of the rotation.
Dynamic MRI also

56. ODONTOID ABNORMALITIES
Persistent Ossiculum Terminale :
 Also called Bergman Ossicle.
 Results from failure of fusion of the terminal ossicle to
the rest of odontoid
 Normally fusion occurs by 12 yrs of age
 Stable anomaly when isolated with normal height of dens

57. Persistent Ossiculum Terminale
May mimic type I odontoid # (avulsion of terminal ossicle) :
difficult to differentiate at times.

58. ODONTOID ABNORMALITIES
Os Odontoideum :
 Refers to an independent osseous structure lying cephalad to
the axis body in the location of odontoid process.
 Cruciate lig incompetence & AAS common
 May mimic type II odontoid #
Os odontoideum Type II fracture
Well corticated, convex
upper margin of C1
Sharp, jagged un-
corticated margin of axis
Hypertrophied & rounded Normal ant arch C1
Moves with ant arch C1 Does not

59. Os odontoideum

60. Os odontoideum- Dystopic types

61. TRAUMA : Atlas and Occiput
Jefferson fracture :
 involves the anterior
&posterior arches of
atlas with instability
 Isolated # of post arch
due to hyper-extn injury

62. ODONTOID FRACTURE
 Type I : avulsion # of tip
of odontoid by the alar
ligament
 Type II : transverse # at
base f Dens
 Type III : # of superior
portion of axis body with
extn through one or both
articular facets

63. ODONTOID FRACTURE

64. CVJ-traumatic AAD

65. CVJ- trauma

66. CVJ-trauma

67. CVJ-trauma

68. HANGMAN FRACTURE
# of neural arch of C2
that occurs in sudden
hyperextension injuries
like windshield injuries
and in judicial hanging

69. CHIARI MALFORMATIONS
 Chiari I- elongated,
peg like cerebellar
tonsils are displaced
inferiorly through
Foramen Magnum
 Syrinx in 20-40%
 25% show BI, Klippel-
Feil syndrome &
atlanto-occipital
assimilation

70. ACM I with syrinx

71. ACM-II

72. CHIARI MALFORMATIONS
Chiari II-
herniation of vermis, IV
ventricle & medulla into
spinal canal with kinking
and displacement of
normal structures.
Chiari III-
f/o Chiari II with
occipital encephalocele.

73. Inflammatory, Arthritic & Infectious Disorders
 Rheumatoid Arthritis (most common)
 Psoriatic arthritis, osteoarthritis, CPPD etc.
 Tuberculosis
 Fungal infections

74. RHEUMATOID ARTHRITIS
 Cervical spine involved in 44-88% patients. Degree of Cx
spine involvement correlates with the duration & severity
of disease.
 Anterior AAS (MC, 50-70%)
 Sub axial subluxation (20-25%)
 BI (less common, 10-15%),most dangerous
 Posterior & Rotatory AAS rare
 Neurological impairment in 11-58% cases
 Vascular compression of basilar, spinal arteries

75. RHEUMATOID ARTHRITIS

76. CVJ-rheumatoid

77. RA- Sub axial Subluxation
 2nd MC subluxn in RA
(MC is ant AAS). Occurs
d/t facet joint arthritis,
ligamentous laxity & disc
involvement that lead to
‘step ladder’ deformity
 Normal Cx sag diameter
at C3-7 is 14-23 mm. <14
mm is critical for cord
compression (10mm
cord, 2mm dura & 2mm
CSF)

78. TUBERCULOSIS
Tuberculosis of atlanto-axial region is rare (<1% of cases of
spinal TB)
It may present with-
i) retropharyngeal abscess
ii) AAD/AAI
iii) varying grades of bone destruction

79. TUBERCULOSIS

80. TUBERCULOSIS

81. Koch’s

82. CVJ Koch’s
Pre ATT Post ATT

83. Tuberculoma:

84. TUMORS: Astrocytoma

85. Multiple myeloma

86. Neurofibroma

87. Intradural Lipomatosis

88. CVJ-meningioma

89. Tumors: Meningioma

90. MISC I : OPLL with Cord Myelomalacia

91. Misc II :Demyelinating

92. 3D-MDCT IN CVJ

93. 3D-VRT

94. 3D-VRT

95. THANK YOU!