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

3. 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.

4. 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
1
2
Tip of dens
3
Dens
5
4
Body of
dens
6

5. 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

6. CV Junction

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

8. 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

9. 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)

10. 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
SESagittal 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

11. X-ray

12. X-ray

13. X-ray

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

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

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

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

18. Chamberlain’s line
Synonym
Chamberlain's
(Palato-occipital Line)
Definition
Joins posterior
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.

19. Mc Gregor’s line
Synonym
McGregor’s Line
Definition
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.

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

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

22. Welcher’s Basal Angle
Synonym
BASAL ANGLE
Definition
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

23. 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

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

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

26. 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”

27. 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)

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

29. BASILAR INVAGINATION

30. BASILAR INVAGINATION

31. KINEMATIC MRI IN BI

32. 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

33. 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

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

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

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

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

38. AAD

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

40. AAD with cord compression

41. 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

42. 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

43. 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.

44. 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

45. 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%.

46. Atlas assimilation with CVJ anomaly

47. ATLAS ASSIMILATION

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

49. 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.

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

51. 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.

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

53. 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

54. 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

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