This document discusses abnormalities of the craniovertebral junction (CVJ). It begins by defining the anatomical structures that make up the CVJ. It then covers the embryology and normal anatomy, including range of motion measurements. Radiological assessment criteria are outlined. Various congenital and acquired disorders are described such as basilar invagination and atlantoaxial subluxation. Specific conditions involving the occiput, atlas, and odontoid are also detailed.

1. CranioVertebral Junction
abnormalities
dDr Mohammad Mushtaq
Resident Neurosurgeon
Neurosurgery unit , ATH.

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. Embryology of the CV junction
4th occipital sclerotome,
the proatlas and C1
cervical sclerotome
gives rise to C1.
 Apex of Dense… proatlas.
 Body of Dense…C1 and
C2 sclerotome.
 AXIS develops from five
primary and two
secondary centers
ossifications.

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
Tip of dens
Body of
dens
Dens

5. Anatomy of the CV junction
ATLANTO-AXIAL JOINT:
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.  Ligamentous structures of CV junction
 Anterior atlanto ocipital membrane
 Alar ligament
 Apical dense ligament
 Tectoral membrane
 Cruciate ligament
 Posterior atlanto-occipital membrane

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. Radiological criteria for assessing CVJ
instability
predentalspace inchildsupto 8years greaterthan 5mm,
adultsgreaterthan 3mm
open mouthviewx.ray or coronalct.........latmasses C1
displacement6mm
verticaltranslationb/w clivus and odontoid 2mm,
disruptionof ligamentousstructure

11. X-ray

12. X-ray

13. Lines and Angles
The important lines are
 Chamberlain’s line
 Wackenheim’s clivus canal line
 Mc Gregor’s line (basal line)
 McRae,s line
Basal angle
Bull,s angle

14. Chamberlain’s line
Chamberlain‘s line (Palato-occipital Line)
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

15. Mc Gregor’s line
McGregor’s Line
Line drawn from posterior
tip of Hard palate to lowest part of Occiput
Odontoid tip >4.5mm above = Basilar Invagination

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

17. McRae’s Line
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

18. Fishgold bimastoidline. a line drawnb/w tipsof
mastoids. normalodontoidis2mmabove it.
FishGold diagastricline. A linedrawn b/w the two diagastric
notches.normal distanceof atlantooccipitaljointshouldbe
10 mm.

19. Welcher’s Basal Angle
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 achondroplasiaaaasdaaaaaaaaa

20. Platybasia –refersonlyto anabnormally obtuse basal angle, may be
asymptomatic, and isnota measureofbasilar invagination.

21. 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

22. Lymphatic drainage
 Occipitoatlantoaxial joint drain through
retropharyngeal gland to deep cervical lymph
channels.
 Paeds. nasopharyngeal infections cause
inflammatory reaction of CVJ.
 C1-2 sublaxation
 Refferd as GRISEL SYNDROME

23. Signs and sympyoms
 Myelopathy different degrees of extremities
weakness
 Brainstem symptoms
 Cranial nerves deficit loss of gag
reflex,nystagmus,hearing loss
 Vascular compromise syncope,vertigo,episodic
hemiparesis,transient loss of vision,altered conscious
level
 Restricted neck movement
 Neck and occipital pain

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

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

26. Basilar invigination….
The upward displacement of upper cervical spine
including odontoid through the foramen magnum
into posterior fossa.

27. Pathogenesis
1. Emberyological dysgenesis,genetics,
maldevelopment of craniovertebral transition
region.
2. Secondary abnormally alignment of fascet joints of
atlas and axis leading to progressive slippage of atlas
over axis which results in odondoid tip invigination
superoir and posterior into cranio cervical cord.

28. Associated conditions
Down syndrom
Klippel feil syndrom
Acm
Syringomyelia
Rheumatoid arthritis
Post trauma
Paget disease

29. Classification
Type1. the odontoid tip inviginates into foramen magnum
indented into brainstem. atlanto odontoid distance
increases. odentoid tip is above CL,McR,wccl.
volume of posterior fossa and Cl angle z normal.
Type2. odontoid tip,ant arch of C1 and clivus migrate
superiorly in unison, results in small post fossa causing
ACM. odontoid tip is only above CL not wccl,McR.

30. Type A.
Based on mechanical instability.just like type1 but
normal horizontal poition of fascet joint changes into
oblique position.which leads progressive slippage.
Type B.
there is congenital dysgenesis , and atlantoaxial
joints were normal or entirely fused.

31. Treatment
Type1.
85% can be reduced with traction
Transoral decompression and posterior fusion
Its superior to include craniovertebral realignment
procedure.
Type2.
only 15% reduced with traction.foramen magnum
decompression is appropriate

32. BASILAR INVAGINATION : CT
Sag & Coronal view

33. BASILAR INVAGINATION

34. BASILAR INVAGINATION

35. KINEMATIC MRI IN BI

36. 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

37. 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

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

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

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

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

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

44. AAS with cord compression

45. 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

46. ATLANTO-AXIAL SUBLUXATION (AAS) : rare
types
 Posterior AAS – rare, associated with deficient odontoid
process.
 Rotatory AAS -

47. ATLANTO-AXIAL ROTATORY SUBLUXATION
Less common cause of Torticollis in children. Subluxation usually
occurs within normal range of rotation of A-A joint.
Fielding types:
 Type I :TAL ..intact, facet injury... bilateral (AD less than 3mm)
 Type II : TAL.. Injured, facet injury... unilateral (AD 3.1 to 5mm)
 Type III : TAL.. Injured, facet injury.... bilateral >5mm AD
 Type IV : Incompetence of odotoid with posterior dispacement
DIAGNOSIS:
X-Ray : asymmetry of lateral masses on open mouth odontoid view. Lateral
mass that has rotated forwards appear wider and closer to midline.

48. ATLANTO-AXIAL ROTATORY
SUBLUXATION
CT SCAN

49. ATLANTO-AXIAL ROTATORY SUBLUXATION
Dynamic CT:

50. 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

51. 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%.

52. Atlas assimilation with CVJ anomaly

53. ATLAS ASSIMILATION

54. classictriadconsistsoflowposteriorhairline,shortneckand limitationof
neckmovements.
KLIPPEL-FEIL SYNDROME :

55. 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.

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

57. 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

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

59. Treatment protocol of cv junction

60. THANK YOU