This document discusses the anatomy, embryology, biomechanics, imaging and classification of abnormalities at the craniovertebral junction. It defines the craniovertebral junction and describes the important bones, ligaments, blood supply and development from somites. The biomechanics of the atlanto-axial and atlanto-occipital joints are explained. Common radiological measurements used to evaluate the craniovertebral junction are provided. Overall, the document provides a comprehensive overview of the normal anatomy and evaluation of abnormalities at the cranio-vertebral junction.

1. CRANIO-VERTEBRAL JUNCTION
ANATOMY AND ANOMALIES
Dr SAMEEP KOSHTI

2. • DEFINITION
• ANATOMY OF THE CRANIOVERTEBRAL
JUNCTION
• EMBRYOLOGY AND DEVELOPMENT OF
CRANIOVERTEBRAL JUNCTION
DISORDERS
• IMPLICATIONS OF CRANIOVERTEBRAL
ABNORMALITIES
• BIOMECHANICS OF ORTHOSIS
• CLASSIFICATION OF CRANIOVERTEBRAL
JUNCTION ABNORMALITIES
• CLINICAL PRESENTATION
• NEURO IMAGING
• TREATMENT

3. DEFINITION
• Craniovertebral junction
• refers to the occipital bone that surrounds the foramen magnum
and the atlas and axis vertebrae.
• It is a transition zone b/w a mobile cranium & relatively rigid spinal
column.

4. ANATOMY OF THE CRANIOVERTEBRAL JUNCTION
• Bone-Ligament Complex
• Blood Supply
• Lymphatic Drainage

6. CVJ BIOMECHANICS
•Occiput-C1 joint (A-O JOINT)
•ball-and-socket type
•allows slightly more flexion-extension than the other levels
of the cervical spine,
•Quite rigid in axial rotation and lateral bending.

7. • C1-C2 joints (A-A JOINT):
• The biconvex articular surfaces
• allow gliding and wide rotation of C1 around the dens.
• the most flexible motion segment in the entire spine with respect to axial rotation,
allowing a bilateral range of motion of 90 degrees.
• More than half of all cervical axial rotation occurs at the C1-C2 motion segment, a point
that should be kept in mind when one is considering atlanto-axial arthrodesis.
• In a child,
• up to 5 mm of anterior-posterior translation between the dens and the anterior atlas ring is considered
normal.
• When the transverse component of the cruciate ligament has been disrupted
• the intact alar ligaments limit displacement to between 5 and 6 mm.
• Once both the alar ligaments and the transverse portion of the cruciate ligament are
disrupted
• anterior-posterior translation exceeds 6 mm. After age 8 years, the predental space excursion must be
limited to 3 mm.

10. LIGAMENTS OF CVJ
•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 – No clinical significance
• Anterior & posterior A-O membranes
• ALL
• PLL
• Tectorial membrane
• Ligamentum flavum
• Capsular ligaments

14. TRANSVERSE LIGAMENT OF ATLAS
• Caudal crus & Rostral crus (Fasciculi longitudinales) fibres :
• join with transverse ligament on its dorsal aspect to form Cruciate ligament
of atlas.
• effectively limits anterior translation and flexion of the atlanto-axial joint.

15. ALAR LIGAMENT
•2 strong cords that attach to the dorsal lateral body of the
dens.
•They limit:
• the head –atlas rotatory movement on the odontoid axis
• strengthen the A-O capsule.

16. APPLIED : ALAR LIGAMENT
• Failure of one alar ligament :
• results in moderate rotary atlantoaxial instability.
• Bilateral transection of the alar ligaments :
• causes craniovertebral instability.
• APPLIED :TRANSVERSE ATLANTAL LIGAMENT
• strongest and thickest ligament of the entire spine.
• It is the predominant stabilizer of the atlas, constraining C1 around the dens.
• Following injury, the transverse ligament is incapable of repair.
• Its injury renders C1 grossly unstable and mandates a C1-C2 fusion.
• Axial rotation within the cervical spine occurs primarily at the atlantoaxial joint.
• Rotation exceeding 50 degrees is associated with a risk of an atlantoaxial facet interlock.
• If the transverse ligament is injured, the anterior arch can sublux, leading to a unilateral
dislocation facet interlock at less than 40 degrees.
• unilateral dislocation facet interlock at less than 40 degrees.

17. • Rotation of more than 35 degrees produces an angulation of the
contralateral vertebral artery with an associated risk of vascular injury.
• This fact has implications for wrestling and football injuries, head rotation
maneuvers during anesthetic induction, and forced chiropractic
manipulations.
• In addition, paraspinal muscles help maintain craniocervical alignment
during rotation.
• The craniovertebral junction is therefore inherently less stable in pediatric
patients owing to underdeveloped musculature and in situations involving
neuromuscular blockade, such as during general anesthesia.

19. TECTORIAL MEMBRANE
• Dorsal to the cruciate ligament.
• strong band of longitudinally oriented fibres
• attached to the dorsal surface of the C3 vertebra, axis body & to the body of
dens.
• It is the rostral extension of the PLL of the vertebral column.
• Essential for limiting flexion.

21. ANTERIOR ATLANTO-OCCIPITAL MEMBRANE
• is continuous caudally
• with the anterior Atlanto axial ligament &
• through it to the ALL of the spinal column.

22. BLOOD SUPPLY
• To the odontoid process :
• from anterior and posterior ascending vessels from the vertebral arteries,
• with a contribution from the carotid arteries, which form an apical arcade around the alar
ligament.
• Thus, the odontoid process blood supply is vulnerable in type II odontoid fracture.
• Also there is pharyngovertebral veins with frequent lymphovenous anastomoses.
• This connection may provide an additional route for septic involvement of the
craniovertebral complex, which can result in osteomyelitis of the bone as well as joint
effusions.

27. LYMPHATIC DRAINAGE
• Primarily into :
• the retropharyngeal lymph nodes and then into
• the upper deep jugular cervical chain.
• These nodes also receive drainage from :
• the nasopharynx, paranasal sinuses, and retropharyngeal area.
• APPLIED :
• Hence, a retrograde infection from these regions may affect the synovial lining
of the craniovertebral joint complex, with
• a resultant inflammatory effusion, instability, and possible neurological deficit,
contributing to so-called Grisel’s syndrome.

28. MUSCLES AT CVJ
•only a minor role related to CVJ stabilization &
•do not limit the movements of the joints.
•Their principal function is :
• one of initiating & maintaining movement at the CVJ.

30. ARTERIES AT CVJ
• The major arteries related to CVJ are
• vertebral,
• Postero inferior cerebellar arteries (PICA), and
• the meningeal branches of the vertebral, and external and internal carotid
arteries.
• The branches arising from the vertebral artery in the region of the
Foramen Magnum are the
• posterior spinal,
• anterior spinal,
• PICA, tonsillomedullaryPICA segment (Most intimately related to FM)
• anterior and posterior meningeal arteries.

32. VEINS AT CVJ
• In the region of the FM are divided into three groups:
• Extra dural veins (extraspinal & intraspinal part)
• Intra dural (neural) veins,
• Dural venous sinuses ( superior petrosal, marginal & occipital)
• The three groups anastomose through bridging and emissary veins.

33. EMBRYOLOLGY OF CV JUNCTION

34. SOMITES
•Differentiate into three components:
•Outer Dermatome
•Inner Myotome
•Medial Sclerotome
• Forms vertebral bodies
•42 pairs of somites at 4th week.

39. 4th OCCIPITAL SCLEROTOME (PROATLAS in
LOWER ANIMALS )
• Divided into the hypocentrum, centrum &
the neural arches:
1. Hypocentrum
• forms the vestigial condylus tertius or
anterior tubercle of the clivus.
2. Centrum
• forms the apex of the dens, also forms the
apical ligament (AL) of dens (AL may contain
notochordal tissue, a rudimentary IV disc).
3. Neural Arch
a) ventral part:
• forms the ant. margin of FM, 2 occipital
condyles & the alar & cruciate ligaments.
b) dorsal part
• forms paired rostral articularfacets, lateral
masses of C1 & superior portion of the post.
arch of the atlas.

40. ATLAS
• Major portion formed by first spinal
sclerotome.
• Trasitional vertebra as centrum of
sclerotome is separated to fuse with the
axis body forming the odontoid process.
• Hypocentrum :
• forms the anterior arch of the atlas.
• Neural arch of the first spinal
sclerotome:
• forms the inferior portion of the
posterior arch of atlas.

41. AXIS
• Develops from 2nd spinal sclerotome.
• Hypocentrum
• disappears during embryogenesis.
• Centrum
• forms the body of the axis vertebra &
• Neural arch
• develops into the facets & the posterior arch
• odontoid base:
• At birth : is separate from the body of axis by a
cartilage (Neural central synchondrosis)
• which persists until the age of 8 yrs ,
• later the center gets ossified
• may remain separate  Os-odontoidium.
• The apical segment :
• is not ossified until 3 years of age ,
• at 12 years if fuses with odontoid to form
normal odontoid
• If failure  leads to Os terminale

42. REGULATION OF SOMITES CONTROL
•segmentation of somites to form vertebral primordia and in
•specification of each vertebra by:
• highly conserved DNA sequences :
• “homeobox” (Hox genes) and
• “paired box” (Pax genes) sequences.
• They encode transcription factors that modulate skeletal
morphogenesis

43. IMAGING OF CVJ
• LATERAL PROJECTION OF SKULL X-RAY:
• Palato–occipital (Chamberlain’s line)
• Palato–suboccipital line (McGregor line)
• Foramen magnum line (McRae line)
• Height of the posterior cranial fossa(Klaus Index)
• Wackenhein’s clivalcanal line
• Bull’s angle (Atlanto-palatal angle)
• Atlanto-Occipital joint angle

44. • FRONTAL PROJECTION OF SKULL X-RAY:
• Bimastoid line (Fischgold& Metzer)
• Bidigastric line (Fischgold& Metzer)
• FOR DIAGNOSIS OF PLATYBASIA:
• Basal angle (Welcher)
• Boogard’sangle

45. to recognise basilar invagination which
is said to be present if the tip of the dens
is >3 mm above this line.

46. •Modification of the Chamberlain line
•used when the opisthion is not
identified on plain radiographs.
If the tip of the dens lies more than 4.5
mm above this line it is indicative
of basilar invagination.

47. •Normal position of the tip of dens is
5mm below this line.
•If the tip of the dens migrates above
this line it indicates the presence
of basilar invagination (atlanto-axial
impaction).

48. •Wackenheim’s line (also known as
the clivus canal line or basilar line)
•Normally the tip of the dens is
ventral and tangential to this line.
•In basilar invagination odontoid
process transects this line.

51. WELCHER BASAL ANGLE
formed by:
•line joining the nasion with the centre
of the pituitary fossa
•&
•line joining the anterior border of
the foramen magnum with the centre
of the pituitary fossa
•normal: 125°-143°
•platybasia: >143°
•basilar kyphosis: <125°

55. CLASSIFICATION OF CVJ ABNORMALITIES
1.Congenital anomalies and malformations
2.Developmental and acquired abnormalities

56. Congenital anomalies and malformations
A. Malformations of the
occipital bone
1. Manifestations of the
occipital vertebra
a. Clivus segmentations
b. Remnants around the
foramen magnum
c. Atlas variants
d. Dens segmentation
anomalies
2. Basilar invagination
3. Condylar hypoplasia
4. Assimilation of the atlas
B. Malformations of the
atlas
1. Assimilation of
the atlas
2. Atlantoaxial
fusion
3. Aplasia of the
atlas arches
C. Malformations of the
axis
1. Irregular atlantoaxial
segmentation
2. Dens dysplasias
a. Ossiculum terminale
persistens
b. Os odontoideum
c. Hypoplasia-aplasia
3. Segmentation failure of
C2-C3

57. Developmental and acquired abnormalities of the craniocervical
junction
• A. Abnormalities at the foramen magnum
1. Secondary basilar invagination (e.g., Paget’s disease, osteomalacia, rheumatoid cranial
settling, renal [vitamin D–resistant] rickets)
2. Foraminal stenosis (e.g., achondroplasia )
• B. Atlantoaxial instability
1. Errors of metabolism (e.g., Morquio’s syndrome)
2. Down syndrome
3. Infections (e.g., Grisel’s syndrome)
4. Inflammatory disorders (e.g., rheumatoid arthritis)
5. Traumatic occipitoatlantal and atlantoaxial dislocation; os odontoideum
6. Tumors (e.g., neurofibromatosis, syringomyelia)
7. Miscellaneous (e.g., fetal warfarin syndrome, Conradi’s syndrome)

58. Signs and Symptoms of Craniovertebral Anomalies (Insidious or Rapid
Onset of Signs and Symptoms)
• Head tilt
• Short neck, low hairline, limitation of neck motion
• Web neck
• Scoliosis
• Features of skeletal dysplasias
• Neck pain and posterior occipital headache
• Basilar migraine
• Isolated hand or foot weakness
• Quadriparesis/paraparesis/monoparesis
• Sensory abnormalities
• Nystagmus—usually downbeat and lateral gaze
• Sleep apnea
• Repeat aspiration pneumonia, dysphagia
• Tinnitus and hearing loss
• Vertigo

59. • Clinical presentation may be insidious or may occur as false localizing signs or,
infrequently, as a rapid neurological progression followed by sudden death.
• Congenital abnormalities :
1. Abnormal general physical appearance.
• The head may be cocked to one side
• Klippel-Feil syndrome may manifest as a classic triad
• abnormally low posterior hairline,
• limitation of neck motion, and
• short neck together with facial asymmetry, neck webbing, and scoliosis.
• skeletal dysmorphic states

62. 2. M.C. Symptom:
• neck pain originating in the suboccipital region with radiation to the cranial vertex (85%) .
• Central cord syndrome is often seen in children with basilar invagination
• mimics a lower cervical spinal cord disturbance.
• Sensory abnormalities usually manifest as neurological deficits related to posterior column dysfunction.
• Brainstem and cranial nerve deficits cause abnormalities such as
• dysphagia and sleep apnea.
• Not uncommonly, internuclear ophthalmoplegia is present,
• leading to a misdiagnosis of mesencephalic and upper pontine disturbance.
• Downbeat nystagmus is present with strictly compressive lesions of the craniovertebral border with or
without an associated Chiari malformation.
3. Basilar Migraine
• which affects about 25% of children with basilar invagination and medullary compression,
• usually involves compression of the vertebrobasilar arterial system.
• Mechanism:
• Excessive skeletal mobility due to craniovertebral instability  repeated trauma to the anterior spinal
artery, perforating vessels of the craniocervical region, as well as the vertebral and basilar arteries 
spasm or occlusion and attendant neurological deficit.

63. • The most common neurological deficit encountered in affected children is
• myelopathy
• the most common cranial nerve dysfunction is :
• hearing loss, occurring in 25% of cases.
• increased incidence of this finding in the Klippel-Feil syndrome.
• Unilateral or bilateral paralysis or dysfunction of the soft palate or pharynx
• aspiration pneumonia
• poor feeding and inability to gain weight.
• Vascular symptoms such as intermittent attacks of
• altered consciousness,
• transient loss of visual fields,
• confusion, and
• vertigo appear in 15% to 25% of patients with abnormalities of the craniovertebral junction.
• These symptoms may be provoked by extension or rotation of the head, as with
manipulation of the head and neck.

66. •The third condyle (also known
as condylus tertius or median occipital
condyle)
•is a rare anatomic variant of
the occipital condyles.
•It is a small separate ossicle at the
anteromedial margin of the occipital
condyle formed by the failure of the
embryonic proatlas (4th occipital
sclerotome) to unite with the condyle
proper.

68. ATLANTO-OCCIPITAL ASSIMILATION
It is the fusion of the atlas (C1) to the occiput and
is one of thetransitional vertebrae.
occurs in approximately 0.5% (range 0.25-1%) of
the population.
Clinical presentation
It is typically asymptomatic but symptoms from
nerve or vascular compression can occur.
Gross anatomy
Fusion of C1 to the occiput can be either:
complete: C1 not identifiable
incomplete: C1 partially identifiable
Decreased Clivus canal angle
Example of transitional vertebrae

69. PLATYBASIA
characterised by abnormal flattening of the skull base as
defined as a base of skull angle over 143º.
Clinical presentation
Asymptomatic unless it is associated with basilar
invagination.
etiology
congenital
achondroplasia
Down syndrome
Chiari malformations
craniocleidodysostosis
craniofacial anomalies
osteogenesis imperfecta
acquired
Paget disease
osteomalacia
rickets
trauma
fibrous dysplasia
hyperparathyroidism
hypoparathyroidism

70. BASILAR INVAGINATION
• Basilar invagination,
• is a congenital or acquired craniocervical junction abnormality where the tip of the odontoid
process projects above the foramen magnum.
• defined as the upward displacement of vertebral elements into a normal foramen magnum with
normal bone.
• In contrast, basilar impression
• due to, however, softening of bones at the base of skull.
• Secondary to bony pathology.
• Pathology
• It may be congenital or acquired and is often associated with platybasia.
• There is stenosis of the foramen magnum and compression of the medulla oblongata resulting in
neurological symptoms, obstructive hydrocephalus, syringomyelia or even death

71. • Causes:
• Congenital
• osteogenesis imperfecta
• Klippel-Feil syndrome
• achondroplasia
• Chiari I malformation/Chiari II malformation
• cleidocranial dysostosis
• Schwartz-Jampel syndrome
• Acquired
• rheumatoid arthritis
• Paget disease
• hyperparathyroidism
• osteomalacia/rickets

72. • Classification
• A classification system has been proposed based on the
• absence (group I) and
• presence (group II) of Chiari malformation, and
• can be of use in planning surgical management.
• Brainstem compression relates to odontoid process indentation in group I, while
reduced posterior cranial fossa volume is the cause in group II.
• TWO TYPES:
• In the ventral variety,
• there is shortening of the basiocciput  so that the clivus is short and horizontally oriented,
• In the paramesial type,
• condylar hypoplasia may be present  so that the clivus becomes dorsally displaced into the posterior fossa
and may be of normal length.
• The occipital hypoplasia may be unilateral, leading to torticollis.
• The distinction between these two types is not clinically rigid, because a mixture often occurs.

73. • In general
• the axis body becomes elongated and
• the true odontoid process is small.
• Of greater significance is the abnormal clivus-odontoid articulation.
• Results in abnormal clivus-canal angle  produces a ventral indentation on the pons,
medulla, or cervicomedullary junction.

74. • With Chiari malformation
• associated with basilar invagination in about 25% to 30% of individuals.
• Mx:
• ventral decompression of the bony abnormality at the cervicomedullary junction should be
performed before any posterior surgical procedure. (Otherwise unfavorable results in up to 30% of
individuals.)
• The reason is
• ventral distortion and
• resultant compression of the pontomedullary or cervicomedullary junction during prone positioning.
• With SyringoHydromyelia and hindbrain herniation
• perform a posterior operative procedure.
• resolves in up to 76% of patients after ventral decompression,
• because of relief of cerebrospinal fluid (CSF) flow obstruction at the foramen magnum and
• restoration of posterior fossa volume.

75. Chiari Malformation
• Classification is based on the morphology of the malformations:
• Chiari I:
• >5mm descent of the caudal tip of cerebellar tonsils past the foramen magnum.
• most common and
• the least severe of the spectrum,
• often diagnosed in adulthood.
• Chiari II: (aka Arnold-Chiari Malformation)
• brainstem, fourth ventricle, and >5 mm descent of the caudal tip of cerebellar tonsils past the foramen magnum with spina
bifida.
• less common and
• more severe,
• almost invariably associated with myelomeningocele.
• Chiari III:
• herniation of the cerebellum with or without the brainstem through a posterior encephalocele.
• Chiari IV:
• Cerebellar hypoplasia or aplasia with normal posterior fossa and no hindbrain herniation.
• Chiari type III and IV malformations :
• are exceedingly rare and
• generally incompatible with life and are.

79. PONTICULUS POSTICUS
• Due to calcification of the oblique atlanto-occipital ligaments.
• aka
• Kimerle foramen,
• foramen arcuale atlantis,
• arcuate foramen
• The ponticulus posticus means "little posterior bridge" in Latin
• an abnormal small bony bridge formed
• between the posterior portion of the superior articular process and the posterolateral portion of
the superior margin of the posterior arch of the atlas
• The sulcus situated on the posterolateral margin of the atlas forms a groove for the:
vertebral artery ( atlantic portion V3 ) pass through this foramen.
• It has a variable morphology, can be complete or incomplete and may be unilateral or
bilateral.
• More common in female

80. TREATMENT OF CVJ PATHOLOGY
• The factors that influence the specific treatment of craniovertebral junction
abnormalities are
• (1) reducibility of the bony lesion
• relieving compression on neural structures
• (2) the mechanics of compression and direction of encroachment,
• (3) the cause of the pathologic process as well as the presence of hindbrain herniation,
syrinx, and vascular abnormalities, and
• (4) the presence of abnormal ossification centers and epiphyseal growth plates

81. •The primary aim
• to relieve compression at the cervicomedullary junction.
• Stabilization is paramount in reducible lesions to maintain neural
decompression.
• Irreducible lesions require decompression : VENTRAL vs POSTERIOR
• Ventral decompression
• approaches through a transpalatopharyngeal route,
• a LeFort drop-down maxillotomy, or
• a lateral extrapharyngeal route.
• Endoscopic
• Endonasal/Transcervical/transoral
• Dorsal compression states,
• a posterolateral decompression is required.
• If instability is present :
• Posterior fixation is mandatory.

82. The management of craniovertebral instability
• associated with skeletal dysmoprhisms and connective tissue diseases
• in very young children is often challenging.
• Mx:
• to identify the potential for osseous development through radiographic recognition of epiphyseal
growth plates on thin-section CT studies.
• In the absence of growth plates,:
• skeletal development can be permitted while the occipitocervical region is externally supported with custom-
built cervical orthoses that are frequently revised.
• Periodic clinical and radiographic evaluation is essential.
• Following bony development of the craniovertebral junction at 3 to 4 years of age, surgical intervention can be
undertaken if needed.
• Skeletal traction should be performed with use of an MRI-compatible crown halo device placed
below the equator of the cranium.

83. • Reducible lesions that are the result of inflammatory states or recent trauma:
• respond to conservative management with external immobilization once reduction is
achieved.

84. BIOMECHANICS OF ORTHOSIS
• An orthosis
• used as load-sharing devices to reduce the external loads applied to the spine while an injury or a
fixation fusion is healing.
1. The halo brace:
• most effective at constraining cervical motion at all levels,
• provides the best control of motion at the craniovertebral junction immobilization and the least
control at the cervicothoracic junction.
2. The soft cervical collar :
• provides little immobilization and tends only to remind the patient to restrict motion.
3. Molded collars, four-poster braces, sternal-occipital-mandibular immobilization,
and cervicothoracic braces
• are intermediate in their abilities to control flexion and extension, lateral bending, and axial
rotation.

87. SOFT
CERVICAL
COLLAR

88. • A 18-year-old woman with basilar
invagination and tonsillar herniation of
7 mm. with atlas assimilation.
• A: in flexion shows the tip of the
odontoid 8.26 mm above the
Chamberlain’s line;
• B: in extended position shows the tip of
the odontoid 4 mm above the
Chamberlain’s line;
• C: anterior dislocation of the facet joint
of C1 over C2 facetary of 2 mm;
• D: posterior dislocation of the C1 facet
joint over the facet of C2 of 3 mm,
ranging 5 mm in dynamic exam.
• This patient underwent a craniocervical
fusion concomitant to the posterior fossa
decompression.

89. • Forty-year-old woman with a
tonsilar herniation of 5 mm and
basilar invagination.with atlas
assimilation and a congenital C23
fusion
• A, B and C: Pre-operative dynamic
imaging,
• A: showing a atlanto-dental interval
of 3.27 mm,
• but no signs of facet dislocation in
flexion or in extension (B and C);
• D: few months after posterior fossa
decompression
• showing an evident facet joints
dislocation (the assimilated lateral
mass of C1 was dislocated posteriorly
over the superior facet joint of C2).
• symptoms of dizziness and cervical
pain when flexing the neck and
• an occipto-cervical fixation was
proposed but the patient declined
surgical treatment because she was
not doing well with depression and
mood disorders.