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. CV anomalies are defects of
development, not necessarily congenital and may not manifest at birth.
It is a complex process.
Mesodermal somites numbering 42 appear at
the 4th week
Ventromedial part of the somatomes
migrate and cluster around notochord-Sclerotomes
A fissure in each sclerotome separate a
denser caudal half from loosely arranged cranial half.
Caudal half joins with cephalic half of
adjacent sclerotome - future vertebra
Mesenchymal cells of the fissure condense
to form I.V.D.
Notochord disappears at the vertebral
bodies, but persist as disc (nucleus pulposus)
This membranous stage is followed by
chondrification and ossification.
Out of 4 occipital sclerotomes the first
2 form basiocciput, the III Jugular tubercles and the IV (Proatlas)
form parts of foramen magnum, atlas and axis.
Dysplasia of the occiptal segments may
flatten the clivus - platybasia.
When the basiocciput and rim of foramen
magnum are underdeveloped, the odontoid and arch of atlas may grow
normally to over hang along the sides. Odontoid and arch of atlas
The proatlas may develop into separate
vertebrae - Occipital vertebra, hypochondral bow of proatlas may
persist to gain attachment to the atlas, clivus or even to the apical
segment of the dens - responsible for anti-cervico medially compression.
The axis has a fully developed center
from the second sclerotome which form the caudal part of the body and
At birth odontoid base is separate from
the body of axis by a segment of cartilage which persists until the age of
eight and the center gets ossified., may remain separate as Os-
The apical segment is not ossified until
3 years of age. At 12 years if fuses with odontoid to form normal odontoid.,
failure leads to Os terminale.
Classification CV anomalies:
|| Genetic and miscellaneous:|
Malformations of occipital bone:
Remnants around foramen magnum
Abnormal occipto atlantal ligament
Malformation of atlas
Failure of segmentation from
Atlanto axial fusion
Aplasia of atlas arches
Malformation of axis
Irregular atlantoaxial segmentation
Ossiculum terminale persistence
Segmentation falilure of C2-3
Errors of metabolism
Down's syndrome (lax joints)
Often the anomalies are in different
combinations and hence the difficulty in an appropriate terminology in
every case. Certain terms are conventionally used to express the
anomalies, as follows
1. Platy basia:
Flatness of the base of skull. Angle
formed by the clival line and a line drawn along the floor of ant. cranial
fosse exceeds 140 degrees.
Platy basia alone not associated with
other conditions does not produce any symptoms.
2. Basilar Invagination:
Vertebral column invaginates into the
posterior fossa which is of 2 types:
The anterior type has a short clivus
horizontally placed, with the anterior lip of the foramen magnum
invaginated in relation to the spinal column.
The other is paramedian invagination
associated with hypoplasia of the occipital condyles. Thus the atlas may
get invaginated. The hypochondral bow of the proatlas may persist to gain
articulation or fusion with lower end of clivus, ant. arch. The mass of
bone may cause ant. compression. There is associated soft tissue anomalies
of hind brain in 25-30% of cases. In certain diseases of bone like
hyperparathyroidism, pagets or osteomalacia, there is softening of the
base of skull which gets invaginated. This is called basilar impression or
secondary basilar invagination.
3. Assimilation of atlas:
Assimilation of atlas with the occiput is
an expression of nonsegmentation of certain parts of the proatlas and
fusion of the first spinal sclerotome with the proatlas. It occurs in
0.25% or less. However its occurrence along with other CV anomalies is
frequent. It could be partial or complex and may restrict occiptial
movement. It is frequent in Klippel-feil syndrome, involving the second
and the third vertebral bodies and may affect the atlanto axial joint.
This combination of assimilation of atlas and segmental failure of the II
and III vertebral bodies exert an abnormal strain on the atlanto axial
joints from childhood. In course of time the ligaments become lax and
mobility increases predisposing to atlanto axial dislocation.
4. Os Terminale:
Refers to the nonfused terminal part of
the odontoid derived from the centrum of the IV occipital sclerotome. This
apical segment is usually about 12mm in length, but can be very small. In
case of disruption at the interface and if atlanto axial dislocation
occurs, the remaining part of the odontoid may compress the cervico
5. Os odontoideum:
This term has been used to denote a
separate piece of bone present posterior to the anterior arch of atlas.
The odontoid base fails to fuse with the axis. These are only few odontoid
base falls to the above specification. But the diagnosis of Os odontoideum
is much more frequent in clinical practice. Careful exam reveals a small
hypoplastic odontoid at the upper border of the body of the axis. It is
generally believed that traumatic fracture leaves an irregular margin,
though the margin may be rounded enough to be indistinguishable from the
developmental anomalies. Many of the patients have history of fall. Dens
lacks a good nutrient artery. Blood supply thro' the body of axis is
limited due to interposition of cartilage between body and the odontoid
process. An injury in early childhood probably leads to Os-odontoideum in
later life due to avascular necrosis. In the absence of strong reasons to
consider embryological basis, traumatic theory is more rationale.
Pathogenesis of Neural involvement:
Neural involvement is basically due to 3
Mal aligned bony components of the spinal
canal compress underlying cord due to dislocation of the joints, the
commonest is Atlanto axial dislocation.
Encroachment into the spinal canal may
also occur due to formation of the abnormal bone masses around the CV
junction. Occasionally the foramen magnum may be narrowed or the rest of
arch of the atlas may be deformed to cause compression of spino medullary
Lastly, associated Chiari malformation
and syrinx may cause further neural compression.
A-A dislocation is the commonest
abnormality, be it congenital or acquired. A dysplastic odontoid provides
a vulnerable situation. The transverse ligament may be basically in-
competent or become so after a minor trauma. If the dislocation is sudden
and severe, an acute quadriparesis may occur. Abnormal mobility in flexion
may cause transient neural compression resulting in sudden transient
deficit and occasionally Lhtermitte's sign. In course of time the
dislocation may become fixed leading to progressive deficit. If it goes on
for years vascular damage may happen with no recovery even after adequate
decompression. Deformities involving the facet joints between atlas and
axis may give rise to rotatory dislocation . Such deformities cause only a
neck tilt and pain without neuro deficit.
Occipito-atlantal dislocation is rare.
In basilar invagination, there is
crowding of structures in the small post. fossa resulting in compression
of medulla, long tract involvement and lower cranial nerve deficits.
Rarely there is vertebral art. compression leading onto VBI.
Prevalence appears to be high as observed
by neurosurgeons in India although it is yet to be corroborated by
epidemiological studies. The abnormalities may have a familial occurrence.
In one series they affect children and young adults primarily. Majority of
patients present in their second or third decade. There is male
preponderance (1:5:1). H/o. trauma is often available. Many children have
URI preceding the onset of symptoms.
Progressive weakness of limbs, stiffness,
difficulty in walking and neck pain are the modes of presentation in
75-85% of cases. Smaller number present with neck tilt, neck pain, cough
headaches, occipital cephalalgia without any deficit. Symptoms of lower
brain stem dysfunction, such as dysphagia, dysphonia, nasal regurgitation,
sleep apnoea are due to basilar invagination.
Physical appearance is often striking.
Short stature, short neck, low hairline, head tilt, facial asymmetry, web
neck, or scoliosis occur in different combinations.
High arched palate, hemiatrophy of
tongue, and syndactyly may be associated. Evidence of high cervical cord
compression with or without sensory involvement is common. Involvement of
one limb or one sided limbs may be misleading . Crossed hemiparesis may
suggest cervico medullary junction involvement. Small muscle atrophy due
to 'central cord syndrome' like effect of the lower cord level due to
upper cord compression is seen in 22%. Spino thalamic involvement is
uncommon. Posterior column involvement is seen in 60%. Sphincter
disturbance is rare. Associated syrinx may produce dissociated or
suspended sensory loss. Lower cranial nerves are involved in about 18%.
Cerebellar involvement is seen in about 16%. Mirror movements of the hands
are often seen in klippel Feil syndrome due to inadequate decussation of
pyramidal tract at medulla.
MRI has totally changed the prospects of
investigation of spinal lesions and more so at CV junction. The soft
tissue details can be imaged with a high degree. CT scan with
reconstruction is still preferred by some to study bone details. X ray
with chamberlin line, mcgregor line etc have become history.
invagination(odontoid at the level of IAM)
|3D CT transoral view of odontoid(basilar invagination)
posterior fixation with wiring and plating after odontoidectomy
Though a number of bony and ligamentation
anomalies have been described, consequences are mainly due to (A) A -A
dislocation (B) malformed components of bone producing compression.
In early stages of A-A dislocations, most
of them are reducible and require only stabilization.
Irreducible types require open reduction (operative
reduction). Operative treatment has involved thro' several modifications.
The first effort was in 1910 by Osgood, who tried to reduce the
dislocation by pushing backwards the atlas via the pharynx while the
posterior arch of atlas was pulled back with a thick silk thread, which
was then tied to spinous process of axis. This was the beginning.
Gallow popularized the technique of
midline wiring which kept the atlas and axis is opposition. The wire
retains an interposed only bone draft. Several modification were
suggested. Screw fixation of facet junctions, Halifax clamps, contoured
rods are the latest. Hartshell frame is still being used by many. Some
have recommended methylmethacrylate use. All these methods are effective
when reduction of dislocation is adequate.
Instances of redislocation by snapping of wire,
loosening of screws are not rare.
In the fixed or irreducible variety foremen magnum
decompression along with C1 & C2 laminectomy is recommended by few and
claim to have satisfactory results, if done after a period of skull
traction. Oppel was probably the first to operate by
Removing the compressing element form it front is more rationale.
Recently this has become the preferred procedure. The
arch of the atlas, the odontoid and part of the axis can be excised. In
addition, the thick ligament and chronic granulation tissue which
contribute to compression can be excised.
The ant aspect of CV junction can be
approached by Trans
pharyngeal, Transpalato pharyngeal, Trans maxillary (Le fort -
with maxillary down fracture) routes. It is generally accepted that a
stabilization procedure is necessary following ant. decompression either
in the same sitting or as a II stage procedure. Of late ant. stabilization
following decompression has been tried in some centers. Some feel a
stabilization procedure is not required in selected cases.
|Basilar invagination - Achondroplasia
wiring after odontoidectomy
Irrespective of methods used it is
essential to immobilize its CV junction with collar till bony fusion
occurs, which may take 3 months. Ideal will be the Halo frame.
Significant relief in 70% of cases
following ant. decompression can be expected. Reduction in spasticity is
appreciated in the immediate post operative period.
Fatal meningitis, post operative
dislocation are possible complications.