cvj anomalies

8/8/2019 Cvj Anomalies

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The C-V junction is a transition site between mobile cranium and relatively rigid spinal column. It isalso the site of the medullo spinal junction. CV anomalies are defects of development, not necessarily

congenital and may not manifest at birth. Development: 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 invaginate-Basilar

invagination. The proatlas may develop into separate vertebrae - Occipital vertebra, hypochondral bow of proatlasmay 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 articular facets. At birth odontoid base is separate from the body of axis by a segment of cartilage which persists untilthe age of eight and the center gets ossified., may remain separate as Os- odontoidium. The apical segment is not ossified until 3 years of age. At 12 years if fuses with odontoid to formnormal odontoid., failure leads to Os terminale. Classification CV anomalies:

Developmental Genetic and

miscellaneous:

Malformations of occipital bone: Clivus segmentation Remnants around foramen magnum Basilar invagination Condylar hypoplasia

Abnormal occipto atlantal ligament Malformation of atlas Failure of segmentation from occiput

Atlanto axial fusion Aplasia of atlas arches

Malformation of axis Irregular atlantoaxialsegmentation Dens dysplasias Ossiculum terminale persistence Osodontoideum Segmentation falilure of C2-3 Neural dysgenesis

Errors of metabolism Down's syndrome (lax joints)

Achondroplasia

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 theatlas 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 isassociated soft tissue anomalies of hind brain in 25-30% of cases. In certain diseases of bone likehyperparathyroidism, pagets or osteomalacia, there is softening of the base of skull which getsinvaginated. 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 theproatlas 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 andmay 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 atlasand 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 occipitalsclerotome. 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 odontoidmay compress the cervico meduallary region. 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 theabove 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 isgenerally believed that traumatic fracture leaves an irregular margin, though the margin may berounded enough to be indistinguishable from the developmental anomalies. Many of the patientshave 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 childhoodprobably 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 mechanisms. 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 junction. 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 odontoidprovides a vulnerable situation. The transverse ligament may be basically in- competent or become soafter 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 leadingto 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 giverise 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 incompression of medulla, long tract involvement and lower cranial nerve deficits. Rarely there is

vertebral art. compression leading onto VBI. Clinical features: Prevalence appears to be high as observed by neurosurgeons in India although it is yet to becorroborated 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 orthird decade. There is male preponderance (1:5:1). H/o. trauma is often available. Many childrenhave URI preceding the onset of symptoms. 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 asdysphagia, dysphonia, nasal regurgitation, sleep apnoea are due to basilar invagination. Signs: Physical appearance is often striking. Short stature, short neck, low hairline, head tilt, facialasymmetry, web neck, or scoliosis occur in different combinations. High arched palate, hemiatrophy of tongue, and syndactyly may be associated. Evidence of highcervical cord compression with or without sensory involvement is common. Involvement of one limbor one sided limbs may be misleading . Crossed hemiparesis may suggest cervico medullary junctioninvolvement. 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. Posteriorcolumn involvement is seen in 60%. Sphincter disturbance is rare. Associated syrinx may producedissociated 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 Feilsyndrome due to inadequate decussation of pyramidal tract at medulla. Imaging: 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 preferredby some to study bone details. X ray with chamberlin line, mcgregor line etc have become history.

Atlanto- Axial subluxation platibasia basilar invagination(odontoid at the level of IAM)



3D CT transoral view of odontoid(basilar invagination)

AP view lat. view posterior fixation with wiring and plating after

odontoidectomy Management: Though a number of bony and ligamentation anomalies have been described, consequences aremainly 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 bypushing 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 bymany. Some have recommended methylmethacrylate use. All these methods are effective whenreduction 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 laminectomyis 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 ant. route. 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 tocompression 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 astabilization procedure is necessary following ant. decompression either in the same sitting or as a IIstage 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 AP view LAT

view

posterior 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. Outcome: Significant relief in 70% of cases following ant. decompression can be expected. Reduction inspasticity is appreciated in the immediate post operative period. Fatal meningitis, post operative dislocation are possible complications.

cvj anomalies

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