Elucidating the pathophysiology of syringomyelia
The CSF cisterns are poorly developed in these patients, theoretically because the CSF cisterns did not expand during development because the outlets of the fourth ventricle are obstructed Drainage of CSF through the myelomeningocele in utero encourages herniation of the posterior fossa structures through the foramen magnum.
Following repair of the myelomeningocele, obstruction of the CSF pathways in the basilar cisterns, and often at the cerebral aqueduct, prevent normal CSF flow, which results in hydrocephalus.
Syringomyelia occurs as a consequence of another abnormal process.
There is general agreement that in syringomyelia the CSF pathways are encroached upon by an underlying condition.
Cerebral findings include focal cortical dysplasia, gray heterotopias in the hemispheric white matter and subependymal zone of the lateral ventricles, and thickening of the massa intermedia.
The posterior fossa in Chiari II malformation is even smaller than in Chiari I malformation.
The mechanism is initiated by the Chiari malformation partially obstructing CSF pathways at the foramen magnum, which prevents the normally rapid efflux and influx of CSF between the head and the spine that compensates for brain expansion and contraction during the cardiac cycle.
To reverse this process, Gardner performed a surgical procedure that removed the bone from the posterior aspect of the foramen magnum, opened the fourth ventricle to the subarachnoid space, and plugged the obex.
In the 1970s Logue introduced a less-invasive alternative to Gardner’s procedure.
Chiari type IV malformation was extremely rare and was characterized by severe cerebellar hypoplasia, but with the cerebellum and brain stem remaining within the posterior fossa.
Mortality in infancy is the rule with this malformation.