Cerebrospinal fluid pressure-gradients in spina bifida cystica, with special reference to the Arnold-Chiari malformation and aqueductal stenosis.

Ten infants with spina bifida cystica were investigated during life by simultaneous ventricular and intraspinal CSF pressure recordings, and 11 post-mortem specimens were studied by means of crystic resin castings of the ventricles. The results indicate marked pressure differentials between the lateral ventricles and intraspinal CSF pathways, which contribute to the moulding of the Arnold-Chiari malformation as a sliding hernia. Similar pressure differentials may exist at the incisura, with moulding of tissues producing blockage of the aqueduct and the subarachnoid pathways. A valvular action was demonstrated, in which baseline pressure differences were exaggerated by the infant's straining (e.g. crying, sucking), and it seems that complete dissociation between the two pressures may develop as a result of periods of partial dissociation. Removal of the meningocele sac increased the peaks in recordings of intraspinal pressure produced by straining. If it is carried out when there is a valvular effect, it seems that it will hasten the onset of established ventriculo-spinal pressure dissociation and uncompensated hydrocephalus by leading to impaction of the Arnold-Chiari malformation in the foramen magnum. The results indicate that even after birth the CSF pathways of babies with spina bifida cystica are in a plastic and changeable condition, with competition between constricting and distending forces. The demonstration that pressures tend to be low in the spine and to become lower before exacerbation of hydrocephalus suggests that all the intracranial manifestations of spina bifida cystica may be due to low intraspinal pressure, which results from initial failure of the neural tube to close during embryogenesis.