The association of hydrocephalus and Arnold--Chiari malformation with spina bifida in the fetus.

Twenty-one fetuses with spina bifida and twenty apparently normal fetuses of between 14--23 weeks gestation were examined for the presence of hydrocephalus and Arnold--Chiari malformation. Sacral, lumbo-sacral, lumbar, thoraco-lumbo-sacral and thoraco-lumbar lesions were found. Some were closed, some were open. The amount of neural tissue at the site of the lesion was very variable. In three cases, diastematomyelia was found. The heads of spina bifida fetuses were not enlarged. Hydrocephalus was found in eleven of them and the Arnold--Chiari malformation in twelve. In nine fetuses the abnormalities co-existed. Hydrocephalic brain showed depression of the tentorium, abnormalities in the corpus callosum and absence of the lateral fissure. The more cephalad and extensive the spinal lesion, the more likely it was to be accompanied by brain abnormalities. Isolated sacral defects were not associated either with hydrocephalus or with the Arnold--Chiari malformation. Pathological changes in the brain occurred in the presence of both open and closed spinal lesions and were apparently unrelated to fetal age. No evidence was found as to the sequence in which these brain abnormalities appeared.