Type I schizencephaly: CT and neuropathologic findings.

Type I schizencephaly, which is less commonly recognized than the type II variety, consists of a "fused" cleft in the cerebral mantle. Its CT appearance is significantly different from the type II variety, and it may be confused with postdevelopmentally acquired lesions. The CT appearance of eight cases (seven girls and one boy, aged 10 months to 18 years) of type I schizencephaly was correlated with clinical findings and previously recorded neuropathologic features. Presenting symptoms included developmental delay, seizures, and hemiparesis. CT findings in each case showed a unilateral, cortically lined cleft in the parasylvian region extending from the hemispheric surface to the ventricle. Micropolygyria was present in the cortex lining the cleft, and in two of eight patients was also visible elsewhere in the cerebral cortex. Those with associated microcephaly (four of eight patients) had significantly more severe neurologic deficits than did those without microcephaly. CT findings in type I schizencephaly are characteristic and show excellent correlation with neuropathologic specimens. The appearance of these lesions can be explained on the basis of a disorder of neuronal migration in early gestation and they should not be confused with postdevelopmentally acquired lesions.