Coexistence of schizencephaly and middle cranial fossa arachnoid cyst: a report of two patients.

Two patients are presented with large cerebral schizencephalic clefts and large temporal arachnoid cysts. Neuropathological studies suggest that arachnoid cysts may either arise due to an aberration in the formation of the subarachnoid space or by its splitting. A recently proposed theory for the formation of schizencephaly is that this condition is an extreme variant of cortical dysplasia, in which the infolding of cortex extends all the way into the lateral ventricle. In light of these data, and based on the imaging findings in our two patients with large cerebral schizencephalic clefts and large temporal arachnoid cysts, we propose that the mechanism which causes schizencephaly (deep cortical infolding) may lead to some kind of a traction effect and splitting of the leptomeninges resulting in the formation of an arachnoid cyst adjacent to the schizencephalic cleft. This appears to be a significant observation because the pathogenesis of arachnoid cysts is still controversial.