Schizencephaly(Gr.Scheizein to cleave, slit, split) was originally described by Yakovlev and Wadsworth as “congenital clefts in the cerebral mantle”, extending from the pial surface to the ventricles. The lips of the defects were closed in some cases, forming a seam (closed lip lissencephaly). In other cases, hydrocephalus caused the lips to separate, creating a gap in the cerebral mantle (open lip schizencephaly). As in porencephaly, the thin subpial and ependymal membranes along the outer and inner borders of open lip lesions may rupture, creating a communication between the lateral ventricles and the subarachnoid space. Yakovlev and Wadsworth thought schizencephaly was a malformation caused by failure of development (agenesis) of brain tissue, dating back to the first two months of fetal life. Neuropathologists have dismissed the agenesis hypothesis in favor of an encephaloclastic process and have even discouraged the use of the term schizencephaly. However, the term is used by neuroradiologists, and, thanks to modern imaging, the frequency of schizencephaly appears to be considerably higher than had been previously appreciated.