Specific Imaging Findings

Schizencephaly is a hemispherical cerebral cleft that extends from the cortex to the ependymal surface of the lateral ventricles and is lined by the gray matter. The gray matter lining the cleft is morphologically abnormal, with pachygyric or micropolygyric appearance, and its continuity with the sulcal cortex gives the appearance of “diving gyri”. The cleft can be large, filled by CSF (open lips or type II schizencephaly), or small, virtually invisible, with gray matter lining the cleft apposed on both sides of the defect (closed lips or type I schizencephaly). In type I schizencephaly, when a cleft is not clearly visible, a small focal deformity of the lateral ventricle, with the ependyma “pointing” to the schizencephaly, can offer a clue to the diagnosis. Another helpful finding is that of prominent venous vasculature overlying the cleft. In large clefts, remnants of the brain parenchyma or ependymal lining are visible in the form of so-called “roofing membranes”, or “cords”. Schizencephaly can be uni- or bilateral, most commonly found in the insula and/or the perirolandic gyri. Associated abnormalities, which are often visible on MRI, are hypoplasia of optic chiasm and pituitary gland, and dysgenesis septum pellucidum and corpus callosum (together forming septo-optic dysplasia); opercular syndromes with hypoplastic sylvian fissure and perisylvian polymicrogyria, and hippocampal abnormalities with temporal horns enlargement. Rarely gliosis and/or calcifications can be observed in the adjacent areas.