Schizencephaly (cleft brain) consists of a unilateral or bilateral full thickness cleft of the cerebral hemispheres with communication between the ventricle and extra-axial subarachnoid spaces. The walls of the clefts may be widely separated or closely adjacent, bilateral clefts are usually symmetric. The clefts are most often found in the perisylvian area. The cortex surrounding the cleft is polymicrogyric, for this reason schizencephaly is considered a disorder of cortical organization. However, an abnormal proliferation of the neuronal precursor is  also possible, especially when open lip clefts, with absence of development of a large part of one cerebral hemisphere, are considered. Schizencephaly may be due to regional absence of proliferation of neurons and glia or to abnormal cortical organization. Local failure of induction of neuronal migration or focal ischemic necrosis with destruction of the radial glial fibres during early gestation, have been hypothesized.
Although schizencephaly is usually sporadic, familial occurrence has been reported. Several sporadic patients and two siblings of both genders harbouring germline mutations in the empty spiracles homeobox gene EMX2 have been described. However, the role of the EMX2 gene has not been confirmed and the pattern of inheritance of schizencephaly is still unclear. Clinical findings include focal seizures in most patients (about 80% of cases in one large review), usually beginning before age 3 years in bilateral cases. Bilateral clefts are associated with microcephaly, severe delay and spastic quadriparesis whereas patients with unilateral schizencephaly most often have hemiparesis or may be brought to medical attention after seizure onset without having any other neurological abnormality.

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