Patient is an eleven months old child who presented with epilepsy.
There is evidence of a large CSF cleft lined with gray matter in the left frontal lobe extending up to the left lateral ventricle. A similar smaller cleft is seen on the right side. The septum pellucidum was absent.
Schizencephaly is the presence of gray-matter-lined clefts that extend through the entire cerebral hemisphere from the lateral ventricle to the cerebral cortex. At the margins of these clefts, the pial covering of the brain and the ependymal lining of the ventricle are extremely close to each other and may fuse, producing a pial-ependymal seam. Usually the gray matter along the cleft is polymicrogyric.
Presenting symptoms relate to the amount of involved brain. Patients with a narrow, unilateral cleft usually present with seizures and mild hemiparesis or visual difficulties, depending upon the location of the cleft within the hemisphere. They are otherwise developmentally normal. Patients with progressively larger clefts present with progressively larger neurological deficits as more brain is missing. Patients with bilateral clefts tend to be severely retarded with early epilepsy, severe motor deficit and maybe blindness.
These defects may represent a failure of a portion of the germinal matrix to develop or a segmental failure of neuronal migration. Similar defects can also be found as a result of secondary destruction of the cerebral wall during the early stages of development. These clefts tend to involve the precentral and postcentral gyri and the adjacent frontal cortex and extend down into the region of the insula. Bilateral involvement is seen in approximately 35% of patients with schizencephaly. Heterotopias may be encountered in the walls of the lesion and ventricles. The size of the defects varies from a large cyst like area filled with CSF and covered by a thin membrane to smaller, narrow clefts. The clefts may be "closed" in which only a double layer of cortex (with a variable subarachnoid space and draining vein) is seen extending from the surface to the ventricle. They may be "open" in which there is wide communication between the subarachnoid space and ventricle through a broad hemispheric cleft.
Multiplanar MRI shows the clefts and their extension towards the lateral ventricles. The cortex adjacent to the clefts almost always has an abnormal gyral pattern that can usually be demonstrated pathologically as polymicrogyria. Heterotopias may be seen. An important feature is the presence of a ventricular dimple and is almost always seen with closed or minimally open lips. Mild hypoplasia of the corpus callosum may be seen. The septum pellucidum is absent or nearly completely absent in 70% to 90% of affected patients. Of those with absence of the septum pellucidum, 30% to 50% will have optic nerve hypoplasia on clinical examination.