Hemimegalencephaly: a clinicopathological study of four cases.

Pathological findings in four cases of hemimegalencephaly are presented. These cases demonstrated diffuse enlargement of the cortex with disappearance of horizontal layering of the neurons restricted to one hemisphere. In all cases there was marked enlargement of a high percentage of neurons. The nosological situation is discussed and is considered to be heterogeneous; cases 1-3 had cerebral lesions without lesions of the skin or viscera. In these three cases, significant glial abnormalities were found in only one. These cases and others quoted in the literature were considered to be a separate entity completely different from Bourneville's tuberous sclerosis. The aetiology of this developmental malformation remains unknown; genetic factors were not found. Case 4 was associated with a cardiac lesion and with a linear sebaceous naevus characteristic of Solomon's syndrome. Periventricular tumours resembling candlewax drippings were noted. This case, close to Bourneville's disease, could be incorporated into the framework of neuroectodermoses together with tuberous sclerosis.