Hemimegalencephaly involves a major dysgenetic process in one cerebral hemisphere and sometimes of the cerebellum, in which the volume of the abnormal brain is increased (Friede 1989). This group of conditions presents with developmental delay and usually intractable hemiseizures and hemiparesis. Where the epilepsy is not controlled by drugs, early hemispherectomy is usually indicated, but with concern about bilateral involvement (Chugani 1996). A number of conditions are associated with hemimegalencephaly, including the linear sebaceous naevus syndrome (Levin et al. 1984), neurofibromatosis (Ross et al. 1989), and Proteus syndrome (Cohen 1988).