We observed 4 children with
hemimegalencephaly, (3 boys, 1 girl aged 3-7 years). One child had a
linear sebaceous nevus. All patients had a similar clinical, EEG, and neuroradiologic pattern. All patients had macrocrania,
hemiparesis,
hemianopsia, and psychomotor retardation of variable degree. All cases had an
epileptic syndrome with onset during the first days or the first months of life. The
seizures were consistently similar: partial
motor seizures, generally hemiclonic and asymmetric brief
tonic seizures, in series, involving predominantly one side of the body, contralateral to the cerebral damage. The EEG was initially characterized by a hemihypsarrhythmia and afterward, over the malformed hemisphere, by a rather high-frequency background activity associated with almost continuous transients of spikes, sharp waves, and spike and waves that progressively involved the contralateral hemisphere.
Hemispherectomy was performed in two children with sudden and complete recovery from
seizures and improvement in psychomotor development. Macroscopic examination was consistent with the computed tomography (CT) scan and magnetic resonance imaging (MRI) showing
pachygyria and poorly represented white matter. Histologic examination showed the characteristic absence of cortical neuronal layering, and the presence of giant neurons, neuronal heterotopias, and
gliosis. For
hemispherectomy to be successful, we believe prolonged EEG monitoring is needed to verify that no
seizures are originating in the normal hemisphere.