Subcortical heterotopia: a distinct clinicoradiologic entity.

PURPOSE To investigate the clinical syndrome and associated brain anomalies in a group of patients with subcortical heterotopia. METHODS The seizure history, developmental history, family history, electroencephalographic results, imaging studies, and pathologic results (where available) of 13 patients with subcortical heterotopia were reviewed retrospectively. The patients ranged in age from 1 month to 39 years (mean, 11 years; median, 3 years) at the time of the most recent update of their records. RESULTS Fifteen hemispheres were involved in 13 patients. The cerebral cortex overlying the heterotopia was thin with shallow sulci and the affected part of the hemisphere was small as compared with the contralateral hemisphere. The corpus callosum was hypogenetic or agenetic in nine patients and the basal nuclei were dysplastic or hypoplastic in 11 patients. Most patients were developmentally delayed as children, had mild hemiplegia or hemihypesthesia contralateral to the affected hemisphere(s), and had partial epilepsy, most commonly evidenced by partial motor seizures in the body half contralateral to the malformation. Age at seizure onset varied from infancy to the second decade. Electroencephalographic results showed slow wave background with spike and spike wave complexes in the affected hemisphere. CONCLUSION Subcortical heterotopia seems to have characteristic clinical, electrophysiological, and imaging manifestations. These results suggest that affected patients may be conveniently grouped together to study treatment outcomes.