Double cortex. A neuronal migration anomaly as a possible cause of Lennox-Gastaut syndrome.

Band heterotopia, or "double cortex," is a neuronal migration disorder that consists of a symmetrical subcortical neuronal band. The overlying cortex may be normal or macrogyric. We describe two severely mentally retarded girls, aged 14 and 18 years, who had band heterotopia and Lennox-Gastaut syndrome. Band heterotopia was evident in both hemispheres as a subcortical symmetrical layer isointense with gray matter on magnetic resonance T1- and T2-weighted images. Both patients had atonic seizures, atypical absences, and tonic seizures. The electroencephalograms in both cases showed frequent generalized paroxysms and slow background activity. The association of a Lennox-Gastaut syndrome with double cortex in these two patients and in a previously reported autopsy-confirmed case suggests that this malformation may be responsible for other similar cases.