Nodular heterotopia is built upon layers

Abstract

Gray matter heterotopia, agglomerates of morphologically normal cortical neurons at an abnormal site, is the most common human neuronal migration disorder. Heterotopia can be unilateral or bilateral, subependymal or subcortical, or it can extend from the subependymal region to the subcortex.1 Most individuals with heterotopia come to medical attention because of epileptic seizures, although the spectrum of clinical presentation is wide.2 A lingering question concerns precisely how impairments in neuronal migration give rise to diverse syndromes. For instance, the most notable feature of lissencephaly, subcortical band heterotopia (SBH), and nodular heterotopia (NH) is a failure in the migration of early postmitotic neurons from their site of birth in the ventricular zone to the cortical plate. This migration failure results in the thickened and abnormally laminated cerebral cortex found in lissencephaly, the abnormal band of neurons found beneath the cerebral cortex in SBH, and the neuronal nodules lining the ventricular zone or just beneath a normal-appearing cerebral cortex in NH.3 As yet undetermined is whether other cellular defects occur in these syndromes, in addition to the migration defects. A better understanding of the functional organization of heterotopic nodules could also have practical implications for the planning of surgical treatment for the associated epilepsy. There appears to be no difference in …