Cortical malformations

The formation of the normal human cortex is the result of complex, precisely timed sequences of processes taking place during embryogenesis and any insult (either genetic or environmental) involving one or more of the leading processes of corticogenesis may result in cortical malformation. Malformations of cortical development (MCDs) are defined in their broadest sense as malformative lesions of the cortex resulting from derangements of normal processes that take place during the first two trimesters of human pregnancy and involve cells that, under normal circumstances, participate in the formation of the cortical mantle. The etiology of malformative disorders is often uncertain and the mechanisms by which they generate epilepsy and neurological disorders are not completely understood; however, over the past decade, molecular, biological and genetic studies of cortical development have greatly expanded our knowledge of the normal mammalian brain's development and derangements. Several disorders of cortical development have been recognized, and for some of them specific causative genetic defects have been identified. Although the precise incidence of MCDs is not known, it appears that they are more common than recognized in the pre-magnetic resonance imaging era, particularly in patients with epilepsy since MCDs can be intrinsically epileptogenic, presumably owing to an abnormal rearrangement of the intralesional circuitry. In this chapter the major cortical malformations, their classification, their possible etiology, and their involvement in generating epileptic seizures and epilepsy syndromes are presented.