Lissencephaly (LIS) (derived from the Greek words lissos meaning smooth and enkephalos meaning brain) is a neuronal migration disorder characterized by absent (agyria) or decreased (pachygyria) convolutions, producing a smooth cerebral surface (Friede1989). Several different types of LIS have been recognized. The most common, known as classical LIS or type 1 LIS, features a very thick cortex (10–20 mm vs. the normal 4 mm) and no other major brain malformations. The cytoarchitecture consists of four primitive layers, including an outer marginal layer which contains Cajal–Retzius neurons (layer 1), a superficial cellular layer, which contains numerous large and disorganized pyramidal neurons (layer 2) corresponding to the true cortex, a variable cell-sparse layer (layer 3), and a deep cellular layer (composed of medium and small neurons) which extends through more than half the width of the mantle (layer 4) (Golden and Harding 2004)(Fig. 46.1). Subcortical band heterotopia (SBH) is a related disorder in which there are bilateral bands of gray matter interposed in the white matter, between the cortex and the lateral ventricles (Barkovich2000) (Fig. 46.2). This may appear as a solid band of heterotopic tissue or as numerous islands of radially oriented gray matter separated by white matter. Pyramidal cells in the heterotopic band may be smaller than normal compared to those in the overlying cortex, which usually appears structurally normal, with the exception of shallow sulci (Golden and Harding 2004).
|Title of host publication||The Causes of Epilepsy: Common and Uncommon Causes in Adults and Children|
|Publisher||Cambridge University Press|
|Number of pages||7|
|ISBN (Print)||9780511921001, 9780521114479|
|Publication status||Published - Jan 1 2011|
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