Polymicrogyria and schizencephaly

The causal disease The term polymicrogyria defines an excessive number of abnormally small, and partly fused, cortical gyri, that produce an irregular cortical surface (Barkovich et al. 2005). Polymicrogyria has been ever more recognized since the advent of magnetic resonance imaging (MRI). Its pathogenesis is not understood; brain pathology demonstrates an abnormally developed thin cortical ribbon, with loss of neurons in middle and deep cortical layers (Englund et al. 2005), variably associated with an unlayered cortical structure (Fig. 48.1A, B). There is causal heterogeneity. A variety of intrinsic, genetically determined mechanisms have been associated with polymicrogyria (Golden and Harding 2004). However, autopsy observations in fetuses demonstrate that acquired disruption of cortical development is also possible, acting from the third to fifth month of gestation and interfering with the later stages of neuronal migration and causing postmigrational destruction (Friede 1989; Golden and Harding 2004). Polymicrogyria is a common cortical malformation and is associated with a wide spectrum of anatomic patterns (Table 48.1). It can appear as an isolated manifestation or be associated with multiple different conditions including metabolic disorders, especially Zellweger syndrome, or intrauterine hypoperfusion or infection, especially with cytomegalovirus, toxoplasma, and syphilis (Golden and Harding2004), fetal alcohol syndrome (Reinhardt et al. 2010), and be part of multiple congenital anomalies/mental retardation syndromes. Affected patients may have a wide spectrum of clinical problems other than those attributable to the polymicrogyria.