An autopsy case of refractory epilepsy due to unilateral polymicrogyria in a 65-year-old man: Histogenesis of four-layered polymicrogyric cortex.

Polymicrogyria (PMG) is a complex malformation accompanied with abnormal cortical laminations (two-, four- or six-layered cortex), and horizontally oriented myelinated fiber layer is evident in four-layered PMG in older individuals. Here we report a 65-year-old man with refractory epilepsy, in whom postmortem examination revealed four-layered PMG in the left hemisphere. We carried out a histological and immunohistochemical study to clarify the nature of the myelinated band in four-layered PMG cortex. The myelinated band contained no or only few neurons. GFAP- and aquaporin-1-immunoreactive astrocytes were found in the subcortical white matter as well as in the myelinated band. By contrast, GFAP- and aquaporin-1-immunoreactive astrocytes were not found in the band of Baillarger. These findings suggest that the myelinated band in PMG cortex is not the band of Baillarger and that the immunohistochemical characteristics of astrocytes in the myelinated band in PMG cortex are similar to those of the subcortical white matter. Previous studies suggest that PMG is not a cell migration disorder but a post-migration malformation. Taken together, it is likely that the myelinated band in PMG cortex represents abnormality of axonal growth or myelination after migration has terminated.