Microgyria

Microgyria (from Greek mikros-small and gyros-convolution), an abnormality in brain development, characterized by very narrow, thin convolutions throughout the surface of the brain or only in a particular section [see figure and separate table (pp. 23-24), fig. 7]. The etiology and pathogenesis of M., as well as the other conditions, are not sufficiently clarified; the presence of M. can be explained by the arrest of brain development when the brain still has very thin convolutions; or M. can be regarded as compensatory phenomena in quantitative or circulatory disorders. M. most often occurs in microcephaly, porencephaly (see), as well as in a fully normally developed brain, especially in old age. When examining a microgyric brain, it is noted that the convolutions are longer than ordinary ones, and therefore they are more convoluted, their grooves are more superficial; sometimes the convolutions bulge above the surface of the brain and give this part of the brain a cauliflower appearance-status verrucosus deformans. The picture of cortical structure in microgyria varies—slight deviation from normal, preservation of embryonic type of structure; in some cases, the cortex forms numerous folds, indenting into the white matter, and resembles glandular tissue; or a very narrow strip of cortex, curved like a garland, is accompanied by a layer of myelinated fibers and a layer of gray matter (Mittelschicht), considered as heterotopic; similar heterotopias are also found around the ventricles; in the molecular layer, the presence of embryonic cells (Cajal's) is often noted. The clinical picture is characterized mainly by a change in intellect (see Microcephaly).