Specific Imaging Findings

Polymicrogyria is characterized by an irregular cortical surface, apparent thickening of the cortex, “stippled” gray–white matter junction, and a greater than expected number of abnormally small gyri, usually without T2 signal abnormality in the myelinated brain. High-resolution images reveal that the cortical ribbon itself is thin, and the apparent thickening results from juxtaposition of the small folds. The perisylvian cortex is the site most commonly affected by polymicrogyria; however, any region of the cortical mantle can be involved. Cortical involvement can be restricted to a single focus or it can affect extended areas, as seen in cases of uni- or bilateral, symmetrical or asymmetrical, diffuse polymicrogyria. The imaging appearances of polymicrogyric cortex can be heterogeneous, ranging from multiple abnormal small gyri to a relatively smooth cortical surface and an overall coarse appearance. Diffuse coarse polymicrogyria can have the appearance of cortical palisades. The sulcation pattern is aberrant, without a recognizable pattern. Sulci may be shallow or deeply indent the parenchyma. Polymicrogyria may be associated with schizencephaly, corpus callosum dysgenesis, cerebellar hypoplasia, periventricular and subcortical heterotopias. An imaging protocol including volumetric T1-weighted images with thin sections (< 1.5 mm) and reconstruction in the three orthogonal planes is optimal for evaluation of these abnormalities.