Polymicrogyria without porencephaly/schizencephaly. MRI analysis of the spectrum and the prevalence of macroscopic findings in the clinical population.

Although the diagnosis of polymicrogyria currently depends largely on non-invasive imaging, no large imaging-based studies of polymicrogyria have been reported. Previous anatomic studies of polymicrogyria have been based on autopsy studies and most of the cases in those series were associated with porencephaly or schizencephaly. This retrospective MRI analysis of a group of patients with polymicrogyria, without associated porencephaly or schizencephaly, was conducted to elucidate gross morphological findings of polymicrogyria in a clinical population. Seventy-one patients with polymicrogyria diagnosed by MRI were reviewed by two radiologists. The location of polymicrogyria, the associated white matter anomalies and other associated central nervous system anomalies were assessed. The polymicrogyria was unilateral in 30 (42%) patients, bilateral in 41 (58%) patients. The lobes involved in polymicrogyria were frontal 69%, parietal 63%, temporal 38%, and occipital 7%. The cortex in the Sylvian fissures was involved in 80%. The striate cortex, cingulate gyrus, hippocampus and the gyrus rectus were often spared. Diminished volume of white matter was noted in 48%, perivascular space dilatation in 27% and large cortical veins in 51%. Polymicrogyria develops in specific topological regions, the majority being centered around the Sylvian fissures, and a minority in the inferior and medial aspects of the cerebral hemispheres or the occipital lobes. Diminished volume of the white matter and dilated perivascular spaces deeply embedded close to the dysplastic cortex and abnormal cortical venous enlargement superficial to the dysplastic cortex may be useful adjuncts in making the diagnosis.