Polymicrogyria true HP:0002126 SNOMEDCT_US:4945003 MSH:D065706 More grooves in brain UMLS:C0266464 Polymicrogyria is a common malformation of cortical development, where there is abnormal layering, excessive gyration (folding), and gyral fusion in the cerebral cortex. Polymicrogyria may be bilateral, or less commonly unilateral. It occurs most frequently in the perisylvian cortex (80%) and can result in the Sylvian fissure having an abnormal extension and orientation. Polymicrogyria, one of the most common malformations of cortical development, is characterized histologically by the appearance of an excessive number of small cortical folds, often fused together, with disordered cortical lamination. Polymicrogyria is a congenital malformation of the cerebral cortex characterized by abnormal cortical layering (lamination) and an excessive number of small gyri (folds). human_phenotype Malformations of Cortical Development