Perisylvian polymicrogyria (HP_0012650, a Human Phenotype Ontology term) is polymicrogyria (an excessive number of small gyri or convolutions) that is maximal in perisylvian regions (the regions that surround the Sylvian fissures), which may be symmetric or asymmetric and may extend beyond perisylvian regions. The Sylvian fissures often extend posteriorly and superiorly. Also known as: Frontoparietal polymicrogyria.