Polymicrogyria Perisylvian polymicrogyria 2014-02-06T07:47:51Z The Sylvian fissure (also known as the lateral sulcus) separates the frontal and parietal lobes superiorly from the temporal lobe inferiorly. HP:0012650 HP:0007095 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. UMLS:C3279675 Frontoparietal polymicrogyria