Lissencephaly HP:0002537 Fewer or absent grooves in brain UMLS:C0266463 Lissencephaly (LIS, which subsumes the terms agyria and pachygyria), together with subcortical-band heterotopia (SBH) comprises a spectrum of malformations of cortical development caused by insufficient neuronal migration. The key features of LIS are an abnormally thick cortex with reduced or absent formation of the cerebral convolutions, while SBH consists of abnormal bands of neurons beneath a normal cortex, although the cerebral gyri may be separated by unusually shallow sulci. A spectrum of malformations of cortical development caused by insufficient neuronal migration that subsumes the terms agyria, pachygyria and subcortical band heterotopia. See also neuropathological definitions for 2-, 3-, and 4-layered lissencephaly. UMLS:C1879312 HP:0001339 SNOMEDCT_US:204036008 Abnormal cortical gyration