Lissencephaly 6-layered lissencephaly 2019-04-09T12:02:50Z A malformation of the pachygyria-agyria spectrum. A 6-layered cortex is characterized by bands of ectopic neurons of varying shape and size organized in columns or clusters, lying in a reduced rim of white matter. Layers I and II of the cortex are well defined, and pyramidal and polymorphic neurons of layers III, IV, V, and VI are found more or less in their appropriate location.