Heterotopia or neuronal heterotopia are macroscopic clusters of misplaced neurons (gray matter), most often situated along the ventricular walls or within the subcortical white matter. The phenotype is Gray matter heterotopia (Human Phenotype Ontology entry HP_0002282). Also known as: Gray matter heterotopias, Grey matter heterotopia, Grey matter heterotopias, Heterotopia, Heterotopias, Neuronal heterotopia.