Malformations of Cortical Development

Categories

• group I: abnormal cell proliferation or apoptosis
• group II: abnormal neuronal migration
• group III: abnormal cortical organization

Group	Characteristics	Conditions
Group I	abnormal proliferation of neuronal and glial cells	Microcephaly macrocephaly FCDs without and with balloon cells (Taylor dysplasia types IIa and IIb), hemimegalencephaly, tuberous sclerosis, dysembryoplastic neuroepithelial tumors (DNETs), gangliogliomas, gangliocytomas
Group II	abnormal neuronal migration	Lissencephaly Band Heterotopia
Group III	abnormal cortical organization	Polymicrogyria, schizencephaly, type I FCDs, mild MCDs

Group	Affected step of development	MCDs resulting from the disturbance	Short definition of the MCD
Group I	Progenitor cell proliferation and apoptosis	Microcephaly Macrocephaly Hemimegalencephaly Focal cortical dysplasia || Abnormally small head and brain Abnormally big head and brain Overgrowth of (part of) a cerebral hemisphere Disturbed lamination and dysmorphic neurons
Group II	Neuronal migration	Lissencephaly type I Periventricular heterotopia (PH) Subcortical band heterotopia/double cortex || Absence of normal convolutions/folds Neurons accumulating at the ventricles underneath a normal cortex Band of grey matter located between the lateral ventricular wall and the cortex
Group III	Neuronal organisation	Cobblestone lissencephaly/lissencephaly type II Polymicrogyria Schizencephaly || Overmigration of neurons to localize on the surface of a brain with reduced gyri Too many (usually small) folds/convolutions Fluid-filled cleft from ventricle(s) to pia lined by heterotopic grey matter