Hemihydranencephaly is a severe cephalic disorder characterized by complete or almost complete absence of the cerebral cortex with preservation of meninges, basal ganglia, pons, medulla, cerebellum, and falx. It is a special type of hydranencephaly. Hemihydranencephaly is a severe cephalic disorder characterized by complete or almost complete absence of the cerebral cortex with preservation of meninges, basal ganglia, pons, medulla, cerebellum, and falx. It is a special type of hydranencephaly.