Cephalothoracopagus janiceps malformation. A contribution to the pathogenesis of cerebral malformation.

We report the first histologic findings of the CNS in cephalothoracopagus janiceps monosymmetros. The findings are compared with the other ten reported cases of this type of conjoined twin. The faces and CNSs showed asymmetry of development manifested chiefly in the prosencephalon, specifically the cortical gyri, corpus callosum, and subependymal mantle layer. It is difficult to explain discordance for congenital malformations in monovular or conjoined twins by either genetic or environmental mechanisms. It appears related to the vascular supply of the brain and a state of chronic ischemia rather than to a discrete insult and developmental arrest at a specific time during embryogenesis.