In this anomaly the cranial vault fails to form and the top of the skull is open. Cranioschisis (also called acra-nia) is caused by the failure of the cranial neuropore to close during the 4th week of development of the skull vault. Cranioschisis is always associated with anencephaly (absence of brain) because, due to exposure to the amni-otic fluid, the brain tissue degenerates. Children with Cranioschisis and anencephaly can not survive.