abnormal neural tube morphology/development craniorachischisis CRN MP:0008784 MPheno.ontology the most severe form of neural tube defect leaving the neural tube open from the midbrain or rostral hindbrain to the base of the spine; in mammals, craniorachischisis arises as a failure of a de novo closure event occurring during primary neurulation at the boundary of the future hindbrain and cervical spine (day 22 postfertilization in humans and E8.5 in mice); craniorachischisis totalis, the most complete form of craniorachischisis, presents anencephaly and total spina bifida together and is lethal