A very rare disorder characterized primarily by the premature fusion of skull bones (sagittal), the Dandy-Walker malformation and a buildup of fluid in the brain (hydrocephalus). The Dandy-Walker malformation is where a cyst develops in the back of the brain and interferes with the movement of fluid through the brain resulting in an accumulation of fluid. See also Craniosynostosis, sagittal, with Dandy-Walker malformation and hydrocephalus