anencephaly /an′ensef″əlē/ [Gk, a + encephalos, without brain] , a lethal neural tube defect in which absence of major portions of the brain and malformation of the brainstem occur. The cranium does not close, and the vertebral canal remains a groove. It is thought to be caused by a combination of genetic and environmental factors. It can be detected early in gestation by amniocentesis and analysis or by ultrasonography. See also neural tube defect. −anencephalous, adj.
