Anencephaly refers to a congenital condition characterized by a failure in development of the two (2) hemispheres of the brain, the mesencephalon, and diencephalon.

The condition produces severe neurologic deficits and is incompatible with life. It is a birth defect in which the brain and neural tube fail to develop or develop incompletely and the skull does not close. Anencephaly, likewise refers to congenital absence of most of the brain and spinal cord.