Anencephaly is absence of the cerebral hemispheres. It is usually accompanied by a defect in the formation of the skull posteriorly, leaving the back of the head without skeletal protection.
In anencephaly, the residual brain tissue consists of highly malformed neural tissue, which may be exposed completely or thinly covered with skin. Parts of the brain stem and spinal cord also may be missing or malformed. Infants are stillborn or die within days or weeks.
Treatment of anencephaly is palliative only.
Hydranencephaly is a type of anencephaly.