A congenital malformation due to failure of the neural tube to close at the rostral end, which consists of the absence of the cerebral hemispheres in all cases and of the diencephalon and midbrain in most cases (see figure below). Macerated brain stem tissue is visible through a wide defect in the skin and skull and the pituitary gland is usually present although small. The body often shows disproportionate enlargement of the shoulders. A full term anencephalic may be stillborn or live for a few hours or days. Its incidence ranges from 1 to 6 per 1000 births and is much more common in males. Some studies have shown that anencephalic infants are capable of a simple form of learning (viz., habituation).
