Because these nervous system abnormalities are so severe, almost all babies with anencephaly die before birth or within a few hours or days after birth.\n\nAnencephaly is a condition that prevents the normal development of the brain and the bones of the skull. This condition results when a structure called the neural tube fails to close during the first few weeks of embryonic development. The neural tube is a layer of cells that ultimately develops into the brain and spinal cord. Because anencephaly is caused by abnormalities of the neural tube, it is classified as a neural tube defect.\n\nBecause the neural tube fails to close properly, the developing brain and spinal cord are exposed to the amniotic fluid that surrounds the fetus in the womb. This exposure causes the nervous system tissue to break down (degenerate). As a result, people with anencephaly are missing large parts of the brain called the cerebrum and cerebellum. These brain regions are necessary for thinking, hearing, vision, emotion, and coordinating movement. The bones of the skull are also missing or incompletely formed.

Visually assessable vertical indentation, cleft, or depression of the nasal bridge, ridge and tip.

Distance between the medial and lateral canthi is more than 2 SD below the mean for age (objective); or, apparently reduced length of the palpebral fissures.

A type of cleft lip presenting as a midline (median) gap in the upper lip.

Cleft palate of the midline of the palate.

A gap (cleft) affecting one of the alveolar ridges, which are the protuberances in the mouth that contain the sockets (alveoli) of the teeth. An alveolar cleft can affect all structures of the alveolar ridge, including the gingiva, other mucosa, periosteum, alveolar bone, and teeth. Alveolar cleft occurs in response to divergence from normal development during frontonasal prominence growth, contact, and fusion. The most common alveolar portion of the cleft is located between the lateral incisor and the canine.

Absence of the globe or eyeball.