Anencephaly

Absence of the brain and cranial vault (top of the skull) at birth. Most infants with anencephaly are stillborn or survive only a few hours. Anencephaly is detectable early in pregnancy by measurement of the maternal alpha-fetoprotein, by ultrasound scanning, by amniocentesis, or by fetoscopy; if anencephaly is detected, termination of the pregnancy may be considered. Anencephaly is due to a failure in the development of the neural tube, which is the nerve tissue in the embryo that normally develops into the spinal cord and brain. (See also neural tube defects.)