- A neural tube defect (NTD) that occurs when the cephalic (head) end of the neural tube fails to close, usually between the 23rd and 26th days of pregnancy, resulting in the absence of a major portion of the brain, skull, and scalp. Infants with this disorder are born without a forebrain, the largest part of the brain consisting mainly of the cerebrum, which is responsible for thinking and coordination. The remaining brain tissue is often exposed; it is not covered by bone or skin. Infants born with anencephaly are usually blind, deaf, and unconscious. Although some individuals with anencephaly may be born with a rudimentary brainstem, the lack of a functioning cerebrum permanently rules out the possibility of ever gaining consciousness. Reflex actions such as respiration (breathing) and responses to sound or touch may occur. The disorder is one of the most common disorders of the fetal central nervous system. Approximately 1,000 to 2,000 babies are born with anencephaly each year in the U.S. The disorder affects females more often than males. There is no cure or effective treatment for anencephaly and the prognosis (outlook) for affected individuals is very poor. Most infants with anencephaly do not survive infancy. If the infant is not stillborn, then he or she will usually die within a few hours or days after birth. Anencephaly can often be diagnosed before birth through screening of the mother's blood for the level of alpha-fetoprotein (AFP) and an ultrasound examination. The addition of ample folic acid to the diet of women of child-bearing age significantly reduces the incidence of neural tube defects. Therefore it is recommended that all women of child-bearing age consume 0.4 mg of folic acid daily. All women who could possibly become pregnant should consume 400 micrograms (400 mcg) of synthetic folic acid daily from vitamin supplements and/or fortified foods in addition to eating food folate in a healthful diet. This will reduce the risks not only for anencephaly but also for spina bifida, another common and major type of neural tube defect.
* * *Congenital defective development of the brain, with absence of the bones of the cranial vault and absent or rudimentary cerebral and cerebellar hemispheres, brainstem, and basal ganglia. SYN: anencephalia. [G. an- priv. + enkephalos, brain]- partial a. SYN: hemicephalia.
* * *an·en·ceph·a·ly .an-(.)en-'sef-ə-lē n, pl -lies congenital absence of all or a major part of the brain
* * *n.partial or complete absence of the bones of the rear of the skull, the meninges, and the cerebral hemispheres of the brain. It occurs as a developmental defect, and most affected infants are stillborn; if born live they do not survive for more than a few hours. Anencephaly is often associated with other defects of the nervous system, such as spina bifida. Prenatal screening tests for anencephaly include detection of alpha-fetoprotein levels and ultrasound scanning.
* * *an·en·ceph·a·ly (an″ən-sefґə-le) [an-1 + Gr. enkephalos brain] congenital absence of the calvaria, with cerebral hemispheres missing or reduced to small masses attached to the base of the cranium; complete absence of the brain is rare. Cf. meroanencephaly.
Medical dictionary. 2011.