Anencephaly
| Anencephaly | |
|---|---|
 |
|
| A side view of an anencephalic fetus | |
| Classification and external resources | |
| Specialty | Medical genetics; pediatrics |
| ICD-10 | Q00.0 |
| ICD-9-CM | 740.0 |
| OMIM | 206500 |
| DiseasesDB | 705 |
| MedlinePlus | 001580 |
| eMedicine | neuro/639 |
| MeSH | C10.500.680.196 |
Anencephaly is the absence of a major portion of the brain, skull, and scalp that occurs during embryonic development. It is a cephalic disorder that results from a neural tube defect that occurs when the rostral (head) end of the neural tube fails to close, usually between the 23rd and 26th day following conception. Strictly speaking, the Greek term translates as "no in-head" (that is, totally lacking the inside part of the head, i.e. the brain), but it is accepted that children born with this disorder usually only lack a telencephalon, the largest part of the brain consisting mainly of the cerebral hemispheres, including the neocortex, which is responsible for cognition. The remaining structure is usually covered only by a thin layer of membrane— skin, bone, meninges, etc. are all lacking. With very few exceptions, infants with this disorder do not survive longer than a few hours or possibly days after their birth.
The National Institute of Neurological Disorders and Stroke (NINDS) describes the presentation of this condition as follows: "A baby born with anencephaly is usually blind, deaf, unaware of its surroundings and unable to feel pain. Although some individuals with anencephaly may be born with a main brain stem, the lack of a functioning cerebrum permanently rules out the possibility of ever gaining awareness of their surroundings. Reflex actions such as breathing and responses to sound or touch may occur."
The cause of anencephaly is disputed.
Folic acid has been shown to be important in neural tube formation since at least 1995, and as a subtype of neural tube defect, folic acid may play a role in anencephaly. Studies have shown that the addition of folic acid to the diet of women of child-bearing age may significantly reduce, although not eliminate, 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, especially those attempting to conceive or who may possibly conceive, as this can reduce the risk to 0.03%. It is not advisable to wait until pregnancy has begun, since, by the time a woman knows she is pregnant, the critical time for the formation of a neural tube defect has usually already passed. A physician may prescribe even higher dosages of folic acid (4 mg/day) for women having had a previous pregnancy with a neural tube defect.
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