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Anencephaly is the absence of a large part of the brain and the skull.

Alternative Names

Aprosencephaly with open cranium


Anencephaly is one of the most common neural tube defects. Neural tube defects are birth defects that affect the tissue that becomes the spinal cord and brain.

Anencephaly occurs early in the development of an unborn baby. It results when the upper part of the neural tube fails to close. Why this happens is not known. Possible causes include environmental toxins and low intake of folic acid by the mother during pregnancy.

The exact number of cases of anencephaly is unknown, because many of these pregnancies result in miscarriage. Having 1 infant with this condition increases the risk of having another child with neural tube defects.


Symptoms of anencephaly are:

  • Absence of the skull
  • Absence of parts of the brain
  • Facial feature abnormalities
  • Heart defects

Exams and Tests

An ultrasound during pregnancy is done to confirm the diagnosis. The ultrasound may reveal too much fluid in the uterus. This condition is called polyhydramnios.

The mother may also have these tests during pregnancy:

  • Amniocentesis (to look for increased levels of alpha-fetoprotein)
  • Alpha-fetoprotein level (increased levels suggest a neural tube defect)
  • Urine estriol level

A pre-pregnancy serum folic acid test may also be done.


There is no current treatment. Talk to your health care provider about care decisions.

Outlook (Prognosis)

This condition usually causes death within a few days after birth.

When to Contact a Medical Professional

A provider usually detects this condition during routine prenatal testing and ultrasound. Otherwise, it is recognized at birth.

If anencephaly is detected before birth, further counseling will be needed.


There is good evidence that folic acid can help reduce the risk of certain birth defects, including anencephaly. Women who are pregnant or planning to become pregnant should take a multivitamin with folic acid every day. Many foods are now fortified with folic acid to help prevent these kinds of birth defects.

Getting enough folic acid can cut the chance of neural tube defects in half.

For specific recommendations, see folic acid (folate).


Finnell RH, George TM, Mitchell LE. Neural tube defects. In: Rimoin D, Pyeritz RE, Korf B, eds. Emery and Rimoin's Principles and Practice of Medical Genetics. 6th ed. Elsevier Ltd; 2013:chap 114.

Kinsman SL, Johnston MV. Congenital anomalies of the central nervous system. In: Kliegman, RM, Behrman RE, St. Geme JW III, Schor NF, Stanton BF, eds. Nelson Textbook of Pediatrics. 19th ed. Philadelphia, PA: Elsevier Saunders; 2011:chap 585.

Review Date:4/21/2015
Reviewed By:Neil K. Kaneshiro, MD, MHA, Clinical Assistant Professor of Pediatrics, University of Washington School of Medicine, Seattle, WA. Also reviewed by David Zieve, MD, MHA, Isla Ogilvie, PhD, and the A.D.A.M. Editorial team.

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Outcome Data

No data available for this condition/procedure.

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