Acrania, Anencephaly, and Encephelocele – Fetal Development

Posted On: May 11, 2016 By Nathan D. Fox, MD

Acrania refers to the absence of a fetal skull with freely-exposed brain tissue to amniotic fluid.  Anencephaly refers to the absence of the upper portion of the fetal brain.

Acrania often results in anencephaly, and some believe it is a precursor to all cases of anencephaly. Both can be seen on ultrasound in the first trimester. Unfortunately, the prognosis is uniformly dismal as these are lethal disorders.

Acrania and Anencephaly

Acrania and anencephaly are forms of neural tube defects (NTD) of the fetus. Neural tube defects (NTD) are the second most common congenital anomaly in the United States, second to cardiac malformations, which are associated with substantial morbidity and mortality.

The majority of NTDs are isolated malformations of multifactorial origin; for example, traits or conditions influenced by environmental and genetic factors. However, there is a higher prevalence of karyotypic (genetic) abnormalities among fetuses with NTDs, especially when other congenital abnormalities are found. Trisomy 18 is the most common genetic abnormality associated with NTD. For this reason, fetal karyotyping can help with diagnostic evaluation and recurrence risk counseling.

Decrease Recurrence of NTDs

NTDs recurrence rate is approximately 2 to 5 percent. Folic acid supplements and dietary fortification (including more micronutrients in food) have been shown to decrease the occurrence and recurrence of NTDs. The American College of Obstetricians and Gynecologists, the Centers for Disease Control, and the American Academy of Pediatrics recommend that women with a previously affected child, and those on anticonvulsant medicine, take 4 mg of folic acid per day beginning at least one month before conception and continue through the first trimester. Pregnancies supplemented with folic acid had a 72 percent reduction of NTDs recurrence.


Encephelocele is a condition where there is a defect in the fetal skull allowing a portion of the fetal brain to protrude through the defect. The skull defect can be small or large, and prognosis depends on the size of the defect. However, there is typically significant neurologic impairment. Encephelocele occurs sporadically, and may be associated with NTDs when very large. There are syndromes associated with this disorder as well, including Meckel-Gruber.

To learn more about NTDs, including acrania, anencephaly, and encephelocele, contact Maternal Fetal Medicine today.

Carnegie Imaging for Women blogs are intended for educational purposes only and do not replace certified professional care. Medical conditions vary and change frequently. Please ask your doctor any questions you may have regarding your condition to receive a proper diagnosis or risk analysis. Thank you!

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