Acrania, Anencephaly, and Encephelocele – Fetal Development

Posted On: March 8, 2023 By CIW

Acrania, anencephaly and encephalocele are part of the subset of birth defects called neural tube defects (NTDs). NTDs occur when the neural tube, a structure that forms the early brain and spine, fails to close within the first month of pregnancy.  NTDs are the second most common birth defect in the United States and are associated with substantial morbidity and mortality. The three major types of NTDs are acrania/anencephaly, encephalocele and myelomeningocele.

The majority of NTDs are multifactorial, meaning they result from a combination of factors such as genetic predisposition and environment; a single underlying cause is not always found. However, NTDs can be associated with genetic abnormalities, especially when other birth defects are found. For this reason, testing the fetus for genetic disorders can help with diagnostic evaluation and recurrence risk counseling.

Risk Factors for Neural Tube Defects

Anyone can have a baby that develops an NTD, although there are many conditions that increase the risk of having an NTD. These include:

  • Previous pregnancy affected by NTD
  • Other family history of NTD
  • Obesity
  • Diabetes
  • Use of medications that inhibit folate
  • Opioid use in early pregnancy
  • Increased body temperature in early pregnancy

Pregnancies with the highest risk are those with a family or personal history of NTDs. Patients with a history of pregnancy or children with an NTD have an increased rate of recurrence of approximately 2-5%.

If you’re at risk for an NTD, create a treatment plan with your obstetrician or maternal fetal medicine specialist, including careful monitoring throughout pregnancy as well as folic acid supplementation before conception and throughout the first trimester.

What is Acrania?

Acrania is the absence of the fetal skull, which results in brain tissue being exposed to the amniotic fluid. It is thought that acrania is the precursor to anencephaly in what is called the acrania-exencephaly-anencaphaly sequence. Acrania can be seen on ultrasound in the first trimester. Unfortunately, these are lethal disorders, which means that babies who are born with anencephaly cannot survive for very long after birth. Prior to the fortification of food with folic acid in the United States, the incidence of these conditions was about 1 in 1,000 births; since then, the incidence has decreased dramatically. Acrania can be definitively diagnosed on ultrasound by 12 weeks and can sometimes be diagnosed earlier.

What is Anencephaly?

Anencephaly refers to the absence of the upper portion of the fetal brain. It is thought to result from acrania, as the amniotic fluid is toxic to and eventually destroys the exposed fetal brain tissue. The remaining parts of the brain remain exposed, not covered by bone or skin. This NTD affects one out of every 4,600 pregnancies in the United States and is a fatal condition. Anencephaly is universally able to be diagnosed on a second trimester ultrasound.

What is Encephalocele?

Encephalocele is an NTD where there is a defect in the fetal skull allowing a portion of the fetal brain to herniate through the skull. This can result in a small or large protrusion at the back of the neck, top of the forehead, or between the eyebrows. Unlike acrania/anencephaly, this defect is still covered with skin or a membrane, so the brain tissue is not exposed to amniotic fluid. The prognosis depends on the size of the defect as well as what area(s) of the brain are affected. There is typically significant neurologic impairment in most cases of encephalocele. Encephalocele affects about one in every 10,000 births. There are genetic syndromes associated with this disorder, such as Meckel-Gruber. Children born with encephalocele can suffer from developmental and cognitive delays, visual impairment and small head size (microcephaly).

Prenatal Screening and Diagnosis

Acrania, anencephaly and encephalocele can be detected during an ultrasound. In some circumstances, especially if high quality ultrasound is not available, a blood test called maternal serum alpha fetoprotein (AFP) can be used to screen for open NTD.  Increased AFP can also be detected in the amniotic fluid after amniocentesis in pregnancies affected by open NTD.

How to Treat Encephalocele

In cases in which encephalocele is not lethal, the exposed brain tissue can be covered and the opening in the skull closed during surgery.

These procedures need to be performed very shortly after birth, which is why it’s always better to know about these conditions through ultrasound imaging so you can create a plan for delivery. It is recommended to meet with a pediatric neurosurgeon prior to birth to discuss the surgical plan. Whether surgery (or surgeries) can correct the condition or not, babies born with encephalocele may have neurological symptoms such as:

  • Developmental delay
  • Complete muscle weakness or lack of muscle coordination
  • Vision problems
  • Intellectual disability
  • Seizures

Acrania/anencephaly is not treatable and is fatal shortly after delivery.

Prevention of NTDs

Folic acid supplements and dietary fortification (including more micronutrients in food) have been shown to decrease the occurrence and recurrence of NTDs. Folic acid is a B vitamin that is used to make new cells in the body, including the formation of the neural tube. Everyone needs folic acid, but it is especially important in pregnancy. Foods that are high in folic acid include:

  • Bread
  • Cereal
  • Pasta
  • Flour
  • Corn meal
  • Beans
  • Dark leafy vegetables
  • Eggs
  • Fresh fruits and fruit juices
  • Liver

Look for products that say “fortified” or “enriched,” as these are often terms used to refer to added folic acid. The United States grows grains that are enriched in folic acid, which has contributed to a national decline in incidences of NTDs. However, folic acid from food alone may not be sufficient in early pregnancy, therefore the American College of Obstetricians and Gynecologists (ACOG) recommend daily supplementation with 400 micrograms of folic acid for average-risk patients. Most prenatal vitamins include this amount of folic acid, but it is important to check the ingredients of your prenatal vitamin.

Since the recurrence risk for NTD is high, ACOG, the Centers for Disease Control, and the American Academy of Pediatrics recommend that patients with an above-average risk of NTD take additional folic acid supplementation. Specifically, those with a previously affected pregnancy, who have an NTD themselves or for whom the father of the pregnancy has an NTD should take 4 mg of folic acid per day (10 times the dose recommended to average-risk patients) beginning at least one month before conception and continuing through the first trimester. Pregnancies supplemented with folic acid have a 72% reduction of NTD recurrence. If you have a different risk factor for NTD (such as a medication use), check with your doctor for the specific amount of folic acid that is recommended for you.

Your Partner in Maternal Fetal Health

The expert obstetricians and gynecologists at Maternal Fetal Medicine Associates are here every step of the way to ensure that, when it’s time, you deliver a healthy baby in a safe way. From pre-conception counseling all the way through to delivery, we’ll monitor your progress and adjust your care accordingly.

To learn more about NTDs, including acrania, anencephaly and encephalocele, don’t hesitate to contact Maternal Fetal Medicine Associates today. We’ll describe the risks, diagnosis, and treatment options you can expect so you aren’t left in the dark about your obstetrical care.


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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