Anencephaly is the absence of a major portion of the brain, skull, and scalp. It is the most severe and single most common prenatally detected neural tube (spinal cord) defect. Any exposed brain tissue is eventually destroyed and forms a bloody, fiber-like mass with no higher order brain function. Despite the severe brain abnormalities, the facial bones and base of the skull are nearly normally formed. The frontal bone, however, is always absent and the brain tissue is always abnormal.
Anencephaly accounts for approximately one-half of all cases of neural tube defects. The incidence of anencephaly in livebirths and stillbirths has been estimated as 0.3 per 1000 by the Centers for Disease Control. Female fetuses are 3-4 times more commonly affected than males. Mothers who have diabetes prior to conceiving or are obese are at an increased risk of having a baby with this condition. Mothers who take folic acid supplements prior to conceiving can reduce, but not eliminate, the possibility of having a baby with this condition.
In first trimester fetuses with anencephaly, the upper portion of the brain (the cerebral hemispheres) will be in direct contact with the amniotic fluid because the skull is absent. By ultrasound, the appearance will resemble “Mickey Mouse ears.” In the second trimester, the upper brain portions, above the level of the eyes, will not be visible by ultrasound because they are no longer present. Often, the amount of amniotic fluid surrounding the fetus is significantly increased (polyhydramnios). In postnatal studies, 13% to 33% of anencephalic infants have additional major congenital anomalies. The major consideration in the differential diagnosis is to distinguish anencephaly from the presence of amniotic bands. With amniotic bands, there should be evidence of other defects. Amniotic bands are often associated with oligohydramnios. Other conditions in the differential diagnosis include ruptured encephalocele and iniencephaly.
Management Options and Outcomes
Of those fetuses with anencephaly, a small portion will die while still in the uterus. Approximately 25% will have excessive amniotic fluid around the fetus (polyhydramnios). This may cause extra stretching of the uterus resulting in preterm contractions. The maternal serum alpha-fetoprotein (AFP) levels are elevated in approximately 90% of cases of anencephaly. All cases of significantly elevated maternal serum AFP levels need to be followed with a sonographic examination to confirm dating of the pregnancy and evaluate fetal anatomy. If there are no other abnormalities and the anencephaly is considered isolated, then a test to determine if there is a chromosomal abnormality may be recommended. Most fetuses with anencephaly deliver around 37 weeks of gestation. If the fetus appears to have anencephaly, the parents may be offered termination of pregnancy if the diagnosis is made prior to 24 weeks of gestation. Cesarean delivery is indicated only for maternal health considerations or, perhaps, if the fetus is breech.
Candidacy for Fetal Treatment
There is no fetal intervention for anencephaly.
Surgical treatment is not applicable in anencephaly.
The diagnosis of anencephaly can be confirmed on physical examination when the following criteria are met: a large portion of the skull is absent, the scalp is absent over the skull defect, and a hemorrhagic, fibrotic mass of tissue is exposed to the environment. Most newborns will die within the first few hours or days of life, though about 10% may live up to one week (9% of infants).
A family history of spina bifida and/or anencephaly is one of the strongest risk factors for recurrence, with a recurrence risk of between 2% and 5% following a single case. Some cases of anencephaly are associated with chromosomal abnormalities such as trisomies 13 and 18, and triploidy. For women who have previously had a fetus or infant affected with anencephaly, the Centers for Disease Control and Prevention (CDC) recommends increasing the intake of folic acid to 4000 mcg (4mg) per day beginning at least 1 month prior to conception (Committee on Genetics,1999).
A Difficult Diagnosis
The Fetal Health Foundation was founded by parents seeking hope for a fetal diagnosis. We try to provide accurate medical information, support, and hope. In the case of a diagnosis like this, we also want to offer resources that can help parents make the most of their time with their child.
Further reading and resources:
Read the story of our board member, Aran, meeting her daughter, Brianna Marie.
Read about memorial photography work of Now I Lay Me Down To Sleep. We are grateful for these volunteers.
Wondering how you can help someone during a difficult pregnancy? We share our thoughts.