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Anencephaly

What is anencephaly?

Anencephaly is a form of neural tube defect (NTD) that hampers the normal brain and skull development [1]. Babies affected by this condition are often stillborn or die within a few hours or days of birth.

Anencephaly Pathophysiology

The neural tube, a narrow layer of cells, ideally folds and closes in the first month (the third and fourth weeks) of pregnancy to form your baby’s brain and spinal cord [2]. Sometimes, the head end (anterior neuropore) of the tube fails to fold and close, leading to the lack of major parts of the brain and skull.

Anencephaly Pictures

Anencephaly Pictures

What causes anencephaly?

Doctors still do not know the exact causes responsible for anencephaly as various genetic and environmental factors are believed to contribute to this congenital defect. Several risk factors have been identified, including:

  • Failing to take enough folic acid, a B vitamin known to prevent various NTDs when taken in the first weeks of pregnancy, can lead to various NTDs including anencephaly [3].
  • Genetic factors may play a vital role in causing the defect in some rare cases, where the fetus inherits the condition in either autosomal dominant or autosomal recessive pattern [4]. Changes in certain genes like the MTHFR (responsible for providing the instructions to produce the protein necessary for processing folic acid) have been found to play a significant role in causing the problem [5].
  • Maternal hyperthermia or abnormally high body temperature (maternal fever during the early weeks of gestation is also considered a risk factor)
  • Maternal type 1 diabetes mellitus or pre-gestational insulin-dependent diabetes mellitus (IDDM) [4]
  • Amniotic band disruption sequence, resulting from ruptured amniotic membranes, can interrupt the growth of normally developed tissues, including the brain and head

What are the signs and symptoms of anencephaly?

  • Absence of the bones covering the top and back of the head
  • Bones missing from the sides and front of the head
  • Folded ears [6]
  • Abnormal facial features [7]
  • Cleft palate
  • Congenital heart defects [3]
  • A ‘frog eye’ appearance due to the absence of the cranial bone [8]

Associated complications often include polyhydramnios (excessive amniotic fluid in the womb) due to the baby’s inability to swallow the fluid.

Can anencephaly be prevented?

Following a healthy diet rich in various vitamins and minerals, especially folic acid, as soon as you plan to conceive or at least as soon as you find out you are pregnant can help to reduce the chances of having a child with anencephaly [9]. It is recommended to take a folic acid supplement daily as most women do not get the recommended amount (400 mcg) [10] of the vitamin from their regular diet.

How is anencephaly diagnosed?

Although, in most cases it is not diagnosed before the 15th and 18th week, it is possible to detect the defect much earlier (10th to 12th week) [11]. However, sometimes it is not possible to confirm the diagnosis before the baby is born.

Prenatal Diagnosis

  • Ultrasound examination
  • Blood test for detecting high levels of AFP (alpha-fetoprotein, produced by the fetal liver cells) as it indicates a neural tube defect [9]
  • Amniocentesis for assessing the levels of AFP and acetylcholinesterase (abnormally high levels indicate anencephaly or another NTD)
  • Fetal MRI (can be performed at any stage in pregnancy)

Diagnosis after Birth

The characteristic physical symptoms are enough for making and confirming the diagnosis after the baby is born [12].

Anencephaly

Anencephaly

Anencephaly Differential Diagnosis

  • Amniotic band syndrome (when a construction band goes through the head) [8]
  • Severe cases of microcephaly (small head with an underdeveloped brain)
  • Encephalocele (another NTD)
  • Exencephaly (sometimes considered to precede anencephaly)

Anencephaly Treatment and Management

There are no treatments for the absent or under-developed brain [9]. Aggressive resuscitation is not provided in many cases as it is not possible for the baby ever achieving a normal and conscious existence.

Doctors often recommend termination of pregnancy when the diagnosis is confirmed at the prenatal stage. Many anencephalic babies carried to full term do not even survive birth. Those who do are provided with clinical measures like nutrition, hydration and feeding assistance while their exposed brain areas are protected as well. Artificial ventilation, drug therapy (e.g. antibiotics) and surgery for correcting any organ defects are often regarded futile by physicians [13].

What is the life expectancy for anencephaly patients?

The survival rate is remarkably low with 7% of the affected babies dying in the womb, 20% dying during delivery and 50% living for only a few minutes to a day. The life expectancy for the rest (23%) of the patients ranges from a few days to a few weeks [14].

Anencephaly Incidence

It is considered the most common neural tube defect along with spina bifida, occurring in about 1 out of every 1,000 pregnancies. However, its prevalence in newborns is quite low as most women carrying an anencephalic child suffer miscarriage. In the United States, the incidence is estimated to be around 1 in 10,000 [5].

In some very rare cases, the babies survive for a few months to years, with the longest survivors including Nickolas Coke (3 years 11 months) from Pueblo, Colorado and Vitoria de Cristo (2 years five months) from Brazil [13].

What is the recurrence risk associated with anencephaly?

Ninety percent of infants born with anencephaly do not have any family history of this disorder. However, hereditary factors may play a role in some cases as parents who already had a baby with the condition are 4%-5% more likely to have another affected pregnancy [9]. The recurrence risk rises to 10%-13% with couples who had two babies with the defect.

What are the risks to the mother?

There is no substantial risk of complications for the mother, apart from premature contractions, water breaking and labor due to the polyhydramnios associated with anencephaly [15]. But the emotional distress is great for both parents.

Anencephaly ICD-9 and ICD-10 Codes

The ICD-9 code used for the condition is 740.0 [16] while its ICD-10 code is Q00.0 [17].

Anencephaly Support Group

NIH/National Institute of Neurological Disorders and Stroke

P.O. Box 5801

Bethesda, MD 20824

Fax: (301)402-2186

Tel: (301)496-5751

Email: [email protected]

Website: http://www.ninds.nih.gov/

Published on December 23rd 2013 by under Birth Defects.
Article was last reviewed on 23rd December 2013.

  • Comments

      One Response to Anencephaly

      1. kathleen Rogers says:

        My anaaesephalic baby died as she was being born. I wondered, since my husband was working on an experiment with silver nitrate and he had an accident with it (silver nitrate) being broken in the lab at the time of conception…could that have made the child develop this way? One wonders, why, why…we know of no other in the family. Thanks

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