Anencephaly

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Anencephaly
Anencephaly side.jpg
The side view of the head of an anencephalic fetus
ICD-10 Q00.0
ICD-9 740.0
OMIM 206500
DiseasesDB 705
MeSH C10.500.680.196

Overview

Anencephaly is a cephalic disorder that results from a neural tube defect that occurs when the cephalic (head) end of the neural tube fails to close, usually between the 23rd and 26th day of pregnancy, resulting in the absence of a major portion of the brain, skull, and scalp. Children with this disorder are born without a forebrain, the largest part of the brain consisting mainly of the cerebral hemispheres (which include the isocortex, which is responsible for higher level cognition, i.e., thinking). The remaining brain tissue is often exposed - not covered by bone or skin.

Historical Perspective

Classification

Pathophysiology

The cause of anencephaly is disputed. Neural tube defects do not follow direct patterns of heredity, though there is some indirect evidence of inheritance[1], and recent animal models indicating a possible association with deficiencies of the transcription factor TEAD2.[2]

Etiology and Risk factors

Folate deficiency

Drugs

Genetics

Syndromes

Anencephaly is associated with

  1. Trisomy 13 or 18
  2. Meckel-Gruber syndrome
  3. Roberts syndrome
  4. Jarcho-Levin syndrome
  5. HARD (hydrocephalus, agyria and retinal dysplasia)
  6. OEIS complex (omphalocele, exstrophy of the cloaca, imperforate anus and spinal defects)
  7. Limb-body wall complex (LBWC)

Amniotic bands

If a pregnant mother develops amniotic bands, it could effect the normal development and growth of the central nervous system. It could result in neural tube defects including anencephaly

Pregestational diabetes

Maternal Obesity

Toxins

Anencephaly and other physical and mental deformities have also been blamed on a high exposure to such toxins as lead, chromium, mercury, and nickel. [3]

Differentiating Anencephalopathy from other Disorders

There are many false diagnoses for anencephaly, as it is not a common diagnosis, often confused with exencephaly or microcephaly.

Epidemiology and Demographics

Incidence

In the United States, approximately 1,000 to 2,000 babies are born with anencephaly each year. In 2001, the National Center for Health Statistics reported 9.4 cases among 100,000 live births

Demographics

The highest prevalence has been seen among the Hispanic population. Female babies, whites and children born to mothers who are at extreme of ages are more likely to be affected by the disorder. Worldwide, Ireland and British Islands has higher prevalence as compared to Asia and Africa which has a lower prevalence rate.

Recurrence rate

Like any other neural tube defect, the recurrence rate of anencephaly is 2-4% if one sibling is affected and 10 percent if two siblings are affected. This familial tendency is due to genetics, environmental factors, or both.

Risk Factors

Studies show that a woman who has had one child with a neural tube defect such as anencephaly, has about a 3% risk to have another child with a neural tube defect. It is known that women taking certain medication for epilepsy and women with insulin dependent diabetes have a higher chance of having a child with a neural tube defect. Genetic counseling is usually offered to women at a higher risk of having a child with a neural tube defect to discuss available testing.

Screening

Natural History, Complications, Prognosis

There is no cure or standard treatment for anencephaly and the prognosis for affected individuals is poor. Most anencephalic babies do not survive birth, accounting for 55% of non-aborted cases. If the infant is not stillborn, then he or she will usually die within a few hours or days after birth from cardiorespiratory arrest.

In almost all cases anencephalic infants are not aggressively resuscitated since there is no chance of the infant ever achieving a conscious existence. Instead, the usual clinical practice is to offer hydration, nutrition and comfort measures and to "let nature take its course". Artificial ventilation, surgery (to fix any co-existing congenital defects), and drug therapy (such as antibiotics) are usually regarded as futile efforts. Clinicians and medical ethicists may view the provision of nutrition and hydration as medically futile. Occasionally some may even go one step further to argue that euthanasia is morally and clinically appropriate in such cases.

Prenatal screening and diagnosis

Ultrasound

Anencephaly can often be diagnosed before birth through an ultrasound examination. The maternal serum alpha-fetoprotein (AFP screening)[4] and detailed fetal ultrasound[5] can be useful for screening for neural tube defects such as spina bifida or anencephaly.

Diagnostic Criteria

Clinical features

Infants born with anencephaly are usually blind, deaf, unconscious, and unable to feel pain.

Physical Examination

Neurologic

Reflex actions such as breathing and responses to sound or touch may occur. Although some individuals with anencephaly may be born with a rudimentary brainstem, which controls autonomic and regulatory function, the lack of a functioning cerebrum is usually thought of as ruling out the possibility of ever gaining consciousness, even though it has been disputed specifically. [6]

Laboratory Findings

Imaging Findings

Other Diagnostic Studies

Management

So far, prevention is the best management of anencephaly.

Medical Therapy

Surgery

At his point in time there are no surgical options available.

Prevention

Recent studies have shown that the addition of folic acid to the diet of women of child-bearing age may significantly reduce, although not eliminate, the incidence of neural tube defects. Therefore, it is recommended that all women of child-bearing age consume 0.4 mg of folic acid daily, especially those attempting to conceive or who may possibly conceive, as this can reduce the risk to 0.03%.[7] It is not advisable to wait until pregnancy has begun, since by the time a woman knows she is pregnant, the critical time for the formation of a neural tube defect has usually already passed. A physician may prescribe even higher dosages of folic acid (4 mg/day) for women who have had a previous pregnancy with a neural tube defect.

Pregnancy management

Anencephaly has a poor pregnancy outcome. Majority of the fetuses are either stillborn or die soon after birth, however, few infants do manage to live up to 28 days. Therefore, mothers are counselled regarding the termination soon after the prenatal diagnosis. Vaginal delivery is the preferred mode unless there are any maternal indications


References

  1. Shaffer LG, Marazita ML, Bodurtha J, Newlin A, Nance WE (1990). "Evidence for a major gene in familial anencephaly". Am. J. Med. Genet. 36 (1): 97–101. doi:10.1002/ajmg.1320360119. PMID 2333913.
  2. Kaneko KJ, Kohn MJ, Liu C, Depamphilis ML (2007). "Transcription factor TEAD2 is involved in neural tube closure". Genesis. 45 (9): 577–87. doi:10.1002/dvg.20330. PMID 17868131.
  3. Goldsmith, Alexander (1996, quoted by Millen and Holtz, "Dying for Growth")
  4. Joó JG, Beke A, Papp C; et al. (2007). "Neural tube defects in the sample of genetic counselling". Prenat. Diagn. 27 (10): 912–21. doi:10.1002/pd.1801. PMID 17602445.
  5. Cedergren M, Selbing A (2006). "Detection of fetal structural abnormalities by an 11-14-week ultrasound dating scan in an unselected Swedish population". Acta obstetricia et gynecologica Scandinavica. 85 (8): 912–5. doi:10.1080/00016340500448438. PMID 16862467.
  6. Merker B (2007). "Consciousness without a cerebral cortex: a challenge for neuroscience and medicine". The Behavioral and brain sciences. 30 (1): 63–81, discussion 81–134. doi:10.1017/S0140525X07000891. PMID 17475053.
  7. anencephaly at NINDS

de:Anenzephalie it:Anencefalia he:אננצפלוס nl:Anencefalie fi:Aivottomuus sv:Anencefali



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