Anencephaly

Anencephaly is a congenital birth defect and a type of neural tube defect.

The disease is related to the following processes:  congenital and has an incidence of about  0 / 100.000.

Presentation

Anencephalic becomes apparent at birth. The neonates usually present with absence of the skull with exposed rudimentary brain tissue. There is also craniofacial disfiguration. The ears may be folded and cleft palate may also be present. There are a number of other defects including congenital heart defects.

Workup

  • Ultrasound is a valuable tool in early prenatal diagnosis of anencephaly [5]. Anomaly scans are usually performed during between the 15th and 20th week of gestation.
  • Amniocentesis is done for determining the levels of α fetoprotein (AFP) in the amniotic fluid [6] [7]. Higher levels of AFP are associated with a greater risk for the development of anencephaly and other neural tube defects.
  • Urine examination is done to determine the levels of estriol.
  • Blood tests are performed to evaluate the levels of α fetoprotein in the blood.
  • Fetal magnetic resonance imaging (MRI) is an important technique that can detect this condition prenatally. It can be performed at any time during pregnancy. Any fetal anomaly shows up at once.

Treatment

No current therapy is available for correction of this defect in-vitro or even after birth. Abortion upon early diagnosis of congenital anomalies on ultrasound is still debated upon due to ethical issues.

Supportive therapy is given to the neonates to keep them warm and to prevent the contact of exposed tissues with hazardous substances. The parents are also counselled and the mother is advised to take folic acid supplementation in the next pregnancy in order to prevent anencephaly and other neural tube defects.

Prognosis

Anencephaly is rarely compatible with life. 75 % of the cases are still born. The remaining 25 % of the neonates die within an hour or at the latest, a week after birth. Ideally, anomaly scans should be performed prenatally and if anencephaly is detected, the pregnancy should be terminated.

Etiology

Neural tube defects are implicated in the genesis of anencephaly and are caused by the following:

  • Folic acid (folate or vitamin B9) deficiency in expectant mothers [1] [2] [3].
  • Use of certain anti-epileptics, anti-diabetics, folate anti-metabolite drugs during pregnancy.
  • Exposure to mycotoxins or heavy metals during or just prior to pregnancy when organs are being formed.
  • Gene anomalies have also been implicated in the etiology of anencephaly. Changes in genes related to folic acid processing, especially methylenetetrahydrofolate reductase (MTHFR) contribute in the development to the disease. A membrane-associated signally complex protein encoding gene VANGL1 has also been detected in association with anencephaly. These, however, play a minor role [4].
  • Other factors playing a role in development of this condition include diabetes mellitus, obesity, and exposure to extremes of temperature in early pregnancy.

The condition is closely related to spina bifida, another of the neural tube defects in which spine fails to develop.

Epidemiology

Anencephaly is a sporadic disorder, with unequal geographical distribution. The prevalence of this condition is 1:10,000. The exact prevalence of anencephaly is unknown due to high incidence of miscarriages. The risk of anencephaly is higher in children born to women who have given birth to anencephalic children before. Female newborns are affected more as compared to males. Hispanics have a higher incidence of the disease as compared to Native Africans.

The reason for anencephaly for being relatively prevalent is that most of the neural tube defects arise during the 3rd and 4th week of pregnancy, the time when women are still unaware of pregnancy.

There is a slight familial tendency to anencephaly and it may run in families with a history of congenital birth defects. The pattern of inheritance is however, still unclear.

Sex distribution
Age distribution

Pathophysiology

Most of the organs develop during the 3rd and 4th week of pregnancy. Neural tube is the structure that gives rise to the central nervous tissues, brain and spinal cord in fetuses. Normally, neural tube starts as a sheet of cells that soon come together to form a tube and ultimately closes at 24th to 26th day. When the cephalic or the “head end” of the neural tube fails to close properly, the brain tissues are exposed to the surrounding amniotic fluid, the pressure of which causes regression of the tissues. As a result, brain tissues fail to develop. These cases are usually born with exposed head tissues. The remaining brain tissue is often not covered by meninges, skin or bone.

Although central brain stem might be present, the most of the forebrain, the cerebrum and cerebellum are absent in such babies. Although the breathing reflex is present in such babies, they never gain consciousness due to the absence of cerebrum.

Prevention

  • Folic acid should be incorporated in the diet of pregnant women [8] [9]. Multivitamin therapy containing folic acid is helpful in prevention. Folic acid supplementation should be started one month before pregnancy in case of planned pregnancies. At least 400 micrograms per day of folic acid should be taken. Women with family history of anencephaly or those who have taken anti-seizure drugs are usually recommended higher doses.
  • Food rich in folate, like asparagus, spinach, Brussels sprouts, green leafy vegetables, oranges, nuts, peas, beans, whole grains and beef liver should be incorporated in diet.
  • Routine ultrasounds should be done, especially in the first and the last trimester of pregnancy.
  • Avoiding smoking and alcohol consumption during pregnancy can also lower the risk [10].
  • Genetic counseling of parents should be done for assessment and strategy planning for the prevention of anencephalic births.

Summary

Anencephaly or “open skull” is a congenital anomaly of the neonates in which part of or whole of the head, brain or skull are absent. The children with anencephaly show gross facial and cephalic deformities. As a relatively prevalent disorder, anencephaly is one of the common causes of still births and neonatal deaths in high risk populations.

Patient Information

Anencephaly is partial or complete absence of brain and head. The children born with anencephaly are severely disfigured, having exposed internal head structures. Blindness and deafness is common in these children. The problem arises due to the deficiency of a vitamin, folic acid, in diet. Such babies usually die soon after they are born. Intake of folic acid during pregnancy can reduce the risk of this disorder.

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References

  1. Erickson JD. Folic acid and prevention of spina bifida and anencephaly. 10 years after the U.S. Public Health Service recommendation. MMWR. Recommendations and reports : Morbidity and mortality weekly report. Recommendations and reports / Centers for Disease Control. Sep 13 2002;51(RR-13):1-3.
  2. Oakley GP, Jr., Erickson JD, James LM, Mulinare J, Cordero JF. Prevention of folic acid-preventable spina bifida and anencephaly. Ciba Foundation symposium. 1994;181:212-223; discussion 223-231.
  3. Schorah CJ, Smithells RW, Scott J. Vitamin B12 and anencephaly. Lancet. Apr 19 1980;1(8173):880.
  4. Sergi C, Gekas J, Kamnasaran D. Recurrent anencephaly: a case report and examination of the VANGL1 and FOXN1 genes. Fetal and pediatric pathology. Jul 2013;32(4):293-297.
  5. Guibaud S, Bonnet M, Coicaud C, et al. [Ultrasonography and alpha fetoprotein determination: two complementary tests in the prenatal diagnosis of anencephaly]. Journal de genetique humaine. Mar 1980;28(1):61-62.
  6. Milunsky A, Alpert E, Charles D. Amniotic fluid alpha-fetoprotein in anencephaly. Obstetrics and gynecology. Apr 1974;43(4):592-594.
  7. Amniotic-fluid alpha-fetoprotein measurement in antenatal diagnosis of anencephaly and open spina bifida in early pregnancy. Second report of the U.K. Collaborative Study on Alpha-fetoprotein in Relation to Neural-tube Defects. Lancet. Sep 29 1979;2(8144):651-662.
  8. Youngblood ME, Williamson R, Bell KN, Johnson Q, Kancherla V, Oakley GP, Jr. 2012 Update on global prevention of folic acid-preventable spina bifida and anencephaly. Birth defects research. Part A, Clinical and molecular teratology. Oct 2013;97(10):658-663.
  9. Sever LE. Use of folic acid supplementation in the periconceptional period provides great promise for the primary prevention of the neural tube defects (NTDs), anencephaly, and spina bifida. Journal of nurse-midwifery. Sep-Oct 1992;37(5):350.
  10. Golding J, Butler NR. Maternal smoking and anencephaly. British medical journal. Aug 20 1983;287(6391):533-534.

  • A case-control study of pesticides and fetal death due to congenital anomalies - EM Bell, I Hertz-Picciotto, JJ Beaumont - Epidemiology, 2001 - journals.lww.com
  • A ten-year study of anencephaly - G Smilkstein - California medicine, 1962 - ncbi.nlm.nih.gov
  • Concentrations of iodothyronines and thyrotropin do not reliably predict fetal thyroid status in pregnancies complicated by maternal thyroid disorders or anencephaly - DR HOLLINGSWORTH - Journal of Clinical , 1983 - Endocrine Soc
  • Anencephalic infants as organ donors: a question of life or death - B Brandon - Case W. Res. L. Rev., 1989 - HeinOnline
  • Adrenal gland structure and the development of hyaline membrane disease - RL Naeye, HT Harcke Jr, WA Blanc - Pediatrics, 1971 - Am Acad Pediatrics
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