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Definition: Anencephaly from Black's Medical Dictionary, 43rd Edition

The term given to the condition in which a child is born with a defect of the skull and absence of the cerebral hemispheres; the brain stem and cerebellum are also atrophic. It has an incidence of 0·65 per 1,000 live births. Miscarriage (or therapeutic abortion) are common but if the pregnancy goes to term the infants do not live very long. It is possible to detect the presence of anencephaly in the fetus by measuring the level of ALPHA-FETO PROTEIN in the mother's serum or in the amniotic fluid. (See also SPINA BIFIDA.)


Summary Article: Anencephaly
From The Encyclopedia of Neuropsychological Disorders
DESCRIPTION

Anencephaly is a neural tube defect that develops as a result of the rostral neuropore failing to close during the third and fourth weeks of gestation. Anencephaly corresponds with a broader spectrum of disorders called cephalic disorders, referring to improper development of the brain and head. At birth, infants present with an absence of a major portion of the brain, skull, and scalp (Beers, Porter, & Jones, 2006). This leads to the infant being born without a forebrain or cerebrum and often without bone and skin (Golden & Bonnemann, 2007).

Although a brainstem may be present, which may correspond with reflexive actions such as breathing and response to sound and touch, the absence of the forebrain and cerebrum eliminates the possibility of infants ever gaining consciousness. At most, infants are born unconscious and present as blind, deaf, and unable to feel pain. Although most fetuses succumb to spontaneous abortion or are stillborn, those who survive birth usually die within a few days (Dox, Melloni, Eisner, & Melloni, 2002) and none live past infancy (Judd, 2007). Consequently, there is no treatment for anencephaly. Rather, regulation of the mother's diet, particularly supplementation with folic acid, has been shown to significantly reduce the incidence of anencephaly as well as other neural tube defects.

NEUROPATHOLOGY/PATHOPHYSIOLOGY

Anencephaly occurs in 0.1–0.7 per 1,000 births, and females predominate in ratios ranging between 3:1 and 7:1 (Ropper & Brown, 2005). Although the cause of anencephaly is unknown, theories have emerged. As with many presentations, genetics has been suggested as a potential source of risk for the presentation. There is a 3% increased chance for anencephalic development if one prior pregnancy has presented with the defect, and there is as high as a 10% chance if this has occurred for more than two prior pregnancies. However, it is noted that 95% of anencephalic defects occur in families with no reported history of the disease (Beers et al., 2006).

Geographic location has also been associated with the presentation. For example, higher incidence of anencephaly has been noted in Ireland and Wales than in comparison to the United States and France. This has led some to postulate the role of population genetics and environmental toxins in the development of anencephaly. However, geographic location also influences dietary practices that themselves are linked to anencephaly and other neural tube defects. As a result, the true role of geographical location in the risk of anencephaly requires further investigation as it may be an indirect correlate.

Regarding diet, although its role in the manifestation of anencephaly is still being investigated and debated (Harding & Copp, 1997), compelling evidence exists suggesting the role of folic acid in the development of the presentation. Specifically, taking folic acid supplements during the first trimester has been shown to significantly reduce the incidence of anencephaly as well as various other neural tube defects.

Infants with anencephaly present without the cerebral cortex and white matter of the brain, as well as large portions of the scalp and cranial bones. The brainstem, cerebellum, and spinal cord are generally present, but may be malformed themselves. Specifically, aplasia of descending tracts is commonly noted in the medulla and spinal cord, and the spinal leptomeninges are excessively vascular and contain islands of heterotopic neurological tissue (Bell, Gordon, & Maloney, 1981). A hemorrhagic nubbin of nerve, glial, and connective tissue is often viewable (Ropper & Brown, 2005).

NEUROPSYCHOLOGICAL/CLINICAL PRESENTATION

Anencephaly always leads to death, with 65% of fetuses dying in utero (Ropper & Brown, 2005). Of those infants that make it to the full term, most die within a few days after birth or are stillborn (Dox et al., 2002). Surviving infants do not live past infancy (Judd, 2007). For those that survive for this short amount of time, they are unconscious, blind, deaf, and unable to feel pain. Nevertheless, they will many times respond reflexively to stimuli from touch and sound and also breathe reflexively (Judd, 2007). Spontaneous movements of limbs may be observed as can papillary light reactions, ocular movements, corneal reflexes, and, in a few, crying and feeding reflexes (Ropper & Brown, 2005).

DIAGNOSIS

Anencephaly is usually diagnosed in very specific ways. With refined imaging in ultrasound, neural tube defects, including anencephaly, are being identified earlier in the pregnancy (Cuckle, 1994). In addition, anencephaly can be anticipated if the mother's serum levels of α-fetoprotein (AFP) and acetylcholine esterase are elevated (Ropper & Brown, 2007). More accurate predictions can be obtained by analyzing the level of AFP in the amniotic fluid by way of an amniocentesis (Brock & Sutcliffe, 1972).

TREATMENT

There is no treatment for anencephaly, and the prognosis is extremely poor with the few infants that do not die in utero or present as stillborn dying a few hours to days after birth. Consequently, treatment is supportive in nature and directed at parents and family.

Although there is no intervention that may be implemented, as suggested, preventive measures can be taken in the form of dietary supplementation with folic acid at about 0.4 mg per day. This has been shown to decrease the likelihood of most neural tube defects by as much as 70% (Judd, 2007).

Bibliography
  • Beers, M. H.; Porter, R. S.; Jones, T. V. (2006). The Merck manual of diagnosis and therapy (18th ed.). Merck Whitehouse Station, NJ.
  • Bell, J. E.; Gordon, A.; Maloney, A. F. J. (1981). Abnormalities of the spinal meninges in anencephalic fetuses. Journal of Pathology, 133, 131-144.
  • Brock, D. J. H.; Sutcliffe, R. G. (1972). Alpha-fetoprotein in the antenatal diagnosis of anencephaly and spina bifida. Developmental Medicine and Child Neurology, 23, 155-159.
  • Cuckle, H. S. (1994). Screening for neural tube defects. In G. Bock; J. Marsh (Ed.), Neural tube defects (pp. 253-266). John Wiley Chichester.
  • Dox, I. G.; Melloni, B. J.; Eisner, G. M.; Melloni, J. L. (2002). Melloni's illustrated medical dictionary (4th ed.). The Parthenon Publishing Group London.
  • Golden, J. A.; Bonnemann, C. G. (2007). Developmental structural disorders. In Goetz, C. G. (Ed.), Textbook of clinical neurology (3rd ed.,pp. 561-591). Saunders Elsevier Philadelphia.
  • Harding, B.; Copp, A. J. (1997). Malformations. In D. I. Graham; P. L. Lantos (Eds.), Greenfield's neuropathology (6th ed.,pp. 397-533). Oxford University Press New York.
  • Judd, S. (Ed.) (2007). Congenital disorders sourcebook. Omnigraphics Detroit, MI.
  • Ropper, A.H. Brown, R.H. (2005). Adams and Victor's Principles of Neurology (8th Ed.). McGraw-Hill (pp New York. 850-894).
  • J. Aaron Albritton
    Chad. A Noggle
    Copyright © 2011 Springer Publishing Company

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