Anencephaly

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Anencephaly is characterized by a total (holo) or partial (mero) absence of the brain with absence of the cranial vault (calvaria) and covering skin.

Fig. 2. Anencephaly

Fig. 2. Anencephaly

Photograph sources: Latin American Collaborative Study of Congenital Malformations (ECLAMC); CDC–Beijing Medical University collaborative project.

Key findings in anencephaly (see Fig. 2):
  1. Type – holoanencephaly (panel a: total absence) is the most common type of anencephaly; meroanencephaly (panel b: partial absence).
  2. Covering – no skin covering residual brain tissue or cranial vault (calvarium).

Diagnosis

Prenatal. Anencephaly is diagnosed prenatally but should always be confirmed postnatally. Use programme rules (standard operating procedures [SOPs]) to decide whether to accept or not accept prenatal diagnoses without postnatal confirmation (e.g. in cases of termination of pregnancy or unexamined fetal death).

Postnatal. The newborn examination confirms the diagnosis and will distinguish anencephaly from the other anomalies of the brain and cranium.

Clinical and epidemiologic notes

Anencephaly is a lethal condition and is often an isolated, non-syndromic anomaly.
  • Eyes are normally formed; bulging is a result of absence of the frontal portion of the cranial vault.
  • Cerebellum, brain stem and spinal cord are intact.
Additional clinical tips:
  • Anencephaly can be confused with:
    • Craniorachischisis characterized by anencephaly plus rachischisis, a contiguous upper spine defect without meninges covering the neural tissue.
    • Amniotic band or limb-body wall spectrum, which have other findings (facial schisis, limb and ventral wall anomalies, bands) and allow the differentiation from typical anencephaly

Checklist for high-quality reporting

Anencephaly – Documentation Checklist
Describe defect in detail:
  • Extent – holoanencephaly versus meroanencephaly.
  • Cervical spine – document no contiguous defects.
  • Whether a non-contiguous spina bifida is present (location).
  • Whether amniotic bands are present
  • Take and report photographs: Show clearly  the missing cranium; can be crucial for review.
  • Describe evaluations to find or rule out related and associated anomalies: 
  • Eyes protruding but normally developed (do not include as an associated anomaly).
  • Head circumference will be small – do not code as microcephaly.
  • Report whether autopsy (pathology) findings are available and if so, report the results.
Page last reviewed: March 10, 2021
Content source: Division of Birth Defects and Developmental Disabilities, NCBDDD, Centers for Disease Control and Prevention