anencephaly

Anencephaly is a severe congenital neural tube defect in which the cephalic (head) end of the neural tube fails to close during early embryogenesis, usually by the 28th day after conception. This results in the absence of a major portion of the brain and skull, leaving a rudimentary brainstem and exposed neural tissue. The condition is incompatible with long-term survival, and affected infants rarely live beyond the first hours or days after birth.

The cause is multifactorial, involving genetic susceptibility and environmental influences. Known risk factors include maternal folate deficiency, maternal diabetes, and exposure to certain anticonvulsant medications (such as valproate) during early pregnancy. The recurrence risk after one affected pregnancy is higher than in the general population, though precise risk varies with family history and other factors.

Prenatal diagnosis is possible through screening tests such as maternal serum alpha-fetoprotein and fetal ultrasound, typically conducted in the first or second trimester. Ultrasound findings may show absence of the cranial vault and exposed brain tissue, with MRI providing additional detail when needed. Postnatal diagnosis relies on physical examination and imaging studies.

There is no curative treatment for anencephaly. Management focuses on counseling and palliative care; decisions about pregnancy continuation or termination may be made based on gestational age, local laws, and parental preferences. Prevention relies on folic acid supplementation before conception and during early pregnancy, which reduces the risk of neural tube defects in general. Public health measures such as folic acid fortification have contributed to lower NTD rates in many regions.