A stillborn fetus shows absence of the cranial vault with exposed, disorganized brain tissue. The maternal serum alpha-fetoprotein was markedly elevated. This anomaly results from failure of closure of which structure?

• A Anterior neuropore ✓
• B Posterior neuropore
• C Cranial neuropore only at the level of the fourth somite
• D Rostral membrane of the fourth ventricle

Explanation

Anencephaly results from failure of closure of the anterior (rostral) neuropore around day 25, leaving the brain open to amniotic fluid with subsequent degeneration of exposed tissue and absence of the calvaria. Because neural tissue is exposed, alpha-fetoprotein leaks into amniotic fluid and maternal serum, rising markedly. Failure of posterior neuropore closure produces spina bifida variants involving lower spinal levels, not the cranium.

Reference: Langman's Medical Embryology, 14th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.