Failure of neuropore closure during the fourth week of gestation can produce either cranial or caudal neural tube defects depending on which neuropore fails. Anencephaly specifically results from failure of closure of the:

• A Posterior neuropore
• B Anterior neuropore ✓
• C Neural plate hinge points only
• D Rostral neuropore with intact cranial vault

Explanation

The rostral or anterior neuropore closes around day 25 and the caudal or posterior neuropore around day 27. Failure of anterior neuropore closure prevents brain and calvarial development, producing anencephaly with an open defect and absence of the skull vault; these fetuses show elevated maternal serum AFP. Posterior neuropore failure produces spina bifida aperta variants such as myelomeningocele. Elevated amniotic fluid acetylcholinesterase alongside raised AFP helps confirm open defects prenatally.

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

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Written and medically reviewed by the StethoPrep medical team.