Failure of neural tube closure at the caudal neuropore (closes at ~day 27) results in which developmental anomaly?
- A Anencephaly
- B Encephalocele
- C Spina bifida (lumbosacral) ✓
- D Meningocele of the cervical spine
Explanation
The neural tube closes in a zipper-like fashion bidirectionally from the cervical region. The cranial neuropore closes at approximately day 25, and failure results in anencephaly. The caudal neuropore closes at approximately day 27, and failure results in spina bifida (lumbosacral level), as this is the last segment of the neural tube to close. Spina bifida lesions include spina bifida occulta, meningocele, and myelomeningocele. Encephalocele is due to a skull defect with herniation of brain/meninges, not simply neuropore failure. Folic acid supplementation reduces NTD risk by supporting thymidylate synthesis required for rapidly dividing neural tube cells.
Reference: BD Chaurasia's Human Anatomy, 8th ed.
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