A newborn is noted to have a large meningomyelocele at the lumbosacral level, with neural tissue exposed and paraplegia below L3. This defect results from failure of which embryological process?
- A Secondary neurulation — failure of caudal cell mass canalization
- B Neural crest cell migration
- C Primary neurulation — failure of posterior neuropore closure ✓
- D Notochord induction of overlying ectoderm
Correct answer: C. Primary neurulation — failure of posterior neuropore closure
Explanation
Primary neurulation involves folding of the neural plate to form the neural tube; the posterior (caudal) neuropore normally closes by day 27 of development. Failure of posterior neuropore closure at the lumbosacral level results in spina bifida cystica, specifically meningomyelocele, where spinal cord and meninges herniate through the vertebral defect. The accompanying neurological deficit (paraplegia) arises from the exposed, dysplastic spinal cord tissue. Maternal folate deficiency is the major preventable risk factor.
Reference: BD Chaurasia's Human Anatomy, 8th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.