Etiology

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• Maternal risk factors
  • Folate deficiency during pregnancy due to:
    • Insufficient folate supplementation
    • Drugs that interfere with folate metabolism
      • Methotrexate
      • Anticonvulsants: valproate, carbamazepine
      • Sulfonamides, trimethoprim
• Pregestational diabetes mellitus

Closed spinal dysraphism

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Spina bifida occulta

• Description
  • Most common closed NTD
  • Cause: failure of vertebral arch fusion
  • Vertebral bone defect without herniation
  • The spinal cord, meninges, and overlying skin remain intact.
• Clinical features
  • Most commonly affects the lower lumbar or sacral region
  • Often asymptomatic (may be an incidental finding in imaging)
  • Possible symptoms at the level of the vertebral defect:
    • Lumbar skin dimple
    • Collection of fat
    • Patch of hair
• Diagnostics
  • Normal AFP

Diagnostics

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Prenatal period

• Screening test (16–18 weeks’ gestation): ↑ AFP in maternal serum (MSAFP)
  • MSAFP is only elevated in open NTDs.
    • Because the fetal tissues (which are producing AFP) are directly exposed to the amniotic fluid, there is a significantly increased leakage of AFP from the fetus into the amniotic fluid.
  • MSAFP is not elevated in spina bifida occulta.
• Ultrasonography (18–20 weeks’ gestation)
  • Characteristic findings depend on the specific defect.
    • Findings in anencephaly
      • Cranial vault and brain tissue are absent.
      • Residual, disorganized cerebellar and/or brainstem tissue may be present.
      • Bulging eyes and underdeveloped forehead
      • Associated with polyhydramnios
• Amniocentesis: ↑ AFP and ↑ AChE in amniotic fluid (increase in open NTDs only)
  • During fetal development, AChE is present in the developing nervous system tissues, including the neural tube.
  • Used as confirmation test when MSAFP is elevated but ultrasound findings are inconclusive
  • When both AFP and AChE are elevated, an open NTD is very likely.