Spina Bifida vs. Anencephaly: Neural Tube Defects Compared

Both are neural tube defects (NTDs) resulting from failure of neural tube closure during weeks 3–4 of embryogenesis. They represent a spectrum of severity.

Spina Bifida (Open Spinal Dysraphism)

• Pathology: Posterior neuropore fails to close → vertebral arch defect → meninges ± spinal cord protrude.
• Types:
  • Occulta: Closed skin defect only; often asymptomatic; tuft of hair, lipoma, dimple.
  • Meningocele: Meninges herniate; cord intact; minimal neurologic deficit.
  • Myelomeningocele (MMC): Cord + meninges herniate; most common & severe; paralysis, sensory loss, neurogenic bowel/bladder, Chiari II malformation, hydrocephalus (80–90%).
• Incidence: ~3–4/10,000 births (folic acid fortification reduced).
• Management: Prenatal (fetal surgery MOMS trial) or postnatal MMC repair; VP shunt for hydrocephalus; lifelong multidisciplinary care.

Anencephaly

• Pathology: Anterior neuropore fails to close → absence of cranial vault, cerebral hemispheres, skull; brainstem may persist.
• Outcome: Incompatible with sustained life; stillbirth or death within hours/days.
• Incidence: ~1–2/10,000 births.
• Prenatal diagnosis: Ultrasound (absent calvarium, "frog eye" sign); α-fetoprotein ↑ in maternal serum/amniotic fluid.

Shared Etiology & Prevention

• Folic acid (400–800 µg/day) preconception through 1st trimester → ↓ NTD risk by 50–70%.
• Risk factors: Prior NTD pregnancy, maternal diabetes, obesity, antiepileptics (valproate, carbamazepine), hyperthermia, genetic variants (MTHFR C677T).
• Recurrence risk: 2–3% after one affected pregnancy; higher with two.

Key Differences Summary

Feature	Spina Bifida (MMC)	Anencephaly
Neuropore	Posterior	Anterior
Brain	Intact (Chiari II)	Absent cerebral hemispheres
Survival	Variable; often decades with care	Hours–days; non-viable
Functional impact	Paralysis, neurogenic bladder/bowel, hydrocephalus	No consciousness

Folic acid fortification and preconception supplementation remain the most effective public health interventions for both conditions.