Neural Tube Defects

Snapshot

• A 38-year-old woman at 12 weeks gestation presents to her obstetrician for prenatal care. She denies any vaginal discharge, bleeding, and at times notices fetal movement. She has a medical history of seizures. Laboratory testing is significant for an elevated α-fetoprotein level. On ultrasound, polyhydramnios is appreciated with an absence of the brain and calvaria. It was explained to her that her fetus is diagnosed with anencephaly.

Introduction

• Embryology
  • neurulation
    • at the third week of gestation
    • the process of neural tube formation which gives rise to the
      • spinal cord and cerebrum
    • impairment in neurulation results in
      • neural tube defects
    • process
      • the notocord induces the formation of the neural plate
      • the neural plate (neuroectoderm) will give rise to the central nervous system
        • elevation of the lateral edges of the neural plate develop
          • the neural folds which eventually form the
            • neural tube
      • the neural tube fuses in the
        • cervical region and then fuses
          • in both the cephalad and caudal direction, eventually forming the
            • cranial neuropore
              • closes on day 25
              • forms three primary vesicles
                • forebrain (prosencephalon) which forms into
• telencephalon
• diencephalon
  • midbrain (mesencephalon) which forms into
• mesencephalon
  • hindbrain (rhombencephalon) which forms into
• metencephalon
• myelencephalon
  • caudal neuropore 
    • closes on day 27
      • failure to close leads to spina bifida
  • the neural crest cells give rise to the
    • peripheral nervous system and non-neural structures
• Etiologies
  • folic acid deficiency 
  • syndromes such as
    • Chiari II malformation
  • medications such as
    • valproic acid and other
      • folic acid antagonists such as
        • carbamazepine
        • phenobarbital
        • phenytoin
        • sulfasalazine
        • triamterene
        • trimethoprim

Neural Tube Defects