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 Neural Tube Defects Neural Tube Defect Comments Anencephaly Cranial neural tube is exposed due to failure of the rostral neuropore to close at day 25 Findings ↑ AFP ultrasonography shows absence of the brain and calvaria polyhydramnios This is not compatible with survival Spina bifida occulta Secondary tofailure of the caudal neuropore to close without herniation Findings normal AFP tuft of hair or skin dimple at site of bony defect Spina bifida with meningocele Secondary to failure of the caudal neuropore to close with protusion of the meninges through the bony defect Findings ↑ AFP associated with spina bifida cystica Spina bifida with meningomyelcele Secondary to failure of the caudal neuropore to close with protusion of the meninges and spinal cord through the bony defect Findings ↑ AFP associated with Chiari II malformation Spina bifida with myeloschisis Secondary to failure of the caudal neuropore to close with the spinal cord able to be seen externally Findings ↑ AFP ↑ AChE