Neural tube defects and spinal dysraphism: Viva

Branch 1: Classification and definition

The candidate should define neural tube defects as the failures of the neural tube to close during the third and fourth week of embryogenesis, and give the open and closed classification. The open defects expose neural tissue to the amniotic fluid and include anencephaly, the encephalocele, and the myelomeningocele. The closed defects cover the malformation with skin and include the meningocele, the spina bifida occulta, and the occult dysraphic states. ^[1]

If the examiner presses for the occult dysraphic states, the candidate should name the lipomyelomeningocele, where a lipoma tethers the conus, the diastematomyelia, where a bony spur splits the cord, the dermal sinus tract, where an epithelial track runs to the spinal canal, and the tethered cord syndrome, where a thickened fatty filum anchors the cord. A strong candidate explains that the open lesion is the neonatal emergency while the tethered cord is the childhood problem, and that the Chiari II malformation and the hydrocephalus belong almost exclusively to the myelomeningocele phenotype. ^[1]