Postnatal surgery, or surgery that occurs post-birth, was very common in the past. In the case of myelomeningocele, it involved closure of the sac protruding from the spinal cord in order to prevent infection. Nonetheless, postnatal surgery does not prevent the developed myelomeningocele. To learn more, be sure to check out this study by Sileo et al., 2019: https://obgyn.onlinelibrary.wiley.com/doi/full/10.1002/uog.20215
This is a more traditional type of surgery, and is performed around 24-48 hours after birth by a neurosurgeon, aiming to close the gap in the spine.
Hydrocephalus is a buildup of fluid in the brain. To minimize pressure in the brain, it would require postnatal surgery for shunt placement.