Most babies born with spina bifida have hydrocephalus. In addition to the lesion in the spinal cord, structural abnormalities in parts of the brain can develop before birth. This prevents proper drainage of the CSF which increases the pressure and can compress the brain further.
Open spina bifida is strongly associated with hydrocephalus. Although the baby may not have enlarged ventricles before birth, once the surgery to close the spina bifida lesion is carried out, the CSF may have nowhere to go. It accumulates in the ventricles, resulting in hydrocephalus. Checking the baby’s head circumference in the early days after back surgery usually picks this up, so the baby can be treated.
Some babies with spina bifida develop hydrocephalus in the womb, as the Chiari II (a problem with the cerebellum associated with open spina bifida) disrupts the CSF flow.