This is a condition where there is a problem with cerebrospinal fluid (CSF), which surrounds the brain and spinal cord. CSF normally moves around the brain and spinal cord, cushioning it, and is eventually absorbed into the bloodstream. Levels can rise if the flow is blocked, if CSF is not properly absorbed or the brain is making too much of it. Too much CSF puts pressure onto the brain. The condition is common in babies who have open neural tube defects, where the spinal column does not close properly. Genetic abnormalities and certain infections can also cause hydrocephalus.

Before birth, ultrasound may show enlargement of the ventricles of the brain. This may prompt further evaluation with fetal MRI.

Prognosis is largely dependent on the cause. Hydrocephalus not caused by infection generally has the best outlook.

Hydrocephalus caused by neural tube defects may improve  after in utero closure of the spinal defect. Other causes of hydrocephalus are usually treated after the baby is born, often by placing a shunt which is a drainage tube into the enlarged ventricles to remove excess CSF into the peritoneal cavity.