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Congenital hydrocephalus is a condition present at birth in which excess cerebrospinal fluid (CSF) collects within the brain. The brain's passageways (ventricles) may not drain or absorb fluid properly, leading to increased pressure within the brain. Early treatment—within a baby's first 3 to 4 months—is important to help limit or prevent brain damage.

Usually a baby with congenital hydrocephalus will have a noticeably bigger head than other babies the same age.