Why are some people born with hydrocephalus?

A structural defect: The body is assembled by the organization of a very large number of cells into various structures. One such structure is the sac that holds the brain and spinal cord suspended in a fluid, a system that is a very effective shock absorber. If the production of that fluid exceeds its drainage, too much accumulates, and that is hydrocephalus.

Fetal defects.: Open neural tube defect such as spina bifida; fetal torch infections; stenosis of the sylvian aqueduct; agenesis of the corpus callosum; dandy-walker posterior fossa cyst; intracranial hemorrhage/tumors; porencephaly/schizencephaly are among the most common etiologies. >90% of spina bifida or encephalocele cases can be prevented with Folic Acid 1-5 mg orally preconceptionally.