Malabsorption of CSF may be caused by congenital abnormalities, infection, hemorrhage, trauma or neoplasm. Electron microscopic changes are consistent with reduced activity of the choroid plexus and flattened ependyma. The most common congenital abnormalities causing CSF malabsorption are stenosis of the aqueduct of Sylvius and myelomeningocele. Patients with hereditary X-linked hydrocephalus are usually retarded and display multiple other CNS abnormalities, frequently agenesis of the corpus callosum. Mutations in the gene encoding the L1 neuron adhesion molecule have been described and may be responsible for this disorder.
Intraventricular hemorrhage is the most common cause of hydrocephalus among premature infants.
Small premature infants are more likely to have such a hemorrhage, and the larger the hemorrhage, the worse the neurological prognosis. One half of tumors in the pediatric age group are in the posterior fossa, where the cerebellum and brain stem are housed. Children with brain tumors are thus particularly prone to present with hydrocephalus. Head trauma, and subarachnoid hemorrhage in older age groups probably cause hydrocephalus by hemorrhage into, and scarring of, the subarachnoid spaces at the base of the brain. Venous outflow obstruction from the cranium may also cause CSF malabsorption.