Hydrocephalus occurs when there is active distention of the ventricular system of the brain. It can result from abnormal cerebrospinal fluid (CSF) production, obstruction of CSF flow, or impaired CSF absorption. It can be congenital (eg, aqueductal stenosis) or acquired (eg, meningitis). There are communicating and noncommunicating forms of hydrocephalus.

Noncommunicating hydrocephalus is due to an obstruction of CSF flow within the ventricular system. Some cases are due to congenital malformations affecting the ventricular system, whereas other cases are due to mass lesions or tumors compressing part of the ventricular system.

Communicating hydrocephalus occurs when there is no obvious sign of obstruction within the ventricular system and is often due to impaired CSF absorption in the arachnoid villi surrounding the brain. Causes of communicating hydrocephalus include overproduction of CSF due to choroid plexus tumors, normal pressure hydrocephalus, and sequelae of meningitis or subarachnoid hemorrhages.

Increases in intracranial pressure (ICP) usually accompany the development of hydrocephalus. Signs and symptoms usually reflect increased ICP and may include headache, nausea / vomiting, and papilledema. Infants with hydrocephalus can develop an enlarged head circumference and a bulging anterior fontanelle. Due to their closed fontanelles, older children may experience more acute manifestations including diplopia, lethargy, seizures, bradycardia, or sixth-nerve palsies. Acute cases of hydrocephalus can lead to hemodynamic instability, coma, or death. Chronically, patients can develop intellectual impairment or memory changes, coordination and motor problems, urinary incontinence, and visual impairments.

Hydrocephalus due to an acute increase in ICP is a medical emergency and can potentially become fatal without neurosurgical intervention. Patients with more indolent hydrocephalus who lack symptoms of increased ICP can sometimes be monitored clinically and radiologically. Definitive treatment of hydrocephalus usually requires the placement of a ventriculoperitoneal shunt; however, there are several other treatment options available for select patient populations. Prognosis depends on the cause of hydrocephalus and timing of medical intervention.