Hydrocephalus Basics

Hydrocephalus is an abnormal accumulation of cerebrospinal fluid (CSF) within the brain’s ventricular system and subarachnoid space. The accumulating fluid enlarges the ventricles and can impair brain function. CSF normally circulates through the ventricles, around the brain and spinal cord, and is absorbed into the bloodstream. Hydrocephalus develops when that system fails: CSF flow is obstructed, absorption is reduced, or—rarely—production exceeds absorption. A blockage at the cerebral aqueduct, for example, acts like a closed downstream valve: CSF continues to collect above the obstruction, stretching the ventricles. Obstructive, or noncommunicating, hydrocephalus occurs when a blockage lies within the ventricular pathways. Communicating hydrocephalus occurs when CSF can leave the ventricles but is not adequately absorbed from the subarachnoid space. Either pattern can raise intracranial pressure (ICP), although pressure and symptoms vary with the cause, acuity, and age of the patient. The infant skull can expand at its unfused sutures. Therefore, an infant may show accelerating head growth before severe headache is apparent. In an older child or adult with a rigid skull, even a modest increase in intracranial volume can produce headache,...