Hydrocephalus is a medical condition in which there is an abnormal accumulation of cerebrospinal fluid (CSF) within the brain's natural fluid containing spaces called ventricles. This causes increased intracranial pressure inside the skull. In infants and young children, whose skull bones are not yet fused together, this can produce progressive enlargement of the head. In older children or adolescents, whose skull bones are more rigidly fused, the increased pressure inside the head can cause headache, nausea, visual impairment, lethargy, seizures and mental disability.
Hydrocephalus can be caused by congenital or acquired factors. Congenital causes include Arnold–Chiari malformation, craniosynostosis, Dandy–Walker syndrome, and Vein of Galen malformations. Acquired causes include hemorrhage, meningitis, head trauma, tumors, and cysts.
The two types of hydrocephalus are non-communicating hydrocephalus and communicating hydrocephalus.
In non-communicating hydrocephalus, the cerebral fluid within the brain in ventricles is obstructed such that it cannot flow out to the water space that surrounds the brain, called the subarachnoid space. This obstruction may occur in passageways between the ventricles (the foramen of Monroe or the aqueduct of Silvius) or the outflow passageways (the foramen of Luschka and the foramena of Magendie), which conduct the water to the subarachnoid cisterns located at the base of the skull. Such blockage of cerebral fluid flow causes expansion of the ventricles located proximal to the point of obstruction.
In communicating hydrocephalus, the cerebral fluid flows into and through all of the normal brain fluid spaces, but if fails to undergo effective re-absorption back into the venous bloodstream so for that reason backs up and expands all of the brain ventricles. This type of hydrocephalus commonly occurs after prior meningitis infection or prior hemorrhage into either the ventricles or the subarachnoid fluid space.
Treatment of hydrocephalus usually requires either implantation of tubing, called a shunt, to conduct the trapped cerebral fluid outside of the head to another part of the body where it can be reabsorbed in the bloodstream. In some cases of obstructive hydrocephalus, though, an endoscope can be used to create an opening, called an ostomy, which routes the cerebral fluid around the obstruction within the brain.