Hydrocephalus: Hydrocephalus is an abnormal buildup of cerebrospinal fluid (CSF) in the ventricles of the brain. The fluid is often under increased pressure and can compress and damage the brain.

Hydrocephalus can arise before birth or any time afterward. It may be due to many causes including a birth defect, hemorrhage into the brain, infection, meningitis, tumor, or head injury. Most forms of hydrocephalus are the result of obstructed CSF flow in the ventricular system. With birth defects, physical obstruction of CSF flow in the ventricular system is usually the cause of the hydrocephalus. Hydrocephalus is a common companion of spina bifida (meningomyelocele).

What is termed "hydrocephalus ex-vacuo" occurs when there is damage to the brain caused by stroke or injury, and there may be an actual shrinkage of brain substance. "Hydrocephalus ex-vacuo" is essentially only hydrocephalus by default; the CSF pressure itself is normal.

Normal pressure hydrocephalus (NPH) can also occur due to a gradual blockage of the CSF drainage pathways in the brain. Although the ventricles enlarge, the pressure of the CSF remains within normal range. NPH is characterized by memory loss (dementia), gait disorder, urinary incontinence and a general slowing of activity.

In old age or persons with Alzheimer's disease, the entire brain may shrink and the CSF fills up the space created by the shrinkage. This is not due to hydrocephalus.

The diagnostic signs and symptoms of hydrocephalus depend upon the age of the person:

• In infants the most obvious sign of hydrocephalus is usually an abnormally large head. (That is one reason a baby's head should be measured at every well-baby visit). Symptoms of hydrocephalus in an infant may include vomiting, sleepiness, irritability, an inability to look upwards, and seizures.
• In older children and adults there is no head enlargement from hydrocephalus, but symptoms may include headache, nausea, vomiting and, sometimes, blurred vision. There may be problems with balance, delayed development in walking or talking, and poor coordination.

Irritability, fatigue, seizures, and personality changes such as an inability to concentrate or remember things may also develop. Drowsiness and double vision are common symptoms as hydrocephalus progresses.

Treatment of hydrocephalus involves the insertion of a shunt to let the excess fluid exit and relieve the pressure on the brain. The shunt is a flexible, plastic tube with a oneway valve. The shunt is inserted into the ventricular system of the brain to divert the flow of CSF into another area of the body, where the CSF can drain and be absorbed into the bloodstream.

The prognosis (outlook) with hydrocephalus depends the cause and the timing of the diagnosis and treatment. Many children treated for hydrocephalus are able to lead normal lives with few, if any, limitations. In some cases, cognitive impairments in language and non-language functions may occur. Problems with shunts such as infection or malfunction require revision of the shunt.

Hydrocephalus is sometime called "water on the brain." The word "hydrocephalus" in Greek literally means "watery head."