What is Hydrocephalus?

Hydrocephalus can be defined broadly as a disturbance of formation, flow, or absorption of cerebrospinal fluid (CSF) that leads to an increase in volume occupied by this fluid in the central nervous system (CNS). This condition also could be termed a hydrodynamic disorder of CSF. Acute hydrocephalus occurs over days, subacute over weeks, and chronic over months or years. Conditions such as cerebral atrophy and focal destructive lesions also lead to an abnormal increase of CSF in CNS. In these situations, loss of cerebral tissue leaves a vacant space that is filled passively with CSF.

The ventricular system is made up of four ventricles connected by narrow passages.. Normally, CSF flows through the ventricles, exits into cisterns (closed spaces that serve as reservoirs) at the base of the brain, bathes the surfaces of the brain and spinal cord, and then reabsorbs into the bloodstream. CSF has three important life-sustaining functions: 1) to keep the brain tissue buoyant, acting as a cushion or "shock absorber"; 2) to act as the vehicle for delivering nutrients to the brain and removing waste; and 3) to flow between the cranium and spine and compensate for changes in intracranial blood volume (the amount of blood within the brain).

The causes of hydrocephalus are still not well understood. Hydrocephalus may result from inherited genetic abnormalities (such as the genetic defect that causes aqueductal stenosis) or developmental disorders (such as those associated with neural tube defects including spina bifida and encephalocele). Other possible causes include complications of premature birth such as intraventricular hemorrhage, diseases such as meningitis, tumors, traumatic head injury, or subarachnoid hemorrhage, which block the exit of CSF from the ventricles to the cisterns or eliminate the passageway for CSF into the cisterns.

Symptoms of hydrocephalus vary with age, disease progression, and individual differences in tolerance to CSF. In infancy, the most obvious indication of hydrocephalus is often the rapid increase in head circumstance or an unusually large head size. In older children and adults, symptoms may include headache followed by vomiting, nausea, papilledema (swelling of the optic disk, which is part of the optic nerve), downward deviation of the eyes (called "sunsetting"), problems with balance, poor coordination, gait disturbance, urinary incontinence, slowing or loss of development (in children), lethargy, drowsiness, irritability, or other changes in personality or cognition, including memory loss.

Normal flow and absorption through the subarachnoid space is dependent on proper CSF pressure in the head (called intracranial pressure). A build up of CSF often causes a dangerous increase in pressure. The combination of CSF buildup and the subsequent increase in intracranial pressure can stress brain tissue and can cause the characteristic symptoms of hydrocephalus, though they also may occur with normal pressure.

Hydrocephalus produces different combinations of these signs and symptoms, depending on its cause, which also varies by age. For example, a condition known as normal pressure hydrocephalus, which mainly affects older people, typically starts with difficulty walking. Urinary incontinence often develops, along with a type of dementia marked by slowness of thinking and information processing.

The most common treatment for hydrocephalus is the surgical insertion of a drainage system, called a shunt. It consists of a long flexible tube with a valve that keeps fluid from the brain flowing in the right direction and at the proper rate. One end of the tubing is usually placed in one of the brain's ventricles.