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 Overview

Hydrocephalus is a disorder in which an excess amount of cerebrospinal fluid (CSF) accumulates in the ventricular system of the brain. The primary causes vary and children of all ages (and even adults) can be affected. The most common treatment requires the surgical insertion of a tube (a shunt) that drains the CSF from the brain into another part of the body, like the belly(abdomen).

 How Hydrocephalus Develops

The human brain contains fluid-filled cavities called ventricles. There are four inter-connected ventricles in the human brain: two lateral ventricles, the third ventricle, and the fourth ventricle. The ventricles are filled with fluid called cerebrospinal fluid (CSF). The CSF is produced within the ventricles by specialized cells (in the choroid plexus).

The CSF flows through the ventricles (from the lateral to the third to the fourth) and then exits the fourth ventricle to surround the surfaces of the brain and spinal cord. The CSF is then absorbed over the surface of the brain by the arachnoid villi. Normally, the rate of CSF production within the ventricles and the rate of CSF absorption over the surface of the brain is balanced. Hydrocephalus develops when an imbalance occurs such that CSF absorption is relatively impaired. This results in the accumulation of CSF within the ventricles. This leads to dilation of the ventricles and exertion of increased pressure on the normal brain tissue.

One of the most common causes of an imbalance in CSF production and absorption is a physical obstruction to the flow of CSF somewhere within the ventricular system. This prevents the CSF from reaching the surface of the brain, where it would normally be absorbed. Specific causes of this include: congenital conditions (like aqueductal stenosis and those associated with spina bifida) or acquired conditions (like brain tumours). Hydrocephalus may also be caused by obstruction to CSF absorption over the brain surface itself. This usually results from the formation of scar tissue as a result of previous brain hemorrhage, meningitis, or severe head injury.

Although hydrocephalus can be caused by an overproduction of CSF, this is extremely rare, accounting for less than 1% of all cases.

 Epidemiology

The reported incidence of infantile hydrocephalus is approximately 2 to 4 per 1000 live births. It ranks as the second most common congenital neurological malformation in North America, after spina bifida. However, this is probably a gross underestimate of the overall incidence, since many cases of hydrocephalus are associated with other conditions and are not diagnosed until later in life. The annual incidence of newly diagnosed hydrocephalus requiring shunt surgery has been estimated at 1 per 12,615 population in a Canadian study. Based on the 1988 United States National Health Interview Survey, it has been estimated that there are 125,000 people with shunts in the United States, with new shunts being inserted at a rate of over 18,000 per year.

 Treatment

Current treatment of hydrocephalus consists, almost exclusively, of surgical therapy. In some cases, if the hydrocephalus is caused by a discrete obstructing mass, e.g., a tumour, the mass may be surgically removed and normal CSF flow may then be restored. In such cases, the hydrocephalus is usually temporary and easily relieved. However, in most cases, this is not possible and more definitive treatment of the hydrocephalus itself is required. There are currently two main forms of surgical treatment for hydrocephalus and the principle behind each is to bypass an area of obstruction of CSF flow.

 1-CSF Shunt

A CSF shunt is a silastic tube that serves to drain CSF from the ventricular system into some other part of the body where it can be absorbed .A shunt usually remains in place for life. This represents, far and away, the most common form of treatment of hydrocephalus. In its most usual form, the CSF shunt consists of a silastic proximal (ventricular) end that is inserted through the skull (via a small hole), through the brain substance, and into the cerebral ventricles. This is then connected to a valve mechanism on the skull surface. The valve mechanisms vary, but in general, they serve to control the amount of CSF that flows out of the ventricle by regulating the pressure. This valve is then connected to a second, much longer, distal silastic tubing that is tunneled just underneath the skin to drain into the peritoneal cavity of the abdomen (ventriculoperitoneal (VP) shunt). Less commonly, the distal tubing may drain into the right atrium of the heart (ventricuolatrial (VA) shunt) or the pleural cavity of the chest (ventriculopleural shunt). In any case, the idea is to drain the CSF from the ventricles into another body cavity that will then absorb the CSF. In a small number of cases, it may be possible to drain the CSF from the lumbar spine area into the peritoneal cavity (lumboperitoneal (LP) shunt). This is becoming a less and less common procedure.

While the principle of a CSF shunt sounds quite simple in theory, it is not without potential complications. Approximately 40% of shunts experience mechanical failure in the first year that requires re-operation. While most such failures do occur in the first 1 or 2 years, children are at life-long risk for developing shunt failure and needing further surgery. In total, approximately 80% of all children who receive a shunt will need at least one further surgical shunt revision at some point in their lives.

 2-Endoscopic third ventriculostomy

Endoscopic third ventriculostomy (ETV) is a relatively new technique. This technique is feasible for only a very select group of children with hydrocephalus. The procedure involves placing a small endoscopic camera through a hole in the skull, through the brain substance, and into the cerebral ventricles. Once inside the ventricular system, the camera and probe are carefully manipulated into the third ventricle. A small hole is then created in the floor of the third ventricle. This hole serves as the bypass outlet to let CSF flow around the obstructing lesion and be reabsorbed by the normal surrounding brain mechanisms.

This procedure is technically much more difficult than a CSF shunt. As such, it does carry a small risk of significant peri-operative injury, including severe brain hemorrhage. Even if it is performed successfully, a number of the patients eventually develop failure of the third ventriculostomy and require re-operation (either a repeat attempt at third ventriculostomy or insertion of a CSF shunt).

 Long-term Complications of Hydrocephalus

Hydrocephalus is associated with a very wide spectrum of potential disability. Some of the long-term complications include:

• infection and malfunction of the CSF shunt
• varying degrees of physical and cognitive impairment
• seizures (convulsions) in approximately 30-40% of children
• chronic headache

 It is very important to remember, however, that many children with hydrocephalus can lead near normal lives and avoid these complications entirely. The most important determinant is usually the underlying cause of the hydrocephalus and the severity of the hydrocephalus.