What is a Shunt?

A shunt is a mechanical device designed to transport the excess CSF from or near the point of obstruction to a re-absorption site and it is implanted under the skin.

There are many different types of shunts, but there is no perfect shunt. The quest continues for one, the shunt manufacturers are always trying to achieve this goal.

The shunt has 3 components. The first portion is the called the shunt catheter or proximal portion of the shunt. This is a small narrow tube (catheter), which is implanted into the ventricle of the brain, above where the obstruction has occurred. It is then connected to the valve and reservoir. The valve controls how much fluid is withdrawn from the brain, it is then stored in the reservoir until it is released to drain down the distal (bottom) end. The distal end is a small, narrow piece of tubing (catheter) which leads to the point where the excess CSF will drain and be absorbed by the body.

The absorption site is usually the abdomen (peritoneum). This is the preferred location for the placement of the distal end of the shunt. This type of shunt implantation is referred to as a ventriculo-peritoneal (VP) shunt. The pleural (lung) cavity (ventriculo-pleural) shunt, or the atria of the heart, ventriculo- atrial (VA) shunt can be used also. The gallbladder or bladder can be used, but this is only when there is no other site that is suitable.

Shunts are composed of a silicone elastomer (plastic) and are often impregnated with barium. In general, there are fixed shunts or programmable shunts. The fixed shunts usually have a choice of three different types of valves (low, medium, and high). A programmable shunt allows your physician a greater range of choices in choosing the pressure at which the fluid drains. The pressure can be easily changed as the neurosurgeon has a magnetic device to change the setting, in the convenience of his office. Newborns and infants often are implanted with a fixed shunt, when they are older and in need of a revision, the doctor may then decide to replace the valve and reservoir unit with a programmable one.

You should know that the shunt performs two functions. It allows fluid to go only in one direction and the valve allows fluid to flow out only when the pressure in the head has exceeded some value (usually referred to as the "opening pressure"). This system regulates the amount of the CSF in the body so that not too much is taken, nor too little.

Having a shunt is a lifetime commitment. Once a shunt is implanted, it is not a "one time" operation. Life expectancy of a shunt averages 10 years. However, a shunt can last 5 minutes to many years. It is wise to always be aware of the warning signs for a "shunt malfunction." (Please refer to the Signs of Hydrocephalus and Shunt Malfunctions.)