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Differences Among Shunts

The following excerpt is taken from Chapter Four of Hydrocephalus: A Guide for Patients, Families, and Friends by Chuck Toporek & Kellie Robinson, copyright 1999 by O'Reilly & Associates, Inc. For book orders/information, call 1-800-998-9938. Permission is granted to print and distribute this excerpt for noncommercial use as long as the above source is included. The information in this article is meant to educate and should not be used as an alternative for professional medical care.

Not all shunts are created equal. How are you, as the patient, to know which shunt valve has tested better, is more reliable, and is best for you? Choose a good neurosurgeon and trust his recommendations. However, this does not mean that you have to be in the dark about which shunt is recommended for you or how it works. Being informed, able to visualize how the shunt works, and able to ask questions about it helps many people relax, trust, and get on with treatment. Your neurosurgeon may have samples of the shunts he recommends. You can ask to see models in order to understand how the shunt will operate.

Check with your neurosurgeon to see what type of shunt will be used (e.g., flow-control, anti-siphoning, programmable, etc.) and who manufactures it. Although your neurosurgeon will keep records of the type of shunt valve you have, knowing this information can be useful later in case of an emergency.

Shunts can vary by the materials they are made of and standards they are manufactured under, as well as by their features.

Materials and components

Nearly all shunts used for treating hydrocephalus today are made out of, or contain, silicone and plastic. Some shunts are made entirely of silicone and plastic to reduce the risk of metal components interfering with CT and MRI equipment, while other shunts contain some non-magnetic metal components in addition to the silicone and plastic. Most shunt valves and catheters contain dots or stripes of barium sulfate, a radiopaque material.

Manufacturing and testing standards

Shunts are manufactured and tested in various ways. Some shunt manufacturers build their shunts in clean rooms similar to those used by most computer chip manufacturers. These clean rooms meet strict international standards for a sterile, dust-free environment. Unfortunately, not all shunts are made this way.

Some shunt manufacturers test each and every valve they make by putting them through a series of rigorous tests. These tests not only include pressure testing to verify the valves' pressure, but subjecting shunts to extreme heat and cold, shock tests, and numerous CT and MRI scans to ensure they work properly. In these cases, if a shunt valve passes all of the tests, it is then sterilized and packed for distribution. If it fails, the shunt valve gets tossed (as it should). However, some shunt manufacturers only test a few shunt valves from a specific batch, or may only pressure test them prior to sterilization. Again, trust your neurosurgeon to use shunts that are produced by a manufacturer who adheres to strict production and testing practices.

Common features

Shunt valves share many common features. For instance, most shunt valves and catheters are equipped with a radiopaque material, usually barium sulfate, which allows them to be viewed in the body by X-rays and CT scans.

Most shunt valves include a bulb reservoir so that surgery doesn't need to be performed to test the shunt system. The reservoir gives your neurosurgeon access to CSF in the shunt, enabling him to perform a shunt tap. A shunt tap is done by inserting a small-gauged needle through the scalp, penetrating the bulb of the reservoir. By performing a shunt tap, your neurosurgeon can:

  • Measure ICP

  • Remove CSF from the shunt system for analysis.

  • Inject a radioisotope into the shunt valve to follow and quantitate the flow of CSF with an isotope camera (gamma camera)
The bulb reservoir is designed to enable small-gauged needles to be inserted, and this in no way compromises the function of the shunt valve. However, shunt taps need to be performed under sterile conditions to reduce the risk of introducing bacteria directly into the shunt valve.

Warning: Do not depress the bulb reservoir of your shunt. This should only be done by your neurosurgeon. Improper or unnecessary depression of the bulb reservoir can overdrain the ventricles or cause an obstruction in the shunt.

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