What is a Shunt?
The most common treatment for hydrocephalus is the surgical placement of a medical device called a shunt. A shunt, in its simplest form, is a flexible tube called a catheter, which is placed into the area of the brain where cerebrospinal fluid (CSF) is produced. This area of the brain is known as the lateral ventricles. The tubing is then passed under the skin to another region of the body, most often the abdominal cavity, or heart, diverting the excess CSF away from the brain, where it can be absorbed naturally by the body. By draining the extra fluid to another location in the body, it is relieving pressure on the brain.
A shunt consists of three major components:
An inflow or proximal catheter, which drains CSF from the lateral ventricles. This tube leaves the brain through a small hole drilled in the skull and then runs for a short distance under the skin.
A valve mechanism, which regulates intracranial pressure by controlling fluid flow through the shunt tubing. This device is connected to the proximal catheter and lies between the skin and the skull, usually on top or the back of the head, or just behind the ear. Valves operate within a specific pressure range. There are many types of valves and shunt manufacturers. Your doctor will determine the type of valve based on his/her experience, preference, and your needs.
An outflow or distal catheter, which runs under the skin and directs CSF from the valve to the abdominal (peritoneal) cavity, heart or another suitable drainage site.
Ventriculoperitoneal (VP) shunts. This type of shunt diverts CSF from the ventricles of the brain into the peritoneal cavity, the space in the abdomen where the digestive organs are located. The tip of the distal catheter rests in this cavity near the loops of the intestine and bowel but not inside them. The CSF shunted to this area is reabsorbed into the bloodstream and is eventually excreted through normal urination.
Adjustable (programmable) valves regulate the ICP based on a pressure setting, like the fixed pressure valve, but the setting can be adjusted by your doctor using an external adjustment tool applied outside the body if there needs to be a change in how much CSF is draining. This allows your health care professional to non-invasively change or program the valve pressure setting during an office visit. The number of available settings depends on the valve model and manufacturer.
These valves are designed to be adjusted by a strong magnetic field found in the external adjustment tool. Some of these valves may be susceptible to adjustment by strong environmental magnetic fields and care must be taken to keep toys with magnets and other sources of magnetic fields away from the implanted device. Some adjustable valves incorporate mechanisms that cannot be adjusted by magnetic fields other than those produced by the programmer. It’s important to ask your doctor what precautionary measures should be taken.
