Hydrocephalus: An Owner’s Manual Part 5 of 6
The Shunt Itself
What is a Shunt?
The shunt itself is a silastic tube about the diameter of a wet spaghetti noodle. It has two ends, proximal and distal, and one valve. There is usually a reservoir which can be needled to gain CSF as well. Often, though not always, the reservoir and the valve are located together.
The proximal end of the shunt is the head end, with the tip usually in the ventricle (one of the cavities in which CSF is produced).
The distal end of the shunt is usually in the belly, or peritoneum. This is not truly in the stomach, but in the space around the stomach and intestines, where the catheter floats among these structures. The CSF exits the distal end of the shunt and is reabsorbed into the bloodstream, where it circulates back to the head and is reused.
The valve is the crucial and significant mechanical part of the shunt. It is placed inline between the proximal and distal tubing, usually under the skin of the skull behind the hairline. It is the ‘unsightly bump’ seen atop the head of an infant, the lump visible after the head has been shaved for a shunt revision.
The function of the valve is to provide a certain resistance to flow of CSF so that overdrainage does not occur. Without the valve, it is possible that too much CSF would drain, creating its own set of problems.
There are a number of valves from different manufactures. In general, they can be divided into programmable and nonprogrammable valves. Programmable valves can be adjusted with a magnet held over the scalp. The advantage of this: the valve setting can be adjusted without requiring an operation; nonprogrammable valves do not have this option—if the valve setting is wrong, surgery is required to replace the valve. Note that programmable valves may have to be reset after an MRI. It is at least conceivable that a programmable valve could be reset in other situations of modern life, though this is apparently rare.
All valves are subject to mechanical failure and tend to be a choke point in the shunt system.
Risks & Benefits of Surgery
Most of the time, shunt placement is done without a hitch. However, the procedure is not without certain risks. For most individuals, the benefits far outweigh the risks.
The benefits of shunting include treating the hydrocephalus and its attendant signs and symptoms. Symptoms are what a patient complains of (headache, nausea, vomiting, double vision, blurred or decreased vision, clumsiness, etc.) and signs are what a physician discovers on examination (decreased consciousness, abnormal eye movements including sunsetting and crossed eyes, enlarging head circumference in infants, etc.). Another benefit not to be overlooked is the opportunity for an individual to reach their full potential. Even in non-life threatening cases of hydrocephalus, the hydrocephalus can cause memory disturbance and cognitive decline.
With the above said, it should be recognized there are many risks of shunting. The biggest risk is infection, perhaps as high as ten percent. This includes superficial wound infection, infection of the shunt itself, ventriculitis (an infection of the ventricles where CSF is produced), and peritonitis (infection of the belly cavity). Most cases of infection occur within thirty days of surgery, though the risk is elevated for as long as six months. Most cases of infection will require removal of the shunt, perhaps with a prolonged hospitalization.
Other risks include intracranial hemorrhage (bleeding), stroke, and injury to the bowel. The need for revision is always out there as well, usually because of infection or obstruction, occasionally because of misplacement of the distal catheter outside of the peritoneum.
In preterm infants, there is a risk the peritoneum will not have enough absorptive capacity. For this reason, shunting is avoided in these cases.
Ventriculoperitoneal shunts can cause or enlarge inguinal hernias, much more commonly in boys. Small boys should be checked for hernia in the months following shunt placement. If possible, hernias should be repaired prior to shunting.
With a ventriculoatrial catheter, in which the distal catheter is placed in the heart, there is a potential for clotting of the end of the distal catheter. Also, if the shunt becomes infected, the infection can track directly into the blood stream—a decided disadvantage. For this reason, the usual shunt of choice today is a ventriculoperitoneal shunt.
Rarely, ventricular shunts are placed to other parts of the body, the most common being a ventriculopleural shunt. These are exceptional cases, with their own attendant risks.
Shunt Failure v. Infection
When a shunt fails, the signs and symptoms of hydrocephalus return.
The usual cause of shunt failure is either obstruction or infection.
A shunt can fail in the absence of infection. The usual cause for this is obstruction, usually the proximal end or the valve. In such a case, the surgeon will perform a revision, replacing just that part which is obstructed, if possible.
In the case of shunt infection, the shunt will usually (but not always) shows evidence of malfunction as well. Such cases can be very complicated to treat, especially if the patient is shunt dependent. Generally, these are treated with IV antibiotics in combination with revision. Usually the entire shunt system has to be pulled and replaced. If the infection is significant and the patient is shunt dependent, the entire shunt is removed and an external ventricular drain (which drains CSF to a bag at the bedside) is placed. This may be required for a week or more, during which the patient must remain hospitalized.
If the patient is not shunt dependent (as in normal pressure hydrocephalus), the infected shunt is removed, the patient is treated with IV antibiotics, and the shunt is replaced at a later date. No external ventricular drain is necessary.
Note that essentially all children and most adults are and should be considered shunt dependent from the moment a shunt is placed. In the absence of information one way or the other, the neurosurgeon will assume shunt dependence.
Disclaimer: The information contained in this blog is simply that, information. I am not doling out specific medical advice. Nothing contained herein is meant to replace a complete evaluation by a qualified member of the medical establishment. This page is nonfiction.