Hydrocephalus occurs when there is an excess buildup of cerebrospinal fluid (CSF) in the ventricles of the brain. The job of the shunt is to provide a path for that excess fluid to drain. The shunt itself is a valve that is connected to two catheters. The parts of a shunt system are:
  • Proximal Catheter - this catheter is placed in the ventricle that is enlarged and is called the proximal catheter. Occasionally the proximal cathether can be placed in the lumbar of the spine which is often done when the ventricles are too small to accomodate a catheter.
  • Shunt Valve- This is the actual hardware that maintains a constant intracranial pressure (ICP) by allowing CSF to drain in a controlled fashion. The proximal catheter connects to one end of the shunt valve and the distal catheter connects to the other end.
  • Distal Catheter - The distal catheter starts at the shunt valve and can terminate in several different locations depending on the circumstances.
The proximal catheter can be placed in several locations and the approaches are named for the lobe of the brain that the catheter is inserted through. The diagrams below show the lobes of the brain and placement of the proximal catheter and shunt valve. The diagram on the right, which is brought to you courtesy of the Johnson & Johnson Codman website, only shows occipital and frontal, but parietal is also a possibility.

The medical illustration is provided courtesy of Alzheimer's Disease Research, a program of BrightFocus Foundation.

To make this a little more real, below are two pictures of actual infants:

A frontal shunt placement (thanks Eli!)   A parietal shunt placement

Where the proximal catheter and shunt valve are placed is dependent upon which ventricles are enlarged, the structure of the skull and the neurosurgeon's preference. Once the hair grows out the shunt is much less noticeable.

The next thing to look at is the shunt valve itself. Most people don't bother with the valve part of the title, if someone says shunt this is the part that they are talking about. Shunts are designed to maintain a specific intracranial pressure. This is also refered to as the "opening pressure" of the shunt because it is the pressure at which the valve will open to allow CSF to flow. The opening pressure is generally expressed in mm H20 (millimeters of water).

There are two basic types of shunts:

  • Fixed Pressure - The opening pressure of these shunts cannot be changed. If a change in pressure is required due to over or underdrainage, surgery must be done to remove and replace the shunt with a new one. Typically the fixed pressure shunts come in three different settings: high, medium and low.
  • Programmable - The opening pressure of these shunts can be changed via an external magnet so that surgery is not necessary for a pressure change. There are two manufacturers of programmable shunts, Codman (a Johnson & Johnson Company) which has 18 different pressure settings and Medtronics which has 5. The one down-side of a programmable shunt is that large magnetic fields can change the pressure setting. As a result, if an MRI is needed the shunt will need to be reprogrammed immediately following the MRI. This does not mean that an MRI can't be done, it just means that you need to set up having the shunt reprogrammed ahead of time. Reprogramming is very simple, they just lay a device over the shunt and push a button, then use an x-ray to verify the setting. I have had several people ask about accidental reprogramming. This is incredibly rare and you can read more about this in a 7 year study about the overall performance of the Codman Hakim Programmable valve here. I do not have similar information on the Medtronics valve, if anyone has any such links please send them to me.

Below are pictures of two shunts made by Codman. The picture on the left is a fixed pressure shunt and the picture on the right is a programmable, and also happens to be the exact shunt that our son Owen has:

Most shunts have a small resevoir so that the shunt can be "tapped". This is a term you will hear often and it is when the neurosurgeon places a small needle into the resevoir to take a sample of CSF. A shunt tap can provide information on intracranial pressure and the sample of CSF removed can be tested for infection. They can also inject a radioactive dye into the shunt system so that the flow of CSF can be tracked to determine if the system is working correctly.

You will often be asked the question "What type of shunt do you (or does your child) have?". You could answer with programmable or fixed pressure, but most likely what the person is asking is, "Where does the proximal catheter start and where does the distal catheter end?" Most proximal catheters are placed in one of the ventricles of the brain and those shunt system names start with "ventriculo". If the proximal catheter starts in the lumbar of the spine, the shunt system name will start with "lumbo".

Where the distal catheter terminates is how you get the second half of the name for the shunt system. The most common place is in the peritoneal cavity, which is the space surrounding the stomach. If the distal catheter ends here, then the shunt system name ends with "peritoneal". In infants and young children extra catheter tubing is coiled up in the peritoneal cavity so that the catheter need not be replaced as the person grows. If for some reason the peritoneal cavity cannot be used, such as when there are problems with the stomach, then the next most common place is the right atrium of the heart. The name of these shunt systems ends in "atrial". The final place where the distal catheter can be terminated is into the pleural space that surrounds the lungs and those shunt systems end in "pleural".

So the most common shunt system that starts in a ventricle and ends in the peritoneal cavity is called a ventriculoperitoneal shunt or VP shunt. If the same system terminates in the atrium of the heart it is a ventriculoatrial or VA shunt. If it terminates in the pleural space then it is a ventriculopleural or VPL shunt. If the system starts in the lumbar space and ends in the peritoneal cavity then you get a lumboperitoneal or LP shunt, and so on.


Anti-Siphon Devices
In the diagrams above you can see that the proximal end of the catheter is generally placed much higher in the body than the distal end. When a person is upright this setup allows gravity to pull the CSF down through the valve system, which is known as siphoning and is a major cause of overdrainage. To counter this an anti-siphoning device may be used. This device may either be built into the shunt valve, as is the case with our son's Codman programmable valve, or it may be a separate device placed in the shunt system. These devices are designed to even out the flow as the person changes position.

Shunt Failure
Shunt failures are something that one has to be constantly on the lookout for. The rate of shunt failures in children under the age of one is very high. Even though it lessens over time, it never really goes away. Everyone who has a shunt or who cares for someone with a shunt should know the signs and symptoms of a shunt failure. When a shunt fails it no longer allows the appropriate amount of CSF to drain and therefore the CSF will start to build up again putting pressure on the brain.

The classic symptoms of a shunt failure in an infant include:
  • Sleepiness or lethargy
  • Increase in head circumference
  • Fontanelle (aka soft spot) is bulging and firm when infant is sitting upright and calm
  • Irritability
  • Vomiting
  • Swelling along the shunt tract
  • Downward deviation of the eyes
  • Prominent scalp veins
  • Loss of previous abilities
  • Seizures
  • Headache
  • Loss of balance
For older children and adults you can also look for a change in vision, which is harder to spot in the little ones.

For infants who still have an open fontanelle (soft spot), pay close attention to how it behaves when everything is fine so that you will know that it is behaving differently when something goes wrong. It should sink down a bit and be soft when they are upright, and bulge slightly and be firm when they are lying down. Each child will have a different norm, so it's important to know what that norm is so that you can recognize when it changes. If the fontanelle stays firm and bulging even when they are upright then there may be a problem. If it sinks down drastically and continues to sink down when they are upright then either they are dehydrated or they are overdraining (see below). Try giving them some extra fluids to see if the soft spot returns to normal.

During the years before the soft spot closes you should also measure their head circumference regularly to look for sudden increases. It will vary by a few millimeters throughout the day and that is normal. It can also be difficult in really young infants because their head shape will often change throughout the day or across a week. So try to measure in the same spots every day, and look for dramatic changes such as more than a centimeter in one or two days.

I have had parents describe shunt failures that follow the classic symptoms and were easy to spot. The one shunt failure we have lived through started out with a buildup of the CSF along the shunt track for a month or so as the catheter slowly clogged up before it finally failed completely. At this point we very quickly went to having a good number of the classic symptoms including increase of head circumference, bulging fontanelle, vomiting and sleepiness. I have had other parents say that their child showed none of the classic signs and they were just able to tell because their child started acting differently.

The most important thing to remember is that if you think something might be wrong you should have a neurosurgeon check it out. It's better to go in and have them say, "Nope, nothing wrong" than to risk possible brain damage due to a shunt malfunction.

Shunt Infection
I placed infections in a separate section because it is quite possible to have a shunt that is working properly that also gets infected. Most shunt infections occur within three months of the shunt placement, but it can happen at any time. A fever with no other obvious cause, especially soon after a shunt placement should be checked out. Redness or swelling along the shunt tract is also something to watch out for and should be reported immediately. Remember that shunts are placed in the brain and if they get infected, the brain can get infected. So take any indication of a shunt infection seriously and call your neurosurgeon promptly. If there are active symptoms of a shunt infection you should probably call your neurosurgeon while driving to the emergency room as these infections can be deadly.

If an infection is suspected the shunt can be "tapped", meaning that a small amount of CSF can be removed by placing a needle into the resevoir of the shunt. The CSF can then be tested for infection. If a shunt becomes infected, the general procedure is to remove the existing shunt system and place an external drain while antibiotics are given for about a week to clear up the infection. Once the infection is gone a new shunt system is placed.

Now having said all of this about shunt infections, you do sometimes have to do a reality check. People get sick without it being a shunt problem and in the wintertime children can get sick often. You really don't want to be freaking out about the shunt every time they get a basic childhood illness. For example, I brought Owen into the pediatrician with a temperature of 104 with no other obvious symptoms. It wasn't his normal pediatrician, it was just the doctor on call. She immediately said that we should take him to the local neurosurgeon to get the shunt tapped and not even wait for a trip down to Duke. I explained that while the odds were not zero of it being a shunt infection, the fact that it had been a year since his shunt was placed meant that the odds of it being something else were far greater. She settled for just calling Dr. Grant, Owen's neurosurgeon down at Duke, who basically told her the same thing that I did.

What the pediatrician did not take into account is the fact that tapping a shunt is not without risk. If the child has an active infection or virus and you put a needle through the skin to the shunt, you risk introducing that infection or virus into the shunt system - thus causing the exact thing that you were worried about. You could walk into the shunt tap with a case of roseola, which is what Owen turned out to have, and walk out with a shunt infection. So if there is no redness or swelling along the shunt tract and it has been a while since the shunt was placed, it is probably best to rule out other things before tapping the shunt. The general procedure seems to have been that if Owen had worsened he would have been admitted to the hospital for observation, but probably still would have waited for the tap until the lab tests for all other normal illness possibilities had come back negative. If the shunt has recently been placed then you should suspect a shunt infection much more quickly.

We actually experienced a shunt infection and if you would like to read about the details of what happens with one you can click here.

Over or under drainage
It is possible for the shunt valve to be working properly, but to have the pressure setting not be appropriate. There must be a balance between the amount of CSF that is being produced and the amount that is being drained. Drain too much and the brain tissue loses its support and can collapse inward, drain too little and the pressure builds up. The pressure setting required to maintain this balance can change over time.

If the CSF is being drained more quickly that it can be replaced, overdrainage occurs. In infants you can look for a fontanelle that sinks considerably when the child is sitting or standing. It will normally sink down a little bit, but if it sinks radically or sinks and continues to sink there may be an overdrainage problem. In any age you can look for irritability when sitting or standing that goes away when they lay down.

Underdrainage looks pretty much like a shunt failure in the sense that the symptoms are the same. The only difference will be that when the shunt is tapped or replaced it will be found to be functioning properly.

If the shunt is programmable different pressure settings can be tried to see if that alleviates the symptoms. If the shunt is a fixed pressure type it will need to be replaced to change the setting. In this case the neurosurgeon may try Intracranial Pressure (ICP) monitoring first to determine the actual pressure inside the brain before putting in a new shunt.

A Note for New Parents
It is important that you know what type of shunt system your child has, the make and model of the shunt and whether or not it is programmable. If it is programmable you should receive a card at the hospital that tells you what the current pressure setting is and you should make sure it gets updated each time the pressure setting is changed. If you are traveling and have a problem, or have to go into the emergency room, it is much better to know this than to have to wait for someone to look it up or to call for records. It is also a good idea to have your own copies of the last few CT scans or MRI's. This way you can bring them with you when you travel. Without a past scan to compare to, there is no way to know if the ventricles have enlarged if you suspect a shunt failure. It could take some time to get these records if you are at a different hospital than your normal one and a lot of precious time could be wasted.

The last thing to make certain of before you leave the hospital is who you should contact in case of an emergency with the shunt. Do you just call the neurosurgeon's office, or is there a special after hours number for an on call service? If your preferred neurosurgeon is several hours away from home, is there a local neurosurgeon that can act as a backup for small things like checking an incision? Having all of this put together ahead of time will bring peace of mind knowing that you are prepared.

Legal Disclaimer: While every effort has been made to make certain that the information contained in this website is accurate, it must be remembered that the content is managed by a parent, not by a doctor. Information contained here is for general support purposes only and is no substitute for the care of a physician.