Placement of cerebral spinal fluid (CSF) shunt systems to treat hydrocephalus is a common medical procedure and a life-saving treatment for many patients. These shunt systems drain excess fluid from the brain to another part of the body where the fluid is absorbed as part of the circulatory process. CSF shunts contain three main components: an in-flow tube (catheter), a valve that regulates the flow of fluid, and an outflow catheter that carries the fluid to the abdomen or the heart where the fluid can be absorbed.

Types of CSF Shunt Valves

There are two types of CSF shunt valves: fixed and adjustable. Fixed shunt valves allow CSF fluid to drain when CSF pressure exceeds a certain “fixed” threshold. Adjustable shunt valves allow for changes to the amount of fluid that flows through the valve. There are two types of adjustable CSF shunt valves: magnetic externally adjustable and non-magnetic externally adjustable.

Magnetic Externally Adjustable Shunt Valves

Magnetic externally adjustable shunts have mechanical parts that can be moved non-invasively from outside the body. To adjust these valves, a clinician places a magnetic tool on the skin near the valve and manually rotates it. The magnetic field of the programming tool passes through the skin to adjust the position of the valve. This process, setting a valve to drain more or less fluid from the brain, is sometimes called “programming,” although the process involves no electronics. Once implanted, no additional surgical procedures are required to change the setting of a magnetic externally adjustable shunt valve.

Non-Magnetic Externally Adjustable Valves

These types of shunts DO NOT use an external magnetic field for valve adjustments. Some valves have self-adjusting flow-regulating mechanisms, while others can only be adjusted using minimally invasive surgical procedures.

CSF shunt systems typically require monitoring and regular medical follow up. When there is reason to suspect that a CSF shunt system is not functioning properly (for example, if the symptoms of hydrocephalus return), medical attention should be sought immediately.

Some of the most common risks of CSF shunts include infection, shunt malfunction, and improper drainage.

Infection from a shunt may produce symptoms such as a low-grade fever, soreness of the neck or shoulder muscles, and redness or tenderness along the shunt tract.

Shunt malfunction is most commonly due to a blockage or some obstruction within the shunt system. If the blockage is not corrected, symptoms of hydrocephalus will return. In some cases, shunt blockage may require surgery to replace the affected component or components.

Overdrainage occurs when the shunt allows CSF to drain from the ventricles more quickly than it is produced. Overdraining can cause the ventricles to collapse, tearing blood vessels and causing headaches, hemorrhages (subdural hematomas), or a condition where the ventricles decrease in size until they are too small (slit ventricle syndrome). Symptoms of overdrainage often include headache and are similar to the symptoms of underdrainage (hydrocephalus).

Underdrainage occurs when CSF is not removed quickly, fluid builds up in the ventricles and the symptoms of hydrocephalus recur.

Overdrainage and underdrainage of CSF can be addressed by adjusting the drainage pressure of the shunt valve; if the shunt has a magnetically adjustable pressure valve, these changes can be made noninvasively.

Other problems that can occur with these devices are:

• Catheters harden (calcify) or break
• Catheters may disconnect from the valve and reservoir unit
• Valves may break or stick
• Fixed pressure valves may be set to the wrong pressure
• Catheters may be too short and need to be lengthened

MRI and CSF Shunts

Magnetic Resonance Imaging (MRI) is an important screening and diagnostic device that relies on powerful magnetic fields, which could potentially adjust a patient’s CSF valve. Patients with CSF shunts should inform their health care providers prior to receiving MRI due to the potential of the MRI magnetic field to change their implanted device.

Symptoms of hydrocephalus

Patients and caregivers should be aware of the symptoms of hydrocephalus because they are similar to symptoms of underdrainage of a CSF shunt system. Symptoms of hydrocephalus may be expressed differently in patients of different ages. In patients with CSF shunt systems, these symptoms can indicate problems with the shunt system that need to be evaluated by a physician.

Symptoms commonly found in infants and younger children:

• Distended scalp veins
• Downward gaze (sometimes called “sunset eyes”)
• Enlargement of the head
• Enlarged and bulging fontanel
• Feeds poorly/Decrease in appetite
• High-pitched cry
• Irritability
• Lethargy
• Recurrent vomiting

Symptoms commonly found in older children, teens, and adults:

• Decrease in appetite
• Deteriorating mental capabilities
• Difficulty in walking
• Double vision
• Headache
• Incontinence
• Increased intracranial pressure
• Irritability
• Lethargy
• Nausea
• Personality changes
• Restlessness
• Seizures
• Vomiting

If you have a CSF shunt or you care for someone who has one, the following strategies may help prevent unintended changes to your CSF shunt valve:

Know your Shunt

• Make sure you know what type of CSF shunt you have (or that the person you are caring for has). Knowing the shunt type can help you get appropriate treatment if a shunt-related problem occurs. This is particularly important if you need medical attention in an emergency, where the doctors may not be familiar with all of your medical history or have access to your medical records.
• The only sure way to know if an adjustable shunt valve setting has changed is to have the pressure setting checked by a physician with an X-ray or specialized magnetic tool known as a shunt checker. Only a qualified physician should check your shunt valve setting. It is preferable to have the shunt checked by a clinician (e.g. neurosurgeon) who can also adjust the setting if necessary. Shunt checkers are specific to each shunt device manufacturer. It is important that the shunt checker be compatible with the shunt.

Know your Risk of Harm is Low

• The FDA believes that serious adverse events due to unintended changes in magnetic externally adjustable CSF shunt valve settings are rare compared to other CSF shunt malfunctions such as blockage or infection. Early detection of unintended changes can be maximized through maintaining routine physician visits, checking and resetting valves following MRIs, and understanding the symptoms of over or underdrainage.
• Unintended changes in shunt valve setting are usually not life-threatening. Headache is often the first symptom when a shunt is not draining properly. For most patients, problems with drainage are addressed before health conditions worsen. However, young children with shunts may not be able to communicate that they are experiencing headache and may progress to additional symptoms before they receive medical care. The degree of symptoms depends on how much the setting changed, for how long the setting was changed, and how sensitive the patient is to changes in pressure. In some cases, the patient could experience symptoms of hydrocephalus. In other cases, the patient could experience no symptoms at all.
• Additional data is needed to understand the possible relationship between magnetic externally adjustable CSF shunt valves and magnets found in the environment. However, it is reasonable to assume that a shunt valve that is manipulated by a hand-held magnetic tool may also be vulnerable to other external magnetic sources. This is why FDA recommends keeping magnets some distance away from shunts with magnetic externally adjustable valves.

Some children may be more prone to force trauma (blows to the head) due to their developmental stage and physical ability. Additionally, children may be exposed to different types of magnetic sources than adults, for example in toys or in sources closer to the ground. Children may also need assistance caring for their device or with their activities of daily living, which can expose them to multiple caregivers. Some ways you can help keep your child safe include:

• Be aware of strong magnetic sources and keep them away from your child, particularly at the site of their device. Inform children how to interact safely with known magnetic sources that they may encounter at home, school, or at other activities. For example, encourage your child to use a cell phone on the opposite side of the head from the shunt.
• Be aware that strong forces can cause physical damage to implanted CSF shunts. For example, some amusement park rides, contact sports, or playground injuries can damage a shunt. If in doubt about whether or not a certain activity may damage your child’s shunt, contact your physician.
• Read label information and talk to the child’s health care professional when considering which CSF shunt to use. Important factors to consider include the child’s age and size, other medical conditions, as well as the child’s ability to tolerate the device for the time it will be used. In addition, not all pediatric patients are alike. Devices might need to be changed or replaced as children grow.
• Be alert for signs of device problems because some children may not be able to communicate discomfort or distress.
• Watch for signs of infection around the device location, such as redness, swelling, discharge, heat, or pain.
• Make sure that the people with whom your child is in regular contact, such as family members, teachers, babysitters, coaches, etc., know about your child’s shunt, what exposures and activities might place the child at risk for device damage, what health symptoms to look for that might indicate a problem, and what to do in case of a shunt-related problem.