Hydrocephalus, the build-up of fluid in the brain, is typically relieved with a shunt that diverts cerebrospinal fluid (CSF) to either the abdominal cavity or the right atrium of the heart. Adjustable shunt valve settings allow the surgeon to select the valve’s pressure.

CSF shunt systems are commonly used to treat hydrocephalus. Uncontrolled hydrocephalus can cause symptoms including headaches, nausea, vomiting, sleepiness, failing mental function, blurred vision and loss of coordination. Left undertreated, hydrocephalus can be fatal.

Magnets can inadvertently make changes to externally programmable shunts for hydrocephalus, which require adjustments to patient valve settings. Sources of magnetic field interference can be external (e.g. from a cell phone or MRI machine) or internal (from a cochlear implant, for example), according to the FDA in 2019.

Here are six things to know about shunts and magnetic field interference:

    1. Be aware of sources of external magnets.

      Potential magnetic field interference can come from cordless drills, cell phones, electronic tablet devices, metal detectors and earbuds/headphones. In 2018, the FDA noted, “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 (in the environment),” noting that more research is needed on the subject

To date, FDA studies conclude that magnetic handheld devices are safe as long as they are kept at least two inches away from the shunt valve, although the agency notes that differences in body physiology and magnet characteristics may affect results. The FDA advises that hydrocephalus patients using earbuds or a cell phone should use these on the opposite ear from where the shunt is located.

    1. Take note of internal magnets.

      Magnetic hearing devices (such as cochlear implants and bone conduction and middle ear hearing devices) may interact with shunts if the two are placed too close to each other. In this case, magnetic field interference could be avoided by putting the programmable CSF shunt valve on the contralateral side of a hearing device.

A study of magnetic field strength of four bone conduction hearing devices and interaction with programmable shunt valves concluded it was safe to use the devices together but recommended at least a 5 mm distance in the case of one hearing device.

In addition, the FDA recommends checking shunt valve settings after placement or adjustment of other devices that contain magnets to ensure that the setting has not changed. For patients requiring bilateral hearing implants, the implanting physician should position the CSF shunt valve and the ipsilateral hearing implant at a maximum distance from one another to avoid issues with magnets and shunts for hydrocephalus, according to the FDA.

    1. Sometimes there are magnets you can’t avoid such as magnetic resonance imaging (MRI) and other imaging scans.

MRIs may pose a risk to certain shunts’ valve settings. Before a patient has an MRI, they should tell the MRI technologist about any programmable shunts. Their doctor should arrange to have their shunt setting checked after the MRI, and reprogrammed if necessary.

    1. Unintended shunt valve changes can lead to serious issues.

      Signs of shunt malfunction may include headache, lethargy, vomiting, vision changes and behavioral changes. Symptom severity depends on how much the setting changed, for how long and how sensitive the patient is to pressure changes. Overdrainage symptoms can include severe headache, nausea, vomiting and seizures and underdrainage may cause a recurrence of hydrocephalus symptoms.

Parents and caregivers of children with magnetic CSF shunt systems should be told of possible interference, keep children away from magnets, encourage use of cell phones on the opposite side of the head from the shunt, know symptoms of magnetic interference and how to get help.

    1. Not all valves will be affected equally.

      In three bench studies, Codman Certas® Plus programmable valves demonstrated no setting changes from common household magnets in over 2,200 exposures at close proximity (<5 mm). 1,2,3 * Watch a short video with details about the study here.

Non-clinical testing demonstrated that the Certas valve is MR Conditional, meaning a patient with this device can be scanned safely, immediately after placement under specified conditions. Testing shows that the valve mechanism is resistant to unintended changes in the setting of  a 3 Tesla MRI, although a clinician should confirm the valve setting after an MRI procedure.

    1. Any unintended CSF shunt valve changes should be reported

      through the FDA MedWatch Program or the FDA Medical Product Safety Network (Med Sun) if your facility participates in the program.

The agency advises including the following information with any report:

    • The suspected distance of programmable shunt from the magnetic source
    • Identification of suspected magnetic source(s)
    • Severity of patient symptoms
    • Change in valve setting value from intended setting
    • Manufacturer and brand of the CSF shunt or brand of hearing device
    • Patient age, gender, underlying diagnosis for shunt
    • Other medical devices in region of shunt (for example cochlear implant)
    • Device evaluation post-explant, if available


δ Testing included 6 samples of each valve, tested 162 times per product at a distance of 4.3 mm on average.

* Benchtop studies are not necessarily indicative of clinical performance.

  1. Data on file. Jacobs Institute Engineering Solutions. Hydrocephalus Shunt Valve Assessment. February 5, 2019. Integra LifeSciences, Plainsboro, NJ, USA.
  2. Data on file. Jacobs Institute Engineering Solutions. Hydrocephalus Shunt Valve Assessment. Oct. 16, 2019. Integra LifeSciences, Plainsboro, NJ, USA.
  3. Data on file. Jacobs Institute Engineering Solutions. Magnetic Influence of CHPV, CERTAS, and Strata II Shunt Valves. September 16, 2021. Integra LifeSciences, Plainsboro, NJ, USA.
Certas Plus Programmable Valve
Indications: The CODMAN CERTAS Plus Programmable Valve is an implantable device that provides constant intraventricular pressure and drainage of CSF for the management of hydrocephalus. The CODMAN CERTAS Tool Kit allows the noninvasive reading or adjustment of the valve setting.
Contraindications: These devices are contraindicated in patients receiving anticoagulants or known to have a bleeding diathesis.
Avoid shunt implantation if infection is present within the body. Delay the shunt procedure when infections such as meningitis, ventriculitis, peritonitis, bacteremia, and septicemia are present. The BACTISEAL Catheters are contraindicated in patients with known hypersensitivity to rifampin or clindamycin hydrochloride.
Warnings • Choose an implantation site for the valve where the tissue over the valve is not too thick (i.e. tissue thickness < 10 mm). Otherwise locating, reading, and adjusting the valve with the tool kit may be difficult (i.e.; multiple attempts may be required) or impossible. If unable to adjust the valve, the valve will maintain a constant operating pressure and the patient should be informed of this risk. • Testing shows that the valve mechanism is resistant to unintended changes in the setting in a 3 Tesla MRI. However, the clinician should confirm the valve setting after a magnetic resonance imaging (MRI) procedure. • Read MRI Information before performing an MRI procedure on a patient implanted with the valve. • Do not interchange the CODMAN CERTAS Tool Kit (82-8851) components with the CODMAN CERTAS Therapy Management System TMS (82-8850) components. • The Indicator Tool has a precise operating mechanism and is vulnerable to damage if mishandled. Store and carry all components of the Tool Kit in the storage case when not in use to prevent damage. Replace the Indicator Tool immediately if dropped (or suspected of being dropped) to ensure accurate performance. Replacement Indicator Tools are available from your local Codman representative.
Precautions • Use only the CODMAN CERTAS Tool Kit to adjust the setting of the CODMAN CERTAS and CODMAN CERTAS Plus Programmable Valves. • Excessive swelling may make it difficult to determine and/or adjust the performance setting. • See instructions for using the Low Profile Locator Tool in these instances. • If difficulty correctly positioning both Locator Tools persists, wait until the swelling is reduced or confirm the valve setting with x-ray.
Failure to accurately position the Locator tool could result in an inaccurate indication of the performance setting, potentially leading to a false reading (i.e. an incorrect number may appear in the window of the Indicator Tool). The Locator Tool must be precisely aligned with both the valve’s direction of flow and the center of the hard valve mechanism for an accurate indication reading. Alignment can be more challenging if tissue thickness is > 10 mm above the valve. In these instances, verify the valve setting with x-ray or fluoroscopy.

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