Magnets and Shunt Valves

In 1955, a child with severe spina bifida and hydrocephalus, or water on the brain, was born to John W. Holter, a toolmaker in Stamford, Connecticut, and his wife. Charles Casey Holter, like other children at the time, did not survive this severe congenital disorder. His condition, however, prompted his father to invent the first hydrocephalus shunt valve, allowing the excess cerebrospinal fluid (CSF) in the brain to be diverted to other parts of the body and absorbed.

Although not a cure for hydrocephalus, Holter’s valve system was the first effective treatment. Descendants of the first Holter valve have saved the lives of millions of children. I used one just this morning to treat a tiny baby here at Doernbecher Children’s Hospital.

Modern shunt valves work on basically the same design, over 50 years later. There have, however, been improvements. Some valves, for example, have different settings to slow down or speed up the flow of CSF, making adjustments for a particular patient’s condition. Before these ‘programmable’ valves, neurosurgeons like myself had to perform an operation to change a valve setting (by going under the skin and changing the entire valve!). Now, we just use a magnetized programming device to non-invasively change a valve’s setting.

Like everything, programmable valves have drawbacks. One is that magnetic fields out in the day-to-day patient environment can accidentally reset a valve, and cause headaches or even dangerous shunt failure and return of acute hydrocephalus.

According to some manufacturers, accidental resetting should not generally occur from exposure to most day to day magnetic fields, such as security scanners at the airport, home kitchen microwave ovens, and smart phones (http://www.medtronic.com/for-healthcare-professionals/products-therapies/neurological/shunts/strata-nsc-lumboperitoneal-adjustable-pressure-shunts/indications-safety-warnings/index.htm).

Recently, though, physicians have reported accidental valve resets by a number of day-to-day devices. My friends and colleagues at the University of Michigan have just reported that iPad 2s can reset some valves (although only if placed within a couple of inches of the valve): http://thejns.org/doi/full/10.3171/2012.3.PEDS1211.

A Japanese group has even reported valve resets caused by the Nintendo DS video game: http://www.ncbi.nlm.nih.gov/pubmed/21946726.

Unfortunately, which valve might be reset by which magnet, at what distance, and under what circumstance, is often unknown. So what should patients and parents do?

My advice is: when in doubt, play it safe. Keep toy magnets or electronic devices with magnetic fields, away from a programmable shunt valve whenever possible. If you are unsure, ask your doctor’s office. Most importantly, if a patient with a hydrocephalus shunt and a programmable valve experiences symptoms of shunt malfunction (for example, severe headache, change in mental function, altered level of consciousness, or sudden loss of vision), seek immediate medical attention.

Hydrocephalus shunt valves, including magnetically programmable ones, are terrific advances, especially when safely and properly used.

Hydrocephalus - 'water on the brain'