Assessing the risk of magnetic interaction between auditory implants and programmable ventriculoperitoneal shunts

Purpose This study investigated whether the magnetic field of the internal magnet of cochlear implants and bone-anchored hearing aids (BAHA) would be sufficient to affect a programmable ventriculoperitoneal (VP) shunt. Current guidelines suggest against implanting these hearing devices ipsilateral to a programmable VP shunt, but the exact nature of the interaction has not been quantified. Methods The magnetic field strength (mT) was measured at 0 and 10 mm from the edge of both the Cochlear Implant CI512 (Cochlear Corporation) magnet and BAHA Attract magnet. Next, the hearing devices were placed into their anatomical positions in a 3-D clay model, along with three different types of programmable VP shunts. The valve setting was measured before and after exposure. Results At 10 mm, neither device generated a magnetic field sufficient to adjust the VP shunt valve. In the clay model, the valve settings were not affected by the presence of any device. Conclusion Neither the cochlear implant nor the BAHA subcutaneous internal magnets generated sufficient magnetic field to reprogramme the valves of commonly used programmable VP shunts. The magnetic field from each device decreases dramatically at 10 mm. Further clinical studies to help mitigate the current restrictive guidance should consider involvement of VP shunt manufacturers to inform future shunt development and design.