Magnet displacement: a rare complication following cochlear implantation.

The purpose of this paper is to describe cases which reported complication after cochlear implantation in children: displacement of magnet from the receiver pocket, possibly aided by the use of magnetic toys. We observed magnet displacement in two female children from the same family and in one male child. Age at implantation was 23, 51, and 24 months, respectively. Magnet displacement occurred at 37, 16, and 32 months, respectively after the initial surgery. The magnets were replaced under general anaesthesia and we did not observe recurrent magnet dislodgement. Measurements indicated that forces required to remove the magnet from its pocket were not greater than those exerted by magnetic toys or the magnet used in the external sender coil. Although magnet displacement is not common after cochlear implantation, it is a major complication in children where subsequent general anaesthesia and surgery are necessary to replace the magnet. Therefore, we propose that pockets for removable magnets of cochlear implants used in children should be redesigned to increase forces to remove the magnet or that removable magnets not be used at all.

Clinical evaluation of cochlear implant sound coding taking into account conjectural masking functions, MP3000™.

Efficacy of the SPEAK and ACE coding strategies was compared with that of a new strategy, MP3000™, by 37 European implant centers including 221 subjects. The SPEAK and ACE strategies are based on selection of 8-10 spectral components with the highest levels, while MP3000 is based on the selection of only 4-6 components, with the highest levels relative to an estimate of the spread of masking. The pulse rate per component was fixed. No significant difference was found for the speech scores and for coding preference between the SPEAK/ACE and MP3000 strategies. Battery life was 24% longer for the MP3000 strategy. With MP3000 the best results were found for a selection of six components. In addition, the best results were found for a masking function with a low-frequency slope of 50 dB/Bark and a high-frequency slope of 37 dB/Bark (50/37) as compared to the other combinations examined of 40/30 and 20/15 dB/Bark. The best results found for the steepest slopes do not seem to agree with current estimates of the spread of masking in electrical stimulation. Future research might reveal if performance with respect to SPEAK/ACE can be enhanced by increasing the number of channels in MP3000 beyond 4-6 and it should shed more light on the optimum steepness of the slopes of the masking functions applied in MP3000.