Cochlear implant revision: effects of reimplantation on the cochlea.

The removal of an indwelling cochlear implant electrode followed by reinsertion of a new device has been a maneuver of uncertain consequences to the cochlea and its surviving neural population. The present study was conducted in an attempt to elucidate the factors that determine whether a reimplantation procedure will be successful. Cochlear implantation followed by explantation and subsequent reimplantation was performed in eight adult cats. Evaluation of cochlear histopathology suggested a significant increase in electrode insertion trauma when there was proliferation of granulation tissue in the round window area and scala tympani. In other cases, atraumatic reinsertion was achieved without apparent injury to the cochlea. The results of a survey of cochlear implant manufacturers and surgeons indicate that electrode replacement can usually be accomplished without adverse effects. Difficulties have been encountered, however, in removing implants with protuberant electrodes and when reimplantation was attempted on a delayed basis following explantation.