Histopathology of cochlear implants in humans

The insertion of an intrascalar electrode array during cochlear implantatio n causes immediate damage to the inner ear and may result in delayed onset of additional damage that may interfere with neuronal stimulation. To date, there have been reports on fewer than 50 temporal bone specimens from pati ents who had undergone implantation during life. The majority of these were single-channel implants, whereas the majority of implants inserted today a re multichannel systems. This report presents the histopathologic findings in temporal bones from 8 individuals who in life had undergone multichannel cochlear implantation, with particular attention to the type and location of trauma and to long-term changes within the cochlea. The effect of these changes on spiral ganglion cell counts and the correlation between speech c omprehension and spiral ganglion cell counts were calculated. In 4 of the 8 cases, the opposite, unimplanted ear was available for comparison. In 3 of the 4 cases, there was no significant difference between the spiral gangli on cell counts on the implanted and unimplanted sides. In addition, in this series of 8 cases, there was an apparent negative correlation between resi dual spiral ganglion cell count and hearing performance during life as meas ured by single-syllable word recognition. This finding suggests that abnorm alities in the central auditory pathways are at least as important as spira l ganglion cell loss in limiting the performance of implant users.