The insertion of an intrascalar electrode array during cochlear implantation 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 patients who had undergone implantation during life. The majority of these were single-channel implants, whereas the majority of implants inserted today are 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 comprehension 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 ganglion cell counts on the implanted and unimplanted sides. In addition, in this series of 8 cases, there was an apparent negative correlation between residual spiral ganglion cell count and hearing performance during life as measured by single-syllable word recognition. This finding suggests that abnormalities in the central auditory pathways are at least as important as spiral ganglion cell loss in limiting the performance of implant users.

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Table 1: Width at half maximum for average NRT tuning curves. The widths were obtained by fitting Gaussian curves to the tuning curves. For electrodes 1 and 20 the half-width-at-half-maximum is indicated. For electrodes 6, 11 and 16, full-width-at-half-maximum is indicated. Widths are indicated in number of electrode distances. The reduction of width due to modiolus hugging was significant for electrodes 1, 6 and 20 Electrode numberTuning width before Tuning width after (base to apex) modiolus hugging modiolus hugging 18 .9 (± 0.6) 6.2 (± 0.6) 61 0.9 (± 0.3) 9.4 (± 0.3) 11 12.3 (± 0.6) 11.2 (± 0.8) 1613.4 (± 0.5) 12.8 (± 0.6) 20 8.5 (± 0.3) 6.6 (± 0.4) Discussion and conclusionModiolus hugging gave a small but significant reduction of spread of neural excitation on the basal and apical apart of the Nucleus CI24R(CS) cochlear implant. There was no significant effect on the mid-section of the implant array. To our knowledge, our results are the first within-subject demonstration of the effect of modiolus hugging. Our intra-operative measurements had to be performed at a high stimulus level. At lower stimulation levels, closer to those an implant user would typically use, the reduction of the spread of excitation may be more pronounced, as is also suggested by Cohen et al. (2003). We conclude that modiolus hugging improves stimulation selectivity. This may improve speech discrimination and be beneficial for implant users.