Histopathology of Cochlear Implants in Humans

TLDR

Cochlear implantation with intrascalar electrode arrays causes immediate inner‑ear damage and can lead to delayed trauma that may impair neuronal stimulation, yet only fewer than 50 temporal‑bone specimens have been examined—most from single‑channel implants—while contemporary devices are multichannel. This report examines histopathologic findings in temporal bones from eight patients who received multichannel cochlear implants, focusing on trauma type, location, and long‑term cochlear changes. The authors quantified spiral ganglion cell counts and assessed their correlation with speech comprehension, comparing implanted ears to contralateral unimplanted ears in four cases. No significant difference in spiral ganglion cell counts was observed between implanted and unimplanted sides in three of four cases, and a negative correlation between residual cell counts and single‑syllable word recognition suggests central auditory pathway abnormalities are as important as spiral ganglion loss in limiting implant performance.

Abstract

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.