Abstract
HYPOTHESIS: Years of implantation, surgical insertion approach, and electrode length will impact the volume of new tissue formation secondary to cochlear implantation. BACKGROUND: New tissue formation, fibrosis, and osteoneogenesis after cochlear implantation have been implicated in increasing impedance and affecting performance of the cochlear implant. METHODS: 3-D reconstructions of 15 archival human temporal bones from patients with a history of cochlear implantation (CI) were generated from H&E histopathologic slides to study factors which affect volume of tissue formation. RESULTS: Years of implantation was a predictor of osteoneogenesis (r = 0.638, p-value = 0.011) and total new tissue formation (r = 0.588, p-value = 0.021), however not of fibrosis (r = 0.235, p-value = 0.399). Median total tissue formation differed between cochleostomy and round window insertions, 25.98 and 10.34%, respectively (Mann-Whitney U = 7, p = 0.018). No correlations were found between electrode length or angular insertion depth and total new tissue (p = 0.192, p = 0.35), osteoneogenesis (p = 0.193, p = 0.27), and fibrosis (p = 0.498, p = 0.83), respectively. However, the type II error for electrode length and angular insertion depth ranged from 0.73 to 0.90, largely due to small numbers of the shorter electrodes. CONCLUSIONS: With numbers of cochlear implant recipients increasing worldwide, an understanding of how to minimize intracochlear changes from implantation is important. The present study demonstrates that increasing years of implantation and inserting electrodes via a cochleostomy compared with a round window approach are associated with significantly greater degree of new tissue volume formation. While previous studies have demonstrated increased intracochlear damage in the setting of translocation with longer electrodes, length, and angular insertion depth of CI electrodes were not associated with increased tissue formation.