Hypothesis This study evaluates the types and degree of tissue response adjacent to the electrode of multichannel cochlear implants. Background cochlear implant electrodes have been classified as biocompatible prostheses. Nevertheless, in some reports, electrode extrusion, chronic inflammation and even soft failure of the implant system have been attributed to a tissue response to the electrode. Methods All celloidin embedded temporal bones with multichannel cochlear implants from the temporal bone collection of the Massachusetts Eye and Ear Infirmary were included in the study. A total of 28 temporal bones from 21 subjects were identified and processed for histology. The severity of cellular response including eosinophil and lymphocytic infiltration, giant cell reaction, new bone formation and fibrosis were scored on a scale from 0 to 3 at three 1mm-segments along the electrode: 1- first 1mm at the cochleostomy, last 1mm from the tip of electrode, and midway between these proximal and distal segments. The values were compared using the Wilcoxon test. Results A granulomatous reaction to the electrode was observed in 27 (96.4%) temporal bones. Eosinophil infiltration was observed in 7 (25%) temporal bones, suggesting an allergic reaction. The Inflammatory response to the electrode was significantly greater at the basal turn of cochlea close to the cochleostomy (p< 0.05) than distal to it. Conclusion An Inflammatory response is common after cochlear implantation and it is more robust at the cochleostomy than distal to it, suggesting the role of trauma of insertion as a contributing factor.

Objectives Although published reports have not demonstrated a positive correlation between the number of residual spiral ganglion cells (SGC) and word recognition scores in patients with unilateral multichannel cochlear implants, this study was designed to retest this hypothesis in patients with bilateral multichannel cochlear implants. Materials and Methods From a pool of 133 temporal bones, all subjects with bilateral multichannel cochlear implants who were deafened bilaterally by the same etiology were studied. A total of 12 temporal bones from 6 subjects were identified and processed after death for histology. The SGCs were counted by standard techniques. The differences between left and right SGC counts as well as the differences in word recognition scores were calculated for each subject. Correlation analysis was performed between the differences of SGC counts and the differences of word recognition scores. Results Differences in SGC counts were highly correlated with the differences in word recognition scores (R=0.934, P-value= 0.006). Conclusion This study suggests higher residual SGCs predicted better performance after implantation in a given patient. The results also support attempts to identify factors which may promote survival of SGCs.