Does Residual Spiral Ganglion Cell Count Predict Performance in Patients with Bilateral Multichannel Cochlear Implants?

Abstract

Objectives: Although published reports have not demonstrated a positive correlation between residual spiral ganglion cells (SGC) and word recognition in patients with unilateral multichannel cochlear implants, this study was designed to determine whether word recognition scores after implantation are a function of residual SGCs in patients with bilateral multichannel cochlear implants. Methods: Study Design: Retrospective case series. Setting: Temporal bone banks of Massachusetts Eye and Ear Infirmary and House Research Institute. All subjects with bilateral multichannel cochlear implants who were deafened bilaterally by the same etiology were studied. A total of 8 temporal bones from 4 subjects were identified and processed after death for histology. The SGCs were counted by standard techniques. The differences between the better and worse SGC counts as well as the differences in Consonant Nucleus Consonant (CNC) scores were calculated for each subject. Correlation analysis was then performed between the differences of SGC counts and the differences of CNC scores. Statistical power was calculated to illustrate how the results can be used to estimate the sample size as a function of effect size. Results: Differences in SGC counts were highly correlated with the differences in CNC word scores (Pearson’s correlation = 0.972, P = 0.028) such that with a power of 95% and α = 0.05, only 4 cases were needed to show the same effect size. Conclusions: This study suggests the higher residual SGCs predicted better performance after implantation. The results also justify any attempts to reduce the effect of insertional trauma which may adversely affect SGC count.