The COCHLEA: A New Functional Outcome Measure for Pediatric Cochlear Implant Patients

Abstract

The goal of this study was to determine the relationship between psychophysical measures of electric hearing and neural survival in Nucleus-22 cochlear implant users.Methods: The temporal bones of 2 subjects with Nucleus-22 cochlear implants were obtained at autopsy. Histologic procedures were used to quantify spiral ganglion cell survival as a function of longitudinal cochlear distance and to estimate the radial distance between each electrode and the spiral ganglion cells in Rosenthal's canal. Psychophysical measures of threshold, maximum acceptable loudness level, and dynamic range were obtained for each stimulable electrode prior to death. Both subjects were tested with short phase-duration (200 microseconds per phase) pulses; subject 2 was also tested with long phase-duration (1260 microseconds per phase) pulses.Results: Correlation coefficients were calculated for threshold, maximum acceptable loudness level, and dynamic range and spiral ganglion cell density as a function of distance along Rosenthal's canal. No significant correlations were observed in subject 1, who had extensive neo-ossification in the basal and middle turns of the cochlea. Weak correlations were observed in subject 2, but relationships were in unexpected directions: Spiral ganglion cell density was positively correlated with threshold (r ϭ 0.502, P Ͻ 0.05) and negatively correlated with dynamic range (r ϭ Ϫ0.533, P Ͻ 0.05). Radial distance was not correlated with any of the psychophysical measures in either subject.Conclusion: There was no consistent relationship among threshold, maximum acceptable loudness level and dynamic range, and spiral ganglion cell survival in the 2 Nucleus-22 cochlear implant users studied.Significance: These data suggest a complex relationship among neural survival, electrode location, and behavioral measures of hearing, and indicates that threshold, maximum acceptable loudness level, and dynamic range are influenced by factors other than the proximity and number of surviving sprial ganglion cells.