Effect of Electrode to Modiolus Distance on Electrophysiological and Psychophysical Parameters in CI Patients With Perimodiolar and Lateral Electrode Arrays

Objectives: To investigate the intracochlear position of the latest Cochlear Nucleus 532 electrode array compared with the straight Nucleus 522 and the precurved 512 arrays and determine the effect of the electrode-modiolus distance on electrically evoked compound action potential, C-levels, electrically evoked stapedius reflex thresholds (ESRTs), and impedances. Methods: Postoperative high-resolution cone beam computational tomography images of 30 patients with Cochlear Nucleus 532, 522, and 512 implants were evaluated using the Comet (Cochlea Measurement Tool) program to determine the distance between the 22 individual electrode contacts and the medial wall. ESRTs were documented intraoperatively and electrophysiological as well as psychophysical parameters were measured at multiple time points including the first fitting after the initial activation. Results: The electrode-modiolus distance in perimodiolar arrays is uniformly small across the array, whereas in a straight electrode carrier it varies significantly along the length of the array. Electrically evoked compound action potential thresholds and C-levels are larger with increased distance to the modiolus. Impedances and stapedius reflex thresholds do not differ significantly between the arrays. Our results show that the electrode position has a significant effect on both electrophysiological and psychophysical parameters, while impedances and ESRTs are not impacted. Conclusion: Novel tools can be used in the evaluation of high resolution cone beam computational tomography images to determine individual electrode-modiolus distances after cochlear implantation. The results of this study suggest that the correlations between electrode-modiolus distance and electrophysiological and psychophysical parameters are not sufficiently strong to adjust CI-fitting based on imaging data.