Effect of peri-modiolar cochlear implant positioning on auditory nerve responses: A neural response telemetry study

Conclusions. There was no evidence that a reduction in current was needed for nerve stimulation as a result of modiolar placement of a cochlear implant. However, modiolus hugging did reduce the spread of excitation for the basal and apical electrodes. This improved stimulation selectivity may result in improved speech discrimination by implant users. Objective. To test the effect of modiolar placement of a cochlear implant on stimulation thresholds, and to confirm whether peri-modiolar electrode placement resulted in the hypothesized reduced spread of excitation. Material and methods. Auditory nerve responses were measured by means of neural response telemetry (NRT) in 14 subjects. All subjects received a Nucleus CI24R(CS) Contour implant. For each subject, the stimulation threshold and response growth rate were determined on all the odd-numbered electrodes, using a masker-and-probe paradigm. In addition, the spatial spread of excitation was measured on electrodes 1, 6, 11, 16 and 20, using a variable-masker paradigm. All NRT measurements were performed intra-operatively, both before and after peri-modiolar placement of the electrode by removal of a surgical stylet. Results. Removal of the stylet had no significant effect on the threshold and growth rate of NRT responses. It caused a reduction in the spread of excitation for electrodes 1, 6 and 20, but not for electrodes 11 and 16.