Intracochlear Position of Cochlear Implants Determined Using CT Scanning versus Fitting Levels: Higher Threshold Levels at Basal Turn

Objectives: In this study, the effects of the intracochlear position of cochlear implants on the clinical fitting levels were analyzed. Design: A total of 130 adult subjects who used a CII/HiRes 90K cochlear implant with a HiFocus 1/1J electrode were included in the study. The insertion angle and the distance to the modiolus of each electrode contact were determined using high-resolution CT scanning. The threshold levels (T-levels) and maximum comfort levels (M-levels) at 1 year of follow-up were determined. The degree of speech perception of the subjects was evaluated during routine clinical follow-up. Results: The depths of insertion of all the electrode contacts were determined. The distance to the modiolus was significantly smaller at the basal and apical cochlear parts compared with that at the middle of the cochlea (p Conclusions: The stimulation levels of the cochlear implants were affected by the intracochlear position of the electrode contacts, which were determined using postoperative CT scanning. Interestingly, these levels depended on the insertion depth, whereas the distance to the modiolus did not affect the stimulation levels. The T-levels increased toward the basal end of the cochlea. The level profiles were independent of the overall stimulation levels and were not affected by the biographical data of the patients, such as the duration of deafness, age at implantation or time since implantation. Further research is required to elucidate how fitting using level profiles with an increase toward the basal end of the cochlea benefits speech perception. Future investigations may elucidate an explanation for the effects of the intracochlear electrode position on the stimulation levels and might facilitate future improvements in electrode design.
Audiol Neurotol 2016;21:54-67

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