Intraoperative Intracochlear Electrocochleography and Residual Hearing Preservation Outcomes When Using Two Types of Slim Electrode Arrays in Cochlear Implantation

Objectives: To report residual hearing preservation outcomes in patients with low frequency hearing, after cochlear implant (CI) electrode insertion with two types of electrode arrays: one straight and other perimodiolar, when using intraoperative intracochlear electrocochleography (ECochG) during (CI) electrode insertion. Study Design: Prospective, randomized study. Setting: Tertiary referral otology center. Patients: Fifteen patients ranging from 33 to 54 years old (mean 51.19). They had been diagnosed with a bilateral, profound sensorineural hearing loss and treated with a unilateral cochlear implant: eight of them with the CI532 and seven of them with the CI522 (Cochlear Ltd, Sydney, Australia). Intervention: Pure-tone audiometry was performed preoperatively and at 1 and 6 months postoperatively. Interoperatively, intracochlear ECochG was performed using the apical-most electrode. The amplitude of the first harmonic was plotted and monitored in real time by the audiologist-surgeon team during their CI electrode insertion. The different ECoch patterns of the insertion track were recorded and analyzed. Results: In 12 cases ECochG responses were successfully recorded. In three cases no ECochG responses could be recorded with no residual hearing observed postoperatively in two of them. With respect to the first harmonic amplitude changes, we found: four cases with an overall increase in amplitude measured from the beginning of insertion until completion, all of them showed residual hearing (<15 dB HL) at 6 months postoperation. Three cases with an increasing amplitude at the beginning of insertion, with a decrease in amplitude as insertion progressed to completion, in two cases dropping of residual hearing (15-30 dB HL) were observed after 6 months postoperation and, in one case, complete residual hearing was observed at 6 months postoperatively. And finally five cases presented amplitudes at the start of insertion with modifications of amplitude during the insertion dynamic, with increasing and descending in amplitude range during the whole insertion, two of them showed residual hearing at 6 months postoperation and three cases a drop of residual hearing (15-30 dB HL) was observed after 6 months postoperation. No statistical differences between CI532 and CI522 electrodes were found. Data of the ECochG responses are also presented (p value >= 0.05). Conclusion: ECochG is a useful tool to evaluate the residual hearing in CI patients with straight and perimodiolar cochlear implant. More studies are needed to fully understand the relationship between ECochG and the presence of residual hearing, cochlear trauma, and functional outcomes.