Changes in the Area Adjacent to the Internal Receiver-Stimulator of Cochlear Implant: A Retrospective Study.

Background In some patients with cochlear implants, bony resorption at the internal receiver-stimulator site can be observed on postoperative computed tomography. Therefore, it is essential to elucidate the effects of the internal receiver-stimulator on the scalp and bony bed over time. Objective We aimed to evaluate how the internal receiver-stimulator of a cochlear implant device changed the thickness of the surrounding scalp and skull over time using computed tomography. Methods This retrospective study evaluated patients who underwent cochlear implantation and received two computed tomography scans postoperatively for different indications at a tertiary referral centre. The main outcomes were scalp thickness and bony bed depth. Results Fourteen ears were included in this study. There was very good inter-rater reliability, with a Cronbach's alpha of 0.94. The mean scalp thickness over the internal receiver-stimulator was 6.02 (+/-2.4) mm in the first scan and decreased with no significant change to 5.62 mm (+/-1.64) in the second scan (p = 0.59, paired t-test). The mean depth of the bony bed increased significantly from 1.39 mm (+/-0.93) to 2.62 mm (+/-1.24) (p = 0.03). Conclusion There was no change in the thickness of the scalp overlying the internal receiver-stimulator indicating that the scalp was more resistant than the bony skull to the tensile pressure exerted by the internal receiver-stimulator. In contrast, the bony bed depth of the internal receiver-stimulator increased over time. This can result in decreased internal receiver-stimulator protrusion and decreased risk of device displacement and migration.