Prevalence of Extracochlear Electrodes: Computerized Tomography Scans, Cochlear Implant Maps, and Operative Reports

Abstract

Extracochlear electrodes were correctly identified audiologically in 60% of cases and in surgical reports in 6% of cases; however, it is possible that at least a portion of these cases involved postoperative electrode migration. Given these findings, postoperative CT scans can provide information regarding basal electrode location, which could help improve programming accuracy, associated frequency allocation, and audibility with appropriate deactivation of extracochlear electrodes.

Detection of Extracochlear Electrodes in Cochlear Implants with Electric Field Imaging/Transimpedance Measurements:

“…The contact impedances were only useful in identifying extracochlear electrodes if the extracochlear electrodes were in air. This is consistent with the study by Holder et al (2018) , showing that a substantial subset of live CI users with extracochlear electrodes, as clinically identified by CT scanning, had normal contact impedances. Furthermore, normal contact impedances were seen on the extracochlear electrodes in the four intraoperative SCINSEV recordings in live patients during insertion (Fig.…”

“…One finding associated with poor performance is the presence of extracochlear electrodes ( Hilly et al 2016 ; Rivas et al 2008 ), defined as individual electrodes on the electrode array that are located outside of the cochlea due to incomplete insertion or extrusion. The prevalence of extracochlear electrodes is estimated to be between 9.2% and 13.4% ( Coombs et al 2014 ; Holder et al 2018 ). The mechanism behind extracochlear electrodes is commonly categorized into incomplete insertion, for example, due to ossification or cochlear malformations, or electrode migration post-implantation ( Holder et al 2018 ).…”

“…The prevalence of extracochlear electrodes is estimated to be between 9.2% and 13.4% ( Coombs et al 2014 ; Holder et al 2018 ). The mechanism behind extracochlear electrodes is commonly categorized into incomplete insertion, for example, due to ossification or cochlear malformations, or electrode migration post-implantation ( Holder et al 2018 ). In case of incomplete insertion, the surgeon is aware of the extracochlear electrodes and the auditory map can be adjusted accordingly.…”

“…Furthermore, in many countries, CT scans have to be separately scheduled, are time-intensive, costly, and involve radiation, which is particularly worrisome in children because of the long-term neoplasia induction risks ( Brenner & Hall 2007 ). Other clinical measures such as ECAPs and auditory mapping seem insufficient for detection of extracochlear electrodes, as an ECAP response and auditory response can be present in case of extracochlear electrodes, possibly stimulating the same tonotopic region as the most basal intracochlear electrode ( Holder et al 2018 ). Although it has been reported that basal contact impedances increase over time when electrodes migrate outside of the cochlea ( Dietz et al 2016 ), contact impedances are in the normal range for the majority of these CI users ( Coombs et al 2014 ; Holder et al 2018 ).…”

Pre- and post-operative imaging of cochlear implants: a pictorial review

“…However, the authors perform—and recommend to do so—a post-operative examination in every patient to confirm the correct position of the implant electrode. Information regarding basal electrode location helps improving programming accuracy, associated frequency allocation, and audibility with appropriate deactivation of extracochlear electrodes [ 44 ].…”