Misplaced cochlear implant electrodes outside the cochlea: a literature review and presentation of radiological and electrophysiological findings

Hypothesis: It is possible to detect when misplacement and malposition of the cochlear implant (CI) electrode array has occurred intraoperatively through different investigations. We aim to explore the literature surrounding cochlear implant misplacements and share our personal experience with such cases to formulate a quick-reference guide that may be able to help cochlear implant teams detect misplacements early. Background: Misplacement and malposition of a cochlear implant array can lead to poor hearing outcomes. Where misplacements go undetected during the primary surgery, patients may undergo further surgery to replace the implant array into the correct intracochlear position. Methods: Systematic literature review on cochlear implant misplacements and malpositions and a retrospective review of our program's cases in over 6,000 CI procedures. Results: Twenty-nine cases of CI misplacements are reported in the English literature. Sixteen cases of cochlear implant misplacements are reported from our institution with a rate of 0.28%. A further 12 cases of intracochlear malpositions are presented. The electrophysiological (CI electrically evoked auditory brainstem response, transimpedance matrix) and radiological (X-ray and computed tomography scan) findings from our experience are displayed in a tabulated quick-reference guide to show the possible characteristics of misplaced and malpositioned cochlear implant electrode arrays. Conclusion: Both intraoperative electrophysiological and radiological tests can show when the array has been misplaced or if there is an intracochlear malposition, to prompt timely intra-operative reinsertion to yield better outcomes for patients.