Detection of Cochlear Implant Electrode Extrusion With Electric Field Imaging

Introduction: Extrusion of basal electrodes after full insertion of a cochlear implantation occurs in a subset of primarily lateral wall electrodes. A migrating electrode often renders suboptimal cochlear implant performance, and early detection and management is necessary to optimize outcomes.

Currently, detection of electrode extrusion mainly relies on imaging modalities such as computed tomography (CT) which is costly, requires access to a CT scanner, and exposes patients to ionizing radiation. There are known limitations of using single electrode impedance measures to detect extrusion, such that when extracochlear electrodes contact middle ear fluid or tissue, the impedance may appear normal. Electric field imaging (EFI) is an emerging technique that may detect electrode extrusion more reliably compared to standard methods. We aim to demonstrate the value of EFI in accurately detecting electrode extrusion in a cohort of patients.

Methods: We identified 31 patients with Advanced Bionics CI and available EFI, and these were reviewed by a senior cochlear implant Audiologist. EFI readings were categorized as either normal or abnormal with suspected extrusion. EFI categorization was then correlated with objective data – either CT scan and/or operative note report – to determine accuracy.

Results: Twenty-seven patients exhibited normal-appearing EFI whereas 4 patients had abnormal EFI with suspected extrusion. In all four patients with suspected extrusion, extracochlear electrodes were confirmed - three on post-operative CT and one with direct visualization intraoperatively. Seven of the patients with normal-appearing EFI were found to have disabled basal electrodes.

Conclusions: This preliminary data demonstrate that EFI is a reliable screening tool for cochlear implant electrode extrusion but is not able to detect selective disabled electrodes. In patients who have possible electrode extrusion based on EFI results, consideration should be given for temporal bone CT imaging.