Misplaced Cochlear Implant Electrodes Outside the Cochlea: A Literature Review and Presentation of Radiological and Electrophysiological Findings

Abstract

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.

A scoping review on the clinical effectiveness of Trans-Impedance Matrix (TIM) measurements in detecting extracochlear electrodes and tip fold overs in Cochlear Ltd devices

“…Studies were conducted in North America-the United States [ 33 ], Europe- including the United Kingdom [ 32 ], Netherlands [ 24 , 28 ], Germany [ 26 ], Finland [ 25 ], Italy [ 30 ], Spain [ 27 ], Belgium [ 31 ], Asia Pacific-Australia [ 34 ]. One study was an international multicentre collaboration (Australia, Germany, and Spain) [ 29 ].…”

“…Only three studies were prospective longitudinal [ 27 , 29 , 31 ], by measuring TIM intraoperative and at postoperatively (01,03,06 and 12 months) to predict CI outcome as a function of electrode array position. Six studies were retrospective in nature [ 25 , 26 , 28 , 32 , 33 , 34 ]. One [ 24 ] was a proof-of-concept study examining the potential use of TIMs in intraoperative measurements [ 30 ], and one study [ 29 ] was a prospective multicentre study designed for the detection of TFO.…”

“…One of the most significant clinical applications of TIM in CI is the detection of TFO, which can lead to decreased performance and reduced hearing ability in CI recipients [ 24 ]. Five studies in the review demonstrate that TFO tests demonstrate 100% sensitivity and specificity when compared to intraoperative imaging [ 24 , 26 , 28 , 33 , 34 ]. The findings denote that TIM measurements can effectively detect TFO and offer advantages over the current gold standard of radiological imaging.…”

“…In general, TIM is found to be useful in both lateral wall and SME arrays [ 26 , 27 , 30 , 32 , 34 ]. Fewer studies have explored whether TIM recording could provide information about the peri-modiolar vs lateral position of the electrode array [ 26 , 27 ] and its relation to electrode performance, with only one study designed to evaluate the listening effort of peri-modiolar vs lateral wall electrodes in an electrode discrimination test [ 27 ].…”

“…This would minimize radiation exposure, duration of the surgery and in turn minimize the overall burden on operating theatre. Five studies [ 24 , 26 , 28 , 33 , 34 ] have reported same point of TIM and imaging measurement intraoperatively to check the electrode positioning. While current evidence is not definitive with respect to the replacement of imaging in CI, early reports from the studies within this review are encouraging.…”