Objective Findings with Malpositioning of a Nucleus 24RE(CA) Cochlear Implant

Abstract

Although the electrode array had folded up on itself during insertion, intraoperative electrode impedances and VIII nerve responses, as well as postoperative electrically evoked auditory brainstem responses, were within normal limits. However, averaged electrode voltages, obtained with the Nucleus Crystal Integrity Test system, were abnormal and consistent with a low-impedance pathway between the apical and middle portions of the electrode array.

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

“…It is possible but very difficult to detect undesired array positions including TF in the use of peri-modiolar electrode arrays (51), as well as translocation or kinking into the scala vestibuli (52,53) using NRT and impedance. However, cases of malposition have also been missed with reported normal intraoperative readings (14,54,55). In-keeping with this, within our own series of malpositions (Table 3), impedances are often normal, and ECAP may be present or absent on affected electrodes.…”

Intraoperative Conebeam CT for Assessment of Intracochlear Positioning of Electrode Arrays in Adult Recipients of Cochlear Implants

“…Electrophysiologic measurements, such as impedance or neural response telemetry, can be performed immediately after implantation to verify the normal function of the electrode array; however, some intraoperative electrophysiologic measurements have been reported to be normal or near-normal in cases of misplacement. 5,22,23 In the present study, 1 patient presented with a foldover of the array, but intraoperative electrophysiologic measurements did not indicate abnormalities, so imaging was the exclusive method used to diagnose this misplacement. In the absence of postoperative imaging or in the case of misdiagnosis by fluoroscopy, a misplacement outside the cochlea might only be suspected at the first mapping, generally about 2-4 weeks after implantation, and then confirmed by HRCT.…”

Piloting the recording of electrode voltages (REVS) using surface electrodes as a test to identify cochlear implant electrode migration, extra-cochlear electrodes and basal electrodes causing discomfort

“…In other intra-cochlear modes, where a single electrode acts as the return electrode (pseudomonopolar and bipolar modes), the polarity of the voltage recorded is determined by whether the return electrode is located in a more apical or basal position than the active electrode (Hughes et al, 2004). EVs show these same patterns in both straight and curved electrode arrays (Cullington and Clarke, 1997) (Pijl et al, 2008). EV measurements in all stimulation modes are effective at identifying open circuits on individual electrodes; short circuits and partial short circuits are evident in common ground mode and bipolar modes, where the return electrode(s) is on the array (Hughes et al, 2004).…”