Transimpedance Matrix Measurements Reliably Detect Electrode Tip Fold-over in Cochlear Implantation.

OBJECTIVE During cochlear implantation, electrophysiological tests are performed to document safe technical functioning of implant and electrodes. In rare cases, the apical part of the electrode folds over during insertion. The data from transimpedance matrix (TIM) measurements enable the generation of a heat map or TIM profile measuring the spatial distribution of voltage. The aim of this study was to determine the accuracy of heat-map TIM profiles and compare them with spread of excitation (SOE) measurements and intraoperative imaging for prediction of electrode malposition. STUDY DESIGN Non-randomized study. SETTING Tertiary referral center. PATIENTS AND INTERVENTIONS One hundred patients who underwent cochlear implantation with completed TIM measurements, SOE data and perioperative imaging met the inclusion criteria and were enrolled. MAIN OUTCOME MEASURE The electrophysiological data on the electrode array positioning was compared with temporal bone imaging. RESULTS In seven cases, TIM measurements showed irregular results. In two cases, irregular TIM profiles were registered, but SOE data and 3D x-ray of the temporal bone didn't display deviated electrode positioning. A 3D x-ray of the skull displayed electrode tip fold-over in four cases and electrode buckling in one case. Sensitivity of TIM measurements and SOE data was 100%, specificity of TIM measurements was 97.89%, and specificity of SOE data was 98.93%. CONCLUSION Out of 100 patients using TIM measurements for detection of electrode malpositioning, no false negative cases were detected. TIM measurements successfully detect electrode malposition in an intraoperative setting. Different heat map patterns may be observed depending on location and type of malposition.