Detection of “tip fold-over” of the cochlear implant electrode array with transimpedance matrix (TIM) measurement

Abstract

In recent years, the cochlear implant has become a routine and effective treatment tool for severe hearing loss and total deafness. One of the commonly used and effective innovations of our time in cochlear implantation is the perimodiolar thin electrode array. The atraumatic electrode array, which closely embraces the central axis of the cochlea (modiolus), has served its popularity with very convincing results, with its performance in both electrophysiological measurements and acoustic hearing preservation. However, very few publications describe the frequency of improper positioning of the electrode array, which is known as 'tip fold-over'. The aim of our study is to incorporate a software technique, the transimpedance matrix (TIM), into routine intraoperative electrophysiological measurement methodologies to provide a potential objective diagnostic opportunity for early detection of tip fold-over of the electrode array. Following bilateral cochlear implantation of a three-year-old child, postoperative radiography showed the correct position of the electrode array on the left side, while tip fold-over of the intracochlear electrode array was detected on the right side. Following imaging, a TIM study was performed as an electrophysiological method. During the procedure, the measuring device transmits a voltage of the order of 1 V to the nearby structures of the cochlea at a constant current at the designated stimulus electrodes. Measuring electrodes were used to register the voltage measured on the tissues, and then converted into a TIM. Electrode tip fold-over was previously diagnosed by radiological examination, while it can also be diagnosed by objective electrophysiological measurements now, and these two tests correlate well. Standard radiological imaging techniques for electrode positioning can be supplemented or replaced by easy-to-perform, effective objective electrophysiological studies. Tip fold-over can be detected intraoperatively, even before wound closure, if the electrode array is in the wrong position, thus reducing the radiation exposure associated with radiological examinations as well as reducing relevant costs. Orv Hetil. 2021; 162(25): 988-996.