Intraoperative Measured Electrocochleography and Fluoroscopy Video to Detect Cochlea Trauma

HypothesisGross electrode movements detected with intraoperative, real-time X-ray fluoroscopy will correlate with fluctuations in cochlear output, as measured with intraoperative electrocochleography (ECochG).BackgroundIndications for cochlear implantation (CI) are expanding to include patients with residual hearing; however, implant recipients often lose residual hearing after CI. The objective of this study was to identify probable traumatic events during implantation by combining electrophysiological monitoring of cochlear function with simultaneous X-ray monitoring. The surgical timing of these apparently traumatic events was then investigated.MethodsFor 19 adult patients (21 surgeries, 2 bilateral), the ECochG responses were measured during implantation of a cochlear nucleus slim modiolar electrode (CI532/CI632, Cochlear Ltd Australia Nucleus slim modiolar). Simultaneous fluoroscopy was performed, as well as a postoperative cone-beam computed tomography (CT) scan. For all patients, pre- and postoperative audiograms were recorded up to 1 year after surgery to record the loss of residual hearing.ResultsElectrode insertions for 21 surgeries were successfully monitored. A drop in ECochG response was significantly correlated with reduced hearing preservation compared with patients with preserved responses throughout. Drops in the ECochG response were measured to occur during insertion, because of movement of the array after insertion was complete, including while sealing of the electrode array at the round window or coiling of the array lead within the mastoid cavity. In some patients, a reduction in cochlear output, resulting in poor ECochG response, was inferred to occur before the beginning of implantation.ConclusionThe combination of perioperative ECochG measurements, microscope video, fluoroscopy, and postoperative CT scan may inform on what causes the loss of residual hearing after implantation. These findings will be used to improve the surgical procedure in future.