The importance of intra-operative imaging during cochlear implant surgery

Two unusual cases of cochlear implant (CI) surgery complication are reported: introduction of the electrode array into the superior semicircular canal with normal morphology and a growing amplitude of neural potential (neural response imaging, NRI) during intra-operative monitoring control. In the first case, a two-year-old patient affected by congenital sensorineural profound deafness was bilaterally implanted with two Clarion 90 k devices and intra-operative electrophysiological and radiological controls were performed. After introduction of the array in the right side NRI was performed and a neural potential was found only on two apical electrodes. Radiological intra-operative control with antero-posterior trans-orbital plain films was performed to assess the position of the electrodes inside the cochlea. Radiography showed the electrode array in the superior semicircular canal in the right ear. The electrode array was removed and reinserted correctly. In the second case, a 72-year-old man underwent left cochlear implantation for sensorineural profound deafness of unknown origin. Intra-operative electrophysiological testing (NRI) showed the presence of neural potential on three tested channels. In this case, as routinely employed since 2006, an intra-operative static fluoroscopy control was performed, this showed the electrode array in the superior semicircular canal. The electrode array was removed and reinserted correctly. In conclusion, intra-operative monitoring tests during CI surgery play different roles: measurement of impedances and NRI can evaluate the integrity of implant electrodes and the status of the electrode cochlea interface, but they cannot be the only way to confirm correct positioning of the array. In our opinion the intra-operative radiological check is helpful during CI surgery, especially when there is any doubt about correct electrode insertion.