Electrocochleography in Round Window Vibrant Soundbridge Implantation

Abstract

Objective: Determine the efficacy of electrocochleography (ECoG) monitoring to optimize the fitting of the floating mass transducer (FMT) of the Vibrant Soundbridge (VSB) on the round window membrane (RWm) niche in patients with conductive and mixed hearing loss. Method: Intraoperative ECoG monitoring in 41 patients with conductive and mixed hearing losses during surgery for VSB FMT RWm placement. Threshold and amplitude of click evoked compound action potentials (CAPs) were evaluated as a function of different middle ear locations and procedures for fitting the FMT on the RW niche. Results: Successful FMT/RWm coupling with optimal CAPs responses requires: 1) removing part of the bony lip to obtain a complete view of the RWm, a full RWm/FMT contact; 2) drilling on the bony floor facing the RW to facilitate a perpendicular FMT/RWm; 3) interposing fascia between the FMT and RWm and all around the FMT to avoid contact with the surrounding bone; 4) locating the FMT approximately 1 mm inside the RW niche and placing a cartilage disk on the lateral face of the FMT to ensure stability of the coupling; 5) verifying that the footplate is not fixed. Conclusion: Intraoperative ECoG monitoring verified that if the FMT is not in full close contact with the RWm and not free to vibrate without any contact with bone structures, the transfer of the FMT vibratory energy supplied to the cochlea will be incomplete and insufficient to fully compensate for sensorineural loss.