MRI Scanning and Incus Fixation in Vibrant Soundbridge Implantation

Abstract

OBJECTIVE: Presentation of patient data after Vibrant Sound-bridge (VS) implantation/explantation with respect to magnetic resonance imaging (MRI) compatibility and stability of incus fixation of the implant. STUDY DESIGN: In a retrospective case review, we report on two patients who had to be diagnosed by cranial MRI scans after previous implantation of a VS. Moreover, in one of these cases, the incus was removed after explantation of the VS because of a peripheral hearing loss. This enabled a microscopic evaluation of the incus. At the long process of the incus, the floating mass transmitter (FMT) has been fixed for 4 years. SETTING: Tertiary referral center. SUBJECTS: Two patients who fulfilled, at the time of implantation, the criteria for implantation of a VS. RESULTS: In both cases, no demagnetization of the external magnet nor of the FMT were found. Device function after the MRI scans were normal. Pure-tone audiometric thresholds remained unchanged after the MRI scanning and the scanning-related magnetic forces. In both cases, the FMT fixation of the incus was found to be regular. In one case, the fixation was checked by an additional tympanoscopy 1 year after the implantation, and in the other case it was assessed by recording the functional gain of the VS (which was normal) after the MRI scanning. One patient complained about a transient hyperacuity due to the loudness during the MRI scanning procedure. MRI scans showed a blackening of the implant area with spherical distortions of the picture. CONCLUSION: Although MRI scanning (at 1.5 tesla [T]) with the FMT in place did not lead to adverse effects in the two patients, systematic in vitro studies are required to determine a possible magnetization threshold that could impair the VS function when MRI scans are applied in those patients. The microscopically observed erosions of the long process of the incus after 4 years of FMT clamp fixation show similarities to findings after stapes revision surgery. However, this limited experience in one case does not allow us to make conclusions on the long-term stability of the incus fixation.