前庭神経鞘腫の磁気共鳴画像法における人工内耳の位置最適化

This study aimed to determine the optimal placement of the cochlear implant (CI) magnet to ensure the visibility of the inner ear and internal auditory canal (IAC) on postoperative magnetic resonance imaging (MRI) scans in patients treated for vestibular schwannoma (VS).

Nine patients who underwent CI either simultaneously with VS resection or sequentially after gamma knife surgery between January 2021 and June 2024 were retrospectively reviewed. Three patients had the CI placed in the conventional position, while six had it positioned farther from the external auditory canal (EAC) at a more vertical angle (alternative positioning). Postoperative temporal MRI scans were analyzed for inner ear and IAC visibility. Postoperative brain computed tomography (CT) scans underwent three-dimensional reconstruction to measure the distances from the CI magnet to the EAC and IAC, and the nasion-EAC-magnet angle.

Among the six patients in the alternative positioning group, five showed unobstructed IAC visibility, with both magnet-to-EAC and magnet-to-IAC distances exceeding 90 mm. The remaining patient in this group, whose distances were below 90 mm, showed obscured IAC structures due to artifacts. All three patients in the conventional positioning group had distances less than 90 mm and exhibited obscured IAC visibility. A strong correlation was observed between the magnet-to-EAC and magnet-to-IAC distances.

Optimal positioning of the CI magnet, particularly maintaining a distance greater than 90 mm from the EAC, is crucial for achieving clear postoperative MRI visualization of the IAC in patients undergoing VS treatment.

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