Cochlear Implantation and Facial Nerve Stimulation: Clinical and Anatomic Correlations.

Objectives: One rare complication of cochlear implantation (CI) is facial nerve stimulation (FNS). The aim of the study was to analyze the location and insertion depths for electrode contacts causing FNS. The anatomical variance of the human facial nerve canal (FNC) was explored to elucidate the mechanisms underlying FNS.

Methods: Data were collected from adults that had received a CI from a single tertiary care center. Medical records from 307 patients were retrospectively reviewed. The Uppsala human temporal bone library was leveraged to analyze anatomical structures relevant to FNS. Micro-computed tomography (CT) images of temporal bones (n = 246) were used for three-dimensional (3D) analyses after rendering. Data from synchrotron radiation phase-contrast imaging (SR-PCI) of 83 human temporal bones were analyzed.

Results: Nineteen (5.8%) patients experienced FNS. No statistical difference in FNS rates between lateral wall (LW) and peri modiolar (PM) electrodes was found (p > 0.05). Electrode contacts with an angular insertion depth from 250° to 340° were associated with FNS. Analyses of the macerated temporal bones and corrosion casts showed that the average distance between the cochlea and the FNC was 0.3 mm and the closest position of the FNC varied from 253° to 304°.

Conclusion: The labyrinthine segment of the FN is in close proximity to the cochlea and can be affected by dehiscence. Typically, the bony partition between the FNC and the cochlea is thicker than the modiolar wall and provides insulation against electrical stimulation from nearby CI electrodes. FNS may occur from both LW and PM electrodes.

Level of evidence: 3: