Cochlear Implantation and Facial Nerve Stimulation: Clinical and Anatomic Correlations

Area of Science:

• Otolaryngology
• Neurosurgery
• Medical Imaging

Background:

• Facial nerve stimulation (FNS) is a rare complication of cochlear implantation (CI).
• Understanding the anatomical relationship between the facial nerve canal (FNC) and the cochlea is crucial for mitigating FNS.
• Electrode design and placement are potential factors influencing FNS occurrence.

Purpose of the Study:

• To analyze the location and insertion depths of electrode contacts associated with FNS.
• To investigate the anatomical variations of the human FNC in relation to the cochlea.
• To elucidate the mechanisms underlying FNS in CI patients.

Main Methods:

• Retrospective review of medical records from 307 adult CI patients.
• Analysis of micro-computed tomography (CT) scans (n=246) and synchrotron radiation phase-contrast imaging (SR-PCI) data (n=83) from human temporal bones.
• Three-dimensional (3D) reconstruction and analysis of anatomical structures using the Uppsala human temporal bone library.

Main Results:

• FNS occurred in 5.8% of patients (19/307).
• No significant difference in FNS rates was observed between lateral wall (LW) and perimodiolar (PM) electrodes.
• Electrode contacts between 250° and 340° angular insertion depth were associated with FNS.
• The average distance between the cochlea and the FNC was 0.3 mm, with the closest FNC position ranging from 253° to 304°.

Conclusions:

• The labyrinthine segment of the facial nerve is anatomically close to the cochlea, increasing susceptibility to stimulation.
• FNS can occur with both LW and PM electrodes, primarily related to specific insertion depths.
• Dehiscence in the bony partition between the FNC and cochlea can contribute to FNS.