Implanting straight into cochlea risks the facial nerve: a Cartesian coordinate study

Area of Science:

• Anatomy
• Neurosurgery
• Medical Imaging

Background:

• Cochlear implantation requires precise electrode array insertion via the round window.
• Minimizing cochlear trauma and ensuring placement in the scala tympani are critical for successful outcomes.
• Understanding the anatomical relationships of the insertion trajectory is essential for surgical safety.

Purpose of the Study:

• To define the optimal straight-into-cochlea line for round window electrode insertion.
• To assess the proximity of this line to the facial nerve, incus, and mastoid size.
• To identify potential risks associated with this insertion pathway.

Main Methods:

• High-resolution CT scans of ten craniums (5 large, 5 small mastoid pneumatization) were analyzed.
• The straight-into-cochlea insertion line was determined using 3D coordinates from the round window to 6mm into the cochlea.
• Distances to the facial nerve (fallopian canal) and incus were measured using FIJI software.

Main Results:

• The straight-into-cochlea insertion line was frequently close to the facial nerve (50% within 1.0 mm).
• The line was consistently 4.7-7.8 mm from the incus apex.
• No correlation was found between line position and mastoid pneumatization size.

Conclusions:

• The straight-into-cochlea insertion trajectory, when using round window access, places the facial nerve at risk.
• Precise anatomical landmark registration is vital for safe cochlear implant electrode placement.
• Further research may be needed to refine surgical techniques and minimize neurological risks.