Lateral Semicircular Canal Pressures During Cochlear Implant Electrode Insertion: a Possible Mechanism for Postoperative Vestibular Loss.

HYPOTHESIS: Insertion of cochlear implant electrodes generates transient pressure spikes within the vestibular labyrinth equivalent to high-intensity acoustic stimuli.
BACKGROUND: Though cochlear implant (CI) surgery is regarded as having low risk of impacting the vestibular system, several studies have documented changes in vestibular function after implantation. The mechanism of these changes is not understood. We have previously established that large, potentially damaging pressure transients can be generated in the cochlea during electrode insertion, but whether pressure transients occur within the vestibular labyrinth has yet to be determined. Here, we quantify the exposure of the vestibular system to potentially damaging pressure transients during CI surgery.
METHODS: Five human cadaveric heads were prepared with an extended facial recess and implanted sequentially with eight different CI electrode styles via a round window approach. Fiber-optic sensors measured intralabyrinthine pressures in scala vestibuli, scala tympani, and the lateral semicircular canal during insertions.
RESULTS: Electrode insertion produced a range of high-intensity pressure spikes simultaneously in the cochlea and lateral semicircular canal with all electrodes tested. Pressure transients recorded were found to be significantly higher in the vestibular labyrinth than the cochlea and occurred at peak levels known to cause acoustic trauma.
CONCLUSION: Insertion of CI electrodes can produce transients in intralabyrinthine fluid pressure levels equivalent to high-intensity, impulsive acoustic stimuli. Results from this investigation affirm the importance of atraumatic surgical techniques and suggest that in addition to the cochlea, the vestibular system is potentially exposed to damaging fluid pressure waves during cochlear implantation.