Loss of saccular function after cochlear implantation: the diagnostic impact of intracochlear electrically elicited vestibular evoked myogenic potentials.

Cochlear implant surgery has become a successful procedure for deaf patients to restore their hearing again. Some of the patients, however, complain of persisting dizziness after the surgery which can have a major impact on their quality of life. Neurotological tests of the vestibular system were applied in a total of 18 cochlear implantees pre- and postoperatively. In addition, vestibular evoked myogenic potentials were evoked intraoperatively to investigate possible interferences of the electrically stimulated cochlear implant electrode (eVEMP) with vestibular receptor cells of the saccule in more detail. After cochlear implantation, the saccular function was impaired in the majority of the patients. However, eVEMPs could be recorded intraoperatively in all patients by intracochlear, high-level electrical stimulation via the cochlear implant electrode. In essence, acute, short-term dizziness after cochlear implantation seems to result primarily from a transient vestibular deficit of various origins. In contrast to this, chronic, persisting dizziness after cochlear implant surgery is largely based on a dysfunction of the saccular macula which is an integral component of the otolith system. This saccular impairment is induced most likely by the insertion trauma of the cochlear implant electrode when advancing it into the inner ear. A possible coactivation of the inferior vestibular nerve by the electrical stimulation might play an additional role in the pathogenesis of the persisting postsurgical dizziness. (c) 2008 S. Karger AG, Basel