BASIC AND CLINICAL RESEARCH ON MECHANISMS OF TINNITUS IN ACOUSTIC

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In order to clarity the mechanisms of tinnitus in acoustic neuroma, we investigated the transient evoked otoacoustic emissions (TEOAEs) which reflect the cochlear micromechanics related to the active motile property of outer hair cells. Dysfunctions of the cochlear efferent nervous system including the outer hair cells have been postulated as one of the mechanisms of tinnitus. We recorded TEOAEs in 95 acoustic neuroma patients and 50 Meniere's disease patients as controls in order to clarify the relationship between the hearing level and TEOAEs in cochlear and retrocochlear hearing impairments. Mean hearing level of the acoustic neuroma patients whose TEOAEs could be obtained was 28.4(]SY.+-。[)14.6dB and that of the Meniere's disease patients was 28.3(]SY.+-。[)12.5dB.Although there were 3 acoustic neuroma patients with TEOAE in spite of hearing impairment over 60 dB,deterioration in TEP (one of the TEOAE parameter) was found compaing with healthy side ear. From these results, we conclu … More ded that there must be an affection to the cochlea in almost all acoustic neuroma patients. Thus, the normal TEOAEs seem to be uncommon in the acoustic neuroma patients with mederate or severe hearing impairment.We also conducted the study on the nature of tinnitus in acoustic neuroma. A series of 85 patients who had undergone hearing-preserved operation (the middle cranial fossa approach or the extended middle cranial fossa approach type III) of a unilateral acoustic neuroma was analyzed about pre and postoperative tinnitus. They consisted of 37 successful hearing-preserved cases and 48 hearing-loss cases. Obvious differences between hearing-preserved cases and hearing-loss cases were not found about improvement or worse of their tinnitus. Subjective expressions of tinnitus nature among acoustic neuroma patients were various, therefore, it was thought that a speculation about prognosis of tinnitus will be difficult, but tinnitus of acoustic neuroma patients in both cases was mostly mild and not so painful for their quality of life. Less