Effects of contralateral white noise stimulation on transitory evoked otoacoustic emissions in patients with acoustic neuroma.

Transitory evoked otoacoustic emissions are normal phenomena observed in most persons with hearing levels greater than 35 dB. Further, masking of the contralateral ear produces amplitude reductions in the transitory evoked otoacoustic emissions. We have undertaken a study of transitory evoked otoacoustic emissions in 20 patients with acoustic neuroma. All patients were assessed for transitory evoked otoacoustic emissions bilaterally, with and without contralateral masking with white band noise at 40, 50, and 60 dB. We found that transitory evoked otoacoustic emissions were present in 30% of ears with tumor and that the presence of transitory evoked otoacoustic emissions is associated with improved preoperative hearing levels, but that tumor size is not associated with the presence or absence of transitory evoked otoacoustic emissions. The amplitude of transitory evoked otoacoustic emissions from ears with tumor, when present, is decreased when compared with normal ears of normal patients. Further, with contralateral masking little of the amplitude reduction observed in normal patients is observed in the ears with acoustic neuroma. However, with masking of the contralateral ear, the ear without tumor demonstrated significantly greater amplitude reductions than normal ears from normal patients (p = 0.0006). Pertinent anatomy and possible explanations for these findings are discussed.