Paradoxical effects of contralateral white noise on evoked otoacoustic emissions in ears with acoustic neuroma

A contralateral suppression effect on evoked otoacoustic emissions (EOAEs) is usually present in normally hearing subjects and in patients with sensor ineural hearing loss, while it is absent or reduced in ears to which the ve stibular nerve has been cut and in ears with acoustic neuroma (AN). To date , a paradoxical effect, that is an increase in EOAE amplitude during contra lateral stimulation, has been described in one ear with sensorineural heari ng loss of unknown aetiology and in three ears with AN (two in the present paper). Evidence has been provided that the contralateral suppression effec t on EOAEs is accomplished largely, if not entirely, via the medial olivoco chlear bundle (OCB). According to clinical data the absence or the reduced amount of contralateral suppression effect on EAOEs may be attributed to a totally, or partially, damaged or malfunctioning medial OCB. The way in whi ch a contralateral noise may increase EOAE amplitude is more difficult to e xplain. One attractive hypothesis is that this paradoxical effect is a resu lt of some pathological adaptive process in the medial OCB.