[Assessment of cochlear function with distortion products of otoacoustic emissions in acoustic neuroma].

Unilateral hearing loss (HL) caused by an acoustic neuroma (AN) is regarded to be neural ("non-cochlear"). By using otoacoustic emissions it is possible to prove concurrent sensory (cochlear) HL. We prefer distortion-product otoacoustic emissions (DPOAE) because these are more frequency-specific and stable. From April 1994 to May 1996, we examined preoperatively 24 patients with radiologically proven AN. Pure-tone audiometry, DP-grams, brainstem-evoked response audiometry (BERA) and vestibular studies were performed in all cases, while special auditory tests (Fowler, Carhart) and short increment sensitivity indices were also performed in 12 cases. BERA was pathological in 23 cases and latencies were borderline in one case. After comparing audiograms and DP-grams we found 13 patients with sensory HL, 4 patients with combined sensorineural HL and 7 patients with neural HL. There was a strong correlation between the results of DPOAE and the results of special auditory test (phi = 0.63) whereas there was no correlation between tumor size and cochlear function. The result showed that the typical HL caused by AN was a combined sensorineural loss. DPOAE were not suited for the detection of AN but were able to give exact information about any remaining cochlear function.