[Distorsion-products otoacoustic emissions in acoustic neuroma]

Eight cases with surgically confirmed 1.5-3.5 cm acoustic neuromas were tested through measuring distorsion-products otoacoustic emissions (DPO), which objectively reflects the cochlear status. Only one frequency (Ft) corresponding to behavior threshold highest dB HL is selected as a frequency site of DPO. The DPO is collected at a level of 75 dB SPL with equilevel of stimuli f1 and f2 and proper frequency separation (f2/f1 = 1.2). The frequencies of stimuli f1 and f2 can be calculated through the formula Ft=2f1-f2. Six cases with less than 3.0 cm neuromas had normal amplitude of DPO. Decreased amplitude of DPO is found in two cases suffered from 3.0-3.5 cm neuromas. The discrepancy between behavior threshold and amplitude of DPO can be an important indication for distinguishing early retrocochlear lesions, for instance, acoustic neuroma.