Transiently evoked otoacoustic emissions in patients with cerebellopontine angle tumors.

Transiently evoked otoacoustic emissions (TEOAE) are generally present in ears with normal hearing, but absent in ears with cochlear hearing losses greater than 25-30 dB; they have been demonstrated previously in a few ears with retrocochlear hearing losses greater than 30 dB across the frequency range 0.25-8 kHz. To assess the potential of TEOAEs in the diagnosis of retrocochlear hearing losses, measurements were made in 45 patients with retrocochler disorder attributable to confirmed cerebellopontine angle (CPA) tumors. Transiently evoked OAEs elicited by click stimuli were recordable in 21 (47%) of the ears with tumor. Nine of these had normal hearing at two or more octave frequencies across the range 0.5-4 kHz and so might be expected to have TEOAEs regardless of the type of disorder. The other 12 ears had recordable TEOAEs despite hearing threshold levels greater than 25 dB between 0.5 and 4 kHz. The absence of TEOAEs in the remaining 24 ears (53%) indicated a significant outer hair cell component to the hearing loss. Neither age nor sex were significant factors in the occurrence of TEOAEs. The TEOAE test gives useful differential diagnostic information when emissions are recorded in ears having hearing threshold levels greater than 25 dB at all frequencies. In such ears there is relatively normal cochlear function at the level of the outer hair cells, at least at some frequencies, and hence, by inference, there must be a retrocochlear disorder.