Contralateral suppression of transient evoked otoacoustic emissions in patients with cerebello-pontine angle tumor.

OBJECTIVE: During measurement of transient evoked otoacoustic emissions (TEOAEs), acoustic stimulation of the contralateral ear reduces or suppresses TEOAE amplitude. This is thought to be due to the inhibitory control that the medial efferent auditory nerve exerts on outer hair cell (OHC) function. The main aim of this study was to investigate the effect of cerebello-pontine angle (CPA) tumor on the medial efferent nerve pathways to both tumor and non-tumor ears by examining alterations in TEOAE amplitude that result from contralateral acoustic stimulation. DESIGN: Contralateral suppression of TEOAEs using broadband noise was measured preoperatively in 17 patients with unilateral CPA tumor and 17 normally hearing controls, matched for age and gender. RESULTS: The control ears demonstrated significantly more suppression than the tumor and non-tumor ears in the patient group. There was, however, no significant difference in suppression between the tumor and non-tumor ears, and the statistical correlation for suppression between them was high. There was no effect of gender, hearing threshold levels, or size and type of tumor on suppression, although there was an effect of age on suppression in both the control and patient groups where suppression reduced as age increased. Four of the 17 patients had TEOAEs, which were clearly present in the tumor ear despite substantial hearing loss, three of which had no measurable hearing. CONCLUSIONS: It is hypothesized that neural compression by CPA tumor disrupts the medial efferent nerve control mechanism to the OHCs of tumor ears. It also is hypothesized that neural compression reduces transmission of afferent nerve impulses from the tumor ear, which cross over to the medial olivo-cochlear complex and reduce the inhibitory control of OHC function in the non-tumor cochlea.