Contralateral transient evoked otoacoustic emissions following acoustic neuroma surgery

This study aimed to evaluate the effect of acoustic neuroma surgery on the contralateral cochlear function using transient evoked otoacoustic emissions (TEOAEs) and to test whether changes in TEOAEs differ according to the type of surgical approach. Forty four patients were included in this study. TEOAEs were recorded in both ears one day before (D0) and one month after surgery (D30). At D30, 20.5% of the patients showed an increase, 22.7% showed a decrease in contralateral TEOAEs amplitude and 56.8% remained stable. In the ear ipsilateral to the neuroma, TEOAE amplitude was significantly lower at D0 in the "increased" group compared to the "decreased" one. In the contralateral ear, TEOAE amplitude was significantly lower at D0 and D30 in the "increased" group compared to the "decreased" one and at D0 compared to the "stable" one. According to the surgical approach the patients were divided into two groups: a Translabyrinthine (TL) group (56.8% patients), and a retrosigmoid (RS) group (43.2% patients). The percentage of patients who presented an "increase" in TEOAEs amplitude in the contralateral ear was higher in the RS group (31.5) compared to the TL one (12%). The PTA lost at D0 was significantly higher in the TL group compared to the RS group. The TEOAE amplitude was significantly higher at D0 in both ipsi- and contralateral ears in the TL group compared to the RS one. These results suggest that acoustic neuroma removal is responsible for changes in contralateral TEOAEs. It can be hypothesized that changes in the efferent fibers secondary to surgery could partly explain these results.