Low-tone air-bone gaps after endolymphatic sac surgery

Abstract

Objectives: We detected chronic low-tone air-bone gaps (LTABGs) in some patients with Meniere's disease after endolymphatic sac surgery. The aim of the present study was to elucidate the mechanism of LTABGs after endolymphatic sac surgery.

Methods: We investigated 50 patients with Meniere's disease, who underwent surgery more than two years prior. LTABGs were defined as the three-tone-average=20dB formulated by (a+b+c)/3, where a, b, and c are ABGs at 0.25, 0.5, and 1kHz, respectively (ABG ±). The intra-operative finding was focused on identifying operculum (OPC ±).

Results: The ratio of post-operative ABG(+) was 50.0% (25/50). The ratio of intra-operative OPC(+) was 72.0% (36/50). The surgery results were as follows: the ratio of complete vertigo suppression (VS(+)) was 84.0% (42/50), air-conduction hearing gain (aHG(+)) was 40% (20/50), bone-conduction hearing gain (bHG(+)) was 64% (32/50), and speech discrimination gain (SDG(+)) was 28% (14/50). The post-operative ABG(+) was commonly observed in patients with intra-operative OPC(+) (chi-square test, p=0.013). aHG(+) and SDG(+) results were related to the post-operative ABG(+) (chi-square test, p=0.021 and p=0.0018, respectively).

Conclusions: These data suggest that intra-operative OPC(+) may be causative for post-operative ABG(+), resulting in post-operative aHG(+) and SDG(+). Thus, as enlarged vestibular aqueduct syndrome and superior semicircular canal deficiency syndrome exhibit LTABGs due to the third mobile inner ear window, endolymphatic sac surgery with adequate endolymphatic sac decompression and exposure to high doses of steroids, might induce LTABGs and the beneficial results of endolymphatic sac surgery.