Objectives/Hypothesis: The goal of this study was to identify the clinical significance of the low-frequency air–bone gap (LFABG) that often develops after endolymphatic sac surgery. Study Design: Prospective study. Methods: Sixteen patients who had been diagnosed with definite Meniere disease and underwent endolymphatic sac surgery were studied. The surgical outcome was evaluated based on the 1995 guidelines of the American Academy of Otolaryngology–Head and Neck Surgery. The number of patients who developed LFABGs (a mean air–bone gap >10 dB HL at 250, 500, and 1,000 Hz) after surgery was determined, and the significance of the LFABGs was evaluated by analyzing their relation with the surgical outcome. Results: The vertigo spells of nine patients were completely controlled (class A). The number of vertigo spells was reduced by 60% to 99% in 6 patients (class B) and by 20% to 59% in 1 patient (class C). Postoperative LFABGs were observed in 13 patients. The mean LFABG of the patients in class A was significantly larger than that of the patients in classes B and C (25.0 ± 7.6 dB nHL in class A vs. 10.0. ± 7.5 dB nHL in class B and C; P = .005). Conclusions: Based on the data of the current study, we conjectured that the correlation of large LFABGs with excellent vertigo control in this study may be due to a third window phenomenon related to bony decompression of the endolymphatic sac and duct, and may serve as a favorable prognostic marker.
