Abstract:

Objective    Recording and analyzing vestibular evoked myogenic potentials (VEMP) and pure tone audiometry(PTA) in large vestibular aqueduct syndrome(LVAS), may reveal the function of the saccule and vestibular nerve, describe the characteristics of PTA, and investigate its clinical application and significance in LVAS.  Methods    The results of the examination and clinical symptoms of 22 cases of LVAS (42 affected ears) who were all underwent high resolution CT scan of inner ear, PTA and VEMP were summarized and analyzed. Results    25 of 42(59.5%) affected ears which were excited by VEMP with bilateral short sound stimulation showed a high amplitude and/or low threshold. 30 of 42(71.4%) affected ears excited by PTA showed mixed hearing loss with the feature of significant air-bone gap in low and intermediate frequency (below 2KHz). In the low-threshold group of VEMP, the mean value of the vestibular aqueduct was (4.30±0.53) mm, and the pure tone average of the air-bone gap in low frequency was (36±17) dB HL. 19 ears were easily influenced by external factors or fluctuations of internal cranial pressure caused by fever. In the non-low threshold group of VEMP, the mean value of vestibular aqueduct was (2.80±0.67) mm, and the pure tone average of the air-bone gap in low frequency was (32±15) dB HL. 4 ears were easily influenced by external factors or the fluctuations of internal cranial pressure caused by fever.  Conclusions    The average value of vestibular aqueduct diameter is larger in patients with a lower VEMP threshold whose subjective hearing are affected by the external factors orthe fluctuations of internal cranial pressure caused by fever. But there is no correlation between the degree of the hearing loss with the mean value of vestibular aqueduct, nor with the characteristics of VEMP.

Key words: Large vestibular aqueduct syndrome; Vestibular evoked myogenic potentials; Mixed hearing loss; High amplitude; Low-threshold