Learning Objectives: 1. Appreciate the issues regarding bone conduction in high frequencies. 2. Recognise the risk of extended high frequency hearing loss with middle ear surgery and its possible significance.
Introduction: Permanent hearing loss in the extended high-frequency range (8–16 kHz) occurs in up to 50% of patients following otherwise successful middle ear surgery. The mechanisms of this high-frequency loss are poorly understood, but hypotheses include supraphysiological ossicular movement and noise exposure from drilling and suctioning. High-frequency loss could also be conductive and result from physical changes to the conductive mechanism. Previous research has been limited by difficulties measuring high-frequency bone-conduction thresholds, and thus distinguishing between conductive and sensorineural loss. We present a small pilot study demonstrating that high-frequency hearing loss can be composed of both conductive and sensorineural components.
Methods: A giant magnetostrictive transducer was modified for audiometric use and testing was conducted to establish the reliability and validity of thresholds measured using the device. Air- and bone-conduction audiometric thresholds at 0.5–16 kHz were then measured preoperatively and at 1 week, 1 month, and 3 months postoperatively in four patients; three undergoing stapedectomy and one ossiculoplasty.
Results: Testing in normal hearing listeners showed that the modified transducer could be used to measure high-frequency bone-conduction thresholds with a level of reliability comparable to standard bone-conduction testing. The pilot study identified two clear cases in which an initial transient conductive high-frequency loss was documented concurrently with a persistent high-frequency sensorineural loss.
Conclusions: These results suggest that extended high-frequency hearing thresholds as measured using the modified bone-conduction transducer are a more sensitive measure of operative trauma to the cochlea that may be used to determine the efficacy of interventions to protect the ear from surgical trauma.
