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Distinguishing Between Conductive and Sensorineural Extended High-Frequency Hearing Loss Following Middle Ear Surgery

Presenting Author: Philip Bird

Published online by Cambridge University Press:  03 June 2016

Philip Bird ,
Melissa Babbage  and
Greg O'Beirne
Philip Bird
Affiliation:
University of Otago
Melissa Babbage
Affiliation:
University of Canterbury, CHCH, New Zealand
Greg O'Beirne
Affiliation:
University of Canterbury
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Abstract

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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.