Effect of round window reinforcement on hearing: A temporal bone study with clinical implications for surgical reinforcement of the round window

Abstract

Hypothesis: Round window reinforcement leads to conductive hearing loss. Background: The round window is stiffened surgically as therapy for various conditions, including perilymphatic fistula and superior semicircular canal dehiscence. Round window reinforcement reduces symptoms in these patients. However, it also reduces fluid displacement in the cochlea and might therefore increase conductive hearing loss. Methods: Perichondrium was applied to the round window membrane in nine fresh-frozen, nonpathologic temporal bones. In four temporal bones cartilage was applied subsequently. Acoustic stimuli in the form of frequency sweeps from 250 to 8000Hz were generated at 110 dB sound pressure level. A total of 16 frequencies in a 1/3-octave series were used. Stapes velocities in response to the acoustic stimuli were measured at equally spaced multiple points covering the stapes footplate using a scanning laser Doppler interferometry system. Measurements were made at baseline, after applying perichondrium, and after applying cartilage. Results: At frequencies up to 1000 Hz perichondrium reinforcement decreased stapes velocities by 1.5 to 2.9 dB compared with no reinforcement (p value =0.003). Reinforcement with cartilage led to a further deterioration of stapes velocities by 2.6 to 4.2 dB at frequencies up to 1000 Hz (p value=0.050). The higher frequencies were not affected by perichondrium reinforcement (p value=0.774) or cartilage reinforcement (p value=0.644). Conclusion: Our results seem to suggest a modest, clinically negligible effect of reinforcement with perichondrium. Placing cartilage on the round window resulted in a graded effect on stapes velocities in keeping with the increased stiffness of cartilage compared with perichondrium. Even so, the effect was relatively small.