Effect of round window removal on auditory thresholds in cats.

Round window fistula is a recognized and proven pathological entity that can cause sudden hearing loss. The study reported here, using cats, measured changes in the brainstem evoked response threshold to click stimuli after total removal of the round window membrane. The results showed an immediate 25 dB threshold decline followed by a further 35 dB decline over four hours. The response threshold then remained constant for 20 hours. In one animal there was no response to a stimulus of 110 dB SPL immediately post-op, and this animal, on re-examination, had a hole in the basilar membrane. In two animals, a membrane formed spontaneously over the round window area. In one, the response threshold did not change postoperatively, and in the other the threshold partially recovered following an initial decline.