Ultrasonic irradiation through the round window. Functional and morphological findings in sound-conditioned cats

Ultrasound was presented though the round window in 9 sound-conditioned cats at levels approximating clinical usage. Threshold shifts were mild to moderate and confined to 4 kHz and higher. There was total loss of function at 16 kHz in 2 animals. Threshold shifts correlated with cochlear histological findings as shown by reconstruction. There were three main types of lesions: abnormalities of supporting structures, hair cell loss, and lesion of Reissner's membrane. Supporting structure damage was the most frequent. The cristae of the semicircular canals did not show any lesions, though some saccular damage was noted. These changes were not observed in 4 control animals. Some conductive damage was noted as a result of probe placement. High frequency loss can be expected with the round window approach at irradiation levels of 52 mW for 20 min, or stronger.