A quantitative study of the sequence of topographical changes in the organ of Corti following acoustic trauma.

The organs of Corti of 30 guinea pigs were examined quantitatively by scanning electron microscopy either immediately or 1, 3, 7 or 14 days after exposure to 3 kHz at 125 dB SPL for 30 min. Lesions (0.1-4.15 mm in length) were observed in 70% of the organs of Corti. There was no significant change in lesion length with recovery from the exposure. Early changes in hair cells consisted of stereocilia abnormalities, predominantly amongst inner hair cells and the first row of outer hair cells. The proportion of affected cells increased towards the centre of lesions, where supporting cells were affected also. Subsequent to exposure, affected hair cells were either lost or remained with stereocilia abnormalities but did not recover. Regions showing supporting cell damage were replaced within 3 days by inner sulcus and Claudius cells. Despite similar changes to stereocilia, inner hair cells were more resistant to necrosis than outer hair cells, suggesting that the nature of stereocilia damage does not necessarily indicate the fate of hair cells.