Tympanic membrane displacement patterns in experimental cholesteatoma.

Tympanic membrane (TM) stiffness changes in the pars tensa in response to experimentally induced ear canal cholesteatoma by obstruction of the ear canal were studied. To this aim TM displacement versus pressure was measured with a high resolution, differential moiré interferometer. The measurements were performed on fresh, isolated gerbil temporal bones after removal of the cholesteatoma bulk. Besides an overall stiffness reduction we found that local stiffness variations were present in nine out of 18 studied ears. The stiffness changes as a function of time after ear canal obstruction had a pattern similar to those previously shown to develop in response to various forms of otitis media, showing that the TM stiffness properties decrease in a similar way in response to different inflammatory middle ear diseases. The stiffness changes correlated with an increased overall TM thickness and increased thickness of the lamina propria in particular as measured in histology sections. The stiffness changes may play an important role in the pathophysiology of cholesteatoma.