The clinical significance of the tympanic isthmus related to the development of cholesteatoma.

The epitympanum is separated from the mesotympanum by the ossicles, tendons and tympanic mucosal folds except at two narrow openings, the anterior and posterior tympanic isthmuses. Using large numbers of fresh cadaver temporal bone specimens, anatomical boundaries of the tympanic isthmus were defined and pathological variations were investigated in relation to the development of aural cholesteatoma. A total of 170 temporal bone specimens were examined under the operating microscope. Five of these were found to have middle ear diseases, most of which were cholesteatoma or a preliminary state of cholesteatoma, with their tympanic isthmuses obstructed or narrowed. Pneumatization of the mastoid was inhibited in all of the pathological specimens. From the results of temporal bone dissection supplemented by analysis of surgical findings in cholesteatoma, we have divided acquired cholesteatoma into two types: the pars flaccida-type cholesteatoma (attic retraction-type) and the pars tensa type. The close relationship between the development of cholesteatoma and occlusion of the tympanic isthmus is examined herein.