Although most of acquired middle ear cholesteatomas are considered to be formed by retraction of tympanic membrane (TM), there are some cases in which TM epidermis extends into the medial surface of the TM from the margin of its perforation, so-called secondary cholesteatoma. This type of cholesteatoma was found in 14 of 460 ears (3.0%) with acquired middle ear cholesteatoma operated on in our hospital from 1992 to 2007. An irregular margin of the perforation was found in 9 of 14 ears. The epidermis was found to be extended into the medial surface of the TM at the perforation edge adjacent to the malleus manubrium in all the cases. We classified them into three types, mesotympanic (MT) type. (5ears), in which cholesteatoma matrix was localized within the mesotympa-num, protympanum (PT) type.(4ears), in which cholesteatoma extended into the eustachiantube and the spratubal recess, and retrotympanic (RT) type. (5ears), in which choleateatoma extended towards the incudostapedial joint and the retrotympanic cavity. Although cholesteatoma matrix could be removed without mastoidectomy in the MT-type, the PT-type in which cholesteatoma matrix located anterior to the malleus-head or supratubal recess, often required mastoidectomy with anterior tympanotomy. The RT-type tended to have greater air-bone gap, due to destruction of the incudostapedial joint by the choleateatoma extention along the incus long process.
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