Stages of gerbilline cholesteatoma (reproduced with modification with permission from Henry et al. [30]). Stage I is accumulation of keratin debris on outside surface of tympanic membrane; stage II is medial displacement of tympanic membrane into middle ear without contact with middle wall of bulla; stage III is contact of cholesteatoma with prominence of cochlea (arrows point to early bone erosion); stage is IV cholesteatoma filling bulla; stage V (not shown) intracranial extension of cholesteatoma (reproduced with modification with permission from [30]).
