Morphologic development of experimental cholesteatoma.

Using light microscopy, we studied the morphologic events of cholesteatoma progression 8 months after ligation of the ear canal in 14 Mongolian gerbils. Although we observed a wide range of progression, four stages of morphologic development could be clearly distinguished among the 28 specimens: stage I, an orthokeratotic plug in the ear canal without tympanic membrane involvement; stage II, partial retraction of the tympanic membrane; stage III, the interface between cholesteatoma encapsulated within the tympanic membrane and mucosal membranes covering the promontorial wall of the middle-ear cavity was characterized by a buildup of granulation tissue with prominent macrophage infiltration; and stage IV, bone destruction. Chronic inflammation was observed in some but not all stage II to IV cases. Our results indicate that hyperkeratosis is a primary event in cholesteatoma development, that the development of the granulation tissue with activated macrophages may be responsible for the bone destruction, and that acute or chronic inflammation is not a prerequisite for the development of cholesteatoma or the bone resorptive process.