Cholesteatoma in the oval window niche.

The histopathological changes in the oval window niche into which a cholesteatoma is spreading are described in 14 temporal bones. Extension of the matrix into the niche was found commonly. In some cases the matrix passed from the facial canal to the promontory but failed to reach the niche. The perimatrix of the cholesteatoma was composed of inflamed and vascularized granulation tissue or fibrocystic tissue. A matrix covering the walls of the niche and the footplate of the stapes or the oval window was rarely found. It was surrounded by a thin layer of non-inflamed fibrous or fibrocystic tissue which covered the niche. Bone destruction of the superstructures of the stapes was observed in 12 of the 14 cases examined. The footplate of the stapes was partially or totally destroyed in 4 cases. Bone destruction of the tympanic portion of the facial canal adjacent to the oval window niche was present in all cases. Our present studies further suggest that surgical removal of a cholesteatoma from the niche may be difficult, even when done very carefully.