[Residual cholesteatoma: an experimental study in guinea pigs].

The mechanisms of formation of the "open" and "closed" types of residual cholesteatoma were investigated in guinea pigs. An autogenous free skin graft taken from the posterior auricle (2x2mm, full-thickness) was transplanted into the dorsal otic bulla. In the left ear, a graft was placed on the bony surface following removal of the mucous membrane and drilling with a diamond burr (group A). In the right ear, another graft was placed directly on the intact mucosa (group B). After completion of these procedures, the opening of the bulla was closed with dental cement and the wound was sutured. The animals were sacrificed at 2, 4, 8 and 32 weeks after transplantation for histological study. In group A, an epidermal cyst formed within two weeks of transplantation in 10 of 17 animals. In all 16 animals in group B, the graft adapted, retaining its original flat shape, and resembling the open type of residual cholesteatoma. Differences in the shape of the epidermal transplant are thought to be due to formation of granulation tissue around the graft.