GROWTH AND DIFFERENTIATION OF MEATAL SKIN-GRAFTS IN THE MIDDLE-EAR OFTHE RAT

Objective: To determine the behavior of epidermal cells after transpla ntation in the middle ear. Design: In a rat model, full-thickness meat al skin grafts were transplanted into the middle ear and studied morph ologically and immunohistochemically with the use of antibodies direct ed against different cytokeratin (Ck) polypeptides, which are markers of different types of epithelial cell differentiation. Results: The gr afts had either transformed into epithelial cysts or had become integr ated into the middle ear epithelium. The epithelium of the integrated grafts showed gradual transition into the epithelium of the middle ear . A clear distinction between epidermal cells and middle ear epitheliu m could be made only on the basis of their Ck profiles. The Ck profile s of the grafts revealed a decrease in the expression of epidermal Cks , while nonepidermal Cks became expressed. These changes can be ascrib ed to replacement of the dermal mesenchyma by mesenchyma from the midd le ear. In two ears with superimposed infection, the graft epithelium showed expansive growth. Conclusions: Meatal epidermis is well tolerat ed in the middle ear, but superimposed infection can induce expansive growth. These findings favor the concept that the progressive growth o f cholesteatoma is related to the presence of inflammatory processes.