[Experimental middle ear cholesteatoma originated from free skin graft of the external ear]

The pathogenesis of middle ear cholesteatoma has been thought to be invasion of squamous epithelium originated from the external ear skin including the tympanic membrane. There is no evidence, however, that the external ear skin has more potential to form cholesteatoma than that of other sites. In this report experimental middle ear cholesteatoma of guinea pigs originated from the external ear skin was histologically compared with that originated from the auricular skin. Cholesteatoma as dermal cyst was seen in the middle ear of almost all animals (25/28 = 89.3%), using a free skin graft (3 x 3 mm), regardless of the skin taken from superior (group A) or inferior (group B) part of the external ear, or the auricle (group C) eight weeks after skin implantation. The activity of epithelium such as keratinization was evident in group C. There is, however, no obvious difference in surrounding granulation tissues among group A, B, and C. In a half of this series, cyst wall was broken and its contents (debris) mainly consisted of keratin were put on surrounding granulation tissues three weeks after skin implantation. Striking keratinized epithelium and subepithelial inflammations in relation to the amount of debris were observed at the eighth week. These findings suggest that the external ear skin does not have specific potential to form cholesteatoma and keratin plays some roles in growth of cholesteatoma.