The early stages of polyp formation.

The purpose of this study is to describe polyp formation in the mucosa of the middle ear as a possible model for the pathogenesis of nasal polyps. In 65 Wistar rats, the eustachian tube was occluded on the left side for up to 20 months; 60 right-sided, nonoccluded ears served as controls. Following occlusion, the middle ear mucosa was examined for signs of polyps. Signs of polyp formation or fully developed polyps were seen in 14 (22%) of the middle ears, and were only seen in middle ears with signs of actual or previous infection. It was established that the first stages of polyp formation include epithelial rupture, proliferation of fibrous tissue through the epithelial defect, and epithelialization of the prolapsed fibrous tissue by proliferation and migration of epithelial cells from the surrounding epithelium until there is full epithelial covering of the polyp. This report discusses whether the described middle ear model may form basis for the explanation of the pathogenesis of nasal polyps.