Polyp Pathogenesis-A Histopathological Study in Experimental Otitis Media

Abstract

We examined the mucosa of 50 rat middle Cars in an experimental model of acute otitis media, in order to obtain information on the mechanisms of polyp formation- The right middle Car of 25 rats was inoculated with type 3 pneumococci. and the left Car served as a control. The animals were killed, the middle Car bulla removed, and the mucosa was dissected from the bone, stained PAS-alcian blue and embedded as a whole-mount. The whole-mounts were examined in a light microscope for polypous mucosal prominences. Serial sections were made of all polyps, and of relevant parts of the mucosa. 15 polyps were found in II (44%) of 25 infected Cars: none were found in normal control Cars. Goblet cell density was increased in polyps and the surrounding epithelium. Epithelial microruptures were seen in areas with widespread inlra-epithelial liquid vacuoles and subepithelial accumulation of liquids, luminally migrating inflammatory cells, increased vascularization and edema. Connective tissue of the lamina propria was prolapsed through most ruptures. Some prolapses showed signs of re-epithelialization. while others had a full epithelial lining that resembled a fully dew eloped polyp. Our findings support our Carlier theory on nasal polyp pathogenesis, based on the following stages: i) Localized rupture of the epithelial lining, ii) Luminal protrusion of the lamina propria through the epithelial defect. iii) Re-epilhclialization of protruded tissue, and formation of a polyp, iv) Growth of the polyp. Infection of the upper respiratory airways is common, and because polyps were found in areas with respiratory-like epithelium, the present findings and theories may be applicable to conditions in the human nasal passages.