Mast cells in human middle ear mucosa in health and in disease.

The distribution of mast cells was studied in normal human middle ear mucoperiosteal lining and in middle ear biopsies of patients with acute and chronic otitis media. The mast cells were identified on the basis of the metachromatic staining for their cytoplasmic granules with Giemsa and toluidine blue. Only a few mast cells located in proximity to blood vessels in the lamina propria underneath the epithelial layer were observed in normal middle ear mucoperiosteum. The number of mast cells in acute inflammatory reactions and in the normal middle ear lining was similar. By contrast, the mast cell count was significantly increased in chronic inflammatory reactions. The population density of the mast cells was the highest in the subepithelial layer of cholesteatoma, in regions where the lamina propria showed fibrosis and infiltration with chronic inflammatory cells, and around mucous glands. The presence of increased numbers of mast cells in chronic otitis media is consistent with our previous finding of high levels of histamine in middle ear effusions. It is postulated that mast cells play an important role in the pathogenesis of chronic otitis media through the release of their active biochemical mediators.