Mast cell clusters in pars tensa membranae tympani in acute otitis media: a possible role in perforation healing.

Mast cells are known to reside in pars flaccida membranae tympani and other parts of the middle ear mucosa in both rats and humans. However, the normal pars tensa contains no or only a few mast cells along the manubrial vessels. We examined the pars tensa of 25 rats in an experimental model of acute otitis media and found 13 mast cell clusters in 6 membranes. A majority of clusters were located in the anterior, superior quadrant and contained from 3 to 23 cells. The mast cells resided immediately under the inner epithelial lining or in the intermediate, fibrous layer. In two membranes mast cell clusters were found in the margin of apparently healed spontaneous perforations. We conclude that mast cells in some cases infiltrate pars tensa membranae tympani in the late and receding phase of acute otitis media. As these cell clusters in some cases were found immediately around apparently healed membrane perforations, we propose that the mast cell might participate in the repair processes of tympanic membrane perforation healing. This is supported by recent studies in wound healing and functions of a number of mast cell mediators.