Tympanic membrane changes after installation of polyethylene grommets. An experimental study in the rat.

The object of this study was to establish the morphological changes which occur when a polyethylene grommet is implanted in the normal tympanic membrane of experimental animals. We found a serous effusion around the grommet and in the attic during the first weeks after installation. All the grommets had been displaced away from the tympanic memebrane in a medical direction into the middle ear cavity. The displacement was most likely brought about by a squamous cell epithelial and connective tissue hyperplasia, which reached its maximum after 2--3 weeks. Neither atrophy, atelectasis, nor retraction was observed, whether in the pars flaccida or the pars tensa. A greyish, horseshoe-shaped configuration was seen in all specimens in the undisturbed front quadrants. No firm histo-pathological correlation was found to explain these changes. In these studies in the rat, the perforation appeared to heal, although delayed, in the same way as after a central perforation, once the polyethylene grommet had been ejected.