Tympanic membrane changes resulting from different methods of transmyringeal middle ear ventilation

This experimental study was designed to evaluate the morphologic changes of the tympanic membrane in the rat after different methods of transmyringeal ventilation. Artificial ventilation was obtained in two principal ways, either by making tympanic membrane perforations with delayed healing or by inserting a tympanostomy tube. Perforations occupying the upper rear quadrant of the tympanic membrane were made by diathermy or by a carbon dioxide laser with healing times of 12 to 15 days and 18 to 21 days, respectively. Compared with the healing times of perforations made by lancet (9 to 11 days), the healing pattern was considerably delayed. The structural changes of the healed tympanic membrane were minimal, but the connective tissue remained thickened for several months. Repeated insertion of tympanostomy tubes caused a remarkable thickening (30-fold) of the tubulated quadrants. The thickened tympanic membranes were characterized by a hyperplastic, dense connective tissue containing sclerotic plaques. Similar changes, though less pronounced, were also seen after reiterated myringotomies without tube insertion.