Yutaka Takeyama

Role of Outer and Middle Layers in Healing Process of Tympanic Membrane Perforations

This study was designed to demonstrate how each layer of the guinea pig tympanic membrane responds during the healing of a perforation. Epidermal growth factor (EGF) and platelet-derived growth factor (PDGF) were employed to stimulate the healing process of the outer and middle layers, respectively.The tympanic membrane was perforated by an electrical burn, and each growth factor was injected daily into the otic bulla through the external auditory meatus. The tympanic membrane perforations were examined with hematoxylin-eosin and immunohistochemically with bromodeoxyuridine. The maximal thickness of each layer at the margin of the perforation was measured light microscopically and the labeling index of bromodeoxyuridine was calculated.Tympanic membrane perforations closed more rapidly in the PDGF-treated than in the EGF-treated ears. Significant proliferation of the epithelial layer was obtained with both treatments. However, proliferation of the middle layer was greater in the PDGF-treated than the EGF-treated ears. These results suggest that proliferation of the middle layer stimulates the epithelial layer and that proliferation of the epithelial layer directly quickens the closure of perforation of the tympanic membrane.