Collagen types in the middle ear mucosa.

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The distribution of various collagen types--in particular that of type II as the major collagen in cartilage--in normal auricular structures is discussed with reference to a 1994 report by Ovesen describing the presence of collagen type II in normal middle ear mucosa. In contrast to this report, no collagen type II is normally found in the normal mucosa of the middle ear, while multiple structures of the normal middle and inner ear (which mostly consist of cartilage or have at least a cartilaginous origin) contain this unique collagen type. This indicates that the collagen type II staining previously observed in the normal middle ear mucosa is most likely an artifact. Of the at least 18 collagen types now known, interstitial and ubiquitously present types I, III and V can be found in the normal middle ear. The minor cartilage collagen types IX and XI have been found in cartilage of the middle (and inner) ear. The basement membrane collagen type IV is normally present in different microanatomical settings, particularly in the epithelial and endothelial basement membranes. In general, an exclusive morphometric estimation of area changes for collagens, particularly for collagen type IV, regardless of any tissue localization seems to be of minor value, since no attribution can be drawn to any of the histoanatomical structures present in the ear. The presence of further collagen types has not yet been tested in normal auricular structures.