The purpose of this study was the comparison of morphological changes in the inflammatory and the normal middle ear mucosa in pigs, which have an air cell system similar to that in human beings, by the electron microscopy.
Otitis media was effected in the each right ear of 4 pigs by the transcanal injection of glycerin into the middle ear cleft at 1 and 2 weeks after birth. The left ears remained normal. Two of the pigs were sacrificed respectively at each of 1 and 6 months after birth. Middle ear mucosal samples for scanning (SEM) and transmission electron microscopy (TEM) were obtained from the Eustachian tube, middle ear cleft, and air cell system. The specimens were fixed in 2.5% glutaraldehyde within 3 hours after sacrifice, buffered in 0. 1 M cacodylate at pH 7.2 and postfixed with 1% osmium tetroxicide for 2 hours. After being dehydrated through ascending grades of alcohol, the samples for SEM were dried to a critical point in liquid carbon dioxide, mounted on aluminium stabs, spattercoated with gold and viewed by scanning electron microscopy Hitachi S430. The samples for TEM were embedded in Epok 812, sectioned by microtome and stained with lead citrate and uranyl acetate. Grids were viewed and photographed with transmission electron microscopy Hitachi HS9 and H800.
In the normal ears, the epithelial cells consisted of ciliated cells, non-ciliated cells, secretory cells and basal cells. Each ciliated cell had 80 to 100 cilia which were about 5 to 8μ in length. There were 3 types of secretory cells: one with only light secretory granules, one with only dark secretory granules and the other with both light and dark secretory granules. Non-ciliated cells had no cilia or secretory granules but had microvilli on their flat or mildly bulging surfaces. The ciliated cells were distributed most densely in the Eustachian tube and tubal orifice of the middle ear cleft, decreasing in number towards the air cell system. In the Eustachian tube, a high density of cilia was noted to occur regulary near the pharyngeal orifice. The secretory cells were distributed in the same way as the ciliated cells. However the non-ciliated cells were distributed in a reverse pattern. In the air cell system, the epithelial cells consisted of only flat non-ciliated cells and there were no ciliated or secretory cells. The features at 1 month after birth were the same as those 6 months after birth.
In the inflamed ears, the construction and distribution of epithelialcells were the same as in normal ears. However the cilia were deformed or missing and were irregularly detached from all epithelial cells in some places of the Eustachian tube and middle ear cleft at 1 month after birth. On the other hand ciliated cells, bulging secretory cells and columnar cells were increased in numbers in the Eustachian tube and middle ear cleft at 1 month after birth. It was observed that these features had returned to normal by 6 months after birth. In the air cell system, SEM revealed hardly any changes at 1 and 6 months after birth compared with the normal cases, whereas any TEM showed subepithelial thickening in the air cell system persisting even at 6 month after birth.
Although it was functioning actively in the normal Eustachian tube and middle ear cleft, the muco-ciliary system seemed stimulated in the inflamed cases-seen by the increase of ciliated cells, bulging non-ciliated cells and columnar cells. The inflammatory changes in the Eustachian tube and middle ear cleft which appeared at 1 month after birth returned to normal at 6 month after birth. However in the air cell system without epithelial changes, the subepithelial thickening remained at 6 month after birth. These results suggest that inflammation which effects the air cell system where there is no muco-ciliary system is prolonged more easily than in the Eustachian tube or middle ear cleft which has a muco-ciliary system.
