The Effect of Chronic Middle Ear Inflammation on the Develop- Ment of the Mastoid Air Cell System

The effect of chronic middle ear inflammation on the development of mastoid air cell system was investigated in piglings, whose tympanic bullae closely resemble the human mastoid air cell system. Experimental chronic otitis media was produced by the injection of glycerin into the middle ear cleft of piglings aged from 5 days to 5 weeks after birth. The piglings were subsequently decapitated and the temporal bones removed at 50 days, 2 months, 4 months and 6 months after birth, to examine and compare the degree of pneumatization of the tympanic bullae histologically, against that of non-treated control group. In the non-treated control group free of inflammations, the tympanic bullae were developed as a result of the bone formation by the osteoblasts, and the air cell system was developed widely inside of the cortex due to the bone resorption by osteoclasts. On the other hand, in the tympanic bullae of treated animals, non-specific chronic middle ear inflammation was noted and, although the bone formation by osteoblasts progressed as in normal tympanic bullae, very few osteoclasts were observed. This suggested reduced bone resorption by osteoclasts due to the inflammatory stimulus. Moreover, it was found that later the time of removal of the temporal bone, the larger the proportion of the bone mass occupying the tympanic bullae, and only slight remnants of the air cell system was detectable near the middle ear cleft in glycerin treated 6 months old piglings. The tympanic bullae and the air cell system of normal piglings were well developed due to the bone formation and the bone resorption inside the cortex, whereas the tympanic bullae of piglings afflicted with chronic otitis media in the early stages of life exhibited retardation of pneumatization arizing from the disturbance of bone resorption by inflammatory stimulus, resulting in thickened residual bone mass with development. Therefore, the development of air cell system was inhibited severely in spite of the normal growth of tympanic bulla itself. In conclusion, it was thought that affliction with chronic middle ear inflammation in the early stages of life induces the inhibition of pneumatization by hindering the developmental process of the air cell system.