It is generally believed that an intimate connection exists between chronic middle ear inflammatory conditions and inhibited growth of the pneumatized cellulae. In our previous report, we demonstrated the process of inhibited pneumatization in experimental studies using pigs. In the present study the histological study for the process of pneumatization was done using frontal sections of temporal bones by 100 sides of human fetuses between 16th and 36th week of pregnancy.
Until the middle phase of pregnancy, the cavities of mesotympanum, epitympanum and antrum are observed around the otic capsule but the other cells are not observed. The formation of these cavities is done only by absorbing the spongy bone sorrounding the otic capsule. In the late phase of pregnancy, the lateral development of temporal bone begins to start, especially in that portion which later gives rise to the mastoid process. The development of cavities in this portion is more active than other lateral portions. In these lateral portions, the expansion of pneumatic space is rapid and the formation of cellulae is heralded by the active bone metabolism, both by absorbing the bone tissues and by making new trabecular bones. This active bone metabolism is similar to the one that we observed in the experimental study using pigs. By the normal process of the pig's pneumatization with active bone metabolism, the middle ear inflammatory stimulus influenced adversely this active bone metabolism and inhibited the growth of cellulae causing inhibited pneumatization. From the results of this human fetal study, it is clear that the experimental inhibitory process of pneumatization seen in pigs will also apply to the human temporal bone, and the portion with active bone metabolism will be more affected.