Developmental anatomy of the eustachian tube and middle ear in mice.

PURPOSE: It is generally accepted that the development of the tubotympanum has significant bearing on the susceptibility to ear infection. A detailed study of the differentiation of ciliated cells in secretory elements will be useful in understanding both the normal physiology and the pathology of the tubotympanum. METHOD: Serially sectioned temporal bones of 76 mice ranging from gestational age day 11 to postnatal day 21 were examined microscopically. RESULTS: During the period of gestation, the tubotympanic recess was formed at the 12th day and began to extend to form the middle ear between the 13th and 14th days. A rapid increase in the volume of the tubotympanic recess was observed between the 15th and 16th days when a definitive division of the tubotympanic recess into the eustachian tube and middle ear cavity was observed. Postnatally the tubotympanum attained an adult form around day 9, and the maximum change of middle ear volume was noted on day 11, when the mesenchymal tissue in the middle ear cavity disappeared completely. Development of the ciliated cells was observed concurrently in both the eustachian tube and middle ear on the 16th gestational day, one day earlier than the appearance of the epithelial secretory cells in both the eustachian tube and middle ear. The number of ciliated cells and secretory cells increased rapidly after birth. Tubal glands were well developed with evidence of secretory activity around the time of birth. CONCLUSIONS: Based on these findings, one can conclude that the mucociliary defense system starts to develop during the fetal stage and is well established immediately after birth.