[Temporal bone study of residual mastoid inflammation in ears with normally appearing tympanic membrane]

We examined 395 temporal bones with an intact tympanic membrane to explore the relationship between residual inflammation in the middle ear cavity and development of mastoid pneumatization. Histopathological changes were studied in the middle ear cavity. Mastoid pneumatization was classified as good or poor based on the extent of mastoid tip development to the lateral semicircular canal. Specimens were 344 temporal bones with well-pneumatized mastoid and 51 with poorly-pneumatized mastoid. Otitis media was noted in 119 (34.6%) bones in the good group and 9 (17.6%) in the poor group. In well-pneumatized mastoid, chronic inflammatory changes were frequently observed at the lower portion of mastoid cells, the round window niche, and the tympanic sinus. In contrast, no such incidence of inflammatory change was noted in poorly-pneumatized mastoid. Our findings indicate that an intact tympanic membrane does not always mean freedom from mastoid inflammation, especially when the mastoid is well-pneumatized. This makes it important to check for possible remaining otitis media in patients with a well-pneumatized mastoid, even if the tympanic membrane appears normal.