Observation of apoptosis and bone lamella structures in the human mastoid

Hypothesis To investigate the localization of apoptotic cells and the lamellar bone structure in mastoid bone tissue, focusing on the mechanism of the development of mastoid pneumatization in humans. Background The biological mechanism of poor development of the mastoid air cells found in patients with otitis media (OM) has not yet been fully clarified, as there have been few immunohistochemical research studies to examine the cell biology involved. Methods We evaluated the localization of apoptotic cells and the lamellar bone structure in 112 human mastoid bones harvested during various ear surgeries from 57 patients with OM and 55 patients without OM. We used the TdT-mediated dUTP nick end-labeling (TUNEL) method and a polarizing microscope for observing the apoptotic cells and lamellar bone structure, respectively. Results The TUNEL-positive cell ratio in an arbitrary 500 cells in the specimen (apoptotic index: AI) was 13.8 in the healthy group and 1.2 in the OM group (Mann-Whitney U test, p Conclusion Apoptosis of osteocytes was significantly suppressed in the mastoid bone of the OM patients. Apoptotic osteocytes may be one of the signals of bone resorption in the process of development of the mastoid air cells. The lamellar structure of the mastoid bone suggested that poor development of the mastoid air cells was caused by decreased resorption of the appositional bone.