Multiple osteomas in mice.

Osteomas (dense compact neoplasms of mature bone tissue) are rare in nearly all strains and stocks of mice. Of 224 Him:OF1 mice maintained until natural death or until terminally ill, 116 (51.8%) had one or more osteomas. Osteomas had a predilection for the skull and the larger bones of the limbs. Plasma alkaline phosphatase concentrations were elevated significantly in osteoma-bearing mice (446 +/- 153 U/liter versus 206 +/- 65 U/liter in age-matched controls without osteomas). Only very large osteomas resulted in clinical signs, and longevity was not shortened. Histologic examination showed clearly separated dense bony tissue irregularly arranged and forming a mosaic pattern, with distinct cement lines and medullary spaces filled with fibroreticular connective tissue. Electron microscopic examination revealed virus-like structures in osteoblasts, osteocytes, and fibroblasts and in the place of remnants of necrotic cells.