Abstract

Osteoid osteoma and osteoblastoma are uncommon benign bone tumors which originate from osteoblasts in animals. Both tumors have similar characteristics. Osteoid osteoma is well described in humans, but there known to be only two cases in domestic animal species. Differentiating the diagnosis of osteoid osteoma from osteoblastoma by using immunohistochemistry was aimed in this study. A 12-year-old mix breed female dog was brought to the clinic with complaints of swelling in proximal forelimb and progressive loss of motion. Animal was died during surgery. In necropsy, tissue samples were taken from the mass and fixed in %10 formalin. Samples were stained with hematoxylin and eosin, Masson’s trichrome and Alizarin Red S. For revealing of cell differentiation, ABC-P method was applicated to adhesive section by using BMP6, S100, vimentin ve p53 markers. Macroscopically, proximal humerus was swollen. Cut section was generally lytic within bone residues. Soft tissue was haemorrhagic and edematouse. Microscopically, osteoblasts and hypervascular nidus were surrounded by large sclerotic and mineralized bone tissue. Large lytic areas were also observed. Masson’s trichrome revealed sclerosis and Alizarin Red S revealed osteoid matrix. Immunohistochemically, BMP6 was moderately reacted in osteoid matrix and S100 was moderately reacted with nerve fibers in nidus. Vimentin had strictly positive reaction in fibrocytes. P53 was negative in osteoblasts.

In conclusion, this case is the third reported in domestic animals and the second in dogs. Also osteoid osteoma is evaluated for the first time by immunohistochemistry in animals.

Keywords: Dog; Immunohistochemistry; Osteoblastoma; Osteoid osteoma: Pathomorphology