Abstract
The clinical, radiographic, and pathologic features of a canine giant cell tumor of bone are compared with those of a giant cell reparative granuloma of bone. The giant cell bone tumor usually emerges from the epiphysis of long bones as a rapidly developing lytic bone lesion without periosteal new bone formation. The giant cell reparative bone granuloma originates preferentially in flat bones on the skull and mandible as a result of trauma-associated intraosseous hemorrhage, with new bone formation and sclerosis. Histologically, the neoplastic giant cells are scattered diffusely throughout the tissue, in contrast to the inflammatory giant cells that accumulate at the periphery of hemorrhages or around bone spicules. This peripheral accumulation is accompanied by a prominent collagenous and reticulum stroma. The morphologic and histochemical features of the giant cells can not be used as reliable tools to differentiate these two conditions.