A resected, bisected giant cell tumor of bone. Notice the typical brownish color of this lesion, due to the repeated hemorrhage and accumulation of hemosiderin pigment. Usually arise in the third to the fifth decade of life. Slightly more common in females.
Tumors are usually large and distinctly red.
Areas of hemorrhage and cystic degeneration are frequent. Histologically, the tumor is composed of mononuclear cells and many multinucleate cells, often with 40 to 100 nuclei. The nuclei of the mononuclear cells and the giant cells are identical. This is an important distinguishing feature of this tumor from other giant cell containing tumors and other lesions of bone, such as pigmented villonodular synovitis, or brown tumors due to hyperparathyroidism. Some reparative bone formation can be seen in older lesions.