Giant cell tumors of bone containing large amounts of hemosiderin: MR-pathologic correlation.

We present three giant cell tumors of bone that contained large amounts of hemosiderin and compare their MR appearance with intraoperative findings and histological characterization. Histologically, hemosiderin was found in multinucleated giant cells, mononuclear stromal cells, and xanthoma cells. All cases showed markedly decreased signal areas on both T1- and T2-weighted MR imaging due to hemosiderin deposition; this made evaluation of the integrity of the adjacent cortices difficult. In one case, extraosseous tumor extension appeared as a signal void area on MR imaging. Findings on immunohistochemical studies suggested the giant cells may have a histiocytic nature. Because the tumor cells themselves have a phagocytic nature, the decreased signal areas in and around giant cell tumors should be regarded as active tumor tissues in delineating the tumor on MR imaging.