Fine-needle aspiration of brown tumor of bone: cytologic features with radiologic and histologic correlation.

We report the case of a 40-year-old man with tertiary hyperparathyroidism due to end stage renal disease who initially presented with acute-onset paraplegia, elevated serum parathyroid hormone, and multiple bone abnormalities, including a large extradural intraspinal mass seen by magnetic resonance imaging. In contrast with imaging features, fine-needle aspiration cytology showed numerous benign-appearing multinucleated osteoclast-type giant cells that are the characteristics of either brown tumor or benign giant cell tumor of bone. Sheets of mononuclear spindled stromal cells were also noted. A core-needle biopsy confirmed the diagnostic features of brown tumor of hyperparathyroidism.