Brown tumors are tumors of bone that arise in settings of excess osteoclast activity, such as hyperparathyroidism[1], and consist of fibrous tissue, woven bone and supporting vasculature, but no matrix. They are radiolucent on x-ray. The osteoclasts consume the trabecular bone that osteoblasts lay down and this front of reparative bone deposition followed by addition resorption can expand beyond the usual shape of the bone, involving the periosteum and causing bone pain. The characteristic brown coloration results from hemosiderin deposition into the osteolytic cysts. Also characteristic of giant cell tumors of the bone.
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