What is the primary cause of the brown color in a brown tumor of bone?

The brown color seen in a brown tumor of bone is primarily due to the pervasive presence of hemosiderin, which is a form of iron-storage complex in the body. In conditions such as hyperparathyroidism, there is an increased remodeling of bone caused by high levels of parathyroid hormone, leading to resorption of bone, which releases iron from bone marrow. This process, alongside the accompanying hemorrhage and vascularity, results in the deposition of hemosiderin, giving the tumor its characteristic brown color.

Brown tumors are also indicative of osteitis fibrosa cystica, a specific manifestation associated with hyperparathyroidism. However, the presence of hemosiderin directly explains the pigmentation seen in these lesions, rather than merely the disease itself. While malignancies in bone can lead to various pathologies, including secondary conditions that might yield discoloration, it is not accurate in the context of the specific brown coloration seen in brown tumors caused by hemosiderin deposit from prior hemorrhage.