What condition is characterized by the presence of a brown tumor?

The presence of a brown tumor is specifically associated with osteitis fibrosa cystica, a condition linked to hyperparathyroidism. In this scenario, elevated levels of parathyroid hormone (PTH) lead to increased bone resorption, resulting in cystic bone lesions and areas of hemorrhage, which give the tumor its brownish appearance. The term "brown tumor" refers to the brown coloration due to the presence of hemosiderin and other products of bone resorption.

In contrast, osteoporosis is characterized by a reduction in bone density without the formation of distinct cystic lesions. Paget's disease involves excessive bone remodeling but does not typically present with brown tumors. Osteomalacia, primarily a deficiency of vitamin D leading to weakened bones, also does not involve the formation of these tumors. Thus, osteitis fibrosa cystica distinctly features brown tumors as a result of the underlying pathophysiology of chronic hyperparathyroidism.