棕色瘤中心包含破骨细胞、单核细胞、成纤维细胞，并伴有局灶性出血。出血形成的血铁黄素使病变肉眼观察呈深棕色。现今这种病变不常见，因为它出现之前甲状旁腺功能亢进已被治愈。
The center of the "brown tumor" contains osteoclasts and mononuclear cells and fibroblasts with focal hemorrhages. The hemosiderin from the hemorrhage produces the grossly brown color. Such lesions are nowadays uncommon because hyperparathyroidism is treated before such lesions develop.