Brown tumour. Light micrograph of a section of bone affected by brown tumour, showing bone destruction by osteoclast cells. Despite the name, this is not a true tumour. It is caused by overactivity of the parathyroid glands (hyperparathyroidism). These glands regulate the body's calcium levels by producing parathyroid hormone. Their overactivity leads to the body acting to remove bone calcium, causing tiny fractures and haemorrhaging. The brown colour of the tumour is caused by haemosiderin, a product of blood breakdown. The condition may also cause kidney stones, vomiting and confusion. Treatment is surgical. Magnification unknown.