Brown tumor – Wikipedia

Brown tumor; Brown tumours of the hands in a patient with hyperparathyroidism. The brown tumor is a bone lesion that arises in settings of excess osteoclast activity, such as hyperparathyroidism.They are a form of osteitis fibrosa cystica.It is not a neoplasm, but rather simply a mass.It most commonly affects the maxilla and mandible, though any bone may be affected.

https://en.wikipedia.org/wiki/Brown_tumor