Osseous metaplasia in a growth hormone-secreting pituitary adenoma

A case of growth hormone-secreting adenoma of the pituitary gland showing osseous metaplasia is described in a 56-year-old acromegalic female. The tumor was composed of nests of densely granulated cells separated by and intermixed with calcifications, trabeculae of mature bone and fat. Calcifications are seldom found in pituitary adenomas. In rare instances, calcium deposits can be prominent enough to lead to the formation of pituitary stones and bone which replace the entire tumor mass. Analogously with metaplastic meningiomas, we propose using the term metaplastic adenoma to define cases with osseous metaplasia in order to distinguish between lesions containing bone from the more frequently seen calcified adenomas.