Malignant hypercalcemia associated with a parathyroid macrocyst and the early genesis of a giant cell tumor.

Parathyroid cysts rarely cause primary hyperparathyroidism. In most cases, the resultant hypercalcemia is mild and detected before any significant skeletal disease develops. We report a patient with severe hypercalcemia, a synchronous brown tumor (osteitis fibrosa cystica) of the maxilla, and a large benign functional parathyroid cyst. The unusual patient presentation and management are described and illustrated. The pertinent literature is reviewed.