Giant functioning cervicomediastinal parathyroid cyst.

A rare case of a large cervicomediastinal parathyroid cyst associated with hypercalcemia and an elevation of serum parathyroid hormone is presented. The pathogenesis of such a large cyst is discussed, hemorrhage into an adenoma being the most likely cause. Clinical investigations which should be carried out for any cystic mass at the root of the neck should include a serum calcium, and if this is found to be elevated, the possibility of the cyst being of parathyroid origin should be considered. In view of the high concentration of parathyroid hormone found within the cyst, aspiration of the cyst contents for parathyroid hormone estimation might well prove a valuable test to confirm the diagnosis.