Functional Parathyroid Cyst

ABSTRACT

Parathyroid cysts are uncommon lesions of the neck and superior mediastinum, rarely large enough to be of clinical significance. They frequently present as a clinical diagnostic problem. They may mimic solitary thyroid nodule. They can be classified as either functioning or non-functioning depending on whether or not they are associated with hypercalcemia. Non-functioning or "true" cysts are those associated with normocalcemia (85%), whereas functioning or "pseudocysts" are those associated with hypercalcemia (15%). The presence of a high content of intact parathyroid hormone (iPTH) in the cystic fluid on fine-needle aspiration (FNA), in conjunction with elevated serum levels of calcium and iPTH is diagnostic of a functional parathyroid cyst, which usually requires surgical removal. We report herein two cases of such a functional parathyroid cyst and present a review of the literature.