[Parathyroid cyst presenting as a mediastinal tumor].

Mediastinal parathyroid cysts are very rare. Since the first report by DeQuervain, 19 cases have been reported. We encountered a case of mediastinal parathyroid cyst presenting as displacement of the trachea. The cyst originated in the lower portion of the left lobe of the thyroid gland and extended to the mediastinum, displacing the trachea and the esophagus. The monolocular mass was a thin walled cyst, and mognetic imaging indicated that it contained watery fluid. The left lobe of the thyroid gland was found to be displaced upward by the tumor, on thyroid scintigram done with technetium-99, which suggested that the cyst originated in the parathyroid gland.