[Cystic parathyroid adenoma. A rare cause of primary hyperparathyroidism].

Two cases of primary hyperparathyroidism associated with parathyroid cysts were identified by an elevated plasma Ca++ level. The diagnosis was established preoperatively by the presence of high quantities of PTH in the cyst fluid in one of the patients. Cysts in the neck or superior mediastinum should raise suspicion of primary hyperparathyroidism.