Parathyroid cyst.

Although parathyroid cyst has been infrequently reported until the past decade, its presumed rarity is attributed to nonrecognition. First reported in 1905, only 58 cases of parathyroid cyst had been documented in the world literature by 1967. Since then, however, substantial literature about this entity has been accumulating. The three cases we are reporting bring the cumulative total to 149. All three have been examined histologically and treated by aspiration or surgical excision. There is confusion clinically with thyroid cysts, and assay of fluid aspirate for parathormone and thyroxine may not accurately distinguish the origin of the cyst. Tissue diagnosis is confirmatory. Parathyroid cysts may be developmental, arising from vestigial remnants of the third and fourth branchial clefts; or coalescence of microcysts with associated hypersecretion may enlarge into macrocysts; or an adenoma may degenerate into a pseudocyst. Hyperparathyroidism, if present, is associated with only the last two.