[Endocrinously active parathyroid cysts. Their diagnosis by the determination of intact parathormone in the cyst fluid].

A 53-year-old woman with recurrent nephrolithiasis was found to have hypercalcaemia of 3.12 mmol/l and an intact parathormone level of 166 pg/ml, indicating primary hyperparathyroidism. Preoperative ultrasound examination to localize the parathyroid adenoma revealed a clear fluid-containing cyst in the right lobe of the thyroid. The aspirated fluid had an intact parathormone level of 306 pg/ml, twice that in serum. The cyst was removed surgically. 14 days postoperatively calcium and parathormone levels in serum had become normal without any calcium administration. Measuring the concentration of intact parathormone in the aspirated cyst fluid made possible not only the distinction from a thyroid cyst but also the precise preoperative localization of the parathyroid cyst.