An uncommon cause of primary hyperparathyroidism is a cystic parathyroid adenoma. This paper describes two patients with hypercalcemia and right knee disease. Their serum calcium concentration was high, phosphorus concentration was low, and parathyroid hormone (PTH) concentration was high. Ultrasound and computed tomography scans of the neck indicated a cystic mass near the thyroid. Parathyroid scintigraphy showed no focal uptake in one patient and low tracer concentration in the cystic mass in the other patient. Following resection of the cystic masses, both were pathologically confirmed to be a cystic parathyroid adenoma with predominantly cystic degeneration. The calcium and PTH concentrations gradually decreased to the reference range. Both patients were stable at their last follow-up. The diagnosis of a functional cystic parathyroid adenoma is highly challenging because of the different clinical manifestations and negative result on parathyroid tracer scintigraphy. For patients with high serum calcium and PTH concentrations and a cystic mass in the neck, resection of the mass and subsequent postoperative pathological diagnosis is necessary even if the clinical diagnosis of a parathyroid adenoma cannot be confirmed preoperatively. Decreases in the PTH and serum calcium concentrations indicate successful resection of a functional parathyroid adenoma.
Keywords: Cystic parathyroid adenoma; case report; hyperparathyroidism; parathyroid hormone; review; single-photon emission computed tomography.