Hypercalcemic Crisis Secondary to A Parathyroid Hormone-Secreting, Intrathymic, Cystic, Parathyroid Adenoma

Objective: To report a rare case of a male patient with primary hyperparathyroidism due to a parathyroid hormone (PTH)-secreting, intrathymic, cystic, parathyroid adenoma. Methods: The pertinent clinical features, laboratory data, radiologic and pathologic findings are reported, along with a brief literature review. Results: A 69-year-old male was followed for asymptomatic hypercalcemia secondary to primary hyperparathyroidism since 2013. He was also incidentally found to have an anterior mediastinal mass on a chest X-ray which remained stable on annual follow-up. He was monitored regularly with serial calcium and renal function tests, with no indication for surgical intervention. Dual-phase ⁹⁹mTc-Sestamibi scan did not localize a culprit parathyroid gland in the neck or upper chest. He presented in 2015 with renal failure and hypovolemic shock secondary to severe hypercalcemia (calcium 17.20 mg/dL, PTH 3,452 pg/mL) requiring intensive care unit admission. Treatment with aggressive hydration, diuresis and pamidronate failed to lower calcium levels. Patient underwent emergent surgical exploration with combined resection of 2 enlarged, eutopic parathyroid glands suspicious for adenoma and the cystic mediastinal mass. PTH levels from fluid within the cystic mediastinal mass were elevated at 1,290,000 pg/mL. Immediate postoperative PTH and calcium levels dropped to 58 pg/mL and 10.80 mg/dL, respectively. Pathology of the mediastinal mass was consistent with ectopic, intrathymic, parathyroid adenoma. Conclusion: Anterior mediastinal mass in the setting of hypercalcemia should be considered as a possible source of ectopic PTH production in the setting of an otherwise negative ^99mTc-Sestamibi parathyroid scan. Definitive treatment by resection of the mass is potentially curative.