Sestamibi-Negative Ectopic Mediastinal Parathyroid Adenoma Presenting With Severe Hypercalcemia and Acute Kidney Injury: A Case Report

Abstract

Background: Primary hyperparathyroidism (PHPT) is most commonly caused by a solitary parathyroid adenoma. Ectopic parathyroid adenomas are uncommon and may pose significant diagnostic challenges, particularly when located in the mediastinum and when conventional localization studies are negative. Case Presentation: A 42-year-old male presented with abdominal pain, vomiting, loss of appetite, weight loss, and generalized body ache for two months. He had previously been diagnosed with hypercalcemia-associated pancreatitis and was treated at multiple healthcare facilities. Evaluation for persistent hypercalcemia raised suspicion of primary hyperparathyroidism; however, a sestamibi scan failed to demonstrate abnormal uptake, and serum parathyroid hormone (PTH) values were variable. He was subsequently referred to our centre with severe hypercalcemia and acute kidney injury. Computed tomography Neck revealed a well-defined lesion measuring 2.7 × 2.3 × 2.8 cm in the right paratracheal region of the upper mediastinum. PTH estimation from aspirated fluid was markedly elevated at 5000 pg/mL. The patient underwent surgical excision of the lesion. His preoperative PTH was 2434 pg/mL, which decreased to 173 pg/mL intraoperatively. Histopathological examination confirmed parathyroid adenoma. At one-year follow-up, the patient remained asymptomatic with normal serum calcium and PTH levels and a serum creatinine of 1.3 mg/dL. Conclusion: This case highlights the importance of considering ectopic mediastinal parathyroid adenoma in patients with PTH-mediated hypercalcemia despite negative sestamibi imaging. Complementary anatomical imaging and targeted biochemical confirmation can facilitate localization and successful definitive surgical treatment.