Synchronous Parathyroid Carcinoma and Contralateral Parathyroid Adenoma: A Rare Multiglandular Cause of Severe Hyperparathyroidism

Background Parathyroid carcinoma is a rare endocrine malignancy accounting for less than 1% of cases of primary hyperparathyroidism, whereas parathyroid adenoma represents the most common etiology. The synchronous occurrence of parathyroid carcinoma and parathyroid adenoma in the same patient is exceptionally uncommon and poses significant diagnostic and surgical challenges. Case Presentation: We report the case of a 64-year-old male who presented with recurrent nephrolithiasis and was found to have severe hypercalcemia and markedly elevated parathyroid hormone levels. Parathyroid scintigraphy and magnetic resonance imaging revealed bilateral parathyroid lesions suspicious for malignancy. The patient underwent surgical exploration with en bloc resection of a left inferior parathyroid gland adherent to the thyroid, including ipsilateral thyroid lobectomy, and focused excision of a contralateral inferior parathyroid lesion. Histopathological examination demonstrated capsular and angioinvasion consistent with parathyroid carcinoma in the left inferior gland, while the contralateral lesion showed features of a benign parathyroid adenoma. Postoperatively, parathyroid hormone levels declined appropriately, and the patient experienced an uneventful recovery. Discussion This case highlights the diagnostic ambiguity that may arise in multiglandular parathyroid disease, particularly when benign pathology coexists with carcinoma. Intraoperative findings such as dense adhesions and gland firmness should raise suspicion for malignancy and prompt oncologic resection to minimize recurrence risk. Careful pathological evaluation remains essential for definitive diagnosis. Conclusion Awareness of this rare coexistence is critical to ensure timely diagnosis, appropriate surgical management, and long-term surveillance.