Primary hyperparathyroidism due to dual parathyroid adenomas: one orthotopic, one intrathymic in ectopic cervical thymus.

Primary hyperparathyroidism is most commonly caused by a single parathyroid adenoma. Multiple and ectopic adenomas are less common and can present diagnostic challenges. We present the case of a 57-year-old woman with hypercalcemia, hypercalciuria, and inappropriately normal parathyroid hormone (PTH) levels. Sestamibi scan did not demonstrate abnormal uptake; however, contrast-enhanced 4-dimensional computed tomography imaging reported 2 candidate lesions described as tubular shaped structures located posterior to the inferior pole of each thyroid lobe. Surgical exploration was performed and the surgical pathology reported hypercellular parathyroid tissue resected from the left inferior thyroid bed and benign thymic tissue with embedded hypercellular parathyroid tissue resected from the right inferior thyroid bed. Postoperative calcium levels normalized, and the patient remained eucalcemic at 1-year follow-up. This case underscores the importance of embryologic understanding and thorough surgical exploration in patients with biochemically confirmed primary hyperparathyroidism and inconclusive imaging.