A Giant Cystic Ectopic Parathyroid Adenoma of the Anterior Mediastinum Mimicking a Mediastinal Tumor: A Diagnostic Challenge.

Abstract

Background: Ectopic parathyroid adenomas represent an uncommon but clinically significant cause of primary hyperparathyroidism, particularly when located in the mediastinum. Their diagnosis may be challenging, especially in the presence of concomitant thyroid pathology, which can obscure imaging interpretation and lead to misleading localization studies.

Case presentation: We report the case of a 63-year-old man who presented with persistent hoarseness and was found to have marked hypercalcemia and elevated parathormone levels consistent with primary hyperparathyroidism. Neck ultrasonography demonstrated multinodular goiter, while dual-tracer technetium-99m pertechnetate and technetium-99m sestamibi scintigraphy with SPECT/CT suggested a functional thyroid adenoma and raised suspicion for a possible parathyroid lesion within the thyroid gland. Fine-needle aspiration with parathormone washout did not confirm an intrathyroidal parathyroid origin. Subsequent cross-sectional imaging revealed a large cystic mass in the anterior superior mediastinum compressing adjacent structures. After medical stabilization with cinacalcet, the patient underwent surgical excision through a right axillary thoracotomy. Intraoperative and biochemical findings confirmed the lesion as the source of excessive parathormone secretion. Histopathological and immunohistochemical examination established the diagnosis of a cystic ectopic parathyroid adenoma. Postoperatively, serum calcium and parathormone levels normalized, and the patient remained free of biochemical evidence of recurrent disease during the available follow-up period.

Conclusion: This case highlights the diagnostic complexity of mediastinal ectopic parathyroid adenomas, particularly in patients with coexisting multinodular goiter and inconclusive scintigraphic findings. Clinicians should maintain a high index of suspicion for ectopic parathyroid tissue in cases of unexplained hyperparathyroidism with negative or discordant cervical imaging, as accurate localization is critical for definitive surgical management.