Abstract
<title>Abstract</title> <p> <bold>Introduction:</bold> Primary hyperparathyroidism (PHPT) typically results from a solitary parathyroid adenoma. Multiple parathyroid adenomas are rare and four parathyroid adenomas clustered in a single ectopic region has never been reported. <bold>Case presentation:</bold> A 32-year-old male patient with ongoing PHPT after resection of a right inferior parathyroid adenoma was referred to our center. Upon admission, reoperative exploration revealed no parathyroid tissue in any of the four normal anatomical locations. Instead, three ectopic parathyroid adenomas were discovered as a single, continuous cluster in the medial side of the right carotid sheath at the thoracic inlet level, extending into the superior posterior mediastinum. After complete excision of these three lesions, the patient developed permanent hypoparathyroidism. <bold>Conclusion:</bold> This first report of collective ectopia of all four parathyroid adenomas in the cervicomediastinum, suggesting an extreme failure of embryonic migration. Surgeons should be aware that an ectopic adenoma may represent only the tip of a contiguous iceberg. </p>