Case Report: Retrosternal parathyroid lipoadenoma in an obese male patient-diagnostic pitfalls and postoperative biphasic parathyroid hormone dynamics.

INTRODUCTION: Parathyroid lipoadenoma is a rare histologic variant of parathyroid adenoma. Its occurrence in the retrosternal mediastinum poses significant diagnostic and surgical challenges. The clinical significance lies not in its rarity, but in the diagnostic pitfalls it presents, particularly when located in the retrosternal mediastinum. We present a case that underscores the pitfalls in preoperative diagnosis and the intricacies of minimally invasive resection. CASE PRESENTATION: A 36-year-old obese man (BMI 31 kg/m2, WHO Class I obesity) presented with an incidental anterior superior mediastinal mass. Preoperative computed tomography revealed a soft-tissue density lesion suspected to be a thymoma. The clinical implications of his recurrent nephrolithiasis and retrospectively identified albumin-corrected hypercalcemia (2.98 mmol/L, serum albumin: 46.5 g/L; reference range: 40-55 g/L) were overlooked. Given the patient's body habitus and the tumor's location cephalad to the innominate vein, subxiphoid video-assisted thoracoscopic surgery (VATS) under artificial pneumothorax was performed. Severe hypocalcemic tetany on postoperative day 1, followed by a characteristic biphasic parathyroid hormone (PTH) response, provided key diagnostic clues and ultimately led to a pathological diagnosis of parathyroid lipoadenoma. CONCLUSION: For patients with a mediastinal mass accompanied by hypercalcemia, comprehensive clinical evaluation is required to exclude ectopic primary hyperparathyroidism, rather than interpreting imaging findings in isolation. Subxiphoid VATS is the preferred technique for high retrosternal tumors in patients with challenging anatomical features. Familiarity with postoperative biphasic PTH changes and Hungry Bone Syndrome is essential for accurate interpretation of perioperative biochemical results.