An exceptionally rare case of a giant parathyroid adenoma with carcinoma-like presentation.

Giant parathyroid adenoma (GPA) is an extremely rare cause of primary hyperparathyroidism (PHPT) and may sometimes mimic parathyroid carcinoma (PC). Parathyroid carcinoma is also a very rare entity. Both preoperative and postoperative diagnosis of the two conditions remains a challenge. The purpose of this article is to present the diagnostic and therapeutic approach used for a 76-year-old female patient with a GPA measuring 5.4 × 2.3 cm, mimicking PC. The patient was referred to our clinic for the management of severe hypercalcemia revealed during the neurological evaluation of psychiatric and cognitive symptoms, confusion, weakness, and bone pain. PHPT was confirmed based on the patient's biochemical profile, which showed extremely high levels of serum calcium and parathyroid hormone (PTH). Wholebody computed tomography revealed a large nodule below the inferior pole of the right lobe of the thyroid gland and no further pathology in other organs. En bloc resection of the tumor with removal of the ipsilateral hemithyroid and other involved tissues was performed. Histopathological evaluation was diagnostic for a GPA. Post-surgery hungry bone syndrome (HBS) developed and was treated. However, the patient succumbed 3 weeks later due to septic shock. GPA is an exceptionally rare endocrine tumor that should be suspected along with PC in patients with significantly elevated levels of PTH and calcium, and/or palpable neck mass. In our case, diagnosis was based principally on histopathological examination together with clinical presentation, biochemical profile, and imaging studies. Resection of the tumor remains the treatment of choice.