An Unusual Case of Primary Hyperparathyroidism: Case Report of a Bifocal Intrathyroidal Parathyroid Carcinoma.

Intrathyroidal parathyroid carcinoma is an extremely rare cause of primary hyperparathyroidism. We reported a 51-year old woman who presented symptoms of hypercalcemia. 99mTc sestamibi single-photon emission computed tomography/computed tomography (CT) revealed a large hypermetabolic nodule in the left thyroid lobe suggestive of hyperfunctioning parathyroid tissue. 11C-methionine positron emission tomography/computed tomography (PET/CT) and 18F-fluorocholine PET/CT confirmed the nodule in the left thyroid lobe and also revealed a hypermetabolic activity on the posterior surface of the lower left pole. The patient underwent a total thyroidectomy and parathyroidectomy, and a diagnosis of bifocal intrathyroidal parathyroid carcinoma was confirmed. We present the first reported case of bifocal intrathyroidal carcinoma and discuss the discordant imaging results.