Parathyroid Carcinoma Mimicking a Parathyroid Adenoma on [18F]F-Choline-PET With Occult Metastases

An 80-year-old man with hypercalcemia and hyperparathyroidism was suspected of having a parathyroid adenoma, which was localized on [18F]F-choline-PET/CT. Still, after surgical removal of the suspected adenoma with an intraoperative parathyroid hormone decrease of >50%, severe hypercalcemia recurred quickly. A repeated [18F]F-choline-PET/CT raised suspicion of a single contralateral parathyroid adenoma or multiglandular disease. Given the inconclusive findings, a histological reassessment of the suspected parathyroid adenoma showed the presence of a singular vessel invasion, which alerted the diagnosis to parathyroid carcinoma. An additionally performed [18F]FDG-PET/CT revealed a liver lesion and MRI confirmed multiple liver metastases, which could not be seen on [18F]F-choline-PET/CT.