Hyperfunctioning Intrathyroidal Parathyroid: a Misleading Preoperative Diagnosis

Hyperfunctioning parathyroid glands may be rarely located in the thyroidal parenchyma and not identified by imaging or during surgical procedures. We present three patients with primary hyperparathyroidism related to hyperfunctioning intrathyroidal parathyroid retrospectively selected among 732 cases from own Institutional parathyroid PET/CT registry from 2018 to 2022. Intrathyroidal parathyroids showed intense ¹⁸F-fluorocholine uptake but a variable echographic pattern, inconstant ^99mTc-MIBI uptake, and atypic iodine-contrast enhancement. Although rare, the possibility of an intrathyroidal parathyroid should be considered when no hyperfunctioning gland is found on preoperative imaging and thorough bilateral neck exploration.