A Large Intrathyroidal Parathyroid Adenoma Presenting as a Cold Lesion on Thyroid Scintigraphy

Intrathyroidal parathyroid adenomas are rare and are often misdiagnosed as thyroid nodules. Accurate diagnosis and preoperative localization is important for a successful surgical outcome, especially in the context of minimally invasive parathyroid surgery. Nuclear medicine imaging has been invaluable in differentiating between thyroid and parathyroid pathologies, but ultrasound scanning also has a prominent role. Cases of intrathyroidal adenomas showing significant uptake of Tc-99m pertechnetate appearing as a hyperfunctioning thyroid nodule have previously been reported. Using sonographic as well as scintigraphic methods of localization, we describe an unusual case of a large intrathyroidal parathyroid adenoma (confirmed on surgery), which appeared “cold” on a Tc-99m pertechnetate scan falsely giving the impression of a hypofunctioning nodule, mimicking thyroid neoplasm. The decision to proceed to surgery without a fine needle aspiration was taken because the clinical picture was more suggestive of a parathyroid adenoma/carcinoma than thyroid malignancy.