ABSTRACT
Thyroid carcinoma accounts for 90% of all endocrine tumors and 1.5% of all malignancies, with approximately 19,000 new cases occurring annually in the United States. Thyroid cancer mortality is 1200 deaths per year, resulting in a relatively high prevalence of disease, with over 200,000 patients living in the United States having undergone thyroidectomy for thyroid cancer and requiring regular assessment (1). In recent years, the number of radiopharmaceuticals used in the detection and ongoing evaluation of thyroid carcinoma has expanded beyond 131Iodine (131I) to include 123Iodine, 201Thallium (Tl), 99mTc-sestamibi, 99mTc-tetrofosmin, 99mTcfurifosmin, 99mTc-(V)-DMSA, 123I/131I-metaiodobenzylguanidine (MIBG), somatostatin receptor (SSR) analogs, 18F-Fluoro-deoxyglucose (FDG), and radiolabeled monoclonal antibodies (2). The utility of these various radiopharmaceuticals is dependent on the histologic type of thyroid cancer present. Thyroid malignancies include mostly differentiated thyroid carcinomas (DTC) (80%) as well as medullary thyroid carcinomas (MTC) (7%), lymphomas (5%), and undifferentiated anaplastic carcinomas (less than 5%). These tumors present specific challenges in imaging. Carcinoma metastatic to the thyroid is not uncommon at autopsy, but it is usually detected clinically as an incidental finding by ultrasonography (US), computed tomography (CT), magnetic resonance imaging (MRI), or even positron emission tomography (PET) with FDG, in a patient who is being treated for a nonthyroid malignancy (3).
