The role of F-18FDG PET in thyroid cancer

Hypofunctioning nodules on scintiscan using Tc-99m Pertechnetate or I-123 h ave a higher probability of malignancy compared to eu- or hyperfunctioning nodules. However, in the preoperative assessment of thyroid nodules, ultras onography and ultrasonography guided fine needle aspiration biopsy play the most important role, especially for papillary thyroid cancer. The problem of differentiating follicular adenoma from highly differentiated follicular carcinoma however remains. Also the additional use of a multi tracer imagi ng strategy (Tl-201/Tc-99m subtraction scan, Tc-99m Sestamibi, Tc-99m Tetro fosmin dual phase scintigraphy) has not solved this problem. Although it is unlikely, the question whether FDG PET is able to give a better differenti ation between benign and malignant tumours in the preoperative assessment o f thyroid nodules is not answered up to now. In contrast to preoperative di agnostics, FDG PET is of great value in the postoperative follow up of diff erentiated thyroid cancer. In case of elevated serum thyroglobulin but nega tive I-131 WBS FDG PET is the method of choice to detect I-131 negative rec urrences and metastases. FDG uptake in metastases from differentiated thyro id cancer is correlated to low differentiation and maybe bad prognosis. The re is also evidence that FDG PET may have a role in the follow up of anapla stic and especially in medullary thyroid cancer in the future.