Thyroid Incidentalomas Detected On F-18-Fluorodeoxyglucose Positron Emission Tomography With Computed Tomography: Malignant Risk Stratification And Management Plan

Objective: The aims of this study were to stratify the risk of malignancy in thyroid incidentalomas detected on F-18-fluorodeoxyglucose positron emission tomography with computed tomography (F-18-FDG PET/CT) using ultrasound features according to guidelines for thyroid nodules and to develop a subsequent management plan.Methods: From a historical cohort of 96,942 consecutive patients who underwent F-18-FDG PET/CT between October 2008 and September 2015, 1342 patients with 1364 nodules underwent ultrasound evaluation for focal uptake in thyroid gland, with a final diagnosis made for 877 patients with 907 nodules, which were included in this study. Ultrasound images were retrospectively reviewed, and they were stratified according to the American Thyroid Association and Korean Thyroid Image Reporting and Data System guidelines. The calculated malignancy risks were compared with the estimated risks suggested by the guidelines.Results: The overall malignancy risk of thyroid incidentalomas detected on F-18-FDG PET/CT was 54.7%. When stratified according to the American Thyroid Association guidelines, the malignancy risks of thyroid incidentalomas with high and intermediate suspicion (93.2% and 45.2%, respectively) were higher than those indicated in the guidelines. The malignancy risks of thyroid incidentalomas with low and very low suspicion (8.1% and 0%, respectively) were within the guideline ranges. These findings were also noted when thyroid incidentalomas were stratified according to the Korean Thyroid Image Reporting and Data System, and in a subgroup of nodules >1 cm.Conclusions: Ultrasound examinations can be used to stratify the malignancy risk of thyroid incidentalomas detected on F-18-FDG PET/CT. The risk of malignancy did not increase in thyroid incidentalomas with low and very low suspicion, indicating that only selective biopsies may be needed in these categories of thyroid incidentalomas.