Interpretation of thyroid incidentalomas in 18F-FDG PET/CT studies

Abstract Objective Thyroid findings or incidentalomas in 18 F-FDG PET/CT studies are relatively frequent, being its clinical significance subject of controversy. The aim of this study was to show our experience in the detection of thyroid incidentalomas by PET/CT studies as well as its follow up. Material and methods A retrospective and descriptive review was conducted on patients who had thyroid incidentalomas detected in 18 F-FDG PET/CT studies between June 2010 and March 2013. Patient's medical records were reviewed for age, genre, maximum standardized uptake value (SUVmax), thyroid diseases, TSH and antithyroid antibodies levels, ultrasound, fine-needle aspiration (FNA) and cytology. Results 4085 PET/CT studies for several purposes were performed. Eighty-three of these studies (2.03%) showed thyroid incidentalomas. Thirty-seven patients showed a diffuse increase of glucose metabolism in the thyroid gland and 46 showed a focal increase of glucose metabolism. Five out of 46 patients with focal uptake were diagnosed of a neoplastic disease by cytology (11%). The SUVmax of malignant pathology did not differ from that of benign thyroid diseases (Mean: 10,26 and 5,92 respectively). Conclusion In our experience, focal thyroid incidentalomas detected in 18 F-FDG PET/CT studies are related to a significant risk of malignancy (11%). Therefore, in these situations, an ultrasound study with fine needle biopsy should be recommended. Moreover, a diffuse increase of glucose metabolism in the thyroid gland is often associated with benign thyroid pathology.