Association of SUVmax with Malignancy in Focal FDG-Avid Thyroid Incidentalomas

Thyroid incidentalomas (TIs) detected on 18F-fluorodeoxyglucose positron emission tomography/computed tomography (FDG PET/CT) are associated with an increased risk of malignancy, particularly in the presence of focal FDG uptake. While quantitative PET/CT parameters, such as the maximum standardized uptake value (SUVmax), have been extensively studied, current management guidelines primarily rely on nodule size and ultrasonographic features. This study aimed to evaluate whether PET/CT-derived radiological parameters provide additional information for malignancy in FDG-avid TIs. This retrospective single-center study included patients with focal FDG-avid thyroid incidentalomas detected on PET/CT who underwent ultrasonographic evaluation and cytological and/or histopathological confirmation. Demographic characteristics, metabolic parameters derived from PET/CT scans, ultrasonographic findings and anatomical localization were documented. Benign and malignant lesions were compared. Receiver operating characteristic (ROC) analysis was conducted to determine the optimal SUVmax cut-off value and logistic regression analyses were employed to identify variables independently associated with malignancy. A total of 53 patients were included, with 13 (24.5%) having malignant thyroid lesions. Malignant nodules demonstrated significantly higher SUVmax values than benign nodules (p=0.008). ROC analysis established a SUVmax cut-off value of 5.8 for discrimination between benign and malignant nodules (AUC: 0.748). Isthmus localization also remained significant in multivariate analysis (p=0.037). No other morphologic or ultrasonographic parameters were significant. In cases of focal FDG-avid TIs, an SUVmax value of ≥5.8 is associated with an increased risk of malignancy and may provide complementary information in risk stratification. However, SUVmax should be interpreted alongside clinical and ultrasonographic findings, not as a standalone decision-making tool.