Contribution of Focal ^{1 8}F-FDG Uptake on Positron Emission Tomography/Computed Tomography to Ultrasonography-Based Malignancy Risk Assessment in Incidentally Detected Thyroid Nodules

The present study sought to evaluate the incremental contribution of the presence of focal FDG uptake and SUVmax on PET/CT in predicting malignancy in incidentally detected thyroid nodules when assessed in conjunction with ultrasonography-based risk features.

In this retrospective study, 304 incidentally detected thyroid nodules identified on PET/CT and confirmed by cytology and/or histopathology were analyzed. The clinical, ultrasonographic, and PET/CT findings were meticulously documented. The presence or absence of focal FDG uptake was subsequently visually assessed on PET/CT images, and SUVmax values were also calculated for FDG-avid nodules. The factors associated with malignancy were evaluated using univariate and multivariate logistic regression analyses.

The overall malignancy rate was 12.2%. The analysis revealed that focal FDG uptake was observed in 97.3% of malignant nodules and in 65.9% of benign nodules (p < 0.001). Among FDG-avid nodules, SUVmax values were significantly higher in malignant lesions (p < 0.001). However, in multivariate models incorporating ultrasonography-based risk features, focal FDG uptake demonstrated only borderline statistical significance (p = 0.055), while SUVmax was not independently associated with malignancy (p = 0.360).

The absence of focal FDG uptake on PET/CT was associated with a very low likelihood of malignancy in incidentally detected thyroid nodules. However, focal FDG uptake should be interpreted in conjunction with ultrasonography-based risk features rather than as an independent decision-making criterion. Although SUVmax values were higher in malignant FDG-avid nodules, SUVmax did not provide independent or additional diagnostic value beyond ultrasonography-based risk assessment.