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

Aim 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. Methods 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. Results 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). Conclusion 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.