Role of multi-modality functional imaging in differentiation between benign and malignant thyroid 18F-fluorodeoxyglucose incidentaloma.

Objective: To evaluate the diagnostic performance of multi-modality functional imaging in differentiating malignant and benign thyroid 18F-fluorodeoxyglucose (18F-FDG) incidentaloma.

Methods: This study included 87 patients with thyroid 18F-FDG incidentalomas detected by 18F-FDG- positron emission tomography/computed tomography (18F-FDG-PET/CT) and diagnosed at surgery or biopsy, who received 18F-FDG-PET/CT, diffusion-weighted MR imaging (DWI) and ultrasound elastography (USE). The metabolic tumor volume (MTV), total lesion glycolysis (TLG), apparent diffusion coefficient (ADC) values and ultrasound elasticity scores of thyroid 18F-FDG incidentalomas were measured and compared in benign and malignant thyroid incidentalomas. The differences of malignant and benign thyroid incidentalomas were tested by χ2 test, Fisher's exact test, t test, or Mann-Whitney U test. The diagnostic performance was evaluated and optimal cut-off values were determined in distinguishing malignant from benign thyroid incidentalomas by receiver operating characteristic curve analysis.

Results: MTV, TLG and USE scores of malignant thyroid incidentalomas were significantly higher than benign; but ADC value was significantly lower. We defined the functional imaging parameters TLG < 2.48, ADC > 1.80 × 10-3mm2/s, and USE score of 1 as markers of benign thyroid incidentalomas and each scored -1 point; TLG ≥ 2.48, ADC ≤ 1.80 × 10-3mm2/s, and USE score of 4 as markers of malignancy and each scored 1 point. Combined multi-functional imaging parameters achieved the highest performance (84.6% sensitivity and 97.1% specificity) for distinguish malignant from benign thyroid incidentaloma with AUC 0.957 (95% CI 0.917, 0.997).

Conclusions: Functional imaging might help to distinguishing malignant from benign thyroid 18F-FDG incidentalomas, and combined multi-functional imaging parameters could improve it.