Preoperative diagnostic accuracy of thyroid follicular carcinoma using fluorine-18-fluorodeoxyglucose-positron...

To evaluate the diagnostic accuracy of fluorine-18-fluorodeoxyglucose-positron emission tomography (¹⁸F-FDG-PET), computed tomography (CT), thyroid markers, and their combination for diagnosing thyroid follicular carcinoma.

We analyzed 53 patients (12, 10, and 31 with follicular cancer, follicular adenoma, and adenomatous goiter, respectively) selected from 12,403 consecutive patients who underwent preoperative ¹⁸F-FDG-PET/CT at our hospital between January 2013 and December 2019. Blood data, including thyroxine, triiodothyronine, thyroid-stimulating hormone, and thyroglobulin levels, as well as the patients' age, sex, thyroid tumor maximum standardized uptake value (SUVmax), and calcification, were compared between the follicular carcinoma and benign thyroid tumor (adenoma and adenomatous goiter) groups. Comparisons were performed using Student's t-test, Mann-Whitney U test, or chi-squared test. For factors showing significant group differences, cut-off values were determined using receiver operating characteristic (ROC) analysis.

Significant differences were observed between the two groups regarding calcification, SUVmax, SUVmax/tumor size, and thyroglobulin levels (all p < 0.01). Peripheral calcification was more common in follicular carcinomas (6/12 cases) than in benign thyroid tumors (1/41 cases). The area under the ROC curve (AUC) was 0.89 for SUVmax, with a Youden index cut-off value of 5.2, yielding 100% sensitivity and 73.2% specificity. For thyroglobulin, the AUC was 0.739, with a Youden index cut-off value of 3379, resulting in 58.3% sensitivity and 87.8% specificity. Only 2.4% of benign thyroid tumors were positive for all three indicators (SUVmax > 5.2, presence of tumor calcification, and thyroglobulin > 3379), whereas 50% of follicular carcinomas were positive for all indicators, corresponding to a sensitivity and specificity for malignancy of 50% and 97.6%, respectively. Notably, no case of follicular carcinoma presented with all three indicators negative or SUVmax < 5.2 (100% specificity).

The combination of high SUVmax, CT-detected calcification, and high thyroglobulin levels strongly suggests follicular carcinoma and may warrant resection.