Background: The objective of the study was to investigate whether metabolic tumor volume (MTV) measured by fluorine-18 fluorodeoxyglucose (18F-FDG) PET/computed tomography (PET/CT) after stratification of serum thyroid stimulating hormone (TSH) levels could predict malignancy in patients with thyroid 18F-FDG incidentaloma.
Materials and methods: A total 262 patients with focal thyroid 18F-FDG incidentaloma undergoing cancer evaluation for nonthyroid cancer or a health checkup were enrolled in this study. We retrospectively evaluated the relationship of the maximum standardized uptake value (SUVmax) and MTV in the prediction of malignant thyroid 18F-FDG incidentaloma.
Results: The prevalence of malignancy was 20.9% (37/177). Malignant thyroid incidentaloma had a statistically significant higher value of SUVmax (malignant: median 4.6, range 1.9–34.9; benign: median 4.1, range 0–28; P=0.030). The value of MTV4 in malignant thyroid incidentaloma was significantly higher than that of benign thyroid incidentaloma (malignant: median 0.16, range 0.02–1.19; benign: median 0.10, range 0–0.65; P=0.032). However, the values of MTV3.5, MTV3, and MTV2.5 did not differ significantly between the groups. After stratification of serum TSH levels (an SUVmax>5 was used as the cutoff point) the sensitivity and specificity for prediction of malignancy were found to be 61.1% [95% confidence interval (CI): 35.7–82.7%] and 68.7% (95% CI: 56.2–79.4%), respectively. The area under the curve (AUC) was 0.655 (95% CI: 0.545–0.755; P=0.0239). When MTV4 greater than 0.07 cm3 was used as the cutoff point, the sensitivity and specificity for prediction of malignancy were 81.2% (95% CI: 54.4–96.0%) and 50.0% (95% CI: 37.0–63.0%), respectively. The AUC was 0.650 (95% CI: 0.534–0.755; P=0.0451). On comparison receiver operating characteristic curve analysis, no significant difference was found between SUVmax and MTV4 in the prediction of thyroid carcinoma (P=0.4346). However, a combination of SUVmax and MTV4 resulted in an AUC of 0.669 (95% CI: 0.554–0.772; P=0.0183).
Conclusion: The SUVmax and MTV4 measured by 18F-FDG PET/CT after stratification of serum TSH levels could predict thyroid cancer in patients with thyroid 18F-FDG incidentaloma. A combination of SUVmax and MTV4 may be more useful for the differentiation of malignant from benign thyroid incidentaloma.