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.
aDepartment of Internal Medicine, Division of Endocrinology and Metabolism
bBiomedical Research Institute
cDepartment of Nuclear Medicine, Pusan National University Hospital
dKim Yong Ki Internal Medicine Clinic, Busan, Korea
Correspondence to Seong-Jang Kim, MD, PhD, Department of Nuclear Medicine, Pusan National University Hospital and Biomedical Research Institute, 179 Gudeok-Ro, Seo-Gu, Busan 602-739, Korea Tel: +82 51 240 7389; fax: +82 51 241 5570; e-mails: email@example.com, firstname.lastname@example.org
Received November 26, 2012
Accepted May 1, 2013