F-18 FDG uptake in papillary thyroid microcarcinoma predicts central lymph node metastases

Objectives In papillary thyroid microcarcinomas (PTMCs), central lymph node metastases (cLNM) are related to more recurrence and cancer-related mortality. The aim of this study was to quantitatively investigate FDG uptake in PTMCs for the prediction of cLNM.

Methods Of 220 PTMC patients underwent with F-18 FDG PET/CT and total thyroidectomy with central lymph node dissection, 91 patients showing focal FDG uptake (focality) in thyroid lesion on PET/CT were enrolled. The maximum SUV of the lesion (SUVmax) were measured on PET/CT images and tumor sizes measured on preoperative US. ROC curve analysis and logistic regression of cLNM were performed by using age, sex, SUVmax, and size as variables. And then, combinations of criteria were evaluated for the prediction of cLNM.

Results Thirty-eight (41.8%) of 91 patients showed focality. Four (4.4%) and sixteen (17.6%) patients showed extrathyroidal extension and cLNM, respectively. In ROC curve analysis of 38 scans showing focality, criterion ‘SUVmax>2.8’ was optimal criterion for cLNM with sensitivity of 90.0% and specificity of 42.9%. In univariate logistic-regression analysis, ‘tumor size>5 mm’ and ‘SUVmax>2.8’ were statistically significantly associated with cLNM (p=0.006, p=0.005, respectively). However, age> 45 (p=0.347), male (p=0.978), and focality (p=0.064) were not. Multivariate analysis revealed that ‘SUVmax>2.8’ was the only statistically significant independent variable correlated with cLNM (p=0.007, OR=4.741, 95%CI=1.529-14.702). Sensitivity, specifivity, PPV, and NPV of combined criterion ‘tumor size>5 mm or SUVmax>2.8’ for cLNM were 81.2%, 65.3%, 50.0%, and 94.2%, respectively.

Conclusions On preoperative PET/CT scans in patients with PTMCs, focality with SUVmax>2.8 is correlated with cLNM regardless of tumor size. And, combined criterion using SUVmax and size of PTMCs showed good diagnostic performance