Feasibility of FDG-PET/CT for the initial diagnosis of papillary thyroid cancer.

To assess the role of [18F]-fluorodeoxyglucose (FDG) positron emission tomography-computed tomography (PET/CT) as a preoperative diagnostic tool in papillary thyroid carcinoma (PTC). From 2011 to 2014, 197 patients with PTC (246 tumor foci in all) underwent FDG-PET. Among these patients, 46 underwent neck dissection for lateral neck metastasis. According to the FDG avidity of the tumor foci or lateral neck metastasis, factors associated with the prognostic value were evaluated by univariate and multivariate logistic regression analyses. Among the 197 patients, 7 (3.6 %) were incidentally found to have non-thyroid origin malignancy. Additionally, 63.0 % (155/246) of PTC foci showed FDG uptake on PET/CT. Univariate analysis showed that the tumor size, the presence of extrathyroidal extension, BRAF mutation, and Hashimoto thyroiditis were associated with FDG avidity. However, except for pathological extrathyroidal extension, the other factors showed statistically significant correlations with FDG avidity (p < 0.001, p = 0.008, and p = 0.009, respectively). FDG uptake in lateral neck node metastasis showed high specificity and negative predictive value (NPV). In four cases of nonspecific findings on ultrasonography (USG)/CT, FDG avidity was helpful to diagnose the presence of lateral neck metastasis. The maximum standardized uptake value (SUVmax) of PET/CT was correlated with the maximum diameter of the involved lateral node. FDG avidity did not show any significance in the recurrence-free survival of both the thyroid tumor and lateral neck metastasis. The FDG avidity of PTC did not show prognostic predictive meaning. However, in the case of lateral neck metastasis, FDG avidity showed high sensitivity and NPV, and could provide better information in cases of nonspecific findings on USG and CT.