Retrospective analyses of false-positive 2-[18F]FDG PET/CT lymph node findings in patients with papillary thyroid cancer

 There are inconsistent results of studies on accuracy of 2-[18F]fluoro-2-deoxy-D-glucose-positron emission tomography/computed tomography (2-[18F]FDG-PET/CT) for cervical lymph node (LN) staging. The aim of this study is to evaluate the accuracy of 2-[18F]FDG-PET/CT in the cervical LN staging of patients with papillary thyroid cancer (PTC) and the factors associated with false-positive LNs in these patients.

 A total of 234 patients with pathologically proven PTC, who underwent 2-[18F]FDG-PET/CT for staging from January 2011 to December 2014, were analyzed. The gold standard for diagnosing LN is a combination of surgical pathology and clinical follow-up. Nodal uptake with a maximum standardized uptake value (SUVmax) > 2.0 was interpreted as PET/CT-positive.

 The sensitivity, specificity, positive predictive value, negative predictive value, and accuracy of 2-[18F]FDG-PET/CT in detecting cervical LN metastases were 42.7% (41/96), 77.7% (248/319), 36.6% (41/112), 81.9% (248/303), and 69.6% (289/415), respectively. The incidence of false-positive LN metastases was 63.4% (71 of 112 LNs). The factors significantly associated with false positives were age < 45 years old (p = 0.032) and SUVmax of the primary tumor < 4.0 (p = 0.021). In addition, false-positive LNs were correlated with a low LN SUVmax, location (central vs. lateral), and direction (ipsilateral vs. contralateral).

 These findings suggest that cervical LN staging by 2-[18F]FDG-PET/CT in PTC patients should be more carefully assessed in patients younger than 45 years old with a primary tumor SUVmax < 4.0 or contralateral LN.