Diagnostic efficiency of ¹⁸F-FDG PET/CT for indeterminate thyroid nodules

Objective: To investigate the diagnostic efficiency of ¹⁸F-FDG PET/CT imaging for indeterminate thyroid nodules. Methods: Sixty-eight patients (24 males, 44 females, age: (52.8 ± 10.58) years) with indeterminate thyroid nodules who underwent ¹⁸F-FDG PET/CT imaging from January 2006 to December 2012 were analyzed retrospectively. The imaging characteristic including clearity of boundary, uniform density, calcification, capsule, mean CT value, nodular size and SUV_max of thyroid nodules were evaluated. The gold standard was postoperative pathological results. Mann-Whitney u test, χ² test and ROC curve analysis were performed to investigate the diagnostic efficiency. Results: Among 68 patients with indeterminate thyroid nodules, 18 were malignant and 50 were benign according to pathological results. Uniform density, calcification, capsule (χ² = 0.21, 0.01, 0.43, all P > 0.05) and mean CT value, nodular size (all AUCs < 0.5) could not differentiate benign from malignant thyroid nodules. However, whether the nodules had clear boundary was significant to differentiate benign from malignant nodules (χ² = 8.06, P < 0.05), and the sensitivity, specificity and accuracy were 55.6%(10/18), 80.0%(40/50) and 73.5%(50/68), respectively. The mean SUV_max of benign and malignant thyroid nodules was 3.16 ± 1.84 and 8.53 ± 7.09, respectively (u = -4.281, P < 0.01). AUC of SUV_max was 0.841(95% CI; 0.726-0.955). According to the maximal Youden index(0.562), 4.25 was chosen as the SUV_max threshold, and its sensitivity, specificity and accuracy were 72.2% (13/18), 84.0% (42/50) and 80.9% (55/68), respectively. Conclusion: Among different characteristics of ¹⁸F-FDG PET/CT imaging, SUV_max of thyroid nodules plays an important role in the differential diagnosis of undetermined thyroid nodules, but CT image features have limited value. (authors)