Objective: Follicular (FN) and Hürthle cell neoplasms (HCN) are considered indeterminate on thyroid fine needle aspiration cytology and are preoperative diagnostic challenges. The role of [(18)F]-2-fluoro-2-deoxy-D-glucose (FDG) in characterizing indeterminate thyroid nodules remains equivocal, because of the increased FDG uptake by some benign thyroid nodules. The objective of this study was to compare the FDG positron emission tomography/computerized tomography (PET/CT) characteristics of follicular (FA) and Hürthle cell adenomas (HCA).
Methods: Twenty-nine patients with 31 thyroid nodules underwent FDG-PET/CT scans of the neck and superior mediastinum for indeterminate FN/HCN, and were later found to have benign adenomas on final histopathology. All scans were reported by a single observer, who was blinded to the surgical and pathology findings. Receiver operating characteristic (ROC) curve analysis of maximum standardized uptake value (SUVmax) and the area under the curve (AUROC) were used to assess discrimination between FA and HCA. Youden index was used to identify the optimal cut-off SUVmax. Sensitivity, specificity, predictive values and overall accuracy were used as measures of performance.
Results: The mean age of our study cohort was 60.7 ± 12.6 years and 77 % of the patients were females. Age of the patients (p = 0.48), their gender (p = 0.52), and the size of thyroid nodules (p = 0.79) were similar for FA and HCA. Increased focal FDG uptake was observed in 100 % of HCA and 52 % of FA (p = 0.02). SUVmax of HCA was significantly higher (p < 0.001) than that of FA. SUVmax of 5 was the best cut-off for discrimination between HCA and FA, with AUROC of 0.90 (95 % CI, 0.79-1.00; p = 0.001). With this cut-off, FDG-PET/CT had sensitivity of identifying HCA of 88 % (95 % CI 47-99 %), specificity of 87 % (95 % CI 65-97 %), positive predictive value of 70 % (95 % CI 35-92 %), and negative predictive value of 95 % (95 % CI 74-99 %). The overall accuracy was 87 %.
Conclusions: HCA shows significantly higher focal FDG uptake as compared to FA and should always be considered in the differential diagnosis of FDG-PET positive thyroid nodules.
Keywords: Follicular; Imaging; Neoplasm; Nuclear; PET/CT; Thyroid.