The Evaluation of Malignancy Rate of Incidental Thyroid Nodules Detected by FDG-PET/CT

ABSTRACT

Objective: 18F-fluorodeoxyglucose positron emission tomography/ computed tomography (FDG-PET/CT) is widely used in investigating and staging malignancies. Malignancy rate is high in thyroid incidentalomas detected by FDG-PET/CT. The objective of this study was to evaluate the malignancy rate of incidental thyroid nodules in patients who had undergone FDG-PET/CT scan. Material and Methods: The reports of 10,197 FDG-PET/CT scans performed between January 2014 and May 2019 were analyzed retrospectively. The patients with incidental thyroid nodules and who underwent fine-needle aspiration biopsy (FNAB) were included in this study. Patients were stratified into two groups: malignant and non-malignant, according to FNAB cytological results. The association between maximum standardized uptake (SUVmax) values, ultrasonography (USG) findings, and cytological results of the biopsied nodules were investigated. Results: A total of 80 patients were included in the study. Forty (50%) of the patients were females, and the mean age was 63.2±11.4 years. Evaluation of FNAB results of 13 (16.3%) showed their malignant status. Of the patients in the malignant group, seven (53.8%) were females (mean age, 60.6±11.8 years). No statistically significant difference between the groups with or without malignancy in terms of gender distribution and mean age (p=0.762, p=0.401, respectively) was observed. The SUVmax value of the malignant group was 15.7 (5.1-29.7) and of the non-malignant group was 4.4 (1.6- 24.1) (p<0.001). Conclusion: We found that the malignancy rate is high in patients with thyroid incidentaloma detected by FDG-PET/CT and those who underwent FNAB, confirming previous results in the literature. It is suggested to evaluate further thyroid incidentaloma cases with high SUVmax values.