FNA indication according to ACR-TIRADS, EU-TIRADS and K-TIRADS in thyroid incidentalomas at 18F-FDG PET/CT.

OBJECTIVE: Focal thyroid incidentaloma (TI) occurs in a 2% of 18F-FDG PET/CT and about one-third of TIs is cancer. Due to the lack of evidence on the optimal management of TI, current guidelines suggest performing fine-needle aspiration cytology (FNA). The study aim was to evaluate the reliability of ACR-TIRADS, EU-TIRADS, and K-TIRADS in indicating FNA in TIs.

DESIGN: We retrospectively reviewed 18F-FDG PET/CT TIs recorded during the period 2016-2019. Enrolled were TIs with histologic outcome and autonomous nodules. Cases with uncertain matching between 18F-FDG PET/CT, US/scintiscan and histology were excluded.

RESULTS: Eighty TIs at 18F-FDG PET/CT (median size 17 mm, median SUVmax 7.85) were included; a 26.2% was cancer. The percentage of nodules classified as high risk according to ACR-TIRADS, EU-TIRADS, and K-TIRADS was 20%, 30%, and 29.8%, respectively. The cancer prevalence in high-risk class was 56.2%, 66.7%, and 65.2% in ACR-TIRADS, EU-TIRADS, and K-TIRADS, respectively. ACR-TIRADS had the lowest number of cases with FNA indication (48%) and the K-TIRADS, the highest one (75%). Evaluating the reliability of the three systems in indicating FNA, we found a 100% sensitivity and NPV for EU-TIRADS and K-TIRADS; while all the three systems showed poor specificity and PPV.

CONCLUSION: All TIRADSs were reliable to stratify the risk of cancer in focal TI. Comparing their reliability in indicating FNA, we found a good performance of EU-TIRADS and K-TIRADS. Considering the high cancer percentage expected in this setting of patients, those TIRADS with higher propensity to indicate FNA should be preferred.