Fluorine-18-Fluorodeoxyglucose-Avid Thyroid Incidentalomas on Positron Emission Tomography/Computed Tomography in Patients with Non-Thyroid Malignancy: Incidence and Possible Nature

Abstract Background: Incidental thyroid lesions carry the risk of being malignant. Hence, they present a potential challenge for clinicians that necessitates careful management. Aim of Study: The aim of this retrospective cohort study was to assess the thyroid incidentalomas detected on fluorine-18-Fluorodeoxyglucose Positron Emission Tomography/ Computed Tomography (18F-FDG PET/CT), as well as to determine a maximal standardized uptake value (SUVmax) cutoff that could potentially help in the diagnostic process. Patients and Methods: Medical records of 1526 patients who performed 18F-FDG PET/CT as part of the diagnostic work up for non-thyroid malignancy were retrospectively reviewed. Patients with thyroid incidentalomas who fulfilled the eligibility criteria were enrolled into the study. The SUV-max of the lesions and the results of histopathological exam-ination were recorded. Receiver-Operating Characteristic (ROC) curve analysis was carried out. Results: Thyroid incidentalomas were detected in 112/1526 patients (7.3%). Of those, only 46 patients (41%) fulfilled the eligibilty criteria. Histopathological examinations [FNAC (n=46), surgery (n=19)] revealed that 11/46 lesions (23.9%) were malignant, whereas 35/46 lesions (76.1%) were benign. The mean SUVmax of malignant lesions (7.05±1.51) was significantly higher than that of benign lesions (3.18±1.74); p=0.001. An SUVmax cutoff value of 5.5 was the most accurate for discriminating between benign and malignant incidenta-lomas, with 90.91% sensitivity and 82.86% specificity; p=0.001. Conclusion: The incidence of 18F-FDG-avid thyroid incidentalomas is relatively high among patients who undergo PET/CT as part of the diagnostic work up for non-thyroid malignancy. The SUVmax values are higher in malignant incidentalomas, yet with a noticeable overlap in the values between benign and malignant lesions. An SUVmax cutoff value of 5.5 can potentially be utilized to predict the nature of incidental thyroid lesions.