Distinguishing thymic cysts from low-risk thymomas via [18F]FDG PET/CT

Background Thymic cysts are a rare benign disease that needs to be distinguished from low-risk thymoma. [ 18 F]fluorodeoxyglucose (FDG) positron emission tomography (PET)/computed tomography (CT) is a non-invasive imaging technique used in the differential diagnosis of thymic epithelial tumours, but its usefulness for thymic cysts remains unclear. Our study evaluated the utility of visual findings and quantitative parameters of [ 18 F]FDG PET/CT for differentiating between thymic cysts and low-risk thymomas. Methods Patients who underwent preoperative [ 18 F]FDG PET/CT followed by thymectomy for a thymic mass were retrospectively analyzed. The visual [ 18 F]FDG PET/CT findings evaluated were PET visual grade, PET central metabolic defect, and CT shape. The quantitative [ 18 F]FDG PET/CT parameters evaluated were PET maximum standardized uptake value (SUVmax), CT diameter (cm), and CT attenuation in Hounsfield units (HU). Findings and parameters for differentiating thymic cysts from low-risk thymomas were assessed using Pearson’s chi-square test, the Mann-Whitney U-test, and receiver operating characteristics (ROC) curve analysis. Results Seventy patients (18 thymic cysts and 52 low-risk thymomas) were finally included. Visual findings of PET visual grade ( P