Objective : To identify and differentiate patients with mediastinal cysts from those with cystic tumors requiring surgery. Methods : A total of 36 patients with mediastinal cystic lesions were enrolled. The patients were separated into two groups based on pathological findings : those with mediastinal cysts (n=23) and those with mediastinal tumors (n=13). The cystic components were measured using imaging parameters including mean computed tomography (CT) value, apparent diffusion coefficient (ADC), T1 signal intensity ratio (T1SI-ratio), and T2 signal intensity ratio (T2SI-ratio), acquired from magnetic resonance imaging (MRI) ; and standardized maximum uptake value (SUVmax) from 18F-fluorodeoxyglucose positron emission tomography/computed tomography (18F-FDG PET/CT). Both groups were statistically compared. Results : Comparative parameters between the cysts and tumors revealed the following ratios : CT value, 40.9±21.2 versus (vs) 24.8±12.9 (p = 0.019) ; SUVmax, 1.18±0.50 vs 4.32±3.52 (p = 0.003) ; ADC, 3.46±0.96 vs 2.68±0.74 (p = 0.022) ; T1SI-ratio, 1.06±0.60 vs 1.35±0.92 (p = 0.648) ; T2SI-ratio, 5.40±1.80 vs 4.33±1.58 (p = 0.194). However, there was no correlation between FDG uptake and ADC value. Conclusions : SUVmax from 18F-FDG PET/CT and ADC derived from MRI were effective in facilitating preoperative diagnosis to differentiate mediastinal cysts from tumors. However, these examinations may be complementary to one another, not dominant
