[18F]FDG positron emission tomography/computed tomography and multidetector computed tomography roles in thymic lesion treatment planning

Rationale: Thymic masses may represent an unsolved diagnostic problem which often require surgical procedures for an accurate staging. A non-invasive way to determine the nature of thymic lesions would help identify the patients which are true candidates for surgery. Our retrospective study aims to assess multidetector computed tomography and 2-[18F]fluoro-2-deoxyglucose positron emission tomography/computed tomography ([18F]FDG-PET/CT) capacity to distinguish benign from malignant thymic lesions. Methods: Helical multidetector CT (MDCT) and [18F]FDG-PET/CT of twenty consecutive patients presenting with a thymic mass at our Institute were retrospectively analyzed. MDCT scans were focused on morphologic features and invasiveness characteristics. Qualitative and semi-quantitative analyses by maximum standardized uptake value corrected for body weight (SUVbw max) were performed on [18F]FDG-PET/CT. In all cases, readers were blinded to pathology findings. Both imaging techniques were correlated to final pathology. Student's t-test was performed on SUVbw max stratified for thymic epithelial tumors. Results: In the group of benign lesions MDCT correctly identified well-defined margins of masses in 8 out of 8 patients whereas [18F]FDG-PET/CT was negative in 7 out of 8 patients. Among malignant lesions MDCT revealed mediastinum fat or infiltration of adjacent organs in 10/12 patients. On the other hand [18F]FDG-PET/CT showed increased radiotracer uptake in 12/12 patients. Conclusions: MDCT and [18F]FDG-PET/CT alone are not able to differentiate the nature of thymic lesions. However, they are two non-invasive complementary techniques which can be used to differentiate benign from high-risk malignant thymic lesions. These findings should be taken into account before surgery is performed as a diagnostic procedure. © 2008 Elsevier Ireland Ltd. All rights reserved.