Characterization of thymic lesions with F-18 FDG PET-CT: an emphasis on epithelial tumors.

Thymic lesions may represent an unresolved diagnostic problem that often requires surgical procedure for an accurate diagnosis and staging. A noninvasive imaging study to determine the nature of thymic lesions would help to identify patients who are true candidates for surgery. Published preliminary clinical observations have suggested a role of fluorine-18 fluorodeoxyglucose (F-18 FDG) positron emission tomography-computed tomography (PET-CT) in the characterization of thymic lesions. Benign uptake of the thymus on F-18 FDG PET-CT is seen in children and young adults, and may also indicate thymic hyperplasia in patients after chemotherapy or with Graves' disease. F-18 FDG PET-CT proves to be effective in differentiating thymic carcinoma from other entities within the thymus, and thymoma from thymic hyperplasia. The intensity of FDG uptake is useful for predicting the grade of malignancy in thymic epithelial tumors. However, the literature is equivocal with regard to the ability of F-18 FDG PET-CT to differentiate between invasive and noninvasive thymomas. Further larger studies are required to clarify the effectiveness and explore more clinical implications of F-18 FDG PET-CT on thymic lesions.