Variation in (18)F-FDG PET findings in a patient with synchronous multiple thymoma

We herein present a case of synchronous multiple thymoma that was suspected based on the findings of positron emission tomography with fluorine-18-labeled-fluorodeoxyglucose ((18)F-FDG PET). The patient was a 70-year-old male with two similarly sized and heterogeneously enhanced masses on the right side of the anterior mediastinum on chest computed tomography. (18)F-FDG PET revealed variation in FDG accumulation between the masses, in which the maximum standardized uptake value was 4.4 in Tumor 1 and 8.7 in Tumor 2. Based on these imaging findings, the masses were suspected to be independent, likely synchronous double primary thymoma. Total thymectomy with removal of the two tumors was performed via median sternotomy. A pathological examination identified Tumor 1 as type AB thymoma and Tumor 2 as type A thymoma. This is the first reported case of synchronous multiple thymoma which was suspected based on a variation in the (18)F-FDG PET findings between the tumors.