Recurrent thymoma: radiological (CT and FDG-PET) and histological (WHO criteria) features.

A 66-year-old man, who had undergone surgical resection of a primary noninvasive thymoma (type B1) in the right anterolateral mediastinum 6 years before, underwent follow-up computed tomography (CT) scanning. The CT scan revealed a few nodules located at the posterior portion of the right thoracic base and just behind the right upper anterior chest wall. Subsequent fluorodeoxyglucose positron emission tomography (FDG-PET) scans showed multiple foci with high [standard uptake value (SUV) 4.3] and low (SUV 2.6) FDG uptake in the right lower posterior area and right upper anterior area of the chest, respectively. The fusion image of the CT and FDG-PET scans demonstrated that the areas of the increased FDG uptake corresponded to those of the nodules on the CT scan. All of the nodules were successfully removed surgically, and the histological features of the nodules indicated that they were type B1 or types B1 plus B2. We regarded the nodule located just behind the right upper anterior chest wall as a type B1 thymoma, whereas those in the posterior area of the right thoracic base as combined thymomas of types B1 plus B2. Our limited experience suggests that the degree of FDG uptake is a reflection of the subtype according to the World Health Organization (WHO) criteria. Furthermore, we showed the role of FDG-PET in the accurate assessment of recurrent thymoma and its therapeutic strategy.