Increased metabolic activity in the thymus gland studied with F-18-FDG PET: Age dependency and frequency after chemotherapy

This study was designed to evaluate the age dependency of F-18-FDG uptake i n the thymus and the frequency of PET confirmation of thymus hyperplasia af ter chemotherapy in cancer patients. Methods: Whole-body FDG PET recordings of 168 patients were retrospectively examined for a retrosternal lesion in the anterior mediastinum that was attributable to the thymus. The patients were assigned to the following four groups: children with malignant lesion s before the first therapy (group Ia; n = 15; mean age +/- SD, 11.9 +/- 3.7 y), children with malignant disease after chemotherapy (group Ib; n = 12; mean age, 10.3 +/- 5.0 y), adults with histologically confirmed malignant l ymphoma before the first therapy (group IIa; n = 37; mean age, 43.9 +/- 16. 7 y), and adult lymphoma patients 3 wk to 4 mo after chemotherapy (group II b; n = 104; mean age, 40.9 +/- 14.6 y). Results: increased FDG accumulation in the thymus was seen in 11 patients (73%) of group Ia and 9 patients (75 %) of group Ib. Thymus hyperplasia was found in 5 patients (5%) of group II b. The eldest of these 5 patients was 25 y old. No increased FDG accumulati on in the thymus was observed in any of the group IIa patients. In cases of visible FDG uptake in the thymus, standardized uptake values did not excee d 4. Conclusion: FDG accumulation in the thymus is a common finding in chil dren and can occasionally be observed in young adults after chemotherapy. K nowledge of the characteristics of a typical retrosternal lesion in conjunc tion with the clinical history allows avoidance of diagnostic uncertainty a nd unnecessary procedures.