J Nucl Med 2001 Apr;42(4):591-5
Increased metabolic activity in the thymus gland studied with (18)f-fdg pet:
age dependency and frequency after chemotherapy.
Brink I, Reinhardt MJ, Hoegerle S, Altehoefer C, Moser E, Nitzsche EU.
This study was designed to evaluate the age dependency of (18)F-FDG uptake in
the thymus and the frequency of PET confirmation of thymus hyperplasia after
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 lesions 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 lymphoma 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 IIb; 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 IIb. The eldest of these 5 patients was 25
y old. No increased FDG accumulation 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 exceed 4. CONCLUSION: FDG accumulation in the thymus is a
common finding in children and can occasionally be observed in young adults
after chemotherapy. Knowledge of the characteristics of a typical retrosternal
lesion in conjunction with the clinical history allows avoidance of diagnostic
uncertainty and unnecessary procedures.
