Increased 18 F-FDG accumulation in the tonsils after chemotherapy for pediatric lymphoma: a common physiological phenomenon.

OBJECTIVE: Increased 18 F-fluorodeoxyglucose (FDG) uptake in the tonsils after the completion of chemotherapy in patients with lymphoma may be misdiagnosed as tumor recurrence. This study aimed to investigate the changes in physiological FDG uptake in the tonsils during and after chemotherapy in pediatric patients with lymphoma.

METHODS: A total of 47 FDG-PET/CT scans acquired from 13 pediatric patients with lymphoma (before chemotherapy [preC] = 9; during chemotherapy [durC] = 12; within 1 month after the end of chemotherapy [endC] = 11; and after achieving complete response [postC] = 15) were retrospectively included in this study. FDG uptake in the palatine tonsils was assessed using maximum standardized uptake value (SUVmax ). The relative size of the palatine tonsils was calculated as the tonsil-pharyngeal ratio (TPR). Serial changes in the SUVmax and TPR were evaluated.

RESULTS: The mean SUVmax was 3.7 ± 1.7, 2.6 ± 0.7, 2.3 ± 0.8, and 6.2 ± 1.6, at the preC, durC, endC, and postC scans, respectively (p < 0.0001); TPR was 59.0 ± 11.2%, 58.3 ± 9.4%, 54.4 ± 7.9%, and 62.2 ± 12.0% in these groups, respectively, with no significant inter-group differences. TPR and SUVmax showed no correlation.

CONCLUSIONS: Increased physiological FDG uptake in the tonsils is commonly observed after the completion of chemotherapy, even in the absence of reactive hypertrophy.