Testicular FDG Uptake on PET/CT in Patients with Lymphoma: Correlation with Age

The purpose of this observational study was to investigate whether the standard uptake value (SUV) measurement has practical utility in distinguishing secondary testicular involvement from physiologic uptake in patients with lymphoma. A Radiology Information System (RIS) search was conducted for all PET/CT studies performed from 2010-2016 on adult male patients with a diagnosis of lymphoma. Patients with clinical or pathologic diagnosis of testicular lymphoma were excluded to undergo a separate analysis. PET/CT images of 606 patients with 1087 scans, in which 2045 testes were included in the field of view, were reviewed and measurements were performed for standardized uptake values of both testicles (SUV_max) as well as of the liver (SUV_max and SUV_mean). The mean SUV_max of the testicles was 3.75 ± 0.90 (range 1.16-8.38). The mean ratio of testis SUV_max / liver SUV_mean (T/L) was 1.78 ± 0.43. Trends in SUV_max and age were significant for a negative correlation by a small magnitude of 0.066 per 10 years (P < 0.001). T/L had similar changes with significant low magnitude decrease with increasing age (0.059 per 10-year increase, P < 0.001). In our separate analysis of 3 patients with clinical or pathology proven testicular lymphoma, the average pathologic SUV_max was 13.47 (range 11.39-15.97). This study has the largest known sample size for quantifying physiologic uptake in the testes. SUV measurements to quantify F-18 Fluorodeoxyglucose (FDG) uptake on PET/CT likely have practical utility in discriminating between physiologic and pathologic uptake of FDG in cases of secondary testicular lymphoma.