Normal uptake of 18F-FDG in the testis: an assessment by PET/CT

The aim of this study was to assess the physiological uptake of 18F-fluoro-2-deoxyglucose (FDG) by an apparently normal testis with combined positron emission tomography-computed tomography (PET/CT) and its correlation with age, blood glucose level, and testicular volume.

The testicular uptake of 18F-FDG, expressed as the standardized uptake value (SUV), was measured on PET/CT images in 203 men. The correlation between SUV and age, blood glucose level, and testicular volume was assessed.

The SUV in the total of 406 testes was 2.44 +/- 0.45 (range 1.23-3.85). The SUV was 2.81 +/- 0.43 (2.28-3.85) for 30-39 years (n = 12), 2.63 +/- 0.45 (1.77-3.75) for 40-49 years (n = 64), 2.46 +/- 0.35 (1.44-3.15) for 50-59 years (n = 82), 2.51 +/- 0.41 (1.50-3.46) for 60-69 years (n = 86), 2.43 +/- 0.47 (1.42-3.29) for 70-79 years (n = 86), and 2.18 +/- 0.45 (1.23-3.03) for 80-89 years (n = 76). When we calculated the mean SUV of bilateral testes in each patient, there were significant statistical differences between those in the age group of 30-39 years and 80-89 years, 40-49 years and 80-89 years, and 50-60 years and 80-89 years, when using an unpaired test with Bonferroni correction. The laterality index (|L - R|/(L + R) x 2) in 203 men was 0.066 +/- 0.067 (0-0.522). There was a mild correlation between the mean SUV and age (r = -0.284, P < 0.001) as well as between the mean SUV and mean volume (r = +0.368, P < 0.001). There was no correlation between the mean SUV and glucose blood level (r = -0.065, P = 0.358).

Some uptake of FDG is observed in the normal testis and declines slightly with age. Physiological FDG uptake in the testis should not be confused with pathological accumulation.