Physiologic Testicular Uptake of 18-F Fluorodeoxyglucose in the Indian Population

The objective of the study is to assess the physiologic uptake of testes in patients undergoing ¹⁸F-fluoro-2-deoxyglucose (FDG) position emission tomography/computed tomography (PET/CT) scans for various malignancies other than testicular malignancy.

The testicular uptake of ¹⁸F-FDG expressed as the standardized uptake value (T) was measured on PET/CT images in 320 men with no known testicular pathology from July 2019 to March 2020 at Tata Main Hospital, Jamshedpur. The ratio of maximum standardized uptake value (SUVmax) of the testis (T) to SUVmax of muscle (M) T/M ratio and to SUVmax of the liver (L) T/L ratio was calculated using SUVmax of right adductor muscle and liver, respectively. Testicular volume was calculated with the measurements taken from the axial, coronal, and sagittal slices of CT images. The correlation of testicular uptake with age, blood serum glucose level, and testicular volume was also analyzed.

The mean age of 320 men was 57 ± 15 years (range: 10-94) and the mean blood glucose level was 107.7 ± 23.5 mg/dl (range: 64-175). Mean testicular SUVmax in 320 men was 2.48 ± 0.80 (range: 0.67-5.5). The mean testicular volume of 640 testes of 320 men was 18.80 ± 4.83 cm³ (range: 3.85-33.56 cm³). The mean values of (T/M) and (T/L) ratios in the studied population were 3.64 ± 1.21 (range: 1.08-5.58) and 0.97 ± 0.251 (range: 0.34-1.88), respectively. The laterality index (L - R/(L + R) ×2) in 320 men was 0.074 ± 0.050 (0.000-0.308). There was a minimal negative correlation between testicular SUVmax and age (r = -0.136, P = 0.15). Mild negative correlation was noted between T/M ratio and age (r = -0.291, P < 0.0001) and between T/L ratio and age (r = -0.182, P = 0.001) in the studied population.

The physiological testicular FDG uptake (SUVmax) of testes was 2.48 ± 0.80 (0.67-5.5) among the Indian population in this study, which has a mild negative correlation with age.