The effects of aging on testicular volume and glucose metabolism: An investigation with ultrasonography and FDG-PET

Objectives: To investigate the effects of senescence on testicular volume and metabolism by quantitative analysis of volumetric and functional data provided by genital ultrasonography (US) and 2-deoxy-2-[¹⁸F]fluoro-D- glucose-positron emission tomography (FDG-PET), respectively. Methods: Three hundred twenty (PET 173, US 147) male subjects (average age, 47.9±24.1 years; range, 11-90 years) who previously underwent US or FDG-PET imaging were included in this retrospective study. Testicular volumes and FDG maximum standardized uptake values (SUV^max) were correlated with age using polynomial regression and Pearson linear regression analysis. Results: With cross-sectional analysis, the best-fit curves demonstrated statistically significant overall correlations between changes in both the volume and metabolism (SUV^max) of the testicle and increasing age (volume: R²=0.42, p=0.0002; SUV^max: R²=0.26, p<0.0001). Testicular volume rapidly increases during puberty and peaks at age 30 years. Subsequently, the volume of the testes stabilizes in a plateau-like manner until age 60 years. After age 60 years, this study shows that testicular volume decreases significantly. Testicular glucose metabolism increases until age 40 years, after which it declines gradually over time at a constant rate. Conclusion: Testicular volume and metabolism appear to be significantly affected by advancing age at different rates during the different stages of lifespan. The rapid increase in testicular volume and metabolism parallel the onset and progression of puberty and positively correlate with increasing age up to ages 30-40 years. Between ages 40 and 60 years, testicular volume and metabolism remain relatively constant with only a minimal decline. After age of 60 years, the testicular volume significantly declines, while testicular metabolism progressively declines until age 90 years.