Nationwide organ volume distributions and cross-sectional age-associated differences in abdominal CT from Japan

Large-scale CT-based reference distributions for abdominal organ volume that incorporate age, sex, and body size are limited. To establish sex- and age-specific reference distributions for major abdominal organ volumes on non-contrast abdominopelvic CT in a nationwide Japanese cohort to provide a foundation for automated clinical assessment.

In this retrospective, multicenter study, we used the Japan Medical Image Database to identify all non-contrast abdominopelvic CT examinations performed in 2024. Unique adults with available data on age, sex, height, and weight were included in this study. The final sample comprised 49,764 examinations (26,456 men and 23,308 women) conducted at nine different institutions. Automated segmentation (TotalSegmentator v2.10.0) was used to produce organ volumes, excluding the hollow viscera. Sex-specific 10th, 25th, 50th, 75th, and 90th percentiles were calculated. Age-volume relationships of body surface area (BSA)-normalized volumes (mL/m²) were modeled using natural cubic splines (four degrees of freedom) separately for each sex.

The median male vs. female volumes (mL) were as follows: liver, 1,194.7 vs 1,024.0; pancreas, 63.7 vs 52.3; spleen, 118.7 vs 95.4; kidneys (total), 268.3 vs 221.2; adrenals (total), 6.7 vs 4.2; iliopsoas (total), 483.4 vs 317.7; and prostate, 25.5 (men only). The age-volume relationships of BSA-normalized volumes showed convex patterns for the liver, pancreas, and kidneys in both sexes and for male adrenal glands; lower values in older age groups for the spleen and iliopsoas in both sexes; and higher values in older age groups for the prostate and female adrenal glands.

This nationwide Japanese CT cohort provides sex- and age-resolved organ volume reference distributions. These distributions may serve as a quantitative reference for clinical interpretation and population-based imaging research.