Approximation of urinary bladder volume with few measurements on cross-sectional imaging

Accurate estimation of urinary bladder volume (UBV) is important for diagnosing and managing bladder disorders. Computed tomography (CT) is often used as a reference standard; however, existing measurement methods vary in complexity and efficiency.

To determine whether UBV can be accurately estimated on CT using a single sagittal measurement compared with multidimensional measurements and reference volumetric analysis.

CT abdomen-pelvis studies of 80 individuals without urinary tract pathology were retrospectively analyzed. Bladder volume was determined using manual volumetric tracing as the reference standard. Sagittal long axis [sagittal length (SL)], sagittal short axis [sagittal short (SS)], and transverse diameter [right-to-left (RL)] were measured, and single- and multidimensional products (SL, SL × SS, SL × SS × RL) were correlated with reference volume using Pearson correlation coefficients. Linear regression models were derived, and agreement was assessed using Bland-Altman analysis.

SL demonstrated the strongest single-dimension correlation with bladder volume (r = 0.92), compared with SS (r = 0.87) and RL (r = 0.68). Multidimensional measurements showed slightly higher correlations (SL × SS: r = 0.98; SL × SS × RL: r = 0.99). A simplified linear formula was derived: Bladder volume (mL) = 5 × SL (mm) - 222. Bland-Altman analysis showed negligible bias and all values within the limits of agreement for the single-dimension model.

UBV can be accurately estimated using a single sagittal CT measurement in healthy individuals. This simplified approach provides a rapid and reproducible alternative to multidimensional methods without meaningful loss of accuracy and may serve as a reference standard for validating ultrasound-based bladder volume estimation.