Ellipsoid vs spherical cap: a new approach to splenic volumetry validated on cadavers

Accurate splenic volumetry is essential in hematologic and hepatic disorders, particularly for monitoring therapeutic response to JAK-2 inhibitors. Ultrasound-based assessment typically applies the prolate ellipsoid formula using three diameters, although the anteroposterior (AP) measurement is often unreliable. This study aimed to validate an alternative two-diameter approach based on the spherical cap formula.

Fifteen autopsy cases underwent splenic ultrasound before organ removal. Longitudinal, transverse, and AP diameters were measured to calculate splenic volume using both the prolate ellipsoid and spherical cap formulas. These values were compared with the true organ volume obtained by water displacement. The protocol was subsequently applied to 101 living outpatients for further comparison between formulas.

In cadavers, ultrasound-derived volumes correlated strongly with actual splenic volumes for both formulas (Spearman's ρ = 0.83 for ellipsoid; ρ = 0.80 for spherical cap). Similar agreement was confirmed in living subjects (ρ = 0.94, p < 0.001). The AP diameter showed the greatest variability and lowest reliability. Histologic analysis demonstrated that splenic weight correlates with white pulp trophism rather than volume.

The spherical cap formula, requiring only longitudinal and transverse diameters, provides an accurate and reproducible estimation of splenic volume comparable to the ellipsoid model. Its simplified application may improve consistency in ultrasound volumetry and enhance clinical utility in hematologic and hepatic follow-up.