Estimating splenic volume: Sonographic measurements correlated with helical CT determination

OBJECTIVE. The purpose of this study was to determine which sonographic measurements of the spleen most closely correlate with splenic volume as determined on helical CT. MATERIALS AND METHODS. From October 17,2000, to April 27,2001,142 consecutive patients prospectively underwent abdominal helical CT and sonography as part of an evaluation for liver disease. Calculations of splenic volumes were based on 10-mm unenhanced images. Maximum length (ML) and width (W), thickness (7), and craniocaudal length (CCL) were measured sonographically. Standard ellipsoid volume formulas (with the addition of new ellipsoid coefficients) and linear regression formulas were calculated for 117 patients whose examinations were performed within 30 days of each other. Mean percent differences, standard deviations, and 95% confidence intervals (CI) were calculated. RESULTS. We calculated the average difference between sonography- and CT-measured volume and the 95% Cl for each of the four initial sonographic volume estimates with the ellipsoid method using two lengths and linear regression using two lengths and compared them to CT-determined volume. The ellipsoid formulas were then adjusted for bias. Linear regression formulas were derived in which splenic volumes were separately calculated on the basis of each of the two lengths. Mean percent differences and standard deviations for ellipsoid formulas with varying coefficients using the three length measurements were also calculated. CONCLUSION. Sonographic measurements allow accurate determination of splenic volume. Estimating splenic volume with the formula 0.524 x W x T x (ML + CCL)/2 provides the greatest overall accuracy.