Objective: Observer error in the sonographic estimation of renal volume in children has not been reported. Knowledge of the possible magnitude of error is important in assessing abnormalities of renal growth. This study was undertaken to determine the error of sonographic measurements of relative renal volume by comparing them with measurements of relative renal function from 99mTc-dimercaptosuccinic acid (DMSA) scintigraphy.
Materials and methods: The study included 52 children, 2 months to 16 years old, who had DMSA scintigraphy and renal sonography on the same day. The sonographic and scintigraphic studies were interpreted independently. Relative function of the right kidney as shown by DMSA scintigrams in the direct posterior view was compared with relative volume as determined with sonography. Renal volumes were calculated by using the formula for a prolate ellipsoid. The standard deviation of the differences (SDD) between relative renal function and relative renal volume was calculated, and the limits of agreement were derived.
Results: Thirty-three children had normal renal morphology on both studies. Twenty-five kidneys in 19 children were abnormal on one or both studies, including 14 definitely scarred kidneys in 12 children. Relative function of the right kidney in patients with normal kidneys was 50.1 +/- 2.5%, including one possible outlying value. Normal relative volume of the right kidney was 49.1 +/- 3.1%. In patients with normal kidneys, the difference between relative function and relative volume of the right kidney was 1.0 +/- 2.8% with 95% limits of agreement of 6.7% and -4.7%. Agreement between relative function and relative volume was worse for children with abnormal kidneys; the mean difference was 2.0%, and the largest observed difference was 10.9%. Correlation between relative renal volume and relative renal function for all patients was high (r = .94), with 95% limits of agreement of 8.6% and -5.8%.
Conclusion: The agreement between relative renal function and relative renal volume was good. In children with normal kidneys, estimated relative renal volume derived from sonography can be expected to lie within 6.7% of the relative renal function determined scintigraphically.