Effect of patient position on sonographically measured renal length in neonates, infants, and children.

Abstract

Renal length as measured on sonography is fundamental in the evaluation of renal disease in children. Understanding the effect of patient position and imaging plane on measured renal length is important for the appropriate use of the standards for interpretation. The goal of this study was to determine how measurement of renal length on sonograms is affected by changes in patient position and imaging plane. One hundred seventy-six neonates, infants, and children who were 2 days to 17 years old underwent sonography froin October 1995 through June 1996. The largest long-axis renal dimension in sagittal, coronal, and prone planes was obtained for each kidney. Data were analyzed separately for each kidney to determine the individual variation of renal length. The correlation between maximum renal length on coronal, sagittal, and prone sonograms was greater than .95 for both right and left kidneys. The coronal plane yielded the largest measured renal length and the prone view, the smallest. The median of the absolute value of the differences between individual renal lengths as measured on sonograms in the different imaging planes was 2-3 mm for both left and right kidneys (mean difference, left kidney = 3.34-3.62 mm; mean difference, right kidney = 3.22-3.68 mm). The coronal and sagittal views yield the longest measurements and prone views, the shortest. Therefore, initial measurements should be made in coronal or sagittal planes. Prone views should be reserved for situations in which the suspicion exists that the kidney was foreshortened on other views. Reference standards done in a particular plane should be applicable in most situations regardless of the patient position necessary to obtain optimum length.