Evaluating kidney stone size in children using the posterior acoustic shadow

Abstract

Ultrasound, not x-ray, is preferred for imaging kidney stones in children; however, stone size determination is less accurate with ultrasound. In vitro we found stone sizing was improved by measuring the width of the acoustic shadow behind the stone. We sought to determine the prevalence and accuracy of the acoustic shadow in pediatric patients. A retrospective analysis was performed of all initial stone events at a children’s hospital over the last 10 years. Included subjects had a computed tomography (CT) scan and renal ultrasound within 3 months of each other. The width of the stone and acoustic shadow were measured on ultrasound and compared to the stone size as determined by CT. Thirty-seven patients with 49 kidney stones were included. An acoustic shadow was seen in 85% of stones evaluated. Stone width resulted in an average overestimation of 1.2 ± 2.2 mm while shadow width resulted in an underestimation of 0.5 ± 1.7 mm (p < 0.001). A posterior acoustic shadow was seen in the majority of stones and was a more accurate measure of stone size. This would provide valuable information for stone management. [Work supported by NIH DK43881 and DK092197, and NSBRI through NASA NCC 9-58.]