Hydronephrotic kidney: pediatric three-dimensional US for relative renal size assessment--initial experience

To prospectively evaluate accuracy of three-dimensional (3D) ultrasonography (US) for assessment of relative renal size in infants and children with hydronephrosis.

Informed consent was obtained from parents and also from children who were older than 8 years. Study was approved by ethics committee. Two-dimensional (2D) US, 3D US, and scintigraphy were performed in 40 patients with hydronephrosis (age range, neonate to 16 years; seven girls, 33 boys) without acute renal disease. Twenty patients also underwent magnetic resonance (MR) urography. US and MR urography were performed by one experienced pediatric radiologist; 3D US and MR urographic volume calculations were performed by specifically trained radiologists. Three-dimensional US was performed with integrated 3D volume probes or external system based on electromagnetic positioning devices. At 2D US, kidney volume was calculated with application of ellipsoid equation. At MR urography and 3D US, real renal parenchymal volume was calculated with subtraction of dilated collecting system. Split renal function was assessed with static renal scintigraphy. Three-dimensional US results were graded with respect to image quality and compared with results of 2D US, scintigraphy, and MR urography by using mean difference percentage and standard deviation of the difference. All investigations were performed with blinding. Inter- and intraobserver variability were calculated with coefficient of variation.

In 76 of 80 kidneys, 3D US image of diagnostic quality was obtained. Three-dimensional US volume measurements compared well with MR urographic measurements (mean difference, -2.5% +/- 7.8 [standard deviation] vs 25.8% +/- 32.2 for 2D US) and with scintigraphically assessed split renal function (mean difference, 1.2% +/- 9.2 vs 15.9% +/- 43.8 for 2D US). Intra- and interobserver variability were +/-6.4% and +/-9.9%, respectively.

Initial experience with renal 3D US indicates that it is an accurate method for assessment of renal parenchymal volume and relative renal size, provided there is no acute renal disease.