A simple method to estimate renal volume from computed tomography.

Introduction: Renal parenchymal volume can be used clinically to estimate differential renal function. Unfortunately, conventional methods to determine renal volume from computed tomography (CT) are time-consuming or difficult due to software limitations. We evaluated the accuracy of simple renal measurements to estimate renal volume as compared with estimates made using specialized CT volumetric software.

Methods: We reviewed 28 patients with contrast-enhanced abdominal CT. Using a standardized technique, one urologist and one urology resident independently measured renal length, lateral diameter and anterior-posterior diameter. Using the ellipsoid method, the products of the linear measurements were compared to 3D volume measurements made by a radiologist using specialized volumetric software.

Results: LINEAR KIDNEY MEASUREMENTS WERE HIGHLY CONSISTENT BETWEEN THE UROLOGIST AND THE UROLOGY RESIDENT (INTRACLASS CORRELATION COEFFICIENTS: 0.97 for length, 0.96 for lateral diameter, and 0.90 for anterior-posterior diameter). Average renal volume was 170 (SD: 36) cm(3) using the ellipsoid method compared with 186 (SD 37) cm(3) using volumetric software, for a mean absolute bias of -15.2 (SD 15.0) cm(3) and a relative volume bias of -8.2% (p < 0.001). Thirty-one of 56 (55.3%) estimated volumes were within 10% of the 3D measured volume and 54 of 56 (96.4%) were within 30%.

Conclusion: Renal volume can be easily approximated from contrast-enhanced CT scans using the ellipsoid method. These findings may obviate the need for 3D volumetric software analysis in certain cases. Prospective validation is warranted.