The researchers attempted to complete this task by prospectively analyzing data of 270 patients (540 kidneys) who underwent CT-urography at their center. Using this data, 3D images of the renal pelvis were created and examined for their morphological characteristics. Due to severe hydronephrosis or large renal cysts, 48 kidneys were excluded from the study, which resulted in a total of 492 kidneys that were used for proper analysis.
Through careful analysis of each kidney, it was determined that the majority of kidneys had a total number of 8 renal calyces (51%), while 30% had 7 calyces. As such, the researchers based their model on a kidney with 8 calyces and developed a naming system which can be found in Figure 1. The main aspect of this study, however, was the classification of the renal pelvis. As described by Dr. Takazawa, a Type I pelvis is one that forms a true pelvis that is not bifurcated, usually with a middle calyx existing in front of the axis of the renal pelvis. The Type I kidneys could be further specified due to the width of the pelvis: Type 1a is standard, Type Ib has a wide pelvis, and Type Ic has a narrow pelvis. In the study, 58% of patients were Type I, of which, 43% were Type Ia, 4% Type Ib, and 11% Type Ic. Type II describes a pelvis that is divided and bifurcated into the upper and lower branch which is always between the upper and middle calices. Of the patients collected in the study, 42% of patients were Type II. Graphics depicting the differences between Type I and Type II can be found in Figure 1.
At the end of his presentation Dr. Takazawa explained the importance of the classification and described one practical difference between Type I and Type II patients. During percutaneous nephrolithotomy for the treatment of staghorn stones, a Type I patient would be able to have one access tract, but the complicated anatomy of a Type II patient would require two access tracts due to the difficulty getting access to the stone (Figure 2). In his closing remarks, Dr. Takazawa told his audience that this system enables endourologists to share common intrarenal information, thus leading to the development of concrete treatment strategies.
Figure 1: Graphic depicting the differences between the Tokyo Metropolitan Ohtsuka Hospital anatomical classification of the pelvicalyceal system. Nomenclature: T = top; U = upper; M = middle; L = lower, B = bottom; A = anterior; P = posterior
Figure 2: Graphic describing the necessity of two percutaneous access tracts for Type II kidneys.
Presented by: Ryoji Takazawa, MD
Authors: Ryoji Takazawa, Sachi Kitayama, Yusuke Uchida, Satoshi Yoshida, Yusuke Kohno, Toshihko Tsujii
Affiliation: Department of Urology and Kidney Stone Center, Tokyo Metropolitan Ohtsuka Hospital, Tokyo, Japan
Written by: Zachary Valley, Department of Urology, University of California-Irvine medical writer for UroToday at the 36th World Congress of Endourology (WCE) and SWL - September 20-23, 2018 Paris, France