WCE 2018: Proposal for a Simple Anatomical Classification of the Pelvicalyceal System for Endoscopic Surgery

Paris, France (UroToday.com) Ureteroscopic and percutaneous stone surgeries are increasing worldwide, but no two patients are alike and some patients’ renal anatomies could differ drastically. Currently, there is no universal nomenclature for the classification of kidney anatomy with regard to the pelvicalyceal system. Due to this, the ability to describe detailed ureteroscopic findings and share common information about the position of a stone or the appropriate puncture site for a percutaneous approach is greatly reduced. Therefore, Dr. Ryoji Takazawa and his team of clinical urologists at the Tokyo Metropolitan Ohtsuka Hospital in Tokyo decided to take matters into their own hands and develop a universal classification system that can be used worldwide. 

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