Image-Based Scoring Systems for Patient Assessment and Outcome Stratification During Percutaneous Nephrolithotomy: Beyond the Abstract

Preoperative nomograms such as image-based scoring systems are methods to assess patients, predict outcomes, and improve treatment. For percutaneous nephrolithotomy (PCNL), four different scoring systems have been developed: Guy’s stone score (GSS), S.T.O.N.E nephrolithometry, Clinical Research Office of the Endourology Society (CROES) nomogram, and Seoul National University Renal Stone Complexity (S-ReSC). Though it has been established that scoring systems are vital in contributing to surgical planning, patient counseling, and outcome assessment, the gold standard for PCNL has yet to be established. “Predictability and Practicality of Image-Based Scoring Systems for Patient Assessment and Outcome Stratification During Percutaneous Nephrolithotomy: a Contemporary Update” by Huynh in Current Urology Reports seeks to review the advantages, disadvantages, similarities, and differences of all four current nomograms after establishing the qualities of an optimal scoring system. 

The review begins by discussing how PCNL outcomes are primarily measured through stone-free rates, but can also be measured through several patient and stone-free characteristics such as stone burden, location, and patient surgeon dependent characteristic features. Unlike many other reviews on NLSS, the authors take the time to establish the characteristics that contribute to the development of the scoring systems, as well as how these enhance the predictability of different metrics. Although stone burden is a widely used outcome success indicator, it is not standardized across the different NLSS’s, and stone location and distribution can also have a substantial impact on stone-free rates. In addition, patient and surgeon dependent characteristic features can contribute to surgical complications that may alter stone free rate. Even further,  anatomical abnormalities and surgeon experience and expertise are also large contributors. 

Few studies have been done to compare the success of all four scoring systems. In contrast, Huynh et. al. addresses the NLSS’s in terms of predictability and practicality of implementation both in the the clinical setting and in outcomes reporting. In terms of development, S.T.O.N.E. Nephrolithometry seemed most advantageous as it was developed based on CT scans, the most common form of preoperative imaging, and literature reviews. Guy’s Stone Score and the CROES nomogram were developed originally on abdomen plain films. However, since Guy’s stone score can be used on multiple imaging modalities, it is more universal. S-ReSC was also developed based on studies at one institution, and not many studies outside of Korea has validated the nomogram. In terms of the variables taken into account for each nomogram, the S-ReSC seems the least comprehensive since it is based on one variable (number of locations involved), though it may be easy to use and reproduce. Guy’s Stone Score, the CROES nomogram, and S.T.O.N.E Nephrolithometry all take into account stone burden in some form. Surgeon expertise is accounted for in only the CROES nomogram, while patient abnormalities and characteristics are only accounted for in the Guy’s stone score. Yet, in terms of practicality, S.T.O.N.E. Nephrolithometry stratifies patients, allowing efficient decision-making and surgical planning. On the other hand, the CROES nomogram grades on a continuous scale instead of dividing scores into discrete groups. Reproducibility seemed to be high in S-ReSC and S.T.O.N.E. Nephrolithometry. 

Since only one study have compared all four studies, the paper addresses mostly GSS, S.T.O.N.E Nephrolithometry and the CROES nomogram, with each study citing different nomograms as the “more successful” scoring system. GSS was cited as the most practical nomogram when considering time for calculating each score and ease of application to patient counseling. Another study proposed a simplified version of the S.T.O.N.E. Nephrolithometry, resulting in the SON score. CROES was named superior in terms of considering patient abnormalities and characteristics. While most literature reviews were unable to conclusively determine a scoring system as superior, GSS seemed to have marginally greater evidence.

While currently unable to name a gold standard NLSS, the authors call for a standard, universal scoring system that is capable of capturing stone-free status and risk of complications, and a proper method for categorizing patients to ease patient counselling, as well as further studies that evaluate the current systems for these traits. 

Written by: Linda My Huynh, Erica Huang, Roshan Patel, Zhamshid Okhunov - Department of Urology, University of California, Irvine 

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