AUA 2013 - Session Highlights: Prediction of single procedure success rate using S.T.O.N.E. nephrolithometry surgical classification system with strict criteria for surgical outcome

SAN DIEGO, CA USA ( - Percutaneous nephrostolithotomy (PCNL) is a commonly employed surgical modality for the treatment of large and complex urinary stones. Although clinical tools/instruments have been developed for outcome prediction, their clinical utility has been limited by ease of use and lack of validation.

auaThe S.T.O.N.E. nephrolithometry scoring system was recently introduced by Okhunov, et al. to improve academic reporting and to predict outcomes of PCNL. The scoring system is based on the 5 most reproducible variables from preoperative non-contrast computer tomography (CT). The components are: stone size (S), tract length (T), degree of obstruction (O), extent of calyceal involvement (N) and stone essence (E) (See Table).

The group from University of Florida validated the S.T.O.N.E. nephrolithometry scoring system in a cohort of patients undergoing PCNL using computerized tomography (CT) imaging with strict criteria for stone clearance as a measure of surgical outcome. The study included 117 patients who underwent PCNL. Their stone-free rate was 75%. Dr. Akhavein demonstrated that patients with higher nephrolithometry scores are more likely to have residual stones (8.9 vs. 10.3, p < 0.0001). Additionally, the parameters that predicted success were stone size and number of calyces involved. Tract length trended towards correlation but did not reach statistical significance. There were 12 (10%) complications. The scoring system was not predictive of adverse events.

The authors of this study concluded that the S.T.O.N.E. scoring system is reproducible and predictive of treatment success. The S.T.O.N.E. scoring system is a promising new tool that can guide surgical decision making, predict surgical outcomes, and improve standardized academic reporting in percutaneous kidney stone surgery. Further multi-institutional studies are necessary to both further validate this model and to determine if other predictive parameters can be added to this system.

A summary of S.T.O.N.E. nephrolithometry scoring system






Stone Size (mm2)





Tract length










Number of calyces

1 -2 calyces

3 calyces

Staghorn stone


Essence (HU)





Best poster from the moderated poster session, Stone Disease: SWL, Ureteroscopy or percutaneous stone removal

Presented by Arash Akhavein, Carl Henriksen, and Vincent G. Bird, MD at the American Urological Association (AUA) Annual Meeting - May 4 - 8, 2013 - San Diego Convention Center - San Diego, California USA

Department of Urology, University of Florida, FL USA


Reported for by Zhamshid Okhunov, MD; UC Irvine Medical Center, Orange, CA USA

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