Indian Journal of Urology
: 2013  |  Volume : 29  |  Issue : 4  |  Page : 364--365

S.T.O.N.E. nephrolithometry for kidney calculi

Kuldeep Sharma 

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Sharma K. S.T.O.N.E. nephrolithometry for kidney calculi.Indian J Urol 2013;29:364-365

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Sharma K. S.T.O.N.E. nephrolithometry for kidney calculi. Indian J Urol [serial online] 2013 [cited 2021 Jun 18 ];29:364-365
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Instruments currently available to predict the percutaneous nephrolithotomy (PCNL) outcomes are cumbersome, unvalidated, and with a limited clinical utility. Recently, Okhunov et al.[1] proposed a novel, quantitative scoring system (SS) (the S.T.O.N.E. nephrolithometry score) using parameters based on non-contrast-enhanced computed tomography scans, to describe and classify the most relevant features that affect the percutaneous management of renal calculi. Medline review of English language studies from 1976 to 2012 was carried out to identify the clinically relevant and reproducible variables that could affect the outcomes after PCNL. These variables are abbreviated using the acronym "S.T.O.N.E." The variables include the stone size (score 1,2,3,4 is 0-399, 400-799, 800-1599, ≥1600 mm 2 respectively), tract length (skin-to-stone distance: Score 1, 2 is ≤100 mm and >100 mm respectively), degree of obstruction (presence of hydronephrosis: Score 1 is nil to mild and 2 is moderate to severe), number of involved calices (score 1,2,3 is up to 2 calyx, 3 calyx and staghorn, respectively) and stone essence (stone density score 1,2 is <950 and >950 HU, respectively). From November 2009 to October 2011, 117 patients, >18 years old were included in the present study. Patient demographics and stone characteristics were compared between the stone-free patients and those with residual stones. The mean stone size in stone-free patients and patients with residual stones was 465 mm 2 and 1064 mm 2 , respectively (P = 0.01). The number of involved calices differed between the two groups (3.3 ± 1.8 vs. 1.8 ± 1.4; P = 0.001). Among the potential variables, an increasing stone size (P < 0.0001), an increasing number of calices (P < 0.0001) and involvement of the renal pelvis (P < 0.007) were associated with residual stones. The skin-to-stone distance, stone density and presence of hydronephrosis were not associated with the presence of residual stones. The S.T.O.N.E. nephrolithometry score was directly related to the presence of residual stones (P = 0.001), Operative time (P = 0.001), estimated blood loss (P = 0.005), length of hospital stay (P = 0.001); and inversely related to stone free rate (SFR) (P = 0.002). Overall, the S.T.O.N.E. nephrolithometry score predicting the stone-free status yielded accuracy of 83.1%, which was greater than any individual component of the score.


Several classification systems have been proposed to describe kidney stones and predict management outcomes but all have some limitations. Thomas et al.[2] proposed the "Guy's stone score" which was calculated using variable pre-operative imaging which is inferior to computed tomography (CT) scan. Mishra et al.[3] proposed staghorn morphometry classification, which required CT urography (not possible in patients with deranged renal function) and a specialized CT scan volumetric assessment software that is not universally available. Zhu et al.[4] proposed mathematical nomograms to predict the outcomes of mini-PCNL but these data are not generalizable to standard PCNL. The need for a comprehensive SS that allows clinicians to visualize the relevant indexes pertinent to management of a renal calculus and develop a mental topography from that score is essential to unify and standardize reporting. Recent experience with the R.E.N.A.L. nephrometry has demonstrated that to be successfully incorporated into clinical practice and academic reporting, such a system needs to fulfill 3 requirements. First, the score must be easy to compose from available pre-operative imaging findings. Second, the variables included must provide detailed information of the individual case. Finally, the SS should provide information regarding post-operative outcomes (specifically the SFR in the case of renal calculi). The S.T.O.N.E. nephrolithometry score was found to be highly predictive of the SFR, with a projected accuracy of 83.1%, greater than any of the individual variables alone. A greater S.T.O.N.E. nephrolithometry score conferred a lower SFR and allowed for sub-classification into the degrees of complexity. A "low complexity" score of 3-5 demonstrated a SFR of 94-100%, a "moderate complexity" score of 6-8 demonstrated a SFR of 83-92% and a "high complexity" score of 9-12 revealed a SFR ranging of 27-64%. To conclude, the S.T.O.N.E. nephrolithometry score provides detailed pre-operative information for each case, providing a simple framework for standardized academic reporting, predictive of the stone-free status and can be used as an adjunct for surgical planning and patient counseling. Additional validation of this SS with external data is important to confirm its general applicability for PCNL.


1Okhunov Z, Friedlander JI, George AK, Duty BD, Moreira DM, Srinivasan AK, et al. S.T.O.N.E. nephrolithometry: Novel surgical classification system for kidney calculi. Urology 2013;81:1154-60.
2Thomas K, Smith NC, Hegarty N, Glass JM. The Guy's stone score - Grading the complexity of percutaneous nephrolithotomy procedures. Urology 2011;78:277-81.
3Mishra S, Sabnis RB, Desai M. Staghorn morphometry: A new tool for clinical classification and prediction model for percutaneous nephrolithotomy monotherapy. J Endourol 2012;26:6-14.
4Zhu Z, Wang S, Xi Q, Bai J, Yu X, Liu J. Logistic regression model for predicting stone-free rate after minimally invasive percutaneous nephrolithotomy.