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Utility of the Guy's Stone Score Based on Computed Tomographic Scan Findings for Predicting Percutaneous Nephrolithotomy Outcomes
Endourology and Stones Utility of the Guy’s Stone Score Based on Computed Tomographic Scan Findings for Predicting Percutaneous Nephrolithotomy Outcomes Fabio C. Vicentini, Giovanni Scala Marchini, Eduardo Mazzucchi, Joaquim F. A. Claro, and Miguel Srougi OBJECTIVE
METHODS
RESULTS
CONCLUSION
To evaluate the ability of the Guy’s stone score (GS) to predict the success rates and complications on the basis of the computed tomographic (CT) scan findings for renal stones treated with percutaneous nephrolithotomy (PCNL). From 2008 to 2012, a total of 147 consecutive patients (155 renal units) who underwent PCNL in a completely supine position were prospectively evaluated. All patients underwent a CT scan preoperatively, and the stones were classified according to the GS. All PCNLs were analyzed to determine the association between the GS and treatment outcomes on the basis of CT findings and complications, according to the Clavien criteria. Of the 155 PCNLs, 27% were classified as GS1, 28.4% as GS2, 27% as GS3, and 17.6% as GS4. Only the largest diameter of the stones differed among the groups (GS1 ¼ 21.4, GS2 ¼ 26.5, GS3 ¼ 31.4, and GS4 ¼ 50.5 mm; P <.001). After stratification according to the GS, the groups differed significantly regarding their operative times (GS1 ¼ 63 28.5, GS2 ¼ 101.4 40.8, GS3 ¼ 127.6 47.6, and GS4 ¼ 153.3 56 minutes; P <.001), tubeless rates (GS1 ¼ 54.8%, GS2 ¼ 45.4%, GS3 ¼ 28.6%, and GS4 ¼ 7.4%; P <.001), blood transfusion rates (GS1 ¼ 0%, GS2 ¼ 2.3%, GS3 ¼ 4.8%, and GS4 ¼ 22.2%; P ¼ .01), complications (GS1 ¼ 4.8%, GS2 ¼ 9.1%, GS3 ¼ 26.2%, and GS4 ¼ 44.4%; P <.001), immediate success rates (GS1 ¼ 95.2%, GS2 ¼ 79.5%, GS3 ¼ 59.5%, and GS4 ¼ 40.7%; P <.001), and number of auxiliary procedures (GS1 ¼ 0.05 0.32, GS2 ¼ 0.28 0.6, GS3 ¼ 0.35 0.66, and GS4 ¼ 0.43 0.59; P ¼ .031). The final success rates after the auxiliary procedures were similar among the groups (GS1 ¼ 97.6%, GS2 ¼ 86.4%, GS3 ¼ 90.5%, and GS4 ¼ 74.5%; P ¼ .19). The GS based on CT findings accurately predicted success rates and complications after PCNL for renal stones. UROLOGY -: -e-, 2014. 2014 Elsevier Inc.
P
ercutaneous nephrolithotomy (PCNL) remains the gold standard treatment modality for large and/ or complex renal stones.1,2 Despite the technique’s introduction more than 30 years ago, a standardized method of preoperatively classifying stone diseases to accurately predict the stone-free rates and complications is still lacking. Several parameters have been associated with postoperative outcomes, including stone diameter, burden, location, and presence of hydronephrosis, among Financial Disclosure: The authors declare that they have no relevant financial interests. From the Section of Endourology, Division of Urology, Hospital das Clinicas, University of Sao Paulo Medical School, Sao Paulo, Brazil; and the Section of Endourology, Division of Urology, Men’s Health Centre, Hospital Brigadeiro, Sao Paulo, Sao Paulo, Brazil Reprint requests: Fabio C. Vicentini, M.D., Section of Endourology, Division of Urology, Hospital das Clinicas, University of Sao Paulo Medical School, R. Dr. Alceu de Campos Rodrigues, 46 cj. 21, Sao Paulo CEP 05455-00, Brazil. E-mail: fabio@ drfabiovicentini.com.br Submitted: October 17, 2013, accepted (with revisions): December 24, 2013
ª 2014 Elsevier Inc. All Rights Reserved
others.3-5 However, these are usually used separately, are not always obtained in a practical manner, and do not precisely predict PCNL outcomes. Recently, distinguished groups have published various methods to classify the stone burden in an attempt to standardize a universal preoperative method to efficiently differentiate groups according to the difficulty of achieving success.6-10 The Guy’s stone score (GS) was published first and proved to be easily applied, correlating well with success and complication rates. Some criticism persists, however, because this score mainly uses kidneys, ureters, and bladder scan (KUB) and intravenous urography findings to calculate the stone-free rates.11 Despite GS’s potential as a practical tool for measuring stone disease severity and facilitating patient counseling and physician intercommunication, its use and validation by other groups are insufficient. Only 1 study applied the GS during preoperative planning with promising initial 0090-4295/14/$36.00 http://dx.doi.org/10.1016/j.urology.2013.12.041
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results, confirming a good correlation of the GS with stone-free rates and with complication rates, when controlling for success with KUB.12 In our study, we used preoperative and postoperative computed tomography (CT) to apply the GS by evaluating the outcomes and complications after PCNL for large stones, classified according to these scores. To the best of our knowledge, this is the first study to classify stones according to the GS and use CT in all patients to control the outcomes.
MATERIALS AND METHODS Study Population A total of 153 consecutive patients who underwent PCNL in the complete supine position (csPCNL) from November 2008 to September 2012 were prospectively evaluated. All patients signed an informed consent form and were counseled about their specific stone burden and the potential benefits and complications of the PCNL procedure. Inclusion criteria comprised renal stones >2 cm (1.5 cm if lower pole), multiple stones, or failure of other treatment modalities. Exclusion criteria were age <18 years, concomitant ureteral calculi, and untreated coagulopathy. Patients with concomitant ureteral stones requiring simultaneous ureteroscopy (URS) in the Galdakao modified-Valdivia position were not included in this analysis.13 A single experienced surgeon (F.C.V.) performed all surgeries using the same technique and similar equipment at 2 different institutions. All patients underwent a noncontrast abdominal CT scan preoperatively, and the stones were classified by 2 distinguished surgeons (F.C.V. and G.S.M.) according to the GS.6 To keep the margin of error low, we standardized the definitions between the 2 people that classified the cases. The score comprised 4 grades (Appendix 1): Guy’s 1 (GS1): a solitary stone in the mid and/or lower pole or in the renal pelvis with normal anatomy; normal anatomy ¼ no dilation, infundibular stenosis, calyceal diverticulum, ureteropelvic junction obstruction, no malrotated, pelvic or horseshoe kidney, and simple collecting system (no duplication or bifid pelvis, no ileal conduit, and so forth) Guy’s 2 (GS2): a solitary stone in the upper pole; multiple stones in a patient with simple anatomy; or a solitary stone in a patient with abnormal anatomy Guy’s 3 (GS3): multiple stones in a patient with abnormal anatomy or in a calyceal diverticulum or partial staghorn calculus (defined as a stone evolving the renal pelvis and at least 2 calices) Guy’s 4 (GS4): a complete staghorn calculus (all calices and the pelvis occupied by stones) or any stone in a patient with spina bifida or a spinal injury. Only patients with clinical neurologic alterations were considered as Guy’s 4 (spinal cord injury, myelomeningocele, and so forth).
Operative Technique Preoperatively, all patients received prophylactic thirdgeneration cephalosporin during the induction of anesthesia or therapeutic antibiotics, according to the urine culture obtained 7 days before surgery. All patients with staghorn stones 2
(GS3 or GS4) began oral antibiotics (nitrofurantoin) 7 days before surgery. All PCNLs were performed in the complete supine position, as previously described.14 Briefly, under general anesthesia, all patients lay in the supine decubitus position, with the posterior axillary line located just outside the border of the surgical table. The flank was extended to increase the space between the last rib and the iliac crest. All csPCNLs were performed without boosters under the flank, and all patients were maintained in the same position during the entire procedure. Tract dilation was performed with fascial dilators (numbers 10F, 20F, and 30F, sequentially), and an Amplatz sheath was placed. Nephroscopy was performed with a 26F rigid nephroscope (Karl Storz, Munich, Germany), and stone fragmentation and suction were performed with an ultrasonic lithotripter. Stone-free status was verified with combined fluoroscopy and flexible nephroscopy. A 16F nephrostomy tube was placed at the end of the procedure in cases of bleeding, residual stones, solitary kidney, suspected pelvic injury, or multiple tracts. A 6F ureteral catheter was routinely placed; in cases of ureteropelvic junction significant edema, extensive pelvic injury, or ureteral manipulation, a double-J stent was used instead. Operative time was considered from the beginning of the cystoscopy for ureteral catheter insertion to the end of the nephrostomy placement.
PCNL Outcome Evaluation A noncontrast CT scan and routine serum examinations were performed during the first postoperative day in all cases. Patients with residual stones underwent consented second-look PCNL (re-PCNL), flexible URS, or extracorporeal lithotripsy, according to the residual stone burden and location. Fever was defined as corporeal temperature >37.8 C. Surgical complications were graded according to the modified Clavien score.3 Blood transfusion was considered for patients with signs of hypovolemia, refractory to crystalloid, or colloid reposition. Success rate was defined as the absence of residual stones or the presence of asymptomatic fragments 4 mm in the final CT. Preoperative, intraoperative, and postoperative data were evaluated.
Statistical Analysis Statistical analysis was performed using SPSS version 20 (SPSS, Inc., Chicago, IL). The results were expressed as the mean standard deviation and range. Groups were compared using one-way analysis of variance for numerical variables and the Chi-square or Fisher exact test for categorical variables. Significance was set at P <.05 (2 tailed).
RESULTS Demographic Data Of the 153 patients, 6 were excluded; 2 were lost to follow-up, and 4 had incomplete imaging analysis at follow-up. Of the 147 remaining cases, 8 required contralateral PCNL. Finally, 155 renal units were treated with csPCNL for analysis. Of the 147 patients, 89 (60.6%) were female, and 58 were male (39.4%). The mean patient age at PCNL was 46.9 12.7 years, and the mean body mass index was 27.89 5.8 kg/m2. Of the 155 PCNLs, 42 (27%) were classified as GS1; 44 (28.4%) as GS2; 42 (27%) as GS3; UROLOGY
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Table 1. Demographic data and stone characteristics of the patients stratified according to the Guy’s stone score N (%) Age, mean (SD) Gender, N (%) Male Female BMI, mean (SD) ASA, N (%) 1 2 3 Previous surgery, N (%) Yes Stone side, N (%) Right Left Stone diameter mm, mean (SD)
Guy’s 1 42 (27)
Guy’s 2 44 (28.4)
Guy’s 3 42 (27)
Guy’s 4 27 (17.6)
47.0 (13.1)
48.0 (11.2)
46.0 (12.9)
46.2 (14.6)
17 (40.5) 25 (59.5) 27.5 (6.0)
22 (50) 22 (50) 27.8 (5.5)
15 (35.7) 27 (64.3) 28.5 (6.3)
7 (25.7) 20 (74.1) 27.3 (5.8) 14 (51.9) 12 (44.4) 1 (3.7)
.90
5 (18.5)
.46 .91
23 (54.8) 17 (40.5) 2 (4.8)
18 (40.9) 23 (52.3) 3 (6.8)
21 (50) 18 (42.9) 3 (7.1)
13 (31)
16 (36.4)
13 (31)
23 (54.8) 19 (45.2) 21.4 (7.0)
26 (59.1) 18 (40.9) 26.5 (9.3)
22 (54.2) 20 (47.6) 31.4 (10.3)
16 (59.3) 11 (40.7) 50.5 (10.5)
ANOVA Posthoc (Tamhane’s) .88 .223 .82
<.001
ANOVA, analysis of variance; ASA, American Society of Anesthesiologists classification; BMI, body mass index; SD, standard deviation.
and 27(17.6% ) as GS4. GS1 (n ¼ 44) included 22 pelvic, 8 midpole, and 12 lower pole calculi. GS2 (n ¼ 44) included 38 multiple calculi, 3 upper-pole calculi, and a single pelvic calculus with renal hydronephrosis in 3 cases. GS3 (n ¼ 42) included 15 partial staghorn calculi, 22 multiple renal calculi with abnormal anatomy, and 5 calyceal diverticula. All renal units in GS4 (n ¼ 27) had complete staghorn calculus; one of these patients was also paraplegic. Patient demographic data and stone characteristics are presented on Table 1. The largest stone diameter was different among the groups (GS1 ¼ 21.4, GS2 ¼ 26.5, GS3 ¼ 31.4, and GS4 ¼ 50.5 mm; P <.001). PCNL Outcomes The differences among the groups were statistically significant after stratification, according to the GS relative to operative times (GS1 ¼ 63.0 28.5, GS2 ¼ 101.4 40.8, GS3 ¼ 127.6 47.6, and GS4 ¼ 153.3 56 minutes; P <.001), tubeless rates (GS1 ¼ 54.8%, GS2 ¼ 45.4%, GS3 ¼ 28.6%, and GS4 ¼ 7.4%; P <.001), number of tracts (GS1 ¼ 1.02 0.154, GS2 ¼ 1.32 0.561, GS3 ¼ 1.45 0.772, and GS4 ¼ 1.96 0.759; P <.001; GS4 >all; GS1
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(GS1 ¼ 95.2%, GS2 ¼ 79.5%, GS3 ¼ 59.5%, and GS4 ¼ 40.7%; P <.001; Table 2, Fig. 1). The global stone-free status (no stones) based on the CT scan of the first operative day was 39.2% and was significantly different among the groups (GS1 ¼ 61%, GS2 ¼ 41%, GS3 ¼ 25.9%, and GS4 ¼ 11.1%; P <.001). The GS also differentiated groups according to the number of auxiliary procedures (extracorporeal lithotripsy or flexible URS) required after the initial csPCNL (GS1 ¼ 0.05 0.32, GS2 ¼ 0.28 0.6, GS3 ¼ 0.35 0.66, and GS4 ¼ 0.43 0.59; P ¼ .031; Table 2). Thirteen patients underwent re-PCNL for residual stones: GS1 ¼ 0% (0), GS2 ¼ 2.3% (1), GS3 ¼ 11.9% (5), and GS4 ¼ 29.7% (8 cases) (P <.001). The global final success rate after the auxiliary procedures and/or re-PCNL was 87.7% for all patients but was not significantly different among GS groups (GS1 ¼ 97.6%, GS2 ¼ 86.4%, GS3 ¼ 90.5%, and GS4 ¼ 74.5%; P ¼ .19; Table 2).
COMMENT In our study, we aimed to validate the GS based on postoperative CT scan findings and to evaluate the score’s capability of predicting PCNL outcomes and complications. In the original study, Thomas et al6 developed the score with the intention of classifying target stones in a fast and effortless manner. If successful, the score would be easily incorporated into daily PCNL-planning routines and not restricted to scientific purposes. This score had an interobserver agreement of 86%, indicating high reproducibility. On the multivariate analysis of 100 PCNL cases, the GS was the only factor to accurately predict stone-free rates, as obtained mainly through KUB, ultrasonography, or CT scans. As CT scans have the highest sensitivity and specificity among imaging modalities in evaluating renal stones, the original GS findings might have been invalidated on comparison with CT scans.11 Our institution uses a prospective protocol of PCNL in the modified supine position.14 All patients are evaluated 3
Table 2. Percutaneous nephrolithotomy in the complete supine position outcomes after stratification according to the Guy’s stone score Variables N (%) of kidneys, PCNL Number of accesses, mean (SD) Surgical time (min), mean (SD) Transfusion rate % (N) Immediate success rate % (N) Complication rate % (N) Clavien 1 Clavien 2 Clavien 3a Clavien 4a Clavien 4b Clavien 5 Tubeless rate % (N) Auxiliary procedures (ESWL/ flexible) mean (SD) Re-PCNL % (N) Final success rate after all procedures % (N)
Guy’s 1
Guy’s 2
Guy’s 3
42 (27) 44 (28.4) 42 (27) 1.02 (0.154) 1.32 (0.561) 1.45 (0.772) 63 (28.5) 101.4 (40.8) 127.6 (47.6) 0% 2.3% (1) 4.8% (2) 95.2% (40) 79.5% (35) 59.5% (25) 4.8% (2) 9.1% (4) 26.2% (11) 1 2 4 1 2 2 5
54.8% (23) 0.05 (0.32)
45.4% (20) 0.28 (0.6)
28.6% (12) 0.35 (0.66)
0 97.6% (41)
2.3% (1) 86.4% (38)
11.9% (5) 90.5% (38)
P
Guy’s 4 27 1.96 153.3 22.2% 40.7% 44.4%
(17.6) (0.759) (56) (6) (11) (12) 3 4 1 1 2 1 7.4% (2) 0.43 (0.59)
29.7% (8) 74.5% (20)
—
<.0014>all;1
.001 .031G4>G1 <.001 .19
ESWL, extracorporeal shock wave lithotripsy; PCNL, percutaneous nephrolithotomy; other abbreviation as in Table 1.
Figure 1. Percutaneous nephrolithotomy in the complete supine position (csPCNL) immediate success on the first postoperative day based on computed tomographic scans and complication rates according to the Guy’s stone score. (Color version available online.)
preoperatively and postoperatively with a CT scan. Therefore, we decided to apply the GS based on CT findings to classify the stone burdens of our cases and to evaluate the outcomes. We verified that the GS was highly efficient in predicting success rates. Unlike Thomas et al,6 we also confirmed that CT-based application of the GS allowed the prediction of other parameters, including operative time, number of tracts, transfusion rate, complications, auxiliary procedures, and re-PCNL rate. Thomas et al6 were unable to demonstrate these, possibly because of their smaller sample size; another explanation would be a better definition of the genuine stone shape on the CT scan, allowing for a more precise differentiation and 4
classification. Our findings were encouraging, as we were able to extrapolate the scores’ use to predict perioperative and postoperative complications, an essential topic of preoperative discussion with patients. The ease and promptness of the application of the GS, independent from computer programs or complex charts, make its use even more attractive in stone clinics. Our success rates were relatively higher than originally described,6 even based on CT findings. The original success rates were 81%, 72%, 35%, and 29% for GS 1, 2, 3, and 4, respectively.6 Mandal et al12 applied the GS to their patients and had a final success rate controlled by KUB of 100%, 74%, 56%, and 0% for GS 1, 2, 3, and 4, respectively. These results are similar to our immediate UROLOGY
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success rates: GS1 ¼ 95.2%, GS2 ¼ 79.5%, GS3 ¼ 59.5%, and GS4 ¼ 40.7%. We had a complication rate of 18.2%, similar to others.15,16 The GS cohort had significantly different complication rates: GS1 ¼ 4.8%, GS2 ¼ 9.1%, GS3 ¼ 26.2%, and GS4 ¼ 44.4%. Furthermore, severe complications (Clavien 3-5) were observed only for G3 and G4 patients. Mandal et al12 also found different rates of complications according to the GS, with G3 and G4 having more severe complications. We believe the GS to be extremely helpful in predicting complications because the complexity of the case increases as the GS increases. Recently, other methods to preoperatively classify the patient’s stone burden have shown a good correlation with PCNL outcomes.7-10 Smith et al7 developed an elegant nomogram for the Clinical Research Office of the Endourological Society (CROES) PCNL study group, investigating the outcomes of a very large database from 96 different centers worldwide. The stone burden, calyceal location, staghorn calculi, and stone count were the most important factors predicting success, with an area under the curve of 0.76. They also applied the GS to the same patients for an area under the curve of 0.69, with a significant difference between the 2 scores (P <.001). Nevertheless, similar to the initial study of Thomas et al,6 the CROES nomogram7,17 did not predict perioperative or postoperative complications. Another critical point relies on the fact that the GS was made by retrospective interpretation of the stone burden and kidney anatomy description rather than by direct analysis of the radiological examination. This most likely led to an incorrect classification of the stones and, consequently, an imprecise comparison of outcomes between the scores. Studies comparing existing stone classification scores and nomograms in a standardized fashion are lacking. We are currently prospectively studying the accuracy and applicability of comparative scores and nomograms for PCNL. Our study is not without limitations. First, a few cases were classified in a retrospective fashion because a small amount of patients were treated before the GS was published. However, we do not consider this a major issue because all CT studies are digitalized and were easily accessed to allow for patient classification. Second, the number of patients is relatively small compared with other recent larger multicenter case series. Nevertheless, we performed a standardized preoperative and postoperative evaluation of all patients with a CT scan, increasing the reliability of the outcome assessments. The analyzed cohort was large enough to identify statistically significant differences among several important parameters. Another limitation is that the stones were classified only by 2 surgeons, which could lead to interpretation bias. However, we did not find important disagreements between the surgeons, further proving the scores’ reproducibility. As strength, this is the first study to use CT scans to preoperatively classify stones and to postoperatively ascertain the actual stone-free status. All UROLOGY
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patients underwent operations by the same experienced surgeon using the same technique, reducing the potential biases in PCNL outcomes. In our study, we found that the GS is an important new tool in urologists’ arsenals in the evaluation of renal stones. The GS allows the accurate, fast, and effortless segregation of patients into different groups, each with a specific expected surgical time, number of tracts, transfusion rate, immediate success rate, complication rate, and number of auxiliary procedures and/or re-PCNL to achieve success. These characteristics are key and should be addressed during preoperative patient counseling. Furthermore, by discussing these parameters with the anesthesiologist panel, they can better prepare for the procedure, aiding the urologist in planning an ideal surgical strategy, leading to fewer complications and improving outcomes. We strongly advocate the incorporation of GS on the basis of preoperative CT scans when planning a PCNL.
CONCLUSION The GS, based on CT scan findings, is highly efficient in predicting success rates and complications after PCNL. It is an easy, fast, and effortless tool for preoperative use and should be incorporated in the routine planning of PCNL. The GS allows better patient counseling and the standardization of outcomes for comparison among distinguished surgical approaches to treat renal stones. Acknowledgments. The authors thank Drs. Marcelo Hisano, Claudio Murta, Artur Brito, Elias Chedid Neto, Fabio M. Torricelli, and Alexandre Danilovic for their help during this study. References 1. European Association of Urology. Turk C, Knoll T, Petrik A, et al. Guidelines on urolithiasis. Available at: www.uroweb.org/ guidelines/online-guidelines/. Accessed October 1, 2013. 2. Preminger GM, Assimos DG, Lingeman JE, et al. Chapter 1: AUA guideline on management of staghorn calculi: diagnosis and treatment recommendations. J Urol. 2005;173:1991-2000. 3. Tefekli A, Ali Karadag M, Tepeler K, et al. Classification of percutaneous nephrolithotomy complications using the modified clavien grading system: looking for a standard. Eur Urol. 2008;53: 184-190. 4. de la Rosette JJ, Zuazu JR, Tsakiris P, et al. Prognostic factors and percutaneous nephrolithotomy morbidity: a multivariate analysis of a contemporary series using the Clavien classification. J Urol. 2008; 180:2489-2493. 5. El-Nahas AR, Shokeir AA, El-Assmy AM, et al. Post-percutaneous nephrolithotomy extensive hemorrhage: a study of risk factors. J Urol. 2007;177:576-579. 6. Thomas K, Smith NC, Hegarty N, et al. The Guy’s stone scoree grading the complexity of percutaneous nephrolithotomy procedures. Urology. 2011;78:277-281. 7. Smith A, Averch TD, Shahrour K, et al. A nephrolithometric nomogram to predict treatment success of percutaneous nephrolithotomy. J Urol. 2013;190:149-156. 8. Okhunov Z, Friedlander JI, George AK, et al. S.T.O.N.E. Nephrolithometry: novel surgical classification system for kidney calculi. Urology. 2013;81:1154-1160. 9. Zhu Z, Wang S, Xi Q, et al. Logistic regression model for predicting stone-free rate after minimally invasive percutaneous nephrolithotomy. Urology. 2011;78:32-36.
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10. Mishra 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. 11. Matlaga BR, Hyams ES. Stones: can the Guy’s stone score predict PNL outcomes? Nat Rev Urol. 2011;8:363-364. 12. Mandal S, Goel A, Kathpalia R, et al. Prospective evaluation of complications using the modified Clavien grading system, and of success rates of percutaneous nephrolithotomy using Guy’s Stone Score: a single-center experience. Indian J Urol. 2012;28: 392-398. 13. Ibarluzea G, Scoffone CM, Cracco CM, et al. Supine Valdivia and modified lithotomy position for simultaneous anterograde and retrograde endourological access. BJU Int. 2007:233-236.
14. Vicentini FC, Torricelli FC, Mazzucchi E, et al. Modified complete supine percutaneous nephrolithotomy: solving some problems. J Endourol. 2013;27:845-849. 15. de la Rosette J, Assimos D, Desai M, et al. The clinical research office of the endourological society percutaneous nephrolithotomy global study: indications, complications, and outcomes in 5803 patients. J Endourol. 2011;25:11-17. 16. Neto EA, Mitre AI, Gomes CM, et al. Percutaneous nephrolithotripsy with the patient in a modified supine position. J Urol. 2007; 178:165-168. 17. Duty B, Okhunov Z, Smith A, et al. The debate over percutaneous nephrolithotomy positioning: a comprehensive review. J Urol. 2011; 186:20-25.
APPENDIX
(Color version available online.)
6
UROLOGY
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METHODS
RESULTS
CONCLUSION
To evaluate the ability of the Guy’s stone score (GS) to predict the success rates and complications on the basis of the computed tomographic (CT) scan findings for renal stones treated with percutaneous nephrolithotomy (PCNL). From 2008 to 2012, a total of 147 consecutive patients (155 renal units) who underwent PCNL in a completely supine position were prospectively evaluated. All patients underwent a CT scan preoperatively, and the stones were classified according to the GS. All PCNLs were analyzed to determine the association between the GS and treatment outcomes on the basis of CT findings and complications, according to the Clavien criteria. Of the 155 PCNLs, 27% were classified as GS1, 28.4% as GS2, 27% as GS3, and 17.6% as GS4. Only the largest diameter of the stones differed among the groups (GS1 ¼ 21.4, GS2 ¼ 26.5, GS3 ¼ 31.4, and GS4 ¼ 50.5 mm; P <.001). After stratification according to the GS, the groups differed significantly regarding their operative times (GS1 ¼ 63 28.5, GS2 ¼ 101.4 40.8, GS3 ¼ 127.6 47.6, and GS4 ¼ 153.3 56 minutes; P <.001), tubeless rates (GS1 ¼ 54.8%, GS2 ¼ 45.4%, GS3 ¼ 28.6%, and GS4 ¼ 7.4%; P <.001), blood transfusion rates (GS1 ¼ 0%, GS2 ¼ 2.3%, GS3 ¼ 4.8%, and GS4 ¼ 22.2%; P ¼ .01), complications (GS1 ¼ 4.8%, GS2 ¼ 9.1%, GS3 ¼ 26.2%, and GS4 ¼ 44.4%; P <.001), immediate success rates (GS1 ¼ 95.2%, GS2 ¼ 79.5%, GS3 ¼ 59.5%, and GS4 ¼ 40.7%; P <.001), and number of auxiliary procedures (GS1 ¼ 0.05 0.32, GS2 ¼ 0.28 0.6, GS3 ¼ 0.35 0.66, and GS4 ¼ 0.43 0.59; P ¼ .031). The final success rates after the auxiliary procedures were similar among the groups (GS1 ¼ 97.6%, GS2 ¼ 86.4%, GS3 ¼ 90.5%, and GS4 ¼ 74.5%; P ¼ .19). The GS based on CT findings accurately predicted success rates and complications after PCNL for renal stones. UROLOGY -: -e-, 2014. 2014 Elsevier Inc.
P
ercutaneous nephrolithotomy (PCNL) remains the gold standard treatment modality for large and/ or complex renal stones.1,2 Despite the technique’s introduction more than 30 years ago, a standardized method of preoperatively classifying stone diseases to accurately predict the stone-free rates and complications is still lacking. Several parameters have been associated with postoperative outcomes, including stone diameter, burden, location, and presence of hydronephrosis, among Financial Disclosure: The authors declare that they have no relevant financial interests. From the Section of Endourology, Division of Urology, Hospital das Clinicas, University of Sao Paulo Medical School, Sao Paulo, Brazil; and the Section of Endourology, Division of Urology, Men’s Health Centre, Hospital Brigadeiro, Sao Paulo, Sao Paulo, Brazil Reprint requests: Fabio C. Vicentini, M.D., Section of Endourology, Division of Urology, Hospital das Clinicas, University of Sao Paulo Medical School, R. Dr. Alceu de Campos Rodrigues, 46 cj. 21, Sao Paulo CEP 05455-00, Brazil. E-mail: fabio@ drfabiovicentini.com.br Submitted: October 17, 2013, accepted (with revisions): December 24, 2013
ª 2014 Elsevier Inc. All Rights Reserved
others.3-5 However, these are usually used separately, are not always obtained in a practical manner, and do not precisely predict PCNL outcomes. Recently, distinguished groups have published various methods to classify the stone burden in an attempt to standardize a universal preoperative method to efficiently differentiate groups according to the difficulty of achieving success.6-10 The Guy’s stone score (GS) was published first and proved to be easily applied, correlating well with success and complication rates. Some criticism persists, however, because this score mainly uses kidneys, ureters, and bladder scan (KUB) and intravenous urography findings to calculate the stone-free rates.11 Despite GS’s potential as a practical tool for measuring stone disease severity and facilitating patient counseling and physician intercommunication, its use and validation by other groups are insufficient. Only 1 study applied the GS during preoperative planning with promising initial 0090-4295/14/$36.00 http://dx.doi.org/10.1016/j.urology.2013.12.041
1
results, confirming a good correlation of the GS with stone-free rates and with complication rates, when controlling for success with KUB.12 In our study, we used preoperative and postoperative computed tomography (CT) to apply the GS by evaluating the outcomes and complications after PCNL for large stones, classified according to these scores. To the best of our knowledge, this is the first study to classify stones according to the GS and use CT in all patients to control the outcomes.
MATERIALS AND METHODS Study Population A total of 153 consecutive patients who underwent PCNL in the complete supine position (csPCNL) from November 2008 to September 2012 were prospectively evaluated. All patients signed an informed consent form and were counseled about their specific stone burden and the potential benefits and complications of the PCNL procedure. Inclusion criteria comprised renal stones >2 cm (1.5 cm if lower pole), multiple stones, or failure of other treatment modalities. Exclusion criteria were age <18 years, concomitant ureteral calculi, and untreated coagulopathy. Patients with concomitant ureteral stones requiring simultaneous ureteroscopy (URS) in the Galdakao modified-Valdivia position were not included in this analysis.13 A single experienced surgeon (F.C.V.) performed all surgeries using the same technique and similar equipment at 2 different institutions. All patients underwent a noncontrast abdominal CT scan preoperatively, and the stones were classified by 2 distinguished surgeons (F.C.V. and G.S.M.) according to the GS.6 To keep the margin of error low, we standardized the definitions between the 2 people that classified the cases. The score comprised 4 grades (Appendix 1): Guy’s 1 (GS1): a solitary stone in the mid and/or lower pole or in the renal pelvis with normal anatomy; normal anatomy ¼ no dilation, infundibular stenosis, calyceal diverticulum, ureteropelvic junction obstruction, no malrotated, pelvic or horseshoe kidney, and simple collecting system (no duplication or bifid pelvis, no ileal conduit, and so forth) Guy’s 2 (GS2): a solitary stone in the upper pole; multiple stones in a patient with simple anatomy; or a solitary stone in a patient with abnormal anatomy Guy’s 3 (GS3): multiple stones in a patient with abnormal anatomy or in a calyceal diverticulum or partial staghorn calculus (defined as a stone evolving the renal pelvis and at least 2 calices) Guy’s 4 (GS4): a complete staghorn calculus (all calices and the pelvis occupied by stones) or any stone in a patient with spina bifida or a spinal injury. Only patients with clinical neurologic alterations were considered as Guy’s 4 (spinal cord injury, myelomeningocele, and so forth).
Operative Technique Preoperatively, all patients received prophylactic thirdgeneration cephalosporin during the induction of anesthesia or therapeutic antibiotics, according to the urine culture obtained 7 days before surgery. All patients with staghorn stones 2
(GS3 or GS4) began oral antibiotics (nitrofurantoin) 7 days before surgery. All PCNLs were performed in the complete supine position, as previously described.14 Briefly, under general anesthesia, all patients lay in the supine decubitus position, with the posterior axillary line located just outside the border of the surgical table. The flank was extended to increase the space between the last rib and the iliac crest. All csPCNLs were performed without boosters under the flank, and all patients were maintained in the same position during the entire procedure. Tract dilation was performed with fascial dilators (numbers 10F, 20F, and 30F, sequentially), and an Amplatz sheath was placed. Nephroscopy was performed with a 26F rigid nephroscope (Karl Storz, Munich, Germany), and stone fragmentation and suction were performed with an ultrasonic lithotripter. Stone-free status was verified with combined fluoroscopy and flexible nephroscopy. A 16F nephrostomy tube was placed at the end of the procedure in cases of bleeding, residual stones, solitary kidney, suspected pelvic injury, or multiple tracts. A 6F ureteral catheter was routinely placed; in cases of ureteropelvic junction significant edema, extensive pelvic injury, or ureteral manipulation, a double-J stent was used instead. Operative time was considered from the beginning of the cystoscopy for ureteral catheter insertion to the end of the nephrostomy placement.
PCNL Outcome Evaluation A noncontrast CT scan and routine serum examinations were performed during the first postoperative day in all cases. Patients with residual stones underwent consented second-look PCNL (re-PCNL), flexible URS, or extracorporeal lithotripsy, according to the residual stone burden and location. Fever was defined as corporeal temperature >37.8 C. Surgical complications were graded according to the modified Clavien score.3 Blood transfusion was considered for patients with signs of hypovolemia, refractory to crystalloid, or colloid reposition. Success rate was defined as the absence of residual stones or the presence of asymptomatic fragments 4 mm in the final CT. Preoperative, intraoperative, and postoperative data were evaluated.
Statistical Analysis Statistical analysis was performed using SPSS version 20 (SPSS, Inc., Chicago, IL). The results were expressed as the mean standard deviation and range. Groups were compared using one-way analysis of variance for numerical variables and the Chi-square or Fisher exact test for categorical variables. Significance was set at P <.05 (2 tailed).
RESULTS Demographic Data Of the 153 patients, 6 were excluded; 2 were lost to follow-up, and 4 had incomplete imaging analysis at follow-up. Of the 147 remaining cases, 8 required contralateral PCNL. Finally, 155 renal units were treated with csPCNL for analysis. Of the 147 patients, 89 (60.6%) were female, and 58 were male (39.4%). The mean patient age at PCNL was 46.9 12.7 years, and the mean body mass index was 27.89 5.8 kg/m2. Of the 155 PCNLs, 42 (27%) were classified as GS1; 44 (28.4%) as GS2; 42 (27%) as GS3; UROLOGY
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Table 1. Demographic data and stone characteristics of the patients stratified according to the Guy’s stone score N (%) Age, mean (SD) Gender, N (%) Male Female BMI, mean (SD) ASA, N (%) 1 2 3 Previous surgery, N (%) Yes Stone side, N (%) Right Left Stone diameter mm, mean (SD)
Guy’s 1 42 (27)
Guy’s 2 44 (28.4)
Guy’s 3 42 (27)
Guy’s 4 27 (17.6)
47.0 (13.1)
48.0 (11.2)
46.0 (12.9)
46.2 (14.6)
17 (40.5) 25 (59.5) 27.5 (6.0)
22 (50) 22 (50) 27.8 (5.5)
15 (35.7) 27 (64.3) 28.5 (6.3)
7 (25.7) 20 (74.1) 27.3 (5.8) 14 (51.9) 12 (44.4) 1 (3.7)
.90
5 (18.5)
.46 .91
23 (54.8) 17 (40.5) 2 (4.8)
18 (40.9) 23 (52.3) 3 (6.8)
21 (50) 18 (42.9) 3 (7.1)
13 (31)
16 (36.4)
13 (31)
23 (54.8) 19 (45.2) 21.4 (7.0)
26 (59.1) 18 (40.9) 26.5 (9.3)
22 (54.2) 20 (47.6) 31.4 (10.3)
16 (59.3) 11 (40.7) 50.5 (10.5)
ANOVA Posthoc (Tamhane’s) .88 .223 .82
<.001
ANOVA, analysis of variance; ASA, American Society of Anesthesiologists classification; BMI, body mass index; SD, standard deviation.
and 27(17.6% ) as GS4. GS1 (n ¼ 44) included 22 pelvic, 8 midpole, and 12 lower pole calculi. GS2 (n ¼ 44) included 38 multiple calculi, 3 upper-pole calculi, and a single pelvic calculus with renal hydronephrosis in 3 cases. GS3 (n ¼ 42) included 15 partial staghorn calculi, 22 multiple renal calculi with abnormal anatomy, and 5 calyceal diverticula. All renal units in GS4 (n ¼ 27) had complete staghorn calculus; one of these patients was also paraplegic. Patient demographic data and stone characteristics are presented on Table 1. The largest stone diameter was different among the groups (GS1 ¼ 21.4, GS2 ¼ 26.5, GS3 ¼ 31.4, and GS4 ¼ 50.5 mm; P <.001). PCNL Outcomes The differences among the groups were statistically significant after stratification, according to the GS relative to operative times (GS1 ¼ 63.0 28.5, GS2 ¼ 101.4 40.8, GS3 ¼ 127.6 47.6, and GS4 ¼ 153.3 56 minutes; P <.001), tubeless rates (GS1 ¼ 54.8%, GS2 ¼ 45.4%, GS3 ¼ 28.6%, and GS4 ¼ 7.4%; P <.001), number of tracts (GS1 ¼ 1.02 0.154, GS2 ¼ 1.32 0.561, GS3 ¼ 1.45 0.772, and GS4 ¼ 1.96 0.759; P <.001; GS4 >all; GS1
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(GS1 ¼ 95.2%, GS2 ¼ 79.5%, GS3 ¼ 59.5%, and GS4 ¼ 40.7%; P <.001; Table 2, Fig. 1). The global stone-free status (no stones) based on the CT scan of the first operative day was 39.2% and was significantly different among the groups (GS1 ¼ 61%, GS2 ¼ 41%, GS3 ¼ 25.9%, and GS4 ¼ 11.1%; P <.001). The GS also differentiated groups according to the number of auxiliary procedures (extracorporeal lithotripsy or flexible URS) required after the initial csPCNL (GS1 ¼ 0.05 0.32, GS2 ¼ 0.28 0.6, GS3 ¼ 0.35 0.66, and GS4 ¼ 0.43 0.59; P ¼ .031; Table 2). Thirteen patients underwent re-PCNL for residual stones: GS1 ¼ 0% (0), GS2 ¼ 2.3% (1), GS3 ¼ 11.9% (5), and GS4 ¼ 29.7% (8 cases) (P <.001). The global final success rate after the auxiliary procedures and/or re-PCNL was 87.7% for all patients but was not significantly different among GS groups (GS1 ¼ 97.6%, GS2 ¼ 86.4%, GS3 ¼ 90.5%, and GS4 ¼ 74.5%; P ¼ .19; Table 2).
COMMENT In our study, we aimed to validate the GS based on postoperative CT scan findings and to evaluate the score’s capability of predicting PCNL outcomes and complications. In the original study, Thomas et al6 developed the score with the intention of classifying target stones in a fast and effortless manner. If successful, the score would be easily incorporated into daily PCNL-planning routines and not restricted to scientific purposes. This score had an interobserver agreement of 86%, indicating high reproducibility. On the multivariate analysis of 100 PCNL cases, the GS was the only factor to accurately predict stone-free rates, as obtained mainly through KUB, ultrasonography, or CT scans. As CT scans have the highest sensitivity and specificity among imaging modalities in evaluating renal stones, the original GS findings might have been invalidated on comparison with CT scans.11 Our institution uses a prospective protocol of PCNL in the modified supine position.14 All patients are evaluated 3
Table 2. Percutaneous nephrolithotomy in the complete supine position outcomes after stratification according to the Guy’s stone score Variables N (%) of kidneys, PCNL Number of accesses, mean (SD) Surgical time (min), mean (SD) Transfusion rate % (N) Immediate success rate % (N) Complication rate % (N) Clavien 1 Clavien 2 Clavien 3a Clavien 4a Clavien 4b Clavien 5 Tubeless rate % (N) Auxiliary procedures (ESWL/ flexible) mean (SD) Re-PCNL % (N) Final success rate after all procedures % (N)
Guy’s 1
Guy’s 2
Guy’s 3
42 (27) 44 (28.4) 42 (27) 1.02 (0.154) 1.32 (0.561) 1.45 (0.772) 63 (28.5) 101.4 (40.8) 127.6 (47.6) 0% 2.3% (1) 4.8% (2) 95.2% (40) 79.5% (35) 59.5% (25) 4.8% (2) 9.1% (4) 26.2% (11) 1 2 4 1 2 2 5
54.8% (23) 0.05 (0.32)
45.4% (20) 0.28 (0.6)
28.6% (12) 0.35 (0.66)
0 97.6% (41)
2.3% (1) 86.4% (38)
11.9% (5) 90.5% (38)
P
Guy’s 4 27 1.96 153.3 22.2% 40.7% 44.4%
(17.6) (0.759) (56) (6) (11) (12) 3 4 1 1 2 1 7.4% (2) 0.43 (0.59)
29.7% (8) 74.5% (20)
—
<.0014>all;1
.001 .031G4>G1 <.001 .19
ESWL, extracorporeal shock wave lithotripsy; PCNL, percutaneous nephrolithotomy; other abbreviation as in Table 1.
Figure 1. Percutaneous nephrolithotomy in the complete supine position (csPCNL) immediate success on the first postoperative day based on computed tomographic scans and complication rates according to the Guy’s stone score. (Color version available online.)
preoperatively and postoperatively with a CT scan. Therefore, we decided to apply the GS based on CT findings to classify the stone burdens of our cases and to evaluate the outcomes. We verified that the GS was highly efficient in predicting success rates. Unlike Thomas et al,6 we also confirmed that CT-based application of the GS allowed the prediction of other parameters, including operative time, number of tracts, transfusion rate, complications, auxiliary procedures, and re-PCNL rate. Thomas et al6 were unable to demonstrate these, possibly because of their smaller sample size; another explanation would be a better definition of the genuine stone shape on the CT scan, allowing for a more precise differentiation and 4
classification. Our findings were encouraging, as we were able to extrapolate the scores’ use to predict perioperative and postoperative complications, an essential topic of preoperative discussion with patients. The ease and promptness of the application of the GS, independent from computer programs or complex charts, make its use even more attractive in stone clinics. Our success rates were relatively higher than originally described,6 even based on CT findings. The original success rates were 81%, 72%, 35%, and 29% for GS 1, 2, 3, and 4, respectively.6 Mandal et al12 applied the GS to their patients and had a final success rate controlled by KUB of 100%, 74%, 56%, and 0% for GS 1, 2, 3, and 4, respectively. These results are similar to our immediate UROLOGY
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success rates: GS1 ¼ 95.2%, GS2 ¼ 79.5%, GS3 ¼ 59.5%, and GS4 ¼ 40.7%. We had a complication rate of 18.2%, similar to others.15,16 The GS cohort had significantly different complication rates: GS1 ¼ 4.8%, GS2 ¼ 9.1%, GS3 ¼ 26.2%, and GS4 ¼ 44.4%. Furthermore, severe complications (Clavien 3-5) were observed only for G3 and G4 patients. Mandal et al12 also found different rates of complications according to the GS, with G3 and G4 having more severe complications. We believe the GS to be extremely helpful in predicting complications because the complexity of the case increases as the GS increases. Recently, other methods to preoperatively classify the patient’s stone burden have shown a good correlation with PCNL outcomes.7-10 Smith et al7 developed an elegant nomogram for the Clinical Research Office of the Endourological Society (CROES) PCNL study group, investigating the outcomes of a very large database from 96 different centers worldwide. The stone burden, calyceal location, staghorn calculi, and stone count were the most important factors predicting success, with an area under the curve of 0.76. They also applied the GS to the same patients for an area under the curve of 0.69, with a significant difference between the 2 scores (P <.001). Nevertheless, similar to the initial study of Thomas et al,6 the CROES nomogram7,17 did not predict perioperative or postoperative complications. Another critical point relies on the fact that the GS was made by retrospective interpretation of the stone burden and kidney anatomy description rather than by direct analysis of the radiological examination. This most likely led to an incorrect classification of the stones and, consequently, an imprecise comparison of outcomes between the scores. Studies comparing existing stone classification scores and nomograms in a standardized fashion are lacking. We are currently prospectively studying the accuracy and applicability of comparative scores and nomograms for PCNL. Our study is not without limitations. First, a few cases were classified in a retrospective fashion because a small amount of patients were treated before the GS was published. However, we do not consider this a major issue because all CT studies are digitalized and were easily accessed to allow for patient classification. Second, the number of patients is relatively small compared with other recent larger multicenter case series. Nevertheless, we performed a standardized preoperative and postoperative evaluation of all patients with a CT scan, increasing the reliability of the outcome assessments. The analyzed cohort was large enough to identify statistically significant differences among several important parameters. Another limitation is that the stones were classified only by 2 surgeons, which could lead to interpretation bias. However, we did not find important disagreements between the surgeons, further proving the scores’ reproducibility. As strength, this is the first study to use CT scans to preoperatively classify stones and to postoperatively ascertain the actual stone-free status. All UROLOGY
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patients underwent operations by the same experienced surgeon using the same technique, reducing the potential biases in PCNL outcomes. In our study, we found that the GS is an important new tool in urologists’ arsenals in the evaluation of renal stones. The GS allows the accurate, fast, and effortless segregation of patients into different groups, each with a specific expected surgical time, number of tracts, transfusion rate, immediate success rate, complication rate, and number of auxiliary procedures and/or re-PCNL to achieve success. These characteristics are key and should be addressed during preoperative patient counseling. Furthermore, by discussing these parameters with the anesthesiologist panel, they can better prepare for the procedure, aiding the urologist in planning an ideal surgical strategy, leading to fewer complications and improving outcomes. We strongly advocate the incorporation of GS on the basis of preoperative CT scans when planning a PCNL.
CONCLUSION The GS, based on CT scan findings, is highly efficient in predicting success rates and complications after PCNL. It is an easy, fast, and effortless tool for preoperative use and should be incorporated in the routine planning of PCNL. The GS allows better patient counseling and the standardization of outcomes for comparison among distinguished surgical approaches to treat renal stones. Acknowledgments. The authors thank Drs. Marcelo Hisano, Claudio Murta, Artur Brito, Elias Chedid Neto, Fabio M. Torricelli, and Alexandre Danilovic for their help during this study. References 1. European Association of Urology. Turk C, Knoll T, Petrik A, et al. Guidelines on urolithiasis. Available at: www.uroweb.org/ guidelines/online-guidelines/. Accessed October 1, 2013. 2. Preminger GM, Assimos DG, Lingeman JE, et al. Chapter 1: AUA guideline on management of staghorn calculi: diagnosis and treatment recommendations. J Urol. 2005;173:1991-2000. 3. Tefekli A, Ali Karadag M, Tepeler K, et al. Classification of percutaneous nephrolithotomy complications using the modified clavien grading system: looking for a standard. Eur Urol. 2008;53: 184-190. 4. de la Rosette JJ, Zuazu JR, Tsakiris P, et al. Prognostic factors and percutaneous nephrolithotomy morbidity: a multivariate analysis of a contemporary series using the Clavien classification. J Urol. 2008; 180:2489-2493. 5. El-Nahas AR, Shokeir AA, El-Assmy AM, et al. Post-percutaneous nephrolithotomy extensive hemorrhage: a study of risk factors. J Urol. 2007;177:576-579. 6. Thomas K, Smith NC, Hegarty N, et al. The Guy’s stone scoree grading the complexity of percutaneous nephrolithotomy procedures. Urology. 2011;78:277-281. 7. Smith A, Averch TD, Shahrour K, et al. A nephrolithometric nomogram to predict treatment success of percutaneous nephrolithotomy. J Urol. 2013;190:149-156. 8. Okhunov Z, Friedlander JI, George AK, et al. S.T.O.N.E. Nephrolithometry: novel surgical classification system for kidney calculi. Urology. 2013;81:1154-1160. 9. Zhu Z, Wang S, Xi Q, et al. Logistic regression model for predicting stone-free rate after minimally invasive percutaneous nephrolithotomy. Urology. 2011;78:32-36.
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10. Mishra 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. 11. Matlaga BR, Hyams ES. Stones: can the Guy’s stone score predict PNL outcomes? Nat Rev Urol. 2011;8:363-364. 12. Mandal S, Goel A, Kathpalia R, et al. Prospective evaluation of complications using the modified Clavien grading system, and of success rates of percutaneous nephrolithotomy using Guy’s Stone Score: a single-center experience. Indian J Urol. 2012;28: 392-398. 13. Ibarluzea G, Scoffone CM, Cracco CM, et al. Supine Valdivia and modified lithotomy position for simultaneous anterograde and retrograde endourological access. BJU Int. 2007:233-236.
14. Vicentini FC, Torricelli FC, Mazzucchi E, et al. Modified complete supine percutaneous nephrolithotomy: solving some problems. J Endourol. 2013;27:845-849. 15. de la Rosette J, Assimos D, Desai M, et al. The clinical research office of the endourological society percutaneous nephrolithotomy global study: indications, complications, and outcomes in 5803 patients. J Endourol. 2011;25:11-17. 16. Neto EA, Mitre AI, Gomes CM, et al. Percutaneous nephrolithotripsy with the patient in a modified supine position. J Urol. 2007; 178:165-168. 17. Duty B, Okhunov Z, Smith A, et al. The debate over percutaneous nephrolithotomy positioning: a comprehensive review. J Urol. 2011; 186:20-25.
APPENDIX
(Color version available online.)
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