Evaluation of preoperative parameters to predict the success of percutaneous nephrolithotomy

Introduction: Percutaneous nephrolithotomy is the gold standard treatment for kidney stones larger than 2 centimeters. Predicting stone-free status and possible complications after percutaneous nephrolithotomy operation is important for patients and surgeons. In our study, we aimed to evaluate the value of preoperative parameters in predicting percutaneous nephrolithotomy success. Materials and Methods: Patients who underwent percutaneous nephrolithotomy between January 2010 and November 2020 in Dokuz Eylul University urology department were included. Patients' demographic characteristics, stone side, size, area, amount, density, localization, skin stone distance, hydronephrosis, opacity and laboratory parameters such as complete blood count, creatinine value, complete urine analysis and urine culture were recorded. GUY's score, S.T.O.N.E score and CROES nephrolitometric score were calculated and recorded for each patients individually. Postoperative residual stone status was evaluated by peroperative fluoroscopy or postoperative direct urinary tract radiography or non-contrast computed tomography. The operation success was defined as no any residual fragments in postoperative imaging modalities. Patients were divided into two groups as successful and unsuccessful and were compared in terms of preoperative, peroperative and postoperative data. Peroperative and postoperative complications were recorded according to the modified Clavien-Dindo classification. Statistical analyzes were performed by using the SPSS 22 package program. Statistical significance level was accepted as p<0.05. Results: 803 patients who underwent percutaneous nephrolithotomy between January 2010 and November 2020 were included in our study. 76 patients who did not meet the study criteria were excluded from the study. 297 (40.9%) of the patients were female, 440 (59%) were male, and the median body mass index of the patients was 25.9 kg/m2 (min: 17.6 - max: 58.7). The median age of the patients was 49 (min:18-max:85). 669 (92%) of the patients had not undergone open surgery on the same side and 28 (3.9%) had a solitary kidney. A total of 53 (7.3%) patients had renal anomalies. Gender, alcohol and smoking habits, presence of stone history in the family, body mass index and comorbid diseases were found to be not statistically significant with the success of the operation. There was no statistically significant relationship between preoperative laboratory parameters and operation success. We found that GSS,S.T.O.N.E nephrolithometry score and CROES nephrolithometry nomogram predicted operation success in our patient group (p<0.001, p<0.001, p<0.001). The median stone size was calculated as 20 mm (min:7-max:50) in the successful group and 25 mm (min:9-max:56) in the unsuccessful group, and the stone size was significantly higher in the unsuccessful group (p<0.001). The median stone area was found to be 118.5 mm² (min:15-max:600) in the successful group and 202 mm² (min:31-max:968) in the unsuccessful group; and it was significantly higher in the unsuccessful group (p<0.001). 351 (43.8%) of the patients had single stones, 255 (35.1%) had more than one and 121 (16.6%) had staghorn stones and it was detected that increasing in stone amount was associated with decreasing in operation success (p<0.001). According to the stone location; 20 (2.8%) patients had upper pole stones, 286 (39.3%) renal pelvis stones, 46 (6.3%) had lower pole stones, 26 (3.6%) had proximal ureteral stones, 121 (16.6%) had staghorn stones and 228 (31.4%) had partial staghorn stones. When the success of the operation was evaluated according to the kidney stone localizations, a statistically significant difference was found between the groups (p<0.001). The median skin to stone distance was 105.66 mm (min:43.67-max:178.33) in successful group and 99.66 mm (min:48.33-max:158.67) in unsuccessful group and the median skin to stone distance was significantly higher in successful group (p<0.001). In logistic regression analysis; stone amount (OR:2.833; 95% [CI]:1.507-5.329;p<0.001), stone location (p<0.001), stone size (OR:1.056; 95% [CI]:1.024-1.088; p<0.001), median skin to stone distance (OR:0.990; 95% [CI]:0.978-0.998; p=0.043) and maximum HU (OR:1.001; 95% [CI]:1.000-1.001; p=0.021) were determined as independent risk factors for the percutaneous nephrolithotomy success. No postoperative complications were detected in 577 (79.4%) of the patients. Clavien 1 complication was found in 17 (2.3%), Clavien 2 complication was found in 79 (10.9%), Clavien 3A complication was found in 38 (5.2%), Clavien 3B complication was found in 14 (1.9), Clavien 4A complication was found in 2 (0.3%) patients. Clavien 4B and Clavien 5 complications were not detected in our study population. Conclusion: Percutaneous nephrolithotomy is a successful treatment for the large and complex renal stones. Preoperative stone amount, stone location, stone size, median skin to stone distance and Hounsfield Unit value (stone density) of the stone were found to be independent predictors in predicting the success of percutaneous nephrolithotomy. Keywords: renal stones, percutaneous nephrolithotomy, stone size, stone area, success, complication