Bilateral urinary calculi with discordant stone composition.

OBJECTIVES: To describe a cohort of bilateral stone formers with significantly different compositions between renal units. METHODS: Patients treated for bilateral nephrolithiasis over a 4-year period (2007-2010) were identified. Stones were categorized by dominant (≥50%) mineralogical component. Patients with significant compositional differences between renal units (discordant stone formers) were compared to patients with a similar stone type in each kidney. RESULTS: Fifteen of the 59 bilateral stone formers (25.4%) were discordant stone formers with significant differences in stone composition between renal units. Forty-four of the 59 patients (74.6%) had the same stone composition on each side. Thirty percent of discordant stones had calcium phosphate as the dominant stone component. Discordant stone formers were younger, had better renal function, and tended to have a larger stone burden (p < 0.05). CONCLUSIONS: A significant minority of bilateral stone formers form a different type of stone in each kidney. Local or micro-environmental etiologies may explain this phenomenon and may also account for failure of preventive therapy in some patients.

Five-year experience with metallic stents for chronic ureteral obstruction.

PURPOSE: We present 5 years of outcome data on metallic ureteral stents in a cohort of patients treated for chronic ureteral obstruction. MATERIALS AND METHODS: We retrospectively identified and analyzed the records of all patients in whom a Resonance® Metallic Ureteral Stent was placed between early 2007 and late 2011 at our institution. We performed a descriptive analysis of key outcomes, including the failure and death rates, and stenting duration, defined as the time from initial stent placement to last stent failure or patient death. We also performed a secondary comparative analysis of patients with a benign vs malignant etiology of obstruction. RESULTS: A total of 139 metallic stents were placed in 47 patients, including 27 (57%) with malignant and 20 (43%) with a benign etiology. Of the patients 15 (32%) had bilateral obstruction. Maximum followup was 59 months (mean 20, median 13, IQR 4-31). Stent failure occurred in 13 patients (28%), including 4 in the benign and 9 in the malignant group (p = 0.35). The median duration of stenting for benign and malignant obstruction was 22 (IQR 9-39) vs 7 months (IQR 3-25) (p = 0.106). Stenting duration was equivalent when controlling for the higher death rate in the malignant group. CONCLUSIONS: Resonance metallic stents are an adequate management strategy for benign and malignant ureteral obstruction. A subset of patients in each group continued to do well at more than a 3-year overall duration of stenting. Failure rates were similar for benign and malignant etiologies.

Comparison of complication rates for unilateral and bilateral percutaneous nephrolithotomy (PCNL) using a modified Clavien grading system.

OBJECTIVE: To compare complication rates of unilateral vs bilateral percutaneous nephrolithotomy (PCNL) using the modified Clavien grading system. PATIENTS AND METHODS: Single-institution retrospective chart review. Identified patients who had synchronous bilateral PCNL (B-PCNL) over an 11-year period (2000-2011). B-PCNL patients were matched by age, gender, and stone burden per renal unit with patients who underwent unilateral PCNL (U-PCNL) over the same period. Complications were recorded and classified using the modified Clavien classification system, and then compared with a two-sided chi-square test of proportions. RESULTS: In all, 47 B-PCNL patients [mean (range) age 54 (14-84) years] and 78 U-PCNL patients [mean (range) age 54 (17-91 years] were compared. The mean (range) stone burden per renal unit was 2.8 (0.7-7.0) cm and 2.9 (0.7-9.0) cm, respectively. The overall complication rate was higher for B-PCNL (53.2% vs 30.8%, P = 0.013). Rates of Grade I and Grade II complications trended toward being higher in the B-PCNL group. Low-grade complications (Grade I and II combined) occurred more often in the B-PCNL group (P = 0.011); the most common low-grade complication was fever. Two procedures terminated for poor visualisation due to bleeding were successfully completed in delayed fashion with no transfusion and were classified as Grade I complications. There were equivalently low rates of Grade III complications. There were no Grade IV or V complications. CONCLUSIONS: B-PCNL carries a higher overall complication rate than U-PCNL when the modified Clavien system is used for classification. Patients undergoing U-PCNL who have more than one tract dilatation have a higher complication rate than those who have only one tract dilatation. High-grade complications are uncommon for both procedures.

Update on the evaluation of repeated stone formers.

Office management of stone disease is an important component of a urologist's practice. Evaluation should include analysis of stone composition, 24-hour urine studies, identification of modifiable risk factors, and targeted dietary, lifestyle, and/or medical therapy. A sizeable portion of investigated etiologies and risk factors for stone disease have centered on the complex interplay between obesity, diabetes, and other disease states that comprise the metabolic syndrome. Alternatives to traditional preventive therapy, such as probiotics and various fruit juices, are still being studied but may prove useful adjuncts to traditional preventive therapy, where the mainstays remain increased fluid intake, dietary modification, and pharmacologic therapy. Future studies on preventive therapy of urolithiasis are likely to focus on strategies to increase compliance, cost-effectiveness, and systems-based implementation.

Mini-percutaneous nephrolithotomy with ureteral access sheath in a transplanted kidney: case report and literature review.

This is the case of a 69-year-old woman with a history of right iliac fossa living-related kidney transplant that developed acute renal failure due to an obstructing stone in the proximal transplant ureter. She was successfully treated with mini-percutaneous nephrolithotomy wherein a 14-Fr tract was created with serial dilation and a 14-Fr ureteral access sheath was used for access. A flexible ureteroscope with holmium laser and a helical wire basket were used to fragment and extract the stone, respectively. A 10-Fr nephrostomy tube was left for postoperative drainage. There are only a few published reports of mini-percutaneous nephrolithotomy in transplant kidneys, but those reports suggest that the procedure is safe and effective.

Three-Dimensional Renal Parenchymal Volume as a Surrogate for Renal Function Estimation in Obstructed Kidneys Undergoing Surgical Repair.

PURPOSE: To investigate the relationship between renal parenchymal volume (RPV) and renal function in obstructed kidneys using a novel three-dimensional (3D) volume-rendering technique. MATERIALS AND METHODS: Forty-seven consecutive patients who underwent pyeloplasty, ureteroureterostomy, or ureteroneocystostomy at a single institution between 2007 and 2013 were reviewed. Patients with preoperative CT scan and split differential functional (SDF) assessment by diuretic renography were included. Those with solitary kidneys and bilateral obstruction were excluded. Baseline serum creatinine (Cr) and estimated glomerular filtration rate (eGFR) as calculated by the modification of diet in renal disease equation were determined. Percent of total RPV for the obstructed kidney was determined using 3D reconstruction software by drawing regions of interest around the borders of the kidney on CT. The renal pelvis, hilar vessels, and hilar fat were excluded. Percent of total RPV was then correlated with SDF. RESULTS: Nineteen patients with both preoperative CT and diuretic renal scans were included. Two underwent ureteroneocystostomy, 1 underwent ureteroureterostomy, and 16 underwent pyeloplasty. Mean serum Cr was 1.07±0.26 mg/dL with a mean eGFR of 69.43±18.90 mL/minute. Mean SDF was 37.32%±11.66% in the obstructed kidneys. There was a statistically significant correlation between percent of total RPV and SDF (R(2)=0.28, p=0.02). CONCLUSIONS: There is a significant correlation between percent total RPV determined by 3D reconstruction of CT scan images and SDF as determined by diuretic renography in obstructed kidneys. CT-based percent RPV has potential as a functional assessment tool in obstructed kidneys. With further validation, it may be used to counsel patients considering surgical repair of ureteral or ureteropelvic junction obstruction.

Nonlinear logistic regression model for outcomes after endourologic procedures: a novel predictor.

The purpose of this study was to design a thorough and practical nonlinear logistic regression model that can be used for outcome prediction after various forms of endourologic intervention. Input variables and outcome data from 382 renal units endourologically treated at a single institution were used to build and cross-validate an independently designed nonlinear logistic regression model. Model outcomes were stone-free status and need for a secondary procedure. The model predicted stone-free status with sensitivity 75.3% and specificity 60.4%, yielding a positive predictive value (PPV) of 75.3% and negative predictive value (NPV) of 60.4%, with classification accuracy of 69.6%. Receiver operating characteristic area under the curve (ROC AUC) was 0.749. The model predicted the need for a secondary procedure with sensitivity 30% and specificity 98.3%, yielding a PPV of 60% and NPV of 94.2%. ROC AUC was 0.863. The model had equivalent predictive value to a traditional logistic regression model for the secondary procedure outcome. This study is proof-of-concept that a nonlinear regression model adequately predicts key clinical outcomes after shockwave lithotripsy, ureteroscopic lithotripsy, and percutaneous nephrolithotomy. This model holds promise for further optimization via dataset expansion, preferably with multi-institutional data, and could be developed into a predictive nomogram in the future.

Contemporary volume-outcome relationships for percutaneous nephrolithotomy: results from the Nationwide Inpatient Sample.

INTRODUCTION/OBJECTIVE: We sought to examine the contemporary relationship between case volume and outcome for percutaneous nephrolithotomy (PCNL) using a publically available administrative database. METHODS: A weighted sample of 7785 patients was obtained from the 2010 Healthcare Cost and Utilization Project (HCUP) Nationwide Inpatient Sample (NIS). ICD-9-CM diagnostic codes were used to identify patients with urolithiasis (592.0, 592.1, and 592.9) who underwent percutaneous nephrostomy with fragmentation (5504). Charlson Comorbidity Indices (CCI) were calculated based on diagnostic codes for all patients. Hospital case volume was quartile classified and we then compared key outcomes (the complication rate, transfusion rate, length of stay [LOS], and in-hospital mortality rate) by volume quartile. We then performed multivariate analysis to examine the effect of CCI, annual volume, and age on key outcomes. RESULTS: The overall complication rate was 17% in the weighted sample. In univariate analysis, statistically significant variation in the complication rate, CCI, transfusion rate, and in-hospital mortality was noted with regard to the hospital volume. The complication rate and transfusion rates varied by case volume, but in a nonlinear fashion, wherein rates were highest at the lowest and highest volume centers. CCI was strongly predictive (p<0.001) of complications and LOS in the multivariate analysis. Case volume was only predictive (p=0.042) of LOS in the multivariate analysis. CONCLUSION: Annual case volume of the treating center was associated with shorter LOS after PCNL, but case volume was not independently predictive of complication or transfusion in multivariate analysis. CCI was a strong independent predictor of complication and LOS.

Small-bore catheter drainage of pleural injury after percutaneous nephrolithotomy: feasibility and outcome from a single large institution series.

BACKGROUND AND PURPOSE: A well-known complication of percutaneous nephrolithotomy (PCNL) is pleural injury. Pneumothorax and hydrothorax sustained during PCNL may necessitate the placement of a chest tube. Current literature describes placement of standard chest tubes as well as small-bore catheters for management of hydrothorax sustained during PCNL. This study aims to better delineate the clinical utility and outcomes associated with use of small-bore catheters when compared with standard chest tubes for managing pneumothorax and hydrothorax after PCNL. PATIENTS AND METHODS: We queried an institutional database of 735 renal units that underwent PCNL for endourologic disease between 2001 and 2013. Postoperative upright chest radiographs were analyzed in patients who needed chest tube placement for pneumothorax or hydrothorax after PCNL. Those who met inclusion criteria were divided based on the size of chest tube placed: Small-bore (8-12F) or standard chest tube (32F). Analysis of clinical outcomes was performed. RESULTS: Of the 735 procedures, 15 (2% of total, 7 right, 8 left) needed chest tube placement for a pleural injury after PCNL. Those who needed chest tube placement had an average stone size of 2.1 cm. Five had large-bore standard chest tubes (32F) and 10 had small-bore catheters (<14F) for management of pleural injury. The average length of time the chest tube stayed in place was 3.9 days (minimum 2, maximum 6) for small bore and 4.4 days (minimum 2, maximum 7) for standard chest tubes. There was a statistical trend toward decreased hospital stay and decreased length of time the chest tube was in place when a small-bore chest tube was used. CONCLUSION: The use of small-bore catheters for management of hydrothorax and pneumothorax have reasonable clinical outcomes when compared with standard large-bore chest tubes after PCNL.

Metabolic syndrome and urinary stone composition: what factors matter most?

OBJECTIVE: To determine which metabolic syndrome (MetS) factors lead to differences in stone composition in a multivariate analysis. METHODS: We retrospectively reviewed medical charts of patients who had a kidney stone removed over a 5-year period (2006-2011). MetS factors (obesity [body mass index {BMI} >30], diabetes mellitus [DM], hypertension [HTN], and dyslipidemia [DLD]) were tallied in each patient. For the latter 3 factors, medical treatment for the condition was used to tag a patient with the condition. Stone composition was determined by the dominant (>50%) component. Statistical analysis was designed to determine which MetS factors were independently associated with differences in stone composition. RESULTS: Five hundred ninety kidney stones were included in the analysis. Patients with MetS had a higher prevalence of uric acid stones and lower prevalence of calcium phosphate stones. HTN and DM were independently associated with differences in composition, specifically uric acid stones (higher proportion), and calcium phosphate stones (lower proportion). Obesity was not associated with differences in composition, although a secondary analysis of morbidly obese patients showed a higher proportion of uric acid stones and a lower proportion of calcium oxalate stones. CONCLUSION: HTN and DM are the MetS factors independently associated with differences in stone composition, specifically the uric acid and calcium phosphate components. Obesity has little effect on stone composition until a very high (>40) BMI is reached. The overall effect of MetS factors on stone type is relatively small, because most stones are calcium oxalate and MetS factors have little impact on calcium oxalate frequency.

Effect of renal function on urinary mineral excretion and stone composition.

OBJECTIVE: To determine the effect of renal function on urinary mineral stone excretion and composition of kidney stones in patients undergoing urologic intervention for nephrolithiasis. METHODS: We performed a retrospective analysis of 158 patients with 193 kidney stones who underwent endourologic intervention for nephrolithiasis. The patients were grouped by the estimated glomerular filtration rate (eGFR). The kidney stone composition and results of the 24-hour urinalysis were reported for each group. Statistical analysis was performed using the chi-square test, Kruskal-Wallis test, and analysis of variance. RESULTS: The kidney stone composition profile differed significantly between the groups, with uric acid stones associated with a lower eGFR and calcium phosphate stones associated with a greater eGFR. A lower eGFR correlated with lower urine pH, lower calcium excretion, and greater oxalate excretion. Excretion of uric acid and the body mass index did not differ between groups. CONCLUSION: Different degrees of renal function correlated with certain types of kidney stones. The urine pH was lower in patients with impaired renal function. Renal function might be an underappreciated factor that affects kidney stone composition and urinary mineral excretion.