Comprehensive analysis of factors associated with significant blood loss during percutaneous nephrolithotomy.

INTRODUCTION: The objective of this study is to conduct a thorough investigation of the risk factors associated with blood loss during PCNL, within the setting of a US urban tertiary care center. MATERIALS AND METHODS: We conducted a retrospective analysis of our endourology database to identify adult patients who underwent PCNL for stone extraction at our tertiary stone center between October 2014 and December 2022. Patients were categorized into two groups based on the extent of blood loss: significant blood loss (SBL) and no significant blood loss (NSBL). The cut-off value for SBL was determined as the median change in hematocrit levels from preoperative to postoperative among patients who required postoperative transfusions. Several factors were evaluated, including stone dimensions, operative details, the presence of preoperative drains, patient position, type of access, access site, number of accesses, tract size, tract length, stone location, number of stones, operative time, and the S.T.O.N.E. Nephrolithometry Scoring System. RESULTS: Our analysis included a total of 695 procedures performed on 674 distinct patients who met our inclusion criteria. Of these, 102 patients (14.7%) were included in the SBL group. Patients in the SBL group had a higher mean number of accesses (1.57 vs. 1.29, P<0.001), were positioned prone more often (96.0% vs. 88.6%, P = 0.025), and underwent fluoroscopic-guided access more frequently (89.9% vs. 64.8%, P<0.001). Additionally, significant differences were observed in stone morphology, with the SBL group having higher rates of complete staghorn stones (42.2% vs. 27.0%, P = 0.019) and lower rates of partial staghorn stones (27.7% vs. 36.8%, P = 0.019). A larger proportion of patients in the SBL group required a 16 French nephrostomy tube for postoperative drainage (13.3% vs. 10.4%, P = 0.041). Lastly, the SBL group had a longer mean operative time compared to the NSBL group (P<0.001). Multiple logistic regression analysis identified stone volume (P = 0.039), number of accesses (P = 0.047), and operative time (P = 0.006) as independent risk factors associated with SBL status. CONCLUSION: Surgical complexity factors such as stone volume, number of accesses, and operative time are linked to a higher risk of SBL during PCNL. Stone volume and the requirement for multiple accesses can usually be estimated with reasonable accuracy before surgery.

Reverse Trendelenburg Positioning Minimizes Stone Retropulsion During Ureteroscopic Laser Lithotripsy: A Prospective Randomized Study.

Purpose: Retropulsion of stone fragments during ureteroscopic laser lithotripsy (URSLL) remains a challenge for urologists and is associated with increased operative time and reduced stone-free rate (SFR). In this study, we compared the rate of retropulsion of ureteral stones during URSLL between the standard dorsal lithotomy (SDL) position and dorsal lithotomy position with reverse Trendelenburg (RT). Materials and Methods: Patients with ureteral stones requiring surgical intervention between May 2019 and January 2022 were randomized to undergo URSLL in either SDL or RT positions. The primary outcome of this study was stone retropulsion. Secondary outcomes included retropulsion to the kidney, SFR, operative time, 30-day emergency department visits and complications, and the need for conversion from semirigid to flexible ureteroscope. Differences between groups were evaluated using the chi-square test, Fisher exact test, Kruskal-Wallis test, or t-test. Results: A total of 114 patients were included in the study, with 57 patients in each group. There were no differences between groups in terms of baseline demographics or stone characteristics. Retropulsion was significantly less frequent in the RT group (68.4% vs 10.5%, p < 0.01). Similarly, the RT group was favored for lower risk of retropulsion into the kidney (40.4% vs 5.3%, p < 0.01), operative time (43.5 vs 33.0 minutes, p = 0.02), and need for ureteroscope conversion (16.7% vs 2.2%, p = 0.04). There was no difference in the SFR (100% vs 95%, p = 0.49). Conclusions: RT positioning during URSLL for ureteral stones significantly decreases the rate of stone retropulsion, operative time, and the need for conversion from semirigid to flexible ureteroscope.

Mini-Incision Direct Festoon Access, Cauterization, and Excision (MIDFACE): A 12-Year Analysis of a Novel Festoon Surgery.

BACKGROUND: Surgical festoon management often entails aggressive dissection, flaps, unsightly scars, prolonged recovery, and high recurrence rates. The authors present outcomes with subjective and objective evaluation of an office-based, novel, minimally invasive (1-cm incision) festoon repair: mini-incision direct festoon access, cauterization, and excision (MIDFACE). METHODS: Charts of 75 consecutive patients from 2007 to 2019 were evaluated. Photographs of 39 patients who met inclusionary criteria were evaluated by three expert physician graders for festoon and incision visibility (339 randomly scrambled preoperative and postoperative photographs taken with and without flash and from four different views: close-up, profile, full-frontal, and worm's eye) using paired t tests and Kruskal-Wallis tests for statistical evaluation. Surveys returned by 37 of 75 patients were evaluated for patient satisfaction and possible contributing factors to festoon formation or exacerbation. RESULTS: There were no major complications in the 75 patients who underwent MIDFACE. Physician grading of photographs of 39 patients (78 eyes, 35 women; four men; mean age, 58 ± 7.7 years) demonstrated statistically significant sustained improvement in festoon score postoperatively up to 12 years regardless of view or flash. Incision scores were the same preoperatively and postoperatively, indicating incisions could not be detected by photography. Average patient satisfaction score was 9.5 on a Likert scale of 0 to 10. Possible factors for festoon formation or exacerbation included genetics (51%), pets (51%), prior hyaluronic acid fillers (54%), neurotoxin (62%), facial surgery (40%), alcohol (49%), allergies (46%), and sun exposure (59%). CONCLUSION: MIDFACE repair results in sustained improvement of festoons with an office-based, minimally invasive procedure with high patient satisfaction, rapid recovery, and low recurrence. CLINICAL QUESTION/LEVEL OF EVIDENCE: Therapeutic, IV.

The effects of continuing aspirin on blood loss and postoperative outcomes in percutaneous nephrolithotomy.

BACKGROUND: Percutaneous nephrolithotomy (PCNL) is an effective surgery for complex kidney stones yet with inherent bleeding risks. It remains unclear whether aspirin should be discontinued prior to PCNL. We aimed to further substantiate the safety of continuing aspirin during PCNL surgery and to determine whether aspirin status affects postoperative outcomes following PCNL. METHODS: We retrospectively queried our endourology database for patients who underwent PCNL from October 2017 to December 2022 at our high-volume tertiary referral center. The three groups were based on aspirin status at the time of PCNL: no aspirin (NA), discontinued aspirin (DA), and continued aspirin (CA). Data collected included demographics, preoperative characteristics, operative parameters, pre and postoperative lab values, transfusions, and complications. RESULTS: A total 648 patients were divided into these study groups: 525 NA patients (81.0%), 55 DA (8.5%), and 68 CA (10.5%). The DA and CA groups were of similar comorbidities, and both were more comorbid at baseline than NA. Postoperative change in lab values and complications did not differ significantly. Rates of postoperative blood transfusion were higher in the CA and DA groups compared to NA and approached statistical significance. There were no significant differences in any postoperative outcomes between the DA and CA groups alone. CONCLUSIONS: In patients on chronic aspirin therapy, continuing aspirin appears equally safe to discontinuing aspirin prior to PCNL. Most patients should not forego the benefits of continuous aspirin for the theoretical risk of bleeding. Patients on prolonged aspirin therapy may be more likely than those who are not on chronic aspirin therapy to require blood transfusions. However, regardless of whether aspirin use is stopped, this may be caused by patient comorbidities rather than higher rates of blood loss.

Displacement of Lower Pole Stones During Retrograde Intrarenal Surgery Improves Stone-free Status: A Prospective Randomized Controlled Trial.

PURPOSE: Lower pole renal stones are associated with the lowest stone-free status of any location in the urinary tract during retrograde intrarenal surgery. Prior work has suggested displacing lower pole stones to a more accessible part of the kidney to improve stone-free status. We sought to prospectively compare the efficacy of laser lithotripsy in situ vs after displacement during retrograde intrarenal surgery for lower pole stones. MATERIALS AND METHODS: Between July 2017 and May 2022 patients undergoing retrograde intrarenal surgery for lower pole stones were randomized into an in situ or displacement group. Demographics, comorbidities, and operative parameters were documented. Primary outcome was stone-free status, determined by combination of abdominal x-ray and renal ultrasound at 30-day follow-up. Secondary outcomes included operative time, 30-day complications, emergency department visits, and readmissions. RESULTS: A total of 138 patients (69 per group) were enrolled and analyzed. Baseline characteristics were similar between groups. Stone-free status significantly favored the displacement group over the in situ group (95% vs 74%, P = .003, n=62 in each group). Operative time, total laser energy usage, 30-day complications, and 30-day emergency department visits or hospital readmissions were similar between groups. On multivariate analysis only study group allocation was significantly associated with stone-free status (P = .024). CONCLUSIONS: Basket displacement of lower pole stones results in a significantly higher stone-free status compared to in situ lithotripsy. The technique is simple, atraumatic, and requires no additional equipment costs and little additional operative time, making it a practical tool in the treatment of lower pole stones.

A prospective randomized study evaluating the necessity of narcotics following ureteroscopy for urinary stone disease.

PURPOSE: To evaluate the efficacy of non-narcotic analgesics and preoperative counseling in managing postoperative pain and narcotic use following ureteroscopic laser lithotripsy (URS). METHODS: Adult patients at a single academic center undergoing URS for nephrourolithiasis were recruited. After informed consent, subjects were randomized into three groups: NARC-15 tablets oxycodone-acetaminophen 5/325 mg (A-OXY), 2. NSAID-15 tablets ibuprofen (IBU) 600 mg, 3. CNSL-15 tablets A-OXY, 15 tablets IBU, and preoperative counseling from the surgeon to avoid narcotic if possible. Patients who did not receive an intraoperative stent were excluded. At the time of stent removal subjects completed the Universal Stent Symptom Questionnaire (USSQ), and a pill count was performed. USSQ pain indices were the primary study endpoint. RESULTS: Of 115 patients enrolled, 104 met the primary endpoint and were included in the analysis. No significant differences were noted in patient demographic, clinical, or operative characteristics. No differences were noted in median USSQ pain indices. The CNSL group used a significantly lower median number of A-OXY pills compared to the NARC group (2.4 vs. 5.4, p = 0.001) and less IBU compared to the NSAID group (3.1 vs. 5.9, p = 0.008). No differences in median total pill count, office calls, medication requests, nor ED visits were noted. CONCLUSION: Our data suggest that patients can achieve equivalent postoperative analgesic satisfaction with non-narcotics compared to opiates following URS. Further, counseling patients on postoperative pain before surgery can reduce the total number of postoperative narcotic and non-narcotic medications taken. We suggest surgeons strongly consider omission of narcotic prescriptions following non-complicated URS.

Long-Term Complications of Open and Robot-Assisted Laparoscopic Radical Prostatectomy in an Afro-Caribbean Population.

Background With the Afro-Caribbean population increasing in the United States, their complication profiles following open (ORP) and robot-assisted laparoscopic (RALP) radical prostatectomy warrants investigation. The purpose of this pilot study was to evaluate differences in long-term complications between ORP and RALP in Afro-Caribbeans. Methods A retrospective review of patients undergoing ORP or RALP between April 2010 and August 2019 at an academic medical center and county hospital was conducted. Patients who identified as Afro-Caribbean with complete data were analyzed. Complications were classified using the Clavien-Dindo system. Age, transrectal ultrasound prostate volume, preoperative prostate-specific antigen, Gleason scores, and long-term complications (persisting to at least 18 months postoperatively) were compared between procedures using the Mann-Whitney U test or Fisher's exact test for statistical significance. Multivariable logistic regression was used to assess the odds of complications. Results This study included 53 Afro-Caribbean patients (mean age±SD; 65.9±6.8 years, 30 ORP, and 23 RALP). Patients treated by RALP were younger and had lower Gleason scores. Patients who were treated by RALP had a lower association to having ≥1 complications compared to those treated by ORP (OR=0.28, 95%CI 0.09-0.89, p=0.024). In addition, >60% of complications had a Clavien-Dindo grade≤II for both procedures. RALP resulted in fewer grade II complications compared to ORP (OR=0.25, 95%CI 0.08-0.81, p=0.046). Conclusions Treatment of Afro-Caribbeans with RALP allows for fewer complications, especially Clavien-Dindo Grade II complications. While previous investigations show that Black populations experience more complications when treated with ORP or RALP compared to other groups, their complication profile is likely not homogenous when considering their sub-ethnic background and must be investigated to understand optimal interventions for prostate cancer.

Do Infection-Associated Stone Subtypes Behave the Same Clinically? A Retrospective Bicenter Study.

Introduction and Objectives: Infection-associated renal stones are commonly composed of magnesium-ammonium-phosphate (MAP) and carbonate apatite (CA). The clinical implications of these two different, but closely related stone types, are unknown. We sought to compare the clinical, microbiologic, and metabolic characteristics of patients with MAP and CA stone types. Methods: We retrospectively reviewed the medical records of patients from two centers (one in the United States and one in Israel) who underwent ureteroscopy or percutaneous nephrolithotomy between 2012 and 2020 and identified patients with a predominant stone analysis component of CA or MAP and clinical data supporting an infection stone. We analyzed and compared demographic data, medical history, postoperative fever, stone and urinary microbiology, and 24-hour urine studies. Results: A total of 79 and 75 patients met the inclusion criteria for the MAP and CA cohorts, respectively. No significant difference was found in patient demographics or comorbidities between the MAP and CA cohort. Female predominance was noted in both. Although there were no significant differences in 24-hour urine parameters between the cohorts, hypercalciuria was common in both cohorts (38% and 32% of patients in the MAP and CA cohorts, respectively). Gram-negative bacteria were more common in the MAP stone cultures. Postoperative fever was significantly more common in the MAP cohort (14.7% vs 3.8%, p < 0.016). Conclusions: MAP and CA stone formers share similar demographic characteristics with a clear female predominance. MAP stones patients appear more likely to develop postoperative fever, possibly related to a higher occurrence of gram-negative bacteria in the stone cultures of the MAP cohort. Although there were no significant differences among metabolic parameters, hypercalciuria was noted in approximately a third of the cohort. The clinical significance of this finding is yet to be determined.

Is metformin use associated with changes in urinary parameters in stone formers?

INTRODUCTION: Diabetes mellitus (DM) is associated with an increased risk of nephrolithiasis and is often treated with metformin. The relationship between metformin and nephrolithiasis formation remains unclear, as studies have demonstrated conflicting results. METHODS: We conducted a cross-sectional analysis of stone-forming patients at our stone clinic prior to the initiation of stone-directed medical management. Patients were grouped based on diabetic status and diabetic medication regimen. Outcomes evaluated were 24-hour urinary parameters and specimen stone type using univariate Kruskal-Wallis and Chi-squared analyses. Multivariate analyses controlling for metabolic syndrome components and HbA1c were performed. RESULTS: Data were available for 505 patients, of whom 147 were diabetic and 358 were not. On multivariate analyses controlling for HbA1c and other comorbidities, diabetic patients on metformin still had worse urinary parameters, including urine pH, than non-diabetic patients (pH=-0.33, -0.37, p<0.05). Patients with DM on metformin did not exhibit significant differences in 24-hour urine findings compared to patients with DM not on metformin (p>0.05 for all urinary parameters). CONCLUSIONS: Stone-forming patients with DM on metformin were associated with urinary abnormalities similar to those not on metformin. Cohort studies comparing urinary parameters of patients prospectively started on metformin are necessary to further elucidate metformin's role, if any, in combatting nephrolithiasis.

The impact of metabolic syndrome components on urinary parameters and risk of stone formation.

PURPOSE: To investigate the relationship between metabolic syndrome (MS) and urinary abnormalities in stone-forming patients. Additionally, to delineate whether severity of urinary derangements is impacted by the number of co-occurring MS components. METHODS: Stone-forming patients who underwent initial metabolic workup prior to medical intervention at a comprehensive stone clinic were retrospectively reviewed and included in the study. Patients were given a six point (0-5) Metabolic Syndrome Severity Score (MSSS) based on the number of co-occurring MS components and split into six respective groups. Baseline clinical characteristics and metabolic profiles were compared between groups. RESULTS: Four-hundred-ninety-five patients were included in the study. Median age and median BMI was 58 years and 27.26 kg/m2, respectively. Several significant metabolic differences were noted, most notably a downward trend in median urinary pH (p < 0.001) and an upward trend in median urinary supersaturation uric acid (p < 0.001) across groups as MSSS increased. Multivariate analysis demonstrated an independent association between higher MSSS and increasing number of urinary abnormalities. A second multivariate analysis revealed that all MS components except hyperlipidemia were independently associated with low urinary pH. Additionally, obesity was independently associated with the greatest number of urinary abnormalities and had the strongest association with hyperuricosuria. CONCLUSIONS: Prior research has attributed the strong association of nephrolithiasis and MS to high prevalence of UA nephrolithiasis and low urinary pH. Our findings indicate that all MS components with the exception of hyperlipidemia were independently associated with low urinary pH suggesting a mechanism independent from insulin resistance.

Prospective Randomized Evaluation of Idiopathic Hyperoxaluria Treatments.

Purpose: Calcium oxalate (CaOx) stone formation is influenced by urinary oxalate excretion. Stone formers with elevated urinary oxalate are commonly prescribed a low-oxalate diet or oral supplementation with vitamin B6 and magnesium to reduce urinary oxalate excretion. This study aims to compare the effects of dietary modification vs supplementation vs a combination of both on urinary oxalate. Materials and Methods: We enrolled patients with a documented history of CaOx stones and newly diagnosed idiopathic hyperoxaluria. Patients were randomized into three treatment groups: low oxalate diet (D), supplementation with 25 mg vitamin B6 and 400 mg magnesium oxide (S), or both low oxalate diet and B6/magnesium supplementation (DS). Baseline and 3-month postintervention 24-hour urine tests were obtained. The primary endpoint was change in 24-hour urinary oxalate (Ox24) at 12 weeks. Secondary endpoints included changes in other 24-hour urine parameters, compliance rates, and adverse effect rates. Results: In total, 164 patients were recruited and 62, 47, and 55 were enrolled into the D, S, and DS groups, respectively. Of these, 99 patients completed the study (56.5% of the D, 72.3% of the S, and 54.6% of the DS groups, respectively). Significant differences were noted in median percent reduction in Ox24 values (-31.1% vs -16.0% vs -23.9%, p = 0.007) in the D, S, and DS groups, respectively. Furthermore, the percentages of patients within each treatment arm who realized a decrease in Ox24 were also found to be significantly different: D = 91.4% vs. S = 67.6% vs DS = 86.7%, p = 0.027. No significant adverse events were observed in any of the study arms. Conclusion: Low oxalate diet is more effective than B6/magnesium supplementation at lowering urinary oxalate in idiopathic hyperoxaluric stone formers. Combination therapy did not produce greater reductions in urinary oxalate than either of the monotherapy arms suggesting it is of little clinical utility. Further study with long-term longitudinal follow-up is required to determine if these treatment strategies reduce recurrent stone events in this population.

Factors Affecting Patient Radiation Exposure During Prone and Supine Percutaneous Nephrolithotomy.

Purpose: Radiation exposure from fluoroscopy poses risks to patients and surgeons. Percutaneous nephrolithotomy (PCNL) has traditionally required fluoroscopy, however, the use of ultrasound (US) has decreased radiation exposure. US guidance in supine PCNL (S-PCNL) may further reduce radiation exposure. In this study, we investigate patient and operative factors affecting fluoroscopy time (second), total radiation dose (mGy), and effective dose (ED, mSv) in patients undergoing US-guided S-PCNL or prone PCNL (P-PCNL). Methods: We performed a retrospective study of patients undergoing US-guided PCNL in prone and supine positions. Patients with multiple access tracts, pre-existing renal access, or fluoroscopic renal access were excluded. Patient demographic and radiologic and operative data were collected, and compared between the two groups. Results: Ninety-nine patients were included: 45 P-PCNL and 54 S-PCNL. There were no significant demographic differences between the two groups. Operative time, access location, tract length, and total radiation dose (mGy) also did not differ. S-PCNL was associated with lower ED (2.92 ± 0.32 mSv vs 5.3 ± 0.7 mSv, p = 0.0014) despite increased fluoroscopy time (86.32 ± 7.7 seconds vs 51.00 ± 5.1 seconds, p = 0.004), and was more likely a mini-PCNL (35.2% vs 15.9%, p = 0.032). In multivariate analysis, S-PCNL remained associated with reduced ED compared with P-PCNL (p = 0.002), whereas body mass index (p < 0.001) and staghorn calculi (p < 0.001) were independently associated with increased ED. Conclusions: We demonstrated that ED in US-guided PCNL is increased in the prone position compared with supine position, and in overweight patients regardless of position. US-guided S-PCNL may decrease radiation exposure to patients and surgeons compared with US-guided P-PCNL.

Deceived by a CT Scan: The Case of the Misrepresented Stone Size.

Background: CT has become the gold standard for radiographic evaluation of urolithiasis. CT is highly sensitive for detecting kidney stones and provides valuable information regarding stone size, composition, location, and overall stone burden. Although CT can provide reliable estimations of stone size, we have encountered an instance in which it can be deceiving. Motion artifact in CT images can cause a warping distortion effect that makes renal stones appear larger than they actually are. Case Presentation: We describe a case of a 37-year-old woman with a history of kidney stones and obesity presenting with intermittent flank pain and gross hematuria, found to have a large lower pole renal calculus that appeared deceptively large on CT imaging. Given the apparent size and location of the stone, the patient was counseled and consented for a percutaneous nephrolithotomy (PCNL). Although the stone was initially suspected to be >2 cm based on the preoperative CT scan, intraoperative pyelography revealed a much smaller than expected radio-dense stone. The patient was stone free after PCNL without any immediate postoperative complications. However, her course was later complicated by delayed bleeding causing significant clot hematuria, perinephric hematoma, and reactive pleural effusion. Conclusion: Although CT is especially valuable in preparing for surgery based on its ability to outline collecting system anatomy, it is important to remember that it can be deceiving. Correlation with kidney, ureter, and bladder radiograph and ultrasound is critical to understanding the clinical case and planning the optimal surgical approach.

Ultrasound-Guided Totally Tubeless Mini-Percutaneous Nephrolithotomy for a Completely Excluded Caliceal Diverticulum Associated with Challenging Anatomy.

Mini-percutaneous nephrolithotomy (mini-PCNL) has been described as a safe and effective technique to eliminate stones in patients in whom a less-invasive approach is desired. It was originally developed to treat stones in the pediatric population, but has since been adapted to serve a role in the adult urologic community. This approach has been reported to result in less blood loss and postoperative pain when compared with traditional PCNL. Herein, we present a case in which a recurrent caliceal diverticulum containing stones was managed using a mini-PCNL technique in a patient who previously failed multiple other retrograde endoscopic approaches.

Peri-Calculus Ureteral Thickness on Computed Tomography Predicts Stone Impaction at Time of Surgery: A Prospective Study.

Introduction and Objectives: Ureteroscopic management of impacted ureteral stones poses multiple challenges. We examined whether ureteral thickness measured on preoperative noncontrast computed tomography (CT) is predictive of stone impaction at the time of ureteroscopy (URS). Methods: Thirty-eight patients with preoperative CT scan and undergoing URS for ureteral stones were prospectively studied. Ureteral thickness directly above, around (peri-calculus ureteral thickness [P-CUT]), and below the calculus were determined on CT scan. The cross-sectional surface area around the stone (P-CUT) was also calculated. Stones were considered impacted at surgery if contrast had difficulty passing, a guidewire could not pass, and the stone was visually impacted >5 on a Likert scale. The surgeon determining intraoperative impaction and the individual measuring the ureteral thickness on CT were blinded. Results: Fourteen of the 38 patients were found to have an impacted ureteral stone at the time of surgery. Patients with an intraoperative finding of an impacted stone had significantly higher ureteral thickness above, around (P-CUT), below the calculus, and P-CUT surface area with all four p-values <0.001. P-CUT surface area was independently predictive of impaction at the time of surgery on multivariate analysis. A mean P-CUT of 6.1 and 1.6 mm and P-CUT surface area of 92.6 and 15.4 mm2 were noted for the impacted and nonimpacted stones, respectively. Conclusion: Ureteral thicknesses above, around (P-CUT), and below the calculus are readily measurable on CT scan. P-CUT surface area can also be calculated for a stronger representation of ureteral thickness. These four parameters are predictive of ureteral stone impaction and useful for surgical planning and patient counseling.

What Factors Drive Staghorn vs Nonstaghorn Pattern Growth in Patients with Metabolic Stones?

Purpose: There has been an increase in the number of staghorn calculi that form in the absence of infection (metabolic staghorns). It is unknown why some large metabolic calculi form as solitary or multiple separate, nonbranching caliceal stones, whereas others develop as staghorn stones forming a cast of the collecting system. We sought to compare these two groups of metabolic stone formers (SFs) in an attempt to shed light on these disparate stone-forming phenomena. Materials and Methods: From January 2017 to September 2018, 190 patients underwent percutaneous nephrolithotomy for stones >2 cm. We identified 86 (45%) patients with a metabolic stone, defined as ≥80% calcium oxalate monohydrate or dihydrate and/or calcium phosphate. Exclusion criteria included stones composed of cystine, >20% uric acid, or any infectious element (struvite or carbonate apatite). Metabolic staghorn and nonstaghorn SFs were compared with respect to medical comorbidity, 24-hour urine parameters, stone and urine microbiology, stone compositions, and intraoperative findings. Statistical differences were assessed using chi-square analysis, Fisher's exact test, and Student's t-test. Results: In total, 25 (29%) staghorn and 61 (71%) nonstaghorn SFs were included for analysis. The groups were statistically similar in age, sex, body mass index, and medical comorbidity. Staghorn SFs had larger stone burdens (p < 0.0001), but did not require more punctures (p = 0.783). Staghorn SFs were more likely to have hyperoxaluria (p = 0.041) and higher mean 24-urine oxalate levels (p = 0.040). There were no other significant differences in 24-hour urine profiles, rates of metabolic abnormalities, stone compositions, stone or urine cultures, presence of collecting system obstruction, or pelvicaliceal anatomy. Conclusions: Although potentially driven by urinary oxalate, whether a metabolic stone will form into a staghorn configuration or not does not appear significantly influenced by standard determinants of stone development, including metabolic profile, cultures, hydronephrosis, and pelvicaliceal anatomy, among others. Further work is needed to elucidate the physicochemical factors that govern the pathogenesis of this increasingly prevalent entity.

Clinical and Metabolic Correlates of Calcium Oxalate Stone Subtypes: Implications for Etiology and Management.

Introduction: Calcium oxalate (CaOx) is the predominate component within renal calculi and can be divided into two subtypes: CaOx-monohydrate (COM) and CaOx-dihydrate (COD). COM and COD form in differing urinary environments, which suggest differential underlying metabolic abnormalities associated with each subtype. We compared clinical and metabolic findings in CaOx stone formers to delineate factors differentiating COD and COM stone formers and the implication this holds in terms of etiology and treatment. Patients and Methods: We identified CaOx stone formers that had passed their stones or had undergone endoscopic extraction between October 2014 and December 2018. Only patients who had a predominant subtype (≥80% COM or COD) and who had a 24-hour urine evaluation before medical management were included. Clinical and metabolic factors were compared in the two subgroups. Results: Out of 157 stone formers, 121 were COM and 36 were COD. COD formers were younger than COM formers with a mean age of 53 ± 16 vs 59 ± 15, respectively (p = 0.038). There were no observable differences in gender, body mass index, hypertension, diabetes mellitus, or hyperlipidemia. COM formers exhibited higher rates of hypocitraturia and hyperoxaluria, p = 0.022 and p = 0.018, respectively. Conversely, COD formers had significantly higher rates of hypercalciuria (47% vs 28%, p = 0.012). Multivariate analysis found hypercalciuria to independently predict COD (p = 0.043) and hyperoxaluria to predict COM stones (p = 0.016). Conclusion: COM formers are more likely to have hyperoxaluria, hypocitraturia, and elevated urinary oxalate levels compared to COD formers. COD formers exhibited higher incidence of hypercalciuria. These data suggest that all CaOx stones are not alike and that distinct metabolic and clinical etiological differences exist that may guide future management and prevention.

Predicting the Impacted Ureteral Stone with Computed Tomography.

OBJECTIVE: To evaluate whether preoperative computed tomography (CT) findings could predict the presence of an impacted stone. Preoperative identification of an impacted ureteral stone may influence patient preparation and operative decisions. Factors predicting ureteral stone impaction have not been clearly identified. METHODS: We identified all patients from June 2014 to July 2016 that underwent ureteroscopic treatment of an impacted ureteral stone. Patients that had ureteral prestenting or previous treatment for their stone were excluded. Noncontrast CT images were reviewed to calculate stone size, stone volume, degree of hydronephrosis (0-3), and Hounsfield units (HU) of the stone as well as the ureter distal and proximal to the stone. These were compared with a control group of patients that had nonimpacted stones. RESULTS: Patients with impacted stones had a greater stone size, volume, HU of the ureter under the stone, HU under/above ratio, and degree of hydronephrosis on univariate analysis. Multivariate analysis demonstrated that HU under the stone was a significant predictor of ureteral stone impaction (odds ratio 1.17; 95% confidence interval 1.11-1.25). Distal ureteral density above 27 HU demonstrated a sensitivity of 85%, specificity of 85%, positive predictive value of 89%, and negative predictive value of 81% for ureteral stone impaction. CONCLUSION: Impacted stones are associated with ureteral density cut-off value of 27 HU or greater. Measuring this value on preoperative noncontrast CT may help predict which patients are more likely to have impacted stones.