ENDOSCOPIC MAPPING OF RENAL PAPILLAE FOR RANDALL''S PLAQUES IN PATIENTS WITH URINARY STONE DISEASE

Purpose

Papillary "Randall's plaques" are theorized to act as nidi for urinary stone formation. The aim of this study was to document the presence, pattern and distribution of Randall's plaques in patients undergoing endoscopic procedures for urinary stone disease.

Materials and Methods

Patients undergoing either ureteroscopy or percutaneous nephroscopy for removal of urinary stones underwent endoscopic mapping of accessible calices. These patients were compared to a smaller group of patients undergoing endoscopic procedures for conditions unrelated to urinary stone disease. In patients found to have papillary plaques the presence, location and pattern of plaques were recorded. Plaque formation was correlated with patient age and sex, and primary composition of extricated stone.

Results

Endoscopic evidence of papillary Randall's plaques was found in 74% of 57 patients having ureteroscopic (21) or percutaneous (36) stone removal. Of 7 patients having endoscopic procedures for conditions unrelated to urinary stone disease 3 (43%) had evidence of papillary plaques. Plaques were found uniformly throughout all calices and most commonly diffusely scattered over the papillary surface. There was no correlation between patient age or sex and the presence of plaques. The incidence of plaques varied with the primary composition of extracted stones, and was 100% for calcium phosphate and uric acid, 88% for calcium oxalate, 33% for cystine and 20% for struvite. The incidence of papillary plaques was significantly more common in patients with calcium oxalate (88 versus 43%, p = 0.023) and calcium phosphate stones (100 versus 43%, p = 0.009) than patients without a history of urinary stone disease.

Conclusions

The endoscopic incidence of papillary Randall's plaques in patients with urolithiasis varies with the primary composition of formed urinary stones. Randall's plaques are found in the majority of patients with calcium urinary stone disease. Our findings suggest that the presence of papillary plaques is associated with calcium nephrolithiasis and may contribute to the pathogenesis of calcium urinary stones.     

Dual energy can accurately differentiate uric acid-containing urinary calculi from calcium stones

Purpose

To retrospectively evaluate the accuracy of dual-energy CT (DECT) in the detection of the chemical composition of urinary calculi in correlation with infrared spectroscopic stone analysis.

Methods

We reviewed the CT scans of 255 patients who underwent DECT due to a clinical suspicion of urolithiasis. Out of this group, we included 64 patients with clinically symptomatic urolithiasis requiring stone removal. After surgical removal of the stone by ureterorenoscopy, chemical composition was analyzed with infrared spectroscopy. We correlated DECT stone characterization results with chemical stone composition based on dual-energy indices (DEI). A total of 213 renal and ureteral stones could be removed and chemically analyzed.

Results

A total of 213 calculi were evaluated. Thirty eight out of sixty four (59 %) patients had >1 stone. DECT was used to differentiate stones by using DEI. Stones harboring calcium (CA) were color-coded in blue, while stones containing uric acid (UA) were colored red. Median DEI in UA-containing stones were 0.001. Non-UA-containing stones had a DEI between 0.073 for pure CA stones and 0.077 containing CA and other substances (p = 0.001; p = 0.03, respectively). Sensitivity of DECT was 98.4 % for differentiation of UA from non-UA-containing calculi. Specificity was 98.1 %. Mean effective radiation dose of DECT was 4.18 mSv (0.44–14.27 mSv), thus comparable to conventional CT scans of the abdomen. Conventional measurement of Hounsfield units did not correlate with stone composition.

Conclusion

DECT with image post-processing reliably discriminates UA-containing calculi from all other stones, but the study offered limitations. Discrimination within the non-UA stones cannot be reliably achieved but is clinically insignificant.

     

Infrared spectroscopy of urinary calculi before 1900 in votive offerings of the Bavarian pilgrimage church at Grafrath

Background

The old urinary calculi of the votive offerings in the pilgrimage church at Grafrath offer the possibility of analysing the components by infrared spectroscopy to give insights into factors that might influence their formation. A total of 166 specimens were taken from 139 objects (134 stones, 5 bones), in some stones from different layers.

Material and methods

Spectral analysis showed typical components for urinary calculi in 127 stones. These were compared with a control group of 98 urinary stones from carriers (77 male, 21 female) during 2007/2008 in Bavaria.

Results

The percentage of occurrence of ammonium acid urate (NH₄U) was high in the old stones (68.0%) versus the 2007/2008 group (1.0%). In uric acid (HS) there was no relevant difference between the two groups, whereas the occurrence of the oxalates whewellite (Whe) and weddellite (Wed) was much less in the old stones (Whe 18.1?C69.4%, Wed 7.9?C26.5 %). The phosphates differ in the components in favour of brushite in the old stones. The high occurrence of NH₄ in the old stones is comparable with (a) the old pre-1900 collection of Norwich (England), especially with the pre-1800 juvenile bladder stones, and (b) urinary stones in endemic areas of stone disease in children such as in North Thailand. Data about the Grafrath stone carriers (name, age, hometown) are not available but can indirectly be derived from the miracle books (1444?C1728) of Grafrath with 12,131 reports; 1,165 had urologic disease of which 70% were children with urinary calculi coming from areas of Upper Bavaria and Swabia.

Conclusion

The finding of a high NH₄U content indicates that this area might have been a stone belt for bladder stones in children. Under- or malnutrition with low protein and low fluid intake may be the aetiologic factor.     

Urinary Calculi as a Late Complication of the Indiana Continent Urinary Diversion: Comparison with the Kock Pouch Procedure

Purpose

Although urinary calculi have been frequent late complications of the Kock continent urinary diversion, they have not been regarded as significant problems in patients with the Indiana pouch because of the lack of foreign material present. However, stones developed in a significant percentage of our patients with an Indiana pouch. We investigated the characteristics of stone formation in patients with the Indiana pouch and compared them to those with a Kock pouch.

Materials and Methods

Detailed clinical courses regarding stone formation were reviewed in 72 patients with a Kock pouch and 54 with an Indiana pouch who had a minimum followup of 12 months.

Results

Stones developed in 7 of 54 patients (12.9 percent) with an Indiana pouch compared to 31 of 72 (43.1 percent) with a Kock pouch. The incidence gradually increased with longer followup but it was lower in the Indiana than in the Kock pouch group (5-year stone-free rate 84 percent versus 66 percent, respectively). Although the stones consisted principally of a mixture of struvite, carbonate apatite and ammonium hydrogen urate, variable amounts of calcium oxalate were identified in 50 percent of the Indiana pouch calculi.

Conclusions

Not only urinary infections but also metabolic factors were considered to be involved in stone formation within the Indiana pouch. However, the substantially higher rate of stone formation in our Kock and Indiana pouch groups than has been reported in the United States suggested that no or infrequent pouch irrigations in our patients were important risk factors for urinary calculi.     

ACCURATE DETERMINATION OF CHEMICAL COMPOSITION OF URINARY CALCULI BY SPIRAL COMPUTERIZED TOMOGRAPHY

Purpose

Choice of efficacious clinical management of symptomatic renal calculi can be facilitated by ascertaining the precise chemical composition of the calculus. Spiral computerized tomography (CT) is becoming a frequently used radiographic examination to establish the diagnosis and severity of calculus disease. Our objective for this study was to determine the precision of spiral CT in identifying the chemical composition of 6 different types of urinary calculi with region of interest measurements using spiral CT.

Materials and Methods

A total of 102 chemically pure stones were separated into 6 groups. The stones along with phantoms containing butter (fat) and jello (water) were mounted vertically in the scanner gantry. Then 1 mm. thickness scanning was performed with a high speed scanner at the 2 energy levels of 80 and 120 kV. The determination of the chemical composition was performed using the absolute CT value measured at 120 kV. and the dual kilovolt CT values measured at 80 and 120 kV. Hounsfield unit at 80 kV. - Hounsfield unit at 120 kV.).

Results

The absolute CT value measured at 120 kV. was able to identify precisely the chemical composition of uric acid, struvite and calcium oxalate stones. It was imprecise in differentiating calcium oxalate from brushite stone and struvite from cystine stone. However, dual kilovolt CT value was able to differentiate these latter stones with statistical significance (p <0.03). Uric acid stones were easily differentiated from all other stones using the absolute CT value.

Conclusions

This study demonstrates that the chemical composition of urinary calculi can be accurately determined by CT scanning in an in vitro setting.     

URETEROSCOPIC MANAGEMENT OF INTRARENAL CALCULI

Purpose

To determine its potential role in stone therapy, we evaluated our experience with the ureteroscopic removal of intrarenal calculi in 100 patients. We review the indications, techniques, stone-free and overall success rates, and complications.

Materials and Methods

From July 1994 to December 1996 ureteroscopic stone removal was attempted in 100 patients a mean of 52 years old who had renal calculi. Indications for treatment included concurrent ureteral stones in 56 cases, and failed extracorporeal shock wave lithotripsy, medical or percutaneous management as well as obesity and anatomical anomalies. There were 2 or more calculi in the affected kidney in 68 patients and stones greater than 6 mm. in 67. Treatment of intrarenal calculi was performed with flexible ureteroscopes, a laser or electrohydraulic lithotriptor and endoscopic graspers. The number and size of calculi were noted in each patient. Stone-free and overall success rates defined as 1 residual fragment less than 3 mm. were noted at 1 and 3-month followup visits.

Results

The overall success rate was 89%. Ureteroscopic treatment of intrarenal calculi resulted in a 77% stone-free rate. Of the 23 patients with residual calculi 12 (52%) had a single residual fragment less than 3 mm. The targeted stone was removed or fragmented in 98 patients (98%) and no ureteral calculi remained postoperatively. As expected, the number and size of the original stones inversely correlated with the success rate. There were no intraoperative complications, and only 3 urinary tract infections and 3 fevers were noted postoperatively.

Conclusions

The use of smaller diameter ureteroscopes, better working instruments and more effective lithotriptors allow calculi in all parts of the collecting system to be engaged and treated. Success rates throughout the whole collecting system are comparable to if not better than those of extracorporeal shock wave lithotripsy and percutaneous approaches.     

Recurrent stone‐forming patients have high visceral fat ratio based on computed tomography images compared to first‐time stone‐forming patients

Objectives

To compare various fat parameters based on computed tomography images between recurrent stone‐forming patients and patients forming stones for the first time.

Methods

Included in the present study were 300 patients with upper urinary tract calculi who had undergone active stone removal in our hospital. Using pretreatment computed tomography images, we measured visceral fat area and volume, subcutaneous fat area and volume, visceral fat area ratio and visceral fat volume ratio. We compared patient backgrounds and these fat parameters between those who recurrently formed stones and those who formed stones for the first time. We also performed logistic regression analysis to identify factors that contribute to severe stones.

Results

A total of 148 (49.3%) patients were recurrent stone‐forming patients. Recurrent stone‐forming patients were statistically significantly younger (P < 0.01) and there were more male patients (P < 0.01). In addition, visceral fat area ratio and visceral fat volume ratio in recurrent stone‐forming patients were significantly higher than those in first‐time stone‐forming patients (P = 0.03 and P = 0.01, respectively). On the other hand, there was no significant difference in visceral fat area (P = 0.32), subcutaneous fat area (P = 0.36), visceral fat volume (P = 0.38) or subcutaneous fat volume (P = 0.23). Receiver operating characteristics analysis showed that area under the curve of visceral fat volume ratio (0.583) for recurrent stones was larger than that of visceral fat area ratio (0.571). In multivariate analysis, increasing visceral fat volume ratio was an independent significant predictor of recurrent stones (P = 0.04).

Conclusions

Recurrent stone‐forming patients have high visceral fat ratios compared to first‐time stone‐forming patients, shown here for the first time.

     

Systemic analysis of urinary stones from the Northern,Eastern, Central,Southern and Southwest China by a multi-center study

Background

To provide some basis for the prevention of urinary stones in general population, we did a systemic analysis of urinary stones from Northern, Eastern, Central, Southern and Southwest China by a multi-center study.

Methods

A total of 11,157 urinary stones from Northern, Eastern, Central, Southern and Southwest China were obtained and analyzed by Fourier transform infrared spectroscopy. Combined with scanning electron microscopy and X-ray energy spectrometer, urinary stones were classified into different types. Furthermore, the correlation between stone types and clinical characteristics, as well as their regional distribution were elucidated.

Results

Calcium oxalate stones were the most common type in each region, followed by calcium oxalate-calcium phosphate mixed stones, uric acid stones and calcium phosphate stones. The distribution of calcium oxalate stones were highest prevalence in Southwest China (67.9%, P?<?0.05), followed by Eastern and Northern China. Anhydrous uric acid stones, with a constituent ratio of 19.3% in Southern China, and 13.7% in Central China, were significantly higher than that in other regions (P?<?0.05). Elements analysis indicated varieties among stone types as well as distribution regions. Moreover, the clinical characteristics were highly correlated with stone types and anatomical locations but not their distribution regions.

Conclusions

The material and elements composition of urinary stones among different regions showed some varieties. Calcium oxalate stone has the highest constituent ratio in Southwest China, while anhydrous uric acid stone has the highest constituent ratio in Southern China. Moreover, the clinical characteristics were highly correlated with stone types and anatomical locations but not their distribution regions.

     

Infrared spectroscopic analysis of urinary stones (including stones induced by melamine-contaminated milk powder) in 189 Chinese children

Aim

The aim of the study was to investigate the composition of the stones in Chinese children with urolithiasis, including peculiar stones induced by melamine-contaminated milk powder.

Materials and Methods

Between 1999 and 2009, 189 urinary stones from children of East China were received at our institution. Among them, 12 stones were received from pediatric stone formers with a history of consuming melamine-contaminated milk powder in 2008; and the remaining stones were defined as “natural” stones. All stones were analyzed by Fourier transform infrared spectroscopy.

Results

Among 177 “natural” stones, whewellite stone (49.72%) was observed most frequently followed by weddellite stone (15.25%), uric acid anhydrous stone (9.6%), carbapatite stone (9.04%), cystine stone (9.04%), ammonium acid urate stone (4.52%), struvite stone (2.26%), and sodium urate stone (0.56%). Twelve young children who consumed melamine-contaminated milk powder were younger than 3 years, and their stones were composed of a mixture of uric acid dihydrate and ammonium acid urate based on Fourier transform infrared spectroscopy. In addition, the stones were radiolucent and could be dissolved by urine alkalinization.

Conclusions

Our study emphasizes the relatively high rate of calcium oxalate stones and cystine stones, and the relatively low rate of struvite stones in Chinese children with urolithiasis. The stones caused by melamine-contaminated milk powder are composed of the mixture of uric acid dihydrate and ammonium acid urate.     

Metabolic risk factors in children with asymptomatic hematuria

Background

Idiopathic or benign hematuria is diagnosed in children after all other possible causes have been ruled out and test results for renal or urologic pathologies are negative.

Methods

To identify possible urinary risk factors for hematuria in children, we retrospectively evaluated clinical onset, family history, and metabolic risk factors of 60 children with idiopathic hematuria but without renal stones or other pathologic conditions that could explain the hematuria. All patients followed the same ambulatory protocol at that used to evaluate kidney stone-formers.

Results

Seven patients had microhematuria, three patients each had microhematuria and gross hematuria, and the remaining 50 patients had gross hematuria onset. A family history of stone disease was found in 63 % of the children. At least one urinary metabolic abnormality was present in 49 patients, while 11 patients had no metabolic abnormality. The most common urinary risk factor was idiopathic hypercalciuria (single or associated), which was found in 43.5 % of patients, followed by hypocitraturia (single or associated), present in 31.7 %. Unduly acidic urine pH as a single abnormality was found in 10 % of this pediatric patient population. We also found hyperoxaluria and, less frequently, hypomagnesuria, and hyperuricosuria.

Conclusions

Asymptomatic idiopathic hematuria in pediatric patients may often be associated to different urinary biochemical abnormalities, similar to what is observed in pediatric kidney stone-formers.

     

Comparison of renal function and metabolic abnormalities of cystine stone patients and calcium oxalate stone patients in China

Purpose

To compare renal function and metabolic abnormalities of cystine stone patients and calcium oxalate stone patients in China.

Methods

Between 2008 and 2011, thirty cystine stone patients were involved in our study, and an equal number of age- and gender pair-matched patients with calcium oxalate stones. Non-stone forming individuals were elected as controls. The evaluation included blood chemistry studies and 24-h urine collection in both groups of patients.

Results

The cystine stone patients had higher mean values of serum blood urea nitrogen, urate and creatinine levels than patients in other two groups. With respect to urine risk factors, cystine stone patients had higher urinary citrate and lower urinary oxalate and creatinine than calcium oxalate stone patients. When compared to non-stone forming individuals, cystine stone patients had higher urinary urate excretion and lower urinary creatinine excretion. Metabolic abnormalities could be demonstrated in 80 % of the cystine stone patients and in 100 % of the calcium oxalate stone patients. We also compared urine risk factors among cystine stone patients with different urine cystine excretion (<1 mmol/24 h, 1–2 mmol/24 h and >2 mmol/24 h). No significant difference was found in urine risk factors among three groups.

Conclusions

This study suggested that cystine stone patients were at greater risk for the loss of renal function than calcium oxalate stone patients, but the risk of the formation of calcium oxalate stones was lower. Our results also indicated that urinary cystine had little or no impact on the excretion of urine chemistries in cystine stone patients.     

Urolithiasis in adult spina bifida patients: study in 260 patients and discussion of the literature

Purpose

To describe incidence and risk factors of urinary tract stones in adult spina bifida (SB) patients. Although spina bifida patients have an allegedly higher risk of urinary tract stones, only two small non-English case series are available and do not provide adequate epidemiological data and analyses on risk factors.

Methods

A total of 260 adult SB patients followed in our centre for 10 years were retrospectively analysed for stone disease. Both a univariate analysis (Fisher’s exact, two-sided Student’s t test) and a binary logistic regression analysis were performed to identify independent risk factors for stone disease.

Results

Of the 260 patients, 24 (9.2 %) were identified with a history of urolithiasis. Fourteen patients (5.4 %) had bladder stones in 26 episodes. Sixteen patients (6.2 %) had upper urinary tract stones: 14 kidney stones and two ureteral stones. Lifetime incidence of both bladder stones and upper tract stones was 2.25 per 1,000 patient-years. Recurrent urinary tract infections (OR 4.34, p = 0.013) and incorporation of bowel tissue into a continent reservoir (including enterocystoplasty) (OR 4.80, p = 0.012) were independent risk factors for bladder stone disease in a multivariate model. An indwelling catheter was an independent predictor for upper tract stones (OR 5.89, p = 0.02).

Conclusions

Urolithiasis, especially in the bladder, is a frequent finding in patients with SB. Bladder stones occur about 10 times more often in SB patients than in the population. In patients without risk factors, frequent ultrasound of the urinary tract is not necessary for the sole detection of stones.     

Long-Term Incidence and Risks for Recurrent Stones Following Contemporary Management of Upper Tract Calculi in Patients with a Urinary Diversion

Purpose

The long-term rate of stone recurrence following contemporary minimally invasive management of calculi was determined in patients with urinary diversion and to identify specific risk factors for these recurrences.

Materials and Methods

We followed for a minimum of 12 months 25 patients (29 renal units) with upper tract calculi associated with urinary diversion, and treated with extracorporeal shock wave lithotripsy and/or percutaneous nephrostolithotomy. The risk of recurrent stones at 5 years was determined by a Kaplan-Meier estimate, while potential risk factors for recurrence were analyzed using a log-rank comparison.

Results

Stones recurred in 8 patients (32 percent) 18 to 61 months (mean 27.0) after treatment. The risk of new stone formation after 5 years was estimated to be 63.3 percent and was significantly greater in patients with recurrent bacteriuria after treatment. Neither stone history, type of procedure used, stone composition nor radiographic status of completion of treatment significantly influenced this risk.

Conclusions

Contemporary management of upper tract calculi in patients with a urinary diversion is associated with a high recurrence rate, especially among those with recurrent bacteriuria, regardless of whether the patient is initially rendered stone-free. Continued close surveillance and antibiotic prophylaxis seem to be essential in this high risk patient population.     

Metabolic abnormalities associated with calyceal diverticular stones

OBJECTIVE: To review the metabolic analyses of patients with calyceal diverticular stones who had surgical treatment of their calculi and to examine the effect of selective medical therapy on stone recurrence, as recent reports suggest that metabolic abnormalities contribute to stone development. PATIENTS AND METHODS: In all, 37 patients who had endoscopic treatment of symptomatic calyceal diverticular calculi were retrospectively reviewed. Stone composition and initial 24-h urine collections (24-h urinary volumes, pH, calcium, sodium, uric acid, oxalate, citrate, and the number of abnormalities/patient per collection) were compared with 20 randomly selected stone-forming patients (controls) with no known anatomical abnormalities. Stone formation rates before and after the start of medical therapy were calculated in the patients available for follow-up. RESULTS: Twelve of the diverticulum patients (five men and seven women) had complete 24-h urine collections, all of whom had at least one metabolic abnormality. Seven patients had hypercalciuria, four had hyperuricosuria and three had mild hyperoxaluria. The most common abnormality was a low urine volume; 11 of the 12 patients had urine volumes of <2000 mL/day (range 350-1950). Ten patients had hypocitraturia in at least one of the two 24-h urine samples; seven had low urinary citrate levels (172-553 mg/day) on both samples. The findings were similar in the control group. The diverticulum patients had 3.1 abnormalities/patient, and the controls had 2.9 abnormalities/patient (P > 0.05). No patients had gouty diathesis and none developed cystine stones. Stone analyses were similar in the two groups; both developed either calcium oxalate or mixed calcium oxalate/calcium phosphate stones. Six patients were followed for a mean of 23.1 months while on selective medical therapy; only one passed any additional stones, thought to be existing calculi, for a remission rate of five of six (83%). CONCLUSIONS: All patients with symptomatic calyceal diverticular stones who had comprehensive metabolic evaluation had metabolic abnormalities. There were similar abnormalities in the control random stone-formers. The abnormalities were corrected with selective medical therapy, as shown by the high remission rate. We recommend that, for patients with symptomatic calyceal diverticular calculi, a metabolic evaluation should be considered to determine stone forming risk factors.     

Metabolic abnormalities associated with renal calculi in patients with horseshoe kidneys

BACKGROUND AND PURPOSE: Horseshoe kidneys are a complex anatomic variant of fused kidneys, with a 20% reported incidence of associated calculi. Anatomic causes such as high insertion of the ureter on the renal pelvis and obstruction of the ureteropelvic junction are thought to contribute to stone formation via impaired drainage, with urinary stasis, and an increased incidence of infection. In this multi-institutional study, we evaluated whether metabolic factors contributed to stone development in patients with horseshoe kidneys. PATIENTS AND METHODS: A retrospective review of 37 patients with horseshoe kidneys was performed to determine if these patients had metabolic derangements that might have contributed to calculus formation. Stone compositions as well as 24-hour urine collections were examined. Specific data points of interest were total urine volume; urine pH; urine concentrations of calcium, sodium, uric acid, oxalate, and citrate; and number of abnormalities per patient per 24-hour urine collection. These data were compared with those of a group of 13 patients with stones in caliceal diverticula as well as 24 age-, race-, and sex-matched controls with stones in anatomically normal kidneys. RESULTS: Eleven (9 men and 2 women) of the 37 patients (30%) with renal calculi in horseshoe kidneys had complete metabolic evaluations available for review. All patients were noted to have at least one abnormality, with an average of 2.68 abnormalities per 24-hour urine collection (range 1-4). One patient had primary hyperparathyroidism and underwent a parathyroidectomy. Low urine volumes were noted in eight patients on at least one of the two specimens (range 350-1640 mL/day). Hypercalciuria, hyperoxaluria, hyperuricosuria, and hypocitraturia were noted in seven, three, six, and six patients, respectively. No patients were found to have gouty diathesis or developed cystine stones. Comparative metabolic analyses of patients with renal calculi in caliceal diverticula or normal kidneys revealed a distinct profile in patients with horseshoe kidneys, with a higher incidence of hypocitraturia. CONCLUSIONS: All patients with renal calculi in horseshoe kidneys were noted to have metabolic abnormalities predisposing to stone formation. In this initial series of 11 patients, hypovolemia, hypercalcuria and hypocitraturia were most common metabolic defects. These findings suggest that metabolic derangements play a role in stone formation in patients with a horseshoe kidney. Patients with calculi in anatomically abnormal kidneys should be considered for a metabolic evaluation to identify their stone-forming risk factors in order to initiate preventative selective medical therapy and reduce the risk of recurrent calculus formation.     

Updates in the Metabolic Management of Calcium Stones

Purpose of Review

Urinary risk factors, such as hypercalciuria, hypocitraturia, and hyperoxaluria, either in combination or alone, are associated with calcium stones. Dietary habits as well as underlying medical conditions can influence urinary risk factors. Evaluation of the conglomerate of patients’ stone risks provides evidence for individualized medical management, an effective and patient-supported approach to prevention.

Recent Findings

Many patients with stones desire prevention to avoid repeated surgical interventions. Yet, recent practice pattern assessments and health care utilization data show that many patients are rarely referred for metabolic evaluation or management. Innovations in metabolic management over the past decade have improved its effectiveness in reducing risk and preventing calcium stones. Although no new pharmacologic agents for calcium stone prevention have recently become available, there is relatively new thinking about some diet-based approaches.

Summary

This review will synthesize current evidence to support individualized metabolic management of calcium stones.

     

Pathophysiologic basis for normouricosuric uric acid nephrolithiasis

BACKGROUND: Low urinary pH is the commonest and by far the most important factor in uric acid nephrolithiasis but the reason(s) for this defect is (are) unknown. Patients with uric acid nephrolithaisis have normal acid-base parameters according conventional clinical tests. METHODS: We studied steady-state plasma and urinary parameters of acid-base balance in subjects with normouricosuric pure uric acid stones. We also tested the ability of these subjects to excrete ammonium in response to an acute acid load. We compared these parameters in patients with pure uric acid stones to patients with mixed uric acid/calcium oxalate stones, pure calcium stones, and normal volunteers. RESULTS: Pure uric acid stone formers have a much higher incidence of either diabetes or glucose intolerance. After equilibration to a control diet, patients with uric acid stones have lower urinary pH and they excrete less of their acid as ammonium. This is compensated by higher titratable acidity and hypocitraturia. Despite their low baseline urinary pH, uric acid stone formers further acidify their urine after an acid load because of a severely impaired ammonia excretory response. Their characteristics are significantly different from normal volunteers and pure calcium stone formers. Patients with mixed uric acid/calcium stones exhibit intermediate characteristics. CONCLUSION: We propose that certain patients with normouricosuric uric acid nephrolithiasis have a renal acidification disease. The primary defect lies in renal ammonium excretion, which may be linked to the insulin-resistant state. Although net acid excretion is maintained at the expense of increased titratable acidity and to some degree hypocitraturia, the compromise is acid urine pH and may result in uric acid nephrolithiasis.     

RENAL STONE RISK ASSESSMENT DURING SPACE SHUTTLE FLIGHTS

Purpose

The metabolic and environmental factors influencing renal stone formation before, during, and after Space Shuttle flights were assessed. We established the contributing roles of dietary factors in relationship to the urinary risk factors associated with renal stone formation.

Materials and Methods

24-hr. urine samples were collected prior to, during space flight, and following landing. Urinary and dietary factors associated with renal stone formation were analyzed and the relative urinary supersaturation of calcium oxalate, calcium phosphate (brushite), sodium urate, struvite and uric acid were calculated.

Results

Urinary composition changed during flight to favor the crystallization of calcium-forming salts. Factors that contributed to increased potential for stone formation during space flight were significant reductions in urinary pH and increases in urinary calcium. Urinary output and citrate, a potent inhibitor of calcium-containing stones, were slightly reduced during space flight. Dietary intakes were significantly reduced for a number of variables, including fluid, energy, protein, potassium, phosphorus and magnesium.

Conclusions

This is the first in-flight characterization of the renal stone forming potential in astronauts. With the examination of urinary components and nutritional factors, it was possible to determine the factors that contributed to increased risk or protected from risk. In spite of the protective components, the negative contributions to renal stone risk predominated and resulted in a urinary environment that favored the supersaturation of stone-forming salts. Dietary and pharmacologic therapies need to be assessed to minimize the potential for renal stone formation in astronauts during/after space flight.     

Clinical utility of computed tomography Hounsfield characterization for percutaneous nephrolithotomy: a cross-sectional study

Background

Computed Tomography (CT) is considered the gold-standard for the pre-operative evaluation of urolithiasis. However, no Hounsfield (HU) variable capable of differentiating stone types has been clearly identified. The aim of this study is to assess the predictive value of HU parameters on CT for determining stone composition and outcomes in percutaneous nephrolithotomy (PCNL).

Methods

Seventy seven consecutive cases of PCNL between 2011 and 2016 were divided into 4 groups: 40 (52%) calcium, 26 (34%) uric acid, 5 (6%) struvite and 6 (8%) cystine stones. All images were reviewed by a single urologist using abdomen/bone windows to evaluate: stone volume, core (HUC), periphery HU and their absolute difference. HU density (HUD) was defined as the ratio between mean HU and the stone’s largest diameter. ROC curves assessed the predictive power of HU for determining stone composition/stone-free rate (SFR).

Results

No differences were found based on the viewing window (abdomen vs bone). Struvite stones had values halfway between hyperdense (calcium) and low-density (cystine/uric acid) calculi for all parameters except HUD, which was the lowest. All HU variables for medium-high density stones were greater than low-density stones (p?<?0.001). HUC differentiated the two groups (cut-off 825 HU; specificity 90.6%, sensitivity 88.9%). HUD distinguished calcium from struvite (mean?±?SD 51?±?16 and 28?±?12 respectively; p?=?0.02) with high sensitivity (82.5%) and specificity (80%) at a cut-off of 35 HU/mm. Multivariate analysis revealed HUD?≥?38.5 HU/mm to be an independent predictor of SFR (OR?=?3.1, p?=?0.03). No relationship was found between HU values and complication rate.

Conclusions

HU parameters help predict stone composition to select patients for oral chemolysis. HUD is an independent predictor of residual fragments after PCNL and may be fundamental to categorize it, driving the imaging choice at follow-up.