Comparison of the bone mineral density status of patients with kidney stones stratified by stone composition.

PURPOSE: Bone loss has been found to occur frequently in patients with particular metabolic disorders that are likely associated with certain kidney stone composition. Thus, we compared the bone mineral density (BMD) of patients with different kidney stone compositions. PATIENTS AND METHODS: A total of 204 consecutive patients who exhibited stone formation with calcium oxalate (CaOx), calcium phosphate (CaP), uric acid (UA), and magnesium ammonium phosphate (MAP) underwent 24 h urine test and BMD measurement. BMD was measured by dual X-ray absorptiometry at the lumbar spine (LS) and femoral neck (FN). The Z-score was used to express BMD. A BMD Z-score ≤ - 2 was defined as a diagnostic threshold for bone loss. RESULTS: Amongst the patients, 38 had an LS BMD Z-score of ≤ - 2, but only 2 had FN BMD Z-score of ≤ - 2. The group with an LS BMD Z-score of ≤ - 2 exhibited significantly larger male - female ratio, higher frequency of hypercalciuria and CaP, and lower frequency of MAP than the group with an LS BMD Z-score of > - 2. Reduced LS BMD was most remarkable in the CaP group, followed by the CaOx, UA, and MAP groups. The LS BMD Z-score of hypercalciuric patients was significantly lower than that of normocalciuric patients only in the CaP group. CONCLUSION: Patients with different kidney stone compositions presented different BMD status. Using this information may facilitate medical decision-making in patients with kidney stone who should undergone BMD earlier.

Urosepsis after ureterorenoscopy, intraoperative recognition of type-IV stones could change clinical practice.

OBJECTIVES: Urosepsis currently accounts for half of all post flexible ureterorenoscopy (F-URS) complications, with an incidence of up to 4.3%. It represents a quarter of all septic episodes in adults and 2% of hospital spendings. The primary objective of this study was to define the predictive clinical parameters that increase the risk of urosepsis after F-URS. SUBJECTS/PATIENTS (OR MATERIALS) AND METHODS: This prospective multicentric study evaluated patients who underwent F-URS for calculus between June 2016 and June 2018 in eleven French centers. Clinical, bacteriological, morpho-constitutional stone data, intraoperative information and complications were compared. Risk factors for postoperative urosepsis were identified and analyzed. RESULTS: We included 486 F-URS in 432 patients. The ureter was prepared using a double J stent in 51% of cases, a digital endoscope was used in 56% of patients with a median operative time of 120 min IQR (90-125) and using a sheath in 90% of cases. Postoperative urosepsis was observed in 18 patients (4%) with a median time to onset of 2 days IQR (1-5). The presence of coronary insufficiency: 3 (17%) vs 14 (3%) p = 0.005, a larger stone diameter: 11 cm [9-17] vs 10 cm [8-13] p = 0.02, a positive preoperative urine culture even when treated: 3 (17%) vs 56 (12%) p = 0.04, as well as the final composition of the type IV calculus (carbapatite or struvite) 5 (28%) vs 20 (4%) p < 0.001, were significantly associated with the occurrence of urosepsis. In multivariate analysis, only the presence of a type IV stone (OR = 14.0; p = 0.025) remained significant. CONCLUSION: Ureteroscopic treatment of a type IV stone (carbapatite or struvite) in a patient should raise concerns about the risk of post-operative urosepsis. When recognized intraoperatively, they should lead to a pyelic urinary sample and prolonged clinical surveillance.

On the rocks: can urologists identify stone composition based on endoscopic images alone? A worldwide survey of urologists.

PURPOSE: As part of the management of nephrolithiasis, determination of chemical composition of stones is important. Our objective in this study is to assess urologists' accuracy in making visual, intraoperative determinations of stone composition. MATERIALS AND METHODS: We conducted a REDCap survey asking urologists to predict stone composition based on intraoperative images of 10 different pure-composition kidney stones of 7 different types: calcium oxalate monohydrate (COM), calcium oxalate dihydrate (COD), calcium phosphate (CP) apatite, CP brushite, uric acid (UA), struvite (ST) and cystine (CY). To evaluate experience, we examined specific endourologic training, years of experience, and number of ureteroscopy (URS) cases/week. A self-assessment of ability to identify stone composition was also required. RESULTS: With a response rate of 26% (366 completed surveys out of 1,370 deliveries), the overall accuracy of our cohort was 44%. COM, ST, and COD obtained the most successful identification rates (65.9%, 55.7%, and 52.0%, respectively). The most frequent misidentified stones were CP apatite (10.7%) and CY (14.2%). Predictors of increased overall accuracy included self-perceived ability to determine composition and number of ureteroscopies per week, while years of experience did not show a positive correlation. CONCLUSIONS: Although endoscopic stone recognition can be an important tool for surgeons, it is not reliable enough to be utilized as a single method for stone identification, suggesting that urologists need to refine their ability to successfully recognize specific stone compositions intraoperatively.

Urinary stone composition in Germany: results from 45,783 stone analyses.

PURPOSE: Stone composition can provide valuable information for the diagnosis, treatment and recurrence prevention of urolithiasis. The aim of this study was to evaluate the distribution of urinary stone components and the impact of different crystal forms according to gender and age of patients in Germany. METHODS: A total of 45,783 urinary stones submitted from 32,512 men and 13,271 women between January 2007 and December 2020 were analyzed by infrared spectroscopy. Only the first calculus obtained per patient was included in the analysis. RESULTS: The most common main stone component was calcium oxalate (CaOx) (71.4%), followed by carbonate apatite (CA) (10.2%) and uric acid (UA) (8.3%). Struvite (2.1%), brushite (1.3%), protein (0.5%) and cystine (0.4%) stones were only rarely diagnosed. CaOx (75%) and UA stones (81%) were more frequently obtained from men than women (p < 0.001). Weddellite (COD) and uric acid dihydrate (UAD) were more common in younger ages than whewellite (COM) and anhydrous uric acid (UAA), respectively, in both men and women. The ratios of COM-to-COD and UAA-to-UAD calculi were approximately 4:1 and 8:1, respectively. The peak of stone occurrence was between the ages of 40 and 59 years. CONCLUSION: Stone composition is strongly associated with gender and age. The peak incidence of calculi in both women and men was in the most active phase of their working life. The distinction between different crystal forms could provide clues to the activity and mechanisms of lithogenesis. Further research is needed in understanding the causative factors and the process of stone formation.

Risk of Symptomatic Kidney Stones During and After Pregnancy.

RATIONALE & OBJECTIVE: There are several well-known anatomical and physiological changes during pregnancy that could contribute to kidney stone formation, but evidence that they increase the risk of kidney stones during pregnancy is lacking. We determined whether there was an increased risk of a first-time symptomatic kidney stone during and after pregnancy. STUDY DESIGN: A population-based matched case-control study. SETTING & PARTICIPANTS: 945 female first-time symptomatic kidney stone formers aged 15-45 years and 1,890 age-matched female controls in Olmsted County, MN, from 1984-2012. The index date was the date of onset of a symptomatic kidney stone for both the case and her matched controls. EXPOSURE: The primary exposure was pregnancy with assessment for variation in risk across different time intervals before, during, and after pregnancy. Medical records were manually reviewed to determine the conception and delivery dates for pregnancies. OUTCOME: Medical record-validated first-time symptomatic kidney stone. ANALYTICAL APPROACH: Conditional and unconditional multivariable logistic regression analysis. RESULTS: Compared with nonpregnant women, the odds of a symptomatic kidney stone forming in women was similar in the first trimester (OR, 0.92; P=0.8), began to increase during the second trimester (OR, 2.00; P=0.007), further increased during the third trimester (OR, 2.69; P=0.001), peaked at 0 to 3 months after delivery (OR, 3.53; P<0.001), and returned to baseline by 1year after delivery. These associations persisted after adjustment for age and race or for diabetes mellitus, hypertension, and obesity. These results did not significantly differ by age, race, time period, or number of prior pregnancies. Having a prior pregnancy (delivery date>1year ago) was also associated with a first-time symptomatic kidney stone (OR, 1.27; P=0.01). LIMITATIONS: Observational study design in a predominantly White population. The exact timing of stone formation cannot be determined. CONCLUSIONS: Pregnancy increases the risk of a first-time symptomatic kidney stone. This risk peaks close to delivery and then improves by 1 year after delivery, though a modest risk of a kidney stone still exists beyond 1 year after delivery.

Trends in urinary stone composition in 23,182 stone analyses from 2011 to 2019: a high-volume center study in China.

PURPOSE: To evaluate the distribution and dynamic trends in constituents of urinary stones in China. MATERIALS AND METHODS: The composition of 23,182 stones were analyzed and then recorded between January 2011 and December 2019. The characteristics in terms of stone patient's gender, age and calendar year were analyzed. RESULTS: Most stones (22,172, 95.64%) had several crystal components, among which 40.25% (8925/22,172) were mixtures with infection components. Calcium oxalate (CaOx) and uric acid (UA) stones were more commonly encountered in men, but calcium phosphate (CaP), magnesium ammonium phosphate (MAP) and carbonate apatite (CA) stones were more prevalent in women (p < 0.05). In males, the proportion of CaOx stones increased up to the age of 40, but subsequently decreased (p < 0.001). Interestingly, females showed an inverse trend regarding CaOx stones (p < 0.001). The proportion of UA stones increased with age (p < 0.001), and CA stones most frequently were recorded at age 20-49. Over the past 9 years, UA, CA, and MAP stones increased over time, whereas there was a tendency for CaOx stones to decrease (p < 0.05). CONCLUSIONS: The scarcity of pure stones and a certain proportion of mixtures with infection stone components (e.g., mixtures of CaOx and CA) suggest that treatment directed against a single stone component is insufficient for effective recurrence prevention. Age and gender were significant determinants of stone composition, and according to the observed chronological trends, it seems that in the future, more UA, CA and MAP stones and fewer CaOx stones may be encountered in the studied population.

What is the exact definition of stone dust? An in vitro evaluation.

PURPOSE: To propose a size-related definition of stone dust produced by lithotripsy of urinary stones. METHODS: Stone dust was defined as particles small enough to adhere to the following criteria: (1) spontaneous floating under 40 cm H2O irrigation pressure; (2) mean sedimentation time of > 2 s through 10 cm saline solution; (3) fully suitable for aspiration through a 3.6 F working channel. Irrigation, sedimentation, and aspiration tests were set up to evaluate each criterion. Primary outcome was particle size limit agreeing with all three criteria. Stone particles with a given size limit (≤ 2 mm, ≤ 1 mm, ≤ 500 µm, ≤ 250 µm, ≤ 125 µm and ≤ 63 µm) were obtained from laser lithotripsy, including samples from prevailing stone types: calcium oxalate monohydrate, calcium oxalate dihydrate, uric acid, carbapatite, struvite, brushite, and cystine. RESULTS: All particles ≤ 250 µm from all stone types were in agreement with all three criteria defining stone dust, except for struvite where size limit for a positive irrigation and sedimentation test was ≤ 125 µm. CONCLUSION: A size limit of ≤ 250 µm seems to generally adhere to our definition of stone dust, which is based on floating and sedimentation proprieties of stone particles, as well as on the ability to be fully aspirated through the working channel of a flexible ureteroscope.

The status and characteristics of urinary stone composition in China.

OBJECTIVES: To explore characteristics of urinary stone composition in China, and determine the effects of gender, age, body mass index (BMI), stone location, and geographical region on stone composition. PATIENTS AND METHODS: We prospectively used Fourier-transform infrared spectroscopy to analyse stones from consecutive patients presenting with new-onset urolithiasis at 46 hospitals in seven geographical areas of China, between 1 June 2010 and 31 May 2015. Chi-squared tests and logistic regression analyses were used to determine associations between stone composition and gender, age, BMI, stone location, and geographical region. RESULTS: The most common stone constituents were: calcium oxalate (CaOx; 65.9%), carbapatite (15.6%), urate (12.4%), struvite (2.7%), and brushite (1.7%). CaOx and urate stones occurred more frequently in males, whereas carbapatite and struvite were more common in females (P < 0.01). CaOx and carbapatite were more common in those aged 30-50 and 20-40 years than in other groups. Brushite and struvite were most common amongst those aged <20 and >70 years. The detection rate of urate increased with age, whilst cystine decreased with age. Obese patients were more likely to have urate stones than carbapatite or brushite stones (P < 0.01). CaOx, carbapatite, brushite, and cystine stones were more frequently found in the kidney than other types, whereas urate and struvite were more frequent in the bladder (P < 0.01). Stone composition varied by geographical region. CONCLUSIONS: The most common stone composition was CaOx, followed by carbapatite, urate, struvite, and brushite. Stone composition differed significantly in patients grouped by gender, age, BMI, stone location, and geographical region.

Dual-Energy CT for Urinary Stone Evaluation.

PURPOSE OF REVIEW: Conventional CT imaging is an excellent tool for the diagnosis of nephrolithiasis however is limited in its ability to detect stone composition. Dual-energy CT (DECT) scans have demonstrated promise in overcoming this limitation. We review the current utility of DECT in nephrolithiasis. RECENT FINDINGS: DECT is superior to conventional CT in differentiating uric acid stones from non-uric acid stones, with numerous studies reporting sensitivities and specificities approaching > 95%. Dose reduction protocols incorporating low-dose CT scans are commonly used, providing significantly lower effective radiation doses compared to conventional CT. DECT remains an effective diagnostic tool in patients with large body habitus. DECT can accurately detect uric acid stones, which can help guide which stones may be suitable to medical dissolution. Further studies evaluating the effectiveness of DECT in guiding management of patients with nephrolithiasis can help to promote its widespread use.

Successful treatment of seminal vesicle calculi and prostatic utricle calculi by transurethral seminal vesiculoscopy.

To investigate the outcomes of transurethral seminal vesiculoscopy (TSV) for the treatment of seminal vesicle calculi (SVC), prostatic utricle calculi (PUC) and combination of them, a retrospective review on 27 patients with SVC and/or PUC who complained of intractable haematospermia was conducted. Patient demographics, disease duration, operation time, stone location and complications were recorded. The calculi in the seminal vesicle and/or prostatic utricle were removed by holmium laser lithotripsy and/or basket extraction. The stone composition was determined in 19 of 27 patients using Infrared spectroscopy. The average age and disease duration of patients were 39.4 years and 23.1 months respectively. The mean operative time was 78.5 min. We detected SVC, SVC and PUC, and PUC in 59.3% (16/27), 33.3% (9/27) and 7.4% (2/27) patients respectively. The stones were mainly composed of calcium oxalate dehydrate (COD), carbonate apatite (CA), COD and calcium oxalate monohydrate (COM), CA and magnesium ammonium phosphate, CA and COM, and COD and uric acid in 42.1% (8/19), 21.1% (4/19), 15.8% (3/19), 15.8% (3/19), 5.3% (1/19) and 5.3% (1/19) cases respectively. No intraoperative and post-operative complications were noted. These results suggested that SVC and PUC can be diagnosed and treated using TSVs.

[Comparison of the composition of DJ tube encrustation and original stone and analysis of its causes].

Objective: To compare the composition of DJ tube encrustation and original stone, and to discuss the causes and prevention of encrustations. Methods: Twenty-five patients with DJ tube encrustation (1 case of INLAY OPTIMA(®) tube, Bard Medical, 16 cases of Universa(®) Firm tube, Cook Medical, 8 cases of Polaris™ Loop tube, Boston Scientific) in our institution from Januarry 2018 to April 2019 wereretrospective analyzed. Stones and encrustations were analyzed using the Fourier transform infrared spectroscopy analysis system to compare the differences in composition. Results: 76% (19/25) patients had the exact same DJ tube encrustations composition as the original stone component; 24% (6/25) patients had DJ tube encrustation and original stone composition inconsistent (5 cases of calcium oxalate stone, 1 case of apatite carbonate.) It maybe related to the control of urinary tract infection after ureteral obstruction. The earliest DJ tube with encrustation was a pre-expansion tube before flexible-ureteroscopy, and the indwelling time was only 18 days. Conclusions: DJ tubes of different brands and models have the risk of formation of encrustation. Most of the encrustation has the same composition as the original stone. The prevention of DJ tube scorpion can be started from: (1) removing the DJ tube within 6 weeks or replace it regularly when necessary; (2) selecting the appropriate tube including diameter and model; (3) actively controlling urinary tract infection; (4) treating the metabolic diseases, such as hypercalcemia, hyperuricemia, et al, and providing personalized guidance for each patient.

Stone composition independently predicts stone size in 18,029 spontaneously passed stones.

PURPOSE: To evaluate whether the size of spontaneously passed stones (SPS) may be associated with clinical parameters. METHODS: A search for SPS was conducted in our electronic stone database, comprising data on stones analyzed over the last 33 years at our institution. Adults with upper urinary tract stones were included. Cases with stenotic urinary tract disease or past history of anastomotic urinary tract surgery were excluded. Stone size expressed as maximal stone diameter (MSD) and stone volume (SV) was compared between groups by one-way ANOVA. Logistic regression analyses were performed to identify predictors of MSD ≥ 6 mm. RESULTS: Overall mean MSD and SV for 18,029 SPS was 4.1 mm and 11.5 mm3, respectively, and significantly differed between stone composition groups (p < 0.001). The lowest mean MSD and SV were found for calcium oxalate monohydrate (3.6 mm and 9.0 mm3, respectively) and the highest mean MSD and SV were found for struvite (7.9 mm and 61.0 mm3, respectively). Stone composition and increasing age were found to be independent predictors of MSD ≥ 6 mm (both p < 0.001). Sex differentiation did not contribute as a predictor of MSD ≥ 6 mm. CONCLUSIONS: Stone composition and-to a lesser extent-age serve as independent predictors of size of spontaneously passed stones. Of particular importance, large spontaneously passed stones of ≥ 6 mm may be frequently found in cystine, brushite or struvite stone formers, whereas a minority of all calcium oxalate stones exceed that cutoff. Future studies shall evaluate these parameters as possible predictors of spontaneous stone passage.

Pediatric urolithiasis in Morocco: Composition of 432 urinary calculi analyzed by infrared spectroscopy.

PURPOSE: Incidence of pediatric urolithiasis is decreasing in most developing countries where endemic bladder stones are less prevalent than in the past years. In parallel, stone composition has changed. Only few data are available in North Africa, except for Tunisia. We report stone composition in the Moroccan pediatric population. MATERIAL AND METHODS: Composition of 432 stones from children (302 boys, 130 girls) was determined by infrared spectroscopy. The samples were collected during the period 1999-2016. Stone morphology, which is an important aspect for etiology was determined by examination of each stone under a stereomicroscope. Stone composition was compared to patients' age and gender. RESULTS: The global male-to-female ratio was 2.32. Regarding stone composition, calcium oxalate was the main component in 51.6% of the stones, followed by struvite (18.1%), ammonium urate (9.5%) and carbapatite (9%). Significant differences were found between males and females: calcium oxalate accounted for 72.3% of stones in girls and 42.7% in boys (P<10-6); conversely, struvite was more frequent in boys than in girls (22.2 vs 8.5%, P<10-4). The same was found for calcium phosphate stones (11.9% in boys; 4.6% in girls, P<0.05). Stone morphology helped us for detecting several pathological conditions: type Ic whewellite stones, as a marker for primary hyperoxaluria, was found in 17.6% of stones and type IIId ammonium urate stones, suggestive for infectious diarrhea, was identified in 20.1% of all stones. CONCLUSION: This is the largest series of pediatric stones in Morocco studied by infrared analysis and morphological examination. LEVEL OF EVIDENCE: 3.

[Dual-energy computed tomography in the diagnostics of urolithiasis].

THE AIM: To assess the diagnostic performance of dual-energy computed tomography (DECT) in the evaluation of the composition of urinary stones "in vivo". MATERIALS AND METHODS: A total of 91 patients aged from 20 to 70 years old (mean 42.7) with urinary stone disease were examined at Sechenov University, including 68 men (75%) and 23 women (25%). Prior to surgery, all patients underwent DECT (Canon, Japan) in order to predict the chemical composition of urinary stones in vivo. Extracorporeal shockwave lithotripsy (ESWL), percutaneous nephrolithotomy (PCNL) and ureteroscopy (URS) was performed in 53 (58.2%), 18 (19.7%) and 20 (22.1%) patients, respectively. Postoperatively, all stones or stone fragments (n=91; 100%) were examined using a comprehensive physical and chemical analysis (X-ray phase analysis, electron microscopy, infrared spectroscopy). RESULTS: In 6 patients (6.6%) staghorn stones were diagnosed, while in 15 (16.5%), 17 (18.7%), 22 (24.2%) and 31 (34.1%) stones were located in ureteropelvic junction, pelvis and ureter, respectively, including 24 patients with lower ureteric stones (26.4%). Prediction of the stone composition in vivo was carried out on the basis of the one indicator, the dual energy ratio (DER). The threshold values of DER for different types of stones were taken from the literature. All stones were divided into 4 groups according to the DECT results: vevellite stones (n=40, 43.9%), Ca-containing stones without vevellite (n=34, 37.3%), uric acid stones (n=10, 10.9%) and struvite stones (n=7, 7.9%). Thus, when comparing the results of DECT and physical and chemical analysis, in the first group four stones were incorrectly assigned by DECT to the group of Ca-containing stones without vevellite and three stones were incorrectly assigned to the group of struvite stones; in the second group four stones were incorrectly assigned to the group of vevellite stones; in the third group one stone was incorrectly assigned to the group of struvite stones; in the fourth group one stone was incorrectly assigned to the group of vevellite stones and one stone in the group of uric acid stones. In order to increase the diagnostic efficiency of DECT, we performed a comprehensive analysis of five specific DECT indicators (stone density at 135 kV, Z eff of the stone, DER, DEI, DED) using discriminant analysis. Thus, the sensitivity, specificity and overall accuracy of DECT with the use of just one indicator (DER) were 83.3%, 89.8%, 86.8% for vevellite, 88.2%, 92.9%, 91.2% for Ca-containing stones without vevellite, 90%, 98.8%, 97.8% for uric acid stones and 60%, 95.3%, 93.4% for struvite stones, respectively. When using discriminant analysis with five specific DECT indicators, higher values of sensitivity, specificity and overall accuracy were seen: 95.2%, 89.8%, 92.3% for a vevellite, 85,3%, 96,4%, 92,3% for Ca-containing stones without a vevellite and 100%, 100% and 100% for both uric acid and struvite stones, respectively. CONCLUSIONS: Dual-energy computed tomography is a highly informative method which allows to perform preoperatively the reliable assessment of the chemical composition. DECT in patients with urinary stone disease allows to optimize the treatment strategy and carry out preventive measures on individual basis, taking into account the stone type.

Dual-Energy CT for Quantification of Urinary Stone Composition in Mixed Stones: A Phantom Study.

OBJECTIVE: The purpose of this study was to assess the feasibility of using dual-energy CT to accurately quantify uric acid and non-uric acid components in urinary stones of mixed composition. MATERIALS AND METHODS: A total of 24 urinary stones were analyzed with micro CT to serve as the reference standard for uric acid and non-uric acid composition. These stones were placed in water phantoms to simulate body attenuation of slim to obese adults and scanned with a third-generation dual-source CT scanner by use of dual-energy modes adaptively selected on the basis of phantom size. CT number ratio, which is distinct for different materials, was calculated for each pixel of the stones. Each pixel was then classified as uric acid and non-uric acid by comparison of the CT number ratio with preset thresholds ranging from 1.10 to 1.70. Minimal, maximal, and root-mean-square errors were calculated by comparing composition with the reference standard, and the threshold with the minimal root-mean-square error was determined. A paired t test was performed to compare the stone composition determined with dual-energy CT with the reference standard obtained with micro CT. RESULTS: The optimal CT number ratio threshold ranged from 1.27 to 1.55, dependent on phantom size. The root-mean-square error ranged from 9.60% to 12.87% across all phantom sizes. Minimal absolute error ranged from 0.04% to 1.24% and maximal absolute error from 22.05% to 35.46%. Dual-energy CT and the reference micro CT did not differ significantly on uric acid and non-uric acid composition (paired t test, p = 0.20-0.96). CONCLUSION: Accurate quantification of uric acid and non-uric acid composition in mixed stones is possible with dual-energy CT.

Kidney stones: Composition, frequency and relation to metabolic diagnosis.

Nephrolithiasis is one of the most frequent urologic diseases. The aim of this paper is to study the composition and frequency of 8854 patient kidney stones and in a subset of them their metabolic risk factors to be related to their type of calculi. Physicochemical and crystallographic methods were used to assess kidney stone composition. In a subset of 715 patients, we performed an ambulatory metabolic protocol with diagnostic purposes. From the total sample 79% of stones were made of calcium salts (oxalate and phosphate), followed by uric acid stones in 16.5%, calcium salts and uric acid in 2%, other salts in 1.9% and cystine in 0.6%. Male to female ratio was almost three times higher in calcium salts and other types of stones, reaching a marked male predominance in uric acid stones, M/F 18.8 /1.0. The major risk factors for calcium stones are idiopathic hypercalciuria, followed by unduly acidic urine pH and hyperuricosuria. In uric acid stones unduly acidic urine pH and less commonly hyperuricosuria are the most frequent biochemical diagnosis. Our results show that analysis of kidney stones composition and the corresponding metabolic diagnosis may provide a scientific basis for the best management and prevention of kidney stone formation, as well as it may help us to study the mechanisms of urine stone formation.

Feasibility of discriminating uric acid from non-uric acid renal stones using consecutive spatially registered low- and high-energy scans obtained on a conventional CT scanner.

OBJECTIVE: The objective of our study was to show the feasibility of distinguishing between uric acid (UA) and non-UA renal stones using two consecutive spatially registered low- and high-energy scans acquired on a conventional CT system. SUBJECTS AND METHODS: A total of 33 patients undergoing clinically indicated dual-source dual-energy CT examinations to differentiate UA from non-UA renal stones were enrolled in this study. Immediately after patients underwent clinically indicated dual-source dual-energy CT, two consecutive scans (one at 80 kV and one at 140 kV) were obtained on a conventional CT scanner over the region limited to the stones identified on the dual-source scans. After 3D deformable registration of the 80- and 140-kV images, UA and non-UA stones were identified using commercial software. The sensitivity, specificity, and accuracy of stone classification were calculated using the dual-source results as the reference standard. RESULTS: A total of 469 stones were identified in the dual-source examinations (26 UA and 443 non-UA stones). The average in-plane stone diameter was 4.4 ± 2.5 (SD) mm (range, 2.0-18.9 mm). The overall sensitivity, specificity, and accuracy for identifying UA stones were 73.1%, 90.1%, and 89.1%, respectively. The sensitivity, specificity, and accuracy were 94.7%, 96.9%, and 96.8% for stones 3 mm or larger (n = 341 [19 UA and 322 non-UA]). CONCLUSION: Accurate differentiation of UA from non-UA renal stones is feasible using two consecutively acquired and spatially registered conventional CT scans.

Radiation Dose Reduction in Dual-Energy CT: Does It Affect the Accuracy of Urinary Stone Characterization?

OBJECTIVE: The purpose of this article is to assess the effect of radiation dose reduction in dual-energy CT (DECT) on the performance of renal stone characterization using a patient cohort. MATERIALS AND METHODS: CT data from 39 unenhanced DECT examinations performed for stone characterization were retrospectively analyzed in this study. Reduced-dose images were simulated at 75%, 50%, and 25% of the routine dose using a previously validated noise-insertion algorithm. Differentiation between uric acid (UA) and non-UA stones was performed using a fixed cutoff value for the dual-energy ratio. ROC analysis was performed to determine optimal cutoff values and the associated sensitivity and specificity. RESULTS: Of the 206 stones found, 43 were UA and 163 were non-UA. The mean (± SD) volume CT dose index (CTDIvol) was 16.0 ± 4.0 mGy at the 100% dose level. The mean noise in 100-kV images increased from 40.9 ± 6.8 HU at 100% dose to 46.8 ± 8.8 HU, 57.7 ± 12.5 HU, and 85.4 ± 22.9 HU at 75%, 50%, and 25% dose levels, respectively. Using the default cutoff value, for stones 10 mm(3) or larger, the sensitivity/specificity were 100.0%/98.8%, 82.8%/98.8%, and 89.3%/98.7%, at 75%, 50%, and 25% dose levels, respectively. ROC analysis showed varying optimal cutoff values at different dose levels. The sensitivity and specificity improved with use of these optimal cutoff values. Differentiation capability decreased for stones smaller than 10 mm(3). CONCLUSION: At 75% of the 16-mGy routine dose, the sensitivity and specificity for differentiating UA from non-UA stones were minimally affected for stones 10 mm(3) or larger. The use of optimal cutoff values for dual-energy ratio as dose decreased (and noise increased) provided improved performance.

[Prevention of recurrence of urolithiasis]. / Rezidivprävention der Urolithiasis.

Urolithiasis is one of the most frequent urological diseases. Identifying the causes of stone formation forms the basis for successful prevention of recurrence. Metabolic diagnostics and measures for prevention of recurrence are based on the assignment of the patient to a low-risk or high-risk group. Analysis of the urinary calculi is an essential prerequisite for identifying patients at risk. The general recommendations on diet and lifestyle are considered to be the basis of treatment. Depending on the type of stone and the individual biochemical risk profile of a patient, these general measures should be supplemented by targeted medical nutrition therapy and pharmacological treatment. Mixed stones can pose a challenge for the treatment and prevention of recurrence. A personalized treatment decision that takes the various components of mixed stones into account could further improve the prevention of recurrence of urolithiasis.