CT attenuation value and shockwave fragmentation

PURPOSE: To evaluate whether, in principle, the mean CT attenuation values of kidney stones could predict fragmentation by shockwaves. MATERIALS AND METHODS: Four types of artificial kidney stones having different CT attenuation values were tested. Artificial stones were weighed and exposed to 700 shockwaves at 21 kV at the focus of an electrohydraulic lithotripter. Fragments were strained through meshes with 2x2-mm and 3.1x3.1-mm openings. The material left on the meshes after shockwave exposure was dried and weighed on a precision scale. Half of all artificial stones were saturated by immersing them in water several days before fragmentation. Fragmentation coefficients (i.e., percent weight loss) were associated with CT attenuation values using a statistical model. RESULTS: Higher CT numbers resulted in lower fragmentation coefficients. Artificial stone weight was inversely proportional to the percent weight loss. Larger fragments were obtained at lower fragmentation coefficients. Statistical analysis revealed that fragmentation can be predicted knowing the weight and the CT number of a stone before shockwave application. CONCLUSION: Prediction of the number of shockwaves necessary for successful SWL could be possible. Our statistical model proved to fit in vitro fragmentation of artificial stones; however, clinical application requires further research.     

Acoustic and mechanical properties of artificial stones in comparison to natural kidney stones

PURPOSE: Standardized and reproducible artificial kidney stone models are important for performing comparative studies of different lithotripsy modalities. The acoustic and mechanical properties of renal calculi dictate the manner by which stones interact with the mechanical stresses produced by shock wave lithotripsy (SWL) or intracorporeal lithotripsy modalities. We have developed a novel artificial kidney stone model that is made of natural substances found in real kidney stones. These stone models appear to be much closer in physical properties to natural kidney stones than previously used stone models. MATERIALS AND METHODS: The acoustic and mechanical properties of six groups of artificial stone models were compared to corresponding natural stones of similar compositions. Moreover, three groups of artificial stone models made of plaster-of-Paris were compared to their natural counterparts. In terms of acoustic properties, stone density was measured using a pycnometer based on Archimedes' principle, whereas longitudinal and transverse (or shear) wave propagation speeds were measured using an ultrasound pulse transmission technique. These values were used to calculate wave impedance and dynamic mechanical properties (bulk modulus, Young's modulus, and shear modulus) of the stones. The microhardness of the stones was measured and the effect of composition on stone fragility was evaluated. RESULTS: Artificial stones, when compared to natural stones of similar composition, showed similar trends in longitudinal and transverse wave speeds, wave impedance, and dynamic elastic moduli. However, values for the artificial stones were uniformly low compared to those of natural stones, suggesting that these artificial stones may be more amenable to shock wave fragmentation. The results of SWL on stone fragmentation of artificial and natural stones also revealed similar trends with the exception of artificial cystine stones which were found to be the most resistant to shock wave fragmentation. CONCLUSIONS: The results indicate that the physical properties of artificial stones made of natural stone materials are comparable to renal calculi of the same chemical composition. The data suggests that these stone phantoms are suitable for performing standardized and reproducible in vitro investigations, especially with regards to fragility of kidney stones of different chemical compositions during SWL.     

Cystine calculi: correlation of CT-visible structure,CT number,and stone morphology with fragmentation by shock wave lithotripsy

Cystine stones are often highly resistant to shock wave lithotripsy (SWL), but it has been reported that cystine stones of "rough" morphology are actually quite susceptible to SWL. Based on the observation that rough cystine stones contain void regions that are visible by helical computed tomographic (CT) imaging, we hypothesized that the internal structure of cystine stones would correlate with the susceptibility of stones to SWL. Cystine stones with average diameters between 4 and 7 mm were scanned using micro and helical CT, classified morphologically according to published criteria, and broken in a research electrohydraulic lithotripter, with fragments sieved through a 2 mm mesh every 50 SWs. Stones with regions of low X-ray attenuation visible on helical CT required only 650 +/- 312 SW/g for total comminution, while those that did not show CT-visible internal structure required 1,046 +/- 307 SW/g (mean +/- SD, P < 0.004). In addition, both average and minimum values for CT number (in Hounsfield units, HU) correlated with SW/g to comminution (P < 0.003 and P < 0.0003, respectively), and these relationships were independent of stone size. This study also confirmed the relationship between the morphological criteria of Bhatta et al. (J Urol 142:937-940, 1989) and cystine stone fragility: Rough stones required 609 +/- 244 SW/g (n = 11), smooth stones 1,109 +/- 308 SW/g (n = 8), and stones intermediate in morphology 869 +/- 384 SW/g (n = 7; rough different from smooth, P < 0.005). In conclusion, cystine stones that appeared homogeneous by helical CT required 61% more SWs for comminution than did stones showing regions of low X-ray attenuation. These findings demonstrate the feasibility of using helical CT to identify cystine stones that will be susceptible to SWL.     

A prospective multivariate analysis of factors predicting stone disintegration by extracorporeal shock wave lithotripsy: the value of high-resolution noncontrast computed tomography

OBJECTIVE: To assess the value of noncontrast computed tomography (NCCT) as a possible predictor of renal stone disintegration by shock wave lithotripsy (SWL). PATIENTS AND METHODS: The study included 120 consecutive patients (71 males, 49 females; mean age: 42.6 yr) with a solitary renal stone of 0.5-2.5 cm in length. NCCT was performed using a multidetector row CT scanner at 120 KV and 240 mA, with 1.25-mm collimation. A bone window was used to measure stone attenuation values. SWL was performed with an electromagnetic lithotripter. Failure of disintegration was defined as no fragmentation of the stone after three sessions. The impact of patients' sex, age, and body mass index (BMI) and the stones' laterality, location, volume, mean attenuation value, and the skin-to-stone distance on disintegration were evaluated by univariate and multivariate analyses. RESULTS: Failure of disintegration was observed in 15 patients (12.5%). BMI and stone density >1000 HU were the significant independent predictors of failure (p=0.04 and 0.02, respectively). The success rate of extracorporeal SWL at 3 mo was 87.5% (105 of 120 patients); 90 patients were stone free and 15 had residual fragments<4 mm. The only significant predictor of residual fragments was stone density (p<0.001). CONCLUSIONS: Obesity and increased stone density as detected by NCCT are significant predictors of failure to fragment renal stones by SWL. An alternative treatment should be devised for obese patients with stone density>1000 HU.     

Progress in the use of helical CT for imaging urinary calculi

Helical CT has become the preferred method to diagnose urinary calculi in patients presenting with abdominal or flank pain. Recent in vitro studies have shown that CT also can display the internal structure in stones with remarkable detail. Because some stones respond better to SWL than others, knowing stone structure at diagnosis could be helpful in choosing among treatment options. This paper examines the potential for CT to be used in this way. Older CT technology proved to be problematic, in that all studies using low-resolution CT will suffer from an artifact in which stone size affects apparent CT attenuation values. Thus, the observation that stones with low measured CT attenuation break more easily than stones with high attenuation could be attributable entirely to an artifact of stone size. Most stones are composed of more than one mineral, and heterogeneity of composition may contribute to variability in stone response to SWL. Older technology is not useful in evaluating stone composition, but current and emerging CT machines have sufficient resolution to determine the composition and structure of stones inside the patient, provided proper viewing windows are used. Continuing improvement in image resolution in helical CT promises to provide information about stone composition and structure that will ultimately lead to better care for patients with stone disease.     

Is measurement of stone surface area necessary for SWL treatment of nonstaghorn calculi?

BACKGROUND AND PURPOSE: The size of urinary tract stones is usually assessed by the longest diameter (LD) alone. Logically, however, two-dimensional measurement of the stone surface area (SSA) susceptible to shockwaves would give more useful information for the planning of treatment by extracorporeal shockwave lithotripsy (SWL). This has been shown for staghorn calculi. The aim of this study was to determine for nonstaghorn kidney and ureter stones whether the LD alone identifies as reliably a subgroup of patients with a stone of a certain size as does the SSA. Furthermore, we sought to determine whether the LD alone indicates as reliably the number of patients who would be rendered stone free after one SWL session within a certain subgroup as would the SSA. PATIENTS AND METHODS: Retrospectively, SWL treatment and radiographic data of 330 patients who had undergone SWL for a single stone were analyzed. RESULTS: Ureteral stones were significantly smaller on average, and ureteral stone patients needed fewer SWL treatment sessions and fewer shockwaves to become stone free. Stratification of both kidney and ureteral stones by either LD or SSA resulted in comparable groups of patients. There were no significant differences in patient, stone, or treatment data. More importantly, the stone-free rates after one treatment did not differ significantly. CONCLUSION: The LD does accurately reflect the size of a nonstaghorn kidney or ureteral stones. Therefore, the measurement of LD, as generally practiced, appears clinically sufficient and appropriate for the assessment of stone size prior to SWL in both kidney and ureteral stones.     

The use of chemical treatments for improved comminution of artificial stones

PURPOSE: The acoustic and mechanical properties of various stone compositions are significantly different and thus result in varying degrees of fragility. Consequently, results to shock wave lithotripsy (SWL) are influenced accordingly. We report the results of a study of fragility of various stone compositions, and the influence on each stone's baseline physical properties and fragility when exposed to various chemolytic solutions. MATERIALS AND METHODS: Before SWL artificial stones of differing compositions were irrigated with various chemolytic solutions. Calcium oxalate monohydrate (COM) stones were treated with ethylenediaminetetraacetic acid (EDTA), stones composed of magnesium ammonium phosphate hydrogen were treated with hemiacidrin, and stones made of uric acid (UA) were treated with tromethamine. Synthetic urine served as a control for all stone groups. Using an ultrasound transmission technique, longitudinal wave propagation speed was measured in all groups of artificial stones. Stone density was also measured by using a pycnometer (based on Archimedes' principle). Based on these measurements transverse (shear) wave speed (assuming a constant Poisson's ratio), wave impedance and dynamic mechanical properties of the artificial stones were calculated. Moreover, the microhardness of these artificial stones was measured, and fragility testing using SWL with and without pretreatment with the previously mentioned chemolytic solutions, was performed. RESULTS: Wave speed, wave impedance, dynamic mechanical properties and microhardness of EDTA treated COM stones and tromethamine treated UA stones were found to decrease compared to untreated (synthetic urine) control groups. The suggestion that chemolytic pretreatment increases stone fragility was verified by the finding of increased stone comminution after SWL testing. Combining this medical pretreatment and SWL, the findings demonstrate a significant impact of various solvents on stone comminution, in particular EDTA treated COM stones, tromethamine treated UA stones and hemiacidrin treated magnesium ammonium phosphate hydrogen stones. These data suggest that by altering the chemical environment of the fluid surrounding the stones it is possible to increase the fragility of renal calculi in vitro. CONCLUSIONS: These results indicate that appropriate chemical treatments may provide a useful adjunctive modality for improving the efficacy of stone comminution during shock wave lithotripsy.     

Extracorporeal shockwave lithotripsy for kidney stones reduces blood pressure: use of 24-hour ambulatory monitoring for study of blood-pressure changes induced by SWL

PURPOSE: To investigate the effects of shockwave lithotripsy (SWL) on blood pressure with the use of 24-hour ambulatory blood-pressure monitoring (ABPM). PATIENTS AND METHODS: We studied three groups of patients. Group I consisted of 60 patients with kidney stones treated with SWL. Group II was formed by 30 patients with stones in the lower third of the ureter treated in situ with SWL, and group III consisted of 30 patients with ureteral stones treated with ureteroscopy (URS). The ABPM measurements were performed before stone treatment, immediately after, and then every 3 months through 1 year. RESULTS: There was no new onset of hypertension in any group. The prevalences of hypertension before stone treatment were 21 (35%), 12 (40%), and 9 (30%) for groups I, II, and III, respectively. One-year post treatment, the numbers of hypertensive patients found for groups I, II, and III were 15 (25%), 11 (33.3%), and 8 (22.2%), respectively. In group I, a statistically significant decrease in blood pressure values was noted 1 year post-treatment (p<0.05). This decrease was related (p<0.05) to the power (r=0.35), as well as to the product of the number and the power (r=0.25), of the shockwaves applied. CONCLUSION: Extracorporeal lithotripsy for kidney stone may be responsible for a drop in blood pressure possibly caused by alteration in intrarenal metabolism.     

Influence of alkaline solutions on chemolitholysis and lithotripsy of uric acid stones. An in vitro study

OBJECTIVES: This study was performed to look for an improvement of therapeutic strategies with regard to the treatment of uric acid stones using artificial stones made of uric acid (BON(N)-STONES) which are comparable to their natural counterparts. MATERIALS AND METHODS: Using an experimental arrangement simulating the physiological conditions in the upper urinary tract the efficacy of different alkaline solutions and artificial urine in dissolving artificial uric acid stones (BON(N)-STONES) was investigated. The dissolution of natural uric acid stones was measured and investigations on shock wave lithotripsy (SWL) combined with initial chemolytic treatment of the stones were performed. RESULTS: The efficacy of alkaline solutions, especially THAM at a pH of 10, in dissolving artificial uric acid stones was demonstrated. The investigations on SWL showed a significant improvement on stone comminution of artificial uric acid stones after initial chemolytic treatment with THAM. CONCLUSIONS: New basics to improve dissolution of uric acid stones have been developed by performing standardized in vitro investigations. The suggestion was confirmed that stone fragility and thus SWL can be improved by varying the physical properties of uric acid stones through initial treatment with THAM solution.     

Ordnance gelatine as an in vitro tissue simulation scaffold for extracorporeal shock wave lithotripsy

In vitro shock wave lithotripsy (SWL) research is typically performed utilizing wet coupling lithotriptors with a mesh basket model. This model does not take into account shock wave energy attenuation through tissue. Models using dry coupling lithotriptors rely on immersion chambers and face similar limitations. Ordnance gelatin (OG) displays strength and viscous properties similar to human tissue and is therefore widely used for ballistic tissue injury research. We present our initial experience using an OG tissue simulating scaffold for dry coupling SWL research. Using 10% OG prepared in a disc-shaped mold (five stone wells/gel), we tested the model using a Modulith SLX-F2 lithotriptor and artificial stone phantoms. Following a test of concept run on an empty gel mold and a material integrity check for leakage, we shocked 60 stones (30 narrow focus [NF], 30 wide focus [WF]) in human pooled urine. Half were shocked using gels containing open-ended wells with the remainder closed-ended wells. Fragmentation coefficients (FC) were calculated across both foci and gel models. All gels successfully completed 5,000 shocks (1,000/well) without loss of gel integrity or fluid leakage. The mean FC using open-ended wells was 77.9 ± 7.6% NF and 74.4 ± 4.8% WF, and for closed wells 75.9 ± 8.0% NF and 67.1 ± 3.5% WF. The total model cost including the preparation of gels and begostones was assessed at approximately $1 per stone (Canadian). Ordnance gel serves as an excellent surrogate tissue shockwave scaffold providing an easily manufactured, reproducible and inexpensive model for dry coupling SWL research.     

Chemolitholysis and lithotripsy of infectious urinary stones - an in vitro study

OBJECTIVES: This study was performed to look for an improvement of therapeutic strategies with regard to the treatment of infectious urinary stones using artificial stones made of struvite and apatite ('Bon(n) stones') which are comparable to their natural counterparts. MATERIALS AND METHODS: Using an experimental arrangement simulating the physiological conditions in the upper urinary tract, the efficacy of artificial urine (pH 5.7), Suby G solution (pH 3.6), mixtures of artificial urine with Suby G (pH 3.9 and pH 4.1) in dissolving artificial struvite and apatite stones (Bon(n) stones) was investigated. The dissolution of natural infectious urinary stones was also measured. Additionally, investigations on shock-wave lithotripsy (SWL) combined with initial chemolytic treatment of the stones were performed. RESULTS: The efficacy of Suby G solution in dissolving artificial stones was demonstrated. Direct comparison of chemolysis of natural and artificial stones showed no statistical difference between infectious urinary stones and Bon(n) stones of the same material. The investigations on SWL showed a significant improvement on stone comminution, especially of artificial apatite stones after initial chemolytic treatment with Suby G. CONCLUSION: New basics to improve dissolution of infectious urinary stones have been developed by performing standardized in vitro investigations. Local chemolysis with Suby G is an effective tool in the treatment of infectious stone disease. SWL can be improved by varying the physical properties of infectious stones through initial treatment with Suby G solution.     

Benefits of ureteroscopic pneumatic lithotripsy for the treatment of impacted ureteral stones.

PURPOSE: Although new forms of lithotripsy, such as new-generation shockwave and laser lithotripsies, have recently been developed, the optimal treatment for impacted ureteral stones (IUS) remains controversial. We investigated, retrospectively, the outcome of IUS treated with ureteroscopic pneumatic lithotripsy. PATIENTS AND METHODS: Twenty-two IUS cases were treated using ureteroscopic pneumatic lithotripsy. Of 22 stones, 8 (36%) were treated by ureteroscopic pneumatic lithotripsy as initial treatment and 14 (64%) with pneumatic lithotripsy as an auxiliary treatment after SWL. The stone sizes ranged from 7 to 16 mm with 14 located in the proximal, 3 in the middle, and 5 in the distal ureter. RESULTS: Twenty stones (91%) were effectively fragmented by ureteroscopic pneumatic lithotripsy and eliminated within 1 month after treatment. One stone could not be observed with the ureteroscope secondary to the kinking and stricture of the ureter under the stone, and the stone moved into the kidney during the procedure. The stone was subsequently treated successfully with SWL. One other stone was first fragmented into two pieces; and one big piece, which migrated into the kidney, was treated successfully with SWL. Complications such as bleeding, ureteral injury, and perforation did not occur. Although a few small fragments migrated into the kidney during the procedure in three cases, the overall stone-free rate at 1 month after a one-session treatment with pneumatic lithotripsy was 91%. CONCLUSION: Impacted ureteral stones can be treated effectively with ureteroscopic pneumatic lithotripsy in both the short and the long term.     

Calcium stone fragility is predicted by helical CT attenuation values

BACKGROUND AND PURPOSE: Helical CT has become the preferred method for imaging urinary calculi, and so it would be useful if data from helical CT could also be used to predict the number of shockwaves (SWs) needed to break a given stone. METHODS AND MATERIALS: We measured the number of SWs required to comminute calcium stones in vitro. RESULTS: The SW requirement correlated with stone size (volume, weight, diameter) and with helical CT attenuation values when the scans were performed at 3-mm collimation. When CT scans were performed at 1-mm collimation, the number of SWs needed for comminution did not correlate with helical CT attenuation values. This result indicates that the correlation with 3-mm scans was attributable to volume-averaging effects, in which smaller stones yield smaller attenuation values. That is, attenuation values from helical CT at larger beam collimation widths contain information about stone size that can be exploited to predict the fragility of calcium stones. We observed that for calcium stones, the number of SWs to comminution was generally less than half the stone CT attenuation value in Hounsfield units. This "half-attenuation rule" predicted the number of SWs needed to complete fragmentation for 95% of calcium stones (24/24 calcium oxalate monohydrate, 13/13 hydroxyapatite, 8/10 brushite stones). CONCLUSION: This in vitro study suggests that it may be possible to predict effective SW dose using helical CT prior to lithotripsy.     

A practical formula to predict the stone-free rate of patients undergoing extracorporeal shock wave lithotripsy

ObjectivesWe studied patients who underwent extracorporeal shock wave lithotripsy (SWL) to investigate the factors influencing the outcome, and built a logistic regression model to estimate the stone-free rate (SFR) after SWL.Material and methodsFrom January 2013 to December 2013, we retrospectively reviewed the clinical status of 641 patients with a solitary urinary calculus who underwent SWL in our hospital. Univariate logistic regression was used to identify the factors leading to a high SFR, and significant factors were further analyzed by multivariate logistic regression. After the optimal model had been developed, we placed it on the website so others could calculate the SFR at their institutions.ResultsThe overall SFR for all patients, patients with ureteral stones, and patients with renal stones were 54.8%, 67.8%, and 46.7%, respectively. Multivariate logistic regression showed that body mass index (BMI), stone length, stone width, and stone location were the independent factors that affected the overall successful rate. Stone length was the only significant factor to predict SFR for ureteral stones. BMI, stone length, and stone width were significant SFR predictors for renal stones. A logistic regression model was designed to estimate SFR, which has a sensitivity of 77.8% and specificity of 75.5%.ConclusionBMI, stone length, stone width, and kidney and ureteral stones were all prognostic factors influencing the outcome of SWL. We built a logistic regression formula to predict the SFR, which helps urologists to select patients for SWL.     

Percutaneous stone implantation in the pig kidney: a new animal model for lithotripsy research

PURPOSE: This report describes a new animal model for research on the parameters of shockwave delivery and the mechanisms of shockwave action in SWL. MATERIALS AND METHODS: Female pigs (approximately 45 kg) were anesthetized for creation of an upper pole peripheral caliceal access. The tract was dilated with a 30F Nephromax balloon and Amplatz sheath, and a 24F rigid nephroscope was used to guide a gypsum artificial stone into a lower pole calix. An internal ureteral stent was then placed. After a 2-hour recovery period, lithotripsy was performed using an unmodified Dornier HM3 lithotripter. Following SWL, en bloc excision of the urinary tract was performed, and the stone fragments were collected. RESULTS: As observed by nephroscopy, most stones were surrounded by urine that was free of clot or debris. Urine output was >1 mL/kg per minute by the time the animal was positioned for SWL after a 2-hour observation period. When the conditions of shockwave (SW) exposure were 400 SWs, 20 kV, and 120 SW/min, the efficiency of stone fragment recovery was 85% +/- 2% (N = 6 stones). CONCLUSIONS: This procedure provides a minimally invasive method for placement of model stones of clinically relevant size within the pig kidney. Stone implantation is efficient and permits experiments to be conducted in 1 day. Stone fragmentation can be quantitated, and the animal can serve as its own control. Long-term experiments are also feasible. Overall, this new animal model is appropriate for experimentation on the parameters of SW delivery in SWL.     

The impact of caliceal pelvic anatomy on stone clearance after shock wave lithotripsy for pediatric lower pole stones

PURPOSE: The clearance rather than stone disintegration of lower pole stones after shock wave lithotripsy (SWL) is significantly inferior according to the other localizations of the kidney. We retrospectively evaluated the impact of caliceal pelvic anatomy on stone clearance after SWL for pediatric lower pole stones. MATERIALS AND METHODS: We treated 163 renal units (RUs) in children 16 years old or younger with SWL between March 1992 and February 2002. In 36 RUs stones were localized in the lower calices. All patients were treated with sedoanalgesia except 3 (8%) who were treated under general anesthesia. Patients were evaluated by excretory urography and ultrasonography 12 weeks after the last session, and were designated as stone-free or with residual stone. The lower infundibular length, width, length-to-width ratio, pelvic caliceal height and lower infundibulopelvic angle were determined on standard excretory urography before SWL. All measurements were done by 1 urologist who was unaware of the results. Statistical analysis was performed with chi-square, Fisher's exact and Mann-Whitney U tests. ROC analysis was done to determine the cutoff points of caliceal anatomy measurements for stone clearance. RESULTS: We treated 36 RUs in 23 males and 10 females with isolated lower caliceal stones. Median patient age was 10.5 years (range 2 to 16). Median stone burden was 0.7 cm (range 0.2 to 4), and median number of shock waves and energy used for the entire patient population was 1,500 and 17.2 kV, respectively. Overall stone-free rates for the 36 RUs were 61% after a median treatment session of 1 (range 1 to 7) and retreatment rates were 39%. Of the patients rendered free of stones 13 (59%) were treated in a single SWL session and 9 (41%) underwent 2 or more sessions. Median lower infundibular length, width, length-to-width ratio and pelvic caliceal height in the stone-free and residual stone group were 25.5, 28.0 mm, 4.5, 5.0 mm, 6.4, 5.5 mm and 21.5, 21.5 mm, respectively (p = 0.810, 0.327, 0.511 and 0.511). Median lower infundibulopelvic angle in the stone-free and residual stone groups was 92.50 and 92.50 degrees, and 60.0 and 54.50 degrees, respectively (p = 0.860 and 0.089). On ROC analysis no parameter predicting stone-free rate and cutoff points of caliceal anatomy measurements for stone clearance was found. CONCLUSIONS: Our results suggest that caliceal pelvic anatomy in pediatric lower pole stones has no significant impact on stone clearance after SWL. There was a highly significant relation between retreatment rates and stone burden, which should be considered for determining the treatment modality.     

Effect of potassium citrate therapy on stone recurrence and residual fragments after shockwave lithotripsy in lower caliceal calcium oxalate urolithiasis: a randomized controlled trial

BACKGROUND AND PURPOSE: To evaluate the efficacy of potassium citrate treatment in preventing stone recurrences and residual fragments after shockwave lithotripsy (SWL) for lower pole calcium oxalate urolithiasis. PATIENTS AND METHODS: One hundred ten patients who underwent SWL because of lower caliceal stones and who were stone free or who had residual stone 4 weeks later were enrolled in the study. The average patient age was 41.7 years. All patients had documented simple calcium oxalate lithiasis without urinary tract infection and with normal renal morphology and function. Four weeks after SWL, patients who were stone free (N = 56) and patients who had residual stones (N = 34) were independently randomized into two subgroups that were matched for sex, age, and urinary values of citrate, calcium, and uric acid. One group was given oral potassium citrate 60 mEq per day, and the other group served as controls. RESULTS: In patients who were stone free after SWL and receiving medical treatment, the stone recurrence rate at 12 months was 0 whereas untreated patients showed a 28.5% stone recurrence rate (P < 0.05). Similarly, in the residual fragment group, the medically treated patients had a significantly greater remission rate than the untreated patients (44.5 v 12.5%; P < 0.05). CONCLUSION: Potassium citrate therapy significantly alleviated calcium oxalate stone activity after SWL for lower pole stones in patients who were stone free. An important observation was the beneficial effect of medical treatment on stone activity after SWL among patients with residual calculi.     

Urolithiasis update: Evaluation and management

Urolithiasis is a worldwide disease which has affected humans from ancient eras to modern times. Recently, societal changes have altered the epidemiology of urinary calculi. The incidence of urolithiasis is higher in industrialized countries. Obese people are known to have a higher risk of stone formation. Metabolic syndrome has resulted in an increasing rate of nephrolithiasis among women. There are many useful tools for diagnosing urolithiasis, including conventional plain radiography, intravenous urography, ultrasonography, computed tomography (CT), and nuclear medicine. Nonenhanced CT has high sensitivities and specificities. It can be rapidly performed without intravenous administration of contrast material and can therefore be used in patients with severely impaired renal function. Beyond that, it can reveal extraurinary causes of flank pain. However, concerns about radiation exposure and costs remain. Since ancient times, hundreds of natural plant extracts and more recently, synthetic chemicals have been proposed to eliminate urinary calculi. Clinical trials demonstrated that calcium channel blockers and adrenergic antagonists are effective in enhancing stone passage. Shock wave lithotripsy (SWL) can successfully treat renal calculi. A meta-analysis study revealed that SWL is more effective in treating urinary calculi with a lower-frequency mode. Highly dense stones are more refractory to SWL. The stone composition can be evaluated by preoperative CT attenuation values. Patients with preoperative Houndsfield units (HUs) of >750 have a 10.5-times greater chance of needing three or more sessions of SWL treatment compared to patients whose HUs are <750. Ureteroscopy is a safe treatment for managing ureter stones when performed by experienced hands and ureteroscopy is preferred over SWL in patients with a larger upper-ureter stone, those who are pregnancy, and those with bleeding diathesis.     

Is stone clearance after shockwave lithotripsy in patients with solitary upper-caliceal stone influenced by anatomic differences in the pelvicaliceal system?

PURPOSE: We investigated the effect of pelvicaliceal differences on stone clearance after extracorporeal shockwave lithotripsy (SWL) in patients with solitary upper-caliceal stones. PATIENTS AND METHODS: The clinical records of patients with solitary upper-caliceal stones who underwent SWL between 1996 and 2004 were reviewed. After excluding patients with hydronephrosis, significant anatomic abnormalities, non-calcium stones, metabolic abnormalities, recurrent stone disease, multiple stones, and previous renal surgery, 42 patients with a mean stone size of 153.47 mm2 (range 20-896 mm2) were enrolled in this study. They were divided into three groups according to stone burden (group 1 < or =100 mm2, group 2,101 mm2-200 mm2, and group 3 >200 mm2). Upper-pole infundibulopelvic angle (IPA), infundibular length (IL), and infundibular width (IW) were measured from intravenous urograms. Results: Of the total, 29 patients (69%) were stone free after SWL treatment. The differences in the upperpole IPA, IL, and IW of stone-free patients and patients with residual stones were not statistically significant (P = 0.85, P = 0.89, and P = 0.37, respectively). Again, there were no statistically significant differences in terms of upper IPA, IW, and IL in comparing the three groups divided by initial stone size. Conclusion: Upper-caliceal anatomy does not exert a significant impact on stone clearance after SWL for isolated upper-caliceal stones. To best of our knowledge, this is the first study to investigate the effects of pelvicaliceal anatomy on SWL treatment for upper-caliceal stones, so there is a need for further investigations to confirm our findings.     

The effect of fat and nonfat components of the skin-to-stone distance on shockwave lithotripsy outcome

BACKGROUND: Few studies have addressed the effect of skin-to-stone distance (SSD) on the success of extracorporeal shockwave lithotripsy (SWL). Nevertheless, the effect of the two components of SSD, that is, the fat SSD (FSSD) and nonfat SSD (NFSSD) components, was not previously investigated. Methods: In this prospective study, all patients (n = 113) who had single radio-opaque kidney stones and underwent SWL for the first time between January 2006 and June 2007 were recruited. SSD, FSSD, and NFSSD were measured by noncontrast CT scan at 0°, 45°, and 90° and the average was calculated. The outcome was defined as successful (completely stone free or residual fragments ≤ 3 mm) or unsuccessful (residual fragments > 3 mm or complete failure of fragmentation). RESULTS: Sixty-nine (61%) patients had successful treatment. On univariate analysis, SSD, FSSD, and NFSSD were significantly lower in the successful group compared with those with unsuccessful outcome (71.9 ± 13.3 vs. 86.2 ± 25.1 mm [p = 0.001], 27.2 ± 10.3 vs. 36.1 ± 17.3 mm [p = 0.011], and 44.7 ± 7.2 vs. 50.1 ± 13.9 mm [p = 0.02], respectively). The muscle component of the NFSSD was also lower in the successful group (21.5 ± 4.1 vs. 25.2 ± 10.0 mm [p = 0.01]). On multivariate analysis, factors that independently predicted treatment success were SSD, stone attenuation, and stone size but not the FSSD or NFSSD. Conclusions: Although the total SSD appeared to be a significant predictor of SWL success, its fat and nonfat components did not independently predict the final outcome and only appeared to be important through their contribution to the total SSD.