Objectives: To evaluate the radiological characteristics of renal stones on plain X-ray film of the kidneys, ureters and bladder (KUB) area as predictors of stone fragility during shock wave lithotripsy (SWL).Patients and Methods: This prospective study included 336 patients who had a single renal pelvic stone .20 mm and were managed by SWL at 3 different centers. The patients were classified according to the radiological appearance of the stone on KUB film in terms of homogeneity,smoothness of the outline, and radiodensity in comparison to the last rib. The primary endpoint was the stone-free rate (SFR) within 3 months post-SWL. Multivariate regression analysis was used to compare the results.Results: The overall SFR was 71.43%. SFR was significantly higher in heterogeneous compared with homogenous stones (86% vs. 53%; 

Abdel Hafez, A

Elkoushy, MA

Nady, M

Salah, E

English

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African Journal of Urology1110-5704Vol. 17, No. 2, 201137      37-42Original article Predicting The Fragility Of Renal Calculi In Response To Shock Wave Lithotripsy Through Their Radiographic AppearanceMA Elkoushy1, M. Nady2, A. Abdel Hafez3, E. Salah2Departments of Urology, 1Suez Canal (Ismailia), 2Al-Azhar (Assiut), and 3Sohag Universities, EgyptABSTRACTObjectives: To evaluate the radiological characteristics of renal stones on plain X-ray film of the kidneys, ureters and bladder (KUB) area as predictors of stone fragility during shock wave lithotripsy (SWL).Patients and Methods: This prospective study included 336 patients who had a single renal pelvic stone ≤20 mm and were managed by SWL at 3 different centers.  The patients were classified according to the radiological appearance of the stone on KUB film in terms of homogeneity, smoothness of the outline, and radiodensity in comparison to the last rib. The primary endpoint was the stone-free rate (SFR) within 3 months post-SWL. Multivariate regression analysis was used to compare the results.Results: The overall SFR was 71.43%. SFR was significantly higher in heterogeneous compared with homogenous stones (86% vs. 53%; p<0.01) and in rough compared with smooth surface calculi (77% vs. 61%, p<0.01). SFRs for stones with density less than, similar to or higher than that of the last rib were 82%, 69% and 56%, respectively (p<0.01). Multivariate analysis showed a positive proportional relationship between stone fragility (SWL outcome) and one or more favorable radiological criteria. Conclusion: The radiological characteristics of renal calculi could predict their fragility after SWL. Stones which were heterogeneous, rough, or less dense than the last rib on KUB film were more likely to disintegrate during SWL.Key Words: Shock wave lithotripsy, renal calculi, radiography, urolithiasis                     Corresponding Author: Dr. Mohamed Ali Elkoushy, Department of Urology, Suez Canal University, Ismailia, Egypt, Email: melkoushy@yahoo.com  Article Info: Date received: 25 January 2011                        Date accepted (after revision): 11 April 2011 INTRODUCTION                                                    Shock Wave Lithotripsy (SWL) has radically changed the management of urolithiasis since its introduction in the early 1980s. It replaced most other treatment modalities for upper urinary tract calculi as a safe, effective, reliable, non-invasive outpatient procedure. SWL is suitable as single modality for treatment of 70% of non-selected upper urinary stones and in combination with other endourologic procedures in 20% of complex upper tract stones1. A Kidneys Ureters and Bladder (KUB) film is often required to plan lithotripsy treatment in which the appearance of the stone (size, shape and radiodensity) is often used to predict the success of therapy2,3. However, compared with other stone characteristics, the relative importance of stone radiodensity in predicting treatment outcome remains to be proved. The aim of this study was to determine pre-therapeutic criteria that would predict results in term of stone clearance after SWL.38PREDICTION OF STONE FRAGILITY FOR SWL BY PLAIN RADIOGRAPHYrepeated biweekly until the patients became stone-free, or for a maximum of 3 sessions if not stone-free. All the radiological parameters of stones were evaluated by a fixed team consisted of 2 authors and a radiologist to avoid inter-observer bias. Patients were evaluated after one week and then bi-weekly by history and clinical examination together with KUB and AUS to evaluate the presence of complications and to assess stone clearance. The treatment was terminated if satisfactory fragmentation was achieved.  Failure of SWL was considered if the stone did not fragment well after 3 SWL sessions and/or had not cleared within 3 months from the date of the first session. The patients were then redirected for alternative stone management. Data analysis was performed using the commercially available SPSS for Windows version 17 (Chicago, IL). Descriptive data were presented as means and standard deviation. Fisher’s exact test was used for comparing SFR between groups (2-tailed p<0.05 accepted as statistically significant). Factors with significant impact on SFR in univariate analysis were further analyzed using multivariate analysis.RESULTS                                                            Sixty five percent of the patients were males with a mean age of was 39 ± 4.4 (range 18 – 51) years and a mean body mass PATIENTS AND METHODS                                     This multicenter prospective study included 336 patients with single renal pelvic stones ≤20 mm in the largest diameter treated at 3 different centers. SWL was done using the electromagnetic Siemens Lithostar lithotripter. The exclusion criteria were age <16 years, stone >20 mm in largest diameter, multiple calculi, radiolucent stones, morbid obesity, uncorrectable bleeding disorders, associated distal obstruction, and previous SWL failure.Patients were evaluated with full history, clinical examination and urinalysis with culture and sensitivity when indicated [culture was obtained in 105 (31.1%) patients with pyuria]. Laboratory investigations included serum creatinine, blood sugar, full blood count, liver enzymes and coagulation profile. Electrocardiography was performed in all patients.  Imaging studies included KUB,  Intavenous Urography (IVU) and Abdominal Ultrasound (AUS).  All patients were informed about their treatment options including success rate, the need for retreatment, the expected time needed for stone clearance, analgesia, risks and possible complications. SWL was started at a low energy level (10 Kv) and after 100-200 shocks the energy was gradually increased in a stepwise manner to the highest level the patient could tolerate. Intravenous sedation in the form of pethidine 50 mg infusion was administered and the calculus was monitored fluoroscopically. The procedure was terminated when disintegration was satisfactory or when 4000 shock waves had been given at 14-15 Kv. Radiological characteristics of the stone were assessed on the KUB in terms of the homogeneity of its texture, smoothness of its surface, and its radiodensity in comparison to the last rib (Table 1). Stone-free rate was defined as complete clearance of the stone fragments or the presence of clinically non-obstructing fragments ≤3 mm. SWL was Table 1: Radiological characteristics of stonesRadiological characteristic Number %Texture Homogenous 147 43.8Heterogeneous 189 56.3SurfaceSmooth 123 36.6Rough 213 63.4Radiodensityin relationto last ribLess dense 147 43.8Similar 108 32.1More dense 81 24.1Total 336 100.039PREDICTION OF STONE FRAGILITY FOR SWL BY PLAIN RADIOGRAPHYindex of 29.7 ± 8.4 kg/m2 and a mean stone size of 12 ± 2.3 mm. The overall SFR was 71.43%. The SFR of renal pelvic stones after SWL was stratified according to their radiological appearance (Table 2). In terms of stone texture, patients who had heterogenous calculi had a higher SFR than those with homogeneous stones (86% vs. 53%; p<0.01). In terms of stone surface, patients with rough stones had a higher SFR than those with smooth stones (78% vs. 61%, p<0.01) even after adjustment for stone size. The lower the density of the stone (compared to the last rib), the greater the SFR (p< 0.01) even after correction for stone size (Table 2). There was no statistical difference between groups in terms of number of shock waves required for successful clearance (p=0.2).Multivariate analysis showed that both radiographic criteria (stone density, smoothness and homogeneity) as well as stone size had a prognostic impact on SWL outcome (Table 3). There was a positive proportional relationship between stone fragility and one or more favorable radiological criteria (Fig. 1). SFR approached 100% for heterogeneous, rough and less dense stones <15 mm in size. On the contrary, homogenous, smooth, highly dense and large stones had a lower SFR after SWL.DISCUSSION                                                             SWL is a widely accepted, noninvasive option for the treatment of urinary calculi, although contemporary success rates have a broad range (46 to 91% with efficiency quotient 0.36-0.67)4-9. This is due to many factors including the type of lithotripter used, accurate focusing, operator experience and the stone characteristics. Radiographic appearance, stone size, multiplicity, location and chemical composition of the calculi have a pronounced impact on the results of SWL10. The sensitivity and specificity of radiological parameters for prediction of treatment success were determined by some authors to be 84.2% and 80.6%, respectively11. There is a relationship between the composition of calculi, their radiographic appearance and SWL results. Calculi predominantly formed of calcium oxalate dihydrate (COD) have been described as rough with a density lower than or equal to that of bone, and have a favorable SWL prognosis. Conversely, calculi predominantly formed of calcium oxalate monohydrate (COM) have been described as homogenous, denser than bone, with smooth surface and unfavorable SWL prognosis. The effect of stone composition on resistance to shock waves has been characterized by its appearance on KUB films2,12,13. Thus, it is possible to predict, to a great extent, the chemical composition of a stone by KUB or computed tomography12, 14 . p-valueResidual stonesNo (%)Stone-freeNo (%)Radiological characteristic0.000169 (46.9)78 (53.1)Homogenous Texture27 (14.3)162 (85.7)Heterogeneous0.00248 (39.0)75 (61.0)SmoothSurface48 (22.5)165 (77.5)Rough0.00127 (18.4)120 (81.6)Less denseRadiodensityin relationto last rib33 (30.6)75 (69.4)Similar36 (44.4)45 (55.6)More denseNA96 (28.57)240 (71.43)TotalTable 2: Stone-free rates after SWL stratified by radiological stone characteristics40PREDICTION OF STONE FRAGILITY FOR SWL BY PLAIN RADIOGRAPHYStone composition is an independent variable that may be useful to predict SWL success. The concept that renal stones of different types have variable susceptibility to shock waves has been appreciated since SWL came into common use, and this was termed “stone fragility”. If stone fragility could be predicted before treatment, stones that would not break easily by SWL could be treated by other methods. Stone fragility is related to stone composition: uric acid stone require the fewest shock waves to break, while cystine stones are least fragile15.  In line with the present study, others have found that stones up to 15 mm in diameter that are more radio-dense than bone are difficult to break whereas those less dense are more likely to break with SWL16.  Spiral CT scan has been used to predict stone fragility. Stone density >1000 HU indicates less fragility with poor results after SWL, while density <600 HU predicts for successful SWL, independent of stone size and location5, 17. Clearance rates following SWL with stone attenuation values <500 HU are as high as 98%, with 500-1000 HU 67% and >1000 HU only 54%17.  Stones with attenuation >1000 HU should receive a greater number of shock waves or be treated with another modality (e.g. ureteroscopy or percutaneous nephrolithotomy) to save cost and renal damage from excess inefficient shock waves17.Stone fragility in response to SWL shows marked variability and even knowledge of major stone composition does not allow adequate prediction of its fragility to SWL. The CT attenuation value of kidney stones is affected by several factors such as the size of the stone, its composition, the energy of the CT machine and the slice thickness (collimation) used to image the stone18.  Mattelaer and colleagues observed that high radio-density stones needed an average Table 3: Multivariate analysis of factors affecting stone-free rate after SWLVariablesStone freeMean ± SD/ No (%)ResidualsMean ± SD/ No (%) p-valueAge (yrs) 39.1 ± 7.8 43.0 ± 5.7 0.79Mean stone size (mm) 10.5 ± 1.7 11.7 ± 2.1 0.01Fluoroscopy time (min) 2.2 ± 1.2 2.4 ± 1.3 0.18Energy Used 6.7 ± 0.9 6.9 ± 1.2 0.09Total number of shocks 3893 ± 51 3978 ± 193 0.21SexMale   132   (25.9) 56    (74.1)0.10Female 108   (19.0) 40    (81.0)LateralityLeft 142  (29.0) 55   (71.0)0.001Right 98   (16.4) 41    (83.6)Radiological characteristicHomogenous 78 (53.1) 69 (46.9)0.01Heterogeneous 162 (85.7) 27 (14.3)Smooth 75 (61.0) 48 (39.0)0.03Rough 165 (77.5) 48 (22.5)Less dense 120 (81.6) 27 (18.4)0.01Similar 75 (69.4) 33 (30.6)More dense 45 (55.6) 36 (44.4)41PREDICTION OF STONE FRAGILITY FOR SWL BY PLAIN RADIOGRAPHYof 1.7 times more shock waves than low radio-density stones of the same size to attain comparable stone free rates19. CT attenuation values at small collimation (1-3 mm) have greater ability to predict stone composition in vitro, but this remains to be verified in clinical practice20. Uric acid calculi may be differentiated from calcium stones based on their HU, but this distinction can also be made by characteristic radiodensity of that stone type on the KUB film plus urinary pH3. Recently, Arshadi and colleagues assessed the accuracy of radiological characteristics in estimating the success rate of SWL in patients with kidney calculi and concluded that calculus density compared with the adjacent bone, and calculus shape could predict the success rate of SWL11. These findings support the results in the present series. Bon et al reported that dense, smooth calculi larger than 15 mm and located in the lower calyx were characterized by unfavorable prognosis for SWL21. They reported that the SFR was 79.4% for rough, less dense calculi and 33.6% for smooth or denser calculi.  SWL success rate was 65% for COD stones which are rough and less dense versus 41% for COM stones which are homogenous and of higher density21. The present study showed that the overall SFRs were 82%, 69% and 56% for stones with density lower than, similar to or greater than bone density, respectively. Aeberli et al found no correlation between stone radiodensity and disintegration, but their results were not stratified according to stone size and location22. Krishnamurthy et al found that stone radiodensity alone did not predict the SWL outcome for stones <10 mm in the renal pelvis. However, with increased stone size >10 mm, this parameter was useful and could be used in combination with other stone parameters to select appropriate therapy23.CONCLUSIONS                                                      The efficacy of SWL in the management of renal stones is related to the radiological Fig. 1: R = Rough, S = Smooth, L = Less dense, D = Similar density to rib, H = Hyperdense, T = Heterogeneous, M= Homogenous* One favourable radiological criterion, ** Two favourable radiological criteria,*** Three favourable radiological criteria.0102030405060708090100RLT (60)***SLT (24) **SHT (14)*RDT (36)**RHT (31)**SDT (26)*RDM (29)*RLM (47) **SLM (16)* SDM (17)RHM (10)*SHM (26)Radiographic Characteristics of Stones in KUBPercetages of SFR% Successful % Failure42PREDICTION OF STONE FRAGILITY FOR SWL BY PLAIN RADIOGRAPHYcharacteristics of the stone which reflect its composition and fragility, such as homogeneity, smoothness and radiodensity in relation to the last rib. 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Predicting The Fragility Of Renal Calculi In Response To Shock Wave Lithotripsy Through Their Radiographic Appearance

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Predicting The Fragility Of Renal Calculi In Response To Shock Wave Lithotripsy Through Their Radiographic Appearance

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