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Saudi Journal of Kidney Diseases and Transplantation
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Year : 2010  |  Volume : 21  |  Issue : 4  |  Page : 660-665
Factors affecting urinary calculi treatment by extracorporeal shock wave lithotripsy

Department of Diagnostic Radiology and Urological Surgery, Jordan University Hospital, Amman, Jordan

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Date of Web Publication26-Jun-2010


Extracorporeal Shock Wave Lithotripsy (ESWL) is still the treatment of choice for most renal and upper ureteric stones; however the outcome depends on multiple factors. The objective of this study was to investigate the effects of stone density, as measured by Hounsfield Units (H.U) by non-contrast Computerized Tomography (CT), stone size and stone location on ESWL treatment outcome of urinary calculi in Jordanian patients. 65 patients underwent clinical, biochemical and radiological assessments followed by ESWL treatment. Statistical analyses including chi-square, analysis of variance (ANOVA), correlation, regression were performed for statistical significance between ESWL treatment, stone fragmentation and stone density, size and location in the renal pelvis. ESWL success rate was high (94%) for low density stones (< 500 Hounsfield units). In general CT densities of 750 Hounsfield units or less were almost always successfully treated by ESWL. An inverse association between ESWL treatment outcome and stone size was also documented. CT stone density and stone size combined account for nearly 73% of the variation in the number of shock waves required to attain fragmentation. Stones located in lower calyceal area had less success rates. In conclusion, stones with higher density, large size and lower location may better be managed by percutaneous nephrolithotomy.

How to cite this article:
Tarawneh E, Awad Z, Hani A, Haroun AA, Hadidy A, Mahafza W, Samarah O. Factors affecting urinary calculi treatment by extracorporeal shock wave lithotripsy. Saudi J Kidney Dis Transpl 2010;21:660-5

How to cite this URL:
Tarawneh E, Awad Z, Hani A, Haroun AA, Hadidy A, Mahafza W, Samarah O. Factors affecting urinary calculi treatment by extracorporeal shock wave lithotripsy. Saudi J Kidney Dis Transpl [serial online] 2010 [cited 2022 Nov 27];21:660-5. Available from: https://www.sjkdt.org/text.asp?2010/21/4/660/64636

   Introduction Top

Extracorporeal Shock Wave Lithotripsy (ES­WL) is still the treatment of choice for most renal and upper ureteric stones especially those with size range of 10-20 mms. [1] The success rate of this treatment modality is in the range of 60-90% in various series. [1],[2],[3] However, the outcome of ESWL treatment depends on many factors including, stone size, site, composition and the presence of obstruction or infection. [4],[5]

Different techniques have been used to de­termine the chemical composition of urinary calculi in vivo since it has emerged as the main factor determining the outcome of ES­WL. [6],[7],[8] Nowadays, Non-Contrasted Compute­rized Tomography (NCCT) has become the diagnostic modality of choice to evaluate renal colic and to distinguish radiolucent urinary stones from tumors or blood clots. [9],[10],[11] The abi­lity of NCCT to detect density differences as low as 0.5% has been used to determine the composition and fragility of urinary stones, and hence the outcome of ESWL. [12],[13] In pre­vious studies the NCCT attenuation value of urinary calculi has been investigated as a method to predict the outcome of ESWL for two main purposes: avoiding the extra medical costs associated with nonproductive ESWL se­ssions, and seeking alternative patient manage­ment strategies. [14]

The objective of this study was to investigate the effects of stone density as measured by H.U. on NCCT, stone size, and stone location on ESWL outcome and stone fragmentation of urinary calculi in Jordanian patients.

   Patients and Methods Top

73 patients were evaluated, however eight pa­tients were excluded due to elevated creatinine levels (more than 2 mg/dL), single kidney, bleeding diathesis or obstructed kidney. Thus, the analyses, results and conclusions of this study were based on 65 patients. These 65 patients were prospectively followed at the Jordan University Hospital. All 65 patients had initially undergone clinical, biochemical and radiological assessments before ESWL treat­ment sessions. Of the 65 patients, 41 were males (63%) mean age of 44 ± 17 years (17-­76).

Urinary stone sizes ranged between 5-30 mms of which six were located in the upper calyx, ten in the mid calyx, 17 in the lower calyx, 26 in the renal pelvis and six in the ureter. Thirteen patients had stone sizes less than or equal 10 mms, thirty-four had stone sizes of 11-20 mm, while the rest (18 patients) had stone sizes of 21-30 mms. It should be noted that the study had initially included, rather than 73.

The maximal linear diameter of the stone was measured by NCCT scan. NCCT scan using con­tiguous three-millimeter section slices through the stone was performed and viewed on soft tissue setting (window width 350, window level l50 Hounsfield Units). Siemens Somatom Plus 4 scanner, at 120 kV and 206 mA, was used at a scan rate of one second per image. A pixel map of the largest region of interest within the stone was performed and consisted of 100 attenuation values in a 10 Χ 10 matrix; with each value on the pixel map representing the attenuation value for four pixels. The lowest, highest and most common attenuation values were recorded and the mean stone attenuation value was then calculated.

All ESWLs were undertaken by a Siemens Electromagnetic Lithostar Multiline Lithotripter with fragmentation performed under fluoros­copic or ultrasonographic guidance. A maxi­mum of 2800 shock waves were delivered in each treatment session with maximum energy level of four. ESWL treatment was terminated if satisfactory fragmentation was noted earlier before delivering the maximum number of shocks (i.e., 2800). Another ESWL session was undertaken three weeks later if follow up plain x-ray showed significant residual fragments (more or equal 5 mm in diameter). A plain x­-ray was performed six weeks after treatment completion for final assessment of outcome. In 19 patients with stones larger than 20 mms, or lower calyx stones larger than 15 mm, J.J. Stent was inserted prior to ESWL. If a stone was not fragmented at all, or if there were residual fragments 5 mms or larger after four sessions, this was considered as failure and another treat­ment option was sought. Thus the 65 patients were divided into two groups according to the outcomes of ESWLs. The "success group" com­prised patients who had successful stone frag­mentation and subsequent stone clearance. The "failure group" comprised patients who failed to clear the stone because fragmentation either did not occur at all or did occur, but, with significant residual fragments (5 mms or larger in size).

Statistical analyses including chi-square, ana­lysis of variance (ANOVA), correlation, regre­ssion and 95% confidence intervals were per­formed on the data to test the statistical signi­ficance of the various relationships between ESWL outcome and stone fragmentation on one side, stone density, size and location on the other side.

   Results Top

The characteristics of both groups are shown in [Table 1]. The mean stone diameter of the failure group was marginally larger though sta­tistically insignificant (P= 0.676). The mean stone density, of the failure group was nearly 60% larger than that of the success group; 1077 Hounsfield units compared to 672 (P = 0.000). On average, the failure group had re­ceived 2.6 ESWL treatment sessions compared to only 1.4 sessions in the success group; a difference of nearly 86%. On average, nearly 7200 shock waves were delivered to the failure group compared to only nearly 4000 in the success group (both P-values = 0.000).

Stone Density

The patients were further analyzed by divi­ding them into three groups according to stone density. The "low density group" comprised all patients with stone densities of less than 500 Hounsfield units, the "medium density group" comprised all patients with stone den­sities of 500-1000, while, the "high density group" comprised all patients with stone den­sities of more than 1000. ESWL treatment out­comes, according to stone density levels are shown in [Table 2] showing high success rate in low density group (94% ), A chi-square test analysis revealed statistically significant asso­ciation between ESWL treatment outcome and stone density (chi-square = 12.4, df = 2, P = 0.002).

Stone Size

The patients were also analyzed by dividing hem into three groups according to stone dia­meter. The "low diameter group": stone diame­ters of 10 mms or less, the "medium diameter group": 11-20 mms, while, the "high diameter group": 21-30 mms. The ESWL treatment out­comes, in terms of success or failure of stone clearance, according to these three stone dia­meter levels are shown in [Table 3]. Higher success rates were achieved with lower dia­meter, 92%, 74% and only 50% for lower, medium and higher groups respectively (chi­square = 6.8, df = 2, P = 0.033). A positive co­rrelation between the stone diameter in milli­meters and the number of shock waves deli­vered was noted r=0.32,(P = 0.009).

Stone Site

Patients were stratified into two groups ac­cording to stone site; "lower calyceal group" included all patients with lower calyceal stones, and "other group" included the rest of patients. The ESWL treatment outcomes, in terms of success or failure of stone clearance, according to these two stone sites ("lower calyceal" or "other") are shown in [Table 4]. The success of ESWL treatment was only 47% in the lower calyceal stone site group compared to 79% in the case of other stone sites (chi-square = 6.3, df = 1, P-value = 0.012).

Regression analysis was also performed kee­ping number of shock waves delivered as de­pendent variable, while the independent varia­bles were stone density in Hounsfield units and stone diameter in millimeters. Equations 1 and 2 were obtained with only stone density as the independent variable, and both stone den­sity and stone size as independent variables respectively.

Y = 432 + 5.6 X1 (1)

Y = 227 + 5.5 X1 + 17.8 X2 (2)


  • Y: Number of shockwaves required to attain stone fragmentation,
  • X 1 : Stone density in Hounsfield units, and
  • X 2 : Stone diameter in millimeters.
The adjusted R-squares of models 1 and 2 were 0.699 and 0.727, respectively P < 0.001. The adjusted R-squares indicate that stone density alone accounts for nearly 70% of the variation in the number of shock waves re­quired to attain fragmentation, while both, stone density and stone size combined, account for nearly 73% of the variation.

Our data also indicate that stone density in the success group is nearly 750 Houndfield units; indicating successful treatment by ESWL be­low this level and failure above 950 Houndfield units, [Table 5]. The successful outcome was also in general with stone size of nearly 16 mms or less, in 1.7 numbers of sessions and up to 6300 shock waves, [Table 5].

   Discussion Top

ESWL is still considered the best treatment for calculi less than 20 mms, but the outcome of this therapy depends on different factors including stone composition, stone location, pelvicalyceal anatomy and stone size. [4] Stone composition seems to play the most important role in the outcome of treatment, however, still it can not be known accurately before stone retrieval and analysis. The crystals excreted in urine after ESWL can give an idea about stone composition. Urinalysis with scanning electron microscopy and x-ray energy dispersive spec­troscopy for determining stone composition before ESWL still have some limitations. [15],[16],[17]

Plain x-ray has been used to predict the out­come of ESWL treatment by comparing stone density with bone density. However, this me­thod has some disadvantages since the stone diameter and appearance might not be measured accurately, especially in the presence of bowel gas interference or neighboring bony struc­tures and the density measurement is subjec­tive. [1] We used plain CT scan which is a non invasive technique and provides greater densi­ty discrimination than plain x-ray. CT can dis­tinguish density differences as low as 0.5% compared to only 5% discrimination using plain x-ray. [1],[9]

Joseph et al [1] suggested that stones with CT attenuation value of greater than 950 Houns­field units and 7500 shockwaves failed to achieve fragmentation. Gupta et al [21] showed that the worst outcome of ESWL was in pa­tients with calculus densities of more than 750 Hounsfield units and diameters of more than 1.1 cms, and their clearance rate was only 60%. In our study, the success of ESWL treat­ment is almost always guaranteed when the CT attenuation value is less than 750 Houns­field units, while, at the same time, treatment failure is almost certain when the CT attenua­tion value exceeds 950. Stone densities in the range of 750-950 may, or may not, respond successfully to ESWL treatment. Similar to Gupta et al, this study found that stone den­sities of more than 750 Hounsfield units may fail to respond successfully to ESWL treat­ment. However, contrary to Gupta et al, this study revealed that stone diameters of up to 20 mms may still (depending on stone density) respond successfully to ESWL treatment. [21] Similar to Joseph et al, the results of this study clearly reveals that stones with densities ex­ceeding 950 Hounsfield units are difficult to fragment. However, contrary to Joseph et al, up to 6300 shock waves may be attempted before seeking other type treatment (i. e., per­cutaneous nephrolithotomy). Even though the results of this study have identified both stone density and size as significant contributors to ESWL treatment success rate, it also revealed that stone density is the determinant factor of treatment success for stone sizes of 20 mms or smaller.

To date, few clinical studies have compared the stone density with the outcome of ESWL in vivo. In a study of 30 patients, Joseph et al [1] found that patients with calculi of less than 500 Hounsfield units had complete clearance and required a median of 2500 shockwaves, patients with calculi of 500-1000 Hounsfield units had a clearance rate of 86% and required a median of 3390 shockwaves, and patients with calculi of more than 1000 Hounfield units had a clearance rate of 55% only and required a median of 7300 shockwaves. Study by Joseph et al based on 65 patients, showed that stones with densities less than 500 Hounsfield units have 94% clearance rate and required a median of 2800 shockwaves, patients with stone den­sities of 500-1000 Hounsfield units have 76% clearance rate and required a median of 3700 shockwaves, and patients with stone densities more than 1000 Hounsfield units have 42% clearance rate and required a median of 7800 shockwaves.

Pareek et al [23] correlated calculus density with stone clearance in their study of 100 patients. They concluded that patients with residual calculi had a mean calculus density of more than 900 Hounsfield units. However, Pareek et al did not correlate the calculus density with fragmentation. The results of this study con­curs with Pareek et al's results in that stone clearance is unlikely when stone density exceeds 950 Hounsfield units.

The results of this study supports those of Joseph et al [1] in that stone density has an in­verse relation with the ESWL success rate, and CT stone density has a positive correlation with the number of shockwaves needed for fragmentation. Also, the results of this study concurs with the results of previous studies [1],[19]­,[20],[21],[22] in that stone location has a significant effect on fragmentation success and clearance with lower calyceal stones have less success rates compared to other locations.

In conclusion, ESWL treatment outcome is strongly, but inversely, dependent on stone den­sity. Stones with CT densities of 750 Houns­field units or less undergo successful treatment requiring lesser number of shock waves and sessions. Large stones more than 1.7 cm and lower calyceal location are resistant to ESWL.

   References Top

1.Joseph P, Mandal AK, Sharma SK. CT attenua­tion value of renal calculus: can it predict suc­cessful fragmentation of the calculus by extra­corporeal shockwave lithotripsy? A preliminary study. J Urol 2002;167:1968.  Back to cited text no. 1  [PUBMED]  [FULLTEXT]  
2.Lingeman JE, Newman D, Mertz JH, et al. Extra­corporeal shockwave lithotripsy: the Methodist Indiana experience. J Urol 1996; 135:1134.  Back to cited text no. 2      
3.Cass AS. Comparison of first generation (Dornier HM3) and second generation (Medstone STS) lithotriptors: treatment results with 13,864 renal and ureteric calculi. J Urol 1995;153:588.  Back to cited text no. 3  [PUBMED]  [FULLTEXT]  
4.Bon D, Dore B, Irani J, et al. Radiographic prog­nostic criteria for extracorporeal shock-wave lithotripsy. Urology 1996;48:556.  Back to cited text no. 4  [PUBMED]  [FULLTEXT]  
5.Martin TV, Sosa RE. Shockwave lithotripsy. In Walsh PC, Retick AB, Vaughan ED Jr, Wein AJ, eds, Campbeils urology. Philadelphia: WB Saunders Inc, 1998:2735-52.  Back to cited text no. 5      
6.Otnes B. Crystalline composition of urinary stones in recurrent stone formers. Scand J Urol Nephrol 1983;17:179-84.  Back to cited text no. 6  [PUBMED]    
7.Dretler SP, Polykoff G. Calcium oxalate stone morphology: fine tuning our therapeutic distinc­tions. J Urol 1996;155:828-33.  Back to cited text no. 7  [PUBMED]  [FULLTEXT]  
8.Herremans D. Vandeursen H, Pittomvills G, et al. In vitro analysis of urinary calculi: type diffe­rentiation using computed tomography and bone densitometry. Br J Urol 1993;72:544-8.  Back to cited text no. 8      
9.Federle MP, McAninch JW, Kaiser JA, Good­man PC, Roberts J, Mall JC. CT of urinary calculi. AJR Am J Roentgenol 1981;136:255-8.  Back to cited text no. 9      
10.Parienty RA, Ducellier R, Pradel J, Lubrano JM, Coquille F, Richard F. Diagnostic value of CT numbers in pelvicalyceal filling defects. Radiology 1982;145:743-7.  Back to cited text no. 10  [PUBMED]  [FULLTEXT]  
11.Fielding JR, Steele G, Fox A, Heller H, Loughlin KR, Spiral computerized tomography in the eva­luation of acute flank pain: a replacement for excretory urography. J Urol 1997;157:2071-3.  Back to cited text no. 11      
12.Dretler SP. Stone fragility- a new therapeutic distinction. J Urol 1988;139:1124-7.  Back to cited text no. 12  [PUBMED]    
13.Mostafavi MR, Ernst RD, Saltzman B. Accurate determination of chemical composition of urinary calculi by spiral CT. J Urol 1998;159:673.  Back to cited text no. 13  [PUBMED]  [FULLTEXT]  
14.Lingeman JE, Woods JR, Toth PD. Blood pre­ssure changes following Extracorporeal shock­wave lithotripsy and other forms of treatment for nephrolithiasis. JAMA 1990;263:1789.  Back to cited text no. 14  [PUBMED]    
15.Khan SR, Hackett RL, Finlayson B. Morphology of urinary stone particles resulting from ESWL treatment. J Urol 1986;136:1367.  Back to cited text no. 15  [PUBMED]    
16.Bowsher WG, Crocker P, Ramsay JW, Whitfield HN. Single urine sample diagnosis, A new concept in stone analysis. Br J Urol 1990;65: 236.  Back to cited text no. 16  [PUBMED]    
17.Cohen NP, Parkhouse H, Scott ML, Bowsfer WG, Crocker P, Whitfield HN. Prediction of response to lithotripsy: the use of scanning electron mic­roscopy and x-ray energy dispersive spectros­copy. Br J Urol 1992;70:469.  Back to cited text no. 17      
18.Hillman BJ, Drach GW, Tracey P, Gaines JA. CT analysis of renal calculi. AJR Am J Roentgenol 1984;142:549.  Back to cited text no. 18  [PUBMED]  [FULLTEXT]  
19.Sabnis RB, Naik K, Patel SH, Desai MR, Bapat SD. Extracorporeal shock wave lithotripsy for lower calyceal stones: can clearance be pre­dicted? Br J Urol 1997;80:853.  Back to cited text no. 19  [PUBMED]    
20.Madbouly K, Sheir KZ, Elsobsky E. Impact of lower pole renal anatomy on stone clearance after shockwave lithotripsy: Fact or Fiction? J Urol 2001;165:1415.  Back to cited text no. 20      
21.Gupta NP, Ansari MS, Kesarvani P. Role of computed tomography with no contrast medium enhancement in predicting the outcome of extra­corporeal shockwave lithotripsy for urinary cal­culi. Br J Urol 2005;95:1285-8.  Back to cited text no. 21      
22.Abdul-Khalek M, Sheir KZ, Mokhtar AA. Pre­diction of Success rate after ESWL of renal stones. Scand J Urol Nephrol 2004;38:161-7.  Back to cited text no. 22      
23.Pareek G, Aremenakas NA, Fracchia JA. Hounsfield units on CT. predict stone-free rates after ESWL. J Urol 2003;169:1679-81.  Back to cited text no. 23      

Correspondence Address:
Emad Tarawneh
Jordan University, P.O. Box 13200, Amman 11942
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Source of Support: None, Conflict of Interest: None

PMID: 20587869

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  [Table 1], [Table 2], [Table 3], [Table 4], [Table 5]

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