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 Table of Contents  
ORIGINAL ARTICLE
Year : 2013  |  Volume : 26  |  Issue : 2  |  Page : 159-162

Impact of stone density on the outcome of extracorporeal shock wave lithotripsy


Department of Urology, Faculty of Medicine, Menoufia University, Menoufia, Egypt

Date of Submission13-May-2013
Date of Acceptance27-Jun-2013
Date of Web Publication31-Jan-2014

Correspondence Address:
Mohamed H Hamed
MB, BCh, Department of Urology, Faculty of Medicine, Menoufia University, Menoufia
Egypt
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/1110-2098.126152

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  Abstract 

Objectives
This study aims to evaluate the attenuation of renal calculi measured by Hounsfield unit (HU) by noncontrast spiral computerized tomography (NCSCT) as a predictor of calculus fragmentation by extracorporeal shock wave lithotripsy (SWL).
Background
The outcome of extracorporeal SWL is measured in terms of stone fragmentation and clearance. Some authors have suggested that HU of renal calculi by NCSCT may predict stone-free rates after extracorporeal SWL.
Patients and methods
This prospective nonrandomized open study included 100 patients with renal stone up to 20 mm in size. Stone attenuation was measured by HU on NCSCT. Patients were grouped according to stone attenuation as group (1), less than 500 HU, (2), 500-1000 HU, and (3), greater than 1000 HU. Patients were treated subsequently with extracorporeal SWL. The outcome was categorized as stone free, clinically insignificant stone fragments, and residual fragments more than 3 mm.
Results
The rate of stone fragmentation was 100% (41 of 41 cases) in group 1, 95.7% (44 of 46) in group 2, and 0% (0 of 13) in group 3. A statistically significant association was found between SWL treatment outcome and stone density. When we correlated the absolute stone HU measured with the number of shock waves required for complete fragmentation, we found that the mean number of shock waves was 248 122 in group 1, 334 826 in group 2, and 726 077 in group 3 (P < 0.001).
Conclusion
Stone attenuation measured by HU by NCSCT is a predictor of outcome of SWL and suspected number of shock waves required for fragmentation.

Keywords: KUB, noncontrast spiral computerized tomography, stone attenuation, shock wave lithotripsy


How to cite this article:
Sultan SM, Abdel-Elbaky TM, Elsherif EA, Hamed MH. Impact of stone density on the outcome of extracorporeal shock wave lithotripsy. Menoufia Med J 2013;26:159-62

How to cite this URL:
Sultan SM, Abdel-Elbaky TM, Elsherif EA, Hamed MH. Impact of stone density on the outcome of extracorporeal shock wave lithotripsy. Menoufia Med J [serial online] 2013 [cited 2017 Oct 24];26:159-62. Available from: http://www.mmj.eg.net/text.asp?2013/26/2/159/126152


  Introduction Top


The outcome of shock wave lithotripsy (SWL) is measured in terms of stone fragmentation and clearance. Failure of SWL results in unnecessary exposure of renal parenchyma to shock waves and its possible complications. Invariably, alternative treatments are then needed, incurring additional medical expenses [1] .

Because disintegration is the first step in the treatment of renal stones by SWL, the magnitude of response of a calculus to disintegration (i.e. stone fragility) should be considered before using SWL. It is often not possible to predict whether a given stone is amenable to fragmentation by shock waves before starting treatment; however, because there are many factors that affect stone fragility, such as size and composition [2] .

Therefore, from the inception of SWL, factors predicting its outcome have been studied. A number of stone characteristics such as fragility, size, location, and composition are known to affect outcome [3] .

Noncontrast spiral computerized tomography (NCSCT) of the renal tract has emerged as the first-line radiological imaging modality for patients presenting with acute renal colic [4] .

Hounsfield unit (HU) measurement of urinary calculi on pretreatment NCCT may predict the stone-free rate; this information may be potentially beneficial for selection of the preferred treatment option for patients with urinary calculi [5] .


  Patients and methods Top


This is a prospective study that was carried out at the urology department in Menoufia University Hospital between December 2010 and February 2012. The study included 100 patients who presented with renal stones.

Preoperative evaluation

Our study included 100 patients with symptomatic renal stone measured between 5 and 20 mm, either radiolucent or radiopaque.

Patients with multiple renal stones were excluded. In addition, patients with stone less than 5 mm or larger than 20 mm in size, and those with elevated serum creatinine levels ( > 2 mg/dl) and bleeding diathesis were also excluded.

All selected patients were subjected to assessment of complete history and full physical, urological examination, hematological, biochemical, and radiological evaluations.

NCSCT was performed using a multidetector row helical CT scanner (Toshiba Asteion, Japan) for all patients. The images were obtained using the high-quality mode at 200 mA, 120 kV, and 5 mm collimation reconstructed at 3 mm. The postscanning bone window protocol was used to measure the stone attenuation value (HU) for the determination of stone density.

Patients were grouped according to stone density into three groups:

Group 1: stones less than 500 HU, group 2: stones between 500 and 1000 HU, and group 3: stones more than 1000 HU.

Operative procedure

Patients were treated by extracorporeal SWL using the electrohydraulic Lithotriptor MT1-RX (BMA for design and industry; Egypt) under spinal or general anesthesia. Localization was performed using fluoroscopy for both radiopaque and radiolucent stones using iodinated contrast agents for radiolucent stones.

Stones are exposed to shock waves ranging in intensity from 1 to 21 kV, starting with 200 shock waves at 12 kV, followed by 22 kV, with a maximum number of 3000 shocks per session.

The treatment should be started on a lower energy setting with a step-wise power ramping [6] .

Careful control of pain during treatment is necessary to limit pain-induced movements and excessive respiratory excursions.

A change in stone size, outline, or separation indicates fragmentation.

Another SWL session was performed after 3 weeks if follow-up plain KUB (plain abdominal film of the kidneys, ureters, and bladder) showed significant residual fragments ( > 3 mm for radiopaque stones where radiolucence was monitored by ultrasound).

Postoperative follow-up

Patients were instructed to collect post-SWL urine sample for analysis of stone fragments.

All patients were evaluated after 2 weeks after each SWL session with plain KUB, pelvic-abdominal ultrasound, and nonenhanced spiral computed tomography (for radiolucent stones) to assess stone fragmentation.

The SWL result was considered successful with complete clearance of the stone (stone free) or asymptomatic residual fragments less than or equal to 3 mm in size (clinically insignificant stone fragments) and considered a failure with residual fragments more than 3 mm in size after three SWL sessions (residual stone) [7] .

Repeat treatment was carried out if inadequate fragmentation of the stone was observed.

Statistical analysis

Data were statistically described in terms of mean ± SD and percentages when appropriate. For comparison of categorical data, the χ2 -test was used and the student t-test was used for numerical data. P values less than 0.05 were considered statistically significant. All statistical calculations were carried out using the computer program: statistical package for social science version 15 (SPSS Inc., Chicago, Illinois, USA) for Microsoft Windows.


  Results Top


The mean HU measured by NCSCT before SWL treatment was 625.62 ± 310.409 HU. There was no hydronephrosis in 40% of patients; 53% of patients had mild hydronephrosis and 7% of the patients had moderate hydronephrosis. Fifty-eight patients were stone free, 27 had clinically insignificant stone fragments ( < 3 mm), and 15 had significant residual stones.

Of the 100 patients, 41 (41%) were in group 1, 46 (46%) were in group 2, and 13 (13%) were in group 3. The rate of stone fragmentation was 100% (41 of 41 cases) in group 1, 95.7% (44 of 46) in group 2, and 0% (0 of 13) in group 3 (P < 0.001, Graph 1) [Additional file 1].

We found that the mean number of shock waves was 248 122 in group 1, 334 826 in group 2, and 726 077 in group 3. The success rate for stones with density greater than 1000 HU was significantly lower than that for stones with a density of less than 1000 HU. A χ2 -test analysis showed a statistically significant association between SWL treatment outcome and stone density (χ2 = 94, d.f. = 4, P < 0.001, Graph 2) [Additional file 2].

The analysis of stone type in relation to the fragmentation rate showed that determination of HU aids differentiation of urate stones from other types of stones. Thus, calcium oxalate and calcium phosphate had the highest rates of failure whereas urate stones had the highest rates of success.


  Discussion Top


The impact of stone attenuation on SWL outcome has been studied by several investigators [8] . Moreover, because there is marked overlap between attenuation values of different stone classes, stone composition cannot be accurately predicted before the retrieved stones are analyzed. Nakada et al. [9] could differentiate between uric acid and calcium oxalate monohydrate stones using peak attenuation measurement, whereas Sheir et al. [10] could differentiate only between pure stone classes. Thus, determination of stone composition before treatment is difficult and may not be sufficient to allow prediction of the response to SWL. Therefore, pre-SWL radiographic examination should focus on those radiological stone characteristics that influence SWL outcome rather than on stone composition [11] .

Therefore, from the inception of SWL, factors predicting its outcome have been studied. A number of stone characteristics such as fragility, size, location, and composition are known to affect outcome [3] .

The determination of stone density obtained on NCSCT is easy, objective, reliable, and reproducible. NCSCT is noninvasive and provides better density discrimination than conventional radiography; it can be used to detect a density difference of 0.5%, whereas plain radiography requires a density difference of 5% [12] .

A correlation between stone attenuation and stone fragility was first found in vitro. As the attenuation value of calcium stones increases, a greater number of shock waves are needed for fragmentation [13] .

In our study, patients were grouped according to stone density into three groups.

Group 1: stones less than 500 HU, group 2: stones between 500 and 1000 HU, and group 3: stones more than 1000 HU.

It was found that the rate of stone clearance was 100% (27 of 27 cases) in group 1, 96% (25 of 26) in group 2, and 0% (0 of 7) in group 3. When we correlated the absolute stone HU measured with the number of shock waves required for complete fragmentation, we found that the mean number of shock waves was 248 122 in group 1, 334 826 in group 2, and 726 077 in group 3.

A study by Joseph et al. [14] of 65 patients treated with SWL (Dornier Medical Systems Inc., Marietta, Georgia, USA) showed that stones with densities less than 500 HU have a 94% clearance rate and required a median of 2800 shock waves, patients with stone densities of 500-1000 HU have a 76% clearance rate and required a median of 3700 shock waves, and patients with stone densities more than 1000 HU have a 42% clearance rate and required a median of 7800 shock waves.

Tarawneh et al. [15] evaluated 65 patients undergoing SWL treatment. SWL was performed using a Siemens Electromagnetic Lithostar Multiline Lithotripter.

The patients were further analyzed by dividing them into three groups according to stone density. Low-density group: patients with stone densities of less than 500 HU, medium-density group: patients with stone densities of 500-1000, and high-density group: patients with stone densities of more than 1000. SWL treatment outcomes, according to stone density levels, showed a high success rate in the low-density group (94%).

Ouzaid et al. [16] prospectively evaluated 50 patients with urinary calculi of 5-22 mm undergoing extracorporeal SWL (Dornier Medical Systems Inc.). Patients who became stone free or had clinically insignificant stone fragments had a lower density compared with stones in patients with residual fragments [mean (SD) 715 (260) vs. 1196 (171) HU, P < 0.001.

Pareek et al. [17] prospectively evaluated 100 patients. SWL was performed on an electrohydraulic lithotripter (Medstone). The difference in the mean HU values for the stone-free patients was 577.8 ± 182.5 and residual stones groups were statistically significant (910.4 ± 190.2).

Gupta et al. [18] evaluated 112 patients with solitary renal and upper ureteric calculi of 0.5-2 cm, undergoing SWL (Siemens Lithostar Shock Wave System C; Erlangen, Germany). They found that there was a linear relationship between the calculi density and number of SWL sessions required. Patients with calculi of 750 HU or less and a diameter less than 1.1 cm needed three or fewer SWL sessions and the clearance rate was 90%, whereas patients with calculi of more than 750 HU and a diameter of more than 1.1 cm needed three or more ESWL sessions and the clearance rate was 60%.

Perks et al. [19] evaluated 111 patients undergoing initial SWL (Lithotron Ultra) for a solitary renal stone of 5-20 mm. The stone attenuation of the successfully treated patients (stone free and complete fragmentation groups) was 837 ± 277 versus 1092 ± 254 HU for those with treatment failure (incomplete fragmentation; P < 0.01).


  Conclusion Top


Extracorporeal SWL is the treatment of choice for most renal calculi less than 20 mm.

Our study showed that the determination of stone density in HU on pretreatment NCSCT aids prediction of the success of SWL and selection of patients for SWL.

In a CT scan, if the attenuation value is higher than 1000 HU, other modalities for the management of these stones are recommended.


  Acknowledgements Top


Conflicts of interest

None declared.

 
  References Top

1.Nomikos MS, Sowter SJ, Tolley DA. Outcomes using a fourth-generation lithotripter: a new benchmark for comparison?BJU Int 2007; 100 :1356-1360.  Back to cited text no. 1
    
2.Williams JC Jr, Saw KC, Paterson RF, Hatt EK, McAteer JA, Lingeman JE. Variability of renal stone fragility in shock wave lithotripsy. Urology 2003; 61 :1092-1096 Discussion 7.  Back to cited text no. 2
    
3.Bon D, Dore B, Irani J, Marroncle M, Aubert J. Radiographic prognostic criteria for extracorporeal shock-wave lithotripsy: a study of 485 patients. Urology 1996; 48 :556-560 Discussion 60-61.  Back to cited text no. 3
    
4.Fielding JR, Steele G, Fox LA, Heller H, Loughlin KR. Spiral computerized tomography in the evaluation of acute flank pain: a replacement for excretory urography. J Urol 1997; 157 :2071-2073.  Back to cited text no. 4
    
5.Pareek G, Hedican SP, Lee FT Jr, Nakada SY. Shock wave lithotripsy success determined by skin-to-stone distance on computed tomography. Urology 2005; 66 :941-944.  Back to cited text no. 5
    
6.Vandeursen H, Baert L. Prophylactic role of extracorporeal shock wave lithotripsy in the management of nephrocalcinosis. Br J Urol 1993; 71 :392-395.  Back to cited text no. 6
    
7.Pareek G, Armenakas NA, Fracchia JA. Hounsfield units on computerized tomography predict stone-free rates after extracorporeal shock wave lithotripsy. J Urol 2003; 169 :1679-1681.  Back to cited text no. 7
    
8.Perks AE, Gotto G, Teichman JM. Shock wave lithotripsy correlates with stone density on preoperative computerized tomography. J Urol 2007; 178 (3 Pt 1)912-915.  Back to cited text no. 8
    
9.Nakada SY, Hoff DG, Attai S, Heisey D, Blankenbaker D, Pozniak M. Determination of stone composition by noncontrast spiral computed tomography in the clinical setting. Urology 2000; 55 :816-819.  Back to cited text no. 9
    
10.Sheir KZ, Mansour O, Madbouly K, Elsobky E, Abdel-Khalek M. Determination of the chemical composition of urinary calculi by noncontrast spiral computerized tomography. Urol Res 2005; 33 :99-104.  Back to cited text no. 10
    
11.El-Nahas AR, El-Assmy AM, Mansour O, Sheir KZ. A prospective multivariate analysis of factors predicting stone disintegration by extracorporeal shock wave lithotripsy: the value of high-resolution noncontrast computed tomography. Eur Urol 2007; 51 :1688-1693 Discussion 93-94.  Back to cited text no. 11
    
12.Dretler SP, Spencer BA. CT and stone fragility. J Endourol 2001; 15 :31-36.  Back to cited text no. 12
    
13.Saw KC, McAteer JA, Fineberg NS, Monga AG, Chua GT, Lingeman JE, et al. Calcium stone fragility is predicted by helical CT attenuation values. J Endourol 2000; 14 :471-474.  Back to cited text no. 13
    
14.Joseph P, Mandal AK, Singh SK, Mandal P, Sankhwar SN, Sharma SK. Computerized tomography attenuation value of renal calculus: can it predict successful fragmentation of the calculus by extracorporeal shock wave lithotripsy? A preliminary study. J Urol 2002; 167 :1968-1971.  Back to cited text no. 14
    
15.Tarawneh E, Awad Z, Hani A, Haroun AA, Hadidy A, Mahafza W, et al. Factors affecting urinary calculi treatment by extracorporeal shock wave lithotripsy. Saudi J Kidney Dis Transpl 2010; 21 :660-665.  Back to cited text no. 15
    
16.Ouzaid I, Al-qahtani S, Dominique S, Hupertan V, Fernandez P, Hermieu JF, et al. A 970 Hounsfield units (HU) threshold of kidney stone density on non-contrast computed tomography (NCCT) improves patients′ selection for extracorporeal shockwave lithotripsy (ESWL): evidence from a prospective study. BJU Int 2012; 110 (11 Pt BE)438-E442.  Back to cited text no. 16
    
17.Pareek G, Armenakas NA, Panagopoulos G, Bruno JJ, Fracchia JA. Extracorporeal shock wave lithotripsy success based on body mass index and Hounsfield units. Urology 2005; 65 :33-36.  Back to cited text no. 17
    
18.Gupta NP, Ansari MS, Kesarvani P, Kapoor A, Mukhopadhyay S. Role of computed tomography with no contrast medium enhancement in predicting the outcome of extracorporeal shock wave lithotripsy for urinary calculi. BJU Int 2005; 95 :1285-1288.  Back to cited text no. 18
    
19.Perks AE, Schuler TD, Lee J, Ghiculete D, Chung DG, DAH RJ, et al. Stone attenuation and skin-to-stone distance on computed tomography predicts for stone fragmentation by shock wave lithotripsy. Urology 2008; 72 :765-769.  Back to cited text no. 19
    




 

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Abstract
Introduction
Patients and methods
Results
Discussion
Conclusion
Acknowledgements
References

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