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Müllhaupt G et al, 2015: How do stone attenuation and skin-to-stone distance in computed tomography influence the performance of shock wave lithotripsy in ureteral stone disease?

Müllhaupt G, Engeler DS, Schmid HP, Abt D.
Department of Urology, Cantonal Hospital St. Gallen, Rorschacherstrasse 95, 9007, St. Gallen, Switzerland.

Abstract

BACKGROUND: Shock wave lithotripsy (SWL) is a noninvasive, safe, and efficient treatment option for ureteral stones. Depending on stone location and size, the overall stone-free rate (SFR) varies significantly. Failure of stone disintegration results in unnecessary exposure to shock waves and radiation and requires alternative treatment procedures, which increases medical costs. It is therefore important to identify predictors of treatment success or failure in patients who are potential candidates for SWL before treatment. Nowadays, noncontrast computed tomography (NCCT) provides reliable information on stone location, size, number, and total stone burden. The impact of additional information provided by NCCT, such as skin-to-stone distance (SSD) and mean attenuation value (MAV), on stone fragmentation in ureteral stone disease has hardly been investigated separately so far. Thus, the objective of this study was to assess the influence of stone attenuation, SSD and body mass index (BMI) on the outcome of SWL in ureteral stones.
METHODS: We reviewed the medical records of 104 patients (80 men, 24 women) with ureteral stone disease treated consecutively at our institution with SWL between 2010 and 2013. MAV in Hounsfield Units (HU) and SSD were determined by analyzing noncontrast computed tomography images. Outcome of SWL was defined as successful (visible stone fragmentation on kidney, ureter, and bladder film (KUB) or failed (absent fragmentation on KUB).
RESULTS: Overall success of SWL was 50% (52 patients). Median stone attenuation was 956.9 HU (range 495-1210.8) in the group with successful disintegration and 944.6 (range 237-1302) in the patients who had absent or insufficient fragmentation. Median SSD was 125 mm (range 81-165 mm) in the group treated successfully and 141 mm (range 108-172 mm) in the patients with treatment failure. Unlike MAV (p = 0.37), SSD (p < 0.001) and BMI (p = 0.008) significantly correlated with treatment outcome.
CONCLUSION: The choice of treatment for ureteral stones should be based on stone location and size as considered in the AUA and EAU guidelines on urinary stone disease. In ambiguous cases, SSD and BMI can be used to assist in the decision. In this study, MAV showed no correlation with fragmentation rate of SWL.

BMC Urol. 2015 Jul 23;15:72. doi: 10.1186/s12894-015-0069-7

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Peter Alken on Wednesday, 20 January 2016 10:08

This is not just another paper on SSD and mean attenuation value (MAV) of stones measured in HU. The authors suggest that SSD measurements may have to be adopted to the lithotripter used and that different MAV measurements offer different quality, which may explain contradictory findings in the literature they have reviewed.

In this series BMI and SSD (0°/45°/90°) and SSD (90°) were significant predictors of success in the univariate analysis but only SSD 90o in the multivariate analysis, which seems to apply specifically to the SLX-F2 lithotripter used in this study. The MAV was measured according to the technique of Eisner et al. (Eisner BH, et al. Computerized tomography magnified bone windows are superior to standard soft tissue windows for accurate measurement of stone size: an in vitro and clinical study. J Urol. 2009; 181: 1710) which the authors think is the most precise and reliable one. In addition they calculated median attenuation values of different stone regions.
The authors did not define ESWL success as is usually done by SFR but stone disintegration determined in the KUB

“In cases of missing or inadequate disintegration in KUB, SWL was repeated once or twice at intervals of 1 day. The clinical outcome was defined as successful (visible stone fragmentation on KUB) or failed (absent fragmentation on KUB) immediately after the last SWL session.”

“Stone fragmentation was visible in 52 (50 %) patients and was not visible in the remaining patients, of whom 49 (94.2 %) needed further treatment: 43 (82.7 %) by URS, 4 (7.7 %) by ureteral stent insertion, and 2 (3.8 %) by further cycles of SWL. The three patients who needed no further treatment showed spontaneous stone passage during the treatment with SWL without stone disintegration.”
“Of the 52 patients who showed good stone fragmentation, 13 (25 %) needed further treatment by URS (8 patients, 15.4 %,), ureteral stent insertion (1 patient, 1.9 %) or further cycles of SWL (4 patients, 7.7 %) because of impacted fragments or distal steinstrasse.

http://storzmedical.com/images/blog/Müllhaupt_2015.png

More than 50 % of the patients finally required URS for stone removal. It is not clear from the data how many patients got a second or third ESWL of if only 6 patients altogether got a re-ESWL.
Despite the significant correlations between the SSDs, the BMI and the disintegration the sensitivity and specificity of the different parameters was low and the original values showed a great overlap.

The interested reader should compare this paper with the referenced literature and the recently reviewed papers by Yazici and especially by Tran:
(Yazici O et al. ( Shock Wave Lithotripsy in Ureteral Stones: Evaluation of Patient and Stone Related Predictive Factors. Int Braz J Urol. 2015 Jul-Aug;41(4):676-82.; Tran T Y et al. Triple D Score Is a Reportable Predictor of Shockwave Lithotripsy Stone-Free Rates Full Access Journal of Endourology. February 2015, 29(2): 226-230.)
The latter is the most appealing to me. But it may be that we have to wait for a Meta-analysis which will tell us that all publications on that topic are not comparable. Then, hopefully commonly accepted measuring methods will be introduced.

This is not just another paper on SSD and mean attenuation value (MAV) of stones measured in HU. The authors suggest that SSD measurements may have to be adopted to the lithotripter used and that different MAV measurements offer different quality, which may explain contradictory findings in the literature they have reviewed. In this series BMI and SSD (0°/45°/90°) and SSD (90°) were significant predictors of success in the univariate analysis but only SSD 90o in the multivariate analysis, which seems to apply specifically to the SLX-F2 lithotripter used in this study. The MAV was measured according to the technique of Eisner et al. (Eisner BH, et al. Computerized tomography magnified bone windows are superior to standard soft tissue windows for accurate measurement of stone size: an in vitro and clinical study. J Urol. 2009; 181: 1710) which the authors think is the most precise and reliable one. In addition they calculated median attenuation values of different stone regions. The authors did not define ESWL success as is usually done by SFR but stone disintegration determined in the KUB “In cases of missing or inadequate disintegration in KUB, SWL was repeated once or twice at intervals of 1 day. The clinical outcome was defined as successful (visible stone fragmentation on KUB) or failed (absent fragmentation on KUB) immediately after the last SWL session.” “Stone fragmentation was visible in 52 (50 %) patients and was not visible in the remaining patients, of whom 49 (94.2 %) needed further treatment: 43 (82.7 %) by URS, 4 (7.7 %) by ureteral stent insertion, and 2 (3.8 %) by further cycles of SWL. The three patients who needed no further treatment showed spontaneous stone passage during the treatment with SWL without stone disintegration.” “Of the 52 patients who showed good stone fragmentation, 13 (25 %) needed further treatment by URS (8 patients, 15.4 %,), ureteral stent insertion (1 patient, 1.9 %) or further cycles of SWL (4 patients, 7.7 %) because of impacted fragments or distal steinstrasse. [img]http://storzmedical.com/images/blog/Müllhaupt_2015.png[/img] More than 50 % of the patients finally required URS for stone removal. It is not clear from the data how many patients got a second or third ESWL of if only 6 patients altogether got a re-ESWL. Despite the significant correlations between the SSDs, the BMI and the disintegration the sensitivity and specificity of the different parameters was low and the original values showed a great overlap. The interested reader should compare this paper with the referenced literature and the recently reviewed papers by Yazici and especially by Tran: (Yazici O et al. ( Shock Wave Lithotripsy in Ureteral Stones: Evaluation of Patient and Stone Related Predictive Factors. Int Braz J Urol. 2015 Jul-Aug;41(4):676-82.; Tran T Y et al. Triple D Score Is a Reportable Predictor of Shockwave Lithotripsy Stone-Free Rates Full Access Journal of Endourology. February 2015, 29(2): 226-230.) The latter is the most appealing to me. But it may be that we have to wait for a Meta-analysis which will tell us that all publications on that topic are not comparable. Then, hopefully commonly accepted measuring methods will be introduced.
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