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Ray AA et al, 2011: Shockwave lithotripsy in patients with horseshoe kidney: determinants of success

Ray AA, Ghiculete D, D'A Honey RJ, Pace KT.
Division of Urology, Department of Surgery, St. Michael's Hospital, University of Toronto, Toronto, Canada.


Abstract

BACKGROUND AND PURPOSE: Horseshoe kidney (HSK) is the most common renal fusion anomaly, with a prevalence of ∼1 in 400 and an incidence of urolithiasis between 20% and 60%. The role of shock wave lithotripsy (SWL) in patients with HSK remains poorly studied.

METHODS: Data from all patients treated since January 1994 with a known HSK was reviewed. Analysis was restricted to all patients with a minimum follow-up of 2 weeks after SWL. Success was defined as patients who were stone-free or had asymptomatic, clinically insignificant residual fragments ≤ 4 mm.

RESULTS: Data from 41 patients with HSK were analyzed (61 calculi). Mean stone size was 91.3 ± 71.6 mm(2); mean body mass index was 27.1 ± 5.3 kg/m(2). At 3 months, the single-treatment success and stone-free rates were 25.0% and 9.1%, respectively. The overall treatment success rate at 3 months was 63.6%, and the stone-free rate was 39.1%. Little incremental benefit was found for more than two SWL treatments per stone. The auxiliary treatment rate was 72.7%, with an efficiency quotient of 10.5%. On multivariate analysis, stone burden (p = 0.074), other calyceal location (p = 0.026), and body mass index (p = 0.013) were found to be prognostic for SWL success.

CONCLUSIONS: Patients with HSK appear to have lower success and stone-free rates after SWL than patients with normal kidneys. This likely has to do with factors such as greater skin-to-stone distance (particularly for calyceal stones) and restricted urinary drainage. SWL may be offered to patients with a HSK once limitations in stone clearance have been considered.

J Endourol. 2011 Mar;25(3):487-93. doi: 10.1089/end.2010.0213. Epub 2011 Mar 1
PMID: 21361827 [PubMed - in process]

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Comments 1

Hans-Göran Tiselius on Wednesday, 08 June 2011 09:24

Stone removal in patients with horseshoe kidneys is often a difficult task, whichever method that is used.

This article reports the results recorded in 41 patients with 61 stones, but only 44 of the stones (72%) were available for 3 month evaluation. A high rate of auxiliary procedures was necessary, but the authors also classified repeated ESWL as an auxiliary procedure. The overall end result (3 months) showed a treatment success of 64% but a stone-free rate of only 39%. The result was numerically better with the Dornier MFL-5000 lithotripter than with Philips Lithtron. The stone-free rate was lower than the average of 55% published in the literature comprising stones in 342 renal units.

Attempts to find reliable predictors for the 3 month success did not reveal anything statistically useful, but for the two-week results, BMI and stone surface area not unexpectedly had an effect on the outcome.

An explanation for the low stone-free rate is difficult to provide without detailed information on the renal anatomy, but in all these patients a reduced fragment clearance should be expected. In addition to the intra-renal anatomical obstacles, the authors believe that the long skin-to-stone distance is of importance. It is, moreover, my own experience that failure to disintegrate stones in these patients – when treated in the supine position - can be explained by the loss of shockwave energy in the nearby skeletal structures. Therefore treatment in the prone position might possibly have resulted in a higher rate of stone disintegration.

The conclusion of the report is, however, that the majority of the patients had their stones disintegrated to the extent that they became asymptomatic.

Hans-Göran Tiselius

Stone removal in patients with horseshoe kidneys is often a difficult task, whichever method that is used. This article reports the results recorded in 41 patients with 61 stones, but only 44 of the stones (72%) were available for 3 month evaluation. A high rate of auxiliary procedures was necessary, but the authors also classified repeated ESWL as an auxiliary procedure. The overall end result (3 months) showed a treatment success of 64% but a stone-free rate of only 39%. The result was numerically better with the Dornier MFL-5000 lithotripter than with Philips Lithtron. The stone-free rate was lower than the average of 55% published in the literature comprising stones in 342 renal units. Attempts to find reliable predictors for the 3 month success did not reveal anything statistically useful, but for the two-week results, BMI and stone surface area not unexpectedly had an effect on the outcome. An explanation for the low stone-free rate is difficult to provide without detailed information on the renal anatomy, but in all these patients a reduced fragment clearance should be expected. In addition to the intra-renal anatomical obstacles, the authors believe that the long skin-to-stone distance is of importance. It is, moreover, my own experience that failure to disintegrate stones in these patients – when treated in the supine position - can be explained by the loss of shockwave energy in the nearby skeletal structures. Therefore treatment in the prone position might possibly have resulted in a higher rate of stone disintegration. The conclusion of the report is, however, that the majority of the patients had their stones disintegrated to the extent that they became asymptomatic. Hans-Göran Tiselius
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