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Year : 2015  |  Volume : 7  |  Issue : 1  |  Page : 46-48  

Shock wave lithotripsy outcomes for lower pole and non-lower pole stones from a university teaching hospital: Parallel group comparison during the same time period

1 Medical Student, University Hospital of Southampton NHS Foundation Trust, Southampton, SO16 6YD, United Kingdom
2 Specialist Nurse in Urology, University Hospital of Southampton NHS Foundation Trust, Southampton, SO16 6YD, United Kingdom
3 Department of Urology, University Hospital of Southampton NHS Foundation Trust, Southampton, SO16 6YD, United Kingdom

Date of Submission10-Aug-2014
Date of Acceptance15-Aug-2014
Date of Web Publication6-Jan-2015

Correspondence Address:
Bhaskar K Somani
Department of Urology, Consultant Urological Surgeon (Stone Lead) and Honorary Senior Lecturer, University Hospital Southampton NHS Trust, SO16 6YD
United Kingdom
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DOI: 10.4103/0974-7796.148601

PMID: 25657543

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Introduction: Shock wave lithotripsy (SWL) is a treatment option for all locations of renal and ureteric stones. We compared the results of SWL for lower pole renal stones with all other non-lower pole renal and ureteric stones during the same time period.
Material and Methods: All SWL procedures were carried out as day case procedures by a mobile lithotripter from January 2012 to August 2013. The follow-up imaging was a combination of KUB X-ray or USS. Following SWL treatment, the stone free rate (SFR) was defined as ≤3 mm fragments.
Results: A total of 148 patients with a mean age of 62 years underwent 201 procedures. Of the 201 procedures, 93 (46%) were for lower pole stones. The non-lower pole stones included upper pole (n = 36), mid pole (n = 40), renal pelvis (n = 10), PUJ (n = 8), mid ureter (n = 3), upper ureter (n = 5) and a combination of upper, middle and/or lower pole (n = 6). The mean stone size for lower pole stones (7.4 mm; range: 4-16 mm) was slightly smaller than non-lower pole stones (8 mm; range: 4-17 mm). The stone fragmentation was successful in 124 (62%) of patients. However, the SFR was statistically significantly better (P = 0.023) for non-lower pole stones 43 (40%) compared to lower pole stones 23 (25%). There were 9 (4%) minor complications and this was not significantly different in the two groups.
Conclusions: Although SWL achieves a moderately high stone fragmentation rate with a low complication rate, the SFR is variable depending on the location of stone and the definition of SFR, with lower pole stones fairing significantly worse than stones in all other locations.

Keywords: Lithotripsy, lower pole stone, outcome, stone free rate, urolithiasis

How to cite this article:
Geraghty R, Burr J, Simmonds N, Somani BK. Shock wave lithotripsy outcomes for lower pole and non-lower pole stones from a university teaching hospital: Parallel group comparison during the same time period. Urol Ann 2015;7:46-8

How to cite this URL:
Geraghty R, Burr J, Simmonds N, Somani BK. Shock wave lithotripsy outcomes for lower pole and non-lower pole stones from a university teaching hospital: Parallel group comparison during the same time period. Urol Ann [serial online] 2015 [cited 2021 Dec 3];7:46-8. Available from: https://www.urologyannals.com/text.asp?2015/7/1/46/148601

   Introduction Top

Since being first introduced in the 1980s [1] extracorporeal shock wave lithotripsy (SWL) has become the treatment of choice for renal and ureteral stones up to 20 mm. It is relatively non-invasive, and has a reasonable efficacy in treating stones in all locations. [2]

Several studies have shown that treatment of lower pole stones (LP) stones has a lower stone free rate (SFR) than other renal or ureteral stones due to the LP anatomy. [3],[4],[5]

In this study, we looked at the outcomes for SWL in both lower pole (LP) and non-lower pole (NLP) stones during the same time period to evaluate if there was a difference in SFR after treatment.

   Materials and methods Top

Between January 2012 and August 2013, 148 patients were treated for renal and ureteral stones using a mobile piezoelectric lithotripter (Wolf Piezolith 3000). Data were collected retrospectively on all patients who underwent SWL in this time period with stone size ranging from ≥4 mm to <20 mm. All patients had IVU or non-contrast CT (NCCT) for diagnosis of stones and plain X-Ray (if radio opaque stone) or USS for follow-up.

Pre-operatively, patients were given a combination of diclofenac 100 mg per rectum, intramuscular pethidine (100 mg/2 ml) and intramuscular metoclopromide (10 mg/2 ml). The maximum number of shocks administered within each operation was limited to 4000 (mean shock numbers were: Lower pole: 3015; non-lower pole: 3140). Post-operatively all patients were given a 7 day course of trimethoprim and oral ibuprofen as pain relief if required.

Multiple variables including patient characteristics such as age, sex and number of procedures, procedural characteristics such as number of shocks and energy of shocks, stone characteristics such as size, location and number, and treatment characteristics such as SFR, stone fragmentation rate and complications were recorded. Following treatment, stone fragmentation was defined as evidence of fragmentation on follow-up imaging and stone free rate (SFR) was defined as stone fragments ≤3 mm on X-Ray KUB or USS.

Stones were classed as lower pole (LP) if they were exclusively within the LP. Stones in all other locations within the kidney and ureter were classed as non-lower pole (NLP). Stones were also called as NLP in case of multiple stones one of which was in LP. This included stones in the upper pole, mid pole, renal pelvis, pelviureteral junction (PUJ), mid ureter or upper ureter.

Data were collated using Microsoft excel. Data analysis was performed using SPSS version 21 and P values were achieved using the χ2 test.

   Results Top

The mean age of the patients for LP and NLP was 54 years (30-86 years) and 52 years (30-80 years), respectively [Table 1]. Male to Female ratios for LP and NLP were 60:33 and 60:48, respectively. A total of 148 patients underwent 201 procedures of which 93 (46%) were for LP stones and 108 (54%) were for NLP stones. Multiple stones were seen in 68/201 (34%). The non-lower pole stones included upper pole (n = 36), mid pole (n = 40), renal pelvis (n = 10), PUJ (n = 8), mid ureter (n = 3), upper ureter (n = 5) and a combination of upper, middle and/or lower pole (n = 6). The mean stone size was 7.4 mm (4-16) for LP stones and 8 mm (4-17) for NLP stones. The majority of stones were left sided for both LP and NLP with right: Left ratios being 41:51 for LP stones and 41:64 for NLP stones. Each side was treated and counted individually.
Table 1: Comparison of patient and procedural characteristics between lower pole and non-lower pole stones

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The mean number of procedures each patient received for LP and NLP stones was 1.6 and 1.3 respectively [Table 2]. The average number of shocks patients received for LP and NLP stones were 3015 (2000-3500) and 3140 (2000-4000), respectively. The average energies for LP and NLP were 17.3 and 16.7 kV, respectively.
Table 2: Comparison of stone and treatment characteristics between lower pole and non-lower pole stones. SFR was
statistically signifi cant higher for NLP stones (P<0.05)

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Although the stone fragmentation rates for LP and NLP stones were 61% and 63% respectively the SFR after treatment completion was 25% (23/93) for LP stones and 40% (43/108) for NLP stones. This was statistically significant with a P value of P = 0.023.

There were three complications treating the LP stones, all of which were renal colic and there were six complications from the NLP stone treatment; five patients had renal colic and one patient suffered from abdominal pain. There were no other major or minor complications.

   Discussion Top

Shock wave lithotripsy (SWL) is the treatment of choice for renal and ureteral stones up to 20 mm as it is non-invasive and has a high efficacy. Our stone fragmentation rates are comparable to other studies using the same lithotripter. [6],[7] Our average stone free rate was 32.8%, which is slightly less than the 36% and 45% achieved by Ng et al. and Wang et al., respectively. [6],[7]

A study by Φbek et al. showed that there was no significant difference in efficacy of treating LP stones compared to middle and upper pole stones but there was reduced SFR for LP stones in comparison to middle and upper pole stones. [8] This is comparable to our study that shows no statistically significant difference between stone fragmentation rates of LP vs NLP stones but does show a statistically significant difference in SFR's (P < 0.05).

This disparity in SFR's is, as several studies have shown, due to the anatomy of the lower pole. A study by Sampaio showed that the position of lower pole stones impedes gravity dependent drainage of fragments after SWL. [9] Other studies have shown that a shorter infundibular length (<22 mm) as well as larger stone size (>10 mm) and burden can decrease stone free rates. [3],[4],[5],[8],[9],[10],[11]

Despite having lower SFR's than percutaneous nephrolithotomy (PCNL) and flexible ureterorenoscopy (fURS), SWL remains the treatment of choice for some stones as hospital stay, complication rate and duration of treatment are lower in comparison. [5],[12],[13] Although our study is a retrospective study, the comparison of outcomes between LP and NLP stones is based on treatment carried out by the same team using the same lithotripter in the same time period minimizing any potential for bias.

The other issue identified in this paper is the disparity in the definition of SFR. Several papers define stone free varying from no evidence of stones either by radiological imaging or ultrasonography to residual stones up to 4 mm in size. [6],[8],[7],[14-16] We have defined stone free as fragments ≤3 mm after a 3 month follow-up. Clarification of stone free rate and the size of clinically insignificant fragments is needed when comparing results from different studies. A consensus should be achieved on a standard definition of levels of stone free rate. [17]

   Conclusion Top

SWL is generally considered a satisfactory treatment for renal and ureteral stones with a moderately high stone fragmentation rate and low complication rate. However the SFR depends on how it is defined and is statistically significantly reduced in patients with LP stones as opposed to NLP stones.

   References Top

Chaussy C, Brendel W, Schmiedt E. Extracorporeally induced destruction of kidney stones by shock waves. Lancet 1980;2:1265-8.  Back to cited text no. 1
Lingeman JE, Coury TA, Newman DM, Kahnoski RJ, Mertz JH, Mosbaugh PG, et al. Comparison of results and morbidity of percutaneous nephrostolithotomy and extracorporeal shock wave lithotripsy. J Urol 1987;138:485-90.  Back to cited text no. 2
Hacker A, Michel MS. Controversy on lower pole stones: Monitor or intervene? Urologe A 2012;51:368-71.  Back to cited text no. 3
Arzoz-Fabregas M, Ibarz-Servio L, Blasco-Casares FJ, Ramon-Dalmau M, Ruiz-Marcellan FJ. Can infundibular height predict the clearance of lower pole calyceal stone after extracorporeal shockwave lithotripsy? Int Braz J Urol 2009;35:140-9.  Back to cited text no. 4
Juan YS, Chuang SM, Wu WJ, Shen JT, Wang CJ, Huang CH. Impact of lower pole anatomy on stone clearance after shock wave lithotripsy. Kaohsiung J Med Sci 2005;21:358-64.  Back to cited text no. 5
Ng CF, McLornan L, Thompson TJ, Tolley DA. Comparison of 2 generations of piezoelectric lithotriptors using matched pair analysis. J. Urol 2004;172:1887-91.  Back to cited text no. 6
Wang R, Faerber GJ, Roberts WW, Morris DS, Wolf JS Jr. Single center North American experience with Wolf Piezolith 3000 in management of urinary calculi. Urology 2009;73:958-63.  Back to cited text no. 7
Öbek C, Önal B, Kantay K, Kalkan M, Yalçin V, Öner A, et al. The efficacy of extracorporeal shock wave lithotripsy for isolated lower pole calculi compared with isolated middle and upper caliceal calculi. J Urol 2001;166:2081-5.  Back to cited text no. 8
Sampaio FJ, Aragao AH. Limitations of extracorporeal shockwave lithotripsy for lower caliceal stones: Anatomic insight. J Endourol 1994;8:241-7.  Back to cited text no. 9
Aboutaleb H, El-Shazly M, Badr Eldin M. Lower pole midsize (1-2cm) calyceal stones: Outcome analysis of 56 cases. Urol Int 2012;89:348-54.  Back to cited text no. 10
Zomorrodi A, Buhluli A, Fathi S. Anatomy of the collecting system of lower pole of the kidney in patients with a single renal stone: A comparative study with individuals with normal kidneys. Saudi J Kidney Dis Transpl 2010;21:666-72.  Back to cited text no. 11
[PUBMED]  Medknow Journal  
Pearle MS, Lingeman JE, Leveillee R, Kuo R, Preminger GM, Nadler RB, et al. Prospective, randomized trial comparing shock wave lithotripsy and ureteroscopy for lower pole caliceal calculi 1cm or less. J Urol 2005;173:2005-9.  Back to cited text no. 12
Srisubat A, Potisat S, Lojanapiwat B, Setthawong V, Laopaiboon M. Extracorporeal shock wave lithotripsy (ESWL) versus percutaneous nephrolithotomy (PCNL) or retrograde intrarenal surgery (RIRS) for kidney stones. Cochrane Database Syst Rev 2009;4:CD007044.  Back to cited text no. 13
Neisius A, Wollner J, Thomas C, Roos FC, Brenner W, Hampel C, et al. Treatment efficacy and outcomes using a third generation shockwave lithotripter. BJU Int 2013;112:972-81.  Back to cited text no. 14
Leong WS, Liong ML, Liong YV, Wu DB, Lee SW. Does simultaneous inversion during extracorporeal shock wave lithotripsy improve stone clearance: A long-term, prospective, single-blind, randomized controlled study. Urology 2014;83:40-4.  Back to cited text no. 15
Mokhless IA, Abdeldaeim HM, Saad A, Zahran AR. Retrograde intrarenal surgery monotherapy versus shock wave lithotripsy for stones 10 to 20 mm in preschool children: A prospective, randomized study. J Urol 2014;191 (5 Suppl):1496-9.  Back to cited text no. 16
Somani BK, Desai M, Traxer O, Lahme S. Stone-free rate (SFR): A new proposal for defining levels of SFR. Urolithiasis 2014;42:95.  Back to cited text no. 17


  [Table 1], [Table 2]

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