REVIEW URRENT C OPINION

Extracorporeal shockwave lithotripsy for upper tract urolithiasis Jack Weaver and Manoj Monga

Purpose of review For the last three decades, extracorporeal shockwave lithotripsy (SWL) has been the mainstay of management of urolithiasis; recognized widely by patients and physicians for its noninvasive approach and good outcomes. Recent challenges by endoscopic approaches have driven ongoing research to refine indications, define outcomes and explore innovations. Recent findings Utilization of SWL remains high, despite increasing utilization of endoscopic approaches. Patient selection is critical – outcomes with percutaneous nephrolithotomy and ureteroscopy after failed SWL are not as good as those obtained in patients who have not had prior SWL. A structured training in ultrasound localization and proper patient positioning can have dramatic impacts on stone-free results. Stone size, location, Hounsfield unit stone attenuation and stone volume remain important predictors of outcomes. Renal cysts may negatively impact outcomes with SWL. Summary These recent studies highlight important considerations for patient selection, SWL technique and follow-up for patients undergoing SWL. New technologies hold promise but require further study. Keywords extracorporeal, indications, lithotripsy, shockwave

INTRODUCTION Extracorporeal shockwave lithotripsy (SWL) has been the mainstay of management of urolithiasis, though over the last decade it has been shadowed by advances in endoscopic procedures. This review will highlight recent articles exploring the utilization, training, indications, outcomes and innovations in the area of SWL.

to note that this study looks specifically at inpatient procedures; changes in SWL in the ambulatory surgery setting would not be captured from this database. As utilization remains high, it is important to be careful with patient selection – two studies report that secondary endoscopic procedures after failed SWL have unfavorable outcomes compared with primary endoscopic procedures in the appropriately selected patients. Zhong et al. [2 ] evaluated outcomes with PCNL for renal stones following failed extracorporeal SWL. In this retrospective study, they reported that patients undergoing PCNL after failed SWL commonly had stone fragments embedded beneath the urothelium. Furthermore, they reported that compared with patients undergoing &

SHOCKWAVE LITHOTRIPSY: UTILIZATION AND TRAINING Despite improvements in endoscopic instrumentation and technique, utilization of SWL has remained stable from 1999 to 2009. Ghani et al. [1] evaluated trends in surgery for upper urinary tract calculi in the USA using the Nationwide Inpatient Sample: 1999–2009. They reported that while there were shifts in inpatient management related to sex, race and age, hospitalization for ureteric calculi remained stable. An increase in utilization of percutaneous nephrolithotomy (PCNL) was identified, but ureteroscopy (URS) and SWL procedures remained stable in the study period. It is important www.co-urology.com

Glickman Urological and Kidney Institute, The Cleveland Clinic, Cleveland, Ohio, USA Correspondence to Manoj Monga, MD, 9500 Euclid Avenue/Q10, Cleveland, OH 44195, USA. Tel: +1 216 445 8678; fax: +1 216 636 0770; e-mail: [email protected] Curr Opin Urol 2014, 24:168–172 DOI:10.1097/MOU.0000000000000024 Volume 24  Number 2  March 2014

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Extracorporeal shockwave lithotri psy Weaver and Monga

KEY POINTS  New anatomical variables identified that impact outcomes with SWL.  Patients undergoing endoscopic procedures after SWL have inferior outcomes.  Novel biomedical device may allow stones to be displaced with ultrasound waves, improving the efficacy of SWL.

primary PCNL without prior SWL, the time for stone extraction was longer (95.8  12.0 vs. 80.6  13.2 min, P ¼ 0.018) the clearance rate was lower in group 1 (83.9 vs. 93.4%, P ¼ 0.021) and the postoperative hemoglobin drop was higher if the patient had initially been treated with SWL (2.22 vs. 1.46 g/dl, P ¼ 0.037). Overall success with PCNL was 92% for stones that had not been fragmented with SWL compared with 64% in stones that had been fragmented. They hypothesized that the fragility of the tissue post SWL and the need for digging and grasping to extract buried fragments lead to more blood loss in patients undergoing PCNL post SWL. Ho et al. [3 ] evaluated outcomes of URS for renal stones less than 2 cm in size, and reported that primary URS (URS was used as first treatment modality) was almost twice as likely to result in total stone clearance (64.3 vs. 39.1%, P ¼ 0.045) compared with secondary URS (URS in patients previously treated with failed extracorporeal shockwave lithotripsy). Both these studies have inherent selection bias related to retrospective studies; yet emphasize the importance of patient selection – as much as possible those patients better served by URS or PCNL should undergo this procedure immediately rather than first undergo a trial of SWL. Is there a way to impact outcomes with SWL using standardized training programs? Okada et al. [4 ] studied the impact of official technical training for urologists on the efficacy of SWL. This study evaluated 33 each of whom had performed at least 100 cases of SWL. After a structured training program, stone-free rates significantly improved from 66.3 to 87.2% (P ¼ 0.0001). There was a significant decrease in the average number of treatments required (1.8–1.4, P ¼ 0.010). After training, there was a significant increase in the utilization of ultrasonography in SWL for renal and proximal ureter stones (from 10.5 to 58.2%, P ¼ 0.0001). The number of SWL procedures performed in the semisupine position using stretcher wedges for distal ureter stones significantly increased from 19.9 to 57.9% &

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(P ¼ 0.0003). After multivariate analyses, the odds ratio (OR) for success after training compared with prior to training was OR ¼ 3.282 (P ¼ 0.0007). For renal and proximal stones, univariate analysis indicated that ultrasonic targeting was a significant factor for success (OR ¼ 2.25, P ¼ 0.012). For distal ureter stones, significantly lower ORs for success was found when SWL was conducted in the prone position (multivariate analysis, OR ¼ 0.23, P ¼ 0.004). This study demonstrates that structured training in ultrasound localization and proper patient positioning can have dramatic impacts on stone-free results.

SHOCKWAVE LITHOTRIPSY FOR RENAL STONES Investigators continue to explore methods of interpreting the preoperative computed tomography (CT) scan to help predict the success with SWL. Tanaka et al. evaluated the stone attenuation value and cross-sectional area on CT as predictive factors for success with SWL [5 ]. In this retrospective study of 75 patients, they found on multivariate analysis that only the stone attenuation value was an independent predictor of SWL success (P ¼ 0.023). Stone location (renal vs. ureteral) had no impact on success. Stone cross-sectional area had a tendency to be associated with SWL success (P ¼ 0.053) but did not reach significance, perhaps because of the sample size. Patients with a favorable stone attenuation [780 HU (Hounsfield units)] and cross-sectional area (0.4 cm2) had an OR for a successful result on SWL of 11.6 [95% confidence interval (CI), 3.9– 54.7, P < 0.001] compared to those with higher attentuations and/or larger cross-sectional areas. Skin-to-stone did not differ significantly between the success and failure groups. Stone size and location have been traditional criteria used to identify those patients best suited for SWL; indeed, typically a lower pole stone greater than 1 cm in size would be steered toward a percutaneous approach. Kim et al. [6 ] performed a retrospective study (n ¼ 22) of such patients, and reported that all patients were rendered stone-free after a mean of 3.8 (2.5) SWL sessions. However, patients with stones over 2 cm needed an average of 2.3 additional SWL sessions compared to patients with stones 1–2 cm (P ¼ 0.039). The authors conclude that SWL is a well tolerated, feasible treatment for solitary, lower calyceal stones over 1 cm. However, our interpretation of the findings is that it supports a cutoff of 1 cm as the upper limit for SWL in the lower pole. Do renal cysts impact outcomes with SWL? Kim et al. [7] reported on a patient with autosomal

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dominant polycystic kidney disease who presented with acute cyst rupture, hemorrhage and septic shock after SWL. There was some suspicion that the cysts may have been complex in characteristic; ¨ cu ¨k the patient required emergent nephrectomy. Gu et al. [8 ] conducted a retrospective study of 21 patients with simple renal cyst(s) greater than 35 mm in diameter. They reported stone-free rates were lower in these patients (33.3%) compared to their control group with no cysts (68.2%, P ¼ 0.017). No difference was noted in stone fragmentation; they attributed the difference in stone-free rates to an issue of clearance of fragments. The authors suggest that if patients with large renal cysts are considering SWL, they should first undergo percutaneous aspiration and sclerotherapy or laparoscopic cyst decortication. Alternatively, they suggest a retrograde ureteroscopic approach. Does the number of shocks administered impact the risk of complication when high-energy SWL settings are utilized? Hadj-Moussa et al. [9 ] conducted a retrospective study of 372 patients undergoing SWL at an energy setting of 24 kV to evaluate whether the number of shocks impacted the likelihood of a complication. The number of shocks utilized increased with increasing patient BMI and increasing stone burden. Overall SWL success rates increased from 65.6% at 4 weeks follow-up to 77.3% at 12 weeks postoperatively. Complication rates for the low, medium and high shock number cohorts were similar at 9.5, 7.8 and 7.2%, respectively (P ¼ 0.63). Complication rates were higher (41%) after unsuccessful SWL, but again did not differ based on the number of shocks administered (P ¼ 0.84). At high voltage, they conclude that there is no relationship between shock number and the rate of short-term complication development. &&

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SHOCKWAVE LITHOTRIPSY FOR URETERAL STONES &&

Phipps et al. [10 ] reported on a unique SWL approach to distal ureteric stones: the transgluteal approach. They conducted a retrospective review of 110 consecutive patients. Thirty-eight patients were treated in the prone position and 72 in the supine position with a transgluteal approach. More patients were stone-free after one treatment session with the transgluteal approach (78%) than the prone approach (40%, P < 0.001). Patients requiring URS after a failed second session of SWL was 37% with the prone approach compared with only 8% with the transgluteal approach. Khalil [11] compared SWL (n ¼ 37) with URS with holmium laser lithotripsy (n ¼ 45) for management of the impacted proximal ureteral stone. 170

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Though the initial stone-free rate after 1 month of the URS group was statistically significantly higher than SWL (80 vs. 67.6%), there was no significant difference at 3 months of follow-up (82.2 vs. 78.4%). SWL patients required more procedures than URS patients (1.5  0.8 vs. 1.02  0.15, P < 0.01). There was no significant difference in the complication rate of the SWL (24%) and URS (16%). Panah et al. [12 ] evaluated factors predicting success with emergency extracorporeal SWL in ureteric calculi. The stone free after emergency SWL was 73.2%; 48% of patients underwent SWL within 24 h of presentation and 78% of patients were treated within 48 h. Early treatment, lower HU and smaller stone size were associated with higher success rates, whereas number of shock waves and maximal intensity used (P values 0.2181 and 0.8172, respectively) did not impact outcomes. &

PEDIATRIC SHOCKWAVE LITHOTRIPSY Two studies evaluated factors that can predict outcomes with SWL in children. El-Assmy et al. [13 ] reported that stone size and HU predict successful SWL in children. They conducted a retrospective study of 57 children (age < 16 years) who underwent SWL monotherapy for renal stones. Only the stone length and number of HU had a statistically significant effect on SWL success. These two factors were further analyzed using a binary logistic regression model. Both factors maintained their statistically significant effect on SWL outcome, indicating that they acted independently. The SWL success rate was 58.6 and 25% for stones less than 12 mm and greater than 12 mm, respectively (P < .016). They also found that greater stone density (>600 HU) was a significant predictor of SWL failure. The authors found no significant association between age or sex on the stone-free status. They also found that the probability of SWL success was the same for the calyceal stones and renal pelvis. El-Nahas et al. [14] utilized a multivariate analysis model for estimating the stone-free probability following pediatric SWL. In a retrospective review of 207 children undergoing SWL monotherapy, they reported that the independent factors that adversely affected the stone-free rate were increasing stone length and calyceal site of the stone. The OR for residual fragments increased by 1.123-fold for each 1 mm increase of the stone length. In comparison to stones in the renal pelvis, the OR of residual stones increased 2.673-fold for upper and middle calyceal stones and 4.208-fold for stones in the lower calyx. Using the logistic regression equation, the authors were able to show the probabilities of being stone-free following SWL in relation to stone &&

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Extracorporeal shockwave lithotri psy Weaver and Monga

lengths and site. They recommend SWL for renal pelvis stones less than 24 mm, upper or middle calyceal stones less than 15 mm and lower calyceal stones less than 11 mm. These two studies agree on stone size as an important predictor of outcomes; why the discrepancy in findings with regards to calyceal location is unclear. Hatipoglu et al. [15 ] conducted a retrospective comparison of SWL (n ¼ 108) and Microperc (n ¼ 37) for treatment of pediatric renal stones. In the SWL group, 29% of patients needed a secondary SWL session and 5% needed a tertiary SWL session. With multiple sessions, 88% of patients were considered treated successfully (residual stone fragments < 4 mm). In contrast, a single Microperc session led to an immediate stone-free rate of 76% that increased to 87% at the 1-month follow-up. Hospital stay (49 vs. 8 h) and fluoroscopy time (147 vs. 60 s) was longer with the Microperc. In summary, there is a trade off – outcomes are similar at 1 month, but SWL require more procedures and Microperc requires more fluoroscopy and longer hospital stays. Garg et al. [16 ] studied the long-term effects of extracorporeal SWL in paediatric patients. They followed 70 children and reported that no patients developed hypertension [measured diastolic blood pressure (DBP) >95th percentile], but four patients had prehypertension (DBP >90th percentile). However, three of these four patients had prehypertension at the time of SWL. The fourth patient was 6 years at SWL and showed an increase in DBP of 10 mmHg over the pre-SWL DBP after 10 years of follow-up. There was no evidence of hyperglycemia or renal atrophy attributed to pediatric SWL. In summary, pediatric SWL appears well tolerated on long-term follow-up. &&

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NEW TECHNOLOGY FOR SHOCKWAVE LITHOTRIPSY Can we move stones into a more favorable location for stone fragmentation or stone clearance? Harper et al. [17 ] evaluated a focused ultrasound to expel calculi from the kidney. A series of 2–8 mm stones (calcium oxalate monohydrate) were implanted in interpolar or lower pole calyces in an animal model. Seventeen of 26 stones (65%) were successfully relocated from the calyx to the renal pelvis [3 ], ureteropelvic junction (UPJ) [2 ] or ureter [12 ]. Stone size did not appear to be associated with successful repositioning. Two calculi were moved out of the calyx but did not reach the renal pelvis. The remaining seven stones were observed to move upon exposure to push bursts but were not dislodged from the calyx. 14.2  7.9 min and a mean of 23  16 push bursts were required. Average estimated displacement was 5.6  2.7 linear cm when comparing fluoroscopic &

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images before and after the treatment. Overall, the morphology of kidneys treated with ultrasonic propulsion was indistinguishable from that of the kidneys of untreated control and sham treated pigs. Gross hematuria was not observed in any experimental group. Creatinine was normal in all pigs based on known reference values for the porcine model. In the author’s observations, pulses that did not relocate the stone toward the UPJ or ureter appeared limited by the alignment angle of ultrasound forces and not because of the inadequate force generation. Pishchalnikov et al. [18 ] evaluated the in-vitro acoustic characteristics of the LithoGold LG-380 Lithotripter and assessed renal injury in a porcine model. They determined that the Lithogold lithotripter energy source is relatively consistent, with a small range in amplitude over settings recommended for clinical use (7 MPa at PL-1 to 19 MPa at PL-9) and reached low maximum pressures (21 MPa at PL-11). At 20 mm, the focal zone of this lithotripter was determined to be wider than any other lithotripter for which characterization data have been reported. Treatment of the pig model produced very minor injury to the renal parenchyma. Kidney injury was limited to areas of hemorrhage in the renal medulla. This was the case not only when treatment followed the slow shock wave (SW)-rate (60 SW/ min), stepwise power ramping protocol recommended by the manufacturer, but also when all SWs were delivered at the maximum power setting (PL-11) at fast SW-rate (120 SW/min). Dai et al. [19] conducted a retrospective analysis of their experience with a new generation electrohydraulic lithotripter: the Medispec E3000. They studied 168 solitary renal and ureteral stones; 75 were treated with a low power ramping protocol (11–12–17 kV) and 93 stones were treated with a high power ramping protocol (15–17–22 kV). There was no significant difference in stone-free rate (SFR) for stones treated with the low power ramping protocol (61.3%) compared to stones treated with the high power ramping protocol (70%, P ¼ 0.42). No significant difference was seen in SFR based on stone location (P ¼ 0.59). Overall, the calculated efficiency quotient (EQ) for the Medispec E3000 is 54%. The EQ for stones managed with the low power ramping protocol was 49.4% and for the high power ramping protocol was 59.5%. There was no significant difference in the number of ancillary treatments between the two treatment protocols (P ¼ 0.18). &

CONCLUSION Patient selection remains critical for patients undergoing SWL; it is now clear that outcomes with salvage URS or PCNL are not as good as those who undergo an endoscopic approach as the first

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modality. Utilizing predictive markers, such as stone attenuation can help identify those patients best suited for SWL. Indeed, prognostic variables are helpful in the management of pediatric patients also. Consideration should be given for the potential impact renal cysts may have on surgical outcome. New technologies hold promise for a continued, and perhaps expanded future for SWL in the stone surgeon’s armamentarium. Acknowledgements None. Conflicts of interest There are no conflicts of interest.

REFERENCES AND RECOMMENDED READING Papers of particular interest, published within the annual period of review, have been highlighted as: & of special interest && of outstanding interest 1. Ghani KR, Sammon JD, Karakiewicz PI, et al. Trends in surgery for upper urinary tract calculi in the USA using the Nationwide Inpatient Sample: 1999– 2009. BJU Int 2013; 112:224–230. 2. Zhong W, Gong T, Wang L, et al. Percutaneous nephrolithotomy for renal & stones following failed extracorporeal shockwave lithotripsy: different performances and morbidities. Urolithiasis 2013; 41:165–168. Success rate with PCNL drops from 92 to 64% if the patient has had prior SWL – if stone burden is large go directly to PCNL. 3. Ho CC, Hee TG, Hong GE, et al. Outcomes and safety of retrograde intra& renal surgery for renal stones less than 2 cm in size. Nephrourol Mon 2012; 4:454–457. Success rate with URS drops from 64 to 39% if the patient has had prior SWL – if stone or patient characteristics suggest URS will be more effective, go directly to URS. 4. Okada A, Yasui T, Taguchi K, et al. Impact of official technical training for uro&& logists on the efficacy of shock wave lithotripsy. Urolithiasis 2013; 41:487– 492. Training in ultrasonography for SWL localization of renal and proximal ureter stones and semisupine positioning using stretcher wedges for distal ureter stones significantly increases stone-free results. The OR of a successful treatment after training was 3.3. This study demonstrates that structured training in ultrasound localization and proper patient positioning can have dramatic impacts on stonefree results. 5. Tanaka M, Yokota E, Toyonaga Y, et al. Stone attenuation value and cross& sectional area on computed tomography predict the success of shock wave lithotripsy. Korean J Urol 2013; 54:454–459. Patients with a favorable stone attenuation (780 HU) and cross-sectional area (0.4 cm2) are 11 more likely to have a successful result with SWL.

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6. Kim TB, Lee SC, Kim KH, et al. The feasibility of shockwave lithotripsy for & treating solitary, lower calyceal stones over 1 cm in size. Can Urol Assoc J 2013; 7:E156–E160. Lower pole stones greater than 1 cm in size will require on average over three SWL sessions to render stone-free. 7. Kim HG, Bae SR, Lho YS, et al. Acute cyst rupture, hemorrhage and septic shock after a shockwave lithotripsy in a patient with autosomal dominant polycystic kidney disease. Urolithiasis 2013; 41:267–269. 8. Gu¨cu¨k A, Oztu¨rk U, Uyetu¨rk U, et al. Do renal cysts affect the success of && extracorporeal shockwave lithotripsy? A retrospective comparative study. Adv Urol 2013; 2013:978180. SWL for renal stones in patients with renal cysts greater than 35 mm in size have a 50% decrease in stone clearance – consider URS or decompression of the cysts prior to SWL. 9. Hadj-Moussa M, Brown JA. Effect of high shock number on acute complica& tion development after extracorporeal shockwave lithotripsy. J Endourol 2013; 27:1015–1019. Number of shockwaves does not impact the risk of complication with high-energy SWL. 10. Phipps S, Stephenson C, Tolley D. Extracorporeal shockwave lithotripsy to && distal ureteric stones: the transgluteal approach significantly increases stonefree rates. BJU Int 2013; 112:E129–E133. Supine transgluteal SWL is superior to prone SWL for distal ureteral stones. 11. Khalil M. Management of impacted proximal ureteral stone: extracorporeal shock wave lithotripsy versus ureteroscopy with holmium – YAG laser lithotripsy. Urol Ann 2013; 5:88–92. 12. Panah A, Patel S, Bourdoumis A, et al. Factors predicting success of & emergency extracorporeal shockwave lithotripsy (eESWL) in ureteric calculi-a single centre experience from the United Kingdom (UK). Urolithiasis 2013; 41:437–441. SWL ureteral stones soon after presentation (

Extracorporeal shockwave lithotripsy for upper tract urolithiasis.

For the last three decades, extracorporeal shockwave lithotripsy (SWL) has been the mainstay of management of urolithiasis; recognized widely by patie...
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