pediatric urinary stones are rare but have lifelong consequences . because children have a small body size and delicate tissues , and because the use of general anesthesia is likely , treatment for pediatric stone disease requires thoughtful consideration and individualized therapy . since extracorporeal shock wave lithotripsy ( eswl ) for pediatric urinary stones was first introduced by newman et al .   in 1986 , numerous reports have demonstrated the efficacy and safety of eswl in the pediatric population [ 4 - 20 ] . eswl is now considered a first - line treatment for pediatric stone disease because of its minimal invasiveness and high success rate . recent reductions in the size of endourological instruments , improvements in electronic video imaging systems , and advancements in endourological skill have given clinicians alternative surgical options such as ureteroscopic surgery ( urs ) or percutaneous nephrolithotomy ( pcnl ) for first- or second - line treatment of pediatric urolithiasis , including in cases of eswl failure . nevertheless , the identification of variables that predict successful outcomes of eswl in the pediatric population would be useful . therefore , we aimed to determine the factors affecting the outcome of eswl for unilateral urinary stones in children by reviewing 17 years of experience at samsung medical center . a total of 81 pediatric patients with urinary stones treated by eswl from january 1995 through may 2012 at samsung medical center were retrospectively reviewed . the following clinical data were documented : age and gender of patients , laterality and location of stones , maximum size of stones , number of eswl sessions , and treatment outcomes after eswl . evaluated treatment outcomes after eswl were stone - free rate at 3 months after eswl , success within a single session , and success within three sessions . we investigated treatment outcomes according to stone location and analyzed the factors affecting success within three sessions . exclusion criteria were disorders of the kidney , liver , intestine , or cardiovascular system ; congenital anomalies of the urinary tract or nervous system ; or psychological problems . children who underwent other surgical procedures such as pcnl or endoscopic treatment before eswl were also excluded . all stones were identified by simple kidney - ureter - bladder x - ray , ultrasonography , or computed tomography scan if necessary . , all patients were routinely evaluated through a medical history , a physical examination , urinalysis , urine culture , serum chemistry profile , and coagulation profile . children with poor cooperation were treated under general anesthesia ; others were treated with analgesia without general anesthesia . children with renal stones or upper ureteral stones were treated in the supine position , whereas children with mid or distal ureteral stones were treated in the prone position . the mpl-9000 lithotripter ( dornier medizintechnik , germering , germany ) was used from january 1995 to may 2008 , and the modulith slx - f2 lithotripter ( storz medical ag , tgerwilen , switzerland ) was used from june 2008 to may 2012 . treatment was initiated at 8.2 kv , which was gradually increased up to 17.0 kv with a maximum of 3500 shocks . the shockwave frequency was 1 hz . the interval between treatment sessions was 2 to 4 weeks to allow passage of fragmented debris and kidney recovery . patients were evaluated 1 and 3 months after the last session by imaging modalities such as kidney - ureter - bladder x - ray , ultrasound , or computed tomography scan , if necessary . success was defined as stone - free status or clinically insignificant residual fragments ( cirfs ) . children who underwent additional procedures ( urs or pcnl ) were not counted as a success . chicago , il , usa ) . a chi - square test and a t test were used to analyze the related parameters and treatment outcomes according to the method of anesthesia . a t test and logistic regression analysis were used to evaluate the factors affecting the outcome of eswl . this study was approved by the institutional review board of samsung medical center . under the board 's approval , a total of 81 pediatric patients with urinary stones treated by eswl from january 1995 through may 2012 at samsung medical center were retrospectively reviewed . the following clinical data were documented : age and gender of patients , laterality and location of stones , maximum size of stones , number of eswl sessions , and treatment outcomes after eswl . evaluated treatment outcomes after eswl were stone - free rate at 3 months after eswl , success within a single session , and success within three sessions . we investigated treatment outcomes according to stone location and analyzed the factors affecting success within three sessions . exclusion criteria were disorders of the kidney , liver , intestine , or cardiovascular system ; congenital anomalies of the urinary tract or nervous system ; or psychological problems . children who underwent other surgical procedures such as pcnl or endoscopic treatment before eswl were also excluded . all stones were identified by simple kidney - ureter - bladder x - ray , ultrasonography , or computed tomography scan if necessary . , all patients were routinely evaluated through a medical history , a physical examination , urinalysis , urine culture , serum chemistry profile , and coagulation profile . children with poor cooperation were treated under general anesthesia ; others were treated with analgesia without general anesthesia . children with renal stones or upper ureteral stones were treated in the supine position , whereas children with mid or distal ureteral stones were treated in the prone position . the mpl-9000 lithotripter ( dornier medizintechnik , germering , germany ) was used from january 1995 to may 2008 , and the modulith slx - f2 lithotripter ( storz medical ag , tgerwilen , switzerland ) was used from june 2008 to may 2012 . treatment was initiated at 8.2 kv , which was gradually increased up to 17.0 kv with a maximum of 3500 shocks . the shockwave frequency was 1 hz . the interval between treatment sessions was 2 to 4 weeks to allow passage of fragmented debris and kidney recovery . patients were evaluated 1 and 3 months after the last session by imaging modalities such as kidney - ureter - bladder x - ray , ultrasound , or computed tomography scan , if necessary . success was defined as stone - free status or clinically insignificant residual fragments ( cirfs ) . children who underwent additional procedures ( urs or pcnl ) were not counted as a success . statistical analyses were performed by using spss ver . 18.0 ( spss inc . , chicago , il , usa ) . a chi - square test and a t test were used to analyze the related parameters and treatment outcomes according to the method of anesthesia . a t test and logistic regression analysis were used to evaluate the factors affecting the outcome of eswl . this study was approved by the institutional review board of samsung medical center . under the board 's approval , the study population was 64 children , 42 boys and 22 girls ( mean age , 9.25.2 years ; range , 0.5 to 15.9 years ) . calculi were on the right side in 34 cases ( 53.1% ) and on the left side in 30 cases ( 46.9% ) . of the 64 patients , 5 ( 7.8% ) had urinary stones in the upper or mid calyx , 5 ( 7.8% ) in the lower calyx , 9 ( 14.1% ) in the renal pelvis , 15 ( 23.4% ) in the upper ureter , 17 ( 26.6% ) in the lower ureter , and 13 ( 20.3% ) in multiple locations . of the 64 patients , 58 ( 90.6% ) were treated by eswl without other surgical procedures and 54 ( 84.4% ) were successfully treated within three eswl sessions . the percentage of treatment success for a single eswl session was 80.0% when the stone was solitary and located in the upper or mid calyx , 80% if in the lower calyx , 77.8% if in the renal pelvis , 93.3% if in the upper ureter , and 70.6% if in the lower ureter . the percentage of treatment success for a single eswl session in patients with stones in multiple locations was 30.8% , which was significantly lower than that for patients with a stone in a single location . the success rate within three eswl sessions was 100% ( 5 of 5 patients ) when the stone was solitary and located in the upper or mid calyx , 100% ( 5 of 5 patients ) if in the lower calyx , 88.9% ( 8 of 9 patients ) if in the renal pelvis , 100% ( 15 of 15 patients ) if in the upper ureter , and 88.2% ( 15 of 17 patients ) if in the lower ureter . to avoid possible injury to developing reproductive systems , 2 of 17 patients ( 11.8% ) with a solitary lower ureter stone were treated with additional urs after a single eswl session . four of 13 patients ( 30.8% ) with stones in multiple locations were treated with additional surgical treatments : two with urs , one with pcnl , and one with urs and pcnl . when the shockwave - related parameters and treatment outcomes were analyzed according to the method of anesthesia , the general anesthesia group was younger ( p<0.001 ) and was more likely to have multiple stones ( p=0.005 ) . the success rate was not significantly different between the two groups ( table 3 ) . transient renal colic , which was managed by antispasmodic and anti - inflammatory treatment , was observed in 3 patients ( 4.7% ) . steinstrasses occurred in 2 of 13 patients ( 15.4% ) with stones in multiple locations and was treated successfully by urs . no other complications occurred in any patients , such as hemorrhage that necessitated transfusion , infection , or injury of other organs . in the univariate analysis , multiplicity ( p<0.001 ) and large stone size ( > 10 mm ) ( p=0.001 ) significantly decreased the success rate within three eswl sessions ( table 4 ) . in the multivariate analysis , multiplicity ( odd ratio [ or ] , 0.080 ; 95% confidence interval [ ci ] , 0.012 to 0.534 ; p=0.009 ) and large stone size ( or , 0.112 ; 95% ci , 0.018 to 0.707 ; p=0.020 ) also decreased the success rate within three eswl sessions ( table 5 ) . since the first report of success of eswl in a pediatric population by newman et al . , numerous reports have shown the safety and efficacy of eswl for treating pediatric urinary stones [ 4 - 20 ] . the joint european association of urology / american urological association nephrolithiasis guideline panel 's 2007 guideline for the management of ureteral calculi states , " treatment choices should be based on the child 's size and urinary tract anatomy . the small size of the pediatric ureter and urethra favors the less invasive approach of eswl " . therefore , eswl remains a first - line treatment option for most pediatric cases of urinary stone disease . in addition to its noninvasive nature , eswl has other advantages in the treatment of pediatric urinary stones . for younger patients , the pediatric ureter is more elastic , more distensible , and shorter , which facilitates the passage of stone fragments and compensates for the narrower lumen . the small body volume of children allows the shockwaves to be transmitted with minimal energy loss . however , the application of many eswl sessions is a burden to pediatric patients because of the likely use of general anesthesia during the procedure and the increased susceptibility of children to radiation exposure . until now , studies on eswl for pediatric urinary stone disease have reported a wide variation in success rate resulting from variation in the methods of different studies , the age of included patients , the machines used , the definition of success , and stone characteristics including size , location , and multiplicity ( table 6 ) [ 4 - 20 ] . thus , care must be taken in interpreting the success rate of different series , because 1 ) some reports on eswl monotherapy report success rates resulting from a single session and others report results from several sessions , and 2 ) some series define success as only a stone - free state whereas others include cirfs . in our study , we analyzed results by several definitions , namely , stone - free rate at 3 months after eswl , success within a single session , and success within three sessions . most previous studies defined success as a stone - free rate at 3 months after eswl , reporting success rates of 71% to 97% . in our study , the stone - free rate at 3 months after eswl was 90.6% . we believe that our analysis of treatment success within one or three eswl sessions is an innovative approach . in clinical practice , an important issue during eswl treatment for pediatric urinary stone disease is the number of eswl sessions required for success . because eswl in pediatric patients frequently requires general anesthesia when a clinician encounters a pediatric patient with stone disease , several factors affect success , such as stone location , size , and multiplicity . we surmised that three sessions of eswl would be a generally acceptable number for patients and their parents ; thus , we analyzed factors affecting treatment success within three eswl sessions . the overall success rates were 70.3% for a single session and 84.4% for three eswl sessions . when urinary stones were not found in multiple locations , the success rate was 80.4% for a single eswl session and 94.1% for three sessions . some studies suggest that no urinary stones in children are insignificant ; others define cirfs as 3 or 4 mm . although children 's ureters are more elastic , more distensible , and shorter than the ureters of adults , thus permitting easier passage of stone fragments , the narrow lumen of the pediatric ureter interferes with the expulsion of stone fragments . our analysis revealed that factors lowering the treatment success rate were stone multiplicity and large size ( > 10 mm ) , as expected from the results of previous reports . when patients with multiple stones were excluded , three patients did not achieve success within three eswl sessions . of these three , one had a 22-mm staghorn stone in the renal pelvis that completely fragmented without complication in 5 eswl sessions . the remaining two patients had lower ureteral stones that were not fragmented in a single eswl session . we did not attempt further eswl because of difficulties with localization over the sacroiliac joint and to avoid possible injury to the developing reproductive systems . an interesting finding of this study was that the success rate did not differ by stone location . when stones are in the lower pole calyx , the success rate of eswl depends not only on successful fragmentation but also on stone fragment clearance . several studies have demonstrated a significantly lower success rate after eswl for lower pole stones than for other kidney locations . however , a recent study by goktas et al .   reported that eswl was highly successful for lower calyceal stones in pediatric patients compared with adults . the study suggested that eswl can be a first - line treatment for managing lower calyceal stones in children . the authors hypothesized that the high success rate of eswl treatment of pediatric lower calyceal stone resulted from 1 ) less shockwave energy loss during travel through the small body volume of a child , 2 ) the shorter ureter length in children , and 3 ) the more elastic and distensible ureters in children . in our study , the success rate for stones in the lower pole calyx was not significantly different from that of stones in other kidney locations : 80% for a single eswl session and 100% for three sessions . concurring with previous reports , we recommend eswl as a first - line treatment , even for stones located in the lower pole calyx . however , our results were from a retrospective analysis with a small number of patients ( n=5 ) ; thus , definite conclusions can not be drawn about the success of eswl for lower calyceal stones . in our study , 2 of 64 patients ( 3.1% ) experienced steinstrasse , which was treated by urs without sequelae . both patients initially had multiple urinary stones . of the possible complications after eswl for pediatric stone disease , steinstrasses seem to be most challenging and mainly results from large fragments or multiplicity . however , with advances in medical technology , the miniaturization of ureteroscopes has made treatment of steinstrasses easier , resulting in fewer complications . therefore , we recommend eswl as a first - line treatment even for large or multiple stones , although this results in a risk of steinstrasse . however , during the study period , our interpretation of stone characteristics including stone location and size did not change . neither did the eswl protocol for stone treatment . to the best of our knowledge , this study includes the largest number of pediatric stone patients in korea . if a child has a large urinary stone ( > 10 mm ) or multiplicity , the parents should be informed of the probability of needing several eswl sessions for complete stone fragmentation . in our 17-year single - institution experience , most pediatric urinary stone patients ( 58 of 64 [ 90.6% ] ) were successfully treated by eswl alone without additional procedures . the factors decreasing the success rate within three eswl sessions were multiplicity or large stone size ( > 10 mm ) . no significant difference in success rate was observed by stone location for patients without multiplicity .
purposeextracorporeal shock wave lithotripsy ( eswl ) is a first - line treatment for pediatric urinary stone disease . 
 we aimed to determine the factors affecting the outcome of eswl for unilateral urinary stones in children.materials and methodsa total of 81 pediatric patients aged 0 to 16 years with urinary stones treated by eswl from january 1995 through may 2012 were retrospectively reviewed . 
 all patients were required to have unilateral urinary stone disease . 
 children who underwent other surgical procedures before eswl were excluded . 
 outcomes evaluated after eswl were the stone - free rate at 3 months after eswl , success within a single session , and success within three sessions . 
 factors affecting the success within three sessions were also analyzed.resultsthe final analysis was for 42 boys and 22 girls ( mean age , 9.25.2 years ) . 
 of these 64 patients , 58 ( 90.6% ) were treated by eswl without other surgical procedures and 54 ( 84.4% ) were successfully treated within three eswl sessions . in the multivariate analysis , 
 multiplicity ( odds ratio [ or ] , 0.080 ; 95% confidence interval [ ci ] , 0.012 to 0.534 ; p=0.009 ) and large stone size ( > 10 mm ; or , 0.112 ; 95% ci , 0.018 to 0.707 ; p=0.020 ) were significant factors that decreased the success rate within three eswl sessions.conclusionsmost of the pediatric urinary stone patients in our study ( 90.6% ) were successfully treated by eswl alone without additional procedures . 
 if a child has a large urinary stone ( > 10 mm ) or multiplicity , clinicians should consider that several eswl sessions might be needed for successful stone fragmentation .