|Year : 2019 | Volume
| Issue : 2 | Page : 109-116
Co-existing pediatric ureteropelvic junction obstruction and vesicoureteric reflux: Prevalence and implications
Shalini Hegde, Prema Menon, Katragadda Lakshmi Narasimha Rao
Department of Pediatric Surgery, Postgraduate Institute of Medical Education and Research, Chandigarh, India
|Date of Web Publication||1-Mar-2019|
Dr. Prema Menon
Department of Pediatric Surgery, Advanced Pediatrics Centre, Postgraduate Institute of Medical Education and Research, Room No. 3103, Level 3-A, Chandigarh - 160 012
Source of Support: None, Conflict of Interest: None
| Abstract|| |
Purpose: The purpose of this study is to ascertain the coexistence of ipsilateral vesicoureteric reflux (VUR) with ureteropelvic junction obstruction (UPJO) and to compare postpyeloplasty outcome in patients with and without associated VUR.
Materials and Methods: Prospective study from 2014 to 2016 of consecutive children (n = 135) undergoing pyeloplasty. Data of patients without (Group 1) and with (Group 2) associated ipsilateral VUR were compared.
Results: Thirty-five patients (25.9%) had ipsilateral VUR along with UPJO (Group 2). This group showed the following unique features: (1) Higher percentage of infants (31/35) compared to Group 1 (62/100) (P = 0.003) (2) VUR in the contralateral (normal) kidney in 21/35 (60%) cases and nil in Group 1 (3) Significantly less preoperative differential renal function in children above 1 year (P = 0.007) (4) Presence of renal scars (18 units) and pyelonephritic changes (6 units) in Group 2 at the 1-year follow-up dimercaptosuccinic acid renal scan. Both groups showed improvement in function 3 months after pyeloplasty with no statistically significant difference. Improvement in drainage on the renal scan was better in Group 1 at 3 months postoperative (P = 0.015) as well as between 3 months and 1-year follow-up (P = 0.052).
Conclusion: The prevalence of VUR was 25.9% in this study and 33.3% in ≤1 year age group. There was a loss of function in delayed presenters with associated ipsilateral VUR. There was delayed drainage postpyeloplasty in patients with VUR. A preoperative voiding cystourethrogram should be done in children <1 year age before pyeloplasty so that associated VUR if detected can be concurrently managed along with pyeloplasty and preserve nephrons affected by the dual pathology.
Keywords: Ipsilateral, outcome, pediatric, pyeloplasty, ureteropelvic junction obstruction, vesicoureteric reflux
|How to cite this article:|
Hegde S, Menon P, Narasimha Rao KL. Co-existing pediatric ureteropelvic junction obstruction and vesicoureteric reflux: Prevalence and implications. J Indian Assoc Pediatr Surg 2019;24:109-16
|How to cite this URL:|
Hegde S, Menon P, Narasimha Rao KL. Co-existing pediatric ureteropelvic junction obstruction and vesicoureteric reflux: Prevalence and implications. J Indian Assoc Pediatr Surg [serial online] 2019 [cited 2020 Nov 23];24:109-16. Available from: https://www.jiaps.com/text.asp?2019/24/2/109/253343
| Introduction|| |
Ureteropelvic junction obstruction (UPJO) and vesicoureteric reflux (VUR) are the most common pathological conditions in pediatric urology, with 9%–14% of patients with UPJO likely to have concomitant VUR.,, Whether the coexistence is a random event, attributable to a single developmental abnormality or due to ureteral kinking and inflammation caused by VUR has not yet been established. Children may present years after a successful pyeloplasty, with urinary tract infection (UTI) and deteriorating renal function due to missed reflux. A diagnostic dilemma exists in casting a net wide enough to identify all cases with associated VUR while avoiding the unpleasant effects of a voiding cystourethrogram (VCUG) in those without the association.,,, There is also a debate as to which of them should be treated first.
The purpose of this study was to assess the prevalence of VUR in all patients diagnosed with UPJO over a 2-year study period and to study the effect of ipsilateral VUR on drainage and differential renal function (DRF) at 3 months and 1 year after the pyeloplasty.
| Materials and Methods|| |
A prospective study was conducted in the Pediatric Surgery department of a tertiary care center from March 2014 to August 2016 of consecutive children, aged between 0 and 12 years diagnosed with UPJO to specifically assess the presence of associated VUR and its implications on the outcome. Approval was taken from the Institute Ethics Committee before the start of the study (1TRG/PG-2014/16137-63).
All patients initially underwent ultrasonography (USG) of kidney, ureter, bladder (KUB) region, blood urea and serum creatinine measurement and urine culture and sensitivity (C and S).
The UPJO was defined by an obstructive drainage pattern on renal dynamic scan using ethylene dicysteine (EC) with a draining per-urethral catheter. Lasix was given at the start of the study. If the renal function tests were normal, the diagnosis was further confirmed by an intravenous urography (IVU) with a draining per-urethral catheter. Retention of contrast in the pelvicalyceal system in the post-lasix 20-min film was considered as UPJO. Use of a draining urinary catheter for EC scan and IVU helped to confirm UPJO in the presence of VUR, especially Grade 3–5. All patients also underwent VCUG in the filling and voiding phase preoperatively. Radiological features of bladder outlet obstruction, for example, posterior urethral valves, and neurogenic bladder, especially in patients with bilateral VUR were carefully looked for on the VCUG as well as by history and clinical examination and ruled out. VUR was graded as per the International study classification.
Patients who had previously undergone pyeloplasty or intervention for VUR and those with other associated urological problems were excluded from the study. The remaining patients were divided into two groups as follows: Group 1: patients with UPJO alone and Group 2: patients with UPJO and associated VUR.
Informed consent was taken from the parents for pyeloplasty and the requirement for preoperative VCUG. All the patients underwent open modified Anderson Hynes pyeloplasty through an anterolateral retroperitoneal approach. Double J (DJ) stent placed at the time of pyeloplasty was removed 2–3 weeks later under short general anesthesia as a day care procedure. Patients were discharged 2 days after the pyeloplasty on uroprophylaxis (oral amoxycillin; 10 mg/kg hs) until DJ stent removal in Group 1 or until advised to stop in Group 2. Parents were advised to maintain preputial hygiene as we have no routine policy of performing circumcision in boys with VUR. Urine C & S was repeated after DJ stent removal.
Postoperatively, renal function and drainage were assessed by diuretic renogram (EC scan) and IVU after 3 months with draining catheter in situ. The EC scan was repeated 1 year after surgery. Subsequently, only USG KUB was performed on a yearly basis.
Some general guidelines were followed in the management of VUR. In asymptomatic VUR of any grade in infants and Grade I–II VUR in children >1 year age, initial conservative management with uroprophylaxis was preferred, and VCUG repeated at 1-year follow-up. Patients with high-grade VUR, recurrent UTI, and/or a single functioning system were advised early endoscopic dextranomer injection or ureteric reimplantation 3–6 months after the pyeloplasty. VCUG was repeated 3 months later to confirm resolution of VUR. Dimercaptosuccinic acid (DMSA) scan was performed in Group 2 patients preoperatively and 1 year after pyeloplasty. Renal scar was defined as the presence of persistent photopenia.
Successful pyeloplasty was defined as resolution of preoperative symptoms, nonobstructive drainage pattern and improvement or maintenance in function on renal dynamic scan and IVU. The stable function was defined as DRF ±5% compared to preoperative values with values above or below that considered as improvement or deterioration. The drainage on renal dynamic scan was defined as follows: unobstructed drainage (UOD): significant clearance by the end of the dynamic study and minimal retention at 3 h; slow UOD: Significant retention with moderate tracer clearance by the end of the dynamic study and minimal retention at the end of 3 h; and delayed drainage: significant retention with moderate tracer clearance by the end of the dynamic study with moderate tracer retention at 3 h.
A scoring system created by us was used to assess function and drainage on IVU [Table 1]. After an initial plain film, nonionic contrast solution was given as intravenous bolus. The first film was routinely taken at 7 min followed by films at 15 min, 30 min, 1 h, 2 h and occasionally at 4 h. Intravenous lasix was then given and the films taken after 5, 10, and 20 min.
|Table 1: Assessment and grading of renal function and drainage on intravenous urography|
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Patients were followed up in the outpatients on a regular basis and only those with at least 1-year follow-up were analyzed.
Discrete categorical data were presented as n (%). Continuous data were written either in the form of its mean and standard deviation or as median and interquartile range. The normality of quantitative data was checked by measures of Kolmogorov–Smirnov tests of normality. For skewed data or ordered categorical data, nonparameteric Mann–Whitney U-test was used for statistical analysis of two groups. For normally distributed data, Student t-test and for categorical data, comparisons were made by Pearson Chi-square test or Fisher's exact test. Intergroup and intragroup comparison of drainage was performed with Chi-square test. All the statistical tests were two-sided and were performed at a significance level of α = 0.05. The analysis was conducted using Statistical software SPSS version 22.0, (IBM Corporation, Armonk, New York, USA).
| Results|| |
A total of 173 patients were investigated for UPJO during the study period. Those with crossing vessel (n=13), previous pyeloplasty elsewhere (n=8), associated vesico-ureteric junction obstruction (n=2), urogenital sinus (n=1), and duplex system (n=3) were excluded. Four patients with papery thin parenchyma and DRF <5% required nephrectomy. Another 7 patients were excluded as they were considered to have only VUR and not UPJO after repeated investigations.
The final analysis was performed in 135 patients who satisfied the eligibility criteria [Table 2]. The prevalence of VUR was 25.9% (35/135) in the study group and 33.3% (31/93) in children aged ≤1 year.
The number of infants in Group 2 was statistically highly significant (P = 0.003). The mean age of presentation above 1 year age was lesser in Group 2, but not statistically significant (P = 0.2234) [Table 2].
All except 7 in Group 1 and 2 in Group 2 had normal renal function tests. The blood urea was 26.357 ± 22.699 mg/dL, (8–142 mg/dL) (median 21 mg/dL) in Group 1 and 21.022 ± 13.69 mg/dL (5–80 mg/dL) (median 15 mg/dL) in Group 2. The serum creatinine levels were 0.528 ± 0.527 mg/dL (0.1–4.8 mg/dL), (median 0.4 mg/dL) in Group 1 and 0.422 ± 0.279 mg/dL (0.1–1.8 mg/dL), (median 0.4 mg/dL) in Group 2. One patient in Group 1 had hypertension and another presented with renal rickets.
On USG, the parenchyma was grossly thin in 70/100 (70%) in Group 1 and 23/35 (65.7%) in group 2. In children >1 year, the preoperative DRF was significantly reduced in Group 2 patients (P = 0.007) [Table 3]. Preoperative IVU did not show any statistically significant difference in the function (P = 0.785) or drainage (0.919) between both groups.
|Table 3: Comparison of pre- and post-operative differential renal function between the two groups|
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Narrow adynamic segment of the ureter at the UPJ was confirmed in all the patients during pyeloplasty. There were no intra-operative or immediate postoperative complications, and the DJ stent was removed uneventfully in all, 2–3 weeks after surgery.
Pre-operative abnormal blood urea and serum creatinine levels normalized after surgery. Although there was a mean increase in DRF in both groups, it was not considered significant as it was within 5% range [Table 3]. IVU showed statistically significant improvement in function (Group 1, P = 0.000, Group 2: P =0.003) and drainage (Group 1, P = 0.00, Group 2: P =0.001).
There was a statistically significant improvement in drainage in Group 1 (P = 0.015) compared to Group 2 on EC scan [Table 4]. This was specifically seen in infants (P = 0.043) but not in older children. On IVU drainage at 3 months postoperative, 18.7% units had a score of 1, 12.5% a score of 2, and 68.8% a score of 3 in Group 2 compared to 5.2%, 22.4%, and 72.4%, respectively, in Group 1.
Within a group, comparison of drainage on renal scan between 3 months and 1 year showed significant improvement in Group 1 overall (P = 0.052) and Group 1 infants (P = 0.054). In all others, although improvement was present, it was not statistically significant.
Bilateral VUR was noted in 23 patients (65.7%) overall in Group 2, including two patients with bilateral UPJO. There were no abnormalities in the bladder or urethra in these patients on the VCUG. The VUR on the side of the UPJO was invariably of a higher or similar grade compared to the contralateral side. Contralateral VUR (i.e., in the kidney without UPJO) was seen only in Group 2 (21/35 patients [60%]) with the following Grades: I: 1 (4.7%); II: 1 (4.7%); III: 14 (66.7%); IV: 5 (23.8%). Gr IV-V VUR was noted in 24 of 37 units (64.8%) ipsilaterally compared to 5 of 21 (23.8%) contralateral units. Of the 37 units in Group 2, DMSA scan showed no scars in 13, scars in 18 units and resolution of pyelonephritic changes in 6 at 1-year follow-up.
Although asymptomatic, three patients were lost to follow-up in Group 1, 3–9 months after surgery without undergoing any postoperative renal scans. The rest are on regular follow up ranging from 12 - 42 months and remain asymptomatic. No patient required redo pyeloplasty, nephrectomy, or percutaneous nephrostomy after pyeloplasty. Two patients in Group 2 with Grade V VUR had recurrent symptomatic UTI which stopped after ureteric reimplantation [Table 5]. Four others managed conservatively for VUR had 2–3 UTIs in the 1st postoperative year. There were no immediate or late postoperative complications except for the above.
|Table 5: Resolution of vesicoureteric reflux in Group 2 patients (n=35, 37 units) with different modalities of management at 1 year follow up|
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| Discussion|| |
Routinely investigating the coexistence of VUR and UPJO is not recommended in the literature. However, we have all encountered some patients who in spite of a satisfactory pyeloplasty show reduction in renal function and delayed or obstructive pattern of drainage on follow-up investigations. In a study by Schuster et al., coexisting VUR occurred significantly more frequently (45% vs. 9%) in the patients who did not show improvement in function after pyeloplasty.
The true incidence of UPJO with associated VUR is under speculation, but the age of the study group during calculation is important. In a 10-year retrospective study, Bomalaski et al. reviewed a total of 1140 patients with VUR and 224 with UPJO. Forty-one patients had both the conditions (39 ipsilateral and six contralateral kidneys) giving an incidence of 17.4% for concomitant ipsilateral VUR with UPJO. In another 10-year retrospective study, Lebowitz and Blickman reviewed 200 children who had undergone pyeloplasty for UPJO and 2800 children with VUR. There was an association of UPJO with VUR in 21 patients (10%) with age ranging from 3 months to 20 years. A higher incidence (14%) was seen by Hollowell et al. in 17 of 147 consecutive patients undergoing pyeloplasty where the age ranged from newborn to 9 years of age. In the present study (n = 135) with age ranging from newborn to 12 years of age, the prevalence was much higher and noted to be 25.9% (35/135). Of the total 93 infants with UPJO, 31 (33.3%) had concomitant ipsilateral VUR. The study shows that overall, children with concomitant VUR and UPJO present earlier with a slightly higher incidence of antenatal diagnosis in group 2. The percentage of infants was higher (P = 0.003), and the mean age of patients above 1 year was also lesser in Group 2. This was despite the delay in diagnosis in some Group 2 patients due to lack of clarity on the true cause of hydronephrosis with investigations having to be repeated more than once.
There were no cases of secondary obstruction due to high-grade reflux alone as all patients were found to have a narrow adynamic segment of 0.5–3 cm length at the time of pyeloplasty. We could rule out pseudo-obstruction by performing all renal scans with a draining catheter.,,
Bomalaski et al. noted that only high-grade VUR was associated with UPJO. In our series also 24 of 37 units (64.8%) had Grade IV-V VUR. An important additional finding was the association of contralateral VUR in 21/35 (60%) patients seen only in group 2. This indicates the more global urological involvement in a subset of patients with UPJO and has not been emphasized in the literature so far. It is important to also make sure that other causes of dilatation of the ureter like bladder outlet obstruction and neurogenic bladder are ruled out from the history, clinical examination, and VCUG.
In Group 2, the high number of patients with bilateral VUR and the low number of patients with bilateral UPJO was striking. This means in effect that the UPJO was predominantly primary and not secondary to the VUR. Moreover, in all the cases in Group 2, the ureter at the UPJO was found to have internal narrowing. Presentation with UTI was only slightly higher in Group 2 and may be due to the early start of prophylactic antibiotic once UPJO was suspected on antenatal USG.
The interpretation of grade of VUR on VCUG in the presence of UPJO is not very straightforward. The ureter may be thin and mildly tortuous. However, the PCS may be found to be grossly dilated due to the UPJO. This may be misinterpreted as a higher grade VUR and should be kept in mind while making interventions in a small infant. If the UPJ is tight, the contrast might not enter the pelvis, or it may enter but get diluted and not be obvious. These situations are likely to be misinterpreted as a Grade 1 VUR. The true grade of the VUR is then visible only in a repeat MCU after the pyeloplasty.
Ipsilateral UPJO and VUR cause a management dilemma as to which condition should be treated first. Conventionally, it has been advocated that pyeloplasty should be done first as VUR tends to resolve with time whereas UPJO worsens with time. A recent study, however, stated that initial injection therapy in 31 units led to resolution of the UPJO in >80% of the patients and reduced pyeloplasty rate to 11.5%. However, the results were based only on VCUG and USG to detect UPJO without subjecting all patients to a renal dynamic scan or IVU. However, we have no patient in our previous clinical experience, whose “UPJO” subsided after successful management of VUR with DHA injection. We, therefore, agree with the traditional advice that pyeloplasty should be done first and should not be delayed until the VUR has resolved. Where there is a doubt in diagnosis, patients should be kept on strict follow-up and studies repeated after 3–6 months.
Concurrently, one should keep a close eye on the VUR. In our study, in children above 1 year, the preoperative DRF was significantly reduced in Group 2 patients (P = 0.007) showing the effect of VUR on renal function with time. Moreover, DMSA scan showed scars in 18 units and pyelonephritic changes in 6. As per the current guidelines, endoscopic treatment or surgery is recommended only in patients with frequent breakthrough infections., However, when VUR is coupled with UPJO, it is better to pro-actively treat VUR also as early as possible to reduce urinary stasis and improve renal function and drainage. Reimplantation is challenging due to the small size of the bladder in infants. Two patients (1 of whom had a single kidney) with persistent grade IV-V VUR, and breakthrough UTIs underwent early ureteric reimplantation. Due to economic considerations, we could inject DHA in only 12 units. This study also shows the natural course of events in the remaining conservatively managed VUR units with 70% showing resolution of VUR by an average age of 1.1 ± 0.36 years. It is known that the kidneys of patients diagnosed with VUR in the 1st year of life are at higher risk of developing new scars in early childhood. The associated renal scars in Group 2 are a cause for concern and require long-term follow-up.
There were some limitations to the study. We were not able to keep a set protocol for all the patients with associated VUR mainly due to financial constraints of not being able to afford endoscopic treatment. The number of patients above 1 year of age in Group 2 was far less compared to Group 1, and the study will have to be conducted on a much larger cohort of patients for better statistical validation. However, it also reflects the fact that children with concomitant VUR present early. Three patients were lost to follow-up in Group 1. Two asymptomatic patients in Group 2 refused repeat VCUG; although, they are on regular follow-up and underwent other investigations. We did not do DMSA scan in Group 1 patients and could not compare the presence of scars in this group. While it may be argued that USG would have been sufficient to note dilated ureter and then perform VCUG only in these patients, our experience has shown that this finding is often missed. While the interpretation of drainage in renal dynamic scan after pyeloplasty is not straightforward and causes of slow drainage are multifactorial, for example, the presence of large palpable mass preoperatively, the status of hydration, etc., associated VUR is an important cause of slow drainage after pyeloplasty and should be controlled as early as possible.
| Conclusion|| |
As one-third of children <1 year had concomitant VUR, compared to the significantly lower incidence in children >1 year, our study suggests that it is better to perform routine VCUG in all children below 1 year age diagnosed with UPJO. An algorithm is proposed for managing similar patients [Figure 1]. The recent European Urology Association guidelines recommend VCUG for all newborns detected to have upper urinary tract dilatation., The presence of VUR affects the drainage of the kidney and predisposes to infection and loss of nephrons. However, the dilatation of ureter is not always picked up on USG in small infants due to bowel gas. Due to the obstruction at the UPJ the dilatation of the ureter may not be appreciated on IVU and diethylenetriamine pentaacetic acid/EC scans. This is more so in infants where overall uptake of contrast by the kidney may be less and in those with poorly functioning kidneys. At the time of surgery, if a dilated ureter is found below the UPJO, the operating surgeon will not be sure if it is due to vesicoureteric junction obstruction, megaureter or VUR if a preoperative VCUG has not been done. In older children, the presence of recurrent UTI or poorly functioning kidneys should warrant a VCUG. The presence of contralateral VUR in a significant number of patients in Group 2 and association with pyelonephritic changes/scars mandates proactive treatment of VUR and close follow-up of these patients. While improvement in drainage was better in Group 1, function improved even in children with associated VUR and pyeloplasty should not be postponed until reflux resolves.
|Figure 1: Proposed algorithm for managing patients with ureteropelvic junction obstruction and ipsilateral vesicoureteric reflux. UPJO: Ureteropelvic junction obstruction, VUR: Vesicoureteric reflux, UTI: Urinary tract infection, USG: Ultrasonography, EC: Ethylene dicysteine, DHA: Dextranomer hyaluronic acid|
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There are no conflicts of interest.
| References|| |
Hollowell JG, Altman HG, Snyder HM 3rd
, Duckett JW. Coexisting ureteropelvic junction obstruction and vesicoureteral reflux: Diagnostic and therapeutic implications. J Urol 1989;142:490-3.
Maizels M, Smith CK, Firlit CF. The management of children with vesicoureteral reflux and ureteropelvic junction obstruction. J Urol 1984;131:722-7.
Bomalaski MD, Hirschl RB, Bloom DA. Vesicoureteral reflux and ureteropelvic junction obstruction: Association, treatment options and outcome. J Urol 1997;157:969-74.
Kim YS, Do SH, Hong CH, Kim MJ, Choi SK, Han SW, et al.
Does every patient with ureteropelvic junction obstruction need voiding cystourethrography? J Urol 2001;165:2305-7.
Estrada CR, Peters CA, Retik AB, Nguyen HT. Vesicoureteral reflux and urinary tract infection in children with a history of prenatal hydronephrosis – Should voiding cystourethrography be performed in cases of postnatally persistent grade II hydronephrosis? J Urol 2009;181:801-6.
Hubertus J, Plieninger S, Martinovic V, Heinrich M, Schuster T, Bürst M, et al.
Children and adolescents with ureteropelvic junction obstruction: Is an additional voiding cystourethrogram necessary? Results of a multicenter study. World J Urol 2013;31:683-7.
St. Aubin M, Willihnganz-Lawson K, Varda BK, Fine M, Adejoro O, Prosen T, et al.
Society for fetal urology recommendations for postnatal evaluation of prenatal hydronephrosis – Will fewer voiding cystourethrograms lead to more urinary tract infections? J Urol 2013;190:1456-61.
Lebowitz RL, Olbing H, Parkkulainen KV, Smellie JM, Tamminen-Möbius TE. International system of radiographic grading of vesicoureteric reflux. International reflux study in children. Pediatr Radiol 1985;15:105-9.
Schuster T, Stehr M, Rossmüller B, Dietz HG, Hahn K. Clinical impact of differential renal function to indicate and assess pyeloplasty and the significance of coexisting vesicoureteral reflux. Clin Nucl Med 2001;26:923-9.
Lebowitz RL, Blickman JG. The coexistence of ureteropelvic junction obstruction and reflux. AJR Am J Roentgenol 1983;140:231-8.
Conway JJ, Maizels M. The “well tempered” diuretic renogram: A standard method to examine the asymptomatic neonate with hydronephrosis or hydroureteronephrosis. A report from combined meetings of the society for fetal urology and members of the pediatric nuclear medicine council – The society of nuclear medicine. J Nucl Med 1992;33:2047-51.
Lee NG, Marchalik D, Lipsky A, Rushton HG, Pohl HG, Song X, et al.
Risk factors for catheter associated urinary tract infections in a pediatric institution. J Urol 2016;195:1306-11.
Kajbafzadeh AM, Tourchi A, Ebadi M. The outcome of initial endoscopic treatment in the management of concomitant vesicoureteral reflux and ureteropelvic junction obstruction. Urology 2013;81:1040-5.
Tekgul S, Riedmiller H, Dogan HS, Gerharz E, Hoebeke P, Kocvara R, et al
. Guidelines on pediatric urology. Eur Urol 2012;62:58-60.
Tekgul S, Riedmiller H, Dogan HS, Gerharz E, Hoebeke P, Kocvara R, et al
. Guidelines on pediatric urology. Eur Urol 2012;62:534-42.
Weitz M, Schmidt M. To screen or not to screen for vesicoureteral reflux in children with ureteropelvic junction obstruction: A systematic review. Eur J Pediatr 2017;176:1-9.
[Table 1], [Table 2], [Table 3], [Table 4], [Table 5]