Predictors of Complications after Pediatric Pyeloplasty: A Retrospective Cohort Study and Meta-Analysis

Abstract

Objective:

Pyeloplasty is the gold standard procedure for treating ureteropelvic junction obstruction (UPJO), but the occurrence of postoperative complications is a major challenge. This study aimed to identify the predictors of postpyeloplasty complications, which are not well characterized in contemporary literature.

Study Design:

We retrospectively analyzed data of children who underwent pyeloplasty in our hospital from January 2011 to August 2022, with a minimum follow-up of 1 year. Furthermore, a systematic review and meta-analysis of studies published from 2000 to 2023 was performed to identify predictors of complications.

Results:

In cohort studies (n = 555), preoperative urinary tract infection (pre-UTI) (odds ratio [OR] = 5.65, 95% confidence interval [CI]: 2.96–10.78, p < 0.001), Double J-stent duration (OR = 1.005, 95% CI: 1.001–1.008, p = 0.005), renal cortical thickness (OR = 0.181, 95% CI: 0.071–0.461, p < 0.001), and collection system separation (OR = 1.170, 95% CI: 1.017–1.347, p = 0.028) were associated with total postoperative complications. Pre-UTI (OR = 4.87, 95% CI: 1.98–11.98, p = 0.001), Double J-stent duration (OR = 1.005, 95% CI: 1.001–1.009, p = 0.019), preoperative renal cortical thickness (OR = 0.197, 95% CI: 0.042–0.928, p = 0.040), and duration of operation (OR = 1.013, 95% CI: 1.003–1.022, p = 0.008) were associated with recurrence. Pre-UTI (OR = 5.33, 95% CI: 2.73–10.38, p < 0.001) and preoperative renal cortical thickness (OR = 0.351, 95% CI: 0.124–0.990, p = 0.048) were predictors of postoperative UTI. In the meta-analysis, sex (I² = 0%, relative risk [RR] = 1.19, 95% CI: 1.01–1.40, p = 0.04), operation methods, and split renal function (I² = 50%, RR = 0.76, 95% CI: 0.59–0.96, p = 0.02) were identified as predictors of postoperative complications.

Conclusions:

We identified the predictors of postpyeloplasty complications. Early identification and treatment can help us reduce the incidence of complications.

Keywords

complications pediatrics pyeloplasty ureteral obstruction meta-analysis

Introduction

Prenatal ultrasound can help detect most cases of fetal hydronephrosis during pregnancy.¹ Prenatally diagnosed hydronephrosis spontaneously resolves in many cases,² but surgical treatment is required in 15%–20% of cases.³ Ureteropelvic junction obstruction (UPJO) is the most common cause of persistent postnatal hydronephrosis,¹ accounting for approximately 10%–30% of children with hydronephrosis.⁴ The estimated incidence of congenital UPJO is 1 per 1000–2000 live births, with a male-to-female ratio of approximately 2–3:1; the left side accounts for about two-third of all cases.^2,5 Without timely treatment, these children may suffer renal impairment,⁶ and pyeloplasty is considered the gold standard for relieving the obstruction.⁷ Surgical options include open operation, laparoscopy, and robot-assisted procedures. Minimally invasive pyeloplasty is a widely used surgical approach, and both laparoscopy and robot-assisted surgeries have success rates of over 90%, similar to open operation.⁶

Although currently used surgical approaches have satisfactory success rates, postoperative complications are still inevitable. The incidence of postoperative complications is up to 20% or more.³ The main postoperative complications include recurrence, urine leak, ileus, infection, obstruction secondary to clot or stent displacement, and blood transfusion.⁸ Postoperative complications may necessitate readmission or even reoperation. Therefore, identifying the factors that affect postoperative complications can help inform interventions to prevent the occurrence of complications.

Currently, there is no clear consensus regarding the specific factors contributing to postoperative complications. However, surgical methods,⁹ surgical access,¹⁰ and drainage technique³ likely play a role. We conducted a retrospective cohort study and meta-analysis of previously published studies to contribute to this ongoing discussion. The objective of this study was to illustrate the factors that may influence postpyeloplasty complications in patients with UPJO. Our findings may provide valuable insights for preventing postoperative complications of pyeloplasty.

Materials and Methods

Retrospective cohort study

This study was approved by the Ethics Committee of Qilu Hospital of Shandong University (Approval No. KYLL-202312-030). No additional patient-informed consent specific to this study was required, given its retrospective nature. The present study followed the Strengthening The Report Of Cohort Studies in Surgery (STROCSS) criterion.¹¹

Study population and design

Our retrospective cohort study included patients aged <18 years who underwent pyeloplasty for UPJO at our hospital between January 2011 and August 2022 and were followed up for a minimum of 1 year after operation. Patients with a previous history of pyeloplasty, other urological malformations, and nephrostomy were excluded, as they may have been more complex cases and could have influenced the outcomes. All patients included in the study underwent the same surgical procedure, pyeloplasty, which involves the reconstruction of the narrowed or UPJO. Additionally, a Double J-stent (DJ) was inserted in all patients.

Exposure and outcomes

Data regarding the following variables were extracted: sex, involved side, weight, age, presence of bilateral hydronephrosis, prenatal detection, calculus, vascular crossing, comorbidities, and urinary tract infection (UTI). Surgical and clinical variables included the surgical approach, operative time, estimated intraoperative blood loss, duration of DJ stent, drainage days, hospital days, and postoperative hospital stay. Preoperative and postoperative laboratory indices and radiological variables included pelvis anterior–posterior diameter, renal cortical thickness, split renal function (SRF), estimated glomerular filtration rate, blood urea nitrogen, serum creatinine, cystatin C, white blood cell count, C-reactive protein, and urine white blood cell.

Outcomes

Complications occurring during follow-up, including recurrence, UTI, urine leak, ileus, incision infection, obstruction secondary to clot or displaced stent, and blood transfusion.

Statistical analysis

Continuous variables were first tested for normality; those conforming to a normal distribution were presented as mean ± standard deviation, with between-group differences assessed by the t-test, while skewed distributed variables were expressed as quartiles (median [interquartile range]) and analyzed using the rank-sum test. Categorical variables were expressed as frequency (percentage), and between-group differences were assessed using the chi-square test. Binary logistic regression models were applied for covariate adjustment. All statistical analyses were conducted using SPSS 26.0 (IBM SPSS Statistics). A p-value of <0.05 was considered indicative of statistical significance.

Meta-analysis

The meta-analysis was conducted after the recommendations of the Cochrane Handbook for Systematic Reviews of Interventions and complied with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA)¹² statement and A MeaSurement Tool to Assess systematic Reviews 2 (AMSTAR2).¹³

Inclusion and exclusion criteria

Inclusion criterion: (1) Original research articles or graduation theses published in English and Chinese core journals; (2) reporting of at least one factor related to complications.

Exclusion criterion: (1) Literature reviews, meta-analyses, or animal experiments; (2) duplicate publications; (3) redo operation for recurrent patients.

Data sources

Three researchers searched the Cochrane Library, PubMed, Embase, Web of Science, CNKI, China Science and Technology Journal Database (VIP), Wanfang database, and Chinese Biomedical Literature Database (SinoMed) for relevant studies published until August 2023. The details of the search strategy are shown in Supplementary Data.

Study selection

Three authors independently selected the studies for inclusion in the meta-analysis. In case of any inconsistencies, the final decision was reached by consensus.

Data extraction and quality assessment

Data from the included studies were independently extracted by three researchers. The extracted contents included the first author’s name, location of study, year of publication, journal of publication, type of study, the number of total cases, and cases with complications.

The quality of the cohort studies was assessed using the Newcastle–Ottawa Scale with a total score of 9.¹⁴ A minimum score of 6 was required for inclusion. The Cochrane risk of bias tool was used for the quality assessment of randomized controlled trials (RCTs).¹⁵

Statistical analysis

RevMan 5.4 (Review Manager) was used to calculate effect sizes, graph forest plots, and assess the quality of RCTs. The chi-square test was used to assess statistical heterogeneity among studies. Q-test was used to assess whether this heterogeneity affected the results. According to the Cochrane review guidelines, in case of small heterogeneity (I² < 50%), a fixed-effects model was used. Otherwise, a random-effects model was used for the meta-analysis. The extracted original data were analyzed using dichotomous methods, and the results were reported as relative risk (RR) with 95% confidence intervals (CIs), calculated by the M-H method (fixed- or random-effects model). Sensitivity analyses and publication bias analyses were performed using Stata 16.0 (Stata Corp LP, College Station, TX, USA). Publication bias was analyzed by Egger’s test and funnel plots. A p-value of <0.05 was considered statistically significant.

Results

Cohort study

Patient characteristics

A total of 555 patients were included in the final analysis; of these, 90 (16.2%) patients developed complications. Thirty (5.4%) patients developed recurrence, and 57 (10.3%) patients developed post-UTI. Patient characteristics, surgical information, and examination results are summarized in Table 1.

Table 1.

Baseline Characteristics of Included Patients Stratified by Complication, Recurrence, and Post Urinary Tract Infection

Total (n = 555)	Noncomplication (n = 465)	Complication (n = 90)	p	Nonrecurrence (n = 525)	Recurrence (n = 30)	p	Non-post-UTI (n = 498)	Post-UTI (n = 57)	p
Sex
Male	389 (82.9%)	80 (17.1%)	0.209	440 (93.8%)	29 (6.2)	0.067	421 (89.9%)	48 (10.2%)	0.948
Female	76 (88.4%)	10 (11.6%)	0.209	85 (98.8%)	1 (1.2%)	0.067	77 (89.5%)	9 (10.5%)	0.948
Side
Left	344 (84.1%)	65 (15.9%)	0.729	386 (94.4%)	23 (5.6%)	0.704	370 (90.5%)	39 (9.5%)	0.340
Right	121 (82.9%)	25 (17.1%)	0.729	139 (95.2%)	7 (4.8%)	0.704	128 (87.7%)	18 (12.3%)	0.340
Bilateral hydronephrosis
No	378 (84.0%)	72 (16.0%)	0.775	426 (94.7%)	24 (5.3%)	0.876	406 (90.2%)	44 (9.8%)	0.429
Yes	87 (82.9%)	18 (17.1%)	0.775	99 (94.3%)	6 (5.7%)	0.876	92 (87.6%)	13 (12.4%)	0.429
Calculus
No	445 (84.1%)	84 (15.9%)	0.410	503 (95.1%)	26 (4.9%)	0.045	474 (89.6%)	55 (10.4%)	1.000
Yes	20 (76.9%)	6 (23.1%)	0.410	22 (84.6%)	4 (15.4%)	0.045	24 (92.3%)	2 (7.7%)	1.000
Prenatal detection
No	170 (85.4%)	29 (14.6%)	0.432	186 (93.5%)	13 (6.5%)	0.380	184 (92.5%)	15 (7.5%)	0.113
Yes	295 (82.9%)	61 (17.1%)	0.432	339 (95.2%)	17 (4.8%)	0.380	314 (88.2%)	42 (11.8%)	0.113
Presence of vascular crossing
No	449 (83.9%)	86 (16.1%)	0.549	507 (94.8%)	28 (5.2%)	0.295	480 (89.7%)	55 (10.3%)	1.000
Yes	16 (80%)	4 (20%)	0.549	18 (90.0%)	2 (10%)	0.295	18 (90%)	2 (10%)	1.000
Pre-UTI
No	433 (87.3%)	63 (12.7%)	0.000	475 (95.8%)	21 (4.2%)	0.002	458 (92.3%)	38 (7.7%)	0.000
Yes	32 (54.2%)	27 (45.8%)	0.000	50 (84.7%)	9 (15.3%)	0.002	40 (67.8%)	19 (32.2%)	0.000
Comorbidities
No	435 (84.8%)	78 (15.2%)	0.024	486 (94.7%)	27 (5.3%)	0.489	465 (90.6%)	48 (9.4%)	0.029
Yes	30 (71.4%)	12 (28.6%)	0.024	39 (92.9%)	3 (7.1%)	0.489	33 (78.6%)	9 (21.4%)	0.029
Surgical approach
laparoscope	409 (82.8%)	85 (17.2%)	0.064	465 (94.1%)	29 (5.9%)	0.639	441 (89.3%)	53 (10.7%)	0.320
Open	34 (87.2%)	5 (12.8%)		38 (97.4%)	1 (2.6%)		35 (89.7%)	4 (10.3%)
Robot	22 (100%)	0 (0%)		22 (100%)	0 (0%)		22 (100%)	0 (0%)
Age (month)	14 (2.99, 67)	8.82 (2.42, 39.25)	0.062	12 (2.82, 64.5)	20 (5.71, 53.5)	0.736	15.5 (3.15, 67)	3.47 (1.95, 17)	0.000
Weight (kg)	12 (7, 20.75)	9.7 (6.5, 15)	0.058	11 (7, 20)	12.9 (7.9, 16.25)	0.886	12 (7, 20.25)	7.5 (6, 12.5)	0.000
Duration of operation (minute)	116 (100, 135)	124 (105, 140)	0.113	116 (100, 135)	137.5 (105, 160)	0.030	116 (100, 140)	120 (102.5, 135)	0.906
Blood loss (mL)	5 (5, 5)	5 (5, 5)	1.000	5 (5, 5)	5 (5, 5)	0.662	5 (5, 5)	5 (5, 5)	0.972
Duration of Double J-stent (days)	98 (79, 121.5)	102.5 (77.25, 154.5)	0.026	98 (78.5, 123)	118.5 (95.25, 190)	0.013	100 (80.5, 123)	98 (69, 151.5)	0.881
Hospital days(days)	14 (12, 17)	15 (13, 18)	0.165	14 (12, 17)	14 (13, 16)	0.933	14 (12, 17)	15 (13, 18)	0.277
APD (cm)	2.3 (1.6, 3.5)	2.5 (1.78, 3.8)	0.003	2.3 (1.65, 3.5)	2.9 (2.03, 4.43)	0.063	2.3 (1.6, 3.5)	2.8 (1.95, 3.7)	0.109
Renal cortical thickness (cm)	0.46 (0.3, 0.8)	0.31 (0.2, 0.5)	0.002	0.4 (0.3, 0.7)	0.33 (0.20, 0.5)	0.018	0.46 (0.3, 0.7)	0.33 (0.22, 0.58)	0.008
Collecting system Separation (cm)	2.5 (1.65, 3.3)	2.7 (2, 4.13)	0.048	2.6 (1.7, 3.4)	2.8 (2, 4.13)	0.115	2.55 (1.7, 3.4)	2.87 (1.9, 4)	0.111
Postoperative hospital stay (days)	9 (8, 10)	9 (8, 10)	0.742	9 (8, 10)	9 (8, 9.25)	0.795	9 (8, 10)	9 (8, 10.5)	0.594
Drainage days (days)	5 (4, 6)	6 (5, 6)	0.054	5 (4, 6)	6 (5, 6)	0.016	5 (4, 6)	5 (5, 6)	0.257
Pre-BUN (mmol/L)	3.5 (2.3, 4.62)	3.66 (2.57, 4.74)	0.859	3.5 (2.3, 4.64)	4 (3.26, 4.67)	0.251	3.6 (2.3, 4.64)	3.4 (2.22, 4.76)	0.444
Pre-SCR (μmol/L)	27 (22.5, 37)	27 (22, 33.25)	0.565	27 (22, 36.5)	28 (22.75, 35)	0.536	27.5 (23, 37)	26 (21.5, 32)	0.116
Pre-cys-C (mg/L)	1.06 (0.88, 1.305)	1.05 (0.88, 1.43)	0.202	1.06 (0.88, 1.31)	0.95 (0.87, 1.20)	0.310	1.05 (0.87, 1.3)	1.16 (0.91, 1.57)	0.014
Pre-WBC (10⁹/L)	7.7 (6.45, 9.62)	8.63 (7.19, 10.66)	0.014	7.75 (6.5, 9.74)	8.54 (7.03, 11.12)	0.094	7.73 (6.49, 9.66)	8.72 (6.84, 10.62)	0.062
Pre-CRP (mg/L)	0.34 (0.1, 1.59)	0.55 (0.1, 1.88)	0.747	0.36 (0.1, 1.66)	0.15 (0.10, 119.17)	0.442	0.34 (0.1, 1.59)	1.26 (0.1, 1.88)	0.700
Pre-UWBC	5.3 (2.2, 13.05)	5 (2.75, 9.55)	0.674	5.1 (2.2, 12.45)	5.8 (3.2, 13.33)	0.268	5.4 (2.2, 12.68)	4.6 (2.45, 10.6)	0.767
Post-BUN (mmol/L)	2.58 (1.6, 3.5)	2.02 (1.64, 2.82)	0.325	2.58 (1.69, 3.40)	1.62 (1.35, 1.79)	0.082	2.58 (1.65, 3.5)	2.02 (1.55, 2.73)	0.294
Post-SCR (μmol/L)	31 (24, 42)	27 (23, 32.25)	0.097	30 (24, 40.5)	32 (24.75, 39.25)	0.922	31 (24, 42)	27 (23.25, 31.5)	0.092
Post-cys-C (mg/L)	0.89 (0.75, 1.09)	0.9 (0.77, 1.25)	0.547	0.89 (0.75, 1.09)	1.10 (0.73, 1.36)	0.398	0.88 (0.74, 1.09)	0.95 (0.84, 1.27)	0.133
Post-WBC (10⁹/L)	7.98 (6.33, 9.82)	9.29 (7.05, 12.6)	0.028	8.25 (6.40, 10.15)	7.43 (5.54, 9.29)	0.491	8 (6.31, 9.99)	9.27 (7.54, 12.78)	0.022
Post-CRP (mg/L)	6.21 (1.87, 12.91)	8.79 (5.55, 28.7)	0.020	6.76 (2.54, 14.02)	4.22 (1.34, 16.5)	0.605	12.75 (6.02, 23.75)	9.20 (5.74, 28.89)	0.012
Post-UWBC	53.8 (28.2, 94.35)	159.95 (64.72, 688.13)	0.000	61.65 (32.70, 116.2)	75 (40.4, 258.45)	0.625	53.98 (28, 93.3)	220.2 (77.55, 839)	0.000

Data shown in bold represent statistically significant differences (P < 0.05).

APD = pelvis anterior–posterior diameter; BUN = blood urea nitrogen; CRP = C-reactive protein; cys-C = cystatin C; Pre = preoperative; post = postoperative; SCR = serum creatinine; UTI = urinary tract infection; UWBC = urine white blood cell; WBC = white blood cell count.

Predictive factors

Univariate results

The univariate analysis identified 11 predictors associated with complications, 6 factors associated with recurrence, and 9 factors associated with post-UTI (Table 1).

Multivariate results

On multivariate analysis, pre-UTI showed a significant association with total postoperative complications (odds ratio [OR] = 5.65, 95% CI: 2.96–10.78, p < 0.001), recurrence (OR = 4.87, 95% CI: 1.98–11.98, p = 0.001), and post-UTI (OR = 5.33, 95% CI: 2.73–10.38, p < 0.001). The incidence of total complications (OR = 1.005, 95% CI: 1.001–1.008, p = 0.005) and recurrences (OR = 1.005, 95% CI: 1.001–1.009, p = 0.019) increased with the increase in the duration of the DJ stent. Patients with a thinner renal cortical thickness prior to operation were more likely to have complications (OR = 0.181, 95% CI: 0.071–0.461, p < 0.001), recurrences (OR = 0.197, 95% CI: 0.042–0.928, p = 0.040), and post-UTI (OR = 0.351, 95% CI: 0.124–0.990, p = 0.048). Compared to the group without complications, the separation of the collecting system (OR = 1.170, 95% CI: 1.017–1.347, p = 0.028) was more severe in the group with complications. The duration of operation (OR = 1.013, 95% CI: 1.003–1.022, p = 0.008) in the recurrent group was longer than that in the nonrecurrent group (Supplementary Fig. S1).

Meta-analysis

Study characteristics and quality assessment

A total of 5899 articles were retrieved, of which 55 studies (3 RCTs and 52 cohort studies) were included in the meta-analysis.^16–70 The total number of patients undergoing pyeloplasty in the 55 studies was 17,623, of which 1909 developed complications. A schematic illustration of the literature screening process is shown in Figure 1. The characteristics of the included studies are shown in Table 2. The NOS score of nine studies was 6, five studies received a score of 8, and the remaining studies received a score of 7 (Table 3). The risk of bias and summary of the RCTs are shown in Supplementary Figure S1.

FIG. 1.

Flowchart of predictors of complications after pyeloplasty study search and screening.

Table 2.

Characteristics of the Studies Included in the Meta-Analysis

Study ID	District	Country	Type of study	Journal	Case/Total cases
Amos Neheman 2018¹⁶	Zerifin	Israel	Cohort study	Journal of Laparoendoscopic & Advanced Surgical Techniques	9/34
Arnaud Bonnard 2005⁴⁵	Paris	France	Cohort study	The Journal of Urology	8/39
D. Bansal 2014¹⁷	Cincinnati	United States	Cohort study	Journal of Pediatric Urology	7/70
David S. Yee 2006¹⁸	Orange	United States	Cohort study	Urology	2/16
Dehong Liu 2017¹⁹	Beijing	China	Cohort study	Journal of Pediatric Urology	26/180
Dh Liu 2017⁴⁶	Beijing	China	Cohort study	Urology	63/762
Edward Riachy 2013²⁰	Cincinnati	United States	Cohort study	The Journal of Urology	4/64
El-Gohary 2012⁴⁷	Abu Dhabi	UAE	Cohort study	Annals of Pediatric Surgery	2/29
Erman Ceyhan 2019²¹	Sıhhiye Ankara	Turkey	Cohort study	Urology	89/490
Fadi Zu’bi 2022²²	Haifa	Israel	Cohort study	Urology	21/185
Fred van der Toorn 2012⁴⁸	Rotterdam	Netherlands	Cohort study	Journal of Pediatric Urology	5/114
Gwen M. Grimsby 2015²³	Dallas	United States	Cohort study	Journal of Endourology	8/101
Haytham Badawy 2015⁴⁹	Alexandria	Egypt	RCT	Journal of Pediatric Urology	4/38
Heidi A. Penn 2010⁵⁰	Kansas	United States	RCT	The Journal of Urology	0/39
Hongchao Chai 2019²⁴	Shijiazhuang	China	Cohort study	Clinical Journal of Medical Officer	96/268
Hong Mei 2016²⁵	Wuhan	China	Cohort study	Journal of Pediatric Surgery	23/48
Hongyang Wang 2022²⁶	Beijing	China	Cohort study	Computational and Mathematical Methods in Medicine	188/504
I.R. Ravish 2007⁵¹	Karnataka	India	Cohort study	Journal of Endourology	6/29
Israel Franco 2007²⁷	New York	United States	Cohort study	The Journal of Urology	3/27
J.S. Valla 2009⁵²	Nice	France	Cohort study	Journal of Pediatric Urology	25/90
Jianghua Jia 2021²⁸	Shijiazhuang	China	Cohort study	Pakistan Journal of Medical Sciences	11/78
Joao A. Barbosa 2013²⁹	Boston	United States	Cohort study	Journal of Pediatric Urology	7/207
Jose H. Amón Sesmero 2009³⁰	Valladolid	Spain	Cohort study	Actas Urológicas Españolas	28/77
June Kim 2012³¹	Busan	Korea	Cohort study	Korean Journal of Urology	4/76
Karen E. Smith 2002³²	San francisco	United States	Cohort study	The Journal of Urology	16/117
Lisandro A. Piaggio2007⁵³	Wilmington	United States	Cohort study	The Journal of Urology	12/78
Long Sun 2023³³	Hangzhou	China	Cohort study	Asian Journal of Surgery	4/33
Longxin Wang 2009⁵⁴	Xian	China	Cohort study	Surgical Endoscopy	5/31
Luis H.P. Braga 2008³⁴	Toronto	Canada	Cohort study	The Journal of Urology	21/401
Luis H.P. Braga 2009⁵⁵	Toronto	Canada	Cohort study	The Journal of Urology	8/108
M.S. Silay 2016³⁵	/	/	Cohort study	Journal of Pediatric Urology	68/575
Mathew D. Sorensen 2011³⁶	Seattle	United States	Cohort study	The Journal of Urology	14/66
Mesrur Selcuk Silay 2019³⁷	Istanbul	Turkey	RCT	World Journal of Urology	6/53
Min Chao 2016³⁸	Hefei	China	Cohort study	Acta Universitatis Medicinal-ics Anhui	17/84
Minki Baek 2018³⁹	Houston	United States	Cohort study	Journal of Pediatric Urology	14/65
Pankaj P. Dangle 2013⁴⁰	Columbus	United States	Cohort study	The Journal of Urology	1/20
Patel Ashay 2016⁴¹	Arkansas	United States	Cohort study	The Canadian Journal of Urology	2/68
P. Bragagnini Rodríguez 2015⁴²	Zaragoza	Spain	Cohort study	Cirugia pediatrica : organo oficial de la Sociedad Espanola de Cirugia Pediatrica	10/71
P. Murthy 2015⁴³	Chicago	United States	Cohort study	The Annals of The Royal College of Surgeons of England	24/92
Richard S. Lee 2006⁴⁴	Boston	United States	Cohort study	The Journal of Urology	1/66
Sang Hoon Song 2017⁵⁶	Ulsan	Korea	Cohort study	PLoS One	9/70
Shyam Sukumar 2014⁵⁷	Quebec	Canada	Cohort study	Journal of Endourology	568/6007
Sinharib Citgez 2020⁵⁸	Istanbul	Turkey	Cohort study	Urologia Internationalis	11/74
Sonia Pérez-Bertólez 2021⁵⁹	Barcelona	Spain	Cohort study	Scandinavian Journal of Urology	42/340
Stephen J. Canon 2007⁶⁰	Columbus	United States	Cohort study	The Journal of Urology	5/46
Steve Kim 2008⁶¹	Los Angeles	United States	Cohort study	The Journal of Urology	5/142
Sung Ho Ju 2011⁶²	Seoul	Korea	Cohort study	Korean Journal of Urology	5/27
Sun Kejian 2004⁷⁰	Shijiazhuang	China	Cohort study	Chinese Journal of Urology	24/68
Thomas Blanc 2022⁶³	Paris	France	Cohort study	European Urology Open Science	24/106
Ulrike Subotic 2012⁶⁴	Zurich	Switzerland	Cohort study	Journal of Pediatric Urology	11/39
Vijaya M. Vemulakonda 2015⁶⁵	Aurora	United States	Cohort study	Pediatric Surgery International	223/4566
Yuanyuan Wang 2017⁶⁶	Xinxiang	China	Cohort study	Master’s thesis of Xinxiang Medical College	19/62
Yuk Him Tam 2018⁶⁷	Hong Kong	China	Cohort study	Journal of Laparoendoscopic & Advanced Surgical Techniques	16/63
Yuzhu He 2020⁶⁸	Beijing	China	Cohort study	Journal of Pediatric Urology	51/277
Zhao Minli 2020⁶⁹	Zhengzhou	China	Cohort study	Chinese Journal of Pediatric Surgery	34/243

Table 3.

Quality Evaluation of the Cohort Studies Included in Meta-Analysis

	Selection				Comparability	Exposure
Study ID	Representativeness of exposure cohort	Selection of nonexposed cohort	Ascertainment of exposure cohort	Demonstration that outcome of interest was not present at start of study	Comparability of exposed and nonexposed cohorts	Method for determination of results	Was the follow-up time long enough	Completeness of follow-up cohort	Quality assessment score
Amos Neheman 2018¹⁶	★	★	★	★	★	★	★		7
Arnaud Bonnard 2005⁴⁵	★	★	★	★	★	★	★		7
D. Bansal 2014¹⁷	★	★	★	★		★	★		6
David S. Yee 2006¹⁸	★	★	★	★	★	★	★		7
Dehong Liu 2017¹⁹	★	★	★	★	★	★	★		7
Dh Liu 2017⁴⁶	★	★	★	★	★	★	★		7
Edward Riachy 2013²⁰	★	★	★	★	★	★	★		7
El-Gohary 2012⁴⁷	★	★	★	★	★	★	★		7
Erman Ceyhan 2019²¹	★	★	★	★	★	★	★		7
Fadi Zu’bi 2022²²	★	★	★	★	★	★	★		7
Fred van der Toorn 2012⁴⁸	★	★	★	★	★	★	★		7
Gwen M. Grimsby 2015²³	★	★	★	★	★	★	★	★	8
Hongchao Chai 2019²⁴	★	★		★	★	★	★		6
Hong Mei 2016²⁵	★	★	★	★	★	★	★		7
Hongyang Wang 2022²⁶	★	★	★	★	★	★	★	★	8
I.R. Ravish 2007⁵¹	★	★	★	★	★	★	★		7
Israel Franco 2007²⁷	★	★	★	★	★	★	★		7
J.S. Valla 2009⁵²	★	★	★	★	★	★	★		7
Jianghua Jia 2021²⁸	★	★	★	★	★	★	★		7
Joao A. Barbosa 2013²⁹	★	★	★	★	★	★	★		7
Jose H. Amón Sesmero 2009³⁰	★	★	★	★	★	★	★		7
June Kim 2012³¹	★	★	★	★	★	★	★	★	8
Karen E. Smith 2002³²	★	★	★	★	★	★	★		7
Lisandro A. Piaggio 2007⁵³	★	★	★	★	★	★			6
Long Sun 2023³³	★	★	★	★	★	★			6
Longxin Wang 2009⁵⁴	★	★	★	★	★	★	★		7
Luis H.P. Braga 2008³⁴	★	★	★	★	★	★	★		7
Luis H.P. Braga 2009⁵⁵	★	★	★	★	★	★	★		7
M.S. Silay 2016³⁵	★	★	★	★	★	★	★		7
Mathew D. Sorensen 2011³⁶	★	★	★	★	★	★	★		7
Min Chao 2016³⁸	★	★	★	★	★	★	★		7
Minki Baek 2018³⁹	★	★	★	★	★	★	★		7
Pankaj P. Dangle 2013⁴⁰	★	★	★	★		★	★		6
Patel Ashay 2016⁴¹	★	★	★	★	★	★	★		7
P. Bragagnini Rodríguez 2015⁴²	★	★	★	★		★	★		6
P. Murthy 2015⁴³	★	★	★	★		★	★		6
Richard S. Lee 2006⁴⁴	★	★	★	★	★	★			6
Sang Hoon Song 2017⁵⁶	★	★	★	★	★	★	★		7
Shyam Sukumar 2014⁵⁷	★	★	★	★	★	★	★		7
Sinharib Citgez 2020⁵⁸	★	★	★	★	★	★	★		7
Sonia Pérez-Bertólez 2021⁵⁹	★	★	★	★	★	★	★		7
Stephen J. Canon 2007⁶⁰	★	★	★	★	★	★	★	★	8
Steve Kim 2008⁶¹	★	★	★	★	★	★	★		7
Sung Ho Ju 2011⁶²	★	★	★	★	★	★	★		7
Sun Kejian 2004⁷⁰	★	★	★	★	★	★	★		7
Thomas Blanc 2022⁶³	★	★	★	★	★	★	★		7
Ulrike Subotic 2012⁶⁴	★	★	★	★	★	★	★		7
Vijaya M. Vemulakonda 2015⁶⁵	★	★	★	★	★	★	★		7
Yuanyuan Wang 2017⁶⁶		★	★	★	★	★	★		6
Yuk Him Tam 2018⁶⁷	★	★	★	★	★	★	★		7
Yuzhu He 2020⁶⁸	★	★	★	★	★	★	★	★	8
Zhao Minli 2020⁶⁹	★	★	★	★	★	★	★		7

Quantitative synthesis

Analysis of data from 1279 robotic and 1405 laparoscopic surgeries from 12 cohort studies and 1 RCT revealed that compared to laparoscopic operation, robotic operation^{16,20,27,33,35,37,41,56,57,61,64,67} (I² = 8%, RR = 0.70, 95% CI: 0.54–0.90, p = 0.007) (Fig. 2) was a protective factor for complications. Analysis of data from 10 cohort studies with 6378 patients (597 complications) revealed that open operation^{17,18,29,36,40,43,44,56,57} was a protective factor compared to robotic operation (I² = 15%, RR = 1.28, 95% CI: 1.05–1.57, p = 0.01) (Fig. 3). Analysis of data from 50 cohort studies and 1 RCT (7553 patients, 916 complications) revealed no significant difference between laparoscopy^{22,26,28,31,45,48,50–57,59} (I² = 37%, RR = 1.15, 95% CI: 0.99–1.35, p = 0.08) and open operation; however, the complication rate of laparoscopic surgery was higher than that of open operation. A larger sample size may have provided a significant result. There was no significant difference in complications between the trans-flank (I² = 33%, RR = 1.30, 95% CI: 0.92–1.86, p = 0.14) and trans-dorsal procedures.

FIG. 2.

Forest plot of robot vs laparoscope for complications after pyeloplasty.

FIG. 3.

Forest plot of open vs robot for complications after pyeloplasty.

Sex

Analysis of data from eight cohort studies (7395 patients, 764 complications) identified male sex^{21,22,26,35,65,68,69} (I² = 0%, RR = 1.19, 95% CI: 1.01–1.40, p = 0.04) (Fig. 4) as a risk factor for complications.

FIG. 4.

Forest plot of gender for complications after pyeloplasty.

Split renal function

Analysis of data from six cohort studies showed that SRF <40^{23,24,34,35,69} (I² = 50%, RR = 0.76, 95% CI: 0.59–0.96, p = 0.02) (Fig. 5) was a protective factor for complications.

FIG. 5.

Forest plot of split renal function <40 for complications after pyeloplasty.

Other factors

We analyzed several other potentially relevant factors, but none was found to be statistically significant (Table 4).

Table 4.

Risk Factors for Postoperative Complications of Pyeloplasty

Factors studied	Exposure/Case	Nonexposed/Control	I ²	p for heterogeneity	Model	RR/OR	95% CI	p
Gender^{21,22,26,35,65,68,69}	5401	1994	0%	0.74	Fixed	1.19	1.01–1.40	0.04
Side^{21,22,24,35,68}	1579	771	0%	0.43	Fixed	1.03	0.86–1.25	0.74
Robot vs laparoscope^{16,20,27,33,35,37,41,56,57,61,64,67}	1279	1405	8%	0.37	Fixed	0.70	0.54–0.90	0.007
Robot vs open^{17,18,29,36,40,43,44,56,57}	993	5385	15%	0.31	Fixed	1.28	1.05–1.57	0.01
Laparoscope vs open^{22,26,28,31,45,48,50–57,59}	1553	6000	37%	0.070	Fixed	1.15	0.99–1.35	0.08
Diversion type (DJS vs PCN)^{21,22,24,35,66,68,70}	1543	334	90%	<0.001	Random	0.51	0.24–1.10	0.09
Ureteral stenting (yes vs no)^{22,31,32,34,35}	1072	210	0%	0.650	Fixed	0.70	0.43–1.12	0.13
Age >6 months^21,24,34	1142	572	0%	0.960	Fixed	0.89	0.72–1.09	0.26
Age >12 months^24,39,65,69	2848	2849	85%	<0.001	Random	1.01	0.58–1.76	0.97
Prenatal diagnosis^21,22,34,69	1075	799	0%	0.590	Fixed	0.92	0.73–1.17	0.51
Split renal function <40^{23,24,34,35,69}	664	827	50%	0.080	Fixed	0.76	0.59–0.96	0.02
Hydronephrosis grade 3 vs grade 4^22,34,35	483	508	37%	0.020	Fixed	0.83	0.55–1.24	0.36
Hydronephrosis grade 1–2 vs grade 3–4^21,22	43	650	78%	0.030	Random	0.54	0.04–8.23	0.66
Surgical assess (flank vs dorsal)^{21,34,35,42,60}	634	940	33%	0.200	Fixed	1.30	0.92–1.86	0.14
Crossing vessel^21–23,35	298	1462	0%	0.640	Fixed	0.81	0.56–1.17	0.26
Stent placement (retrograde vs antegrade)^35,58	512	82	0%	0.490	Fixed	0.71	0.40–1.27	0.25
Weight <10 kg^68,69	339	736	64%	0.060	Random	1.27	0.70–2.31	0.43
Number of laparoscopic openings^19,25,38,62	171	168	0%	0.940	Fixed	1.07	0.71–1.59	0.75
Calculus³⁰	50	582	42%	0.190	Fixed	1.01	0.61–1.66	0.98
VUR^22,34	39	321	71%	0.060	Random	0.90	0.11–7.19	0.92
Bilateral²¹	134	911	0%	0.880	Fixed	1.09	0.73–1.62	0.66

Data shown in bold represent statistically significant differences (P < 0.05).

CI = confidence interval; DJS = Double J-stent; OR = odds ratio; RR = relative risk; PCN = percutaneous nephrostomies; VUR = vesicoureteric reflux.

Sensitivity analysis and publication bias

On sensitivity analyses, the results of the meta-analysis remained largely stable after the exclusion of any individual study. Funnel plots showed no significant asymmetries. In addition, Egger’s test showed no evidence of any significant publication bias (p > 0.05).

Discussion

In our cohort study, four factors were found to be associated with the development of complications, four with recurrence, and two with post-UTI. The presence of pre-UTI was found to increase the incidence of total complications, recurrences, and UTI after operation. Thus, it seems that the effect of pre-UTI may be underestimated and that a complete resolution of the pre-UTI is necessary before operation. Decreased renal cortical thickness has been shown to be associated with an increased incidence of total complications, recurrences, and post-UTI. The results of previous studies are consistent with our analysis that the reduction of renal cortical thickness increases the risk of postoperative complications, UTI, and recurrence.^26,71 This may be attributable to the fact that the reduced thickness of the renal cortex implies a more severe degree of hydronephrosis and impaired renal function. This can also be verified in collection systems. The rate of complications becomes higher with more severe collection system separations in our cohort, and the mean pyelocalix area was found to be associated with postoperative complications in a long-term follow-up.³⁰ DJ stent duration was found to correlate with recurrence, which may be attributable to local inflammation induced by prolonged physical irritation, resulting in scar formation. Obviously, removing the DJ tubes is not as early as possible. Therefore, the appropriate time of removal still needs to be further discussed. Duration of operation is significantly associated with recurrence. The duration of operation is related to the difficulty of the operation, and factors such as severe adhesions may prolong operation time. This may be attributed to higher local leakage and the formation of aseptic inflammation, which aggravates scar formation.

In addition, a meta-analysis of predictors identified four factors associated with the development of complications. Male sex was identified as a risk factor for complications. Previous studies have found a higher incidence of UTI in males than in females,^26,72 but there are also studies that show a higher incidence of UTI in females.⁷³ In conclusion, the point about the association between gender and complications is controversial, which was the motivation for our meta-analysis, and we ultimately concluded that being male is a risk factor for postoperative complications. This may be because of the differences in microbiological profile and antibiotic susceptibility between males and females. The urinary tract pathogens isolated from male patients are more resistant to antibiotics than those from females.⁷⁴ Open operation was associated with the lowest complication rate of all surgical modalities, and laparoscopic operation had the highest complication rate among all surgical approaches. However, this result was obtained by analyzing data from the published literature. Although we screened through the literature, we could not completely exclude the effect of confounding factors such as age. Notably, children with SRF <40% had fewer postoperative complications. This is contrary to our findings for renal cortical thickness. This may be attributable to the fact that patients without loss of renal function tend to present with more severe clinical symptoms or recurrent UTI, which motivates them to undergo operation. Further studies are required to explain this phenomenon.

The cohort study revealed that the causes of each complication are different. Therefore, the risk factors of different complications should be analyzed separately. However, in the meta-analysis, we were unable to analyze the risk factors separately, as most of the studies investigated the risk factors for total complications. Therefore, we could only analyze the predictors of total complications. This may be because of the small sample size in most of the studies, resulting in an insufficient number of various complications. Besides these factors that were included in the meta-analysis, duration of DJ stent,⁷⁵ delayed operation,⁷⁶ and premature delivery²² have also been reported to be potentially associated with the development of complications.

In contrast to similar studies, two systematic reviews and meta-analyses of pyeloplasty outcomes by Valentina Cascini⁷⁷ and Riccardo Autorino⁹ et al. found no significant differences in the complication and failure rates between minimally invasive procedures and open procedures. We included more studies and obtained a different conclusion. A meta-analysis by Liu et al. found no significant difference between DJ, external stented, and stent-less procedures in terms of total complications, but DJ-stented cases had the lowest incidence of urine leakage.³ This is consistent with our study.

This study has many strengths. This is the first meta-analysis of predictors of postoperative complications of pyeloplasty involving a large sample. And we have identified a number of risk factors for complications. However, some limitations of our study should be acknowledged. Our clinical data cover a longer period and include a wide age range of patients, because we considered all of these surgeries to be performed using a uniform surgical approach. Therefore, we consider that the heterogeneity with respect to surgical approaches is small. Some indicators such as differential renal function were not included in our retrospective study because of a large amount of missing data. Technologies such as robotics and laparoscopy were only analyzed as a factor rather than a subgroup. Because of data limitations of previously published studies, we were unable to analyze many factors that we were concerned with in our meta-analysis such as UTI. In addition, we included patients across a wide range of ages, leading to the possibility of some confounding factors in this. This made our cohort study less comparable with the results of the meta-analysis.

Conclusions

This study identified several predictors of total postoperative complications, recurrence, and UTI after pyeloplasty. Therefore, adequate resolution of UTIs prior to operation is necessary, and closer follow-up is required in children who are male and have reduced renal cortical thickness.

Authors’ Contributions

X.Z.: Conceptualization, data curation, formal analysis, investigation, methodology, project administration, validation, writing—original draft, and visualization. Y.Z.: Conceptualization, formal analysis, methodology, project administration, resources, supervision, and writing—review and editing. C.M.: Formal analysis and writing—review and editing. W.W.: Data curation, formal analysis, and investigation. D.S. and Q.X.: Data curation, formal analysis, methodology, and visualization. Y.L., J.H., X.R., and L.Z.: Formal analysis and investigation. G.S. and X.L.: Formal analysis, investigation, and methodology. Z.S., G.M. and Y.J.: Methodology and writing–—review and editing. Z.Z.: Methodology and formal analysis. A.L.: Conceptualization, formal analysis, funding acquisition, methodology, project administration, resources, supervision, and writing–—review and editing.

Footnotes

Author Disclosure Statement

The author states that there are no conflicts of interest.

Funding Information

Financial support was provided by the Qilu Medical Development Fund of Shandong University (34641390220001).

Supplemental Material

Abbreviations

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