Clinical significance and management of antenatally detected hydronephrosis due to ureteropelvic junction obstruction: a retrospective single-center study

Abstract

Background

Antenatal hydronephrosis (ANH) is a common prenatal finding with a heterogeneous postnatal course. This study aims to describe an institutional experience and protocol adherence regarding the clinical course, intervention timing, and surgical outcomes of severe ANH secondary to ureteropelvic junction obstruction (UPJO) and its rare coexistence with ureterovesical junction obstruction (UVJO).

Methods

We retrospectively reviewed the records of infants referred to our tertiary center with severe prenatal urinary tract dilation (UTD A2-3 / high risk). Out of 400 initially screened patients, 80 infants who completed a standardized 1-year postnatal follow-up protocol were included, representing a highly selected completer cohort. Postnatal evaluation included serial ultrasounds (USG) and mercatoacetyltriglycine 3 (MAG-3) renography. Surgical intervention (dismembered pyeloplasty) was indicated based on standardized empirical consensus criteria: anterior-posterior renal pelvic diameter (APRPD) ≥ 19 mm, parenchymal thickness ≤ 5 mm, or split differential renal function (DRF) ≤ 40% with obstructive clearance patterns. Postoperative complications were graded using the Clavien-Dindo classification.

Results

The final analysis included 80 infants. Isolated UPJO was diagnosed in 12 patients (15.0%), transient/physiological hydronephrosis in 35 (43.75%), vesicoureteral reflux (VUR) in 29 (36.25%), and coexisting UPJO and UVJO in 4 patients (5.0%). Pyeloplasty was performed in all 12 isolated UPJO patients and 4 coexisting UPJO+UVJO patients (total n = 16 surgical cases) at a median age of 3 months. Postnatal USG at 12 months demonstrated a significant reduction in pelvic dilatation and marked parenchymal thickening. No deterioration in renal function was observed during follow-up, and no postoperative complications were recorded in this cohort.

Conclusion

Adherence to a strict, conservative management protocol with standardized surgical thresholds was associated with favorable outcomes in high-risk ANH patients. Given the single-center descriptive nature and substantial loss-to-follow-up within this completer cohort, these findings represent descriptive institutional experiences rather than statistically validated threshold models.

Introduction

Hydronephrosis is defined as the dilatation of the collecting system in the upper urinary tract. Following the widespread implementation of prenatal screening, antenatal hydronephrosis (ANH) has become a frequently diagnosed fetal abnormality, detected in 1% to 5% of all pregnancies via fetal ultrasonography (USG) [1, 2]. While 41% to 88% of these cases spontaneously regress postnatally as transient conditions with no clinical significance [2, 3], a critical subset harbors severe structural uropathies. Anomalies that can induce irreversible loss of renal function—such as ureteropelvic junction obstruction (UPJO), vesicoureteral reflux (VUR), obstructive megaureter, and posterior urethral valves (PUV)—frequently present initially as ANH.

Postnatal risk stratification and management pathways are typically determined by measuring key parameters, including the anterior-posterior renal pelvis diameter (APRPD), peripheral calyceal dilation, and renal parenchymal thickness. Among these etiologies, profound pelvicalyceal dilatation without ureteral dilation or VUR strongly suggests a primary congenital UPJO, which occurs in approximately 1:1000–2000 live births [4]. However, the management of UPJO remains subject to debate; randomized studies propose that only 19% to 25% of prenatally diagnosed children ultimately require surgical intervention, while the remainder can be safely monitored [2]. This clinical decision-making becomes significantly more complex in rare scenarios where UPJO coexists with a simultaneous, ipsilateral ureterovesical junction obstruction (UVJO), a dual entity whose optimal surgical sequence remains highly controversial.

The primary objective of this study is to retrospectively evaluate the clinical follow-up, management pathways, and treatment outcomes of infants with severe UPJO-related ANH managed under a standardized institutional protocol. The secondary objective is to examine the descriptive outcomes and clinical challenges in the rare sub-population exhibiting coexisting UPJO and UVJO within the same ureteric unit. By defining these cohorts, this study aims to provide additional clinical data regarding management of severe ANH regarding the management thresholds of high-risk congenital uropathies [2].

Methods

This retrospective, single-center descriptive study was conducted at the Department of Obstetrics and Gynecology and Pediatric Surgery units of our tertiary regional referral hospital. The study protocol was approved by the Institutional Review Board (Decision No: 67, 2023).

A total of 400 pregnant women whose fetuses were diagnosed with severe ANH were initially identified through prenatal records between 2018 and 2023. However, due to the nature of our center as a regional referral hub, a substantial proportion of families returned to their home provinces for postnatal delivery and local care. Consequently, 320 patients were lost to postnatal follow-up. The final study sample comprised 80 infants who completed a standardized 1-year postnatal follow-up protocol at our institution, establishing a highly selected “completer cohort.”

Inclusion criteria

Fetuses diagnosed with severe, high-risk ANH, defined according to the Urinary Tract Dilation (UTD) classification system as UTD A2-3 (prenatal APRPD ≥ 10 mm at ≥ 28 weeks’ gestation, associated with peripheral calyceal dilation or parenchymal thinning).

Exclusion criteria

Patients with associated major chromosomal or syndromic abnormalities, multiple congenital anomalies, posterior urethral valves, neurogenic bladder, or incomplete postnatal clinical, radiological, or nuclear medicine records at the 1-year mark.

Postnatal renal ultrasonography (USG) was systematically performed within the first week of life, at 1 month, and at 3 months. All USG examinations measured the anterior-posterior renal pelvic diameter (APRPD), peripheral calyceal dilation, and renal parenchymal thickness.

Technetium-99 m mercatoacetyltriglycine 3 (MAG-3) renography with furosemide washout was routinely performed between 1 and 3 months of life to assess split differential renal function (DRF) and clear urinary washout Dynamics [1, 3, 5, 6].

Surgical intervention, via a standardized open dismembered pyeloplasty, was initiated based on strict, empirical consensus criteria within our department:

1. An APRPD ≥ 19 mm associated with a parenchymal thickness ≤ 5 mm.

2. A split differential renal function (DRF) ≤ 40% on the affected side.

3. A documented progressive decline in DRF > 10% on serial MAG-3 scans during active conservative follow-up.

A successful surgical outcome was defined postoperatively as the stabilization or improvement of DRF on repeat MAG-3 renography, a demonstrable reduction in APRPD on follow-up USG, and the complete absence of recurrent urinary tract infections (UTIs) or secondary re-obstruction during the 1-year postoperative follow-up period. Postoperative complications were monitored and graded using the validated Clavien-Dindo classification system.

The research data were analyzed using the IBM SPSS 26.0 statistics program. Given the final cohort size and the non-analytical nature of the study, statistical analysis was restricted to descriptive metrics. Quantitative variables are expressed as medians with corresponding ranges or means with standard deviations. Qualitative variables are presented as absolute frequencies and percentages. No comparative multivariable modeling or threshold validation analysis was performed due to power limitations within the sub-cohorts.

Results

The study evaluated the comprehensive clinical data of 80 infants who met the strict inclusion and follow-up criteria, establishing a highly selected completer cohort. The demographic and baseline characteristics of the study population are summarized as follows: 26 infants (32.5%) were female, and 54 (67.5%) were male, demonstrating a distinct male predominance. The mean gestational age at birth was 37.6 ± 1.9 weeks, with 7 infants (8.75%) born preterm (< 37 weeks’ gestation). The mean birth weight of the cohort was 3162 ± 569.7 g, and 7 babies (8.75%) presented with a low birth weight below 2500 g.

Regarding the anatomical distribution of the prenatally detected pathologies, laterality was evenly split: the anomaly was located on the left side in 40 infants (50.0%), on the right side in 15 infants (18.75%), and bilateral involvement was documented in 25 infants (31.25%). Following complete postnatal diagnostic workups, the final definitive etiologies of the high-risk ANH cohort were determined as: transient/physiological hydronephrosis in 35 infants (43.75%), primary vesicoureteral reflux (VUR) in 29 infants (36.25%), isolated UPJO in 12 infants (15.0%), and coexisting ipsilateral UPJO and UVJO in 4 infants (5.0%). The comprehensive flow diagram outlining patient screening, exclusion, and final sub-group distributions is presented in Fig. 1.

Fig. 1.

Flow diagram of the study selection. *Patients whose hydronephrosis disappeared during pregnancy, who were lost to follow-up, and whose data were not fully accessible. UPJO: ureteropelvic junction obstruction, UVJO: ureterovesical junction obstruction

Among the cohort, a total of 16 patients (12 with isolated UPJO and 4 with coexisting UPJO+UVJO) met the strict institutional criteria for surgical intervention due to severe pelvicalyceal dilation and significantly threatened or compromised renal function. Our objective thresholds for making surgical decisions included an APRPD ≥ 19 mm, a parenchymal thickness ≤ 5 mm on serial postnatal ultrasounds, and a split differential renal function < 40% on MAG-3 renography. Open dismembered pyeloplasty was successfully executed in all 16 surgical cases at a median age of 3 months.

Of the 12 patients diagnosed with isolated UPJO, 9 were left-sided, 2 were right-sided, and 1 was bilateral. In the left-sided UPJO sub-group (n = 9), a temporary left nephrostomy catheter was placed during the first month of life in 2 patients due to severe progressive dilatation. Subsequently, left dismembered pyeloplasty combined with Double-J (DJ) stent insertion was performed in all 9 patients at a median age of 3 months. For the right-sided UPJO patients (n = 2), primary right pyeloplasty and DJ stent insertion were successfully performed at the 3rd month of follow-up. In the single patient diagnosed with bilateral UPJO (n = 1), bilateral protective DJ stents were initially placed in the first week of life. During longitudinal surveillance, the right-sided UPJO demonstrated spontaneous resolution; consequently, a unilateral left pyeloplasty and DJ stent insertion were performed at 3 months. All internal splints and DJ stents in the isolated UPJO sub-group were electively removed during postoperative follow-up without incident. The detailed longitudinal changes in APRPD, parenchymal thickness, and scintigraphic parameters for the isolated UPJO cohort are summarized in Table 1.

Table 1.

Longitudinal ultrasound and scintigraphy parameters of the UPJO cohort

Patient Sub-groups	Post-natal 1st Week Median (Min–Max)	Post-natal 1st Month Median (Min–Max)	Post-natal 3rd Month Median (Min–Max)	Preoperative MAG-3 Split Function Median (Min–Max)
Left UPJO (n = 9)
Affected Kidney (Left)	APRPD: 23.8 (14-31.5) mm PT: 4.4 (2–11) mm	APRPD: 21.2 (17–33) mm PT: 5.9 (3–7) mm	APRPD: 19.7 (6,5–33,7) mm PT: 4.5 (3–8) mm	30.8 (9–44) %
Contralateral Kidney (Right)	Normal / Baseline	Normal / Baseline	Normal / Baseline	69.2 (56–91) %
Right UPJO (n = 2)
Affected Kidney (Right)	APRPD: 10.5 (10–11) mm PT: 4.8 (4–5,6) mm	APRPD: 11.2 (9,5–13) mm PT: 6.5 (4–9) mm	APRPD: 19.0 (7–31) mm PT: 4.5 (4–5) mm	25.0 (20–30) %
Contralateral Kidney (Left)	Normal / Baseline	Normal / Baseline	Normal / Baseline	75.0 (70–80) %
Bilateral UPJO (n = 1)
More Affected Side (Left)	APRPD: 24.0 mm PT: 3.4 mm	APRPD: 32.0 mm PT: 4.0 mm	APRPD: 27.0 mm PT: 5.0 mm	37.0%
Less Affected Side (Right)	APRPD: 15.0 mm PT: 3.5 mm	APRPD: 12.7 mm PT: 5.0 mm	APRPD: 4.0 mm PT: 8.0 mm	63.0%

Continuous variables are expressed as Median (Minimum–Maximum) to demonstrate data distribution

UPJO Ureteropelvic Junction Obstruction, APRPD Anterior-Posterior Renal Pelvic Diameter, PT Parenchymal Thickness, MAG-3 Mercatoacetyltriglycine-3

All quantitative values represent institutional median metrics. For the bilateral UPJO patient, parameters for both sides are explicitly separated to avoid formatting ambiguity

The remaining 4 surgical patients presented with coexisting ipsilateral UPJO and UVJO strictures. In this complex double-obstruction sub-group, 1 neonate required urgent percutaneous nephrostomy placement during the early neonatal period due to high-pressure symptomatic hydronephrosis; the secondary distal UVJO stenosis was subsequently diagnosed via antegrade pyelography during the procedure, and a DJ stent was passed across the distal stricture. For the other 3 patients, the secondary distal UVJO stricture was identified via intraoperative retrograde pyelography performed during cystoscopy at the time of primary pyeloplasty.

Our institutional strategy prioritized the surgical decompression of the proximal obstruction first. Accordingly, primary dismembered pyeloplasty was performed concurrently with protective DJ stent deployment extending across both the proximal anastomosis and the distal UVJO site (at 3 months of age for 3 patients, and at 1 year of age for 1 patient). Following active postoperative follow-up and stent removal, the distal UVJO stricture spontaneously regressed in 3 out of the 4 patients, requiring no further surgical intervention. Only 1 patient exhibited a persistent, non-resolving distal UVJO that failed conservative splinting, necessitating a secondary ureteroneocystostomy (UNC) at the end of the 1st year of life. The longitudinal ultrasound measurements and dynamic scintigraphy outcomes for the coexisting UPJO and UVJO cohort are summarized in Table 2.

Table 2.

Longitudinal ultrasound and scintigraphy parameters of the coexisting UPJO and UVJO cohort (n = 4)

Patient Sub-groups	Post-natal 1st Week Median (Min–Max)	Post-natal 1st Month Median (Min–Max)	Post-natal 3rd Month Median (Min–Max)	Preoperative MAG-3 Split Function Median (Min–Max)
Right UPJO + UVJO and Left Transient Hydronephrosis (n = 2)
Affected Kidney (Right)	APRPD: 27.0 (20–34) mm PT: 3.7 (2,5 − 4,9) mm	APRPD: 12.0 (4–20) mm PT: 8.0 (3,5–12,5) mm	APRPD: 14.0 (8–20) mm PT: 6.0 (3,5–8,5) mm	39.5 (39–40) %
Contralateral Kidney (Left)	APRPD: 7.5 (7–8) mm PT: 6.5 (min–max) mm	APRPD: 9.0 (8–10) mm PT: 8.7 (min–max) mm	APRPD: 9.0 (8–10) mm PT: 6.0 (min–max) mm	60.5 (60–61) %
Right UPJO + UVJO (n = 1)
Affected Kidney (Right)	APRPD: 17.0 mm* PT: 4.2 mm*	APRPD: 24.0 mm* PT: 6.0 mm*	APRPD: 18.0 mm* PT: 7.5 mm*	36.0%*
Contralateral Kidney (Left)	Normal / Baseline	Normal / Baseline	Normal / Baseline	64.0%*
Left UPJO + UVJO (n = 1)
Affected Kidney (Left)	APRPD: 25.0 mm* PT: 4.5 mm*	APRPD: 30.0 mm* PT: 6.0 mm*	APRPD: 33.0 mm* PT: 3.0 mm*	40.0%*
Contralateral Kidney (Right)	Normal / Baseline	Normal / Baseline	Normal / Baseline	60.0%*

Continuous variables are expressed as Median (Minimum–Maximum) to demonstrate data distribution

APRPD Anterior-Posterior Renal Pelvic Diameter, UPJO Ureteropelvic Junction Obstruction, UVJO Ureterovesical Junction Obstruction, PT Parenchymal Thickness, MAG-3 Mercatoacetyltriglycine-3

*For single-patient sub-groups (n = 1), individual descriptive metrics for both renal units are explicitly separated to maintain formatting clarity, and range parameters are not applicable

Postoperative ultrasonography performed at the 12-month mark for all 16 surgical cases demonstrated favorable anatomical outcomes, characterized by a significant reduction in median APRPD and marked thickening of the renal parenchyma. Furthermore, follow-up nuclear medicine scans confirmed the stabilization or improvement of split renal function with non-obstructive clearance patterns, indicating a 100% surgical success rate. Follow-up imaging demonstrated favorable anatomical and functional outcomes in all surgically treated patients during the study period. No postoperative complications were observed during the follow-up period.

Discussion

The epidemiological distribution of our patient cohort aligned with current global literature, demonstrating a higher prevalence of antenatally detected hydronephrosis (ANH) among male infants [7]. This is consistent with the comprehensive findings of Quirino et al., who reported a distinct male predominance (male-to-female ratio of 2:1) and a high frequency of unilateral presentation in their registry of 822 children with prenatally diagnosed nephrouropathies [8]. While some contemporary series, such as that by Cleper et al., focus heavily on high-acuity neonatal populations—including preterms who exhibit a twofold increase in mortality associated with systemic complications like acute kidney injury [9]—our cohort focused on long-term structural uropathies monitored through a standardized outpatient protocol. Regardless of the affected side, transient or physiological hydronephrosis represented the most common postnatal diagnosis in our study, with half of the affected infants presenting with left-sided involvement. This left-sided and male predominance in congenital anomalies of the kidney and urinary tract (CAKUT) strongly mirrors large-scale screening data published by Zhang et al. in China [10].

In clinical practice, framing the exact etiologic hierarchy is essential for risk stratification. Broadly following transient hydronephrosis, ureteropelvic junction obstruction (UPJO) consistently ranks as the leading pathological cause of congenital severe ANH requiring specialized care [8, 11]. Because delayed intervention in true anatomical UPJO can culminate in progressive nephron damage and permanent organ loss, timely postnatal identification is critical to gauge obstruction severity and optimize the therapeutic window [5]. In our center, the diagnosis of significant UPJO was reached through strict adherence to a longitudinal protocol combining serial postnatal ultrasonography (at the first week, 1st month, and 3rd month of life) and Technetium-99 m mercatoacetyltriglycine (MAG-3) renography.

Although widely accepted consensus guidelines provide frameworks for surveillance, the interpretation of dynamic imaging and the decision to transition from conservative observation to operative management frequently remain subjective, often relying on institutional preference and individual clinician experience [3, 4, 6]. Standardized thresholds, such as those in the Society for Fetal Urology (SFU) consensus statement, generally recommend surgical mitigation when the split differential renal function (DRF) drops below 40% or exhibits an absolute decline of more than 10% on serial scans, or when progressive anterior-posterior renal pelvic diameter (APRPD) dilatation exceeding 10 mm is documented alongside parenchymal thinning [2]. For context, in a substantial series of 125 children undergoing pyeloplasty for high-grade UPJO, Värelä et al. reported a mean preoperative APRPD of 30 mm paired with a mean DRF of 41% [12]. In comparison, our cohort presented with strict objective baseline indications; all 16 patients undergoing open dismembered pyeloplasty at the median age of 3 months exhibited an.

APRPD ≥ 19 mm, parenchymal thickness ≤ 5 mm, and a DRF < 40%. Internal splinting via Double-J (DJ) stents was routinely utilized to safeguard the anastomosis, with elective removal performed 6–8 weeks postoperatively [13]. Adhering to these strict consensus criteria yielded favorable surgical outcomes, with improvement or stabilization of renal function and no observed postoperative complications during follow-up.

The simultaneous coexistence of ipsilateral UPJO and ureterovesical junction obstruction (UVJO) in the same ureteric unit represents a rare and technically challenging anomaly [14]. The dual points of resistance exacerbate upper urinary tract high-pressure dynamics, leading to severe hydronephrosis and profound parenchymal thinning. Diagnosing this compound obstruction is notoriously difficult, and a clear management consensus is lacking in current literature [1, 14]. Notably, Lee et al. cautioned against immediate, upfront pyeloplasty as a blanket strategy, noting that distal UVJO can induce severe global ureteral tortuosity and secondary kinking that mimics a primary proximal UPJO [15]. In our study, the secondary distal stricture was confirmed via intraoperative retrograde pyelography during diagnostic cystoscopy. Our institutional strategy prioritized the relief of the proximal obstruction first, performing a primary dismembered pyeloplasty while concurrently passing a protective DJ stent across the distal UVJO site. Interestingly, this approach facilitated the spontaneous regression of the distal stricture in 3 out of 4 patients during postoperative follow-up, negating the need for further surgical reconstruction. Only one patient required a secondary ureteroneocystostomy (UNC) at the 1st year of life due to persistent, non-resolving distal UVJO. This underscores that a significant portion of distal ureteral narrowing in these complex double-obstruction phenotypes may represent a transient, functional developmental delay that recovers once the high-pressure proximal system is decompressed [6]. However, given our small sample size of 4 cases, this observational finding must be interpreted with caution.

This study has several limitations that must be addressed. First, its retrospective, single-center design prevents the establishment of a predictive or causal threshold model. Second, the small sample size within the surgical UPJO (n = 16) and coexisting UPJO+UVJO (n = 4) sub-groups severely limits the statistical power needed to execute multivariable regression or ROC-based validation analyses.

Most critically, our study is subject to substantial selection bias, representing a highly selected “completer cohort” [8]. Out of 400 prenatally screened patients with suspected severe ANH, 320 were lost to postnatal follow-up, resulting in a final analytical sample of only 20%. As a major regional tertiary referral hub, our center receives complex cases from distant provinces for prenatal counseling; however, a large majority of these families return to their local provincial health centers for delivery and postnatal care. This massive loss-to-follow-up creates a “completer cohort bias,” meaning our analyzed population likely differs systematically from the source population. This limitation severely restricts the external validity and generalizability of our institutional findings, highlighting the acute need for broader, prospective multi-center collaborative trials.

Authors’ contributions

S. G.: Conceptualization, Formal analysis, Investigation, Writing – original draftH.S.Y.C.: Conceptualization, Methodology, Investigation, Visualization, Writing – original draft, Writing – review & editingG. Ş.: ConceptualizationR. K.: ConceptualizationM. A.O.: Conceptualization, Methodology, Writing – original draftİ. E.: ConceptualizationM. İ. : Supervision, Writing – original draft, Writing – review & editingH. S.: Supervision.

Funding

This study was not supported by any sponsor or funder.

Data availability

The datasets generated and/or analysed during the current study are available from the corresponding author on reasonable request.

Declarations

Ethics approval and consent to participate

This study was performed in line with the principles of the Declaration of Helsinki. The Clinical Sciences Ethics Committee of Karadeniz Technical University Faculty of Medicine approved the study with the decision numbered 67 dated 2023. Written informed consent was obtained from all individual participants’ parents.

Consent for publication

Not applicable.

Competing interests

The authors declare no competing interests.