Aberrant renal vessels crossing the ureter and the ureteropelvic junction: A retrospective computed tomography-based analysis of non-obstructed population

Abstract

BACKGROUND

Crossing renal vessels are recognized as potential extrinsic contributors to ureteropelvic junction obstruction; however, their prevalence and morphological characteristics in adults without urinary tract obstruction remain incompletely characterized.

AIM

To determine the prevalence, vascular composition, morphological patterns, and spatial relationship of renal vessels crossing the ureteropelvic junction (UPJ) or proximal ureter using contrast-enhanced computed tomography (CT).

METHODS

A retrospective review of 197 adult patients (394 kidneys) with normal urological anatomy who underwent contrast-enhanced abdominal CT was conducted. Multiplanar and three-dimensional reconstructions were evaluated to document crossing vessel prevalence, etiology (arterial, venous, or combined), specific anatomical variations (early bifurcations or accessory vessels), spatial orientation (anterior/posterior), and exact intersection distance to the ureteropelvic.

RESULTS

Crossing vessels were identified in 56 of 394 renal units (14.2%), affecting 43 of 197 patients (21.8%), exhibiting a significant male predominance (69.6%, P = 0.007). Presentations were unilateral in 69.8% and bilateral in 30.2% of cases. Arterial anomalies predominated (64.3%), mostly due to early main renal artery bifurcations, while combined arterio-venous crossings occurred in 25% of cases. The spatial orientation was overwhelmingly anterior (98.2%). Direct UPJ intersection (0 mm) was observed in 37.5% of cases, whereas distal ureteral intersections occurred at a mean distance of 16.2 ± 4.5 mm from the junction.

CONCLUSION

Renal vessels crossing the UPJ or proximal ureter are not uncommon incidental anatomical findings on contrast-enhanced CT in adults without obstruction. Their baseline prevalence in an unobstructed cohort highlights that crossing vessels can exist without concurrent obstruction. Contrast-enhanced CT provides detailed anatomical mapping of the vascular course, which may support preoperative planning and help mitigate the risk of inadvertent vascular injury when surgical intervention is indicated. Nevertheless, functional assessment remains necessary when clinically significant obstruction is suspected.

Key Words: Renal artery; Renal vein; Variation; Ureteropelvic junction; Obstruction

Core Tip: This retrospective contrast-enhanced computed tomography study evaluated 197 adult patients with normal urinary tracts to determine the prevalence and morphology of renal vessels crossing the ureteropelvic junction. Crossing vessels were identified in 14.2% of cases, exhibiting a significant male predominance. These vessels were predominantly driven by anterior-crossing arterial anomalies, particularly early main renal artery bifurcations. The substantial baseline prevalence of these crossing vessels in unobstructed kidneys indicates that these vessels can occur incidentally without associated obstruction. While this study does not evaluate functional outcomes, detailed preoperative vascular mapping with contrast-enhanced computed tomography can be a valuable adjunct for surgical planning and mitigate the risk of inadvertent vascular injury.

INTRODUCTION

Congenital anomalies of the kidney and urinary tract (CAKUT) comprise a heterogeneous group of structural abnormalities affecting the kidneys and urinary tract and represent a major cause of chronic kidney disease in children. Their estimated prevalence is approximately 1.6 per 1000 live births, and they account for 20%-30% of congenital abnormalities detected by prenatal ultrasonography[1,2]. CAKUT encompasses a broad spectrum of conditions, including transient hydronephrosis[3], renal agenesis or hypoplasia[4], horseshoe kidney[5], vesicoureteral reflux[6], and ureteropelvic junction obstruction (UPJO)[2,7-13].

UPJO is characterized by impaired urine flow from the renal pelvis into the proximal ureter, potentially resulting in hydronephrosis and, in severe or untreated cases, progressive renal functional deterioration. While predominantly diagnosed in childhood, UPJO is increasingly recognized in the adult population, where its estimated prevalence in the general population ranges from 0.05% to 0.15%, and it accounts for approximately 10%-20% of CAKUT cases[2,7-13]. The clinical presentation and timing of diagnosis vary substantially, with UPJO identified either prenatally through detection of hydronephrosis or postnatally after symptoms, a urinary tract infection, or incidental imaging findings. Differences in reported prevalence between prenatally and postnatally diagnosed populations may reflect variation in study design, diagnostic criteria, and patient selection[14].

UPJO may result from intrinsic or extrinsic mechanisms. Intrinsic obstruction is generally attributed to abnormalities of the ureteropelvic junction (UPJ) wall, including disordered smooth-muscle arrangement, abnormal collagen deposition, impaired peristalsis, congenital narrowing, fibrosis, or scarring. Extrinsic obstruction may be associated with adjacent anatomical structures, particularly renal vessels crossing the UPJ or proximal ureter. These vessels may be arterial, venous, or combined and may arise from accessory renal vessels or from early branching of the main renal vasculature. Crossing vessels were first implicated in UPJO by von Rokitansky in 1842. They are more frequently encountered in adults and older symptomatic children than in neonates and infants. Reported frequencies range from approximately 10%-20% among younger children with UPJO to 30%-70% among older or symptomatic pediatric populations, although estimates vary by population and diagnostic method[15-17].

While the clinical impact of crossing vessels in symptomatic UPJO is well-documented, their baseline prevalence and anatomical characteristics in the normal, unobstructed urinary tract remain poorly understood. It is widely recognized that some individuals possess crossing vessels without ever developing UPJO or hydronephrosis. However, the exact morphological tipping point - why some vessels cause obstruction while others remain incidental - is part of an ongoing clinical debate[1,18]. Moreover, the baseline prevalence, morphological patterns, and spatial relationships of these vessels in adults with a normal, unobstructed urinary tract remain poorly characterized. Establishing a reference anatomical baseline is essential to improve the interpretation of incidental crossing vessels detected during routine diagnostic imaging and to clarify whether their mere presence is sufficient to support an extrinsic mechanism of obstruction. Therefore, the present study aimed to determine the prevalence, vascular composition, morphological patterns, and spatial topography of renal vessels crossing the UPJ or the proximal ureter in adults without imaging evidence of obstruction, as assessed using contrast-enhanced computed tomography (CT).

MATERIALS AND METHODS

Study sample

An archived lot of contrast-enhanced abdominal CT examinations, obtained from the National and Kapodistrian University of Athens, was used for the current retrospective cross-sectional CT-based radioanatomical study. The scans were performed between January 2020 and December 2023. Ethical approval was granted by the institutional review board, approval No. 1037; date: 28 April 2025. For the purposes of this study, normal urological anatomy was defined radiologically as the absence of nephrolithiasis, renal or urinary tract neoplasms, and any degree of hydronephrosis on CT. Where clinical history was available in the imaging request, patients with documented prior UPJO or systemic genitourinary disorders were excluded.

Radiological protocol

All examinations were performed using a 128-slice multidetector CT scanner (Canon Medical Systems, Tochigi, Japan). Imaging was performed using a contrast-enhanced biphasic abdominal CT protocol, with a slice thickness of 1.25 mm. Intravenous iodinated contrast medium (370 mg iodine/mL) was administered via a power injector at a rate of approximately 4 mL/second, followed by a saline flush. The arterial phase was initiated using bolus tracking (triggered at 150 HU within the abdominal aorta) with an average delay of 25-30 seconds, while the portal venous phase was acquired at 70 seconds. Image analysis was conducted using Horos software version 3.3.6 (Horos Project, New York, NY, Untied States).

Image processing

Each dataset was systematically reviewed in axial, coronal, and sagittal planes with multiplanar reconstruction (MPR). Two independent researchers (Paschopoulos I and Gondorf D), blinded to each other’s assessments, evaluated all 394 renal units (100% of the study sample) to identify crossing vessels and perform subsequent morphological measurements. Following this independent pre-consensus assessment, any discrepancies were reviewed and confirmed with a third author (Triantafyllou G), and final disagreements were resolved by a senior author (Piagkou M). Interobserver reliability for categorical variables was assessed using Cohen’s kappa (κ), with values ≥ 0.60 indicating acceptable agreement. For continuous variables, reliability was assessed using a two-way mixed-effects, absolute agreement intraclass correlation coefficient model, with values assessed as < 0.50 (poor), 0.50-0.75 (moderate), 0.75-0.90 (good), and > 0.90 (excellent) reliability.

Methodological protocol

By using MPR (especially coronal and sagittal reconstructions), we identified patients with a crossing vessel at the ureter or UPJ. The ureter was identified by continuously tracing the renal pelvis caudally on the portal venous phase. The UPJ was defined anatomically as the distinct funnel-like narrowing where the wider renal pelvis transitions into the uniform, tubular proximal ureter. For each identified crossing vessel, several morphological and spatial parameters were recorded. Firstly, a crossing vessel was defined as any aberrant renal vascular structure (artery or vein) whose anatomical trajectory intersected the longitudinal axis of the UPJ or proximal ureter. The vessels were categorized by etiology (isolated artery, isolated vein, or combined) and by anatomical variation (early bifurcation or accessory vessel). The spatial orientation relative to the ureter was documented as either anterior or posterior. Finally, the exact distance from the point of vascular intersection to the UPJ was measured. All distance measurements were performed using the digital caliper tool within the Horos software. The shortest linear distance between the inferior margin of the crossing vessel and the UPJ was measured in the optimal MPR plane (coronal or sagittal) that provided an orthogonal view of both structures. A distance of 0 mm was recorded for vessels directly compressing the UPJ. In cases of combined arterio-venous crossings traveling together in a vascular bundle, the intersection distance to the UPJ was recorded based on the lowest vessel (the one situated closest to the junction). The spatial orientation relative to the ureter (anterior or posterior) and the specific etiologies were documented for all involved structures.

Statistical analysis

Statistical analysis was performed using IBM SPSS Statistics (version 30, IBM Corp., Armonk, NY, United States). Continuous variables (such as patient age and distances) were assessed for normality and are presented as means ± SD. Categorical variables (such as sex, laterality, and crossing vessel etiology) are presented as frequencies and percentages. Categorical associations (distribution of specific vessel types across patient sex and laterality) were analyzed using the Pearson χ² test or Fisher’s exact test, as appropriate based on cell counts. For continuous data, comparisons between two independent groups (patient age between groups with and without crossing vessels, and distance measurements between sexes and sides) were performed using the independent-samples t-test (Welch’s t-test) or the nonparametric Mann-Whitney U test when assumptions of normality were not met. Comparisons of continuous variables across three or more groups (distance measurements across type of crossing vessels) were analyzed utilizing the Kruskal-Wallis test. A two-sided P value of < 0.05 was considered statistically significant for all tests. To account for intra-subject correlation in bilateral cases, categorical associations regarding patient sex were analyzed at the patient level (assessing the presence of at least one crossing vessel per patient).

RESULTS

One hundred and ninety-seven patients met the inclusion criteria, with 394 kidneys (197 left and 197 right sides). The overall patient cohort consisted of 102 males and 95 females. The mean age of the study population was 63.2 ± 14.4 years (range: 22-91 years). For the identification of cases and variables, the Cohen’s κ was 1.000 indicating absolute agreement between reviewers. For the continuous measurement of the distance from the crossing vessel to the UPJ, the intraclass correlation coefficient was 0.911 (95% confidence interval: 0.852-0.948) depicting excellent reliability.

A crossing vessel was identified in 56 of the 394 renal units (14.2%), which corresponded to 43 affected patients (21.8% of the 197 patient cohorts). When evaluating patient-level prevalence by sex to account for intra-subject correlation, crossing vessels were found in 29 of the 102 male patients (28.4%) and 14 of the 95 female patients (14.7%). This indicates a statistically significant male predominance, with males having substantially higher odds of exhibiting at least one crossing vessel compared to females (odds ratio = 2.30, 95%confidence interval: 1.13-4.68, P = 0.031). A post-hoc power analysis for this sex difference yielded a statistical power of approximately 84% (alpha = 0.05), supporting the credibility of this primary finding. However, it is important to note that this specific calculation treated individual renal units as independent observations without statistical adjustment for intra-subject correlation (bilateral cases). Thus, the reported odds ratio and P value may overestimate the effective sample size and should be interpreted as exploratory.

Analysis of laterality demonstrated that 31 cases (55.4%) occurred on the left and 25 cases (44.6%) on the right (P = 0.504). The anatomical variation presented bilaterally in 13 patients (30.2%) and unilaterally in 30 patients (69.8%). The patients with the crossing had a mean age of 64.3 ± 15.4 years, compared to the rest of the cohort that had a mean age of 62.8 ± 14.2 years (P = 0.556).

Arterial structures were the primary etiology of ureteral crossing. An isolated crossing artery was observed in 36 cases (64.3%), while an isolated crossing vein was noted in 6 cases (10.7%). Simultaneous crossing of both an artery and a vein occurred in 14 cases (25%) (Figure 1). Statistical analysis revealed that the distribution of these specific crossing vessel types did not significantly differ between sexes (P = 0.884) or between sides (P = 0.306).

Figure 1 Computed tomography scan of 74-year-old female patient exhibiting anterior crossing by both early bifurcated renal artery and vein at the level of the uteropelvic junction. A, B: Left-sided; C, D: Right-sided; E: Bilateral maximum-intensity projection; F: Three-dimensional reconstructions. A, C: Sagittal; B, D, and E: Coronal. 1: Left Ureter; 2: Left early bifurcated renal arteries; 3: Right Ureter; 4: Right Early Bifurcated Renal artery.

Morphological analysis of the crossing vessels revealed distinct anatomical variations. Among the arterial crossings, the most frequent anomaly was an early bifurcation of the main renal artery (42 cases) (Figure 2), followed by the presence of an accessory renal artery (8 cases) (Figure 3).

Figure 2 Computed tomography scan of 54-year-old male patient exhibiting bilateral anterior crossing by early bifurcated renal arteries at the level of ureteropelvic junction (on the left side) and 12.5 mm distally on the ureter (on the right side). A: Coronal; B: Sagittal; C: Three-dimensional reconstruction. 1: Left ureter, 2: Left early bifurcated renal artery; 3: Right ureter.

Figure 3 Computed tomography scan of 55-year-old male patient exhibiting anterior crossing by an accessory renal artery, 19.9 mm distally to the ureter. A: Coronal; B: Sagittal; C: Three-dimensional reconstructions. 1: Ureter; 2: Typical renal artery; 3: Accessory renal artery.

In cases involving venous crossings, the most common variations were early bifurcations of the renal vein (14 cases) (Figure 1) and accessory renal vein (6 cases) (Figure 4).

Figure 4 Computed tomography scan of 64-year-old female patient exhibiting anterior crossing by an accessory renal vein at the level of ureteropelvic junction. A: Coronal; B: Sagittal; C: Three-dimensional reconstruction. 1: Ureter; 2: Accessory renal vein; 3: Typical renal vein.

An anterior trajectory was documented in 55 cases (98.2%) of the crossing cohort (Figures 1, 2, 3, 4 and 5). In contrast, a posterior crossing was identified in only a single case (1.8%) within the study sample (Figure 5).

Figure 5 Computed tomography scan of 65-year-old male patient exhibiting posterior crossing by both accessory renal artery and vein, 15.1 mm distally to the ureter. A: Axial; B: Sagittal; C: Coronal; D: Three-dimensional reconstructions. 1: Ureter; 2: Accessory renal artery; 3: Accessory renal vein; 4: Typical renal artery; 5: Typical renal vein.

Measurements regarding the distance from the crossing vessel to the UPJ revealed two distinct anatomical distributions. Direct UPJ involvement was identified in 21 cases (37.5%), where the vessels intersected the ureter exactly at the junction (0 mm). In the remaining subset of cases, the vessels crossed the proximal ureter distal to the junction. The distance of these distal intersections varied considerably, yielding a mean crossing distance of 16.2 ± 4.5 mm (range: 9.2 mm to 27.8 mm). There were no statistically significant differences between sexes (P = 0.380) and sides (P = 0.712) regarding the measurements. Ιsolated venous crossings intersected slightly further from the UPJ (17.2 ± 4.7 mm) than isolated arterial (16.5 ± 4.2 mm) or combined artery-and-vein crossings (15.2 ± 5.0 mm). However, these differences were not statistically significant (P = 0.420) (Figure 6).

Figure 6 Box plots demonstrating the distal site of crossing (> 0 mm) between the vessel and the ureteropelvic junction, categorized by patient sex. Left: Female (n = 17), male (n = 39), laterality [center: Left (n = 31), right (n = 25)], and vascular etiology [right: Artery (n = 36), vein (n = 6), both (n = 14)]. The central horizontal line within each box represents the median distance, while the lower and upper boundaries of the box indicate the first and third quartiles (interquartile range). The whiskers extend to the lowest and highest values within 1.5 times the interquartile range. Diamond markers denote outlier data points beyond this range.

DISCUSSION

The present contrast-enhanced CT study provides an in vivo anatomical assessment of renal vessels that cross the UPJ or the proximal ureter in adults without imaging evidence of obstruction. Crossing vessels were identified in 56 of 394 renal units (14.2%) and in 43 of 197 patients (21.8%) (Table 1). Almost one-third of affected patients had bilateral crossings. Arterial involvement predominated, most commonly because of early branching of the main renal artery, while combined arterial-venous crossings were also observed. The vessels followed an almost exclusively anterior course relative to the ureter. Approximately one-third crossed directly at the UPJ, whereas the remainder crossed the proximal ureter at a mean distance of 16.2 mm distal to the junction (Table 1). Moreover, a particularly notable finding in our cohort was the significant male predominance, with crossing vessels occurring in 19.1% of male renal units compared to 8.9% of female units. To our knowledge, no previous studies have explicitly compared sex distributions for this specific anatomical variant in a non-obstructed population. This disparity may be rooted in embryological differences during the ascent of the kidneys and the sequential regression of the mesonephric vascular supply. However, as this is a relatively novel observation, it must be interpreted with caution (Table 1).

Table 1 Demographic and anatomical characteristics of renal units exhibiting crossing vessels.

Characteristic	Total/frequency (n = 56)	Percentage (%)	P value
Sex distribution (n = 56)
Male	39	69.6%	0.007a
Female	17	30.4%
Laterality (n = 56)
Left	31	55.4%	0.504
Right	25	44.6%
Vascular etiology
Isolated artery	36	62.5%	0.884 (sex)
Isolated vein	6	10.7%
Combined (artery and vein)	14	23.2%	0.306 (side)
Arterial variations (n = 50)
Early bifurcation of RA	42	84.0%	-
ARA	8	16.0%	-
Venous variations (n = 20)
Early bifurcation of RV	14	70.0%	-
ARV	6	30.0%	-
Topographical trajectory
Anterior	55	98.2%	-
Posterior	1	1.8%	-
Distance to UPJ
Direct Intersection (0 mm)	21	37.5%	0.380 (sex)
Distal Intersection (> 0 mm)	35	62.5%
Mean distal distance ± SD	16.2 ± 4.5 mm		0.712 (side)

^aStatistically significant difference.

RA: Renal artery; RV: Renal vein; ARA: Accessory renal artery; ARV: Accessory renal vein; UPJ: Ureteropelvic junction.

It is well established that CAKUT pose a great developmental risk on children carrying a significant hazard of hydronephrosis, chronic kidney disease and end-stage kidney disease. Therefore, widespread knowledge of the anatomical variations of the area in question is of paramount importance. As UPJO is one of the most common CAKUT numerous studies have assessed its prevalence. Barakat and Drougas[9] state a total prevalence of 0.12% in the general population, results that are in agreement with previous studies. Furthermore, many studies have shown the prevalence of crossing vessels as the etiology of UPJO especially in older children or even adults. Specifically, studies report a prevalence ranging from 12.0% to 60%-70% in different populations of patients with UPJO although the exact role in the etiology of UPJO has remained elusive[8,16,19-22].

Despite the extensive interest on the prevalence of crossing vessels, few studies have identified the type of vessel of interest. To be more precise, Braun et al[19] state that 56.25% of cases involving cross vessel has a crossing artery while the remaining 42.75% related to crossing veins. However, no comment was made regarding potential variations of these structures that may have influenced the anatomy of the area, leading to the obstruction of the UPJ. In contrast with those results, Stern et al[20] indicate that 100% of the cases with UPJO and cross vessel involved an artery while 50% of them had also a crossing vein.

Few studies have evaluated the prevalence of crossing vessels in patients with an apparently unremarkable UPJ. Specifically, Zeltser et al[23] by using endoluminal ultrasonography to characterize crossing vessels in patients with normal UPJ found a 19.2% prevalence of crossing vessels, similar to the 22.7% stated by Leavitt et al[24] and the 14.2% found in the present study. However, although UPJO was not yet found in the series of Zeltser et al[23], all patients underwent ureteroscopy for various indications, therefore, their urinary tracts were not completely normal. Contrary to these findings, Sampaio[25] have described the vascular anatomy of the UPJ using cadaveric kidneys and showed a prevalence of 65.1% of crossing vessels, a result considerably greater than those of other studies. Another critical aspect is the distance of the crossing vessel relative to the UPJ, as this proximity dictates the mechanical risk of obstruction. Historically, Sampaio[25] included vessels within 15 mm of the UPJ as clinically significant, while Zeltser et al[23] and Leavitt et al[24] applied a stricter threshold, including only vessels within 5-6 mm. In clinical practice, vessels crossing directly at the UPJ (0 mm) or within this proximal 10-15 mm zone are classically considered to pose the highest risk for extrinsic compression. Interestingly, in our unobstructed cohort, a substantial proportion (37.5%) of the identified vessels crossed directly at the UPJ (0 mm). This finding is vital, as it empirically demonstrates that even direct anatomical apposition at the most vulnerable stricture point does not universally result in UPJO. Conversely, for the distally crossing vessels in our cohort, the mean distance of 16.2 ± 4.5 mm places them just outside Sampaio[25] traditional high-risk zone. The distal location of these specific vessels likely dissipates potential compressive forces, contributing to the absence of pathological obstruction in these renal units.

Another aspect of interest is the location of the crossing vessel relative to the UPJ and the ureter itself. Specifically, in most cases of the past literature, the vessel passes anteriorly (90%) while in the remaining 10% of the cases it passes posteriorly[23-25]. These results are in compliance with the results of the present study where in 98.2% of the cases the vessels had an anterior course relative to the ureter and in only one case (1.8%) it had a posterior course.

In terms of side of occurrence, only Leavitt et al[24] state the prevalence of crossing vessels in comparison to the side of appearance. Specifically, in 60.1% of the cases the crossing vessels were found on the left side of the patient while the remaining 39.9% on the right. These results are in line to the ones from the present study where 55.4% of the cases were found on the left side and 44.6% of the cases on the right. However, in terms of laterality, no previous study was found that addresses the matter. In our study, as beforementioned, 30.2% of the cases involved a bilateral presence of crossing vessels while in the remaining 69.8% the presence was unilateral.

Furthermore, in studies concerning general population, as the present one, only Leavitt et al[24] state the vessel type in cases of crossing vessels. Particularly, 81.0% of their cases involved an artery while the remaining 19.0% involved a vein, results that slightly differ from those of the present study where 64.3% of cases had a crossing artery while 10.7% of the cases had a crossing vein. However, no mention was made about potential cases in which both artery and vein coexisted as crossing vessels, as in 25% of the cases in the present study, a fact that may explain the difference on the results. Moreover, no previous study made a comparison between sexes in terms of crossing vessels existence, while in our study 69.6% of the cases concerned male patients and the residual 30.4% concerned female patients. Lastly, no previous study addressed the potential variations of vasculature that may influence regional anatomy and lead to crossing vessels and UPJO. Given the common existence of arterial variation like accessory renal arteries, which are found in 21.1% of the general population[26] further research is needed to determine potential correlation. The vascular anatomy of the pelvi-ureteric junction is complex and varies among individuals, a fact that can impact the disease development and its surgical treatment via pyeloplasty and vessel transposition[27,28].

Despite variations in reported rates, these studies consistently indicate that crossing vessels are present in a substantial proportion of patients without UPJO, and that, crossing vessels frequently exist as incidental variations without concurrent UPJO. Therefore, accurate imaging of the anatomical aspect of the area of interest is of paramount importance. CT angiography is a frequently used imaging modality that provides excellent spatial resolution for detecting crossing vessels at the UPJ compared to operative findings[29-31]. Its advantages are various, extending from cost and anesthesia requirements to operator capacity and capability. For all these reasons CTA is widely considered a practical tool for morphological assessment, however, just like any other imaging modality, it cannot determine the functional significance of the crossing vessel. However, studies which included magnetic resonance urography imaging in order to detect potential crossing vessel existence had as well promising results[32].

Given the frequent presence and varied location of crossing vessels, preoperative imaging with CTA can make a great difference and reduce the risk of hemorrhage during surgeries on site. Furthermore, it could play a crucial part in patient counselling as it is known that a crossing vessel reduces the success rate of endopyelotomy[33-35]. A patient-centered approach is of paramount importance in patients with UPJO and extensive knowledge of the regional anatomy and potential existence of crossing vessels is important in order to achieve optimal clinical results and patient satisfaction.

Certain limitations of the present study must be acknowledged. First, the single-center design and the use of a hospital-based cohort undergoing CT for non-urological clinical indications, rather than asymptomatic healthy volunteers, introduce an inherent selection bias that may limit the broad generalizability of the findings. Furthermore, because this study utilized a convenience sample, the overall sample size restricts our statistical power for detecting smaller effect sizes. Specifically, subgroup comparisons involving the isolated venous crossing cohort (n = 6) are severely underpowered and must be interpreted strictly as exploratory. Consequently, the non-significant findings should be interpreted with caution, as they may represent type II errors rather than a true absence of anatomical differences. Second, the study cohort comprised an older adult demographic, which restricts the direct translation of these baseline anatomical findings to pediatric patients, in whom UPJO is most frequently diagnosed. Finally, while contrast-enhanced CT is highly accurate for precise morphological and spatial mapping, it lacks functional or urodynamic capabilities. As a static imaging modality, it cannot determine the physiological impact of a vessel that might be non-obstructive under baseline conditions but could cause intermittent or transient obstruction during periods of high fluid intake or positional shifts. Furthermore, while CT is widely utilized, comparative studies indicate it may occasionally miss small crossing vessels. Mitterberger et al[36] demonstrated that contrast-enhanced color Doppler imaging and magnetic resonance imaging correctly detected all crossing vessels, whereas CT missed some posterior crossing veins, yielding a diagnostic accuracy of 93%. Therefore, the physiological impact or potential subclinical flow impairment caused by these incidental crossing vessels cannot be determined from static imaging alone. Future prospective, multicenter studies incorporating functional imaging modalities are warranted to further elucidate the clinical significance of these anatomical variations.

CONCLUSION

This study demonstrates that aberrant renal vessels crossing the ureter and UPJ are a relatively common anatomical variant in the non-obstructed adult population, with a prevalence of 14.2% and a significant male predominance. These intersections almost exclusively follow an anterior trajectory and are primarily driven by arterial anomalies - specifically early bifurcations - although simultaneous crossings occur in nearly a quarter of cases. The substantial baseline prevalence of these vessels in normal urinary tracts reinforces that they are a common anatomical variant that does not obligate the development of UPJO. In clinical practice, contrast-enhanced CT provides detailed spatial characterization of these vessels, which can serve as a useful tool for anatomical mapping.