Laterality in the Etiology of Ureteropelvic Junction Obstruction Treated With Robot‐Assisted Pyeloplasty

Ureteropelvic junction obstruction (UPJO) is the most common congenital anomaly of the ureter, and dismembered pyeloplasty represents the gold standard treatment [1]. UPJO is caused by various mechanisms, among which a crossing vessel is one of the typical etiologies [1-3]. Now that robot-assisted pyeloplasty (RAP) has become a standard of care for UPJO, crossing vessels should be more accurately identified during the surgical procedure [1-3]. Furthermore, given the anatomical differences between the left and right perirenal vessels, laterality may exist in the etiology of UPJO. However, studies assessing etiologies of UPJO with a focus on laterality are lacking. We retrospectively reviewed 30 patients with UPJO who received RAP at our institution between 2020 and 2025. All patients underwent Anderson-Hynes dismembered pyeloplasty [4] using the da Vinci Surgical System (Intuitive Surgical, Sunnyvale, CA). One patient received secondary RAP due to an anastomotic stricture after primary RAP (i.e., a total of 31 RAP procedures were performed). Upon reviewing medical charts thoroughly, taking note of operation records and preoperative radiological reports, we assessed the etiologies of UPJO with their laterality in each case comprehensively. The cohort consisted of 18 males (60%) and 12 females (40%), with a median age of 53 years (range, 17–83). Of the 30 patients, 19 (63%) had right-sided involvement, while 11 (37%) had left-sided involvement. Median (range) operative time, console time, and estimated blood loss were 218 (133–327) minutes, 163 (80–290) minutes, and 3 (0–220) mL, respectively. Four patients (13%) experienced Clavien-Dindo grade ≥ 3 perioperative complications: two required ureteral stent repositioning under anesthesia due to proximal migration, one underwent debridement by the plastic surgery team for wound dehiscence and necrosis, and one required secondary RAP for an anastomotic stricture after the initial surgery, as stated above. The last case failed to achieve the stent-free condition due to severe adhesion and tension of the anastomotic site, while the others had an uneventful postoperative course. Figure 1A summarizes the etiologies of UPJO in the 30 patients treated with RAP: 14 (47%) were caused by crossing vessels (i.e., “vascular” UPJO), whereas the remaining 16 were caused by “non-vascular” reasons. Notably, right-sided cases (n = 11) were more frequent than left-sided cases (n = 3) in vascular UPJO, although there was no significant difference due to the small sample size (p = 0.11, χ2 test). In contrast, the number of patients was equal on the left and right sides in non-vascular UPJO. Figure 1B illustrates crossing vessels in 14 patients with vascular UPJO. The majority of cases (n = 8) were caused by the inferior polar branch of the right renal artery and/or vein (both artery and vein were involved in four cases), followed by the right gonadal vein (n = 3), the left gonadal vein (n = 2), and the inferior polar branch of the left renal artery (n = 1). In all cases, the crossing vessel was located anterior to the obstruction site. The renal pelvis and ureter were re-anastomosed on its ventral side in 12 of 14 cases, whereas the crossing vessel was sacrificed in the remaining two. Previous studies reporting outcomes of RAP for UPJO have generally assessed the prevalence of crossing vessels; however, none has specifically focused on their laterality [1-3]. To our knowledge, this study is the first to investigate the detailed etiologies of UPJO with an emphasis on laterality in patients treated with RAP. Right-sided cases were more frequent than left-sided cases in vascular UPJO, whereas there was no difference between the left and right sides in non-vascular UPJO. These results highlight the potential laterality in vascular UPJO. Anatomically, the right side is farther from the aorta, which may result in more vascular variations, such as the presence of an inferior polar branch of the right renal artery. This, in turn, makes the perirenal vessels more likely to cross the ureter, ultimately leading to vascular UPJO. For reference, the aforementioned case who underwent secondary RAP had a non-vascular etiology. The patient previously developed bilateral pyelonephritis with septic shock, resulting in a nonfunctional left kidney, and underwent RAP for right UPJO, which revealed severe adhesion of the right ureter to the renal pelvic wall. The patient developed anuria due to an anastomotic stricture after initial surgery, and eventually decided to receive redo anastomosis. Although secondary RAP is generally challenging [5], this case involved a patient with extremely poor baseline conditions. Lastly, limitations of the present study include its retrospective design and small sample size. Nevertheless, recognizing the potential laterality in the etiology of UPJO can help determine intraoperative strategy during RAP. Surgeons should be mindful of the possibility that a crossing vessel undetected on preoperative imaging may be identified intraoperatively, especially in right-sided cases. Further studies are warranted to confirm our results. Satoru Taguchi: conceptualization, data curation, formal analysis, writing – original draft, project administration, methodology. Yoshiyuki Akiyama: data curation, writing – review and editing. Masaki Nakamura: data curation, writing – review and editing. Yusuke Sato: data curation, writing – review and editing. Yuta Yamada: data curation, writing – review and editing. Haruki Kume: supervision, writing – review and editing. The authors have nothing to report. The authors have nothing to report. This study was approved by the Institutional Review Board of the Graduate School of Medicine and Faculty of Medicine, The University of Tokyo (approval number: 3124). Given the retrospective nature of the study, the requirement for written informed consent was waived. Yoshiyuki Akiyama, Yusuke Sato, and Haruki Kume are Editorial Board members of International Journal of Urology and co-authors of this article. To minimize bias, they were excluded from all editorial decision-making related to the acceptance of this article for publication. The other authors declare no conflicts of interest.