With the development of surgical expertise and minimally invasive techniques, as well as general organ scarcity, LDKT with MRA has become increasingly common in recent years [14]. The literature describes that MRA kidney transplantation may be associated with higher complication rates and DGF [7]. In this context, the effects of ligating accessory vessels in MRA grafts compared with anastomosis to the recipient's blood system are the subject of surgical concern. It is discussed that inadequate ligation of accessory arteries may lead to severe postoperative complications such as acute ureteral necrosis or renal infarction [15, 16]. On the other hand, prolonged operative times for anastomosing accessory branches and increased complexity of the operation may affect the outcome of short- and long-term postoperative graft function.

In the present study, we retrospectively investigated the impact of anastomosing versus not anastomosing accessory vessels in MRA-grafts on the postoperative outcome. In our cohort, significant differences between the two groups were seen in the operative time for the anastomosis, time of surgery and WIT, but not in creatinine levels up to 1 year after transplantation, DGF or primary transplant dysfunction and transplant rejection. Interestingly, the operative time was longer than the operative time for the anastomosis alone, suggesting that the complexity of the procedure extends beyond the vascular anastomosis in the presence of MRA. The prolonged operative time may be attributed to several factors, including deviations from standard surgical procedures, the challenge of maintaining precise graft bed positioning, and the need to avoid kink stenosis in the anastomosed arteries under a vigilant renal perfusion monitoring. In this context, detailed anatomical workup prior to LDKT with complex vascular anatomy, newer imaging techniques, such as three-dimensional visualization using virtual reality, could contribute to more detailed planning of the surgery and thus may help to shorten the operative time [17]. Thus, in contrast to the literature described correlation, no negative influence of prolonged operation times on graft function when ARAs were anastomosed was detected [18]. In a study in which the cohort of our center was analyzed from 2011 to 2016, Zeuschner et al. were able to determine a DGF rate of 6.3% [19]. In comparison, the present study showed a slightly higher DGF rate of 10% in the presence of MRA. Nevertheless, the incidence of DGF is still at a low level, consistent with existing literature and less than the comparison group of Zeuschner et al. with 11.5% (robot-assisted versus laparoscopic donor nephrectomy), so that a mere increase in DGF due to MRA is not proven [7].

Proposed by Iwami et al. a cut-off diameter of 2 mm seems worth attempting regarding the success rate and graft function, while cutting of a 2-mm ARA leads to parenchymal loss of less than 8% [20]. Although the mean diameters of ARAs in both groups differed from 1.88 mm to 3.05 mm, our study did not identify a clear cut-off value for performed anastomosis or ligation in our center. Intraoperative described perfusion deficits were seen more frequently in group 1, but in most cases, they could no longer be detected in standardized follow-up Doppler ultrasound during the early postoperative phase (2 weeks). Interestingly, postoperative Doppler sonography showed no significant higher rate of segmental perfusion deficit after ligation. Furthermore, regeneration of the perfusion deficit was seen in group 1 in all cases observed (Table 2, Fig. 1). An underlying mechanism for the complete regeneration may be the small average diameter of the ligated accessory branch, thus supplying a small graft segment that can be compensated by intraparenchymal vessels and a possible formation of collateral vessels could play a role. Ligation of larger accessory arteries would likely lead to necrosis without regeneration. Therefore, vascular events like arterial stenosis in the larger anastomosed ARAs with a wider graft supply area may lead to a lasting segmental infarction in some cases (in group 2). The exact mechanisms remain unclear due to the retrospective nature of the study.

Operative revision in the early postoperative period (Clavien–Dindo IIIb) appeared to be more frequent when ARAs were ligated (Table 2), but as mentioned above, the reasons for reoperation were not vascular, ureteral or bleeding complications, but mainly fascia or wound dehiscence and therefore association with the presence of MRA is unclear. Furthermore, transplant nephrectomies were performed more frequently in group 1, but again, no surgical or other reason related to the presence of MRA was seen.

Moreover, our results were concordant with literature describing the localization of the ARA as a further important parameter, since ligation of an inferior polar branch may reduce nutrient supply to the ureter and therefore cause ureteral necrosis [15]. Although most inferior polar vessels were anastomosed and equal numbers of ureteral necrosis were observed in both groups, the one manifest ureteral necrosis in group 1 was seen in the case of a ligated lower pole artery and also in group 2, the ARA was located at the lower pole. Furthermore, Kok et al. could show a significantly higher rate of urological complications after ligation of inferior pole arteries [21]. In the present study, endourologic procedures were also found to be performed more frequently in group 1, but only the ligation of superior pole arteries was done in the underlying cases. Because upper pole vessels do not usually cause ureteral affection, it remains unclear whether their ligation is the definitive reason for the higher rate of urologic complications in the present study [7].

Overall, the results of our study are consistent with the results of the existing literature identifying MRA grafts as those with a good long-term outcome with modestly increased complication rates and thus recommends them for transplant consideration [6, 8, 9, 14, 22]. When it comes to the question whether ARA ligation causes a higher complication rate, no statistical significance was found, but the rate of reoperations was slightly higher in the group with ligated vessels due to unspecific reasons.

Our study had several limitations. It is a retrospective observational study, which was performed at a single center and therefore its generalizability is limited. Furthermore, the number of patients was small, but comparable to literature. Although the demographic characteristics of the two groups were similar, differences in the localization and diameter of the ligated artery were observed. Therefore, the comparability between the two groups in this real-world data analysis is somewhat constrained. To address this topic in the future, these results should be confirmed in a prospective, multicenter study.