Our present study identified, on CT scan, several patterns according to the disposition of the vascular structures in the renal hilum. The analyses revealed which patterns correlate to a more complex anatomy and longer THC.

To the best of our knowledge, no data are available on intraoperative video documentation review for RHC assessment during RAPN. Previous studies have assessed the importance of SVR. For example, De Backer et al. [5] considered 100 RAPNs and showed that surgical phase duration can be correlated with certain clinical outcomes. Kim et al. [6] tested SVR to assess the Mayo adhesive probability score and perirenal fat dissection time. Additionally, our group used SVR to evaluate WIT during RAPN and its impact on surgical margins and complication rate, in a previous study [7].

We found THC to be a relatively short portion (15%) of the TOT. For the present study, TOT depicts the total console surgery time as the time used to achieve pneumoperitoneum or docking the robot were not taken into account. De Backer et al. [5] also found a short time to hilum control with a median of 16 (±11.5) minutes, as compared to 22 min in our study. This could be due to including patients with redo RAPN and complex vascular anatomy in our cohort. Of the 100 patients in the cohort of De Backer et al., 77 procedures were performed offclamp that requires less dissection of all the hilar structures.

Previous renal surgery was registered in four of the patients who underwent a redo RAPN for tumour resection elsewhere in the kidney than previous resection bed. It correlated to longer THC as more fibrosis around the vascular structures in the hilum needed to be dissected in order to achieve RHC. No statistical correlation was found between longer THC and previous inflammation like pyelonephritis or pancreatitis, previous radiotherapy, or previous immunotherapy. This finding could be biased by the low number of patients (only one or two) who did not have such previous conditions. Though previous abdominal surgery poses surgical challenges for PN [8], several studies identified no impact on the outcomes of RAPN [9, 10]. Redo RAPN is considered an effective approach [11], and evidence indicates good feasibility and safety, though it is a challenging procedure [12]. One challenge is RHC and it makes sense that more time is used to dissect the vascular structures, as more fibrosis around the hilar structures is present from previous RHC. Though RAPN remains the preferred option for treating small renal masses, percutaneous cryoablation is a valid alternative, particularly for challenging patients, as shown by Iossa et al. [13]. Two out of four patients who underwent redo RAPN were performed retroperitoneally. This could have biased our results together with a disproportioned percent of only 18% of the patients performed a retroperitoneally approach. This could also explain why we registered longer THC in the retroperitoneal group.

The anatomy of the renal vascular system and its application to PN was initially presented by Graves in 1954 with a special focus on segmental branching of the renal artery and its role in achieving selective ischemia [14]. Later, Trivedi et al. [15] identified six vascular branching patterns of segmental renal artery in an anatomical study and stated that knowledge of these patterns is essential to effective surgical planning in cases of PN and preventing complications. Clamping the segmental renal artery instead of the main renal artery during PN is a promising technique to decrease WIT, and understanding vascular branching patterns is essential for an appropriate hilar approach. However, selective or superselective clamping do not provide better renal function preservation than renal artery conventional clamping, as shown in systematic reviews [16] and randomized controlled trials [17]. This places doubt on the benefit of these techniques which additionally has higher risk of bleeding. To the best of our knowledge, no data are available on renal vascular anatomy with focus on conventional clamping, and our study identified vascular patterns that help for a more detailed understanding of renal vascular anatomy including cases of renal hilar masses, where RAPN is a promising technique [18].

Multiple authors have described the arrangement of renal hilar structures, through anatomical studies, identifying several patterns [4, 19] which included the renal pelvis into their classifications. We used vascular structures in our classification as only the vein and artery are dissected during the RHC for PN. We identified eight patterns, four for each side, including both the normal structure and variations. A complete understanding of underlying normal and aberrant renal anatomy, coupled with patient- and tumour-specific anatomical characteristics, represents the foundation for proper preoperative surgical planning for PN [20]. We determined that having more than one renal artery requires longer THC as more time is expected to be used to dissect all the arteries to be clamped. In our classification, we did not include small accessory arteries that did not need to be clamped during WIT. An early bifurcation of the renal artery on both sides but especially on the right side, as the artery passes behind the IVC made the dissection of the main artery more difficult, and longer THC was observed.

We did not register a statistical significance between the three surgeons. Larcher et al. [21] indicated that RAPN outcomes might be affected by surgeon experience by shortening WIT and lowering the complication rate. The inhomogeneous surgical experience among the surgical team members and the small sample size caused us to evaluate the surgeons as an independent variable, instead of surgeon’s expertise, and that may have biased our results. Intraoperative bleeding rate was low during RHC and correlated with longer THC as more time was needed to control the bleeding before controlling the renal hilum.

Some patient characteristics and comorbidities were not recorded due to the retrospective design of this study. The study was not blinded because SVR requires a trained kidney surgeon to identify the specific steps of the procedure and no interobserver validation of pattern assignment was attempted. The vascular patterns identified in our study are valuable for cases when clamping of the main artery is chosen; for selective clamping, different intrarenal anatomical patterns should be considered. Despite these limitations, our results can be used to optimise preoperative surgical planning for RAPN and provide a basis for developing a hilum complexity score in the future.