Prone versus lateral retroperitoneoscopic partial nephrectomy for posterior tumors in adults: technique and clinical outcomes

Introduction

Surgical resection is the standard treatment for patients with localized renal tumors (1). As a promising minimally invasive method, laparoscopic partial nephrectomy has been proved to be oncologically equivalent to radical nephrectomy in most cases (2,3). Although retroperitoneoscopic is more difficult than transperitoneal, it has the advantage of not opening the abdominal cavity (4,5). Lateral retroperitoneoscopic partial nephrectomy (RPN) is the traditional approach and has been widely applied in clinical practice in both adults and children. Over the past decades, a new approach with patients in a prone position has been reported in children and brought into focus (6,7). For posterior renal tumors, the prone position seems more conducive to approaching and resecting mass if feasible. However, very limited information is known about this position in adults, let alone comparing with traditional lateral position.

In this study, we aimed to evaluate the feasibility of prone RPN for posterior tumors and associated clinical outcomes by performing lateral and prone RPN in adults. We present this article in accordance with the SUPER reporting checklist (available at https://tau.amegroups.com/article/view/10.21037/tau-2024-735/rc).

Methods

We retrospectively reviewed patients who underwent retroperitoneoscopic partial nephrectomy (RPN) in our department from January 2018 to March 2023 and screened them for eligibility. Preoperative contrast-enhanced computed tomography was utilized to evaluate the renal lesion size and invasive depth. Inclusion criteria were a single, posterior, organ-confined mass of ≤4 cm with endophytic, mesophytic, or exophytic characteristics (8). Patients with tumor size slightly >4 cm were included if resection was considered feasible technically. All patients had a normal contralateral kidney. Based on operative position, the included patients were divided into two groups: lateral RPN and prone RPN. All operations were performed by two experienced surgeons (J.X. and Q.L.) who had more than five years of surgical experience. The demographic information and intraoperative details (operation time, warm ischemia time, blood loss) were collected. Split renal function was evaluated in all included patients using glomerular filtration rate (GFR) before and 3 months after the operation. The follow-up duration was measured from the time of tumor excision. This study was approved by the institutional review board of Suzhou Municipal Hospital (No. KL901440) and conducted in accordance with the Declaration of Helsinki (as revised in 2013). Informed participation consent was obtained from all subjects included in our study.

Prior to anesthetic induction, all patients received preoxygenation with a face mask at an oxygen flow rate of 6 L/min for 5 minutes. Anesthetic induction was initiated with intravenous administrations of sufentanil 0.3–0.5 µg/kg, propofol 1–2 mg/kg, and cisatracurium 0.2 mg/kg, followed by tracheal intubation after 3 minutes. Upon successful intubation, the patients were connected to an anesthesia machine for mechanical ventilation with the following respiratory parameters: tidal volume (VT) of 6–8 mL/kg, respiratory rate (RR) of 10-18 breaths/minute, inspiratory-to-expiratory ratio (I:E) of 1:2, maintaining end-tidal carbon dioxide (PETCO₂) at 35–45 mmHg and oxygen saturation (SpO₂) above 95%. For anesthesia maintenance, a continuous intravenous infusion of propofol at a rate of 2-4 mg/kg, remifentanil at a rate of 0.1–0.3 µg/kg, and cisatracurium at a rate of 0.1–0.2 mg/kg was administered. Additionally, sevoflurane was inhaled at a concentration of 1–1.5%. Arterial blood gas samples were collected before the operation and 30 min after positioning, and were immediately analyzed with a radiometer blood gas analyzer (ABL 800 FLEX, Denmark).

Lateral RPN, as a standard operative position, has been described in detail in previous study (9). As for prone RPN, patients were placed in the prone position with hips at 90 degrees to make lower limbs droop after anesthesia. Two position mattresses were placed under the hips and chest to keep the abdomen in the air (Figure 1A). A 20 mm incision was made below the 12^th rib at the posterior axillary line, and the retroperitoneum was entered by blunt dissection. The vascular forceps were inserted directly into Gerota’s fascia. A 10 mm trocar was positioned 5 cm outside the initial incision, and a 5 mm trocar was positioned 5 cm inside the initial incision along the direction of the erector spinae muscle. Finally, a 10 mm trocar was positioned in the initial incision and used for camera placement. One more trocar, served as an auxiliary trocar, could be placed 5 cm below and lateral to the initial incision for special situation (Figure 1B). After establishing pneumoperitoneum, we expanded Gerota’s fascia incision and cleaned the fat around the lateral psoas muscle. The kidney was mobilized to expose the tumor as needed. The renal artery was isolated and clamped with laparoscopic bulldog clamps. After complete cold excision of the mass, the resection site was sutured carefully and the bulldog clamps on the artery was released (Figure 1C). The drainage was placed around the kidney and removed 3–5 d after the operation. During endoscopic surgery, retroperitoneal pressure for both surgical procedures was maintained at 18–20 mmHg using a carbon dioxide (CO₂) insufflator.

Figure 1 Procedures and information of prone RPN for posterior tumors. (A) Operative position; (B) diagram for trocar position (red point represents primary position, green point represents auxiliary position); (C) resection of right renal hilar tumor with prone RPN. RPN, retroperitoneoscopic partial nephrectomy.

As we know, a variable that emerged as relevant to operation position was tumor location. We found that the more dorsal the tumor was, the more appropriate prone position seemed to be. To quantitate the degree to which the tumor was dorsal, we adopted a dorsal deviation score (DDS), which scored the position of the mass relative to the tangent line. The tangent line referred to the renal pelvis tangent vertical to the maximum long diameter on a cross section. Tumors that were entirely outside the tangent line were assigned 1 point (Figure 2A,2B). The mass that crossed the tangent line received 2 points (Figure 2C,2D). If the mass had greater than 50% of the diameter across the tangent line or was entirely inside the tangent line, a score of 3 points was given (Figure 2E,2F). Renal hilar tumors scored 3 points as well. Given the surgical complexity of renal hilar tumors, they were analyzed as a separate category.

Figure 2 DDS. The dotted line divided kidney into anterior and posterior components. The solid line referred to the renal pelvis tangent vertical to dotted line on a cross line. (A,B) Tumors that entirely outside the solid line were assigned 1 point. (C,D) Tumors that crossed the solid line received 2 points. (E,F) If the mass had greater than 50% of the diameter across the solid line or was entirely inside the solid line, a score of 3 points was given. DDS, dorsal deviation score.

Statistical analysis

All data analysis was performed using IBM SPSS software (version 22.0). Data were expressed as mean ± standard deviation (SD) for continuous variables and as proportion for categorical variables. The independent t-test or Mann-Whitney U test was utilized for continuous variables. Categorical variables were assessed using Chi-square or Fisher tests. P value <0.05 was considered statistically significant.

Results

Baseline demographic information and operative details are shown in Table 1. A total of 101 patients who met inclusion criteria were included in this study. No significant differences in gender (P=0.85), age (P=0.22), and BMI (P=0.67) were observed between lateral and prone RPN group. Tumor details between two groups were comparable as well, including size (P=0.69), classification (P=0.75), characteristics (P=0.80), R.E.N.A.L score (P=0.76) and DDS (P=0.36). There was increased operation time, warm ischemia time, and blood loss in lateral RPN compared with prone RPN (P<0.001, P=0.003, and P=0.03, respectively). No obvious difference existed in preoperative and 3-mo postoperative GFR levels between two groups. In arterial blood gas analysis, no significant differences in PaCO₂, PaO₂, and pH were observed between two groups before the operation and 30 min after positioning (Table 2).

In addition, we separately analyzed intraoperative details between two groups based on location score (Table 3). For slightly posterior tumors (DDS =1), we found no difference in operation time (P=0.14), warm ischemia time (P=0.60), and blood loss (P=0.23) between two groups. However, compared with prone RPN, longer operation time (P=0.03) and warm ischemia time (P=0.02) were spent in lateral RPN in moderate or severe posterior (DDS =2 or 3) non-hilar tumors. As for renal function, the differences in preoperative and 3-mo postoperative GFR levels were insignificant.

Due to the proximity to hilar vessels and the difficult to approach, more surgical technique was needed for hilar tumors. Of the 14 cases with hilar tumors, 8 patients received lateral RPN, while the remaining 6 patients had prone RPN (Table 4). The baseline characteristics were comparable between two groups. We found that prone RPN had shorter operation time (P<0.001) and warm ischemia time (P=0.03) compared with lateral RPN, as well as less blood loss (P=0.043). In addition, there was no significant difference in both preoperative and 3-mo postoperative renal function between two groups.

Although not statistically significant, the incidence of intraoperative complications in lateral RPN group (11.9%) was higher than that in prone RPN (2.4%) (Table 5). Four vascular injuries (6.8%) occurred in lateral RPN, whereas one vascular injury (2.4%) occurred in prone RPN. Two cases (3.4%) in lateral RPN required blood transfusion and one of them was converted to radical nephrectomy, while none occurred in prone RPN. No bowl injury occurred in both groups. Regarding postoperative complications, 3 cases (5.1%) in lateral RPN and 1 case (2.4%) in prone RPN had hemorrhage, and no radiologic intervention or re-operation happened. Three cases of hematuria (2 in lateral RPN and 1 in prone RPN) recovered within one week without further intervention. No urine leak was observed in two groups. The mean length of hospitalization was 7 d.

Discussion

As a well-established procedure, laparoscopic partial nephrectomy can completely remove the mass and achieve effective hemostasis with a low complication rate (10). For experienced laparoscopic urologists, it has become a viable alternative to open surgical procedure. Pellegrino et al. (11) introduced a novel supine anterior retroperitoneal approach (SARA), accessing the retroperitoneal space anteriorly to facilitate ureteral dissection during nephroureterectomy. Although this method can also be performed without entering the peritoneum, we preferred the retroperitoneal approach in our study. Since the adrenal glands, kidneys, and ureters are located in the retroperitoneum, the retroperitoneal approach is more suitable for laparoscopy urological anatomy. It can reduce the disturbance of abdominal organs and the rate of abdominal organ injury or abdominal adhesion (12). In addition, the renal vein is located anterior to the renal artery anatomically, which makes it difficult to isolate the renal artery in transperitoneal approach. This is also the reason why we favor the prone operative position. Initially, our team performed laparoscopic adrenalectomy in the prone position, and found it easy to get direct access to the kidney and renal hilum surprisingly. In spite of limited workspace, it allows clear vision and direct access to renal artery, which is beneficial to the renal artery occlusion in partial nephrectomy, especially complex hilar tumors. Till now, the implementation and relevant literature of this procedure are mainly focused on children (6,13), but rarely on adults. Systematic evaluation of the feasibility for prone RPN in adults is lacking, let alone the comparison with traditional lateral position.

In terms of trocar application, 3 trocars were required for prone RPN compared with 4 trocars in the lateral position. The number of surgeons was reduced to from 3 to 2 in prone RPN as well. For posterior renal tumors, an assistant was needed in the lateral RPN to block the kidney to the ventral side for better exposure of the surgical field, which required the tacit cooperation between lead surgeon and assistants. In the prone position, however, the dorsal side of kidney achieved satisfactory exposure under natural conditions. For difficult and complex operations, the operating space could be expanded by increasing the pneumoperitoneum pressure or by adding an auxiliary trocar. Another advantage of the prone position is the natural traction on the renal vessels from gravity, which helped to simplify the procedure. In our study, the operation time in prone RPN group was significantly shorter than that in lateral RPN. Escolino et al. (6) reported that prone technique yielded faster results than lateral approach in children, which was consistent with our results. Although warm ischemia time was significantly shorter in prone RPN, there was no significant difference in early postoperative renal function. Some studies reported that prolonged warm ischemia time did not lead to further renal function decline when warm ischemia time exceeded 20 min (14,15). Although the association between warm ischemic time and renal impairment was reported before, it was actually due to the association between warm ischemic time and the volume of the excised renal parenchyma and the complexity of the tumor (16-18).

Compared with lateral position, the prone positioning of the patient is more demanding. It is crucial to place the patient correctly on the operative table to accomplish the procedure safely. We placed two position mattresses under the hips and chest to keep the abdomen in the air. On the one hand, a hollow abdomen maximized the working space in the retroperitoneum. Even if the peritoneum was ruptured accidentally during surgery, it had no effect on the space. On the other hand, the abdominal organs were in a state of natural sagging under the influence of gravity. Thus, they would not be affected by respiratory movement. Theoretically, the prone positioning would limit the free movement of the chest and abdomen, increase the cardiopulmonary burden, and then increase the risk of anesthesia. But we found no significant differences in PaCO₂, PaO₂, and pH between the two groups 30 min after positioning. Mezidi et al. (19) found that the prone position had better lung function with increased functional residual air volume and lung compliance in comparison with the supine position. Giebler et al. (20) reported that although high pneumoperitoneum pressure in the retroperitoneum could cause hemodynamic changes such as increased central venous pressure and increased cardiac output, no significant adverse reactions were noticed. Above evidence supported that the prone position had no significant effect on the patient’s cardiovascular function and did not increase the risk during anesthesia. Moreover, the prone position could avoid intraoperative repositioning when performing bilateral kidney surgery. A crucial factor in determining operation position is tumor location, and for posterior renal tumors, the prone position provides a convenient and close approach. In practice, we found that the more dorsal the tumor was, the more appropriate prone position seemed to be. To better describe this phenomenon, an objective index was needed to assess the degree of dorsal deviation. At present, there were several renal tumor scoring systems, such as RENAL (21), PAUDA (22), DAP (23), etc. By learning and using the parameters of these systems for reference, we established a simple scoring method called location score. Based on this score, we believed that in moderate to severe dorsal tumors, the operative efficiency in prone position was higher than that in lateral position.

The separation and occlusion of renal vessels are the key and difficult points in RPN, and vascular injuries were common intraoperative complications (24). In the lateral RPN group of our study, four patients had vascular injuries, of which one patient was converted to radical nephrectomy and failed to save the kidney. Among the patients who underwent prone RPN, only one patient had vascular injury and the vascular injury was successfully repaired. The significant reduction in intraoperative complications is largely related to the better exposition of the kidney vasculature, which facilitates hilar dissection and vascular control (25). Even if vascular injury occurs, it could be reliably repaired to reduce the rate of kidney loss. Although prone RPN has obvious advantages in the treatment of posterior tumors, the following points should be noted during the process: firstly, prone RPN is a challenging procedure that requires surgeons to have extensive experience in laparoscopic surgery; secondly, unfamiliar anatomical view in the prone approach means a relatively long learning cycle; thirdly, conversion to an open procedure may be challenging. It has been reported that the open procedure could be converted by simply expanding incision on the existing trocar in children (7). Additionally, it is noteworthy that prone position surgery may pose elevated risks of complications in elderly patients and those with cardiovascular compromise, obesity, spinal deformities, or preexisting laryngeal and ocular pathologies (26-29). These high-risk cohorts warrant meticulous preoperative risk evaluation, comprehensive diagnostic workup, and enhanced intraoperative monitoring. In our study protocol, we mandated postoperative hospitalization for approximately 7 days to ensure optimal wound healing and surgical recovery.

There are some limitations in this study. Firstly, it was a single-center, retrospective study with relatively small sample size, and further practice is still needed in adults. Another limitation was that laparoscopic surgical techniques were utilized instead of robotic-assisted ones. Single-site robotic surgery may be considered for this surgery due to its minimally invasive nature and enhanced maneuverability (30). Despite these limitations, our study still provided valuable insights into the efficacy and safety of prone RPN for posterior renal tumors.

Conclusions

Prone RPN is a viable option for posterior renal tumors in adults, and has unique advantages in treating moderate to severe posterior tumors, especially hilar tumors. In addition, it has less intraoperative complications compared with traditional lateral position.

Acknowledgments

None.

Footnote

Reporting Checklist: The authors have completed the SUPER reporting checklist. Available at https://tau.amegroups.com/article/view/10.21037/tau-2024-735/rc

Data Sharing Statement: Available at https://tau.amegroups.com/article/view/10.21037/tau-2024-735/dss

Peer Review File: Available at https://tau.amegroups.com/article/view/10.21037/tau-2024-735/prf

Funding: This work was supported by Suzhou Clinical Medical Center for Urology (grant No. Szlcyxzx202106), the Natural Science Foundation of Jiangsu Province (No. BK20240376), Youth Talent Development Program of Gusu College of Nanjing Medical University (grant No. GSKY20240515), and the Doctoral Research Start-up Fund Project of Suzhou Municipal Hospital (grant No. Szslyyrc2023025).

Conflicts of Interest: All authors have completed the ICMJE uniform disclosure form (available at https://tau.amegroups.com/article/view/10.21037/tau-2024-735/coif). The authors have no conflicts of interest to declare.

Ethical Statement: The authors are accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved. This study was approved by the institutional review board of Suzhou Municipal Hospital (No. KL901440) and conducted in accordance with the Declaration of Helsinki (as revised in 2013). Informed participation consent was obtained from all subjects included in our study.

Open Access Statement: This is an Open Access article distributed in accordance with the Creative Commons Attribution-NonCommercial-NoDerivs 4.0 International License (CC BY-NC-ND 4.0), which permits the non-commercial replication and distribution of the article with the strict proviso that no changes or edits are made and the original work is properly cited (including links to both the formal publication through the relevant DOI and the license). See: https://creativecommons.org/licenses/by-nc-nd/4.0/.

References

1. Ljungberg B, Albiges L, Abu-Ghanem Y, et al. European Association of Urology Guidelines on Renal Cell Carcinoma: The 2022 Update. Eur Urol 2022;82:399-410. [Crossref] [PubMed]
2. Uzzo RG, Novick AC. Nephron sparing surgery for renal tumors: indications, techniques and outcomes. J Urol 2001;166:6-18. [Crossref] [PubMed]
3. Piramide F, Kowalewski KF, Cacciamani G, et al. Three-dimensional Model-assisted Minimally Invasive Partial Nephrectomy: A Systematic Review with Meta-analysis of Comparative Studies. Eur Urol Oncol 2022;5:640-50. [Crossref] [PubMed]
4. Killock D. Surgery: retroperitoneoscopic partial nephrectomy: practice is key. Nat Rev Urol 2014;11:365. [Crossref] [PubMed]
5. Wu X, Zhou J, Chen W, et al. Retroperitoneoscopic Clampless, Sutureless Hybrid Therapy in the Management of Renal Hilar Tumors. Ann Surg Oncol 2024;31:681-7. [Crossref] [PubMed]
6. Escolino M, Riccipetitoni G, Yamataka A, et al. Retroperitoneoscopic partial nephrectomy in children: a multicentric international comparative study between lateral versus prone approach. Surg Endosc 2019;33:832-9. [Crossref] [PubMed]
7. Urbanowicz W, Wieczorek M, Sulisławski J. Retroperitoneoscopic nephrectomy in the prone position in children (point of technique). Eur Urol 2002;42:516-9. [Crossref] [PubMed]
8. Finley DS, Lee DI, Eichel L, et al. Fibrin glue-oxidized cellulose sandwich for laparoscopic wedge resection of small renal lesions. J Urol 2005;173:1477-81. [Crossref] [PubMed]
9. Johnston WK 3rd, Montgomery JS, Wolf JS Jr. Retroperitoneoscopic radical and partial nephrectomy in the patient with cirrhosis. J Urol 2005;173:1094-7. [Crossref] [PubMed]
10. Calpin GG, Ryan FR, McHugh FT, et al. Comparing the outcomes of open, laparoscopic and robot-assisted partial nephrectomy: a network meta-analysis. BJU Int 2023;132:353-64. [Crossref] [PubMed]
11. Pellegrino AA, Chen G, Morgantini L, et al. Simplifying Retroperitoneal Robotic Single-port Surgery: Novel Supine Anterior Retroperitoneal Access. Eur Urol 2023;84:223-8. [Crossref] [PubMed]
12. Hua M, Liu W, Wang C, et al. Trans-retro-peritoneal laparoscopic partial nephrectomy for posterior hilar tumor: technical feasibility and preliminary results. Transl Androl Urol 2023;12:1638-44. [Crossref] [PubMed]
13. Leclair MD, Vidal I, Suply E, et al. Retroperitoneal laparoscopic heminephrectomy in duplex kidney in infants and children: a 15-year experience. Eur Urol 2009;56:385-9. [Crossref] [PubMed]
14. Lee H, Song BD, Byun SS, et al. Impact of warm ischaemia time on postoperative renal function after partial nephrectomy for clinical T1 renal cell carcinoma: a propensity score-matched study. BJU Int 2018;121:46-52. [Crossref] [PubMed]
15. Ishiyama Y, Kondo T, Tachibana H, et al. Limited impact of warm ischemic threshold for partial nephrectomy in the robotic surgery era: A propensity score matching study. Int J Urol 2021;28:1219-25. [Crossref] [PubMed]
16. Lane BR, Russo P, Uzzo RG, et al. Comparison of cold and warm ischemia during partial nephrectomy in 660 solitary kidneys reveals predominant role of nonmodifiable factors in determining ultimate renal function. J Urol 2011;185:421-7. [Crossref] [PubMed]
17. Zabell JR, Wu J, Suk-Ouichai C, et al. Renal Ischemia and Functional Outcomes Following Partial Nephrectomy. Urol Clin North Am 2017;44:243-55. [Crossref] [PubMed]
18. Nahar B, Bhat A, Parekh DJ. Does Every Minute of Renal Ischemia Still Count in 2019? Unlocking the Chains of a Flawed Thought Process over Five Decades. Eur Urol Focus 2019;5:939-42. [Crossref] [PubMed]
19. Mezidi M, Guérin C. Effects of patient positioning on respiratory mechanics in mechanically ventilated ICU patients. Ann Transl Med 2018;6:384. [Crossref] [PubMed]
20. Giebler RM, Behrends M, Steffens T, et al. Intraperitoneal and retroperitoneal carbon dioxide insufflation evoke different effects on caval vein pressure gradients in humans: evidence for the starling resistor concept of abdominal venous return. Anesthesiology 2000;92:1568-80. [Crossref] [PubMed]
21. Kutikov A, Uzzo RG. The R.E.N.A.L. nephrometry score: a comprehensive standardized system for quantitating renal tumor size, location and depth. J Urol 2009;182:844-53. [Crossref] [PubMed]
22. Ficarra V, Novara G, Secco S, et al. Preoperative aspects and dimensions used for an anatomical (PADUA) classification of renal tumours in patients who are candidates for nephron-sparing surgery. Eur Urol 2009;56:786-93. [Crossref] [PubMed]
23. Simmons MN, Hillyer SP, Lee BH, et al. Diameter-axial-polar nephrometry: integration and optimization of R.E.N.A.L. and centrality index scoring systems. J Urol 2012;188:384-90. [Crossref] [PubMed]
24. Chaurasia A, Singh S, Homayounieh F, et al. Complications after Nephron-sparing Interventions for Renal Tumors: Imaging Findings and Management. Radiographics 2023;43:e220196. [Crossref] [PubMed]
25. Till H, Basharkhah A, Hock A. What's the best minimal invasive approach to pediatric nephrectomy and heminephrectomy: conventional laparoscopy (CL), single-site (LESS) or robotics (RAS)? Transl Pediatr 2016;5:240-4. [Crossref] [PubMed]
26. Gharib A, Nasiri-Formi E, Karimi M, et al. Frequency of Complications Related to Prone Position During General Anesthesia. Avicenna Journal of Care and Health in Operating Room 2024;2:27-31. [Crossref]
27. Chui J, Craen RA. An update on the prone position: Continuing Professional Development. Can J Anaesth 2016;63:737-67. [Crossref] [PubMed]
28. Ongaigui C, Fiorda-Diaz J, Dada O, et al. Intraoperative Fluid Management in Patients Undergoing Spine Surgery: A Narrative Review. Front Surg 2020;7:45. [Crossref] [PubMed]
29. Bafus BT, Chiravuri D, van der Velde ME, et al. Severe hypotension associated with the prone position in a child with scoliosis and pectus excavatum undergoing posterior spinal fusion. J Spinal Disord Tech 2008;21:451-4. [Crossref] [PubMed]
30. Seeliger B, Diana M, Ruurda JP, et al. Enabling single-site laparoscopy: the SPORT platform. Surg Endosc 2019;33:3696-703. [Crossref] [PubMed]