Abstract
Background/Aim: The robotic retroperitoneal approach for renal mass surgery was introduced in 2018 at the Department of Urology in the clinic of Leverkusen, Germany. Clinical criteria for the choice of the access site (trans- vs. retroperitoneal) are not clearly defined. The aim of this study was to explore the learning curve and the impact of the access site on clinical outcome, in order to elucidate which preoperative clinical criteria should be taken into account when choosing the renal approach site. Patients and Methods: This retrospective study included 107 patients who underwent robotic tumor surgery between June 2018 and March 2022 at the Department of Urology in the Clinic of Leverkusen, Germany. Data from 86 patients with transperitoneal robotic surgery of the kidney and 21 patients with retroperitoneal access were available for analysis. We evaluated the data of patients in a trans- and a retroperitoneal access group. The preoperative clinical data included anthropomorphic data, the Body Mass Index (BMI) as well as the Preoperative Aspects and Dimensions Used for Anatomical Classification of Renal Masses (PADUA) – score. Intraoperative and postoperative data such as blood loss, clamping time, renal function and the learning curve of the surgeons was used to evaluate the outcomes of the two groups. Results: Operation time in the retroperitoneal group was significantly shorter (p=0.015). Operation-specific variables showed no significant difference between the two groups. PADUA score and hilar clamping time showed no difference (p=0.345 and p=0.130, respectively). The learning curve in the retroperitoneal access group unveiled a noticeable difference in the experience and mastery of the involved surgeons. Conclusion: Mastery of the retroperitoneal approach is readily possible for surgeons with previous experience in robotic renal surgery without compromising the operative morbidity. The PADUA-score seems most suitable as a preoperative clinical criterion for choosing the renal approach site.
- Renal cell carcinoma
- robotic surgery
- minimally invasive surgery
- transperitoneal
- retroperitoneal
- learning curve
The growing detection rate of renal masses correlates with expanding availability and use of diagnostic imaging. This consequently led to a higher volume of surgery for small renal masses. The relevant operative techniques were developed accordingly. Both technical and scientific improvements have accompanied the surgical approach for these tumor types (1). Where available, minimally invasive procedures such as partial nephrectomy and laparoscopy are the standard of care, reducing morbidity and hospitalization time of the patients (2). Functional and oncological outcomes are comparable for both laparoscopic and robotic approaches (3). Randomized controlled trials (RCTs) evaluating the surgical access (trans-vs. retroperitoneal) confirm a positive influence on postoperative outcomes for the retroperitoneal approach (4). The surgeon’s decision for operation modalities and the access site is still widely influenced by tumor location and complexity. However, technological improvements and the development of surgeons’ skills allowed to relocate the margin of feasibility of even the most complex surgical procedures.
This study aimed to compare the clinical outcome of transperitoneal and retroperitoneal access sites and the related learning curves in robotic partial nephrectomy in order to elucidate preoperative clinical criteria for the surgeon’s choice of access site (trans- vs. retroperitoneal) as these are not clearly defined in the literature.
Patients and Methods
Patient characteristics. Overall, 107 patients underwent robotic surgery for renal masses between June 2018 and March 2022 in the department of Urology in the clinic of Leverkusen, Germany. Anthropometric, preoperative, imaging, comorbidity, intraoperative and postoperative data, histopathological findings and follow-up were assessed. Preoperative and anthropometric data included age at surgery, sex, diabetic status, smoking status, overall physical status (ASA-Score), body-mass index (BMI) and age-adjusted comorbidity score (AACCI) (5). Preoperative tumor stage and surgical complexity were evaluated using the PADUA-criteria (6). Surgical approach was chosen according to surgeons’ preference. Intraoperative data included the side of the lesion, operation (console) time, blood loss, conversion rate and hilar clamping time. Postoperative assets were: Blood transfusion rate, hospitalization time, creatinine level ratio (pre- to postoperative), complication severity (Clavien-Dindo-Classification; CDS), pathohistological findings and resection margins (7). The cohort was then subdivided into a transperitoneal (TP) and a retroperitoneal (RP) subgroup for further evaluation. The learning curve of both involved surgeons was evaluated separately for the two access groups. Both surgeons are highly experienced specialists in robotic surgery. Further subgroup analysis aimed at elucidating the morbidity of non-malignant renal masses (oncocytoma). The study was approved by the department of Urology in the clinic of Leverkusen’s local Ethics Committee (Ethikkommission der Ärztekammer Nordrhein).
Surgical site access. For transperitoneal access, the patient is placed in lateral position with a padded support behind the sacrum and shoulder. Additional fixation with adhesive tape on the hip and shoulder is provided. The operating table is tilted dorsally by 30°. The camera port is placed at the pararectal muscle in the upper abdomen after. A pneumoperitoneum is established at 12 mmHg. An 8 mm daVinci port is placed under the costal arch and another 8 mm port is placed in the lower abdomen at the anterior midclavicular line. The assistant’s port is inserted between the camera and the caudal port. When performing right-sided surgery, a supplementary 5 mm port at the substernal midline is needed to retract the liver.
The retroperitoneal access uses the same positioning of the patient. Porting is performed at the apex of Petit’s triangle for the 8 mm robotic camera port. A second 8 mm robotic port is placed along the posterior axillary line. Then a 12 mm Air Seal assistant port at the posterior axillary line adjacent to the iliac crest is installed. Subsequently, an 8 mm robotic port is placed along the anterior axillary line. Finally, an 8 mm robotic port is inserted 8 cm ventrally to the anterior axillary line. The DaVinci X-Series (Intuitive Surgical Deutschland GmbH, Intuitive Futures Forum, Berlin, Germany) was used in this series.
Statistical analysis. Prior to analysis of metric variables normal distribution was verified using the Shapiro-Wilk test. If normal distribution was not rejected (p≥0.1), a t-test was applied. If normal distribution was rejected, a Mann-Whitney U-test was used for statistical evaluation of two groups. To compare the frequency distributions of a categorical variable of independent groups, the Chi-Square test or Fischer’s exact test (if there were expected cell frequencies less than five) was used. All tests were calculated as two-sided tests. Statistical significance was set at p<0.05.
The learning curve was evaluated based on the development of raw operation theatre time plotted in chronological order. The slope of the trend line demonstrates the development of a single surgeon as shown in Figure 1, Figure 2 and Figure 3.
Clamping time for both surgical approaches in minutes over the time in days. A) RP approach. (B) TP approach. RP: Retroperitoneal; TP: transperitoneal.
Blood loss during the two described surgical approaches in minutes over time in days after the first operation. The surgeons are shown in different colors. (A) RP approach. (B) TP approach. RP: Retroperitoneal; TP: transperitoneal.
Operation time for both described approaches in minutes over time in days after the first operation. The surgeons are shown in different colors. (A) RP approach. (B) TP approach. RP: Retroperitoneal; TP: transperitoneal.
Descriptive analysis was applied for the subgroup analysis for oncocytomas vs. malignant tumors. Metric variables normal distribution was verified using the Shapiro-Wilk test. If normal distribution was not rejected (p≥0.1), a t-test was applied. If normal distribution was rejected, a Mann-Whitney U-test was used for statistical evaluation of two groups. To compare the frequency distributions of a categorical variable of independent groups, the Chi-Square test or Fischer’s exact test (if there were expected cell frequencies less than five) was used. All tests were calculated as two-sided tests. Statistical significance was set at p<0.05.
Results
Descriptive analysis for all patients and subgroup analysis are shown in Table I and Table II. We observed important differences between TP and RP patients regarding operation time [p=0.015; TP median: 178, interquartile range (IQR)=45-352; RP median: 139, IQR=98-311], smoking status (p=0.04) and perioperative creatinine levels (p=0.019; TP median: 0.91, IQR=0.53-2.3; RP median: 0.83, IQR=0.61-1.99). The creatinine level difference was calculated by subtraction of the preoperative to the postoperative values and showed no significant impact when comparing both approaches (p=0.323; TP median: −0.07, IQR=−0.64-0.56; RP median: −0.03, IQR=−0.48-0.78).
Descriptive parameters of variables of the transperitoneal (TP) or retroperitoneal (RP) approach.
Absolute and relative frequencies of variables of the transperitoneal (TP) or retroperitoneal (RP) approach.
Operation-specific variables showed no significant difference between the two groups. The PADUA score was balanced and was found very similar in both groups. (p=0.345; TP median: 8, range=6-14; RP median: 8, range=6-13). Hilar clamping time also showed no difference in the two groups, although clamping did not always occur in the TP group (p=0.130; TP median: 14, IQR=0-28; RP median: 13, IQR=7-25).
Intraoperative blood loss as an indirect indicator for the complexity of the procedure showed no difference in the two groups (p=0.798; TP median: 50, IQR=0-1,200; RP median: 0, IQR=0-500). The side distribution of treated kidney tumors showed no difference in both groups (p=0.852). The Clavien Dindo score showed no significant difference, even if there was a grade IVa complication in the TP group (p=1.000). With the results of the histopathological tumor classification, it must be taken into account that 16 oncocytomas were included in the calculations. Separate evaluation of the oncocytoma data is included in Table III and Table IV. Operation failure defined as conversion or Clavien-Dindo complication grade ≥3 was necessary in one case.
Descriptive parameters of variables depending on the patient histology.
Absolute and relative frequencies of categorical variables of the oncocytoma (On) or tumor (T) group.
Evaluation of the learning curves revealed the difference in the experience of both surgeons. The curves show no difference in operation time, clamping time or blood loss, when it comes to the established TP approach. The learning curves of the RP access showed a positive slope in operation time and blood loss of surgeon 2 thus showing an incomplete learning process of the surgeon.
Subgroup analysis of the oncocytoma vs. malignant tumors showed no significant difference in all measured parameters except for sex. Herein male patients were overrepresented in the malignant group (p=0.001). The data are shown in Table III and Table IV.
Discussion
Minimally invasive surgery for renal tumors is proven to be safe and effective and is the treatment of choice for small renal masses (8, 9). After introducing partial nephrectomy in laparoscopy, this technique was proven to have acceptable oncological results, although it has higher complication rates than open surgery (10, 11). The limitations of the laparoscopic approach were the limited maneuverability and visibility due to the technical restrictions of the laparoscopic instruments (11). The advantages of this approach could be transferred to robotic surgery and proved to be superior to laparoscopy (12). Especially, complication rates and postoperative morbidity were significantly reduced (13). After Gill et al. presented the first series of laparoscopic retroperitoneal nephrectomies, it took almost 17 years for the first series of robotic retroperitoneal approach (14, 15). In comparison to a transperitoneal approach, the advantages of the retroperitoneal access site are a reduced operation time, a better hilar control and thus a reduced pedicle injury rate (8). Patient selection criteria for a retroperitoneal approach are -as in our department- essentially a dorsal location of the tumor, a multifocality, and comorbidities of the patient and prior abdominal surgery.
The distribution of the PADUA score was similar in both groups, so that the operation time and learning curve were not compromised by a selection bias. One may hypothesize that the surgical experience of one or both surgeons has not yet reached beyond the learning curve to explain some of the surgical complications or the diverging operation times. However, the PADUA score was the central criterion for choosing the access site and thus the most reliable preoperative clinical aspect available. Taking the overall stable results and comparable operation times of both approaches into account, it may be suggested that both imaging data and the PADUA score should be included in the decision-making process for the access site.
Blood loss and clamping time were statistically stable throughout the groups, independently of the PADUA score and the tumor stage. It is expected that these values will also be maintained with larger numbers of patients, since bleeding control is a critical issue during surgery. The fact that some of the TP group did not clamp had no effect on the end result and the amount of bleeding. These results are congruent to the observations of Abaza et al. (16). As in this paper, the authors explored in 2017 the clinical feasibility and morbidity of the retroperitoneal access. In accordance with their results, the authors showed that the retroperitoneal approach requires a short training time for experienced surgeons. In 2020, Hark et al. published a multi-centric evaluation of the retroperitoneal robotic access site (17). In this study, the retroperitoneal approach exceeded the transperitoneal approach in matters of operation time, clamping (ischemia) time and morbidity. As a single-center study with less patients included, we could not verify these results albeit having similar settings in the study design. The study of Eraky et al. shows a similar design as in our study (18). In their results, the complication rate is significantly lower in the RP approach. This was explained by the shorter and faster access to the hilum, thus allowing an early bleeding control.
The evaluation of the learning curves revealed a difference in the experience of the surgeons. The curves show no difference when it comes to the established TP approach. Here the results show that both surgeons overcame the plateau-phase. The more experienced surgeon 1 mastered seamlessly the RP access. Surgeon 2 had reached a proficiency level, however still had not mastered the approach. These results are conclusive to those of Abaza et al. (16). The RP approach can be adopted quickly (in the order of 10 operations) after experience with TP.
Our subgroup analysis of the oncocytoma cohort showed just one significant difference to the malignant group: The predominance of oncocytoma in women has already been confirmed in 2013 by Mauermann et al. (19). A conclusive explanation for this observation is still a matter of discussion and seems to emanate from a multifactorial genesis (20).
The study has obvious limitations, which can bias the results: In contrast to a previously published study, we do not have a multicenter, prospective or randomized setting as other studies (21). Our study is a retrospective, single-center analysis based on clinical observations. However, the study groups show similar baseline characteristics.
Conclusion
Both access sites showed limitations, so that each should be seen as an option for different tumor constellations. The PADUA score and imaging data should be included in the decision-making process for the access site. Our study shows that in experienced hands, the retroperitoneal access can -and should- be adopted in short delay.
Acknowledgements
Statistical analysis was performed by Dr. Silke Lange, medical statistician.
Footnotes
Authors’ Contributions
NF, TK and DP have contributed to manuscript writing, data collection and critical analysis. DP an AMH contributed to manuscript writing, critical analysis and supervision of the first author. All Authors contributed to the article and approved the submitted version.
Conflict of Interest
The Authors declare that they have no conflicts of interest.
- Received February 23, 2023.
- Revision received March 28, 2023.
- Accepted April 4, 2023.
- Copyright © 2023 International Institute of Anticancer Research (Dr. George J. Delinasios), All rights reserved.
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