Factors associated with difficulty in partial nephrectomy are divided into tumor-related factors (tumor size and position) and patient-related factors (BMI, abdominal surgery history, etc.). The RNS is a score of anatomical factors of the tumor and consists of five components: <R>, <E>, <N>, <A>, and <L>. With a total score of 4-6 points being Low, 7-9 points Moderate, and 10-12 points High, it is considered that the higher the score, the longer the operative time and ischemic time of partial nephrectomy. The RNS is widely used because it can be easily evaluated using computed tomography or magnetic resonance imaging . In our institution, the RNS has been used to evaluate preoperative difficulty, with a higher score considered to reflect a longer operative time and ischemic time, as in another report .
Zargar et al. analyzed a total of 1019 cases (452 RAPN cases and 567 laparoscopic partial nephrectomy (LPN) cases) for postoperative urine leakage. On a multivariable analysis, tumor proximity to the collecting system significantly increased the occurrence of postoperative urine leakage (OR=9.2; p<0.01) . Mayer et al. analyzed the factors associated with CSE in 67 patients who underwent LPN or RAPN. The RNS and N-score were associated with CSE . However, since the operative outcomes differ between LPN and RAPN, it is necessary to consider LPN and RAPN separately when analyzing the factors influencing CSE. Yoo et al. evaluated the impact of preoperative ureteral catheter insertion on urinary leakage after partial nephrectomy (PN). Ureteral catheter insertion was reported not to reduce the risk of urinary leakage after PN .
There have been reports concerning the prediction of postoperative complications of PN using the PADUA score and RNS [8.9]. However, the factors associated with CSE in RAPN have not been reported. We evaluated the relationship between CSE and RNS in 101 cases of RAPN in the present study and found significant differences between the two groups regarding the R-score, E-score, N-score, RNS total score and RNS total score excluding the L-score. Furthermore, CSE showed a moderate correlation with the RNS total score excluding the L-score (AUC: 0.848, cut-off: 5, sensitivity: 0.83, specificity: 0.73).
When the cut-off value for the RNS total score excluding the L-score was set to 4, the specificity and the sensitivity were 92% and 46%, respectively. CSE is thus considered unlikely to occur when the cut-off value is ≤4 points. These findings suggest that a ureteral catheter should not be placed in a patient with the RNS total score (excluding the L-score) of ≤4. Eliminating needless ureteral catheter indwelling reduces both the operative time and cost.
Several limitations associated with the present study warrant mention. First, this was a retrospective study. Second, the number of included patients was small. Future studies involving a larger cohort will be required. Finally, a small entry site may not have been found because the ureteral catheter could not be inserted in all cases. Even if there is no ureteral catheter placement, it is possible to identify the entry site (excluding micro entry sites) by improving the visualization by robot surgery. We also consider micro entry sites to not be clinically important. The purpose of ureteral catheter placement is precise closure rather than the identification of the entry sites.