A novel nephrometry scoring system for predicting peri-operative outcomes of retroperitoneal laparoscopic partial nephrectomy

BACKGROUND: Although the impact of tumor complexity on peri-operative outcomes has been well established using several nephrometry scoring systems, the impact of adherent perirenal fat remains poorly defined. This study aimed to develop a novel nephrometry scoring system for predicting the peri-operative outcomes of laparoscopic partial nephrectomy (LPN) by integrating and optimizing the RENAL score (RNS) and Mayo adhesive probability (MAP) score. METHODS: We retrospectively evaluated 159 patients treated with retroperitoneal LPN. The patients’ demographic parameters, RNSs, and MAP scores were evaluated as potential predictors of perioperative outcomes, including operation time, estimated blood loss (EBL), and margin, ischemia, and complication (MIC) achievement rate. The independent predictors were used to develop a novel nephrometry scoring system. The predictive value and inter-observer agreement for the novel nephrometry scoring system were evaluated. RESULTS: Tumor radius (R score), nearness to the renal sinus or collecting system (N score), and posterior perinephric fat thickness were independent predictors of peri-operative outcomes and were used to develop the RNP score. The univariate analysis revealed that the RNP score was significantly associated with operation time, EBL, and MIC achievement rate (P < 0.050). The RNP score was an independent predictor of operation time (P < 0.001), EBL (P = 0.018), and MIC achievement rate (P = 0.023) in the multivariate analysis. The RNP score was not inferior to RNS in the area under the curve for predicting peri-operative outcomes and performed better in inter-observer agreement (76.7% vs. 57.8%) and kappa value (0.804 vs. 0.726). CONCLUSION: The RNP score, combining the advantages of the RNS and MAP score, demonstrated a good predictive value for the peri-operative outcomes of retroperitoneal LPN and better inter-observer agreement.