Zonal NephRo Score: external validation for predicting complications after open partial nephrectomy

The aim of the study was to externally validate the Zonal NePhRO Score (ZNS) published in 2014 as latest and superior nephrometry score in terms of prediction of perioperative complications and outcome of open partial nephrectomies (OPNs). We identified 200 consecutive patients who underwent OPN. Analysis of preoperative CT or MRI scans and retrospective analysis of the patients' clinical records were performed. Tumour complexity was stratified according to the ZNS into three categories: low (4-6), moderate (7-9) and high (10-12) complexity. Predictors for perioperative complications and surgical parameters were identified using univariate and multivariate logistic regression. Tumour complexity was graded in 19.8 % of the cases as low, in 50.3 % as moderate and in 29.9 % as high. In the multivariate analysis, ZNS was significantly associated with a higher complication rate (OR 1.25, 95 % CI 1.04-1.49, p = 0.014), longer ischaemia time (IT) (beta = 1.19, 95 % CI 0.33-2.05, p = 0.007), postoperative drop of estimated glomerular filtration rate (eGFR) (beta = -1.86, 95 % CI -3.71 to -0.01, p = 0.049) and opening of the collecting system (CS) (OR 1.72, 95 % CI 1.40-2.10, p < 0.001). In addition, age and body mass index were identified as independent predictors for complications (OR 1.03, 95 % CI 1.00-1.06, p = 0.043 and OR 1.08, 95 % CI 1.00-1.15, p = 0.031). The present study is the first external validation of the ZNS as a predictor of perioperative complications in patients undergoing OPN. A higher ZNS score was associated with a longer IT, a higher rate of opening the CS and drop of eGFR.