Diameter-Axial-Polar Nephrometry: Integration and Optimization of R.E.N.A.L. and Centrality Index Scoring Systems

Purpose: The R.E.N.A.L. (radius, exophytic/endophytic properties, nearness of tumor to collecting system or sinus, anterior/posterior) and centrality index nephrometry scores enable systematic, objective assessment of anatomical tumor features. We systematically compared these systems using item analysis test theory to optimize scoring methodology. Materials and Methods: Analysis was based on 299 patients who underwent partial nephrectomy from 2007 to 2011 and met study inclusion criteria. Percent functional volume preservation, and R.E.N.A.L. and centrality index scores were measured. Late percent glomerular filtration rate preservation was calculated as the ratio of the late to the preoperative rate. Interobserver variability analysis was done to assess measurement error. All data were statistically analyzed. Results: A novel scoring method termed DAP (diameter-axial-polar) nephrometry was devised using a data based approach. Mean R.E.N.A.L., centrality index and DAP scores for the cohort were 7.3, 2.5 and 6 with 84%, 90% and 95% interobserver agreement, respectively. The DAP sum score and all individual DAP scoring components were associated with the clinical outcome, including percent functional volume preservation, warm ischemia time and operative blood loss. DAP scoring criteria allowed for the normalization of score distributions and increased discriminatory power. DAP scores showed strong linear associations with percent functional volume preservation (r(2) = 0.97) and late percent glomerular filtration rate preservation (r(2) = 0.81). Each 1 unit change in DAP score equated to an average 4% change in kidney volume. Conclusions: DAP nephrometry integrates the optimized attributes of the R.E.N.A.L. and centrality index scoring systems. DAP scoring was associated with simplified methodology, decreased measurement error, improved performance characteristics, improved interpretability and a clear association with volume loss and late function after partial nephrectomy.