Modified C index: Novel predictor of postoperative renal functional loss of laparoscopic partial nephrectomy

We aimed to develop a scoring system to quantify the distance between the renal hilum and renal tumour, termed the modified C index (m-CI), and to predict renal functional loss (RFL) following laparoscopic partial nephrectomy (LPN).

The m-CI was measured by using computed tomography in 113 patients who underwent LPN between May 2003 and June 2014. The RFL following LPN was calculated by examining the estimated glomerular filtration rate (eGFR) and radioisotope renography one year postoperatively. The Pythagorean theorem was used to calculate the distance from the tumour centre to the renal hilum. The distance was divided by the tumour radius to obtain the m-CI. The correlation between the m-CI and the postoperative RFL were evaluated using Pearson's coefficient values. Multivariate logistic regression models were used to assess the potential predictive factors of RFL following LPN. The correlation between the m-CI and the operative time, ischemia time, and blood loss during LPN were also evaluated by the unpaired t-test.

Pearson's coefficient values between the postoperative RFL and the m-CI and C index were 0.294 and 0.173, respectively. In the multivariate analysis, the resected volume (p=0.031) and m-CI (p=0.036) significantly correlated with the postoperative RFL following LPN. The operative time (p<0.001), ischemia time (p=0.028), and blood loss (p=0.047) during LPN was significantly longer and larger, respectively, in the group with shorter m-CI (≤4.5) than in the group with the longer m-CI (>4.5).

The present study demonstrates that the m-CI can predict RFL following LPN, as well as the surgical difficulty.