Is the R.E.N.A.L. nephrometry scoring system predictive of the functional efficacy of nephron sparing surgery in the solitary kidney?

Purpose: We evaluated the ability of renal tumor complexity, as assessed by the R.E.N.A.L. (radius, exophytic, nearness to collecting system, anterior/posterior and location) nephrometry scoring system, to predict the functional efficacy of nephron sparing surgery.

Materials and methods: We evaluated 42 patients who presented with an anatomically (32) or a functionally (10) solitary kidney and underwent partial nephrectomy. Each renal unit was assigned a R.E.N.A.L. nephrometry score using preoperative imaging. The CKD-EPI equation was applied to calculate the estimated glomerular filtration rate. The difference between the estimated glomerular filtration rate at baseline and at postoperative time points served as a measurement of the renal functional loss attributable to partial nephrectomy.

Results: In the 42 patients who underwent partial nephrectomy the mean preoperative estimated glomerular filtration rate was 61.5 ml/minute/1.73 m(2). The median total nephrometry score was 8 (range 4 to 10). In the immediate postoperative period the cohort mean estimated glomerular filtration rate of 48.6 ml/minute/1.73 m(2) was significantly less than the preoperative value (p <0.0001). At 6-month followup the mean estimated glomerular filtration rate had recovered at 54.1 ml/minute/1.73 m(2) but it remained significantly less than the preoperative value (p = 0.0002). We noted no relationship between the postoperative decrease in the estimated glomerular filtration rate and the assigned total nephrometry score or in any individual component of the R.E.N.A.L. scoring system related to the targeted lesion.

Conclusions: Neither the individual components of the R.E.N.A.L. nephrometry scoring system nor the total nephrometry score predicted the realized functional loss, as assessed by the estimated glomerular filtration rate in patients with a solitary kidney treated with nephron sparing surgery. However, nephron sparing surgery was quite efficacious for preserving renal function since only a durable 11.6% decrease was noted in the estimated glomerular filtration rate.