Purpose: The percent of preserved parenchymal mass is the primary determinant of functional outcomes after partial nephrectomy. Accurate methods to predict the percent of preserved parenchymal mass based on preoperative imaging could facilitate patient counseling.
Materials and methods: We evaluated the records of 428 patients who had undergone partial nephrectomy and the studies necessary to assess preserved ipsilateral parenchymal mass and function. Preoperative and postoperative ipsilateral parenchymal volumes were measured from contrast enhanced computerized tomography less than 2 months before and 3 to 12 months after partial nephrectomy and the actual percent of preserved parenchymal mass was determined. The ipsilateral percent of preserved parenchymal mass and the final global glomerular filtration rate were estimated based on preoperative imaging using subjective estimation, quantitative estimation, or estimation derived from the contact surface area or the R.E.N.A.L. (radius, exophytic/endophytic, nearness of tumor to collecting system or sinus, anterior/posterior and location relative to polar lines) score.
Results: Median tumor diameter was 3.5 cm, median contact surface area was 24 cm2 and the median R.E.N.A.L. score was 8. The median actual ipsilateral percent of preserved parenchymal mass was 84% and the preserved percent of the global glomerular filtration rate was 89%. The median estimated ipsilateral percent of preserved parenchymal mass was 85%, 87%, 88% and 83% based on subjective estimation, quantitative estimation, contact surface area and the R.E.N.A.L. score, respectively. Correlations between the actual and the estimated percent of preserved parenchymal mass were relatively weak in all instances (all r ≤0.46). Prediction of the final global glomerular filtration rate was strong for all 4 methods (all r = 0.91). However, a similarly strong correlation was obtained when presuming that 89% of the preoperative global glomerular filtration rate would be saved in each case (r = 0.91). On multivariable analyses a solitary kidney, the preoperative glomerular filtration rate and various estimates of the percent of preserved parenchymal mass were significantly associated with the final global glomerular filtration rate. However, the preoperative glomerular filtration rate proved to be the strongest predictor. It had more than a tenfold impact compared to the estimated percent of preserved parenchymal mass or a solitary kidney.
Conclusions: Currently available methods to estimate the percent of preserved parenchymal mass have important limitations. The final global glomerular filtration rate, which is the most important functional outcome, could be predicted fairly accurately by all tested methods. However, none of them were better than simply presuming that 89% of function would be saved due to strong anchoring to the preoperative glomerular filtration rate.
Keywords: glomerular filtration rate; kidney; nephrectomy; organ preservation; solitary kidney.