Introduction
Percent parenchymal mass preserved (PPMP) is the primary determinant of functional outcomes after partial nephrectomy (PN). Accurate methods for predicting PPMP based on preoperative imaging could facilitate patient counseling.
Methods
428 PN patients with necessary studies to assess ipsilateral parenchymal mass/function preserved were evaluated.
Preoperative/postoperative ipsilateral parenchymal mass were measured from contrast-enhanced CT < 2 months prior and 3-12 months after PN and actual PPMP was determined. Ipsilateral PPMP was estimated from preoperative imaging using subjective estimation (SE) based on surgeon's prior experience, quantitative estimation (QE), or estimation derived from contact surface area (CSA) or R.E.N.A.L. QE of PPMP was derived from free-hand scripting on preoperative CT, presuming that a 10 mm rim around tumor and radially located parenchyma would be excised/devascularized. Final global GFR was estimated: (preoperative ipsilateral GFR × estimated ipsilateral PPMP) + preoperative contralateral GFR.
Results
Median tumor diameter was 3.5cm. Median CSA and R.E.N.A.L. were 24cm2 and 8, respectively. Median actual ipsilateral PPMP and percent global GFR preserved were 84% and 89%, respectively. Median estimated ipsilateral PPMP was 85%/87%/88%/83% based on SE/QE/CSA/R.E.N.A.L., respectively. Correlations between actual PPMP and estimated PPMP were relatively weak in all instances (all r ≤ 0.46). Prediction of final global GFR was strong for all 4 methods (all r = 0.91, Figure A-D); however, similarly strong correlation was also obtained when presuming that 89% of the preoperative global GFR will be saved in each case, which was the median value (r = 0.91, Figure E). On multivariable analyses, solitary kidney, preoperative GFR, and various estimates of PPMP significantly associated with final global GFR. However, preoperative GFR proved to be the strongest predictor; it was >10-fold more impactful than estimated PPMP or solitary kidney.
Conclusions
Currently available methods for estimating PPMP have important limitations. Final global GFR, the most important functional outcome, can be predicted fairly accurately by all of the tested methods but none are better than simply presuming that 89% of function will be saved, due to strong anchoring to preoperative GFR.
Functional recovery after partial nephrectomy is predominantly determined by the percent parenchymal mass preserved. In this study, we introduced several methods for estimating percent parenchymal mass preserved based on preoperative imaging to predict functional outcomes after partial nephrectomy. This revealed statistically weak correlations at the best between estimated and actual percent parenchymal mass preserved. In further analyses regarding prediction of final global GFR, which is the most relevant clinical outcome, the predictive impact of our estimation was substantially limited when compared to that of preoperative GFR. Final global GFR can be predicted fairly accurately by simply presuming that a median value (89%) of the global function will be saved in all cases, due to strong anchoring to preoperative GFR.