Limitations of Parenchymal Volume Analysis for Estimating Split Renal Function and New Baseline GFR After Radical Nephrectomy.

PURPOSE: Accurately predicting new baseline-glomerular-filtration rate (NBGFR) after radical nephrectomy (RN) can improve counseling about RN vs partial nephrectomy. Split-renal-function (SRF)-based models are optimal, and differential parenchymal volume analysis (PVA) is more accurate than nuclear renal scans (NRS) for this purpose. However, there is minimal data regarding the limitations of PVA. Our objective was to identify patient/tumor-related factors associated with PVA inaccuracy.

MATERIALS/METHODS: 598 RN patients (2006-2021) with preoperative CT/MRI were retrospectively-analyzed, with 235 also having NRS. Our SRF-based model to predict NBGFR was: 1.25(GlobalGFRPre-RN )(SRFContralateral ), with SRF determined by PVA or NRS, and with 1.25 representing the median renal-functional-compensation (RFC) in adults. Accuracy of predicted NBGFR within 15% of observed was evaluated in various patient/tumor cohorts using multivariable-logistic-regression analysis.

RESULTS: PVA and NRS accuracy were 73%/52% overall, and 71%/52% in patients with both studies (n = 235, P < .001), respectively. PVA inaccuracy independently associated with pyelonephritis, hydronephrosis, renal-vein-thrombosis (RVT), and infiltrative-features (all P < .03). Ipsilateral hydronephrosis and RVT associated with PVA-underprediction, while contralateral hydronephrosis and increased age associated with PVA-overprediction (all P < .01). NRS inaccuracy was more common and did not associate with any of these conditions. Even among cohorts where PVA inaccuracy was observed (22% of our patients), there was no significant difference in the accuracies of NRS and PVA-based predictions.

CONCLUSIONS: PVA was more accurate for predicting NBGFR after RN than NRS. Inaccuracy of PVA correlated with factors that distort the parenchymal volume-function relationship or alter RFC. NRS inaccuracy was more common and unpredictable, likely reflecting the inherent inaccuracy of NRS. Awareness of cohorts where PVA is less accurate can help guide clinical decision-making.