Parenchymal volume and functional recovery after clamped partial nephrectomy: potential discrepancies.

Background: Parenchymal-volume-analysis (PVA) appears superior to nuclear-renal-scans (NRS) for assessing split-renal-function (SRF). Our objective was to evaluate how ischemia during PN impacts the accuracy of PVA for estimating functional outcomes.

Methods: Partial nephrectomy (PN) patients (2010-2022) with pre/postoperative NRS and cross-sectional imaging were retrospectively analyzed. Differences between NRS and PVA-derived ipsilateral SRF estimates were evaluated in warm/cold ischemia subgroups. The relationship between ischemia time and PVA/NRS discordance was evaluated with linear and segmented-regression. Correction for PVA overestimation was applied to a previously published cohort of PN patients managed with prolonged-ischemia.

Results: Among 437 PN, 246(56%)/191(44%) were managed with warm/cold ischemia, with median ischemia times of 21/28 minutes, respectively. Preoperative PVA and NRS-based ipsilateral SRF estimates were nearly identical (r=0.94). Post-PN, median PVA-based estimates of ipsilateral SRF were significantly higher than NRS-derived estimates for patients managed with warm-ischemia (WI)(44% vs. 42%, P=0.001), which was not observed with hypothermia. Segmented-regression revealed increasing PVA/NRS discordance only after 24 minutes of WI (P=0.04). No relationship was observed between ischemia time and PVA/NRS discordance for hypothermia or limited WI. Correcting for PVA overestimation in an independent cohort demonstrated that functional decline associated with prolonged WI was 2-3 fold greater than estimated by PVA alone.

Conclusions: PVA is highly accurate for predicting SRF in PN patients preoperatively and for assessing functional outcomes in patients managed with hypothermia or limited WI. However, with prolonged WI, there is discordance between parenchymal volume and function that progressively increases beyond 24 minutes. Avoidance of prolonged WI should be considered in patients with solitary kidneys and/or significant pre-existing chronic kidney disease.