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Moving Beyond Linear Dimensions: Using Stone Volume to Better Predict High-Complexity PCNL Outcomes
Grant Sajdak1, Katya Hanessian1, Ala'a Farkouh1
1Department of Urology, Loma Linda University Health, Loma Linda, California, USA.
Introduction And Objective:
Stone diameter, measured in a single dimension, is used for management, billing, and research. Recent evidence has supported the use of stone volume over diameter. The purpose of this study was to compare stone volume and diameter as a predictor for outcomes following percutaneous nephrolithotomy (PCNL).
Methods:
A retrospective review was performed on PCNL patients at a single academic institution between January 2017 and June 2022. Preoperative computed tomography scans were analyzed to assess maximal stone diameter and stone volume using both Enterprise Imaging (ENI) and the scalene ellipsoid formula (ELF). Diameters and volumes were compared and analyzed for association with clinical and operative variables. Statistical analysis was performed using Spearman's rho and binary logistic regression (p < 0.05 significant).
Results:
Among 220 patients, the mean stone diameter was 24.2 mm. The mean stone volume varied by method: 4580 ± 500 mm3 using ENI and 6280 ± 1390 mm3 using the scalene ELF. On univariate analysis, Enterprise and the scalene ELF both significantly correlated with length of stay (ρ = 0.269 and 0.198, respectively, p < 0.001). However, only ENI had a significantly stronger association than diameter in relation to operation time (ρ = 0.516 vs 0.270, p < 0.001). Additionally, only ENI was significantly associated with relative (odds ratio [OR] = 0.9 [0.84-0.95]) and absolute (OR = 0.93 [0.88-0.99]) stone-free status (SFR). Only ENI (OR = 1.08 [1.02-1.15]) and diameter (OR = 1.03 [1.01-1.06]) were significantly associated with any grade of Clavien-Dindo complications. When controlling based on age, gender, body mass index, density, staghorn stones, and stone type on multivariate analysis, only density (OR = 1.002, p = 0.038) and ENI volume (OR = 1.116, p = 0.003) were independent predictors of relative SFR.
Conclusion:
Accurate stone volume assessment correlates more strongly with many pertinent PCNL outcomes than scalene ELF and diameter. Utilization of accurate stone volume in clinical practice could better predict patient outcomes, improve guidelines, and standardize research in high-complexity PCNL.
