The utility of automated volume analysis of renal stones before and after shockwave lithotripsy treatment

Helen Wei Cui,Palle Jörn Sloth Osther,Frederikke Eichner Christiansen,Tze Khiang Tan,Benjamin William Turney

doi:10.1007/s00240-020-01212-8

Helen Wei Cui, Palle Jörn Sloth Osther + Show 3 more

Open Access

https://doi.org/10.1007/s00240-020-01212-8

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Abstract

This study aimed to evaluate the additional utility of an automated method of estimating volume for stones being treated with shockwave lithotripsy (SWL) using computed tomography (CT) images compared to manual measurement. Utility was assessed as the ability to accurately measure stone burden before and after SWL treatment, and whether stone volume is a better predictor of SWL outcome than stone diameter. 72 patients treated with SWL for a renal stone with available CT scans before and after treatment were included. Stone axes measurement and volume estimation using ellipsoid equations were compared to volume estimation using software using CT textural analysis (CTTA) of stone images. There was strong correlation (r > 0.8) between manual and CTTA estimated stone volume. CTTA measured stone volume showed the highest predictive value (r2 = 0.217) for successful SWL outcome on binary logistic regression analysis. Three cases that were originally classified as ‘stone-free with clinically insignificant residual fragments’ based on manual axis measurements actually had a larger stone volume based on CTTA estimation than the smallest fragments remaining for cases with an outcome of ‘not stone-free’. This study suggests objective measurement of total stone volume could improve estimation of stone burden before and after treatment. Current definitions of stone-free status based on manual measurements of residual fragment sizes are not accurate and may underestimate remaining stone burden after treatment. Future studies reporting on the efficacy of different stone treatments should consider using objective stone volume measurements based on CT image analysis as an outcome measure of stone-free state.

Highlights

Current evidence and treatment guidelines for the management of renal tract stones, including the American Urological Association (AUA), European Urology Association (EAU) and United Kingdom NICE recommendations, are1 3 Vol.:(0123456789)Urolithiasis (2021) 49:219–226 guided by the size of the stone both at diagnosis, and of the remaining fragments after initial treatment
Most studies do include the presence of CIRFs as a ‘stone-free’ outcome after treatment, and recommendations for choosing extracorporeal shockwave lithotripsy (SWL), retrograde intrarenal surgery (RIRS) or percutaneous nephrolithotomy (PCNL) are based on these stone-free rates
72 patients undergoing SWL were included in this study for analysis as outlined in Table 1. 69/72 (96%) of SWL treatments were for 1 stone in the same location

Summary

Introduction

Current evidence and treatment guidelines for the management of renal tract stones, including the American Urological Association (AUA), European Urology Association (EAU) and United Kingdom NICE recommendations, are1 3 Vol.:(0123456789)Urolithiasis (2021) 49:219–226 guided by the size of the stone both at diagnosis, and of the remaining fragments after initial treatment. Current evidence and treatment guidelines for the management of renal tract stones, including the American Urological Association (AUA), European Urology Association (EAU) and United Kingdom NICE recommendations, are. Previous studies investigating the efficacy of different treatment modalities for renal tract stones have shown large heterogeneity in the methods used to define outcomes from treatment, including choice of imaging modality, method of measuring stone burden and the size definition of ‘clinically insignificant residual fragments’ or CIRFs [5, 6]. The recent evidence review for the NICE guidelines show the difficulties of comparing outcomes between different stone treatment modalities when the definition of ‘stone-free’ can vary between studies [7]. Most studies do include the presence of CIRFs as a ‘stone-free’ outcome after treatment, and recommendations for choosing extracorporeal shockwave lithotripsy (SWL), retrograde intrarenal surgery (RIRS) or percutaneous nephrolithotomy (PCNL) are based on these stone-free rates. There is no agreement on whether all CIRFs are significant and only completely ‘stone-free’ should be included as a successful outcome of treatment, or whether some residual fragments may be more significant than others based on risk of future symptoms and need for retreatment [8]

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