How to estimate stone volume and its use in stone surgery: a comprehensive review

Comparison of Measurement Methods for Stone Volume Estimation: An In Vitro Study

Introduction: Urolithiasis guidelines still rely on the maximum stone diameter to propose treatment strategy, although this measure is known to have many pitfalls. Stone volume (SV) could represent a more accurate measurement, helping to plan the treatment or follow-up. Various methods to measure SV have been proposed. We aimed to compare different methods to estimate SV. Methods: Fifteen stones (human and artificial) were assessed. Real SV was measured using the water displacement method. Volume estimation included three diameter-based formulas (Ackerman, 4/3 Pi r3 and r3/2) and two 3D segmentation methods (Horos and Kidney Stone Calculator [KSC]). All measurements were done by a single operator. Spearman correlation test and comparative analyses were conducted between the real and the estimated SV. Results: Compared with real SVs, Ackerman and r3/2 formulas estimated volume accurately in 2/15 (13%) of stones each. No accurate measurement was reported using the sphere formula. KSC did estimate volume accurately in 4/15 (27%) stones compared with the reference SV; Horos did it in 7/15 (47%) stones. Both segmentation methods presented strong correlation coefficients (r = 0.9642 and 0.9659, p < 0.0001), while formula correlation was moderate (r = 0.7531, p < 0.0001). Conclusion: Formulas and segmentation methods for SV estimation resulted in divergent outcomes. Segmentation methods (Horos and KSC) presented higher accuracies in SV estimation, compared with real SV. Formulas were the least accurate.

With great power comes great risk: High ureteral stricture rate after high-power, high-frequency Thulium fiber laser lithotripsy in ureteroscopy

PURPOSE

To compare the safety and efficacy of Thulium Fiber Laser (TFL) using either manufacturer presets (MP) or individualized presets (IP) in ureteroscopy.

METHODS

Multi-institutional, retrospective analysis on the first patients treated with SOLTIVE® Premium (Olympus Medical Systems®) TFL in Switzerland in 2020. MP were used at the University Hospital of Geneva, while IP were used at the University Hospital of Zurich. Patient demographics, stone characteristics, and procedural details were collected. Primary outcome was postoperative ureteral stricture (US). Secondary outcome was stone-free rate (SFR).

RESULTS

A total of 158 patients were analyzed, 79 in each group. Demographics were similar between the two groups, except for a lower pre-stenting rate in the MP group (56% vs. 91%; p < 0.001) and a higher rate of ureteral access sheath use in the MP group (65% vs. 44%; p = 0.011). No significant differences in stone burden (median stone diameter 9 mm, median stone volume 267 mm3), nor in the rate of impacted ureteral stones (29% vs. 34%; p = 0.49). Mean power, maximal power, frequency settings, and energy consumption were significantly higher in the MP group. US rate was 11% in MP group compared to 1% in IP group (p = 0.009). MP were a significant predictor of US on multivariable analysis (OR 12.4; p = 0.02), independently from impacted ureteral stones. No difference in SFR between groups (85% and 84%; p = 0.67).

CONCLUSION

High-power, high-frequency laser settings from manufacturer laser presets increase the risk of US, without improving SFR. Future studies shall further evaluate optimal laser settings depending on patient characteristics and intraoperative situation.

Is the ablation stone efficacy and efficiency better with a flexible and navigable suction ureteric access sheath?

OBJECTIVE

To compare the ablation efficacy and efficiency of flexible and navigable suction ureteric access sheath (FANS) and conventional ureteral access sheath (c-UAS) in retrograde intrarenal surgery (RIRS) for kidney stones treatment.

MATERIALS AND METHODS

A retrospective study of 96 patients who underwent RIRS using thulium fiber laser was performed. We divided the patients into Group 1: FANS and Group 2: c-UAS. We assessed the lithotripsy efficiency (mm3/Joules), ablation efficacy (mm3/min), and laser energy consumption (Joules/mm3). The stone-free rate (SFR) was defined as the absence of stone fragments in a non-contrast abdominal computed tomography 4-weeks after the procedure.

RESULTS

Both groups presented comparable stone volume (mm3) and stone density. RIRS with FANS presented a significantly lower surgical time and laser energy consumption (10.9 vs. 12.1 Joules/mm3, p < 0.001). In addition, FANS presented higher ablation efficiency (0.22 vs. 0.09 mm3/Joules, p < 0.001) and ablation efficacy (26.1 vs. 19.9 mm3/min, p < 0.001). SFR was significantly higher in the FANS group (93.7% vs. 75%, p < 0.001).

CONCLUSION

Compared to c-UAS, RIRS with FANS was associated with decreased total operative time and laser energy consumption and presented a significantly higher ablation efficacy and efficiency. Additionally, SFR was significantly higher in the FANS group.

Optimal stone density for ablation lithotripsy with vapor tunnel Ho:YAG pulse modality

INTRODUCTION

Vapor-Tunnel™ (VT) consists of a very long pulse that uses the minimum peak power, causing the energy to pass through a previously created vapor channel or tunnel. There are studies that have shown acceptable ablation lithotripsy efficiency. Nevertheless, there are no in-vivo studies that have compared the VT performance according to the stone density.

METHODS

A retrospective study of 152 patients who underwent RIRS using VT Ho:YAG laser was performed. We divided the patients according to the stone density (Group 1: < 1000UH vs. Group 2: > 1000UH). We assessed the lithotripsy efficiency (mm3/JJ) and the laser-energy consumption (JJ/mm3). The stone-free rate (SFR) was defined as the absence of stone fragments in a non-contrast abdominal computed tomography 4 weeks after the procedure.

RESULTS

Ninety three patients were included in Group 1 and 59 in Group 2. Body mass index was higher in Group 1 and the median stone volume was higher in Group 2 (846 vs. 672 mm3, p = 0.03). Total energy used (11.9 vs. 24 kj, p < 0.001), the laser emission time (19 vs. 30 min, p < 0.001), and the total operative time (60 vs. 85 min, p < 0.001) were lower in the Group 1. SFR was higher in Group 1 (96.7% vs. 57.6%, p < 0.001) with a global SFR of 81.6%. The ablation lithotripsy efficiency was higher in Group 1 (0.053 mm3/JJ vs. 0.035 mm3/JJ, p < 0.001).

CONCLUSIONS

VT Ho:YAG was associated with decreased laser time, operative time and laser-energy consumption in Group 1 than Group 2. Similarly, VT Ho:YAG increased lithotripsy efficiency and the SFR compared to hard stones with the same laser settings and pulse modality.

Comparing Thulium Fiber Versus High-Power Holmium Laser Lithotripsy Combined with the Flexible and Navigable Suction Access Sheath in Flexible Ureteroscopy for Kidney Stone Disease: A Propensity Score Matched Analysis by the Global FANS Collaborative Group

Objective: We aim to evaluate stone-free rate (SFR) and complications after flexible ureteroscopy (F-URS) for kidney stones, using a flexible and navigable suction ureteral access sheath (FANS), comparing thulium fiber laser (TFL) and high-power holmium:yttrium-aluminum-garnet laser (HPHL). Methods: Data from adults who underwent F-URS in 15 centers were prospectively analyzed (August 2023-January 2024). Exclusion criteria were ureteral stones, concomitant bilateral procedures, and renal abnormalities. One-to-one propensity score matching for age, gender, stone location, stone volume, and Hounsfield unit was performed. SFR was assessed using computed tomography scan within 30 days and defined as zero fragments. Data are presented as median (25th-75th quartiles). Multivariable logistic regression was performed to evaluate predictors of SFR. Results: Of included patients, HPHL was used in 114 patients and TFL in 181 patients. After matching, 96 patients from each group with similar baseline characteristics were included. There was no difference between the groups regarding the use of disposable scopes, lithotripsy mode, and ureteroscopy, lasing and total surgical time. There was no case of sepsis, and blood transfusion was necessary for only one patient in the HPHL group. The incidence of transient fever was similar (3.4% in HPHL vs 3.8% in TFL group). Postoperative day 1 loin pain did not differ significantly. Postoperative stay did not differ significantly [1 [0, 2] in HPHL vs 1 [0, 1] days in TFL group, p = 0.12]. Thirty-day SFR was similar (52.1% for HL vs 64.6% for TFL group, p = 0.11). At multivariable analysis, the use of TFL (odds ratio 1.95, 95% confidence interval 1.01-3.82) was significantly associated with higher odds of being stone-free. Conclusions: Both lasers are safe and efficacious and can be suitably used for F-URS with FANS with high SFR and minimal complications.

Which Measure of Stone Burden is the Best Predictor of Interventional Outcomes in Urolithiasis: A Systematic Review and Meta-analysis by the YAU Urolithiasis Working Group and EAU Urolithiasis Guidelines Panel

Background and objective

Stone size has traditionally been measured in one dimension. This is reflected in most of the literature and in the EAU guidelines. However, recent studies have shown that multidimensional measures provide better prediction of outcomes.

Methods

We performed a systematic review and meta-analysis of the prognostic accuracy of measures of stone size (PROSPERO reference CRD42022346967). We considered all studies reporting prognostic accuracy statistics on any intervention for kidney stones (extracorporeal shockwave lithotripsy [ESWL], ureterorenoscopy [URS], or percutaneous nephrolithotomy [PCNL]; Population) using multiplane measurements of stone burden (area in mm2 or volume in mm3; Intervention) in comparison to single-plane measurements of stone burden (size in mm; Intervention) for the study-defined stone-free rate (Outcome) in a PICO-framed question. We also assessed complication rates (overall and by Clavien-Dindo grade) and the operative time as secondary outcomes. Searches were made between 1970 and August 2023. We used the DeLong method to compare receiver operating characteristic (ROC) curves.

Key findings and limitations

Of 24 studies included in the review, 12 were eligible for comparative analysis with the DeLong test following meta-analysis of prognostic accuracy. For prediction of stone-free status, the area under the ROC curve (AUC) was significantly higher for stone volume than for stone size (0.71 vs 0.67; p < 0.001). Subanalyses confirmed this for ESWL and URS, but not for PCNL. For URS, the AUC was also significantly higher for stone area than for stone size (0.79 vs 0.77; p < 0.001). Throughout all analyses, there was no difference in AUC between stone area and stone volume. There was high risk of bias for all analyses apart from the URS subanalyses.

Conclusions and clinical implications

According to the limited data currently available, stone-free rates are predicted with significantly higher accuracy using multidimensional measures of stone burden in comparison to a single linear measurement.

Patient summary

We reviewed different ways of measuring the size of stones in the kidney or urinary tract and compared their accuracy in predicting stone-free rates after treatment. We found that measurement of the stone area (2 dimensions) or stone volume (3 dimensions) is better than stone diameter (1 dimension) in predicting stone-free status after treatment.

Evaluating the effectiveness of AI-powered UrologiQ's in accurately measuring kidney stone volume in urolithiasis patients

Kidney stones and urolithiasis are kidney diseases that have a significant impact on health and well-being, and their incidence is increasing annually owing to factors such as age, sex, ethnicity, and geographical location. Accurate identification and volume measurement of kidney stones are critical for determining the appropriate surgical approach, as timely and precise treatment is essential to prevent complications and ensure successful outcomes. Larger stones often require more invasive procedures, and precise volume measurements are essential for effective surgical planning and patient outcomes. This study aimed to compare the ability of artificial intelligence (AI) to detect and measure kidney stone volume via CT-KUB images. CT KUB imaging data were analyzed to determine the effectiveness of AI in identifying the volume of kidney stones. The results were compared with measurements taken by radiologists. Compared with radiologists, the AI had greater accuracy, efficiency, and consistency in measuring kidney stone volume. The AI calculates the volume of kidney stones with an average difference of 80% compared with the volumes calculated by radiologists, highlighting a significant discrepancy that is critical for accurate surgical planning. The results suggest that artificial intelligence (AI) outperforms radiologists' manual calculations in measuring kidney stone volume. By integrating AI with kidney stone detection and treatment, there is potential for greater diagnostic precision and treatment effectiveness, which could ultimately improve patient outcomes.

Can Artificial Intelligence Accurately Detect Urinary Stones? A Systematic Review

Objectives: To perform a systematic review on artificial intelligence (AI) performances to detect urinary stones. Methods: A PROSPERO-registered (CRD473152) systematic search of Scopus, Web of Science, Embase, and PubMed databases was performed to identify original research articles pertaining to AI stone detection or measurement, using search terms ("automatic" OR "machine learning" OR "convolutional neural network" OR "artificial intelligence" OR "detection" AND "stone volume"). Risk-of-bias (RoB) assessment was performed according to the Cochrane RoB tool, the Joanna Briggs Institute Checklist for nonrandomized studies, and the Checklist for Artificial Intelligence in Medical Imaging (CLAIM). Results: Twelve studies were selected for the final review, including three multicenter and nine single-center retrospective studies. Eleven studies completed at least 50% of the CLAIM checkpoints and only one presented a high RoB. All included studies aimed to detect kidney (5/12, 42%), ureter (2/12, 16%), or urinary (5/12, 42%) stones on noncontrast computed tomography (NCCT), but 42% intended to automate measurement. Stone distinction from vascular calcification interested two studies. All studies used AI machine learning network training and internal validation, but a single one provided an external validation. Trained networks achieved stone detection, with sensitivity, specificity, and accuracy rates ranging from 58.7% to 100%, 68.5% to 100%, and 63% to 99.95%, respectively. Detection Dice score ranged from 83% to 97%. A high correlation between manual and automated stone volume (r = 0.95) was noted. Differentiate distal ureteral stones and phleboliths seemed feasible. Conclusions: AI processes can achieve automated urinary stone detection from NCCT. Further studies should provide urinary stone detection coupled with phlebolith distinction and an external validation, and include anatomical abnormalities and urologic foreign bodies (ureteral stent and nephrostomy tubes) cases.

Risk factors of early infectious complications after ureterorenoscopy for stone disease: a prospective study

PURPOSE

To prospectively evaluate the rate and associated risk factors of early infectious complications after ureterorenoscopy for urolithiasis.

METHODS

After ethical committee approval, 400 therapeutic retrograde ureterorenoscopy procedures between August 3, 2020 and November 24, 2021 were included for analysis in a single-center study. Postoperative infection was defined as an afebrile urinary tract infection, fever (≥ 38 °C) with pyuria (≥ 300 WBC/μL) or proven urinary pathogen, and urosepsis. The primary outcome was the rate of infectious complications after ureterorenoscopy. Secondary outcomes were the perioperative factors that increased the risk of infectious complications within 30 days of surgery using univariate and multivariate logistic regression analysis.

RESULTS

Twenty-nine of four hundred (7.3%) patients developed an infectious complication within 30 days after ureterorenoscopy. Ten (2.5%) patients developed an afebrile urinary tract infection, eight (2.0%) developed fever with pyuria, five (1.3%) febrile urinary tract infection, and six (1.5%) urosepsis. On univariate analysis, preoperative stent-type JFil® pigtail suture stent was significantly associated with the dependent variable (p < 0.001). On multivariate logistic regression analysis, older age (OR 1.035; 95% CI 1.006-1.070; p = 0.02) was found to be significantly associated with developing a postoperative infectious complication.

CONCLUSIONS

A 7.3% rate of postoperative infectious complications and 1.5% urosepsis rate were observed after therapeutic ureterorenoscopy, without the need of intensive care admission. The only significant risk factors were preoperative stent type (JFil® pigtail suture stent) on univariate analysis, and older age on multivariate logistic regression analysis. Further multicentric prospective observational data are needed in this field.

Is "Kidney Stone Calculator" efficient in predicting ureteroscopic lithotripsy duration? A holmium:YAG and thulium fiber lasers comparative analysis

PURPOSE

This study aimed to evaluate the ability of Kidney Stone Calculator (KSC), a flexible ureteroscopy surgical planning software, to predict the lithotripsy duration with both holmium:YAG (Ho:YAG) and thulium fiber laser (TFL).

METHODS

A multicenter prospective study was conducted from January 2020 to April 2023. Patients with kidney or ureteral stones confirmed at non-contrast computed tomography and treated by flexible ureteroscopy with laser lithotripsy were enrolled. "Kidney Stone Calculator" provided stone volume and subsequent lithotripsy duration estimation using three-dimensional segmentation of the stone on computed tomography and the graphical user interface for laser settings. The primary endpoint was the quantitative and qualitative comparison between estimated and effective lithotripsy durations. Secondary endpoints included subgroup analysis (Ho:YAG-TFL) of differences between estimated and effective lithotripsy durations and intraoperative outcomes. Multivariate analysis assessed the association between pre- and intraoperative variables and these differences according to laser source.

RESULTS

89 patients were included in this study, 43 and 46 in Ho:YAG and TFL groups, respectively. No significant difference was found between estimated and effective lithotripsy durations (27.37 vs 28.36 min, p = 0.43) with a significant correlation (r =  + 0.89, p < 0.001). Among groups, this difference did not differ (p = 0.68 and 0.07, respectively), with a higher correlation between estimated and effective lithotripsy durations for TFL compared to Ho:YAG (r =  + 0.95, p < 0.001 vs r =  + 0.81, p < 0.001, respectively). At multivariate analysis, the difference was correlated with preoperative (volume > 2000 mm3 (Ho:YAG), 500-750 mm3 SV and calyceal diverticulum (TFL)), operative (fragmentation setting (p > 0.001), and basket utilization (p = 0.05) (Ho:YAG)) variables.

CONCLUSION

KSC is a reliable tool for predicting the lithotripsy duration estimation during flexible ureteroscopy for both Ho:YAG and TFL. However, some variables not including laser source may lead to underestimating this estimation.