The usefulness of stone density and patient stoutness in predicting extracorporeal shock wave efficiency: Results in a North African ethnic group

Role of Hounsfield Unit in Predicting Outcomes of Shock Wave Lithotripsy for Renal Calculi: Outcomes of a Systematic Review

PURPOSE OF REVIEW

Extracorporeal shock wave lithotripsy success rates depend on several stone and patient-related factors, one of which is stone density which is calculated on computed tomography scan in Hounsfield Units. Studies have shown inverse correlation between SWL success and HU; however, there remains considerable variation between studies. We performed a systematic review regarding the use of HU in SWL for renal calculi to consolidate the current evidence and address current knowledge gaps.

RECENT FINDINGS

Database including MEDLINE, EMBASE, and Scopus were searched from inception through August 2022. Studies in English language analysing stone density/attenuation in adult patients undergoing SWL for renal calculi were included for assessment of Shockwave lithotripsy outcomes, use of stone attenuation to predict success, use of mean and peak stone density and Hounsfield unit density, determination of optimum cut-off values, nomograms/scoring systems, and assessment of stone heterogeneity. 28 studies with a total of 4,206 patients were included in this systematic review with sample size ranging from 30 to 385 patients. Male to female ratio was 1.8, with an average age of 46.3 years. Mean overall ESWL success was 66.5%. Stone size ranged from 4 to 30 mm in diameter. Mean stone density was used by two-third of the studies to predict the appropriate cut-off for SWL success, ranging from 750 to 1000 HU. Additional factors such as peak HU and stone heterogeneity index were also evaluated with variable results. Stone heterogeneity index was considered a better indicator for success in larger stones (cut-off value of 213) and predicting SWL stone clearance in one session. Prediction scores had been attempted, with researchers looking into combining stone density with other factors such as skin to stone distance, stone volume, and differing heterogeneity indices with variable results. Numerous studies demonstrate a link between shockwave lithotripsy outcomes and stone density. Hounsfield unit < 750 has been found to be associated with shockwave lithotripsy success, with likelihood of failure strongly associated with values over 1000. Prospective standardisation of Hounsfield unit measurement and predictive algorithm for shockwave lithotripsy outcome should be considered to strengthen future evidence and help clinicians in the decision making.

TRIAL REGISTRATION

International Prospective Register of Systematic Reviews (PROSPERO) database: CRD42020224647.

Role of Patient Age and Stone Density in Predicting Outcomes of Shockwave Lithotripsy in Lower Ureteral Stones

Background

Shockwave lithotripsy (SWL) is an important tool for treating ureteral stones, especially when ureteroscoy (URS) is not readily available.

Objective

The aim of the study was to identify factors associated with the success of shockwave lithotripsy (SWL) in the treatment of lower ureteral stones.

Methods

Total of 105 consecutive patients with single lower ureteral stones treated with SWL between January 2021 and February 2022 were reviewed retrospectively. Clinical and stone parameters including age, gender, and body mass index (BMI), stone length, and stone density were analyzed. SWL procedures were done using electro-conductive lithotripter Sonolith i-sys (EDAP TMS, Vaulx-en-Velin, France). We evaluated available clinical and radiologic features that might have been related to successful SWL treatment.

Results

Treatment was successful in 67/105 patients (63.8%). Multivariate logistic regression revealed that a successful outcome was significantly related to mean stone density (MSD) (95% CI: 1.004- 1.009) and the patients age (95% CI: 1.022- 1.13). Gender, BMI, and stone length were not an independent predicting factors.

Conclusion

Stone density and patient age were independent predictors of successful outcome after two SWLs in the lower ureter. However, gender, BMI, and stone length did not independently predict treatment success.

Non-contrast computed tomography-based factors in predicting ESWL success: A systematic review and meta-analysis

PURPOSE

We assessed the efficacy of some predictive factors that can be measured with non-contrast computed tomography and may affect ESWL success with a systematic review and meta-analysis.

MATERIALS AND METHODS

All data sources were broadly investigated up to April 2022. Data were extracted from the relevant studies and analyzed with RevMan software. In a random effects model, standard mean difference (SMD) and risk ratio (RR) values were given with 95% confidence intervals.

RESULTS

In total, pooled analysis included 7148 patients in 43 studies. The combined effect estimate showed significant differences between the ESWL success and ESWL failure groups in terms of Hounsfield unit (HU), Hounsfield density (HD), skin to stone distance (SSD), ureteral wall thickness (UWT), stone volume, stone area, abdominal fat parameters, diameter of proximal ureter, and hydronephrosis. However, perinephric stranding and renal cortical thickness were not found to be statistically significant between the study groups.

CONCLUSIONS

HU, HD, SSD, UWT, stone volume, stone area, abdominal fat parameters, diameter of proximal ureter and hydronephrosis are effective factors for prediction of ESWL success. It is important to decide on treatment before the procedure for stones with appropriate diameter for ESWL.

Can we predict the ancillary treatments after extracorporeal shockwave lithotripsy for renal and upper ureteral stones?

OBJECTIVE

To quantify the predictors for the ancillary treatments after extracorporeal shock wave lithotripsy (SWL) for renal and upper ureteral stones.

MATERIALS AND METHODS

From January 2014 to January 2017, patients undergoing SWL using an electromagnetic lithotripter machine (Compact Delta; Dornier MedTech GmbH, Wessling, Germany) for renal and upper ureteral stones ≤ 20 mm were retrospectively reviewed. All patients underwent CT urography prior to SWL. The cohort was subdivided into three groups according to stone attenuation values in Hounsfield Units (HU). Group I; HU < 500 (n = 20), group II; HU 500-1000 (n = 51) and group III; HU ≥ 1000 (n = 180). The parameters included for multivariate analysis were stone size, location, multiplicity, stone attenuation value, number of shocks and stone clearance rate by 3 months. The ancillary treatments were ureteroscopy (URS), ureteral stenting and hospital readmission for pain or fever.

RESULTS

A total of 251 patients were included in the study. The overall SWL success rate was 92.4%. Mean stone size was 10.9 ± 2.1, 11.6 ± 3 and 11.4 ± 3.6 mm and mean stone attenuation values were 364 ± 125, 811 ± 154 and 1285 ± 171 HU for groups I, II and III respectively. The stone clearance rates by 3 months were 96%, 92% and 88.4% for groups I, II and III respectively. On subgroup analysis, group III required ancillary treatments in 70% of patients whereas group I, II, did not require any ancillary treatments. On multivariate analysis, stone multiplicity, stone location (lower calyceal stones) and HU were independent significant predictors for the need for ancillary treatments after SWL (p values < 0.05).

CONCLUSIONS

Patients with stone attenuation value (HU) > 1000, multiple stones and/or lower calyceal stones have higher risk to necessitate ancillary treatments after SWL. These patients would likely benefit from upfront endoscopic lithotripsy for treating symptomatic renal or upper ureteral stones.

The effect of stone and patient characteristics in predicting extra-corporal shock wave lithotripsy success rate: A cross sectional study

Introduction

We determine the effect of patient characteristics (age, sex, and body mass index BMI) and stone characteristics (density, location, and size) by non-contrast computed tomography of the kidneys, ureters, and bladder (CT-KUB) in predicting the success of extracorporeal shock wave lithotripsy (ESWL) in the treatment of kidney and ureteric stones. We present this study to further enrich the knowledge of physicians towards the effect of different patient characteristics upon predicting extra-corporal shock wave lithotripsy success rates.

Methods

We evaluated 155 patients who received ESWL for renal and ureteric stone measuring 3–20 mm (mm), over a 3-month period. The stone size in millimeters, density in Hounsfield units (HU) and its location was determined on pre-treatment CT-KUB. ESWL was successful if post-treatment residual renal stone fragments were ≤3 mm and for ureteric stones should be totally cleared.

Results

The overall success of ESWL treatment was observed in 65.8% of the 155 patients. There was no significant difference seen when the effect of patients age, sex and BMI were studied with ESWL outcome with P values were 0.155, 0.101 and 0.415 respectively. Also, stone location either in the kidney or ureter has no statistically significant effect on ESWL response rate. while stone density and size determined on CT KUB have statistically significant effect on the success rate of ESWL with a P-value of 0.002 and 0.000 respectively.

Conclusions

This study shows that determination of stone density and stone size on CT KUB pre ESWL can help to predict the outcome of ESWL. We propose that stone density <500 HU and stone size < 5 mm are highly likely to result in successful ESWL.

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Previous studies have reported a wide variation of ESWL success rate ranging from 46% to 91%.

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Failure of ESWL results in unnecessary exposure of renal parenchyma to shock waves and complications like renal hematoma.

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Increasing Efforts have been made to determine factors that predict ESWL outcome and improve patients' selection.

External Validation of the S.T.O.N.E. Score in Predicting Stone-Free Status After Rigid Ureteroscopic Lithotripsy

Background

The Size, Topography, Obstruction, Number, and Evaluation of Hounsfield units (S.T.O.N.E.) scoring system has been proposed as a novel prognostic surgical classification for urolithiasis in predicting success rate and complications.

Objective

We carried out an externally validated S.T.O.N.E. score on rigid ureteroscopic lithotripsy (rURS).

Materials and Methods

The data of patients who had undergone rURS between 2012 and 2019 at a tertiary referral center were audited retrospectively. The S.T.O.N.E. score was calculated based on factors determined through preoperative computed tomography images and was analyzed in association with stone-free rate (SFR), operating time, surgical complications, and length of stay (LOS).

Results

A total of 155 patients were included in the study with a median stone size of 10 mm (7–12) and a median S.T.O.N.E. score of 9 (8–10). The overall SFR was 89.68%. SFRs were 100.0%, 97.83%, and 77.42% in low (5), moderate (6–9), and high (10–13) score groups, respectively. The S.T.O.N.E. score (p = 0.002) and stone size (p = 0.037) were predictive factors for SFR in multivariate analysis. Moreover, there was a significant correlation between the S.T.O.N.E. score and operative time, LOS, and presence of complications (r = 0.22, p = 0.006; r = 0.30, p < 0.001; and r = 0.27, p < 0.001, respectively). The area under the curve of the receiving operator characteristics’ curve for the S.T.O.N.E. score was 0.815.

Conclusion

The S.T.O.N.E. scoring system is simple and effective in predicting postoperative outcomes; therefore, this score would be a valuable tool in clinical planning for every patient who undergoes rURS.

Histogram of kidney stones on non-contrast computed tomography to predict successful stone dusting during retrograde intrarenal surgery

PURPOSE

To predict successful dusting of kidney stones during retrograde intrarenal surgery (RIRS) using stone density parameters and histograms measured with non-contrast computed tomography imaging.

METHODS

Medical records of 49 patients who underwent retrograde intrarenal surgery between January 2018 and January 2019 at Kyung Hee University Hospital were reviewed, and the data of 55 stones were evaluated. Patient age, sex, mean stone density, the highest and lowest measured Hounsfield unit (HU), standard deviation and range of the measured HUs, volume of the most measured HU, and success of dusting were evaluated. Histograms of the measured HUs were created and cutoff values for successful dusting were analyzed.

RESULTS

Thirty-two stones were successfully dusted during surgery. Dusted stones had a wider range of HU and higher standard deviation. The volume of the most measured HU was smaller in the dusted stones. Successful dusting could be predicted when the volume of the most measured HU was < 8.9 mm³, with range ≥ 853, or when the volume of the most measured HU was < 8.9 mm³, with range < 853, and the mean stone density was < 355. The histograms of HUs of the dusted stones were wide and rugged, while those of dusting failed stones were narrow and peaked.

CONCLUSION

Evaluation of stone HU histograms showed differences in distribution and proportion. This will help predict surgical outcomes and prepare for intraoperative complications.

Non-Contrast Computed Tomography Scan Based Parameters of Ureteric Stones Affecting the Outcome of Extracorporeal Shock Wave Lithotripsy

Objective 

To compare the non-contrast computed tomography (NCCT) scan-based parameters of ureteric stones affecting the outcome of extracorporeal shock wave lithotripsy (ESWL).

Materials and methods

We retrospectively evaluated the pre-procedure NCCT of 74 patients who had ESWL for solitary ureteric calculi of 5-20 mm in diameter. We assessed the age, sex, basal metabolic index (BMI), laterality, location, presence of double 'J' (DJ) stent, skin to stone distance (SSD), stone maximum diameter, Hounsfield unit (HU), Hounsfield density (HD), area, and volume. All those who had no stone on follow-up imaging within 30 days were declared successful while those who had residual stone were declared failures.

Results

The overall success rate was 78% (58/74). Sixty (81.1%) patients were male. The success of ESWL was correlated with lower SSD, Hounsfield units (HU) and Hounsfield density (HD). However, in multivariate analysis, SSD, Hounsfield unit, and stone area showed correlation with success of procedure but Hounsfield density failed to show correlation. The success rate in patients with stone HU <500, 500-1000 and >1000 were 93.9%, 69%, and 58.3%, respectively. Patients with lower BMI (<30 kg/m²) and HD (<76 HU/mm) were more prone towards success of the procedure than those with higher BMI (>30 kg/m²) and higher HD (>76 HU/mm).

Conclusion

BMI, SSD, stone Hounsfield units and Hounsfield unit density were strong predictors of outcome of ESWL for ureteric stone.