Calcium stone fragility is predicted by helical CT attenuation values

Renal stone density on native CT-scan as a predictor of treatment outcomes in shock wave lithotripsy

Extracorporeal shock wave lithotripsy (ESWL) is considered a standard treatment for nephrolith or kidney stones measuring less than 20 mm. Anatomical, machine-related, and stone factors play pivotal roles in treatment outcomes, the latter being the leading role. This paper examined the relationship between stone density on native CT scans and ESWL treatment to remove renal stones concerning several treatments. One hundred and twenty patients (64 males and 56 females) were enrolled and completed the study from April 2019 to September 2020. Inclusion criteria were a single renal pelvis stone of 5-20 mm to be treated for the first time in adult patients with no urinary or musculoskeletal anatomical abnormalities. We assessed patients' renal function and obtained stone characteristics using a native CT scan. Patients were then scheduled for ESWL by the same machine and operator under fluoroscopy, with two-week intervals between treatment sessions when more than one treatment session was required. Before each new session, a new KUB-US was performed to reevaluate the stone. One hundred and twenty patient records were analyzed, 64 (53.3%) males and 56 (46.7%) females, with a mean age of 38.6 years and a mean stone size of 13.15 mm. Treatment with ESWL cleared stones in 76 (63.3%) patients, while 44 (36.7%) failed the treatment. The mean stone density in patients whose stones were cleared was significantly lower (661 vs. 1001) (P<0.001). Estimating renal calculus (or kidney stone) density on a native CT scan might help prognosticate ESWL treatment outcomes regarding stone clearance rates and the number of sessions required to clear a stone.

Correlative investigation between routine clinical parameters of dual-energy computed tomography and the outcomes of extracorporeal shock wave lithotripsy in children with urolithiasis: a retrospective study

PURPOSE

To evaluate the associations of DECT parameters with extracorporeal shock wave lithotripsy (ESWL) outcomes in pediatric patients.

METHODS

A retrospective study of consecutive patients with calculi who underwent ESWL and DECT in our hospital was performed in 2011-2019. The primary outcome was DECT imaging's correlation with ESWL outcomes. The secondary outcome was to determine DECT parameters independently predicting ESWL outcomes, including stone-free (SF) and residual stone (RS) statuses.

RESULTS

The study included 207 patients. The mean CT attenuations at 140 kVp, 80 kVp, and 120 kVp and effective atomic number (Zeff) were significantly correlated with stone free (SF) and residual stone (RS) (P < 0.05). Areas under the curves (AUCs) of CT attenuations at 120 kVp, 80 kVp, 140 kVp, and dual-energy index (DEI) were 0.784 (95% CI 0.672-0.897), 0.780 (95% CI 0.677-0.884), 0.766 (95% CI 0.658-0.885), and 0.709 (95% CI 0.578-0.840) (all P < 0.05). With cutoffs of 882.5, 1330.5, 1042.5, and 0.103 for CT attenuations at 140 kVp, 80 kVp, 120 kVp, and DEI, respectively, sensitivities and specificities were 75.0% and 31.1%, 83.3% and 31.8%, 80.3% and 31.1%, and 58.3% and 44.7%, respectively.

CONCLUSION

Our results demonstrated that the parameters of DECT could be used to predict ESWL outcomes (especially the SF status) in children with urolithiasis. ESWL success can be accurately predicted by DECT, and it is hard to predict ESWL failure.

Optimization of shockwave lithotripsy use for single medium sized hard renal stone with stone density ≥ 1000 HU. A prospective study

PURPOSE

To identify shock wave lithotripsy (SWL) success predictors in hard renal stones (average stone density ≥ 1000 HU).

MATERIALS

We prospectively evaluated patients who underwent SWL for hard renal stones between April 2018 and December 2020. Radiological parameters were identified, e.g., stone site, size, the average density in addition to stone core and shell mean density, and renal cortical thickness (RKT). SWL sessions were performed using Doli-S lithotripter till a maximum of 3-4 sessions with 2-4 weeks interval. Initial response to SWL included stone fragmentation and decreased stone size after the first SWL. Treatment success was considered if complete clearance of renal stones occurred or in case of clinically insignificant residual fragments ≤ 4 mm after 12 weeks follow up by NCCT.

RESULTS

Out of 1878 patients who underwent SWL, the study included 157 patients with hard renal stones. Treatment overall success was found in 92 patients (58.6%) where 69 patients (43.9%) had complete stone clearance. On multivariate analysis, stone shell density < 901 HU, maximum stone size < 1 cm, RKT > 1.95 cm and initial treatment response were associated with increased the success rate after SWL for hard renal stones (P = 0.0001, 0.009, < 0.0001 and < 0.0001, respectively).

CONCLUSION

In hard renal stones, treatment overall success was found in 58.6% where complete stone clearance was found in 43.9%. Stone outer shell fragility, lower stone size, increased RKT and initial response to SWL were associated with a higher success rate at 12-week follow-up.

Outcomes of extracorporeal shock wave lithotripsy for ureteral stones according to ESWL intensity

Background

We evaluated the treatment outcomes of ureteral stones according to energy intensity generated by extracorporeal shock wave lithotripsy (ESWL).

Methods

We retrospectively analyzed 150 patients who underwent ESWL for treatment of ureteral stones between September 2018 and February 2020. All stones were confirmed by a computed tomography examination, and the size, location, skin-to-stone distance, and Hounsfield units (HU) of the stones were assessed. In addition, patient characteristics including body mass index and estimated glomerular filtration rate, which can affect treatment outcome, were also evaluated. The success or failure of ESWL was confirmed according to the session, and the factors affecting the treatment outcome were analyzed using a logistic regression model.

Results

Of the 150 patients, 82 (54.7%) had stones in the proximal ureter, 5 (3.3%) in the mid, and 63 (42.0%) in the distal ureter. Patients underwent ESWL an average of 1.5 times, and the success rate according to session was 65.3% for the first, 83.3% for the second, and 90.0% for the third session. A multivariate analysis revealed that stone size [odds ratio (OR) 0.81, 95% confidence interval (CI), 0.66–0.99, P=0.049] and HU (OR 0.99, 95% CI, 0.98–0.99, P=0.001) were significant factors affecting the success rate after the first ESWL session; ESWL intensity was not related to success rate. Stone size (OR 0.78, 95% CI, 0.62–0.96, P=0.022) was the only significant factor affecting the success rate in the third session.

Conclusions

Stone size and HU affected the ESWL success rate. ESWL intensity was not significantly related to the success rate, so it should be adjusted according to patient pain and the degree of stone fragmentation.

The Predictive Role of Abdominal Fat Parameters and Stone Density on SWL Outcomes

BACKGROUND

Our aim was to detect the role of radiological abdominal fat parameters by tomography and stone density by plain X-ray on extracorporeal Shock Wave Lithotripsy (SWL) stone-free rate.

METHODS

The patients who had undergone SWL for a single opaque renal stone < 2 cm in diameter and proximal ureteric stone < 1 cm in diameter were collected retrospectively. The characteristics of patients and stones were recorded. The stone attitude, HU, abdominal fat parameters, paraperirenal fat area, perirenal infiltration and severity of hydronephrosis with pre-treatment Non- Contrast Computed Tomography (NCCT) and stone density with radiography were evaluated by a radiologist. Four weeks after the last SWL; all patients were evaluated by plain X-ray and categorized as Stone Free (SF) and Residual Fragment (RF) group.

RESULTS

51 patients with renal stones and 88 patients with proximal ureteral stones were included in the study. 24 (47%) and 63 (71%) patients were classified as SFfor renal and ureteral stones respectively. Only stone size was an independent predictor for stone-free rates after SWL for renal and proximal ureteral stones on multivariate analysis. The Receiver Operating Characteristic (ROC) curves for renal calculi revealed that creatinine level, stone size, stone attitude, Houns-Field Unit (HU) and Skin-to-Stone Distance (SSD) were the predictive factors for the SWL outcome (p< 0.05). The ROC curve for ureteral calculi demonstrated that HU, stone size and attitude were the predictive factors (p< 0.05).

CONCLUSION

All abdominal fat parameters and the stone density were not related to SWL failure. A large follow-up with more patients is essential to confirm the role of radiological parameters on the outcome of SWL.

Effect of JJ stent on outcomes of extracorporeal shock wave lithotripsy treatment of moderate sized renal pelvic stones: A randomized prospective study

PURPOSE

To evaluate the effect of JJ stents on SWL treatment of moderate (15-25mm) renal pelvic stones.

MATERIALS AND METHODS

Between January 2016 and December 2017, a total of 152 adult patients who were planned to undergo SWL for a single radiopaque renal pelvic stone were included in the study. Patients with solitary kidney, congenital abnormality, skeletal tract abnormalities, previous urinary system surgery, hydronephrosis (grade 2 or more), untreated urinary tract infection, bleeding disorder, and suspected pregnancy were excluded. The remaining 114 patients were randomly divided into two groups; non-stented and stented. Twenty-two patients whose stone could not be fragmented despite 3 consecutive sessions were also excluded from the study. A total of 92 patients (54 non-stented and 38 stented) were included in the final analysis.

RESULTS

There was no significant difference in terms of age, sex, body mass index, renal parancyhimal thickness, hydronephrosis, skin-to-stone distance, Hounsfield units, and stone size between the groups. Success was significantly higher in the stented group than in the non-stented group (71% vs. 39%, P=.002). In stone-free patients, the number of emergency department visits and analgesic tablet consumption was significantly lower in the stented group than in the non-stented group (P<.001 and P<.001, respectively). In non- stone-free patients, analgesic tablet consumption was significantly lower in the stented group than in the non-stented group (P=.004).

CONCLUSIONS

Pre-stenting before SWL treatment of moderate sized renal pelvic stones has some advantages in terms of success, emergency service visits, and analgesic tablet consumption.

Noncontrast computed tomography factors predictive of extracorporeal shock wave lithotripsy outcomes in patients with pancreatic duct stones

Purpose

To assess the usefulness of factors unique to NCCT for the prediction of ESWL outcomes in patients with pancreatic duct stones.

Materials and methods

We retrospectively evaluated 148 patients with multiple PDS who had undergone ESWL therapy. All patients received an examination for NCCT both before and after ESWL. The following parameters were measured and recorded: patient characteristics including sex and age; NCCT parameters including mean stone length, mean stone volumes before and after ESWL, mean value of CT attenuation, standard deviation of CT attenuation, variation coefficient of CT attenuation, skin-to-stone distance, and pancreatic duct diameter; ESWL outcome indexes including stone clearance rate calculated using the formula \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\frac{V0 - V1}{V0} \times 100\%$$\end{document}V0-V1V0×100%, and the number of ESWL sessions. All patients were divided into groups based on their SCR: A group (SCR ≥ 90%), B group (SCR between 50% and 90%), and C group (SCR < 50%). Analysis of variance was used among the three groups to evaluate the potential predictors of SCR, and a receiver-operating curve was established to determine the optimal cutoff value.

Results

ANOVA analysis revealed that MSD was the only significant predictor for SCR (p < 0.05), and ROC indicated an optimal cutoff value of +1000.45 HU, with a sensitivity up to 78.0% and specificity of 48.6%. Stones with MSD lower than +1000.45 HU had higher SCR (69.3%) than that of higher-density ones (59.6%). Pearson correlation analysis and histogram indicated a significant positive correlation between ESWL No. and MSL (r = 0.536), MSD (r = 0.250), SDSD (r = 0.247), and PDD (r = 0.227), all values being p < 0.01.

Conclusion

MSD is the optimal predictor of ESWL efficacy, and PDS with lower MSD had a better clearance rate with fewer fragmentation sessions.

A new prediction model for operative time of flexible ureteroscopy with lithotripsy for the treatment of renal stones

This study aimed to develop a prediction model for the operative time of flexible ureteroscopy (fURS) for renal stones. We retrospectively evaluated patients with renal stones who had been treated successfully and had stone-free status determined by non-contrast computed tomography (NCCT) 3 months after fURS and holmium laser lithotripsy between December 2009 and September 2014 at a single institute. Correlations between possible factors and the operative time were analyzed using Spearman’s correlation coefficients and a multivariate linear regression model. The P value < 0.1 was used for entry of variables into the model and for keeping the variables in the model. Internal validation was performed using 10,000 bootstrap resamples. Flexible URS was performed in 472 patients, and 316 patients were considered to have stone-free status and were enrolled in this study. Spearman’s correlation coefficients showed a significant positive relationship between the operation time and stone volume (ρ = 0.417, p < 0.001), and between the operation time and maximum Hounsfield units (ρ = 0.323, p < 0.001). A multivariate assessment with forced entry and stepwise selection revealed six factors to predict the operative time of fURS: preoperative stenting, stone volume, maximum Hounsfield unit, surgeon experience, sex, and sheath diameter. Based on this finding, we developed a model to predict operative time of fURS. The coefficient of determination (R²) in this model was 0.319; the mean R² value for the prediction model was 0.320 ± 0.049. To our knowledge, this is the first report of a model for predicting the operative time of fURS treatment of renal stones. The model may be used to reliably predict operative time preoperatively based on patient characteristics and the surgeons’ experience, plan staged URS, and avoid surgical complications.

Recent advances in lithotripsy technology and treatment strategies: A systematic review update

INTRODUCTION

Shock wave lithotripsy (SWL) is a well - established treatment option for urolithiasis. The technology of SWL has undergone significant changes in an attempt to better optimize the results while reducing failure rates. There are some important limitations that restrict the use of SWL. In this review, we aim to place these advantages and limitations in perspective, assess the current role of SWL, and discuss recent advances in lithotripsy technology and treatment strategies.

METHODS

A comprehensive review was conducted to identify studies reporting outcomes on ESWL. We searched for literature (PubMed, Embase, Medline) that focused on the physics of shock waves, theories of stone disintegration, and studies on optimising shock wave application. Relevant articles in English published since 1980 were selected for inclusion.

RESULTS

Efficacy has been shown to vary between lithotripters. To maximize stone fragmentation and reduce failure rates, many factors can be optimized. Factors to consider in proper patient selection include skin - to - stone distance and stone size. Careful attention to the rate of shock wave administration, proper coupling of the treatment head to the patient have important influences on the success of lithotripsy.

CONCLUSION

Proper selection of patients who are expected to respond well to SWL, as well as attention to the technical aspects of the procedure are the keys to SWL success. Studies aiming to determine the mechanisms of shock wave action in stone breakage have begun to suggest new treatment strategies to improve success rates and safety.

Internal Structure of Kidney Calculi as a Predictor for Shockwave Lithotripsy Success

INTRODUCTION

The internal structure of renal calculi can be determined on CT using bone windows and may be classified as homogeneous or inhomogeneous with void regions. In vitro studies have shown homogeneous stones to be less responsive to extracorporeal shockwave lithotripsy (SWL). The objective was to evaluate whether the internal morphology of calculi defined by CT bone window influences SWL outcome in vivo.

MATERIALS AND METHODS

One hundred eleven patients with solitary renal calculi treated with SWL were included. Treatment data were registered prospectively and follow-up data were collected retrospectively. All patients had noncontrast computed tomography (NCCT) performed before SWL and at 3-month follow-up. The stones were categorized as homogeneous or inhomogeneous. At follow-up, the patient's stone status was registered. Stone-free status was defined as no evidence of calculi on NCCT. Treatment was considered successful if the patient was either stone free or had clinically insignificant residual fragments.

RESULTS

Using simple logistic regression, the odds for being stone free 3 months post-SWL were significantly reduced in the patients with inhomogeneous stones compared with patients with homogeneous stones (odds ratio 0.43 [95% confidence interval 0.20, 0.92; p < 0.05]). However, when adjusting for stone size by multiple logistic regression, including stone size (area) as a covariate, this difference became insignificant.

CONCLUSION

The internal structure of kidney stones did not predict the outcome of SWL in vivo.

Shock Wave Lithotripsy in Ureteral Stones: Evaluation of Patient and Stone Related Predictive Factors

Purpose:

To evaluate the patient and stone related factors which may influence the final outcome of SWL in the management of ureteral stones.

Materials and Methods:

Between October 2011 and October 2013, a total of 204 adult patients undergoing SWL for single ureteral stone sizing 5 to 15 mm were included into the study program. The impact of both patient (age, sex, BMI,) and stone related factors (laterality, location, longest diameter and density as CT HU) along with BUN and lastly SSD (skin to stone distance) on fragmentation were analysed by univariate and multivariate analyses. Results: Stone free rates for proximal and distal ureteral stones were 68.8% and 72.7%, respectively with no statistically significant difference between two groups (p=0.7). According to univariate and multivariate analyses, while higher BMI (mean: 26.8 and 28.1, p=0.048) and stone density values (mean: 702 HU and 930 HU, p<0.0001) were detected as statistically significant independent predictors of treatment failure for proximal ureteral stones, the only statistically significant predicting parameter for the success rates of SWL in distal ureteral stones was the higher SSD value (median: 114 and 90, p=0.012).

Conclusions:

Our findings have clearly shown that while higher BMI and increased stone attenuation values detected by NCCT were significant factors influencing the final outcome of SWL treatment in proximal ureteral stones; opposite to the literature, high SSD was the only independent predictor of success for the SWL treatment of distal ureteral stones.

Clinical factors prolonging the operative time of flexible ureteroscopy for renal stones: a single-center analysis

The objective of the study was to evaluate the clinical factors affecting the operative time of flexible ureteroscopy (fURS). We retrospectively evaluated 233 patients with renal stones who had been treated successfully and had stone-free status 3 months after fURS and holmium laser lithotripsy between December 2009 and December 2013 at a single institute. Operative time was divided into three periods (total, before fragmentation, and after starting fragmentation), and associations between possible factors and these periods were analyzed by a multivariate logistic regression model with backward selection. The mean total operative time was 74.0 ± 32.0 min. There were significant differences in the following clinical factors: sex, body height, stone volume, maximum and mean Hounsfield units (HUs), diameter of the ureteral access sheath, and experience of the surgeon, between patients who underwent procedures with a total operative time of less or more than 90 min. A multivariate assessment revealed four independent factors influencing total operative time (P < 0.05): stone volume (P < 0.001), experience of the surgeon (P < 0.001), maximum HUs (P = 0.014), and lack of preoperative stenting (P = 0.027). Larger stone volume, lower experience level of the surgeon, higher HUs, and the absence of preoperative stenting were identified as parameters prolonging the total operative time of fURS and, in particular, the operative time after starting fragmentation. On the other hand, operative time before starting fragmentation, which represented the time required to identify the stone by ureteroscopy and insert the access sheath, was more difficult to predict preoperatively.

Strategies to optimize shock wave lithotripsy outcome: Patient selection and treatment parameters

Shock wave lithotripsy (SWL) was introduced in 1980, modernizing the treatment of upper urinary tract stones, and quickly became the most commonly utilized technique to treat kidney stones. Over the past 5-10 years, however, use of SWL has been declining because it is not as reliably effective as more modern technology. SWL success rates vary considerably and there is abundant literature predicting outcome based on patient- and stone-specific parameters. Herein we discuss the ways to optimize SWL outcomes by reviewing proper patient selection utilizing stone characteristics and patient features. Stone size, number, location, density, composition, and patient body habitus and renal anatomy are all discussed. We also review the technical parameters during SWL that can be controlled to improve results further, including type of anesthesia, coupling, shock wave rate, focal zones, pressures, and active monitoring. Following these basic principles and selection criteria will help maximize success rate.

Noncontrast computed tomography factors that predict the renal stone outcome after shock wave lithotripsy

OBJECTIVES

Extracorporeal shock wave lithotripsy (ESWL) is a popular treatment for nephrolithiasis. We took advantage of noncontrast abdominal computed tomography (NCCT) to search the possible prognostic factors including abdominal fat distribution influencing stone-free rate.

METHODS

From August 2008 to August 2010, 145 patients who had renal calculus and had undergone ESWL were retrospectively reviewed. All of them received NCCT assessment before ESWL and were followed up after 1 month for stone clearance. These patients were divided into two groups: one was the stone-free group and the other was the residual-stone group. Affecting parameters included stone size, location, stone surface area, Hounsfield unit density (HU density), skin-to-stone distance (SSD), and abdominal fat area as analyzed between these two groups.

RESULTS

Of 145 patients, 70 were stone-free and 75 had residual stone after ESWL treatment and 1-month follow-up. From univariate analysis, stone size, HU density, SSD, and stone surface area were significant predicting factors for ESWL success. On multivariate analysis, the important factors influencing ESWL outcomes were HU density and stone surface area (odds ratio 1.002 vs. 77.18, respectively; P<.05). Abdominal fat accumulation and distribution had no significant difference between these two groups.

CONCLUSION

This study revealed that stone size, HU density, SSD, and stone surface area were associated with stone-free rate after ESWL treatment. Therefore, these factors could be used to assess the feasibility of ESWL before deciding the treatment strategy. Abdominal fat distribution had no significant impact on ESWL outcome for renal stones.

The hounsfield unit value calculated with the aid of non-contrast computed tomography and its effect on the outcome of percutaneous nephrolithotomy

To evaluate the effect of the Hounsfield unit (HU) value, calculated with the aid of non-contrast computed tomography, on the outcome of percutaneous nephrolithotomy (PCNL). Data for 83 patients evaluated in our clinic between November 2011 and February 2014 that had similar stone sizes, localizations, and radio opacities were retrospectively reviewed. The patients were grouped according to their HU value, in a low HU group (HU ≤ 1000) or a high HU group (HU > 1000). The two groups were compared based on their PCNL success rates, complications, duration of surgery, duration of fluoroscopy, and decrease in the hematocrit. There were no significant differences in terms of mean age, female-male ratio, or mean body mass index between the two groups (p > 0.05). The stone size and stone surface area did not differ significantly between the groups (p = 0.820 and p = 0.394, respectively). The unsuccessful PCNL rate and the prevalence of complications did not differ significantly between the two groups (p > 0.05). The duration of surgery, duration of fluoroscopy, and decrease in the hematocrit were significantly greater in the high HU group compared to the low HU group (p < 0.001). Calculating the HU value using this imaging method may predict cases with longer surgery durations, longer fluoroscopy durations, and greater decreases in hematocrite levels, but this value is not related to the success rate of PCNL.

Should low-dose computed tomography kidneys, ureter and bladder be the new investigation of choice in suspected renal colic?: A systematic review

Introduction:

Computed tomography kidneys, ureter and bladder (CTKUB) is the accepted gold standard investigation for suspected renal colic. Dose considerations are particularly pertinent in the context of detecting urolithiasis given the high risk of disease recurrence, which can necessitate multiple radiological examinations over the lifetime of a stone-former. We performed a systematic review of the literature to see whether there was any evidence that reducing the effective radiation dose of a CTKUB compromised the diagnostic accuracy of the scan.

Materials and Methods:

Relevant databases including MedLine, EMBASE, DARE and the Cochrane Library were searched from inception to October 2012. All English language articles reporting on prospective studies where non-contrast, low-dose CT (LDCT) was used to investigate adults (males and non-pregnant females) presenting with flank pain or suspected urolithiasis were included. LDCT was defined as an effective radiation dose <3 mSv per examination.

Results:

Our initial search identified 497 records. After removing duplicates, 390 abstracts were screened, of which 375 were excluded, principally because outcomes of interest were not presented. Six papers remained for the final analysis, reporting on a total of 903 patients. Individual studies showed a prevalence of urolithiasis ranging between 36% and 88%, with additional pathologies found in 5-16%. The effective radiation dose of the LDCT techniques used ranged from 0.5 to 2.8 mSv. The sensitivity of LDCT for diagnosing stone disease was 90-97% with a specificity of 86-100%.

Conclusions:

The sensitivity and specificity of CTKUB for diagnosing urolithiasis remains high, even when the effective radiation dose is lowered. LDCT may miss some small stones (<3 mm), especially in obese patients (>30 kg/m²), but in this group LDCT still identifies most alternative diagnoses. With at least one level 1A and two level 1B studies supporting the use of LDCT, there is Grade A recommendation for its use as the first-line investigation in suspected renal colic in non-obese patients.

Prediction of the energy required for extracorporeal shock wave lithotripsy of certain stones composition using simple radiology and computerized axial tomography

OBJECTIVE

To demonstrate that urinary lithiasis have a specific susceptibility to fracture through extracorporeal shock wave lithotripsy (ESWL), which is common for all calculi with the same composition and which can be estimated before treatment using CT or plain x-ray.

MATERIAL AND METHOD

We present an in vitro, prospective, randomized, blind and multi-centre study involving 308 urinary calculi. 193 of these met the inclusion criteria: whole calculi composed purely of calcium oxalate monohydrate (COM), uric acid (UA) or carbonate apatite (CA), or a mix of oxalate (COMix) and of a size greater than 0.5 cm. The samples were broken using lithotripsy until reaching a pre-established level of comminution. The variables employed were energy dose (Edose) per cm(3) of lithiasis and Edose adjusted to lithiasic surface (EdAJ) per cm(3).

RESULTS

COM was the hardest, requiring an Edose of 119,624 mJ/cm(3) and an EdAJ of 36,983 mJ/cm(3), followed by COMix (75,501/36,983), CA (22,734/21,186) and UA (22,580/6,837) (P < .05). Gmax y Gmda were correlated with Edose (r = 0.434/r = 0.420) and EdAJ (r = 0.599/r = 0.545) (P < .01). UH were correlated, in bone window and soft tissue window, with Edose/cm(3) (r = 0.478/r = 0.539) y EdAJ/cm(3) (r = 0.745/r = 0.758) (P < .01).

CONCLUSIONS

In our in vitro research lithiasis require, due to the specific nature of their composition, a given amount of energy in order to be broken by ESWL, which is inherent to all those sharing the same composition, and can be predicted using CT or plain x-ray.

Radiopacity and hounsfield attenuation of cystine urolithiasis: case series and review of the literature

OBJECTIVES

Given the high recurrence rate of cystine urolithiasis, understanding of the radiographic stone characteristics is important in following cystine stone formers over their lifetime. However, due to their infrequent incidence, in vivo radiographic properties of cystine stones have not been well characterized. The purpose of our study is to characterize the in vivo radiographic properties of cystine urolithiasis.

METHODS

Patients with a cystine stone analysis and noncontrast computed tomography (NCCT) were extracted from our stone clinic database. Stone attenuation in Hounsfield units (HU) was measured for each stone and plain abdominal films (kidney, ureter, and bladder radiograph [KUB]) within 30 days of the NCCT prior to any intervention were reviewed by a blinded radiologist to assess whether urolithiasis could be visualized.

RESULTS

Twenty patients met our study inclusion criteria. When plotted by attenuation, two distinct groups of stone attenuation were noted for cystine stone formers (p<0.001). The largest group (n=16) had an attenuation of <550 HU (424±106 HU), while a distinct second group (n=4) was >850 HU (972±134 HU). Sixteen patients had a KUB, with 88% of the stones being visualized by a blinded radiologist. Stone size and attenuation were not significantly different between visualized and nonvisualized stones via KUB, however, the body mass index was significantly higher in the nonvisualized group (34.4 vs 26.9 kg/m(2), p=0.03).

CONCLUSIONS

Cystine stones were visualized by KUB, which has implications in post-treatment follow-up imaging. Though most cystine stones had an attenuation of <550 HU, a second distinct group of cystine stones were noted to have a high attenuation of >850 HU. HU measurements alone are not sufficient to differentiate cystine stones from other stone compositions.

Predictive factors of the outcome of extracorporeal shockwave lithotripsy for ureteral stones

Purpose

Extracorporeal Shock Wave Lithotripsy (ESWL) has shown successful outcomes for ureteral stones. We investigated predictive factors for failure of ESWL for treating ureteral stones.

Materials and Methods

A total of 153 patients who underwent ESWL between July 2006 and July 2009 for ureteral stones diagnosed by non-enhanced spiral computed tomography were divided into two groups: (group A, stone size ≤10 mm; and group B, stone size >10 mm). The failure was defined as remnant stones >4 mm. We assessed age, sex, body mass index, stone size, laterality, location, skin-to-stone distance (SSD), Hounsfield unit, and the presence of secondary signs (hydronephrosis, renal enlargement, perinephric fat stranding, and tissue rim sign). We analyzed predictive factors by using logistic regression in each group.

Results

The success rates were 90.2% and 68.6% in group A and B, respectively. In the univariate analysis of each group, stone size, SSD, and all secondary signs showed statistically significant differences in terms of the outcome of ESWL (p<0.05). In the multivariate logistic regression, stone size (odds ratio [OR], 50.005; 95% confidence interval [CI], 6.207 to 402.852) was an independent predictive factor in group A. The presence of perinephric fat standing (OR, 77.634; 95% CI, 1.349 to 446.558) and stone size (OR, 19.718; 95% CI, 1.600 to 243.005) were independent predictive factors in group B.

Conclusions

Stone size is an independent predictive factor influencing failure of ESWL for treating ureteral stones. In larger ureteral stones (>10 mm), the presence of perinephric fat stranding is also an independent predictive factor.

Does the Hounsfield unit value determined by computed tomography predict the outcome of percutaneous nephrolithotomy?

PURPOSE

We aimed to evaluate whether the Hounsfield unit (HU) value predicts outcome in percutaneous nephrolithotomy (PCNL).

PATIENTS AND METHODS

One hundred and seventy-nine patients who had undergone PCNL in our clinics in the last 4 years were included. Demographic and clinical data of the patients and complications, if any, were recorded. The mean age of the patients was 45.3 ± 14.3 years (range 5-82 y), and 111 of them were males (62%). The mean stone size and HU values were found to be 693.1 ± 628.0 (95-4200) mm(2) and 706.3 ± 245.0 (214-1325), respectively.

RESULTS

In logistic regression analysis, the size of the stone, the opacity of the stone, and the HU values were found to be independent predictors of the failure of the procedure (P<0.05). A cutoff value of 677.5 was used for the HU in the receiver operating characteristics analysis. Having a HU value under the cutoff value increased the likelihood of procedure failure by 2.65 times, whereas stones residing in the staghorn localization increased failure by 5.68. It was also observed that if the stone's size was 485 mm(2) or more, the chance of failure increased by 1.9, whereas when the stone was nonopaque, failure increased by 6.04 times (P<0.05). There was a positive correlation between hematocrit decrease and a decrease in HU values (P<0.05), but no correlation was observed between the HU values and duration of surgery or fluoroscopy (P>0.05).

CONCLUSION

In addition to the size and location of the stones, the HU value determined in the unenhanced CT scan may be one of the parameters affecting PCNL outcomes. PCNL is a more efficient method in stones with higher HU values. Therefore, the HU values may be a useful tool for the selection of the treatment modality in patients with renal stones.

Analyzing the effect of distance from skin to stone by computed tomography scan on the extracorporeal shock wave lithotripsy stone-free rate of renal stones

Purpose

To determine whether the distance from skin to stone, as measured by computed tomography (CT) scans, could affect the stone-free rate achieved via extracorporeal shock wave lithotripsy (ESWL) in renal stone patients.

Materials and Methods

We retrospectively reviewed the records 573 patients who had undergone ESWL at our institution between January 2006 and January 2010 for urinary stones sized from about 5 mm to 20 mm and who had no evidence of stone movement. We excluded patients with ureteral catheters and percutaneous nephrostomy patients; ultimately, only 43 patients fulfilled our inclusion criteria. We classified the success group as those patients whose stones had disappeared on a CT scan or simple X-ray within 6 weeks after ESWL and the failure group as those patients in whom residual stone fragments remained on a CT scan or simple X-ray after 6 weeks. We analyzed the differences between the two groups in age, sex, size of stone, skin-to-stone distance (SSD), stone location, density (Hounsfield unit: HU), voltage (kV), and the number of shocks delivered.

Results

The success group included 33 patients and the failure group included 10. In the univariate and multivariate analysis, age, sex, size of stone, stone location, HU, kV and the number of shocks delivered did not differ significantly between the two groups. Only SSD was a factor influencing success: the success group clearly had a shorter SSD (78.25±12.15 mm) than did the failure group (92.03±14.51 mm). The results of the multivariate logistic regression analysis showed SSD to be the only significant independent predictor of the ESWL stone-free rate.

Conclusions

SSD can be readily measured by CT scan; the ESWL stone-free rate was inversely proportional to SSD in renal stone patients. SSD may therefore be a useful clinical predictive factor of the success of ESWL on renal stones.

Predicting effectiveness of extracorporeal shockwave lithotripsy by stone attenuation value

PURPOSE

The aim of this study was to evaluate the effect of stone attenuation value on the effectiveness of extracorporeal shockwave lithotripsy (SWL) for upper urinary tract stones.

METHODS

In this prospective study, 99 patients underwent SWL for solitary renal and upper ureteral stones from January 2007 to March 2009. All patients underwent CT scan before SWL. The mean attenuation value of stones in our study was 1213.3 +/- 314.5 Hounsfield units (HU). Group A consisted of 42 patients with stones of attenuation value <1200 HU and group B had 57 patients with stones of attenuation value >1200 HU. Stone size, location, requirement of number of shockwaves, shock intensities (power), retreatment rate, complication rate, auxiliary procedure rate, and effectiveness quotient (EQ) ratio were studied.

RESULTS

The mean total number of shocks required to fragment the stones in groups A and B were 1317.1 +/- 345.3 and 1646.5 +/- 610.8, respectively (p = 0.001), with a mean shock intensity of 12.2 +/- 0.7 and 12.4 +/- 0.5 kV, respectively (p = 0.03). Retreatment was not required in patients of group A, but 14.03% patients in group B required retreatment (p < 0.0001). Clearance rate in group A was 88.1%, whereas in group B it was 82.5% (p = 0.35). Auxiliary procedure rates were 9.5% and 10.5% in groups A and B (p = 0.22), respectively. EQ was 80.4% and 66.2% in groups A and B (p = 0.03), respectively. Complication rates were similar with 2.4% and 3.5% in groups A and B, respectively (p = 0.37). Significant correlation was recorded for total number and intensity of shocks with stone attenuation value.

CONCLUSIONS

The EQ of SWL for upper urinary tract stones was significantly better for stones with lower attenuation value. The number and intensity of shocks required to fragment these stones with lower attenuation value were also significantly lower.

Evaluating the importance of mean stone density and skin-to-stone distance in predicting successful shock wave lithotripsy of renal and ureteric calculi

Shock wave lithotripsy (SWL) is considered the first line treatment for the majority of patients with renal and ureteric calculi, with success rates from contemporary series varying from 60 to 90%. Success is dependent on many patient and stone-related factors. We conducted a retrospective analysis of mean stone CT density (MSD) and skin-to-stone distance (SSD) to determine their influence on the success of SWL of renal and ureteric calculi. Data from all patients treated at the St. Michael's Hospital Lithotripsy Unit from May 2004 to June 2009 were reviewed. Analysis was restricted to those patients with a pre-treatment non-contrast CT scan conducted at our center demonstrating a solitary renal or ureteric calculus < or =20 mm in maximal diameter. Successful treatment of renal stones was defined as those patients who were stone free or had asymptomatic, clinically insignificant residual fragments < or =4 mm in diameter, as measured by KUB X-ray, 3 months after a single SWL treatment. Successful treatment of ureteric stones was defined as being stone free on KUB X-ray, 2-weeks post-SWL. Demographic, stone, patient, treatment and follow-up data were collected from a prospective database and review of CT and KUB imaging by two independent urologists and one radiologist. Data were analyzed with logistic regression, Chi square analysis and ANOVA where appropriate. 422 patients (69.7% male) with a mean age of 51.4 years (SD 12.9) and mean BMI 27.0 kg/m(2) (SD 4.9) were analyzed. Mean stone size was 78.9 mm(2) (SD 77.3) for ureteral stones and 66.1 mm(2) (SD 63.2) for renal stones, with 95 (43.6%) of the renal stones located in the lower pole. The single-treatment success rates for ureteral and renal stones were 62.3% and 68.8%, respectively. On univariate analysis, predictors of SWL success, regardless of stone location, were age (p = 0.01), BMI (p = 0.01), stone size (p < 0.01), MSD (p < 0.01) and SSD (p < 0.01). On multivariate analysis, MSD >900 HU (OR = 0.49, CI: 0.32-0.75) and SSD >110 mm (OR = 0.49, CI: 0.31-0.78) were both significant predictors of outcome. We have identified in a large series of renal and ureteric calculi that both MSD and SSD can reliably predict SWL outcomes. This data can be used in combination with other patient and stone-related factors to facilitate optimal treatment-based decisions and provide patients with more accurate single-treatment success rates for SWL.

Dual-energy computed tomography with advanced postimage acquisition data processing: improved determination of urinary stone composition

INTRODUCTION

The characterization of urinary calculi using noninvasive methods has the potential to affect clinical management. CT remains the gold standard for diagnosis of urinary calculi, but has not reliably differentiated varying stone compositions. Dual-energy CT (DECT) has emerged as a technology to improve CT characterization of anatomic structures. This study aims to assess the ability of DECT to accurately discriminate between different types of urinary calculi in an in vitro model using novel postimage acquisition data processing techniques.

METHODS

Fifty urinary calculi were assessed, of which 44 had >or=60% composition of one component. DECT was performed utilizing 64-slice multidetector CT. The attenuation profiles of the lower-energy (DECT-Low) and higher-energy (DECT-High) datasets were used to investigate whether differences could be seen between different stone compositions.

RESULTS

Postimage acquisition processing allowed for identification of the main different chemical compositions of urinary calculi: brushite, calcium oxalate-calcium phosphate, struvite, cystine, and uric acid. Statistical analysis demonstrated that this processing identified all stone compositions without obvious graphical overlap.

CONCLUSION

Dual-energy multidetector CT with postprocessing techniques allows for accurate discrimination among the main different subtypes of urinary calculi in an in vitro model. The ability to better detect stone composition may have implications in determining the optimum clinical treatment modality for urinary calculi from noninvasive, preprocedure radiological assessment.

Skin to stone distance is an independent predictor of stone-free status following shockwave lithotripsy

INTRODUCTION

In recent years several new parameters such as Hounsefield unit density and skin to stone distance (SSD) have been determined to correlate with successful extracorporeal shockwave lithotripsy (SWL). SSD has been shown to independently predict successful SWL for lower pole calculi. The objective of this study was to determine which stone characteristics on noncontrast computed tomography (NCCT), including SSD, independently predict for SWL success regardless of stone location within the kidney.

MATERIALS AND METHODS

A retrospective review of all 1282 SWL procedures between 2004 and 2007 at a single institution revealed 83 patients meeting inclusion criteria for current study. All patients were treated using a single electromagnetic lithotriptor (DoLi 50; Dornier Medical Systems, Marrieta, GA) with a single technician. Stone-free (SF) status was determined by NCCT or abdominal plain film radiographs at 6 weeks post-SWL. Logistic regression analysis was computed to assess SF rates using SSD, stone size, location, and Hounsefield unit density as predictors.

RESULT

Of the 83 patients, 51 were SF and 32 had residual stones at a mean follow-up of 2.3 months. The mean SSD in the SF group was 83.3 +/- 21.9 mm in comparison to those in the residual stone group who had a mean SSD of 107.7 +/- 28.9 mm (p < or = 0.05). Multivariate logistic regression analysis revealed that SSD was the only significant independent predictor of treatment outcome.

CONCLUSION

SSD is an easily measured parameter on NCCT that independently correlates with SWL efficacy in treating stones in all locations.

Impact of hydronephrosis on treatment outcome of solitary proximal ureteral stone after extracorporeal shock wave lithotripsy

The purpose of this study was to investigate the impact of hydronephrosis on the treatment outcome of patients with a solitary proximal ureteral stone after extracorporeal shock wave lithotripsy (ESWL). A total of 182 consecutive patients who underwent ESWL for a solitary proximal ureteral stone of between 5 and 20 mm in size in our institution were included in this study. The degree of hydronephrosis was defined by renal ultrasonography. Patient data, stone size, shock wave numbers and shock wave energy were also recorded. Treatment outcome was evaluated 3 months after the first session of ESWL. In multivariate analysis, only the maximal stone length (odds ratio [OR], 0.15; 95% confidence interval [CI], 0.03-0.91; p = 0.04) and the degree of hydronephrosis (OR, 0.40; 95% CI, 0.16-0.98; p = 0.045) were significant predicting factors for stone-free status 3 months after ESWL. For stones < or = 10 mm, the stone-free rate decreased from 80% in patients with mild hydronephrosis to 56.4% in those with moderate to severe hydronephrosis. For stones > 10 mm, the stone-free rate decreased further, from 65.2% in patients with mild hydronephrosis to 33.3% in those with moderate to severe hydronephrosis. In summary, patients with a solitary proximal ureteral stone and a stone > 10 mm, the treatment outcome after ESWL was not good if moderate to severe hydronephrosis was noted on ultrasonography. Alternative treatments, such as ureteroscopic lithotripsy, may be appropriate as initial treatment or after failure of one session of ESWL.

Composition and clinically determined hardness of urinary tract stones

OBJECTIVES

To derive hardness factors for crystal phases of urinary tract stones and describe the hardness pattern in a stone population.

MATERIAL AND METHODS

In a retrospective study, recordings from patients treated with extracorporeal shock-wave lithotripsy (ESWL) (stone surface area < or = 100 mm2) were used to derive hardness factors. The number of re-treatments, the number of shock waves and the energy index (the voltage in kilovolts multiplied by the number of shock waves) required for a satisfactory stone disintegration were assumed to reflect the hardness. The stone composition in 2100 patients provided the basis for an average hardness pattern. A hardness index was calculated from the fraction of each crystal phase and its hardness factor.

RESULTS

The hardness factors were as follows: calcium oxalate monohydrate, 1.3; calcium oxalate dehydrate, 1.0; hydroxyapatite, 1.1; brushite, 2.2; uric acid/urate, 1.0; cystine, 2.4; carbonate apatite, 1.3; magnesium ammonium phosphate, 1.0; and mixed infection stones, 1.0. The hardness index for 114 stones (surface area 100-200 mm2) corresponded reasonably well to the ESWL treatment efforts. Calcium oxalate monohydrate, calcium oxalate dihydrate and hydroxyapatite were the most frequently encountered crystal phases in all 2100 stones. Only 21% of the stones were composed of only one crystal phase. There were two, three and more than three crystal phases in 26%, 38% and 15% of the stones, respectively. The hardness index calculated for 2100 stones ranged between 0.70 and 2.33, with a mean (SD) of 1.18 (0.15).

CONCLUSIONS

The hardness factors and hardness index derived in this study might be useful for describing the stone situation in individual patients and groups of patients and for comparison of various treatment strategies.

Stone measurement by volumetric three-dimensional computed tomography for predicting the outcome after extracorporeal shock wave lithotripsy

OBJECTIVE

To evaluate the efficacy of stone volume measured using a three-dimensional (3D) reconstruction of preoperative non-contrast computed tomography (NCCT) as an independent predictor of success after extracorporeal shock wave lithotripsy (ESWL) of upper urinary tract calculi.

PATIENTS AND METHODS

We evaluated preoperative NCCT in 94 patients who had ESWL for solitary upper urinary tract calculi of 4-20 mm in diameter. Axial images were used to measure the skin-to-stone distance (SSD), Hounsfield Unit (HU) density and axial stone diameter. Stone volume was calculated on a volume-rendered 3D image for each stone. Maximum stone length was determined by comparative measurements of each stone in coronal, sagittal and axial planes, and was also measured on a plain abdominal film before ESWL. For ESWL we used the DoliS lithotripter (Dornier Medical Systems, Marrietta, GA, USA). A plain film at 6 weeks was used to categorize patients as stone-free (SF) or with residual stone.

RESULTS

In all, 58 (62%) patients were SF and 36 (38%) had RS; the mean stone volume was significantly different between these groups (274 vs 464 microL, P = 0.002). Logistic regression analysis showed that stone volume was the strongest predictor of SF status (P < 0.001), compared to peak HU (P = 0.015), mean HU (P = 0.04) and axial stone diameter (P = 0.006). The body mass index, SSD and maximum stone length on NCCT or a plain film did not predict success. A stone volume of <500 microL best predicted treatment success (P < 0.001) with 72% of patients with a stone volume of <500 microL having a successful outcome, vs only 27% with a stone volume of >500 microL.

CONCLUSION

Our study suggests that stone volume is an optimal predictor of SF status after ESWL of solitary upper urinary tract calculi.

Effect of skin-to-stone distance on shockwave lithotripsy success

PURPOSE

We evaluated the effect of increased body habitus on stone-free rates after shockwave lithotripsy (SWL), determined by three reproducible skin-to-stone distances (SSDs) on CT.

PATIENTS AND METHODS

We retrospectively reviewed the records of 85 patients with preoperative CT scans available on Stentor Radiology Imaging who underwent SWL with the unmodified Dornier HM3 lithotripter from 2002 to 2007. SSDs were measured at the following angles: 0 degrees (vertical), 30 degrees, and 90 degrees (horizontal). Successful therapy was defined as stone free (residual fragments <2 mm) on follow-up imaging. Data were analyzed using descriptive statistics, Student t test, and the Fisher exact test.

RESULTS

Four hundred and eighty patients underwent SWL at our institution from 2002 to 2007; 85 patients (50.6% men, mean age 50.8 +/- 15.7 years, mean body mass index [BMI] 28.8 +/- 6.6 kg/m2) had preoperative CT scans available for review. On follow-up imaging (142.7 +/- 217.2 days), 49.4% of patients were stone free. Mean SSDs (vertical, 30 degrees, horizontal) in patients who were stone-free v those with residual stone were 104.3 +/- 26.2 mm v 102.6 +/- 29.9 mm (P = 0.79), 103.9 +/- 28.2 mm v 101.0 +/- 31.5 mm (P = 0.66), and 106.6 +/- 25.3 mm v 107.1 +/- 29.3 mm (P = 0.94), respectively.

CONCLUSIONS

Multiple variables have been shown to be associated with SWL success. In our sample of patients with preoperative CT scans, SSD was found to have no effect on SWL success.

Diagnostic performance of low-dose CT for the detection of urolithiasis: a meta-analysis

OBJECTIVE

The objective of our study was to perform a meta-analysis to evaluate the diagnostic performance of low-dose CT for the diagnosis of urolithiasis (seven studies, 1,061 patients).

MATERIALS AND METHODS

The medical literature from 1995 to 2007 was searched using PubMed, Medline, and Cochrane Library databases for articles on studies that used low-dose CT (< 3 mSv dose applied for the entire CT examination) as a diagnostic test for the detection of urolithiasis. Prospective and retrospective studies were included if they separately reported the rate of true-positive, true-negative, false-positive, and false-negative diagnoses of urolithiasis from low-dose CT compared with the positive and negative rates of normal-dose CT or a combination of diagnostic tests. Two readers assessed the quality of the studies.

RESULTS

The pooled sensitivity and specificity of low-dose CT for the diagnosis of urolithiasis were 0.966 (95% CI, 0.950-0.978) and 0.949 (95% CI, 0.920-0.970), respectively.

CONCLUSION

The results of this meta-analysis suggest that a low-dose CT protocol can be used as the initial imaging technique in the workup of patients with suspected urolithiasis.

Stone attenuation and skin-to-stone distance on computed tomography predicts for stone fragmentation by shock wave lithotripsy

OBJECTIVES

To determine whether stone attenuation and the skin-to-stone distance (SSD) can predict for stone fragmentation by SWL independently. Identifying the factors predictive of shock wave lithotripsy (SWL) outcome would help streamline the care of patients with stones.

METHODS

A retrospective review was performed of 111 patients undergoing initial SWL for a solitary, 5-20 mm, renal calculus. Stone size, location, attenuation value, and SSD were determined on pretreatment noncontrast computed tomography. The outcome was categorized as stone free, complete fragmentation <5 mm, and incomplete fragmentation >or=5 mm or unchanged at 2 weeks on kidney/ureter/bladder radiography.

RESULTS

After SWL, 44 (40%) were stone free, 27 (24%) had complete fragmentation, and 40 (36%) of 111 patients had incomplete fragmentation. The stone attenuation of the successfully treated patients (stone free and complete fragmentation groups) was 837 +/- 277 Hounsfield units (HU) vs 1092 +/- 254 HU for those with treatment failure (incomplete fragmentation; P < .01). The mean SSD also differed: 9.6 cm +/- 2.0 vs 11.1 cm +/- 2.5 for the successful treatment group vs the treatment failure group, respectively (P = .01). On multivariate analysis, the factors that independently predicted the outcome were stone attenuation, SSD, and stone composition. When patients were stratified into 4 risk groups (stone <900 HU and SSD <9.0 cm, stone <900 HU and SSD >or=9.0 cm, stone >or=900 HU and SSD <9.0 cm, and stone >or=900 HU and SSD >or=9.0 cm), the SWL success rate was 91%, 79%, 58%, and 41%, respectively (odds ratio 7.1, 95% confidence interval 1.6-32 for <900 HU and SSD <9.0 cm group vs other 3 risk groups; P = .01).

CONCLUSIONS

The results of our study have shown that a stone attenuation of <900 HU, SSD of <9 cm, and stone composition predict for SWL success, independent of stone size, location, and body mass index. These factors will be considered important in the prospective design of a SWL treatment nomogram at our center.

Treatment Selection and Outcomes: Renal Calculi

This article summarizes the history of how renal stones have been treated over the centuries and reviews current treatments and outcomes for renal stones. The authors provide an algorithm based on available outcome data for shock wave lithotripsy, ureteroscopy, and percutaneous nephrolithotomy.

CT visible internal stone structure, but not Hounsfield unit value, of calcium oxalate monohydrate (COM) calculi predicts lithotripsy fragility in vitro

Calcium oxalate monohydrate (COM) stones are often resistant to breakage using shock wave (SW) lithotripsy. It would be useful to identify by computed tomography (CT) those COM stones that are susceptible to SW's. For this study, 47 COM stones (4-10 mm in diameter) were scanned with micro CT to verify composition and also for assessment of heterogeneity (presence of pronounced lobulation, voids, or apatite inclusions) by blinded observers. Stones were then placed in water and scanned using 64-channel helical CT. As with micro CT, heterogeneity was assessed by blinded observers, using high-bone viewing windows. Then stones were broken in a lithotripter (Dornier Doli-50) over 2 mm mesh, and SW's counted. Results showed that classification of stones using micro CT was highly repeatable among observers (kappa = 0.81), and also predictive of stone fragility. Stones graded as homogeneous required 1,874 +/- 821 SW/g for comminution, while stones with visible structure required half as many SW/g, 912 +/- 678. Similarly, when stones were graded by appearance on helical CT, classification was repeatable (kappa = 0.40), and homogeneous stones required more SW's for comminution than did heterogeneous stones (1,702 +/- 993 SW/g, compared to 907 +/- 773). Stone fragility normalized to stone size did not correlate with Hounsfield units (P = 0.85). In conclusion, COM stones of homogeneous structure require almost twice as many SW's to comminute than stones of similar mineral composition that exhibit internal structural features that are visible by CT. This suggests that stone fragility in patients could be predicted using pre-treatment CT imaging. The findings also show that Hounsfield unit values of COM stones did not correlate with stone fragility. Thus, it is stone morphology, rather than X-ray attenuation, which correlates with fragility to SW's in this common stone type.

A Prospective Multivariate Analysis of Factors Predicting Stone Disintegration by Extracorporeal Shock Wave Lithotripsy: The Value of High-Resolution Noncontrast Computed Tomography

OBJECTIVE

To assess the value of noncontrast computed tomography (NCCT) as a possible predictor of renal stone disintegration by shock wave lithotripsy (SWL).

PATIENTS AND METHODS

The study included 120 consecutive patients (71 males, 49 females; mean age: 42.6 yr) with a solitary renal stone of 0.5-2.5 cm in length. NCCT was performed using a multidetector row CT scanner at 120 KV and 240 mA, with 1.25-mm collimation. A bone window was used to measure stone attenuation values. SWL was performed with an electromagnetic lithotripter. Failure of disintegration was defined as no fragmentation of the stone after three sessions. The impact of patients' sex, age, and body mass index (BMI) and the stones' laterality, location, volume, mean attenuation value, and the skin-to-stone distance on disintegration were evaluated by univariate and multivariate analyses.

RESULTS

Failure of disintegration was observed in 15 patients (12.5%). BMI and stone density >1000 HU were the significant independent predictors of failure (p=0.04 and 0.02, respectively). The success rate of extracorporeal SWL at 3 mo was 87.5% (105 of 120 patients); 90 patients were stone free and 15 had residual fragments<4 mm. The only significant predictor of residual fragments was stone density (p<0.001).

CONCLUSIONS

Obesity and increased stone density as detected by NCCT are significant predictors of failure to fragment renal stones by SWL. An alternative treatment should be devised for obese patients with stone density>1000 HU.

In-Vivo Relation between CT Attenuation Value and Shockwave Fragmentation

PURPOSE

To use CT attenuation numbers as a means of determining the susceptibility of an artificial stone to in-vivo fragmentation with extracorporeal shockwave lithotripsy (SWL).

MATERIALS AND METHODS

Four types of artificial kidney stones having different CT attenuation values were used. One randomly selected stone was implanted in the renal pelvis of a kidney of 12 young pigs and exposed in vivo to 2500 shockwaves (21 kV) using an electrohydraulic lithotripter. Bilateral nephrectomy was performed after SWL. Fragments were strained through a mesh with a 3.1-mm grid, and the debris left on the mesh was dried and weighed. Fragmentation coefficients (FCs) were associated with CT attenuation values using a statistical model.

RESULTS

The relation between FC and CT number was significant, indicating that as CT attenuation increases, FC is reduced. Larger stone fragments were obtained from stones with higher CT numbers. Initial stone weight was not a significant explanation for variations in FC.

CONCLUSION

The CT values could be helpful in selecting patients for SWL in the future. However, other parameters such as stone porosity, shape, and roughness also will have to be considered.

Prediction of shockwave failure in patients with urinary tract stones

PURPOSE OF REVIEW

To evaluate recent developments in predicting the failure of shockwave lithotripsy when treating patients with urinary tract stones.

RECENT FINDINGS

Although the features of patients with stones, as well as of the stones themselves, associated with refractoriness to shockwave lithotripsy are fairly well defined, refining the preoperative detection of these traits and optimizing the efficacy of shockwave lithotripsy are still under investigation. Several studies have recently focused on improving the radiological appraisal of stone size and composition through the use of axial computed tomography and reconstruction software. Other investigators have researched techniques to increase the efficacy of the technology underlying shockwave lithotripsy, such as varying the shockwave delivery rate and method.

SUMMARY

Investigators have demonstrated different factors and predictors that affect shockwave lithotripsy for stone disease. Continued research will better define patient selection and the role of shockwave lithotripsy in the treatment of urolithiasis.

Shock wave lithotripsy success determined by skin-to-stone distance on computed tomography

OBJECTIVES

To evaluate whether the skin-to-stone distance (SSD), body mass index (BMI), and Hounsfield unit (HU) density can be used as independent predictors of stone-free (SF) status after shock wave lithotripsy (SWL) of lower pole kidney stones. No studies have evaluated the SSD by non-contrast-enhanced computed tomography (NCCT) as a predictor of SWL success. Studies have suggested that the BMI and HU density of urinary calculi on NCCT may predict the SF rate after SWL.

METHODS

The radiographs of 64 patients treated with SWL (DoliS lithotripter) from March 2000 to April 2004 with lower pole kidney stones measuring 0.5 to 1.5 cm on NCCT were reviewed. The average SSD was calculated by measuring three distances from the center of the stone to the skin (0 degrees, 45 degrees, and 90 degrees angles) on NCCT. The BMI and HU density were determined, and chemical analysis was performed on all stones. Radiographic assessment of the kidneys, ureter, and bladder at 6 weeks categorized patients into the SF or residual stone group. Logistic regression was fit, using SSD, BMI, and HU density as predictors, to assess the SF rates after SWL.

RESULTS

Of 64 patients, 30 were SF and 34 had residual stones. The mean SSD was 8.12 +/- 1.74 cm for the SF group versus 11.53 +/- 1.89 cm for the residual stone group (P <0.01). Logistic regression analysis revealed only SSD to be a significant predictor of outcome (odds ratio 0.32, 95% confidence interval 0.29 to 0.35, P <0.01). An SSD greater than 10 cm predicted treatment failure.

CONCLUSIONS

The SSD may predict the outcome after SWL of lower pole kidney stones. SWL in patients with an SSD greater than 10 cm is likely to fail. The use of the SSD may be transferable to the treatment of all urinary stones, regardless of location.

Extracorporeal shock wave lithotripsy success based on body mass index and Hounsfield units

OBJECTIVES

To determine whether body mass index (BMI) and Hounsfield units (HUs) could be used as independent predictors of stone-free status after extracorporeal shock wave lithotripsy (ESWL). No detailed studies have assessed BMI as an independent predictor of ESWL outcome. Some studies have suggested that HUs of urinary calculi on noncontrast computed tomography may predict the stone-free rate after ESWL.

METHODS

We evaluated 100 patients who had undergone ESWL for 5-mm to 10-mm upper urinary tract stones. The BMI was calculated for each patient. HU determination and chemical analysis was performed for each stone. Radiographic assessment at 6 weeks categorized patients into a stone-free (SF) or residual-stone (RS) group. Statistical analysis, using BMI and HUs as predictors, was performed to assess the stone-free rate after ESWL.

RESULTS

Of 100 patients, 72 were in the SF and 28 in the RS group. The mean BMI for the SF group was 26.9 +/- 0.5 versus 30.8 +/- 0.9 in the RS group (P <0.05). The difference in the mean HU values for the SF and RS groups was statistically significant (577.8 +/- 182.5 versus 910.4 +/- 190.2, respectively; P <0.05). A successful outcome was significantly related to BMI (odds ratio 1.34, 95% confidence interval 1.09 to 1.65, P <0.01) and HUs (odds ratio 1.01, 95% confidence interval 1.007 to 1.019, P <0.01). The following equation was formulated to compute the probability of treatment failure: 1/1 + 2.7(-z), where z = 0.294 BMI + 0.13 HU - 18.98.

CONCLUSIONS

BMI and HUs were statistically significant independent predictors of stone-free rates after ESWL. We believe a predictive model of ESWL outcome may be formulated on the basis of these findings and may be used to select the preferred treatment option for patients with urinary calculi.