THE SUCCESS OF EXTRACORPOREAL SHOCK-WAVE LITHOTRIPSY BASED ON THE ULTRASOUND COLOR-DOPPLER TWINKLING ARTIFACT EVALUATION
Aim of our study was to determine the utility of the ultrasound color-doppler twinkling artifact study for predicting the success of ExtracorporeaL Shock-Wave Lithotripsy (ESWL) of ureteral calculi. To the best of our knowledge, for the first time, similar approach has been used in a patient group.
Materials and Methods
Between July 2015 and September 2016, a total of 178 patients who underwent to ultrasound-guided ESWL for single ureteral stones of 5 to 10 mm were included in this study. All patients underwent a baseline evaluation, including a medical history, a physical examination, a complete blood count, a serum creatinine measurement, determination of the glomerular filtration rate, a urinalysis and a color-doppler ultrasound scan of upper urinary tract. The exclusion criteria were as follows: placement of percutaneous nephrostomy tube or ureteral stent before ESWL. The ultrasound parameters included stone location and stone length. During Color-Doppler ultrasound examination single focal zone was always placed somewhat deeper than the level of the targeted stone. The presence of twinkling artifact, and if detected its signal intensity was recorded. Signal intensities of the twinkling artifacts were classified as follows: twinkling artifact not observed (grade 0); grade 1: focal and hardly observed twinkling artifact; strong signal intensity observed on only some part (grade 2) or all over the stone (grade 3)(1). To investigate the usefulness of color Doppler twinkling artifact study for predicting ESWL success-rate, patients were divided into two subgroups. Patients with no twinkling artifact (grade 0) or with focal and hardly observed twinkling artifact (grade 1) (GROUP A) and patients with twinkling artifact (grade 2 and grade 3) (GROUP B). Patients were followed up every 2 weeks after ESWL with ultrasound. If there were significant fragments others sessions of ESWL were planned. The final results were considered after the complete passage of all fragments or after 3 months from the last ESWL session. The outcome of ESWL was described as a success with stone-free condition or clinically insignificant residual fragments with no symptoms at 3 months after ESWL. Failure was defined as residual stone fragments or no evidence of fragmentation after 3 sessions of ESWL.
The GROUP A consisted of 153 patients (85.9%), and the GROUP B consisted of 25 patients (14.0%). The average stone size (mm) in the two groups was 7,9±1,4 and 8,1±0.5 respectively, which was no significantly different between the two groups. Other ultrasound parameters such as stone location and hydronephrosis were not significantly different. No significant differences in other baseline characteristics were found between the two groups. Overall success rates in the GROUP A and GROUP B were 86.9% (133 patients) and 100% (25 patients) respectively. Mean time to stone free status and the average number of ESWL sessions required for success in the two groups were 18.7±31.7 days compared with 12.2±20.0 days and 1.2±1.2 compared with 1.1±1.5, respectively. However, the subgroup analysis divided by stone size and stone location was not performed because the sample size was relatively small for accurate analysis.
ESWL is a non-contact, non-invasive technique for the treatment of urinary calculi. It is widely used in clinical treatment, and this method of removing stones has advantages such as simple operation, less pain and lower cost(2). Several studies concluded that the outcomes of ESWL correlate with several factors, including type of lithotripter, stone size, stone location, stone composition, calyceal and ureteral anatomy, body mass index and recently the stone attenuation value(3). Many previous studies have investigated the relationship between computed tomography (CT) parameters and successful ESWL. Data revealed that the energy of the shock wave needed for fragmentation was related to stone density, and that the higher the stone density, the stronger the shock wave energy needed to achieve fragmentation(4). A twinkling artifact associated with color doppler ultrasonography of urinary calculi has been described as a rapidly changing mixture of red and blue seen on or behind the stone where the shadowing would be expected on B-mode imaging. The etiology of the artifact is not completely understood, but it has been hypothesized to be from phase or clock jitter, and stone surface roughness. More recent data suggest that twinkling may arise from tiny gas pockets on the stone surface. Several studies have demonstrated the dependence of the twinkling artifact on ultrasound machine settings and stone composition. The twinkling artifact has been observed in 83% to 96% of stones seen on B-mode ultrasonography(5). In the identification of urinary stones this artifact provides additional contribution to gray-scale ultrasound, and increases diagnostic success rates. Some stones do not induce formation of artifact, while others lead to greater amount of artifact. For the first time Chelfouh et al. investigated this correlation. In this in vitro study performed with small number of stones, calcium oxalate monohydrate stones generally did not induce formation of twinkling artifact, while a correlation between calcium oxalate dihydrate stones and twin¬kling artifact was found(6). Bulakçı et al, in vivo, evaluated to the role of twinkling artifact observed in color doppler analysis for the pre¬diction of the mineral composition of urinary stones. Overlapping intensities of the twin¬kling artifact have been also observed among all stone groups. On the other hand, mineral composition of the stones with a density value below 780 HU which also display grade 3 artifact can be evaluated in favour of non-calcium stones(1). In our study we demonstrated that the absence of ultrasound color-doppler twinkling artifact correlate with a higher ESWL success rate for the treatment of ureteral stones. The lower number of patients and the dependence on the sonographer of the ultrasound exam are important limitation of our study. Statistical power of our study was weakened. Therefore, further prospective studies should be conducted with greater number of patients. However we think that these preliminary data which is contributed to the literature will be helpful as guiding tools for future investigations.
Our study shows the utility of the ultrasound color-doppler twinkling artifact study for predicting the success of ESWL of ureteral calculi.
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(2) Yang C, Li S, Cui Y. Comparison of YAG Laser Lithotripsy and Extracorporeal Shock Wave Lithotripsy in Treatment of Ureteral Calculi: A Meta-Analysis. Urol Int 2016; DOI: 10.1159/000452610
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