Materials and Methods
The study included patients aged 18 years or older, who received SWL treatment for ureteral stones above the iliac crest-level between December 2016 and December 2019 at the Urology Department of a University Hospital. This study was approved by the Institutional Review Board on November 21, 2018 (number: 21263603-806.01.03-96286). SWL is the primary treatment option in our clinic as it is the most minimally invasive option. It was applied to all ureteral stones above the iliac crest, regardless of patient selection. The patients who underwent SWL as the primary treatment option between the specified dates were analyzed retrospectively. Patients with congenital abnormalities, coagulopathy, morbid obesity, pain intolerance, stone size more than 15 mm, secondary treatment or renal failure were excluded from the study (URS was performed to these patients). A total of 147 patients with ureteral stones above the iliac crest-level, who underwent non-contrast enhanced abdominal computed tomography (NCCT) before the SWL procedure and when they had ureteral stone which were not passed in four weeks, were included in the clinical study.
A urine culture-antibiogram test was applied to the patients before the procedure. In cases where the urine culture was not sterile, the patients were given an appropriate antibiotic treatment, and SWL treatment was applied after confirming sterile urine culture with the approval of an infectious diseases specialist. SWL was performed by a single urologist (NT) with 30 years of SWL experience using a third-generation lithotripter (Siemens Lithoscope ®, Erlangen, Germany). The procedure was undertaken in the outpatient setting under fluoroscopic control without administering anesthesia. Analgesic and spasmolytic treatment was applied to the patients during the procedures. The patients were placed in the supine position. Treatment was started with an energy level of 60 joules and gradually increased until it reached a maximum value of 120 joules if tolerated by patients. Initially, the shock wave/minute ratio was set to 60 for the first 500 shock waves, and then increased to 90 shock waves/minutes. Although 3000 shock waves were applied in each session, when the clinician deemed it necessary, the number of shock waves was increased to a maximum of 3800. Treatment was terminated when complete fragmentation of the stone was noted on fluoroscopy. If there was persistent or incomplete fragmentation of the stone(s) noted on fluroscopy after the maximum number of shocks had been delivered, a repeat SWL session was performed at five-seven days after the previous one. When appropriate fragmentation was seen in each session, the procedure was scheduled for next sessions. SWL was regarded as a failure if no fragmentation was noted after the third session. The results were defined as stone-free status and treatment failure according to the NCCT evaluation undertaken at three months after SWL. Stone-free status was defined as the absence of stones while treatment failure was indicated by the presence of any residual stone regardless of size. In addition, at the time of SWL or after the procedure before the third-month CT evaluation, URS was performed in all patients who required an additional intervention due to increased pain or steinstrasse (defined as failure).
The demographic characteristics of the patients (age, gender, comorbidity, and history of stone surgery on the same side) and stone characteristics [side of the stone, diameter of the ureter in the proximal of the stone, transverse stone size, stone length, stone volume, mean Hounsfield unit (HU), hydronephrosis degree, distance between the stone and the skin (SSD), and number of stones were recorded. The NCCT images at 4X magnification were used. We evaluated the images in three axes (in the axial, sagittal, and coronal plane measurements). The largest UWT was obtained from NCCT at the stone site. The ellipsoid formula (π × length × transverse size × sagittal size ×0.167) was used when calculating the stone volume. SSD was calculated by measuring the distance from the skin to the stone in a 45 ° posterolateral direction. The characteristics of the SWL treatment applied to the patients (number of sessions, number of shock per session, and amount of energy applied per session) were noted.
The selected cross-section range in NCCT was 1.25 mm. The patients were scanned without a contrast agent using a tube voltage of 120 kV and tube current of 300 mAs. Using the NCCT images taken before each SWL session of each stone, all parameters were measured by a single radiologist (OT) with 15 years’ experience in abdominal radiology, who was blinded to the treatment results of the patients. NCCT was used for follow-up after SWL. The effect of patient- and stone-related parameters on stone-free status was analyzed.
Statistical analyses were performed using the Statistical Package for the Social Sciences (SPSS) version 22.0. The compliance of data to normal distribution was evaluated by the Shapiro-Wilk test. Normally distributed data were indicated by mean and standard deviation values. Non-normally distributed data were reported as median and minimum-maximum values. In the univariate analyses, the chi-square or Fisher’s exact test was used to compare categorical variables, and Student’s t-test or the Mann-Whitney U-test to compare independent samples between the groups. Multivariate (logistic regression) analyses was performed to determine statistically significant independent factors. Statistical significance was considered when the two-tailed p value was <0.05.