The Institutional Review Board of the Kyungpook National University Hospital approved the study protocol based on the Declaration of Helsinki (approval number: KNUH 2019-05-001). In total, 182 patients who underwent URS for ureteral stones in our center from January 2013 to December 2015 were retrospectively included in this study. Patients who underwent retrograde intrarenal surgery due to renal stones were excluded. Patients with preoperative ureteral stent or percutaneous nephrostomy were also excluded in this study. The definition of febrile UTI in this study was occurrence of high fever (>38°C) with pyuria within 1 week after URS without other infectious signs except UTI. A single surgeon performed all operations using an 8.5-Fr semi-rigid ureteroscope (Karl Storz, Tuttlingen, Germany) with 200-µm holmium laser (Lumenis, Tel Aviv, Israel). We divided these patients into two groups according to the presence of postoperative febrile UTI within 2 weeks after URS; Group A (n = 26) included patients with febrile UTI after URS and Group B (n = 156) included patients without febrile UTI after URS.
We evaluated and compared the preoperative clinical data and stone characteristics between patients in the two groups through a review of medical records. The clinical data included age; gender; body mass index (BMI); comorbidities such as hypertension (HTN), diabetes (DM), chronic kidney disease (CKD); and history of previous acute pyelonephritis (APN) and stone surgery; the stone characteristics included laterality, location, mean number of stones, size, and Hounsfield units (HU). Secondary signs included hydronephrosis, hydroureter, unilateral enlargement, perinephric fat stranding, periureteral fat stranding, and tissue rim sign (Fig. 1).
All abdominal UHCT examinations were performed preoperatively with 5-mm cut slices for axial images and 3-mm cut slices for coronal images. The stone size was determined by measuring the longest axis, and HU was evaluated on axial image in the mid-lateral aspect of each kidney using the maximal region on preoperative CT image. Perinephric and periureteric fat stranding were defined as linear areas of soft tissue attenuation in the perinephric and periureteric space, respectively . Positive tissue rim sign was defined as annular soft tissue attenuation (20–40 HU) caused by an edematous ureteral wall surrounding the stone . All the interpretations of preoperative UHCT were simultaneously performed and discussed by one radiologist and one urologist, and presence of secondary signs was determined by the consensus of a radiologist and urologist.
Before URS, all patients were evaluated through physical examination, routine blood tests, urinalysis, urine culture, and radiologic images, including simple X-ray (KUB), and UHCT. Patients whose urine cultures demonstrated bacterial growth on preoperative evaluation were treated with appropriate antibiotics, and the surgery was performed after sterile urine was confirmed. Fluoroquinolone was routinely used as a prophylactic antibiotic for all patients on the day of the surgery.
The surgery was performed under general or spinal anesthesia in the lithotomy position for all patients. After cystoscopy, the hydrophilic guidewire was inserted into the ureter. A semi-rigid ureteroscope was introduced to visualize the ureter and facilitate its placement. Lithotripsy was performed using a laser lithotripter. Irrigation during surgery was manually provided by a surgical assistant (urologic resident) using 50-ml syringe. The assistant was previously trained to maintain the irrigation pressure between 60-120 cmH2O depending on the surgical situation, such as visual clearness and possibility of stone retropulsion. A 1.9-F nitinol stone basket (Zero-tip; Boston Scientific, Spencer, IN, USA) was used to remove remnant stone fragments from the urinary tract. At the end of the surgery, a 6-F double-J stent was routinely placed and maintained for 1 or 2 weeks in all patients.
Data were evaluated using SPSS 18.0 (SPSS, Inc., Chicago, IL, USA). Chi-square test was used to determine the difference in proportions for categorical data, while continuous variables were assessed using Wilcoxon test. Multivariate logistic regression analysis using forward selection was performed to identify the risk factors of febrile UTI after URS. A P value < 0.05 (two-tailed) was considered statistically significant.