Discussion
PBUC analysis is a standard procedure before any stone surgery. PBUC is very important for selecting patients undergoing f-URS to receive prophylaxis and for predicting the risk of postoperative infection complications [1,5]. In a previous meta-analysis, a single preoperative antibiotic dose was shown to reduce postoperative pyuria and bacteriuria, but it did not statistically significantly reduce postoperative urinary tract infections [18]. Theoretically, the effect of PAP is considered to prevent the spread of bacteria during the stone operation; however, the actual efficacy of this application remains uncertain. In our study, PBUC growth was present in 19.4% of the patients. Although there was no growth in the post-treatment control cultures of these patients, it was observed that bacteriuria persisted in RPUC in 27.1%. In light of this information, it is necessary to establish a proper prophylaxis and treatment strategy in patients with a positive PBUC to prevent infectious complications. The AUA guidelines recommend PAP to all patients to reduce urosepsis after f-URS while EAU states that PAP is indicated only for those with a high risk of infection [8-10].
In another previous study, the efficacy of PAP and preoperative antimicrobial treatment was compared using the cultures taken intraoperatively, and growth was found in intraoperative cultures in only 3.2% of the patients who were negative for PBUC and given PAP. In the same study, 43.3% of the cultures taken intraoperatively from patients with a positive PBUC had growth despite appropriate antibiotherapy. That study demonstrated the efficacy of preoperative antimicrobial therapy to be 71.6% [19]. In other words, despite preoperative antimicrobial therapy, 43.3% of the patients had growth in any of the intraoperative cultures taken during surgery; i.e., an existing or different microorganism managed to survive [19].
He et al. administered cefuroxime PAP for three days preoperatively to patients without preoperative urine culture growth and observed reduced growth in RPUC. The authors emphasized that preoperative antibiotic administration should be adjusted according to the risk level and suggested that RPUC showed better bacterial colonization [20]. In our study, we determined that even if the patients with a positive PBUC before the operation were treated, some had growth in RPUC. However, PBUC positivity is not an independent predictive factor for the possibility of growth in RPUC. The efficacy of PAP or antimicrobial treatment before surgery is limited against bacteria that we were not able to detect preoperatively. Therefore, we consider that even if PBUC is negative in patients scheduled to undergo f-URS, we should be prepared for the possibility of a positive RPUC in some patients to ensure that appropriate antibiotherapy is started promptly to prevent alarming complications, such as sepsis.
In the literature, it has been reported that there is significant growth in intraoperative cultures in patients with renal stones and a history of obstructive pyelonephritis [19]. In our study, a statistically significant relationship was found between stone localization and presence of hydronephrosis and RPUC positivity. If a stone is in a location that can cause hydronephrosis (e.g., pelvis and proximal ureter), it can explain a higher rate of growth in RPUC. In patients with urinary system obstruction, infection or bacterial colonization in the upper urinary tract may continue even in the presence of a negative PBUC. Other studies have revealed that in addition to the degree of hydronephrosis, the thickness of the ureteral wall surrounding the stone may also increase. A significant association between ureteral wall thickness (UWT) and degree of obstruction has been demonstrated, and a possible predictive value has been presented [21,22]. Sarica et al. found the cut-off value of UWT as 3.35 mm and they were not able to place a double-J stent in patients with a value over this threshold [15]. The authors considered that if the guidewire required for the double-J insertion could not reach the proximal of the stone, the urine sample obtained preoperatively would also not be sufficient for the culture analysis. Impacted stones have indirect NCCT findings, including changes in UWT, degree of hydronephrosis, and fluid collection around the kidney [23]. Another study revealed that the thickness of the wall immediately surrounding the stone depends on the elapsed time and the degree of inflammatory reactions that occur [24].In our study, the wall tissue thickness at the proximal ureter and pelvis was higher in patients with RPUC growth. However, due to being a confounding factor in the multivariate analysis, it was not included in the model.
In the literature, it was shown that 10.1% of the patients with a negative PBUC were positive for RPUC, but these patients also did not show any signs of infection [4]. Preoperative NCCT findings are important for this patient group. It has been previously emphasized that RPUC can be predicted using certain non-specific findings, such as the thickening of the renal pelvis and stranding of perirenal fat renal in pyelonephritis [25]. Basmacı et al. reported that at a cut-off value of 0, renal pelvis HU had 100% sensitivity and 96% specificity for a positive RPUC[14]. In our study, the HU value was found to be lower in the RPUC group. We certainly do not claim that it is possible to definitively determine the presence of RPUC growth by examining HU. However, we consider that in patients examined for stone disease and planned to undergo f-URS, pelvis HU can predict RPUC growth, and thus help identify those that require wider-spectrum PAP and a more close follow-up in the postoperative period. A low HU value in patients with RPUC growth may be due to bacterial burden colonizing in that location, fragmented urine, and/or increased urine density.