The advantages of CUS compared with urinary diversions, such as ileal conduit or neobladder, are less invasiveness, fewer gastrointestinal complications, shorter operative time, less blood loss, and shorter hospital stay [1, 5, 8]. In contrast, the disadvantage of CUS is the low stent-free rate, which is associated with an increased incidence of UTI and may impair patients’ quality of life [8]. In CUS cases that do not become stent-free, the burden on patients and their families forced to undergo regular stent replacement cannot be underestimated [5]. This is especially true for frail and dependent older patients, or those who have difficulty making regular trips to a hospital [1]. However, this issue is rarely addressed in patients’ health-related quality of life questionnaires [1, 9].

The gold standard for urinary diversion following radical cystectomy is the ileal conduit. We use intracorporeal ileal conduits in many patients because of the feasibility of the procedure and the tolerability of perioperative complications [5]. Nonetheless, CUS, an alternative form of urinary diversion, is indicated in some patients (e.g., history of pelvic radiation therapy, inflammatory bowel disease, multiple comorbidities, and older or frail patients) [4, 6, 10]. In these patients, shorter operative times and fewer complications are desirable. Preserving renal function after surgery is also important, given the possibility of adjuvant chemotherapy.

In CUS, the ureter can be routed retroperitoneally or transperitoneally. The advantages of t-CUS, in which the ureter is not retroperitonealized, include short operative time and feasibility even if the ureter is short. The disadvantage of t-CUS is that the ureter may become entangled with the intestine, causing ureteral or intestinal obstruction [11, 12]. The advantages of r-CUS, in which the ureter is retroperitonealized, include the possibility of fewer gastrointestinal complications compared with t-CUS and the ease of performing total nephroureterectomy for ureteral cancer [13]. The disadvantages of r-CUS are the long operative time and the difficulty routing the ureter retroperitoneally when the ureteral length is insufficient [13]. In this case, an overly stretched ureter may cause insufficient blood flow, leading to ureteral stenosis.

In the present study, the operative time and RARC time were significantly shorter in the t-CUS group compared with the r-CUS group. The estimated blood loss was also significantly less in the t-CUS vs. r-CUS groups. The shorter RARC time may have resulted from a slightly lower rate of lymph node dissection in the t-CUS vs. r-CUS groups. Additionally, compared with the t-CUS group, the r-CUS group had a median CUS time of 35 min longer. This reflects the time required for retroperitonealization of the ureter. The incidence of minor complications within 30 days was significantly higher in the r-CUS vs. t-CUS groups. Notably, the incidence of ileus within 30 days was higher in the r-CUS group vs. the t-CUS group, though the difference was not statistically significant (3% vs. 23%, respectively; p = 0.064). During the median follow-up period of 24.3 months, no ileus was observed in either group after 30 days postoperatively. Ben-David et al. evaluated 69 patients who underwent t-CUS following RARC [14]. The median age was 77 years, and 59% of the patients had an American Society of Anesthesiologists physical status score ≥ 3. The median operative time was 241 min, and the median estimated blood loss was 100 mL, which were comparable to the perioperative outcomes in our t-CUS group. In Ben-David et al.’s study, the incidence of complications within 30 days was 55%, and 10% were gastrointestinal complications (details unknown). The incidence of complications within 30–90 days was 23%, with no gastrointestinal complications.

In radical cystectomy, prolonged operative time increases both the risk of postoperative complications and the readmission rate [15, 16]. Hanna et al. reported that the operative time threshold at which the likelihood of postoperative complications increases significantly was 369 min [16]. In the present study, the median operative time in the r-CUS group was 370 min, exceeding 369 min. On the basis of these findings, we believe that the higher incidence of complications with r-CUS compared with t-CUS was mainly because of the prolonged operative time. Notably, although the rate of hospitalization owing to UTI during the observation period was similar in both groups, the median number of hospitalizations was significantly higher in the r-CUS vs. t-CUS groups (1.0 vs. 2.5, respectively; p = 0.010). The non-inferiority of t-CUS was also demonstrated in terms of the incidence of postoperative UTI. It is unclear why the median number of hospitalizations was higher in the r-CUS group vs. the t-CUS group. In the present study, postoperative eGFR was significantly higher in the t-CUS group compared with the r-CUS group. We believe that this is because the t-CUS group has a higher preoperative eGFR and a lower stent-free rate compared with the r-CUS group, although the difference was not statistically significant.

There are few reports on t-CUS. Furubayashi et al. reported a surgical technique for t-CUS using the transverse mesocolon [13]. In the study, nine patients underwent this procedure, and no intraoperative complications were observed. One patient developed ileus, which resolved with conservative treatment [13]. However, the report did not provide information on the stent-free rate or a comparison of surgical outcomes between t-CUS and r-CUS. In a literature search, we identified no previous reports comparing the surgical outcomes of t-CUS and r-CUS. To our knowledge, ours is the first study to compare the surgical outcomes of t-CUS and r-CUS.

The results of the present study are encouraging for urologists who perform t-CUS and are also useful for urologists who usually perform r-CUS. When the available ureteral length is insufficient, r-CUS is difficult to perform. Specifically, there are cases in which ureteral frozen section analysis was performed multiple times and cases where it was difficult to dissect the lower ureter owing to adhesions. When r-CUS is performed in such cases, we believe that an overly stretched ureter may cause insufficient blood flow, leading to ureteral stenosis. These patients can be converted to t-CUS when necessary if the ureteral length is insufficient.

The present study has limitations that must be considered. First, this was a retrospective study that involved multiple centers, and the study had a relatively small sample size. These issues may limit the generalizability of the findings. Second, CUS patients accounted for only 15.1% of all RARC patients, making it difficult to collect data from a large number of patients. Third, the quality of CUS can vary between surgeons, which may have affected the results of our study.