Currently, no consensus has been reached on the management of complete duplex kidney with concurrent hydronephrosis in the poorly functioning upper pole moiety. At the beginning of the last century, Foley first reported UU as a treatment for duplex kidney [7]. However, for quite a long time, upper pole heminephroureterectomy was the most commonly used management method for this disease. Preserving the poorly functioning upper moiety is believed to increase the risk of hypertension, albuminuria, or even cancer, and ureteroureterostomy might exert adverse effects on the normal lower pole moiety. Due to advances in surgical techniques and an in-depth understanding of UU, in recent years, UU has been gradually adopted by an increasing number of urologists to treat complete duplex kidneys. Accumulating evidence has shown that UU has no harmful impact on the lower moiety and that preserving the upper moiety does not increase the occurrence of hypertension or other diseases. Hence, UU has been acknowledged as a safe and effective treatment for complete duplex kidney [4, 8,9,10].

The use of laparoscopy decreases the rate of open pediatric urologic surgeries, however, robotic surgery is still not widely applied, especially in developing countries. Therefore, laparoscopic UU has been a common choice for the treatment of complete duplex kidney. Laparoscopic UU involves proximal and distal approaches involving the lower pole moiety. Both approaches have been reported to have favorable outcomes and obvious advantages when compared with upper pole heminephroureterectomy. However, which approach is better remains controversial. Chandrasekharam V. et al. [11] reported that the distal approach causes less damage to peripheral tissues and is associated with a lower incidence of postoperative complications than the proximal approach. Storm et al. [12] used the proximal approach and reported favorable surgical outcomes. Thus, the surgical approach should be selected based on the surgeon’s preference and experience. To the best of our knowledge, few studies have compared the two approaches in detail. In the present study, we compared the complexity, peripheral tissue damage and postoperative complications of the two approaches, hoping to provide clinical evidence of laparoscopic UU for the treatment of complete duplex kidney. In our study cohort, there was no significant difference in the overall incidence of complications between the distal UU and proximal UU groups [(8/36) 22% vs. 11/35(31%), P = 0.345]. However, in terms of postoperative complication grades, the proximal UU group had higher grade complications (3 of them had a grade of IV complication). In addition, 2 children in the proximal UU group had serious complications due to anastomotic stenosis, 1 child had ureteral stump infection, and no patient in the distal UU group had anastomotic stenosis or stump infection. There was no difference between the two groups in terms of postoperative urinary system infection, aggravation of hydronephrosis and reoperation rate.

The key points of the proximal approach are as follows: First, the ureter of the upper moiety was horizontally severed at the lower pole of the kidney. Second, the lower moiety of the ureter was dissociated, and a vertical incision of approximately 1 cm was made. The incision should be carefully made so as to avoid severing the normal lower moiety of the ureter. Third, end-to-side anastomosis of the severed upper ureter with the lower ureter was performed. Next, the double J stent was placed. Finally, the dilated upper ureter was dissociated as low as possible and severed. Compared to upper pole heminephrectomy, this approach has distinct advantages. It eliminates the possible complications caused by upper pole heminephrectomy, such as wound bleeding, urinary extravasation and damage to the normal renal tissues in the lower moiety (which may even result in lower pole heminephrectomy) [4, 6].

In our research, proximal UU was less frequently recommended than distal UU due to surgical procedure and risks. In the distal approach, it is easier to dissociate the distal ureter due to its superficial position. Furthermore, a considerable amount of operational space is available. Additionally, the distal approach prevents the dissociation of the colon and thus does not have an impact on gonadal arteries. In addition, there is no need to remove much of the upper ureter; therefore, the damage to the lower ureter and the impact on the ureteral blood supply can be reduced [11]. Furthermore, the distal approach has less impact on the gastrointestinal tract, which ensures a quick recovery. In this study, the operation times of the two groups were 108.42 ± 26.95 min for the distal UU group and 121.46 ± 35.15 min for the proximal UU group. However, if the cystoscopic detection and retrograde intubation times were excluded, the distal group would have a shorter surgery time. The key points of the distal approach are as follows: (1) maintain the integrity of the gonad, gonadal arteries and ureter; (2) and excise the upper pole ureter stump as close to the bladder as possible. (3) ensure the length of the lower ureter incision is the same as the diameter of the upper ureter. If the two does not match, the upper ureter incision must be modified to ensure an open anastomotic stoma. (4) The dissociation of the lower ureter should be minimized to eliminate the impact on the ureteral blood supply and the consequent anastomotic stenosis. (5) During surgery, clamping or gripping should be avoided to minimize the risk of injury.

No consensus has been reached regarding the approach to total ureteral stump excision of the duplex kidney. Some believe that there is no need for total excision because of the low incidence of stump infection and the potential for uroclepsia or neurogenic bladder caused by bladder neck injury after total excision [11, 13]. Chandrasekharam V. et al. [11] reported favorable outcomes with UU without total ureteral stump excision. However, at the 6-year follow-up visit, De Caluwe et al. [14] reported a 10% rate of reoperation for stump excision due to stump infection. Additionally, Ade-Ajayi et al. [15] reported an 8% rate of reoperation caused by stump infection after upper pole heminephrectomy. In the present study, none of the 36 patients in the distal group had stump infection because the ureteral stump. By was nearly completely excised. In contrast, among the 35 patients in the proximal group, due to incomplete ureteral excision, stump infection occurred in one patient who had concurrent upper pole VUR preoperatively, for an incidence rate of 3%. Based on the above evidence, we believe that near-total excision of the ureteral stump is necessary, especially for patients with concurrent upper pole VUR. Needle total ureteral stump excision decreased the incidence of stump infection in the distal group.

A theoretical concern is poor urine drainage in the upper moiety after treating ureterectasia with the distal approach because this approach may lead to reinfection of the urinary system and abdominal pain. In particular, the weak peristaltic function caused by the maldeveloped upper moiety and ureter may require reoperation. Hence, it is believed that horizontal end-to-side anastomosis of the lower moiety combined with removal of the expanded ureter is a favorable management method. To verify this, we followed up patients in the distal group with obvious upper moiety ureterectasia and found no clinical symptoms such as urinary infection. Postoperative imaging examinations such as ultrasound, revealed apparent relief of hydronephrosis and narrowing of the dilated ureter in the upper moiety. Some patients even showed a normal upper moiety in the examinations.

Another concern from clinicians is complications (such as anastomotic stenosis). Mcleod [9] reported a 2% occurrence of anastomotic stenosis after UU among 43 patients with duplex kidney. There was no anastomotic stenosis in 36 patients who underwent distal UU. In the proximal UU group, there were 2 children with severe complications due to postoperative anastomotic stenosis, and hydronephrosis was aggravated with repeated febrile urinary system infections. Hydronephrosis in these two patients was relieved after two or more operations in the later stage. Despite the low incidence of anastomotic stenosis and other adverse reactions in the lower pole collecting system, effective treatments for postoperative complications are still needed. In the proximal approach, upper moiety removal or another end-to-side anastomosis is needed. In the distal approach, an end-to-side anastomosis at a nearby site or a vesicoureteral replantation is needed. Thus, it is more difficult to treat complications at the anastomotic stoma via the proximal approach than via the distal approach. Some studies have reported yo-yo reflux following ureter anastomosis [13], which has not yet been verified [11, 16]. According to Lashley DB [17], no yo-yo reflux occurred in 100 duplex kidney patients who underwent ureteroureterostomy. During our follow-up examination, except for children with anastomotic stenosis or hydronephrosis, the dilated ureters of all the other patients were relieved, and no yo-yo reflux was found postoperatively.

The objective of this study was to compare the distal approach with the proximal approach for UU. Stringent inclusion criteria were applied to ensure that the patients in both groups shared almost the same manifestations of the disease. All the patients enrolled had complete duplex kidneys with concurrent abnormal upper moieties and ureters, together with normal lower moieties and ureters. Many researchers believe that UU can be performed in the lower moiety with concurrent mild reflux, because the probability of reflux in the lower moiety is significantly higher than that in the upper moiety, and favorable outcomes were also found in follow-up studies [12]. The above understanding warrants further exploration of the indications for UU for a complete duplex kidney.

This study has the following limitations: First, the sample size was not large enough to produce more convincing conclusions, which is also a limitation of other studies on UU. Second, this was a single-center retrospective study, which may involve selection bias. Third, the follow-up time of a few patients was short (the shortest follow-up time was 15 months).We hope that prospective studies will be designed under the cooperation of multiple institutions to provide more reliable data for clinical practice.