Discussion

Approximately 62% of UFPs occur at the UPJ and the upper ureter. UFPs are more commonly found in boys (usually older boys) and especially predominant on the left side of the ureter.6 Ureteral polyp is one of the causes of endogenous intermittent hydronephrosis, which consists of mesodermal and normal transitional epithelial cells, and it can cause intermittent hydronephrosis, which was first described by Nesbit (1956) in patients who were having acute attacks of pain but whose pyelograms were normal between attacks.7 When ureteral polyp causes ureteral obstruction, it will result in the clinical symptoms of renal colic, like abdominal pain accompanied by nausea and vomiting. These symptoms generally resolve spontaneously and are followed by a pain-free interval that ranges from days to months. Therefore, in such children, we need to exclude the possibility of ureteral calculi, and a biopsy should be performed when intraoperative malignancy is suspected. When ureteral polyp epidermis is erosive and inflamed, hematuria appears; it is difficult to know the cause of hydronephrosis resulting from ureteral polyps before operation by radiological investigations due to the lack of specific diagnostic methods. Retrograde contrast-enhanced angiography and IVP are commonly used in the diagnosis of UFPs.8 We can see the filling defects in IVP, which is the characteristic X-ray sign of ureteral polyps, because the polyps move with ureteral peristalsis. This image is called “earthworm peristalsis sign”. Two children were diagnosed with this sign preoperation by IVP in our treatment group. Magnetic resonance urography (MRU) is also very helpful in the diagnosis of UFPs. It is less invasive, non-radiating. MRU includes heavily T2-weighted sectional images in orthogonal planes, which allows clear distinction between fluid (bright signal) and tissue (dark signal); the effect should be similar to IVP. All the aforementioned methods to examine polyps need to be identified and diagnosed by experienced doctors.

The treatment of UFPs depends on the location, type (single polyp or multiple polyps) and length of the lesion ureter. Any one of the open, endoscopic, robotic options and laparoscopic method may be available for surgeons to treat UFPs. Open surgery is traumatic and surgical exposure is not superior to that in laparoscopic surgery. Ureteroscopy can be used to diagnose and treat ureteral polyps synchronously and can determine the location, shape and nature of the lesions, making it the preferred treatment. It includes percutaneous antegrade ureteroscope treatment and retrograde ureteroscope treatment.9 Cao et al4 used staged antegrade plus retrograde endoscopic laser polypectomy in six adults. After 3 months of follow-up, five cases showed favorable recovery, while one case showed deterioration of hydronephrosis due to ureteropelvic stenosis. Percutaneous antegrade ureteroscope treatment requires the existence of hydronephrosis and the space for operation. For children with intermittent hydronephrosis, this procedure is not appropriate because there is no hydronephrosis during the asymptomatic stage. Moreover, this procedure may cause kidney injury, uncontrolled bleeding and infection. Retrograde ureteroscope treatment with galvanocautery, laser and biopsy forceps had already been used in adults. Georgescu et al proposed that ureteroscopy should be the gold standard diagnostic method as complete polypectomy could be achieved by ureteroscope approach.10 Sheng et al treated 25 patients with ureteral polyps by ureteroscopy with holmium (12 cases) or thulium laser (13 cases) resection, which were both considered as effective methods to treat UFPs. Both groups had cases of ureteral stricture, but the thulium method did better in reducing the incidence of ureterostenosis.11 Kojima et al reported that they encountered the recurrent UFPs after ureteroscope treatment.12 Children’s ureters are fine, so laser treatment needs a careful operation, or it may lead to ureteral stricture at a specified future date. For inexperienced doctors, ureteroscopy in children’s ureters under limited visual field cannot well determine the number and location of polyps, if the polyps wide base or multiple polyps are prone to have a risk of incomplete polyp treatment, ureterostenosis or ureteral perforation. Therefore, ureteroscope for long ureteral polyps or polys with wide bases is not good, and for ureteral polyps associated with the lesions of intrinsic UPJ, polypectomy alone will not solve the problem. We reviewed case series of pediatric UFPs since 2003 in the English literature (table 2). From the table, we could find that ureteroscopy was helpful in diagnosing UFPs, but the effect of its treatment was not as effective as pyeloplasty. Osbun et al performed robot-assisted laparoscopic excision to deal with UFPs in four children. The mean duration of the follow-up was 29 months after the operation. All cases had improved their symptoms and reduced degrees of hydronephrosis.13 However, the popularity of robots in Chinese hospitals is not high, and the cost of treatment is high, which is difficult for parents to accept.

Laparoscopic pyeloureteroplasty is a mature surgical method for hydronephrosis. For children with short polyp segment ureter (<5 cm), this operation may be the first choice of treatment. In this study, the longest ureteral segment of polyps was 3 cm, and after we released the ureter completely, tension-free anastomosis could be performed for all the patients. In our opinion, in the operation of hydronephrosis caused by polyp, the ureter of polyp segment is generally slightly enlarged; the ureter can be transversely cut to expose the polyp first, so as to understand the polyp condition and the length of the polyp segment; the renal pelvis should not be cut too much or not cut, and attention should be paid to protect the blood supply of the ureter when dissociating the ureter, so as to facilitate tension-free anastomosis and postoperative incision healing. Lu et al14 treated 13 cases of obstruction caused by middle ureteral polyp with laparoscopy and ureteral anastomosis. The median follow-up time was 19.1 months, and the patients recovered well. If the ureter of polyp segment is too long (≥5 cm) and if there is tension or failure of anastomosis during the operation, how should we do in the operation? Renal pelvis flap, Bori flap and intestinal flap have been widely used in the treatment of long ureteral defects. The renal pelvis flap is the preferred method to replace the defect of the upper segment of the ureter, blood supply protection should be paid attention to in the design of cutting, the tubular shape should not be distorted, and there should be no tension when ureteral anastomosis was performed.15 For the intermittent hydronephrosis caused by ureteral polyp, the dilatation of the renal pelvis is not obvious, so it is necessary to carefully select the pelvis flap to replace the defective ureter. Bori flap is more favorable for the treatment of the lower long ureter defect. Routh et al16 applied Bori flap laparoscopically to treat the long ureter defect of five children, and the postoperative average follow-up was 3 years. Among them, two had VUR, and the remaining cases recovered well. However, it has been reported that Bori flap can be used to replace the entire ureter.17 The replacement of intestinal ureter can replace the length of the ureter defect at any site, but postoperative complications, such as mucous obstruction, urinary calculi, urinary tract infection and electrolyte disturbance, may occur, and the long-term complications are irreversible renal damage, and especially the double-focus reconstruction may lead to long-term renal deterioration.18 At present, ileal replacement of the ureter is considered a mature and effective alternative.19 The diameter of the appendix tube in children is close to the ureter, and the peristalsis ability can keep the urine unobtainable; the absorption function is low, and the balance of water and electrolytes will not be disturbed, so it is an ideal choice. Wang et al20 used appendix replacement for ureter to treat nine patients with right complicated ureteral stricture, and the average length of ureteral stricture in nine patients was 3.9 cm; the follow-up period was 4–10 months; and the effect was satisfactory. The replacement of the ureter by the appendix is usually applied in the replacement of the right ureteral lesion, while the replacement of the left ureteral defect by the appendix is rare in the literature. When considering the replacement of the left ureteral defect by the appendix, factors such as the length of the appendix mesangium and the position and length of the appendix should be known in advance.21 Autogenous kidney transplantation can also be used in the treatment of long ureteral defects, but the surgical technique requires higher requirements. Postoperative complications such as thrombosis, severe urinary tract infection and ureteral necrosis may occur and improper use often requires nephrectomy.22

In conclusion, intermittent hydronephrosis associated with abdominal pain occurred in older children, and IVP or magnetic resonance imaging indicated a filling defect in the ureter, highly suggestive of polyp induced hydronephrosis. How to understand the length of polypoid ureteral lesions before surgery still needs to find a better examination method to facilitate the formulation of preoperative surgical plan. The treatment of this hydronephrosis caused by UFPs depends on the location, number, and length of polyps in the affected ureter. If the ureteral segment is short, laparoscopic pyeloureteroplasty is the first choice. For the long segment ureteral defect, individualized treatment should be adopted according to the condition of the child, and urinary system tissue reconstruction should be used as far as possible, followed by intestinal replacement of ureter. With the development of medical technology, artificial ureters that can simulate normal ureter function are constructed in vitro for the repair and reconstruction of long-segment ureteral defects, which are expected to be realized in the future.