Use of Self-Expanding Metallic Ureteral Stents in the Secondary Treatment of Ureteral Stenosis Following Kidney Transplantation

Abstract

Introduction:

To evaluate the safety and efficacy of self-expanding metal stents in the treatment of ureteral stenosis following kidney transplantation.

Materials and Methods:

Seven patients who developed benign stenosis after kidney transplantation were treated by a self-expanding metallic stent implantation from June 2007 to March 2014. All patients had undergone at least one open surgical procedure and one endourologic procedure for treatment of the stenosis. The extent of stenosis varied from 1.2 to 3.7 cm. Ultrasonography, urography, diuretic renography, and urine culture were performed every 3 months after stent insertion. Ureteroscopic examination was performed when needed.

Results:

Stent placement was technically effective in all cases. The mean operative time was 37 minutes (range, 26–59 minutes). Lower urinary-tract symptoms and the ipsilateral flank pain were common early-stage complications and were greatly relieved after an average of 3 months. The mean follow-up duration was 38 months (range, 13–86 months), and no stent migration or fragmentation was observed. Urothelial hyperplasia occurred in only one patient and was effectively managed with a Double-J stent. Five patients had normal stable renal function; the remaining two had impaired renal function, including one patient with a preoperative renal failure who required dialysis at the end of the follow-up period (36 months).

Conclusions:

As an alternative to open surgery, implantation of a self-expanding metal stent is a safe and effective treatment for ureteral stenosis in patients who have undergone kidney transplantation.

Introduction

Ureteral stenosis is one of the most common surgical complications of kidney transplantation, occurring in 0.5% to 10.0% of patients who have undergone this procedure.^1
–3 Open surgery with ureterovesical reimplantation is the treatment of choice for ureteral stenosis. However, repeated open repair is associated with morbidity and may be technically challenging, especially in patients who have undergone multiple open surgeries.⁴ Various minimally invasive techniques of ureterovesical anastomosis have been described, including balloon dilation, endoscopic incisional therapy, and long-term placement of a Double-J stent. However, most of such procedures are reportedly associated with unsatisfactory outcomes.⁵

Self-expanding metallic stents are commonly used to treat vasculobiliary stenosis and have been used to manage malignant and benign ureteral obstructions in native kidneys with a satisfactory success rate.^6,7 However, because the long-term patency of metallic stents in patients with transplant ureteral stenosis has not been clearly established, few reports on the use of these stents in transplant ureteral stenosis exist.^8,9 In this study, we assessed the long-term outcomes of self-expanding metallic stents for the management of ureteral stenosis following kidney transplantation.

Materials and Methods

The implantation of metal stents in this study was approved by the hospital ethics committee. Written informed consent was obtained from all participants. From June 2007 to March 2014, seven patients (four men, three women) aged 32 to 61 years (mean age, 42 years) with benign stenosis after kidney transplantation were treated by implantation of a self-expanding nitinol ureteral stent. The ureteral stenosis was located at the site of ureterovesical reimplantation in all patients. The extent of the stenosis ranged from 1.2 to 3.7 cm. All patients had undergone at least one open surgical procedure and one endourologic procedure (including endoscopic incisional therapy or ureteral dilatation) for treatment of the stenosis. To reduce urothelial hyperplasia, any endourologic procedure (including endoscopic incisional therapy and ureteral dilatation) was performed at least 1 month before metal stent implantation, and a Double-J stent was placed in all patients. Four patients had a history of percutaneous nephrostomy tube placement to relieve the obstruction. The patients' characteristics, such as age, sex, time from transplantation, length of obstruction, and intervention history, are shown in Table 1.

Table 1.

Patients' Data and Treatment Outcomes

Patient no./age(years)/gender	Previous treatments	Renal function	Length of obstruction (mm)	Type of stent (mm)	Follow-up (months)
1/47/M	Open UVJO repair ×2, endoincision with balloon dilation ×2, PCN, DJS	Normal	23	40	51, normal
2/52/M	Open UVJO repair ×1, endoincision with balloon dilation ×3, DJS	Normal	12	40	86, normal
3/61/F	Open UVJO repair ×2, endoincision with balloon dilation ×2, DJS	Impaired	28	40	36, urothelial hyperplasia, fail renal function
4/45/M	Open UVJO repair ×1, endoincision with balloon dilation ×2, DJS	Normal	20	40	34, normal
5/51/F	Open UVJO repair ×1, endoincision with balloon dilation ×1, PCN, DJS	Normal	37	60	27, impaired renal function
6/37/F	Open UVJO repair ×1, endoincision with balloon dilation ×1, PCN, DJS	Normal	33	40	13, normal
7/32/M	Open UVJO repair ×1, endoincision with balloon dilation ×1, PCN, DJS	Normal	24	40	45, normal

DJS=Double-J stent; PCN=percutaneous nephrostomy; UVJO=ureterovesical junction obstruction.

The metal stent (AnDaXing, Beijing, China) used in this study was a self-expanding titanium-nickel alloy stent, as previously described.¹⁰ It was placed in a 7F sheath catheter in its unexpanded form with a supported guidewire. When the supported guidewire is fixed and the sheath catheter is withdrawn, the stent gradually emerges from the sheath and remains in place. The stent has a shaft diameter of 7 mm when fully expanded and is available in lengths of 40 and 60 mm. The stent can be removed using a holmium:YAG laser to break the metal wire.

The essential steps of ureteral stent implantation in the present study were as follows. The patient was placed in the supine position under general anesthesia or continual epidural anesthesia. In patients with a percutaneous nephrostomy, a guidewire was passed into the bladder through the nephrostomy tube and out through the urethra using an F8/9.8 rigid ureteroscope. In patients without a history of percutaneous nephrostomy, the guidewire was retrogradely inserted into the ureter (Fig. 1A). A retrograde ureteroscope was then passed over the guidewire to ascertain the length and degree of the obstruction (Fig. 1B). The stent was placed when the stenosis was longer than 10 mm. It was assembled over the guidewire under fluoroscopic guidance, and the ureteroscope was also used to visualize the ureterobladder junction (Fig. 1C). Flow-controlled antegrade pyelography was performed to confirm the patency of the segment containing the stent (Fig. 1D). At the end of the procedure, a retrograde ureteroscope was used to confirm the expanse of the stent (Fig. 2A, B). A Double-J stent and a 16F Foley catheter were then placed. The catheter was removed 1 day after the operation, and the Double-J stent was removed 1 month later.

FIG. 1.

Essential steps of ureteral stent implantation. (A) The guidewire was retrogradely inserted into the ureter. (B) Retrograde ureteroscopy was performed to ascertain the length and degree of the obstruction. (C) The stent was assembled over the guidewire under fluoroscopic and ureteroscopic guidance. (D) Flow-controlled antegrade pyelography was performed to confirm the patency of the segment containing the stent.

FIG. 2.

Retrograde ureteroscopy was used to confirm the expanse of the stent. (A) Observed in bladder. (B) A closer view.

Ultrasonography, urography, diuretic renography, and urine culture were performed every 3 months after stent insertion. Ureteroscopic examinations were performed when needed.

Results

Stent placement was technically effective in all seven patients. The mean operative time was 37 minutes (range, 26–59 minutes). One patient developed a fever on the first postoperative day, and a urine culture revealed a urinary-tract infection caused by Escherichia coli. The patient was treated with intravenous antibiotics. No other specific perioperative complications were recorded in this series.

Lower urinary-tract symptoms were reported in six patients and were relieved after removal of the Double-J stent. Four patients developed an ipsilateral flank pain that was greatly relieved after an average of 3 months.

The mean follow-up duration was 41.7 months (range, 13–86 months). All stents were patent. No stent migration or fragmentation was observed.

Before surgery, six patients had a normal serum creatinine level and one had impaired renal function (serum creatinine, 2.6 mg/dL). During the follow-up period, five patients maintained normal stable renal function and ureter patency, as shown by diuretic renography. The other two patients had impaired renal function, including the patient with preoperative impaired renal function. Ureteroscopic examination in these two patients revealed a varying degree of urothelial hyperplasia (Fig. 3A, B). However, urothelial hyperplasia-induced obstruction occurred at 18 months in one patient who had impaired renal function preoperatively. This patient was managed with a Double-J stent. Unfortunately, this patient required dialysis at the end of the follow-up period (36 months).

FIG. 3.

Varying degrees of urothelial hyperplasia. (A) Mild urothelial hyperplasia. (B) Urothelial hyperplasia-induced obstruction.

Discussion

Ureteral obstruction occurs in 0.5% to 10.0% of all renal allograft recipients.^1
–3 The most common reason for ureteral obstruction is ureteral ischemia or a faulty surgical technique. In addition, obstruction typically occurs in the early stage; late obstruction is usually caused by ureteral fibrosis or compression of the ureter by surrounding fibrotic tissue.^11,12

The traditional treatment method for ureteral obstruction is open surgery with ureterovesical reimplantation. However, open repair is associated with a high risk of complications, including bleeding, ureteral ischemia, and graft loss, especially in patients who have undergone multiple open surgeries.² With the development of surgical instruments and the advancement of endourologic techniques, various minimally invasive techniques have been reported for the management of ureteral obstruction as an alternative to open surgery.

Percutaneous nephrostomy, which can provide rapid control of an obstructed renal system, has gained wide acceptance for the management of ureteral obstruction in transplanted kidneys. The overall success rates of percutaneous therapy for ureteral strictures are reportedly from 58% to 95%.^13,14 However, percutaneous nephrostomy may be associated with infection, catheter displacement, or hematuria, preventing its perpetual use.

Endourologic treatment using endoscopic incisional therapy or balloon dilation is another useful treatment for ureteral obstruction. With Double-J stent placement, the short-term success rate reportedly ranges from 38% to 80%.^15
–17 However, the long-term (>1-year) success rate is considerably lower at ∼50%.¹⁸ In addition, Double-J stents are associated with several problems, including pain, infection, lower urinary-tract symptoms, and stone formation and migration, preventing their extensive use.^19,20 The need for frequent Double-J stent exchange may lead to a reduced quality of life.

The use of metallic self-expandable stents for the management of ureteroileal anastomotic strictures was first described in 1990 by Gort et al.²¹ Since then, several types of metallic stents have been described for the treatment of benign ureteral strictures with satisfactory success rates.^6,7 However, because the long-term patency of metallic stents in patients with transplant ureteral stenosis has not been clearly established, these stents have been conservatively used in only a few patients with severe chronic graft dysfunction or high surgical risk.⁸ The characteristics of metallic stents used to treat transplant ureteral stenosis are listed in Table 2.

Table 2.

Characteristics of Metal Stents Used to Treat Transplant Ureteral Stenosis

Study	Number of patients	Type of stent	Mean follow-up (months)	Characteristics
Burgos⁸	11	Metallic self-expanding stents	48	The patency rate was 73% (8/11). Three patients (27%) developed stent occlusion.
Boyvat²²	4	Memokath 051 stent	20	One stent migrated and one stent had to be removed due to resistant infection, The other two stents were fully patent at the 18th and 21st month of follow-up.
Bach²³	8	Memokath 051 tents	48	One treatment failure in a patient with an obstructed, dilated, and convoluted ureter. The overall success rate was 87%.
Cantasdemir⁹	1	Memotherm self-expanding metallic stent	36	The stented ureter stayed patent.
Herrero²⁴	2	Self-expanding metallic stent	—	Effective.

Stent migration is one of the most common complications in previous studies.⁷ It especially occurs in patients with soft nonfibrotic stenosis.²⁵ Balloon dilation may widen the ureter too much and cause stent slippage in the early postoperative phase.²⁶ None of the stents in the present study migrated during the follow-up period, which may have been because no other operations (balloon dilation or endoscopic incisional therapy) were performed to dilate the ureter during stent implantation.

Ipsilateral flank pain has not been frequently described in the literature, but occurred in four of our seven patients. Interestingly, the pain always occurred with micturition, and varying degrees of relief were provided when the lower right abdomen was pressed. Urinary reflux or the stent itself may have been the cause of the pain. Voiding cystourethrography would have been a useful method for identification of urinary reflux. However, this is an invasive examination and was not performed in these patients. This symptom was greatly relieved on an average of 3 months after the operation in all four patients.

Urothelial hyperplasia is the most common complication associated with ureteral metal stent implantation. In their experimental study, Barbalias et al.²⁷ stated that the grade of urothelial hyperplasia was proportionally dependent on both the degree of force exerted on the ureteral wall and the extent of ureteral overstretching and resultant urothelial trauma. It is important to avoid overextending the strictured area of the ureter and to always maintain the principle of atraumatic dilation.^28,29 Urothelial hyperplasia-induced obstruction occurred in only one patient with preoperative renal dysfunction. The other six patients recovered well without urothelial hyperplasia-induced obstruction. In the present study, operations such as endoscopic incisional therapy or balloon dilation were performed at least 1 month earlier, and no other operations were performed at the time of metal stent implantation. This may be an important protective factor that can help to avoid urothelial hyperplasia.

Stone formation is another common problem caused by self-expanding metal stents.¹⁰ Stone formation always occurs at the top of the stent when it is outside the ureteral lumen. No cases of stone formation were found among our patients. Stone formation may be a concern associated with the method we previously described.¹⁰ We recommend that metal stents are placed under retrograde ureteroscopy and that no more than 0.2 cm of the stent protrudes into the bladder. In this way, the stent is embedded in the ureteral epithelium, preventing encrustation and stone formation.

Conclusions

Our results show that metal stent implantation is a safe and effective treatment for ureteral stenosis in patients who have undergone kidney transplantation. However, because self-expanding metallic ureteral stents are difficult to remove when complications occur, we suggest that this method can be considered as an alternative to open surgery for patients with a high surgical risk or after a previous failed surgery.

Footnotes

Acknowledgments

This work was partially supported by 2014 Guangdong Province Public Research and Capacity Building Special Foundation (No. 2014A020212344).

Author Disclosure Statement

No competing financial interests exist.

Abbreviations Used

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