Content uploaded by Sarel Halachmi
Author content
All content in this area was uploaded by Sarel Halachmi on Sep 19, 2016
Content may be subject to copyright.
A New Self-Expanding, Large-Caliber Ureteral Stent:
Results of a Multicenter Experience
Boaz Moskovitz, M.D.,*Sarel Halachmi, M.D.,*and Ofer Nativ, M.D.
Abstract
Background and Purpose: Ureteral strictures (US) can be a recurrent chronic illness that leads to severe side
effects and poor quality of life. Several options to treat US exist, including repeated dilations, stents, minimally
invasive reconstructive surgeries, and urinary diversion or nephrectomy. Placement of an ureteral stent is a good
minimally invasive option but has major limitations, such as stent migration, mucosal in-growth, incrustations,
and stent obstruction. Our study aim was to evaluate the safety and the efficacy of a new self-expanding, large
caliber ureteral stent (Allium
).
Patients and Methods: During 2005 to 2011, 49 stents were inserted in 49 renal units (40 patients) for a mean
indwelling time of 17 months (range 1–63 mos).
Results: Migration was observed in seven (14.2%) patients, mandating stent removal. Only one stent was
occluded. In eight renal units, the stents were removed as scheduled, and no reobstruction was detected during
follow-up. Twenty-eight patients currently have a patent stent.
Conclusions: The Allium stent provides an attractive solution for long-term internal ureteral drainage. Its
design allows good anchoring, prevents intraluminal ingrowth, and has the ability of rapid disintegration for
extremely easy removal.
Introduction
Ureteral stents have been used when the patency of
the lumen has been compromised as a result of be-
nign or malignant strictures, obstructing calculi, infiltra-
tive processes, including malignancies, and also extrinsic
compression. Currently, chronic ureteral stenosis is man-
aged by a percutaneous nephrostomy tube or by a poly-
mer or a metal Double J stent. All offer safe and efficient
urinary drainage; however, they are related to many side
effects, including tissue erosion, infection, and tube en-
crustation necessitating frequent replacement (every few
months).
1
Tissue ingrowth and massive encrustation are common
problems that can cause difficulties or inability to remove the
stent. Metal mesh stents have shown more promising results
with a low rate of complications; however, they are not cov-
ered by medical insurance here.
2
For the above mentioned reasons, we evaluate the long-
term feasibility and effectiveness of a new self-expanding,
large caliber ureteral stent (URS) (Allium,
Allium LTD,
Caesarea, Israel), instead of repeated use of a Double J stent
or a nephrostomy tube in patients with chronic ureteral
stenosis.
Patients and Methods
The Allium URS is a fully covered, self-expanding, large
caliber metal stent especially designed for the ureter. The
metal self-expanding component of the stent is made of a
super-elastic nickel-titanium alloy (nitinol). The entire stent is
covered with a new biocompatible, biostable polymer to make
it a nonpermeable tube to prevent tissue ingrowth into the
lumen and early encrustation. The Allium URS comes in two
calibers (24F and 30F) and in two lengths (10 cm and 12 cm).
It has a main body with high radial force with softer end
segments. The main segment is connected with a single
wire passing the ureterovesical junction (UVJ) to an in-
travesical anchor portion (Fig. 1). Longitudinally the URS is
very flexible and has a strong enough radial force to keep the
ureter lumen open by opposing the ureteral wall to allow
intraluminal flow.
The Allium URS comes mounted on a 10F antegrade or
retrograde insertion device. The stent also have a special un-
raveling feature to make its endoscopic removal easy, non-
traumatic, and secure (Fig. 2). The URS does not shorten
during or after its deployment, making its positioning accu-
rate and stable. Because of its anchoring system, it is best used
primarily as a segmental proximal and distal ureteral stent.
Department of Urology, Bnai Zion Medical Center, Rappaport Faculty of Medicine, Technion-Israel Institute of Technology, Haifa, Israel.
*Drs. Moskovitz and Halachmi contributed equally in the preparation of this manuscript.
JOURNAL OF ENDOUROLOGY
Volume 26, Number 11, November 2012
ªMary Ann Liebert, Inc.
Pp. 1523–1527
DOI: 10.1089/end.2012.0279
1523
Insertion of URS was performed under general or regional
anesthesia. The ureters were contrasted antegradely via the
nephrostomy tube or retrogradely by a ureteral catheter that
replaced the Double J stent, with iodine injected under fluo-
roscopic control showing the site of narrowing.
In sequence, a guide wire was introduced and a ureteral
balloon dilator passed over the wire to the site of pathology
and inflated to 20 atm (1.72 MPa) according to the manufac-
turer’s recommendations. After fluoroscopy confirmed dis-
appearance or significant diminution of ‘‘waist,’’ the stent was
inserted into the strictured ureter (retrograde or antegrade)
and its position fluoroscopically confirmed (Fig. 3).
In four different centers (in Israel, Italy, Serbia, and Spain)
and after local Institutional Review Board approval, the
Allium URS was inserted into 49 occluded ureters in 40 pa-
tients. Thirty-one patients had a nephrostomy tube and 9
patients had chronic Double J stent placement. From the
31 patients with a nephrostomy tube, in 20 patients the
URS was inserted antegradely, in 11 combined (antegrade
dilation/retrograde insertion); in the other 9 cases, the URS
was inserted retrogradely.
Follow-up
For patients with underlying malignant obstruction, CT
urography was used to assess renal function and oncologic
status; for patients with nonmalignant obstruction, 6 weeks
after stent insertion, diethylenetriaminepentaacetic acid
(DTPA) renography was performed. If results of renography
did not show obstruction, baseline ultrasonography was
performed; then we used sonography for follow-up looking
for changes in hydronephrosis.
Results
From March 2005 until October 2011, we enrolled 40 pa-
tients (49 ureteral strictures [US]) into the study. The clinical
parameters of the patients who underwent Allium URS in-
sertion and follow-up are shown in Table 1. Seventeen pa-
tients had US after surgery and radiation therapy for
gynecological malignancies, 8 after endoscopic resection of
bladder cancer; 5 strictures occurred at the ureteroenteric
anastomosis after urinary diversion for muscle invasive blad-
der cancer, 5 strictures occurred after endoscopic treatment of
ureteral stones, and 2 strictures occurred in a patient with
FIG. 1. Allium ureteral stent structure; stent flexibility.
UVJ =ureterovesical junction.
FIG. 2. (a–c) The Allium ureteral stent is designed for easy
unraveling.
FIG. 3. Insertion of two consecutive Allium ureteral stents
to a long ischemic ureteral stricture of a transplanted kidney.
1524 MOSKOVITZ ET AL.
ureterocutaneous diversion performed for congenital anoma-
lies that were later complicated and mandated diversion.
All stents were inserted successfully and positioned cor-
rectly in the 49 ureters. No significant adverse events related
to the stent or to the procedure were recorded. During a mean
follow-up time of 21 months (range 1–63 mos), only one of
the stents was occluded after 11 months. In eight ureters, the
stent was removed endoscopically after an average time of
11 months (range 9–12 mos). Stent migration (1–6 mos after
insertion) occurred in seven (14.2%) ureters (five into the
bladder, and two into the renal pelvis). After migration, the
stents were endoscopically removed (except in one patient
who refused any endoscopic treatment). In two patients with
early migration, a new stent was reinserted successfully for an
additional 10 and 12 months, respectively.
All eight patients in whom the URS was removed as
scheduled are asymptomatic with a patent upper urinary tract
after a follow-up time that ranged from 6 to 45 months.
Currently, 28 patients have a patent stent and continue peri-
odic follow-up. Thirteen patients died from their primary
malignancy carrying a patent stent. In eight patients, the stent
was removed at a scheduled time. All of them had immediate
ultrasonography that showed no new hydronephrosis—four
(with no malignant strictures) had nonobstructed DTPA re-
nography 6 to 8 weeks after stent removal, and three patients
who had malignant disease are still await CT urography for
oncologic and uromechanic evaluation. Currently, all three
are asymptomatic regarding urologic symptoms.
Discussion
Independent of the etiology, prolonged obstruction or
narrowing of the ureter can severely compromise the renal
function of the involved kidney. Urinary drainage is neces-
sary for pain relief, to reduce the risk of infection, and above
all, to restore adequate renal function.
URS or percutaneous nephrostomy tubes have been used
when the patency of the lumen has been compromised as a
result of benign or malignant strictures, obstructing calculi,
infiltrative processes, including malignancies, and also ex-
trinsic compression. Both provide safe and efficient urinary
drainage.
2–5
URS are effective but carry various side effects including
infection, bladder irritation, or bleeding and require frequent
replacements every 3 to 6 months. In rare occasions, severe
internal stent encrustation may prevent its endoscopic re-
moval, mandating open surgery.
1,5
A nephrostomy tube has a negative impact on patient
quality of life. It is uncomfortable for the patient and, in ad-
dition, can be associated with infection, skin erosion, tube
encrustation, obstruction, or accidental removal. In this situ-
ation, the patient undergoes frequent replacement with its
inconvenience and costs.
6
A stent is a device that is intended to keep a biologic pas-
sage open. It can vary in shape, length, and dimension, as well
as in physical and biologic properties, and can be designed for
permanent or temporary application. The stents may be fab-
ricated from polymer, metal, biologic material, or combina-
tions of these.
7,8
Currently, chronic benign or malignant ureteral stenosis is
managed by polymer or metal Double J stents. The biologic
properties of stents refer to their interactions with tissue and
body fluids. Therefore, the polymeric Double J stents have to
be changed every 3 to 6 months to prevent the risk of occlu-
sion, encrustation, infection, tissue erosion, and polymer
disintegration.
The Resonancemetal coil stent that has a 6F caliber is
device, Double J in shape, that is designed for long-term in-
dwelling as well as for extreme extrinsic compression. Urine
drainage is carried out by two mechanisms: Capillary-flow
around the coiled external surface of the stent and also
through the stent. Unfortunately, this stent is not included in
the Ministry of Health national medical insurance coverage.
The new large-caliber, self-expanding Allium URS made of
a super elastic nickel-titanium alloy ensures lumen patency by
providing direct wall support. These stents have been fash-
ioned to provide long-term wall support. The entire stent is
covered with a new biocompatible polymer to make it a
nonpermeable tube to prevent tissue ingrowth into the lumen
and early encrustation, thus facilitating its removal even after
a long indwelling period.
The stent also has a special unraveling feature to make its
endoscopic removal, whenever needed, easy, nontraumatic,
and secure.
Table 1. Patient Characteristics and Follow-Up
Mechanism of stricture
No.
patients
Ureteral
units
Indwelling
time (mos)
(range) Migration No.
Stent
obstruction
Ureteral patency
after ureteral stent
removal (mos)
Following surgery/radiation
therapy for gynecologic
malignancy
17 25 1–63 3 (at 3–6 months) 0% 1 patient (45)
3 patients (8–11)
Following surgical and topical
treatment for bladder cancer
8 8 9–13 1 (at 3 months) 0% 1 patient (27)
2 patients (6–11)
Ureteroenteric anasthomosis
stricture after urinary
diversion
5 5 15–17 1 (at 1 month) 0%
Following endoscopic treatment
of ureteral calculi
5 6 1–13 0 16% 1 patient (9)
Ureterocutaneostomy stricture 2 2 2 2 (at 2 months) 0%
Renal transplant 3 3 12–15 0 100%
Total 40 49 Av. 17 months 7 ( 14.2% ) 98% 8
NEW STENT FOR URETERAL STRICTURES 1525
Our study demonstrated that after proper insertion, the
Allium URS provided initial luminal patency in 48 of 49
ureters (98%), proved by either CT urography or DTAP nu-
clear renography. Unfortunately, seven (14.2%) stents mi-
grated, reducing the total success rate to 95%, mandating stent
removal in six patients. One patient with cutanous ureter-
ostomy refused any intervention and remained with an in-
dwelling Foley catheter that passes through the migrated
stent. Three patients had removal and immediate reinsertion
and three other patients had their stent removed after suffi-
cient time; hence, they remain without a stent. In all three, no
clinical symptoms of flank pain or urinary tract infection oc-
curred; immediate ultrasonography did not reveal any new
hydronephrosis. The DTPA scan showed no obstruction in
two and one refused radiation imaging.
Fortunately no encrustations were documented, most
probably because of the thin copolymer that covers the entire
stent lumen, preventing intraluminal ingrowth and hyper-
plastic reaction, allowing the stenotic area to remain open, as
long as the stent is in place.
Liatsikos and associates
9
evaluated the efficacy of the Re-
sonance metallic stent in 18 patients with ureteral obstruction.
Only 44% of the patients maintained patency after a mean
follow-up of 7 months. Most failures occurred within a few
weeks as a result of hyperplastic tissue reaction around the
coils and gross calcification. Newer data provided by Benson
and colleagues
2
showed better results with a metal stent. Out
of 42 renal units with stent insertion, only three (7%) failures
were documented. One stent located at the distal ureter was
obstructed because of encrustation of the bladder anchoring
portion. In this case, the patient who had bladder outlet ob-
struction with significant postvoid residual urine volume had
his intraureteral portion of the stent patent and without
encrustation.
Stent migration occurred only in 7 of the 49 (14.2%) pro-
cedures. In two patients with cutaneous ureterostomy, the
stent migrated within the ureter toward the kidney. In one
patient, the stent was easily removed and the other refused its
removal. This patient’s kidney is drained with an indwelling
Foley catheter that passes easily through the migrated stent
and is replaced every 12 weeks without difficulties. The re-
maining five patients with strictures in various sites of the
middle third of the ureter had their stent removed without
difficulties, and in two of them, a new stent was reinserted
successfully. The anchoring mechanism seems to be less effi-
cient in mid-US probably because its anchoring segment is
also located in the ureter. This is different from ureteropelvic
or UVJ strictures, where the anchoring segment is located in
the renal pelvis and in the bladder, respectively.
Stent migration is a significant problem for both intra-
luminal and endoluminal stents. Motola and coworkers,
10
who described their experience with ureteral stents after
endopyelotomy, reported a 14% migration and reposition-
ing rate. Gibbons
11
initially addressed the problem of
downward migration of soft silicone stents by adding barbs
along its shaft, a stent design that bears his name. All cur-
rently available, completely internalized stents combat mi-
gration with the presence of a proximal and distal J
or pigtail. Nevertheless, peristalsis may discharge a stent
(especially one constructed from softer materials) from the
ureter. One can also speculate that the prevalence of this
complication will increase with the use of stents coated with
hydrophilic materials. Stent migration has been observed
for metallic stents as well. Papdopoulos and colleagues
12
showed their experience with 13 Memokath metallic stents
for the management of US and reported migration in 6 (43%)
of the cases.
In our study, the Allium URS was successfully used in a
wide variety of complex clinical situations, including in pa-
tients who had previous radiation therapy, after surgical
ureteral injury, and even after renal transplant.
In two patients with strictures that were longer than the
stent body length, two successive Allium URS were inserted
at the same procedure, emphasizing the ability to provide a
solution even in such cases.
Our results indicate that the use of Allium URS is feasible,
safe, and effective for long periods without the need for sec-
ondary interventions to maintain ureteral patency (average
17 mos).
A more extensive experience is necessary with a larger
number of patients and longer follow-up to confirm the effi-
cacy of these new stents.
Conclusion
Allium URS are an excellent solution for temporarily long-
term internal ureteral drainage. Insertion of the stent is
simple and its positioning is under fluoroscopy; the removal
can be performed under local anesthesia as an outpatient
procedure. Being covered by a thin copolymer, intraluminal
ingrowth was prevented allowing prolonged indwelling
time and simple removal. The stent is best used for proximal
and distal strictures. Mid-US can also be managed with the
stent; however, most of the migration cases occurred in this
setting.
This minimally invasive treatment alternative is more ef-
ficient than current endoscopic treatments, is safe, tolerated
by the patient, and more cost effective.
Acknowledgments
The authors thank: Dr. Gianpaolo Carrafiello, Department
of Radiology, University of Insubria, Varese , Italy; Dr. Zeljko
Markovic, Dr. Vesna Stojanovic, Dr.Biljana Markovic, In-
stitute of Radiology, and Dr. Jovan Hadzi Djokic, Institute of
Urology and Nephrology, Clinical Center of Serbia, Belgrade,
Serbia; Dr. Ernesto M. Santos,Vascular and Interventional
Radiology Section, Hospital Clinico San Carlos, Madrid,
Spain, for helping in data collection.
Disclosure Statement
No competing financial interests exist.
References
1. Infection and encrustations on stents. In: Yachia D, ed.
Stenting the Urinary System. 1st ed. Oxford, UK: Isis Med-
ical Media Ltd, 1998, pp 71–98.
2. Benson AD, Taylor ER, Schwartz BF. Metal ureteral stent for
benign and malignant ureteral obstruction. J Urol 2011;185:
2217–2222.
3. Praz V, Chollet Y, Jichlinski P. [Indications and methods of
invasive minimal urinary derivations in oncology.] (Fre) Rev
Med Suisse 2007;3:2788–2792.
1526 MOSKOVITZ ET AL.
4. Kanou T, Fujiyama C, Nishimura K, et al. Management of
extrinsic malignant ureteral obstruction with urinary diver-
sion. Int J Urol 2007;14:689-–692.
5. Duvdevani M, Chew BH, Denstedt JD. Minimizing symp-
toms in patients with ureteric stents. Curr Opin Urol 2006;
16:77–82.
6. Stables DP. Percutaneous nephrostomy: Techniques, indi-
cations, and results. Urol Clin North Am 1982;9:15–29.
7. Mardis HK, Kroeger RM, Morton JJ, Donovan JM. Com-
parative evaluation of materials used for internal ureteral
stents. J Endourol 1993;7:105–115.
8. Stent materials. In: Yachia D, ed. Stenting the Urinary
System. 1st ed. Oxford, UK: Isis Medical Media Ltd, 1998,
pp 31–69.
9. Liatsikos E, Kallidonis P, Kyriazis I, et al. Ureteral obstruc-
tion: Is the full metallic double-pigtail stent the way to go?
Eur Urol 2010;57:480–486.
10. Motola JA, Badlani GH, Smith AD. Results of 212 consecu-
tive endopyelotomies: An 8-year follow-up. J Urol
1993;149:453–456.
11. Gibbons RP. Gibbons ureteral stents. Urol Clin North Am
1982;9:85–88.
12. Papadopoulos GI, Middela S, Srirangam SJ, et al. Use of
Memokath 051 metallic stent in the management of ureteral
strictures:A single-center experience. Urol Int 2010;84:286–291.
Address correspondence to:
Sarel Halachmi, M.D.
Department of Urology
Bnai Zion Medical Center
47 Golomb Street
Haifa 31048
Israel
E-mail: Sarel.halachmi@b-zion.org.il
Abbreviations Used
CT ¼computed tomography
DTPA ¼diethylenetriaminepentaacetic acid
URS ¼ureteral stent
US ¼ureteral strictures
UVJ ¼ureterovesical junction
NEW STENT FOR URETERAL STRICTURES 1527
