Hindawi Publishing Corporation
Gastroenterology Research and Practice
Volume 2013, Article ID 642428, 7 pages
A Multicenter, Prospective Study of a New Fully Covered
Expandable Metal Biliary Stent for the Palliative Treatment
of Malignant Bile Duct Obstruction
Bret T. Petersen,1Michel Kahaleh,2,3Richard A. Kozarek,4David Loren,5Kapil Gupta,6,7
Thomas Kowalski,5Martin Freeman,8Yang K. Chen,9Malcolm S. Branch,10
Steven Edmundowicz,11Michael Gluck,4Kenneth Binmoeller,12Todd H. Baron,1
Raj J. Shah,13Timothy Kinney,14William Ross,15Paul Jowell,10and David Carr-Locke16,17
1Charlton 8, GI Endoscopy, Mayo Clinic, 200 1st Street SW, Rochester, MN 55905, USA
2Weill Cornell Medical College, 1305 York Avenue, 4th Floor, New York, NY 10065, USA
3University of Virginia, Charlottesville, VA, USA
4Virginia Mason Seattle Main Clinic, 1100 Ninth Avenue, Seattle, WA 98101, USA
5Thomas Jefferson University, Main Building, Suite 480, 132 South 10th Street, Philadelphia, PA 19107, USA
6Cedars-Sinai Medical Center, 8700 Beverly Bl No. 7511, Los Angeles, CA 90048, USA
7Hennepin County Medical Center, Minneapolis, MN, USA
8GI Division, Department of Medicine, Hennepin County Medical Center, MMC 36, 420 Delaware Street SE,
Minneapolis, MN 55455, USA
9University of Colorado Boulder, Campus Box F735, Anschutz Inpatient Pavilion (AIP), S/M Gastroenterology,
Therapeutic Endoscopy, USA
10Duke University, DUMC 3662, Durham, NC 27710, USA
11Washington University, School of Medicine, 660 South Euclid Avenue, Campus Box 8124, St. Louis, MO 63110, USA
12California Pacific Medical Center, 2351 Clay Street No. 304, San Francisco, CA 94115, USA
13University of Colorado, Campus Box F735, Anschutz Outpatient Pavilion (AOP), Room 2136-A,
P.O. Box 6510, Aurora, CO 80045, USA
14Hennepin County Medical Center, Medicine Office, GI 865B, 701 Park Avenue, Minneapolis, MN 55415, USA
15The University of Texas MD Anderson Cancer Center, 1400 Pressler, Unit Number: Unit 1466, Houston, TX 77030, USA
16Beth Israel Medical Center, 10 Union Square East, Suite 2G, New York, NY 10003, USA
17Brigham and Women’s Hospital, Boston, MA 02215, USA
Correspondence should be addressed to Bret T. Petersen; email@example.com
Received 19 September 2012; Accepted 22 January 2013
Academic Editor: Gianfranco D. Alpini
Copyright © 2013 Bret T. Petersen et al.ThisisanopenaccessarticledistributedundertheCreativeCommonsAttributionLicense,
which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
malignant biliary obstruction. A fully covered biliary SEMS (WallFlex Biliary RX Boston Scientific, Natick, USA) was assessed
for palliation of extrahepatic malignant biliary obstruction. Patients and Methods. 58 patients were included in this prospective,
multicenter series conducted under an FDA-approved IDE. Main outcome measurements included (1) absence of stent occlusion
within six months or until death, whichever occurred first and (2) technical success, need for reintervention, bilirubin levels, stent
patency, time to stent occlusion, and adverse events. Results. Technical success was achieved in 98% (57/58), with demonstrated
acute removability in two patients. Adequate clinical palliation until completion of followup was achieved in 98% (54/55) of
evaluable patients, with 1 reintervention due to stent obstruction after 142 days. Mean total bilirubin decreased from 8.9mg/dL to
acute removal where required, appropriate reduction in bilirubin levels, and low rates of stent migration and occlusion. This SEMS
allows successful palliation of malignant extrahepatic biliary obstruction.
2 Gastroenterology Research and Practice
Endoscopic stent placement is now a standard therapy for
generally employed in patients with benign or indeterminate
life expectancy . Self-expanding metal stents (SEMSs) are
indicated in patients with confirmed inoperable malignant
biliary strictures. Bare SEMS are typically employed at the
porta hepatis, while bare, partially covered, or fully covered
covered SEMSs are prone to late occlusion due to ingrowth
through the struts of the stent or overgrowth at the ends by
fully covered SEMS may be more prone to migration . A
fully covered stent with design features that limit migration
yet facilitaterepositioningor removalwould provide optimal
palliation of malignant strictures without significant risk
related to inaccurate placement, size selection, or ultimate
tissue diagnosis. The WallFlex Biliary RX Fully covered Stent
is designed to meet these needs. This study was undertaken
to evaluate the safety and clinical effectiveness of this new
stent for palliative treatment in patients with inoperable
extrahepatic malignant biliary obstruction.
2. Patients/Materials and Methods
10 centers under an Investigational Device Exemption (IDE)
from the Food and Drug Administration (FDA). The study
protocol and amendments were approved by Institutional
Review Boards at all participating centers. All patients, or
their legal representatives, provided written Informed Con-
sent prior to enrollment. An Independent Medical Reviewer
assessed events of stent occlusion or migration and all
events resulting in death. This expert endoscopist was not
an employee of the sponsor or involved with a participating
Inclusion criteria required (1) presence of inoperable
ical symptoms of biliary obstruction, (3) age 18 or older, and
(4) Willingness and ability to comply with study procedures
and provide signed informed consent. Exclusion criteria
included any of the following: (1) participation in another
investigational study within 90 days prior to consent, (2)
Strictures that could not be traversed by the delivery system,
stent, (6) contraindications to endoscopy, (7) sensitivity to
any components of the stent or delivery system, (8) Active
hepatitis, (9) intrahepatic metastases that extensively involve
both lobes of the liver, and (10) life expectancy of <3 months.
The primary endpoint was adequate clinical palliation
of biliary obstruction, as demonstrated by maintenance of
bilirubin below 3mg/dL or reduction by >30% if the baseline
ever occurred first. A stent was considered occluded if the
value was greater than 3mg/dL and absence of evidence of
stent occlusion until death or 6 months of followup, which-
patient presented with elevation of total bilirubin that the
treating physician deemed to be due to recurrent biliary
Secondary endpoints included (1) ability to deploy the
stent in satisfactory position, (2) ability to successfully repo-
sition or remove the stent, if required, at initial placement or
technical difficulties, (3) occurrence and severity of device
and procedure-related adverse events, (4) need for reinter-
vention, (5) reduction in symptoms of biliary obstruction
(jaundice, pruritus, right upper quadrant pain, fever, nausea,
vomiting, and dark urine) at all visits, (6) patency at 1, 3, and
6 months, and (7) time to stent occlusion.
2.1. Follow-Up Visits. Stent patency at 1 month was assessed
by total bilirubin level and at 1, 3, and 6 months by lack of
obstructive symptoms. Follow-up visits were primarily con-
ducted by phone, with inperson unscheduled visits required
in case of recurrent obstructive symptoms.
2.2. Enrollment and Analysis Cohorts. A total of 74 patients
who signed the informed consent form (ICF) were con-
sidered enrolled. After enrollment, fourteen patients failed
screening relative to eligibility criteria and were withdrawn
from the study without study treatment. Two patients were
successfully treated with the study device but later found not
to have met eligibility criteria. Per protocol, these patients
were not part of the intent-to-treat (ITT) cohort, defined as
had the stent placement procedure initiated. The ITT cohort
and safety. Per protocol, assessment of the primary endpoint
and secondary effectiveness endpoints was performed on the
evaluable cohort, defined as ITT patients with at least one
week of followup. Three patients were excluded from the
evaluable cohort on the basis of death unrelated to the device
device at the index procedure with conversion to another
device (1). Hence, the evaluable cohort had 55 patients.
2.3. Stent Design. The Wallflex Biliary RX fully covered stent
is aradiopaqueSEMSmade ofbraided nitinolwithatranslu-
cent silicone polymer (Permalume) lining of its entire length
taining friction between stent wires and bile duct wall. The
stent ends are flared to minimize risk of migration. Looped
wires at the ends aim to minimize the risk of impaling or
ulcerating the mucosa. The stent has a retrieval loop at the
distal end to facilitate removal or repositioning in the event
of misplacement or migration. The flared ends collapse when
10mm diameters of varying lengths (8mm × 60 and 80mm,
sheath constrains the stent before deployment and can be
advanced to reconstrain the stent, if repositioning is necessa-
ry, after partial deployment down to the marked reconstrain-
ment limit (approx. 80% of the stent length).
10mm × 40, 60, and 80mm).
The delivery system is a coaxial tube design. The outer
Gastroenterology Research and Practice
study noted that the majority (∼80%) of publications on
required to test whether the stent occlusion rate at 6 months
or death was significantly less than 25%, using a 1-sided
binomial test with a significance level of 5% and a power of
90% for an expected stent occlusion rate of 10%.
Kaplan-Meier analysis was used to determine the rates
of survival and stent occlusion based on available followup
information, with censoring for discontinued and deceased
patients and beyond six months after stent placement. The
summarized by the mean and its 95% confidence interval,
based on the normal distribution. A paired t-test was used
to test the significance of reduction in the mean number of
symptoms from baseline to 6 months, using the subset of
patients with paired data available. Effectiveness measures
95% confidence intervals.
2.4. Statistics. A literature review conducted prior to the
covered biliary SEMS report stent occlusion rates of 25%
or less. Therefore, for this study, 55 evaluable patients were
The ITT cohort included 30 men and 28 women, with a
mean age of 68.9 years (range 23–89.8). The top five reported
biliary obstructive symptoms were jaundice (82.8%), dark
ritus (32.8%), and nausea (17.2%). Tumor type and stricture
location are summarized in Tables 1 and 2. Twenty patients
(34.5%) had a previous biliary sphincterotomy.
3.1.StentPlacementandRemoval. Stentplacement(Figure 1)
was technically successful in 57 of 58 patients (98%) in the
ITT cohort (Table 3). Deployment was attempted but failed
in 1 patient due to severe angulation of the duodenoscope.
In this patient the deployment system was removed and a
noninvestigationalbiliary SEMS was placed during the index
Three stents were deployed but immediately removed
from two patients to better match the pathologic anatomy.
In one, a stent that was deemed to be of excessive length
was deployed, but subsequently removed and replaced with
a shorter sent. In the other patient, a 10mm × 60mm stent
within the tight stricture. Both were removed without tech-
proved insufficiently long and a 10mm × 40mm stent placed
through the initially placed stent did not expand completely
nical or clinical complications, after which a 10mm × 80mm
patients underwent attempted stent removal after the initial
stent placement procedure. All 57 ultimately placed study
60mm in 72%, and 80mm in 14% of stents.
stent was placed in good position. Thus, three stents were
successfully removed without adverse events (Table 3). No
3.2. Effectiveness. A summary of key effectiveness results is
had adequate clinical palliation of biliary obstruction until
death or completion of followup. This rate of stent occlusion
Table 1: Types of malignancy at baseline.
(푁 = 58 subjects)
Other undefined malignancy
Retroperitoneal mass, suspect sarcoma
Malignant adenopathy of the porta hepatic
portacaval, and pericardial regions
Peripancreatic malignant lymphadenopathy
Lymphoma to porta hepatis
Table 2: Baseline stricture locations.
Location of stricture
푁 = 58 (%)
Distal common bile duct (CBD)
Proximal common bile duct
Distal CBD and mid CBD
Junction of distal CBD and mid CBD
literature (25%) (푃 < 0.0001). Of the 55 patients, 23 were
continued followup presented with bacteremia, cholangitis,
and fever due to stent occlusion 142 days after stent place-
ment. In this case, the distal end of the stent was collapsed
on itself at the level of the papilla with repositioning wire
tines extending from the papilla which detached during stent
manipulation. The distal end of the stent was balloon dilated,
and a commercial uncovered SEMS was placed inside the
occluded stent with prompt clinical improvement. Another
patient had an ampullary cancer and adequate clinical palli-
ation, but experienced asymptomatic stent migration at day
84, which was deemed a result of response to radiation ther-
apy. The patient did not require restenting. Five additional
patients were dropped from followup for reasons unrelated
to the stent at 33, 45, 50, 138, and 161 days after placement,
including 3 patients that underwent Whipple procedures
despite not originally being considered surgical candidates,
1 patient categorized as lost to followup on day 138 despite
multiple contact attempts after the week 1 visit when no
biliary obstructive symptoms were reported, and 1 patient
who withdrew consent early due to failing health.
Total bilirubin levels at baseline and month 1 were
available for 45 of the 55 evaluable patients. Among them,
44/45 (97.8%) demonstrated successful maintenance of total
level reducing from 8.9mg/dL (range 0.4–27.1) to 1.2mg/dL
41 (70.7 %)
followed to 6 months, 25 died while on study, and 7 were
4 Gastroenterology Research and Practice
Tip of deployment
Air in intrahepatic ducts
Figure 1: (a)–(c) Cholangiographic images of malignant biliary stricture and WallFlex Biliary Stent placement. (a) 254 × 254mm (96 ×
96DPI), (b) 338 × 338mm (72 × 72DPI), and (c) 338 × 338mm (72 × 72DPI).
Table 3: Key effectiveness results.
Adequacy of palliation
Number of biliary obstructive
symptoms at baseline
Mean ± SD (푁)
Number of biliary obstructive
symptoms at month 6
2.7 ± 1.76
0.1 ± 0.46
Range (Min, Max)(1, 8)
Mean ± SD (푁)
Reduction of bilirubin level at
Range (Min,Max)(0, 2)
cirrhosis failed to demonstrate successful reduction in total
bilirubin at the month 1 visit (baseline total bilirubin =
11.0mg/dL; month 1 = 8.0mg/dL). In ten patients month 1
total bilirubin levels were not obtained due to early death
(3) missing blood draw (3), early discontinuation (2), patient
refusal (1), and loss to followup (1).
The mean number of reported biliary obstructive symp-
toms was reduced at each visit compared to the prior visit,
ranging from a baseline mean for all 55 evaluable patients of
Days since index procedure
Freedom from stent occlusion/
patient survival (%)
Freedom from stent occlusion
stent occlusion 81 × 40mm (300 × 300DPI).
the month 6 visit. Analyzing the subset of 23 subjects with
paired data available, there was a significant reduction in
the mean number of symptoms from baseline to 6 months
(푃 < 0.0001). By protocol criteria, stent patency was evident
rate of freedom from stent occlusion, as a function of time
curves in Figure 2. One patient (1.8%) experienced a stent
occlusion. Kaplan-Meier analysis based on the 55 evaluable
of 3.7% (SD 3.6%). The median time to stent occlusion is
at least 210 days. Hence, the study stent appears effective in
providing biliary obstruction-free palliation to most patients
until death or at least 6 months after stenting.
in 91.3% at Month 6.
The estimated patient survival rate and the estimated
3.3. Safety. There were no unanticipated adverse device
effects (UADEs), and no deaths were attributed to the inves-
tigational device. In the ITT cohort, 4 patients experienced
6 serious adverse events (SAE’s) deemed potentially (3)
Gastroenterology Research and Practice5
Table 4: Comparison to recent publications.
5 months6 66 6% (4)94%3% (2) 5% (3) 2% (1)
60 months4 138
21% (29)— 17% (24)7% (9) 4% (5)
11 months 20 14126% (36) 78% 8% (11)10% (14) 6% (8)
Kullman  34 months
20023% (45) 78%0% (0)1% (2)2% (4)
2% (1) Petersen6 months 10
2421% (5)— 0% (0) 0% (0) 4% (1)
2% (4) Talreja 41 months6
18% (11)90% 0% (0)5% (3)2% (1)
29% (20)87% 12% (8)4% (3) 0% (0)
Tringali 30 months
70PC ComVi 30% (21)70% 4% (3)1% (1)0% (0)
∗FC: fully covered; PC: partially covered; UC: uncovered.
or probably (3) related to the study device. Cholecystitis
occurred in 2 patients, 1 of whom also experienced gallblad-
der perforation. In this patient, purulent bile and gallstones
were noted at the time of prior plastic stent removal during
the index procedure. In both patients who experienced
cholecystitis the stents were placed across the cystic duct;
at that level. Both events resolved with antibiotics and
percutaneous gallbladder drain placement. The prevalence
of intact gallbladders among treated patients was not sys-
tematically documented; hence the rate of acute cholecystitis
pancreatitis occurred in one patient who later also developed
self-limited RUQ pain. One patient experienced severe, self-
limited postprocedural nausea. The SAE of cholangitis/stent
occlusion at day 142 noted in the effectiveness section was
reported by the investigator as related to progression of
underlying disease rather than the stent. The stent migration
reported in the effectiveness section was not associated with
an adverse event as it did not lead to patient symptoms.
Six additional patients experienced a total of 7 SAEs
reported as probably or possibly related to the ERCP itself,
including one case of respiratory compromise during proce-
dural sedation, culminating in death 8 days later from result-
ing sequelae and underlying pancreatic cancer, and one case
each of post-ERCP pancreatitis and of postsphincterotomy
procedure related resolved without sequelae.
Studies of endoscopic palliation for malignant inoperable
obstructive jaundice have demonstrated the therapeutic
advantage and cost effectiveness of self-expanding metal
stents compared to surgical bypass or placement of plastic
stents [2, 14, 15]. The efficacy of bare metal stents is limited
overgrowth of tumor and by hyperplastic tissue response at
the short bare segment at the upper end. Thus, the potential
benefit of the central covering is offset by the persistent
risk of occlusion at the uncovered ends [12, 17–19]. Fully
covered designs without sharp wire ends may preclude these
complications and thereby yield prolonged freedom from
stent occlusion. In this series, only one patient experienced
recurrent biliary obstruction, after 142 days.
Recurrent biliary obstruction caused by migration or
stent occlusion remains the most important issue. It is still
unproven whether CSEMS will be a better solution than
uncovered SEMS as evidenced by 2 recently published ran-
showed significantly prolonged stent patency and stent sur-
vival for covered stents. Data from this series and Costa-
magna et al.  suggest that the covered WallFlex stent
design may lead to a lower recurrent biliary obstruction rate
compared to older designs (Table 4). Despite the full length
one stent migrated, and this was asymptomatic in a patient
6 Gastroenterology Research and Practice
with presumed stricture improvement following radiation
therapy. Stent replacement was not required.
This study of a new fully covered SEMS demonstrates
successful endoscopic palliation of unresectable malignant
distal biliary obstruction in 98% of patients, suggesting that
the goals of various stent design features were mostly met. As
in most studies of biliary SEMS, technical placement success
was almost universal. One stent failed to deploy adequately
and was immediately replaced by a commercially available
removed and replaced with different lengths. The narrow
mesh design of the Wallflex stent foreshortens during place-
ment and requiressome attentionto placement, comparedto
the wider mesh nonforeshortening laser cut designs.
lowing the procedure at which they were inserted. Although
there are descriptions of successful removal of uncovered
biliary stents, it is technically difficult to perform and not
predictable . The partially and fully covered metal stents
do not carry labeling for removability in the USA; however,
they have been employed “off-label” for limited durations in
various nonmalignant conditions such as benign strictures
[22, 23] and intractable bile leaks [23, 24]. The partially
covered versions are still prone to proximal ingrowth and
potentially difficult removal [25, 26]. This limits their use
in benign applications, and some authors consider them
inappropriate for use in patients with a life expectancy
greater than 24 months . In this study, we used a fully
covered stent that is retained by collapsible flares at the ends,
which make repositioning or immediate removal relatively
atraumatic and highly predictable. In the porcine model this
stent design was removed shortlyafter placement from all six
animals without difficulty . Similarly, in this study three
patients. If this ease of removal is confirmed in subsequent
studies with longer indwell periods, this stent may alter the
paradigm for palliation of indeterminate biliary strictures
As reported by Siddiqui et al.,  fully covered CSEMS can
ner would be considered “off-label” in the USA. Placement
prior to or at the time of biopsy and prior to assessment of
operability could then proceed without concern about the
likely to resolve with medical therapy, such as strictures
related to lymphoma or IgG4-related disease. Of note in this
series, three patients were originally considered inoperable
but later went on to surgery and en bloc stent removal.
This study is limited by the lack of a comparison group.
within three months, limiting assessment of the duration
of freedom from stent occlusion. Nevertheless, insertion
success, duration of adequate clinical palliation, and compli-
cations were all superior or comparable to most published
data on self-expanding biliary stents. Comparative trials of
metal stents for extrahepatic malignant applications and
versus multiple plastic stents for benign lesions are needed.
The following authors B. Petersen (Olympus America), M.
Kahaleh (Boston Scientific, Fujinon, Emcision, MI TECH,
Lumina, and Boston Scientific), R. Kozarek (Boston Scien-
tific), S. Edmundowicz (Boston Scientific, Olympus Amer-
ica), T. Kowalski (Boston Scientific), R. Shah (Boston Sci-
entific), D. Carr−Locke (US Endoscopy, Telemed, Boston
involved in gastrointestinal endoscopy.
Scientific, Cook Medical, Erbe USA, and BEE Corporation)
disclosed financial relationships with commercial entities
 J. R. Andersen, S. M. Sorensen, A. Kruse, M. Rokkjaer, and P.
Matzen, “Randomised trial of endoscopic endoprosthesis ver-
sus operative bypass in malignant obstructive jaundice,” Gut,
vol. 30, no. 8, pp. 1132–1135, 1989.
copy for palliation of biliary obstruction due to metastatic pan-
creatic cancer,” American Journal of Gastroenterology, vol. 101,
no. 9, pp. 2031–2037, 2006.
of endoscopic versus percutaneous stent insertion in malignant
obstructive jaundice,” Lancet, vol. 2, no. 8550, pp. 57–62, 1987.
 M. J. Levy, T. H. Baron, C. J. Gostout, B. T. Petersen, and M. B.
Farnell, “Palliation of malignant extrahepatic biliary obstruc-
tion with plastic versus expandable metal stents: an evidence-
based approach,” Clinical Gastroenterology and Hepatology, vol.
2, no. 4, pp. 273–285, 2004.
 M. Kahaleh, J. Tokar, M. R. Conaway et al., “Efficacy and com-
plications of covered Wallstents in malignant distal biliary
obstruction,” Gastrointestinal Endoscopy, vol. 61, no. 4, pp. 528–
 H. Isayama, Y. Komatsu, T. Tsujino et al., “A prospective ran-
domized study of ‘covered’ versus ‘uncovered’ diamond stents
for the management of distal malignant biliary obstruction,”
Gut, vol. 53, no. 5, pp. 729–734, 2004.
 G. Costamagna, A. Tringali, D. N. Reddy et al., “A new partially
covered nitinol stent for palliative treatment of malignant bile
duct obstruction: a multicenter single-arm prospective study,”
Endoscopy, vol. 43, no. 4, pp. 317–324, 2011.
 H. Isayama, T. Mukai, T. Itoi et al., “The final report of WATCH
stent as historical control by Japanese multicenter study in
Endoscopy, vol. 76, no. 1, pp. 84–92, 2012.
 E. Kullman, F. Frozanpor, C. Sderlund et al., “Covered versus
uncovered self-expandable nitinol stents in the palliative treat-
no. 5, pp. 915–923, 2010.
 T. J. Song, S. S. Lee, S. C. Yun et al., “Paclitaxel-eluting covered
metal stents versus covered metal stents for distal malignant
biliary obstruction: a prospective comparative pilot study,”
Gastrointestinal Endoscopy, vol. 73, no. 4, pp. 727–733, 2011.
 J. P. Talreja, D. E. Loren, and T. E. Kowalski, “Evaluation of a
fully covered self-expanding metal stent in malignant biliary
Gastroenterology Research and Practice7 Download full-text
obstruction: follow-up of a multi-center study,” Gastrointestinal
Endoscopy, vol. 73, no. 4, p. AB352, 2011.
 J. J. Telford, D. L. Carr-Locke, T. H. Baron et al., “A randomized
trial comparing uncovered and partially covered self-expand-
able metal stents in the palliation of distal malignant biliary
obstruction,” Gastrointestinal Endoscopy, vol. 72, no. 5, pp. 907–
 A. Tringali, M. Marchese, P. Familiari et al., “Self-expandable
partially covered metallic stents to palliate malignant biliary
strictures: evaluation of the ComVi stent,” Gastrointestinal
Endoscopy, vol. 71, no. 5, p. AB309, 2010.
 A. C. Moss, E. Morris, J. Leyden, and P. MacMathuna, “Do the
benefits of metal stents justify the costs? A systematic review
and meta-analysis of trials comparing endoscopic stents for
malignant biliary obstruction,” European Journal of Gastroen-
terology and Hepatology, vol. 19, no. 12, pp. 1119–1124, 2007.
 R. Watson, K. Bangatelos, J. W. Ostroff et al., “Comparison of
metal stent placement following initial metal stent dysfunction
nal Endoscopy, vol. 71, p. AB301, 2011.
 J. N. Rogart, A. Boghos, F. Rossi et al., “Analysis of endoscopic
management of occluded metal biliary stents at a single tertiary
care center,” Gastrointestinal Endoscopy, vol. 68, no. 4, pp. 676–
 K.A.Hausegger,S.Thurnher,G.Bodend¨ orferetal.,“Treatment
of malignant biliary obstruction with polyurethane-covered
Wallstents,” American Journal of Roentgenology, vol. 170, no. 2,
pp. 403–408, 1998.
 W. J. Yoon, J. K. Lee, K. H. Lee et al., “A comparison of cov-
ered and uncovered Wallstents for the management of distal
malignant biliary obstruction,” Gastrointestinal Endoscopy, vol.
63, no. 7, pp. 996–1000, 2006.
 D. H. Park, M. H. Kim, J. S. Choi et al., “Covered versus uncov-
ered wallstent for malignant extrahepatic biliary obstruction:
a cohort comparative Analysis,” Clinical Gastroenterology and
Hepatology, vol. 4, no. 6, pp. 790–796, 2006.
 A. Saleem, C. L. Leggett, M. H. Murad, and T. H. Baron, “Meta-
analysis of randomized trials comparing the patency of covered
vol. 74, no. 2, pp. 321–e27, 2011.
 B. T. Petersen, “SEMS removal: salvage technique or new para-
digms,” Gastrointestinal Endoscopy, vol. 62, no. 6, pp. 911–913,
of covered self-expandable metal stents in benign biliary stric-
tures: a new paradigm? (with video),” Gastrointestinal Endosco-
py, vol. 67, no. 3, pp. 446–454, 2008.
 J. A. Kasher, J. G. Corasanti, P. R. Tarnasky, L. McHenry, E.
outcome of removal of a fully covered self-expandable metal
stent during ERCP,” Gastrointestinal Endoscopy, vol. 73, no. 6,
pp. 1292–1297, 2011.
 M. Kahaleh, V. Sundaram, S. L. Condron et al., “Temporary
testinal Endoscopy, vol. 66, no. 1, pp. 52–59, 2007.
 P. Familiari, M. Bulajic, M. Mutignani et al., “Endoscopic
removal of malfunctioning biliary self-expandable metallic
stents,” Gastrointestinal Endoscopy, vol. 62, no. 6, pp. 903–910,
 M. Kahaleh, J. Tokar, T. Le, and P. Yeaton, “Removal of self-
expandable metallic Wallstents,” Gastrointestinal Endoscopy,
vol. 60, no. 4, pp. 640–644, 2004.
of the role of metallic endobiliary stents in the treatment of
benign bile duct stricture,” Annals of Surgery, vol. 242, no. 1, pp.
ity study of the partially-covered Wallflex metal biliary stent in
a porcine model,” Gastrointestinal Endoscopy, vol. 65, no. 5, p.
 A. A. Siddiqui, V. Mehendiratta, D. Loren, S. K. Hong, and T.
ive and safe to treat distal malignant biliary strictures, irrespec-
terology, vol. 45, no. 9, pp. 824–827, 2011.