Due to the recent introduction of a variety of expansile metallic stents for use in malignant esophageal stricture, more prostheses and their attendant problems will be seen in radiology practice. In this article, the authors review the stent types, their MR imaging considerations, and the complications commonly encountered in their department.
Dr. Nevitt, Dr. Conti, Dr. Hauptmann,
are in the Department of Radiology and
is in the Section of Gastroenterology at Virginia Mason Medical
Center in Seattle, WA. This article was presented at the American
Roentgen Ray Society Meeting, 1997, and the Radiological Society
of North America Annual Meeting, 1997.
ood and Drug Administration (FDA) approval of expandable metallic
stents for use in malignant esophageal stricture has brought forth
widespread demand and use of the device in the medical community.
While conventional (silastic or plastic) esophageal prosthesis
placement has been associated with a 6 to 8% perforation rate and a
high incidence of post-procedural complications,
expandable metal prostheses provide theoretical advantages in the
treatment of malignant strictures, fistulas, and perforations
because of their overall decreased risk of major bleeding and/or
perforation, because there is no need for esophageal dilation to
48- to 5l-French (as is necessary for rigid conventional
prostheses), and because of their easier placement in acutely
Despite the 10-fold cost difference between expandable and
conventional prostheses, expansile metal stents have been shown to
be a cost-effective and safe alternative in the treatment of
malignant esophageal stricture. Recent prospective studies of
conventional versus metallic prostheses by Knyrim et al (Wilson
Cook silicone prostheses vs. uncovered Wallstent
and Siersema et al (latex Celestin prosthesis vs. European Z-stent)
were conducted on 39 and 75 patients, respectively. These studies
demonstrated fewer complications, decreased hospitalization time,
and comparable results of palliation with the expandable metallic
It is therefore important for the radiologist to be able to
identify each of these stents and the potential problems which may
arise, either during deployment or later. At our institution, we
have placed more than 70 expandable metallic stents in more than 57
patients to date. Twenty-nine of these patients required additional
interventions, as a consequence of either procedure-related
complications, prosthesis migration, or tumor progression. The
following report describes and illustrates many of the
complications we encountered with the use of the Gianturco Z-stent
(Wilson-Cook Inc., Winston-Salem, NC), the Wallstent
(Schneider Inc., Minneapolis, MN), the Ultraflex (Microvasive Inc.,
Natick, MA), and the EsophaCoil
(Instent Inc., Eden Prairie, MN) which may direct reintervention
Esophageal cancer carries a poor prognosis, with up to 80% of
patients presenting with advanced disease at diagnosis. While there
have been no significant advances in curative treatment of
esophageal cancer, treatment of the related dysphagia, specifically
with prostheses, has continued to evolve over the last 150 years.
The first esophageal prosthesis was created in 1845 by a French
surgeon, Leroy d'Etoiles, who carved a short tube of decalcified
ivory to make his device.
In 1885, Sir Charles Symmonds introduced the first indwelling tube,
made of boxwood and German silver, which was held in place by
retrograde strings fed through the nostrils and either tied behind
the ears or to a mustache.
The evolution of prostheses led to the use of rigid tubes which
were defined as pulsion tubes (placed antegrade or through a
cervical or thoracic esophagotomy) or traction tubes which were
pulled through the tumor from below (requiring laparotomy and
gastrotomy). Various modifications of these rigid prostheses are
still being used today. However, given the lower morbidity rates of
expandable metallic stent insertion, rigid prostheses may
eventually go the way of boxwood and German silver.
Mounted on or within a delivery catheter, stents can be inserted
over a guidewire after delineation of tumor length radiographically
or endoscopically. Correct positioning of the stent at the time of
placement can be evaluated fluoroscopically and/or endoscopically
and is often dependent upon the regional expertise of the
radiologist and/or gastroenterologist.
Expandable metallic prostheses are placed from the mid and
distal esophagus. Generally, prostheses are not placed above the
region that is 2 cm distal to the cricopharyngeus because of the
sensation of foreign body aspiration and narrowing to the
The original Ultraflex
nitinol mesh stent (figure lA) is delivered within a gelatin mold,
deploying slowly when heated to body temperature. It is
advantageous when placed across acutely angulated stenoses because
of its excellent longitudinal flexibility. Constructed of a single
knitted strand of elastic alloy wire (0.15 mm nitinol alloy), the
Ultraflex possess the least radial force of all of the
self-expanding stents available and is more prone to incomplete
expansion. Accordingly, a newer variety of the prosthesis uses a
larger gauge of wire to produce greater radial force and is
available in uncovered and partially covered forms which are
delivered by virtue of a thread release.
The self-expanding Wallstent
(figure 1B) is formed by a double layer of intertwining stainless
steel mesh with or without silicone sandwiched between the layers.
It is effective in sealing tracheoesophageal and tracheopleural
fistulas (figure 2). The flared wire edges, or "double dogbone"
ends, enable it to maintain position in the absence of a distinct
tumor shelf. Wallstent II
(figure 1E) is a variation of a theme, constructed of a single
layer of stainless steel mesh but without the distal semi-rigid
flaring. It is available with or without a silicone coating.
(Figure 1C) is formed from super-elastic nickel titanium flat wire
shaped into a coil spring design which is wrapped tightly onto a
deployment catheter. Upon release, the stent springs into place,
losing 50% of its original length. Of the available stents, the
EsophaCoil exerts the most external radial force and is potentially
advantageous for especially tight and angulated strictures.
(Figure lD) is a self-expanding wire cage stent which may or may
not be covered with urethane. Placed under fluoroscopic guidance,
the covered Z-stent can be used to seal tracheoesophageal and
All of the self-expansile metal stents, with the exception of
the EsophaCoil, are available with and without an external
covering. The coating helps prevent tumor and hyperplastic
ingrowth, which may result in subsequent luminal stenosis or
occlusion. A disadvantage to adding a coating is the increased
propensity of prosthesis migration.
Wire struts designed to hold stents in position also are
variable components of the different stents. While providing
anchoring stability, they also increase the risk of bleeding, the
formation of granulation tissue, and may predispose to chronic
ulceration and perforation.
In comparing stents to each other, May and coworkers reviewed 87
patients with 96 expandable prostheses placed (Wallstent: 31;
Ultraflex: 35, Z-stent: 30). Early technical success in placement
was universal. Twenty-two percent, 37%, and 10% of patients in
which a Wallstent, Ultraflex, or Z-stent was placed, respectively,
required early reintervention, while 43%, 38%, and 21% of patient,
respectively, required subsequent interventions.
In a comparison of the uncoved Wallstent to the Ultraflex in a
prospective study of 82 patients with malignant dysphagia by
Schmassmann et al, there was increased procedure-related mortality
(16% vs 1%), early complications (32% vs 8%), and severe persistant
pain (23% vs 0%) in the Wallstent patients. However, subsequent
stent dysfunction (7% vs 32%) and need for reintervention (9% vs
34%) were significantly lower in those patients receiving the
MR imaging considerations
Reports describing the effects of MR on gastrointestinal
prostheses are scarce. In a recent publication, Taal et al studied
the magnetic effects exhibited on Z-stents, Wallstents and
Ultraflex stents when placed in a MR bore.
The European model of the Wallstent which was used in this study is
constructed of a titanium based alloy which differs from the
stainless steel construction of the U.S. model. The researchers
found that no significant torque was exhibited on the titanium
based Z-stents and Wallstents. However, the stainless steel
ferromagnetic Z-stents demonstrated appreciable attractive forces
and torque. The authors were uncertain whether this force would be
enough to dislodge a stent, but they go on to recommend similar
guidelines to stainless steel stents placed into the vascular
system, which is to wait a minimum of 6 weeks after deployment to
assure firm implantation.
Of note, most MR magnets used today generate static fields which
are aligned parallel to the patient, and hence parallel to the
esophageal prosthesis, which limits effects of torque. Some open
air magnets, however, align static fields perpendicular to the
patient and hence the stent. This may accentuate torque caused by
ferromagnetic stents in some cases.
In addition to dislodgement concerns, significant ferromagnetic
artifact will be evident with stainless steel stents which can
degrade image quality. No problems with image quality in patients
with titanium based stents have been reported. Review of the
patient's stent construction, time interval from initial placement,
and properties of your institution's magnet will help avoid
potential complications and guide imaging choices.
An increased incidence of device related complications in
patients with esophageal stents has been noted following radiation
and/or chemotherapy. Radiation has been shown to cause esophageal
injury which can manifest as esophagitis, ulceration, and
submucosal fibrosis. These effects may be further potentiated in
patients receiving chemotherapy, and can lead to perforation and
fistula formation secondary to transmural ischemia.
Complications are arbitrarily divided into two categories: those
that require reintervention at the time of or immediately following
the procedure, and delayed problems occurring more than 24 hours
following the insertion. As patients at our institution stay
overnight (or less than 24 hours) after receiving IV sedation, a
contrast swallow is obtained before discharge to detect early
problems which may require additional interventions.
Procedure-related difficulties which require immediate
reintervention include migration, incomplete expansion, and
malposition. Immediate migration of a completely covered prosthesis
is not uncommon. For instance, recent multicenter Z-stent trial
data show a propensity for the stent to migrate into the stomach
when placed near or at the EG junction (figure 3).
At our institution, migrated stents are removed endoscopically with
a polyp snare, although in some centers surgical removal has been
Infolding of the stent will reduce the effective lumen of the
stent. Following deployment, infolding commonly is seen with the
Ultraflex, and to a lesser degree with the Z-stent. This infolding
is remedied by balloon dilation and is encountered less often with
the newer stent models. However, even with the strong radial force
of the EsophaCoil, infolding, which is really side folding, can be
seen (figure 4).
Stent foreshortening is a potential pitfall leading to
malposition. Because of the expansile properties of metallic
stents, all will shorten following release. In particular, the
spring-like deployment of the EsophaCoil, along with a 50%
shortening of the pre-deployment length, are factors leading to
Other immediate complications which may require emergent
surgical intervention include perforation (seen as
pneumomediastinum, pneumothorax (figure 5) and/or contrast
extravasation) and uncontrolled bleeding. Perforation, which may
occur during dilation, can commonly be sealed with covered
prostheses without additional problems. Finally, depending upon the
severity of symptoms, tracheal compression may require immediate
stent retrieval (if possible), intubation, or stent placement into
the pulmonary tree.
As noted, we define delayed complications as those occurring
more than 24 hours following deployment and often occur following
discharge. Delayed complications may therefore present to a
community radiologist at some distance from our tertiary care
center. Complications requiring reintervention include migration,
tube occlusion, and chronic erosions from the anchoring struts,
which can cause bleeding and/or perforation.
Tube occlusion may be divided into several categories: tumor
ingrowth through the prosthesis (uncovered stents); tumor
overgrowth or elicitation of granulation tissue at the ends of the
prosthesis (figure 6); food impaction; and hiatal hernia
intussusception (figure 7). We have found an increased incidence of
tumor ingrowth with Ultraflex prostheses (figure 8) and early
uncovered Wallstents (figure 9) weeks to months after insertion. In
general, endoscopic evaluation of tube obstruction best
characterizes the cause of the blockage.
Migration of the covered prosthesis was particularly prevalent
Z-stent. Migration, a complication seen during deployment, also may
present several weeks after insertion (figure 10).
In summary, because of the recent introduction of a variety of
expansile metallic stents, more prostheses and their attendant
problems will be seen in a general practice. Early and accurate
diagnosis of complications by the radiologist with plain films and
contrast swallow will help to decrease morbidity and mortality and
to guide timely reintervention.