Nagoya J. Med. Sci. 54. 1 - xx, 1992

ESOPHAGEAL STENTING WITH A
SELF-EXPANDABLE METALLIC DEVICE:
A PRELIMINARY STUDYSUMIT Roy l , SANJAY S. BAIJAL l , TSUNEO ISHIGUCHI l , MITSUHIKO HIROSE l ,HIROSHI FuKATSU 1, SHIGEKI ITOH l , SADAYUKI SAKUMA l , and KENJI KASAI 2I Departmentof Radiology, and 2 First Department of Pathology, Nagoya University School of Medicine,
Nagoya 466, JapanABSTRACTThis study was designed to investigate the potential of the Gianturco-Rosch Z stent in the alimentary
canal, using the rabbit esophagus as the animal model. Single stents were implanted in four animals, whichwere followed up for predetermined periods, lasting from 48 hours to 6 weeks. All the stents remained inplace. A florid tissue reaction was noticed, initially manifesting primarily as submucosal cellular infiltration,and mucosal erosion. Over the ensuing six weeks, the acute changes gave way to mucosal regeneration, andthe appearance of granulation tissue in the submucosa. The stented segments remained patent, and feeding
difficulties were limited to the immediate post-procedure period. These preliminary results suggest that peristaltic activity is no contraindication to the use of Z stents, though measures to limit the tissue response need
to be identified.
Key Words: Esophagus, Interventional procedure, Stent, Metallic.

INTRODUCTION
The last few years have witnessed an explosive growth in the number of indications for thepercutaneous implantation of metallic stents. Curiously enough, the extension of this therapeuticmodality to the gastrointestinal tract has met with limited enthusiasm. An anecdotal reportapart l ), the papers by Hayashi et al and Fujiwara's group represent the sum total of the literaturein this area 2•3>.
Conceptually at least, peristaltic activity is a major impediment to the use of metallic stents inthe alimentary canal. This study was designed to investigate the feasibility of using GianturcoRosch Z stents in the gastrointestinal tract.

MATERIALS & METHODS
The rabbit esophagus was selected as the experimental model, with four adult rabbits forming
the study population.
Stent implantation was performed under general anesthesia. After a six hour fast, the animal
was premedicated with 0.01 mg/kg atropine. Pentobarbital 25 mg/kg was administered IV; half
this dose was repeated during the procedure, if the level of anesthesia proved insufficient. Under

Present address of Roy S. and Baijal S.S.: Department of Radiology, Sanjay Gandhi, Postgraduate Institute ofMedical Sciences, Lucknow, India
Received for Publication in April 19, 199159

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fluoroscopic guidance, a 5 Fr multipurpose catheter was introduced through the mouth into theesophagus, and maneuvered into the stomach. It was then exchanged for a 12F Teflon sheath,over a guidewire. After ensuring that the tip of the sheath was in the mid-thoracic esophagus,
the guidewire and coaxial dilator were withdrawn. A 2 cm long Z stent, 1.1 cm in diameter,
made from wire 0.016" in calibre, was backloaded in the sheath. The specifications of the stentwere dictated by our previous experience with the procedure: 1.5 cm long, 8mm diameter stentsof 0.010" wire had consistently migrated into the stomach. The stent was then deployed in theesophagus by the conventional technique (Fig.!). The sheath and pusher were replaced by aFig. 1

Stent in esophagus, immediately after deployment.

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ESOPHAGEAL STENTING WITH METALLIC DEVICE

catheter, and a contrast study was performed (Fig.2).
The rabbit was kept under observation until the effect of anesthesia were off. Measurement ofbody weight at intervals provided the objective parameter of stent function. Daily oral intake
was also monitored. Fluoroscopy was performed once a week to identify any change in stent position.
One animal each was killed two days, one week, four weeks, and six weeks after stent implantation. The thoracic esophagus was carefully dissected from the rest of the mediastinum,and removed en bloc for morphologic, and subsequent histologic examination.

Fig. 2

Post-procedure esophagogram.

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RESULTSAll the procedures were successfully completed at one session. A consistent observation was
the negligible oral intake in the immediate post-implantation period, lasting twenty-four toforty-eight hours. Likewise, there was a drop in boby weight in the first week. None of the stents
migrated distally before death. In every case, the final equilibrium diameter of the stent was alittle more than the diameter at implantation.
Forty-eight hours after stent deployment, the esophagus exhibited an abrupt change in caliber
around the prosthesis. The limbs were clearly visible through the stretched esophageal wall. The
luminal aspect was hyperemic, and studded with mucosal elevations outlining the stent. Macroscopic ulcers were absent. Histologic examination revealed attenuation of the portions of theesophageal wall underlying the limbs, associated with mucosal loss, and disruption of the muscularis. Congested vessels and edema were present in the submucosa (Fig.3).
Within one week, thickening of the wall had rendered the stent invisible from the outside.
The adventitia was otherwise unremarkable. On opening the esophagus, the stent was foundpartially hidden within the depths of the markedly thickened mucosa, though the struts remained intraluminal. Microscopy demonstrated foci of mucosal erosion even in areas that were
not in physical contact with the stent. Prominent cellular infiltration in the submucosa and reactive fibrosis of the adventitia were present (Fig.4).

Fig. 3

Histology of esophagus, 48 hours after stenting (X40 magnification): thinning of tissue layers beneath stent, with mucosal loss (arrow), and disruption of muscular coat (arrowhead).

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ESOPHAGEAL STENTING WITH METALLIC DEVICEFig. 4

Histology of esophagus, 1 week after stenting (XIOO magnification): mucosal erosion,
prominent cellular infiltration, and reactive adventitial fibrosis (arrow).

By six weeks, the alteration in caliber had progressed beyond the margins of the prosthesis. A
focal protrusion was present on the anterior surface, which was adherent to the trachea. Adventitial perforation could not be identified. Filmy adhesions were noticed in the vicinity. The mucosal reaction had progressed to the formation of papillary excrescences enveloping the stent,and offsetting the increase in luminal diameter. The changes were particularly evident at the inferior margin of the prosthesis, resulting in a collar-like thickening covering the bends in thewire (Fig.5). The coexistence of granulation tissue with the cellular exudate, marked the majorchange in the histologic picture. Islands of regenerating epithelium were present in the mucosa(Fig.6).
The results of the examination of the four-week specimen did not dovetail into the pathologic
continuum represented by the other three. The stented segment contained a large trichophy-

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tobezoar. The limbs of the stent were clearly separate from the underlying wall, except for one
bend which had burrowed into an intramural location at a point corresponding to a localized
bulge on the outer surface. Mucosal thickening was largely restricted to this area. Elsewhere, theluminal aspect was relatively featureless, lacking even the normal longitudinal folds. A few shallow, linear depressions were the only other morphologic stigma of stent placement. At microscopy, the extent and degree of cellular infiltration were limited, compared with thtat encountered in the other animals.

Fig. 5

Luminal surface of esophagus, 6 weeks after stenting: bends in wire covered by mucosa (arrow).

DISCUSSION
This laboratory experience does seem to support our hunch that its physical characteristics
provide the Z stent with an intrinsic anchoring capability. The large difference in the luminal
diameters of the esophagus and the stent probably ensures that the centrifugal force exerted by
the limbs is sufficient to hold the device flush against the esophageal wall, thus discouraging migration. The fate of the 8mm diameter stents seems to lend credence to this hypothesis. Whether
some other factor is also causally involved, remains open to question. The presence of a large
phytobezoar in the stented segment in one rabbit, raises the suspicion of secondary motility disturbances also playing a role. Intriguingly, this animal never demonstrated any evidence ofchronic feeding difficulties.
The histologic changes give food for thought. Fujimori et al noticed similar alterations in thedog esophagus following stenting 3). This constellation of histologic findings can be explained byassuming that a metallic stent acts as a source of mucosal trauma, inducing an exaggerated reparative response 4 ). The latter manifests as the papillary fronds visible macroscopically. Cyclic

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ESOPHAGEAL STENTING WITH METALLIC DEVICEFig. 6

Histology of esophagus, 6 weeks after stenting (X40 magnification): regenerating epithelium(arrow); granulation tissue in submucosal layers (arrowhead).

compression and expansion of the stent probably maintain the foci of mechanical irritation, withconsequent persistence of the tissue changes beyond the acute phase. Pressure atrophy underlying the stent seems to be a common phenomenon as we1l 3,4). Adventitial fibrosis presumablycompensates for the anticipated weakening of the esophageal wall.
The significance of the tissue reaction may perhaps be limited, since in the clinical situation,
deployed stents will largely be in contact with a fibrotic or neoplastic surface. Nevertheless, it
should be remembered, the ends of a stent invariably overlap normal tissue, and prudence demands that this issue be addressed further. Perhaps a more compressible stent made from lower
calibre wire would provoke a more muted tissue response.
In conclusion, a Z stent deployed in the esophagus remains in situ, without affecting food

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transit. The prosthesis induces structural changes in the esophagus, with probably neutral clinicalimplications. Further studies are warranted to determine the stent specifications most suitable
for the gastrointestinal tract.

ACKNOWLEDGEMENT
Mr. Narita's contribution to the radiographic aspects of this work is deeply appreciated.

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3)

4)

Dornschke, W., Foerster, E.Ch., Matek, W., and Roell, W.: Self-expanding mesh stent for esophageal cancer
stenosis. Endoscopy, 22, 134-136 (1990).
Hayashi, N., Kimoto, T., Katoh, N., Iwashi, T., Odori, T., Ishii, Y., Yoshioka, T., and Uchida, H.: Expandable
metallic stent for biliary and gastrointestinal strictures: Clinical and experimental results. Presented at the 3rdInternational Symposium on Interventional Radiology and New Vascular Imaging, Nara, May 1990.
Fujiwara, Y., Sawada, S., Tanabe, Y., Yoshida, K., and Katsube, Y.: Experimental evaluation of expandable
metallic stent placement for trachea, esophagus and urethra. Rinsho Hoshasen, 35, 557-562 (1990) (inJapanese, English abstract).
Alvarado, R., Palmaz, J.e., Garcia, OJ., Tio, F.O., Rees, e.R.: Evaluation of polymer-coated balloon-expandable stents in bile ducts. Radiology 170,975-978 (1989).