Indications

The main indication for placement of gastroduodenal stents is obstruction of the stomach, duodenum, or proximal jejunum by unresectable malignant tumors. Advanced carcinoma of the pancreatic head is the most common malignancy causing obstruction in these regions. Other malignancies include cholangiocarcinoma, gastric carcinoma, and metastatic disease to the duodenum or proximal jejunum.

Anastomotic malignant obstruction after gastrectomy or esophagectomy is also an indication for stent placement.3,4 Although stent placement for benign obstruction is still under investigation, it may be a possible alternative treatment when coexisting morbidity involving the cardiopulmonary system limits surgical treatment.⁵

Contraindications

The only absolute contraindication to stent placement is gastrointestinal (GI) perforation with peritonitis or tension pneumoperitoneum. Multifocal small bowel obstruction has been reported as the main cause of clinical failure after stent placement.6,7 Therefore, clear evidence of distal small bowel obstruction is also a contraindication to stent placement. Patients with peritoneal carcinomatosis are at high risk for multifocal small bowel obstruction.

Equipment

Gastroduodenal stents should be flexible enough to allow easy placement along a tortuous GI tract. They should not migrate after deployment and should be conformable in a way that does not permit distortion of the normal anatomy of the upper GI tract. They should have sufficient radial expansile force and diameters large enough to relieve the obstructive symptoms. In addition, such stents should not allow tumor ingrowth and mucosal hyperplasia.

Self-expandable metallic stents have virtually always been used in the stomach and duodenum. Many self-expandable stents composed of a variety of metal alloys with varying structures are available commercially. Although stents made of multiple strands of stainless steel wire have been used frequently, the use of stents woven from a monofilament of nickel-titanium alloy (nitinol) has been increasing recently.

Both covered and bare stents have been used in the stomach and duodenum. Covered stents have the advantage of resisting tumor ingrowth through the stent mesh wire but are prone to migration. They are rigid and require a large delivery system and thus are difficult to deploy at distant locations along a tortuous delivery route. Advantages of bare stents over covered ones include greater flexibility, requirement for a smaller delivery system, and more resistance to migration. When used for long-term palliation of malignant obstruction, they are more prone to obstruction by tumor ingrowth. However, in the majority of cases, tumor ingrowth has not been clinically important because of the limited life expectancy of the patient. Therefore, to date, bare stents have been used much more frequently than covered stents in patients with gastroduodenal obstruction.7–11

Until recently, because stents dedicated to GI use were unavailable, interventionalists used stents designed for esophageal or vascular use, including the Wallstent (Boston Scientific, Natick, Mass.), Ultraflex stent (Microinvasive/Boston Scientific), Gianturco Z-stent (Wilson-Cook, Winston-Salem, N.C.), and EsophaCoil (Intra-Therapeutics, Eden Prairie, Minn.).7–11 The Wallstent endoprosthesis is the most frequently used stent. Vascular Wallstents are very flexible but have a small diameter (16 mm) inadequate for GI use, whereas esophageal Wallstents are sufficiently large (20-25 mm) but relatively rigid. Recently a Wallstent dedicated to GI use has been developed (Fig. 130-1). Available stents range from 18 to 22 mm in diameter and are mounted on 10F delivery systems 230 cm long for endoscopic placement and 160 cm long for peroral fluoroscopic placement. The enteral Wallstent is a bare stent braided from multiple strands of stainless steel wire. Advantages of this stent include high longitudinal flexibility, adequate radial force, and the fact that it uses a small introducer system. Disadvantages of the enteral Wallstent are substantial shortening (≈40%) after deployment, unavailability in a covered version, and potentially traumatic ends of the stent. More recently, a new enteral stent (WallFlex [Boston Scientific]) was introduced that is made of nitinol instead of stainless steel.^12,13 This new stent has been constructed to provide improved flexibility while maintaining lumen integrity, has looped ends to reduce risk of mucosal injury, and has a proximal flared end to minimize risk of stent migration.^12,13 The Ultraflex stent is knitted from nitinol mesh wire, which slowly expands when deployed at body temperature and is available in both covered and bare versions.¹⁴ It has significantly lower radial expansile force than the other stents, but it is highly flexible and thus can be placed across acutely angled stenoses. The stent is available in a 23-mm middle diameter, has a 28-mm funnel-shaped proximal end, and is mounted on a 16F delivery catheter.

The covered version of the stent has a polyurethane external membrane with bare portions at both ends to prevent migration.

The Gianturco Z-stent is available in bare and polyethylene-covered versions. The bare stents are cylindrical or flared at both ends and available in diameters of 15 to 35 mm. The covered esophageal Z-stent is designed with flared ends to prevent migration. The diameter of the stent is 18 mm in its midportion and 25 mm at each end.¹⁵ The stent is delivered through a 28F sheath. The greater inflexibility of these stents limits their use in the GI tract.

In some recent publications from Korea, use of various types of covered enteral stents (Fig. 130-2) has been reported. The Niti-S stent (Taewoong Medical, Ilsan, Korea) and the HANAROSTENT (M.I.Tech, Pyungtaik, Korea) are woven from a single thread of nitinol wire. The stents are covered with polyurethane (Niti-S) or silicon membrane (HANAROSTENT). The diameters of the body of the stents are 16 or 18 mm, and both ends are flared, which increases the size to 20 to 24 mm. They are mounted on an 18F delivery system.¹⁶ These stents are highly flexible and exert adequate expansile force. Recently, Song et al.^17,18 developed a nylon-covered stent (Dual duodenal stent [S&G Biotech, Sungnam, Korea]) that was designed to be placed coaxially. It is mounted on a very low-profile (3.8 mm) delivery system. Other authors have introduced a new duodenal bare metallic stent (BONASTENT M-Duodenal [Standard Sci-Tech Inc., Seoul, Korea]), through which biliary stent placement is safe and effective for palliative treatment of malignant biliary and duodenal obstruction.¹⁹

Technique

Technical Aspects

Peroral Stent Placement

For peroral placement, stents can be placed under fluoroscopic or combined endoscopic-fluoroscopic guidance. Advantages of endoscopic stent placement over fluoroscopically guided placement include direct visualization of the lesion and greater accessibility to the obstruction by straightening of the access route through the distended stomach. However, technical success rates of fluoroscopic placement have been reported to be similar to those of endoscopic placement.3–21 In some cases, fluoroscopic stent placement is successful after failed endoscopic placement. The delivery system of a covered stent is too large to place through the endoscope channel. In addition, accurate stent deployment is performed mainly under fluoroscopic monitoring. Therefore, the techniques used often depend on the referral pattern and available local expertise rather than superiority of techniques.

Fluoroscopic Guidance

The procedure can be performed on a conventional fluoroscopic table or within a vascular-interventional suite. Equipment allowing tilting of the table is desirable. Because of prolonged obstruction, the stomach is usually distended and elongated, which may make catheterization of lesions difficult or even impossible. Therefore, decompression of the stomach with a nasogastric tube for 1 to 2 days before the procedure is mandatory. The procedure is generally performed with the patient under conscious sedation and continuous monitoring of vital signs and oxygen saturation. After anesthetizing the pharynx with topical spray, an angiographic catheter with a guidewire is passed perorally into the stomach or duodenum near the obstruction (Fig. 130-3). A curved 100-cm-long angiographic catheter, such as a 5F multipurpose (Terumo Medical Corp., Tokyo, Japan) or Head Hunter catheter (Wilson-Cook), and a 260-cm, 0.035-inch floppy-tipped guidewire (Radiofocus [Terumo]) are most commonly used. A limited amount of iodinated contrast material is injected through the catheter to identify the proximal extent of the stricture. The catheter is manipulated through the obstruction with standard catheter and guidewire techniques. However, when the patient has a markedly distended stomach, manipulating the obstruction may prove difficult because the catheter and guidewire are frequently looped along the greater curvature of the stomach. A guiding sheath may be helpful to prevent looping of the guidewire in these cases.²² In addition, gastric decompression for several days before the procedure can minimize this problem. After the catheter is advanced as far distally as possible, contrast medium is injected again to demonstrate the distal margin of the obstruction. With the use of a recently developed GI catheter (Song-Lim [S&G Biotech]), the contrast medium can be injected without removing the guidewire from the catheter (Fig. 130-4).²³ The guidewire is exchanged for a long stiff wire (260-cm Amplatz Super Stiff wire [Boston Scientific], Lunderquist Extra Stiff guidewire [Cook Medical, Bloomington, Ind.]). Sometimes the exchange-length guidewire is too short for the procedure because of marked looping of the catheter in the distended stomach. In these cases, use of a 500-cm-long Amplatz Super Stiff wire may solve the problem. Once an exchange stiff wire is placed, looping of the wire is likely to be relieved, and a straight access route can be established.

Prestent balloon dilation is not usually necessary in most cases. Occasionally, however, gentle balloon dilation (10-15 mm) may facilitate rapid expansion of the stent in the presence of very tight obstruction. Furthermore, balloon dilation may be helpful in determining the exact length and location of the proximal and distal extents of the obstruction when they are not clearly demonstrated by injection of contrast material.

A stent of adequate diameter (at least 16 mm) and length should be chosen to completely cover the obstruction. It is important to place a stent that is at least 2 to 4 cm longer than the site of obstruction so it covers 1 to 2 cm distal and 1 to 2 cm proximal to the obstruction to limit tumor overgrowth. A large-diameter stent (at least 18 mm) is recommended to establish a wide lumen and facilitate passage of food through the stent. The stent delivery system is advanced over the wire across the obstruction. During stent deployment, the distal end of the stent shortens toward the obstruction. The stent delivery system may be pulled back if placed too distally. However, a partially deployed stent should not be advanced. When multiple stents are required, the distal stent should be placed initially, with confirmation that it extends well beyond the lesion. At least 1 to 2 cm of the stents should overlap to prevent migration. It is not generally necessary to dilate the stent after deployment, because most stents will slowly self-expand over time. A postinsertion contrast-enhanced study is performed to assess stent position.

Endoscopic-Fluoroscopic Guidance

Patients should be placed in left lateral decubitus or prone position. With use of intravenous conscious sedation, the esophagus and stomach are intubated with the endoscope. If the endoscope can be passed through the obstruction easily, a 0.035-inch guidewire and a catheter are advanced through the endoscope channel, but it is unnecessary to apply excessive force to the endoscope to make it pass through the obstruction. If the endoscope cannot be passed through the obstruction, a guidewire and catheter are advanced to traverse the obstruction under fluoroscopic monitoring, during which the endoscope plays the role of a guiding sheath to provide stability within the distended stomach. Removal of gastric contents by suction may facilitate access to the obstruction and reduce the risk of aspiration. Water-soluble contrast material is injected to identify the length and location of the obstruction. An extralong exchange-length stiff guidewire is placed as far distally as possible.

A stent of adequate diameter (at least 16 mm) and length (at least 2 cm longer than the stricture) should be chosen. The enteral Wallstent is mounted on a 10F delivery system and can be delivered through the working channel of the endoscope. When a larger stent delivery system is used, the endoscope should be removed. The stent is loaded onto the guidewire and advanced under fluoroscopic monitoring. The endoscope can be reinserted alongside the stent delivery system for endoscopic guidance during stent deployment. The stent is deployed under fluoroscopic monitoring, and the distal end should be located at least 1 to 2 cm beyond the obstruction. The proximal location of the stent can be monitored fluoroscopically and endoscopically. Additional stents can be inserted if necessary. Correct position of the stent is demonstrated by injection of contrast medium after the procedure.

Transgastrostomy Stent Placement

As an alternative to the peroral approach, access to the stomach can be achieved by percutaneous gastrostomy (Fig. 130-5). This access allows placement of a stiff sheath to provide greater catheter and wire control. Consequently, such direct access allows successful catheterization in virtually all cases.^5,16 However, percutaneous gastrostomy is an invasive procedure that has its own associated risks and complications, so it should be reserved as a last option. After placement of the stent by means of the gastrostomy route, a gastrostomy tube is left in place until a mature tract develops, usually 10 days after the procedure. Placement of duodenal and biliary stents from a transhepatic approach has also been reported.²⁴ This alternative route is useful in patients with complex surgical anastomoses when peroral stent placement is not possible.