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Plastic Pancreaticobiliary Stents and Nasopancreaticobiliary Tubes: Concepts and Insertion Techniques
The use of plastic pancreaticobiliary stents for drainage of the bile duct was described more than 3 decades ago. These stents are used for a variety of indications, including malignant and benign conditions, and have proven reliable and safe for decompression of the biliary tree. Palliative insertion of biliary stents relieves distal biliary obstruction as effectively as surgical bypass. Although the use of expandable metal stents has increased and replaced the use of plastic stents for biliary use, plastic stents are preferred for nearly all indications for pancreatic stent placement.
Plastic stents are easy to insert, effective for decompression, and inexpensive to use. Plastic stents are available in a variety of configurations and lengths and are composed of Teflon, polyethylene, or polyurethane ( Table 22.1 ). Common configurations are straight, single pigtail, or double pigtail ( Fig. 22.1 ). All plastic stents have limited patency because of occlusion with debris and biofilm ( Fig. 22.2 ) and require periodic replacement when long-term drainage is required. Nearly all stents of the same diameter have similar patency rates. Almost all plastic stents are hollow tubes. Side holes are present in biliary stents to a variable degree but uniformly present in pancreatic duct stents to allow drainage of side branches ( Fig. 22.3 ).
TABLE 22.1
Plastic Biliary and Pancreatic Stents
From ASGE Technology Assessment Committee, Pfau PR, Pleskow DK, Banerjee S, et al. Pancreatic and biliary stents. Gastrointest Endosc. 2013;77:319–327.
| Length (cm) | Diameter (Fr) | Shape * | Flap † | Material | Cost: Stent/System (US$) | |
|---|---|---|---|---|---|---|
| Biliary Stents | ||||||
| Boston Scientific Advanix | 5–15 | 7, 8.5, 10 | CB, DB, DP | S | Polyethylene | 89/219 |
| Cook Endoscopy ‡ | 1–21 | 5, 7, 8.5, 10, 11.5 § | A, C, DP | S, Q | Various ‡ | 69/145 |
| ConMed Hydroduct | 4–15 | 7, 10, 12 § | A, S, C, DP | S | Polyurethane ‖ | 72/146 |
| Hobbs Medical | 4–15 | 7,10 | C, DP | S | Soft polymer blend | 44/90 |
| Olympus Double Layer & QuickPlace V | 3–15 | 7, 8.5, 10, 12 § | CB, DB, S, DP | S, Q | Polyethylene, proprietary ¶ | 78–274/169–365 |
| Pancreatic Stents | ||||||
| Boston Scientific Advanix | 2–18 | 3, 4, 5, 7, 10 | S, SP | S, N | Radiopaque polymer | 77–87/170 |
| Cook Endoscopy ** | 2–22 | 4, 5, 6, 7, 8.5, 10, 11.5 § | S, SP | D | Various ** | 69/145 |
| Hobbs Medical Freeman Flexi | 3–18 | 3, 4, 5, 7 | S, SP | S, N | Soft polymer blend | 44–48/50–54 |
* Shape column: A, angled; C, curved; CB, center bend; DB, duodenal bend; DP, double pigtail; S, straight; SP, single pigtail.
† Flap column: D, 2 internal/external; N, no flaps; Q, 4 internal/external; S, single external/internal.
‡ Multiple stent lines available: Cotton-Huibregtse, polyethylene; Cotton-Leung, polyethylene; Cotton-Leung Sof-flex, polyethylene/polyurethane; ST-2 Tannenbaum, Teflon; Solus, polyethylene/polyurethane; Zimmon, polyethylene.
§ Stents >10 Fr require a 4.2-mm channel duodenoscope.
‖ Covered with hydromer coating.
¶ Proprietary stent with perfluoro inner layer, stainless steel middle layer, and polyamide elastomer outer layer.
** Multiple stent lines available: Zimmon, polyethylene; Geenen, polyethylene; Geenen Sof-flex, polyethylene/polyurethane; Johlin Wedge, polyethylene/polyurethane.
Two stents. A, Straight 10-Fr biliary stent. B, Double-pigtail 10-Fr stent.
( A, Courtesy Olympus Corporation, Center Valley, PA. B, Courtesy Cook Medical, Bloomington, IN.)
Endoscopic photograph of occluded 10-Fr stent exiting the bile duct.
Pancreatic duct stent. Note side holes.
(Courtesy Cook Medical, Bloomington, IN.)
Myriad designs and materials have been proposed and tested to prevent plastic stent occlusion and prolong patency. These include (1) a double-layer design, (2) a star-shaped stent with a limited central lumen, and (3) a biliary stent with an antireflux valve (windsock) designed to prevent stent occlusion from food and vegetable material. However, data on such stents have not convincingly demonstrated prolonged patency rates and have not been widely adopted in clinical practice. In addition to alterations in stent design, a recent preclinical study has focused on the development of a hydrophilic coating to deter stent occlusion. Whether this will translate into prolonged patency remains to be seen.
Stent Systems
A variety of stent systems are available, as discussed in Chapter 4 . Stents smaller than 8.5-Fr diameter are usually placed directly over a guidewire using a pusher tube. Stents greater than 8.5-Fr diameter typically include an inner guiding catheter that passes over the guidewire ( Fig. 22.4 ), whereby the stent and pusher tube are passed over the inner guiding catheter ( Fig. 22.5 ). The inner guiding catheter promotes stability and rigidity, which are necessary to allow stent passage across tight strictures.
Endoscope Requirements
Nearly all commercially available duodenoscopes have a therapeutic channel of 4.2 mm that can accommodate stents up to 11.5 Fr in diameter. However, smaller-diameter working channels—such as those in balloon enteroscopes, standard upper endoscopes, and slim (pediatric) colonoscopes—permit placement of only 7-Fr-diameter plastic stents.
Description of Technique: Biliary
Because 10-Fr stents have superior patency to 7-Fr stents, it is recommended that 10-Fr stents be placed whenever possible in patients with malignant disease to limit the number of endoscopic procedures required for palliation.
Distal Biliary Obstruction
The approach to distal biliary strictures is more straightforward than for hilar tumors and will be discussed separately. After successful deep cannulation of the biliary tree, contrast is introduced to clearly elucidate the stricture margins, allowing for selection of the appropriate stent length. The stricture is then traversed with a guidewire. It is important to pass the wire well proximal to the stricture to prevent wire loss and to provide mechanical advantage, although care must be taken to avoid passing the wire too proximally, which can cause ductal perforation. In general, a biliary sphincterotomy is not required for insertion of stents up to 10-Fr diameter and is not protective of post–endoscopic retrograde cholangiopancreatography (ERCP) pancreatitis after stent placement for malignant biliary obstruction. However, one study showed that in patients with bile leaks, placement of 10-Fr stents without sphincterotomy was associated with a higher rate of post-ERCP pancreatitis. A biliary sphincterotomy is required when multiple stents are placed, as is done in the treatment of benign strictures (see Chapter 43 ).
When placing a single 10-Fr stent, it is rarely necessary to dilate the stricture, especially when placed for a distal stricture, because the mechanical advantage is great enough to overcome resistance. In cases of uncertainty, a 10-Fr dilating catheter (e.g., Soehendra dilator; Cook Endoscopy, Winston-Salem, NC) can be passed through the stricture. If the catheter easily traverses the stricture, balloon dilation is not required. Otherwise, hydrostatic balloon dilation can be performed. When the insertion of multiple stents is planned, stricture dilation is essential. In this setting, more than one guidewire may be placed before insertion of the first stent. Alternatively, a guidewire can be placed after each stent insertion by recannulating the bile duct alongside the stents. A useful tip in placing more than one wire is to pass a large or multilumen catheter over the initial guidewire. This can also be accomplished with a triple-lumen cytology brush sheath by removing the brush and using that lumen for a guidewire. More recently, an “intraductal exchange” can be performed using the Fusion system (Cook Endoscopy) and the short-wire lumen. During each stent placement the wire can be separated from the delivery system to allow additional stents to be placed sequentially using a single guidewire.
When multiple stents are placed, using a slightly longer initial stent is helpful as the friction created by passage of additional stents during insertion may result in proximal movement. If the first stent is too short, it may migrate into the duct. This is usually of no consequence, assuming that the stent is still across the stricture. The length of the stent chosen is based on the distance from the papilla to the proximal edge of the stricture plus an additional 2 cm. In general, 5-cm-long or 7-cm-long stents are of sufficient length for nearly all biliary strictures resulting from pancreatic cancer. Defining the stricture length can be achieved in several ways. One method is to measure during withdrawal of the initial cannulating catheter. When the catheter tip is at the proximal end of the stricture, the endoscopist holds the catheter just outside the biopsy port. The catheter is withdrawn until it is endoscopically visible in the duodenum just distal to the papilla. The distance from the endoscopist's fingers to the biopsy port is measured and represents the stricture length. Anecdotally, this method seems to overestimate the length of the stricture. Another way is to use the radiograph to measure the length of the stricture. When the tip of the endoscope is in contact with the papilla, a radiographic image is captured. The distance from the tip of the endoscope to the proximal edge of the stricture is measured. The diameter of the endoscope is used as a comparison measuring point to determine the true stricture length and account for a magnification factor. The following equation is used to solve for the unknown variable X, which is true stricture length ( Fig. 22.6 ):
Finally, fluoroscopic markers separated by a known distance are available on some catheters and guidewires and can be used as a reference point to the stricture and papilla. Balloon dilation catheters also have radiopaque markers corresponding to the length of the balloon. Excessively long stents should be avoided. Distal migration tends to occur into the duodenum until the proximal flange or pigtail impacts at the top of the stricture, potentially resulting in the distal end of the stent impacting and perforating the lateral duodenal wall ( Fig. 22.7 ).
Once the stent has been selected, placement is undertaken. If a tapered end is present, this represents the proximal end of the stent. Depending on the type of stent system, either the inner guiding catheter alone or the inner guiding catheter and stent are advanced over the guidewire. It is important that the guidewire and inner guiding catheter do not pass too far proximally into the biliary tree during advancement, as this could cause injury to the intrahepatic ducts or liver capsule. Conversely, excessive traction on the wire or inner guiding catheter may result in wire loss. The stent is then advanced over the guide catheter by advancing the pusher tube. The latter has a larger bore that approximates the diameter of the stent. During advancement down the endoscope channel, the elevator should remain closed. When the stent impacts the elevator, the elevator is opened slightly to allow it to emerge from the endoscope channel. The elevator is closed to direct the stent upward and into the papilla. It is imperative to maintain a short endoscope position with the tip as close as possible to the papilla to maintain maximal mechanical advantage. The stent is ultimately advanced into the bile duct using a series of small movements in which the elevator is sequentially lowered to allow advancement of the stent and then closed to advance the stent in a “ratchet-like” manner. Upward tip deflection and withdrawal of the duodenoscope shaft further shortens the scope and provides forward advancement of the stent. It is important to note that allowing more than a minimal amount of stent to be advanced out of the duodenoscope into the duodenum decreases the mechanical advantage and often prohibits forward advancement because of looping and buckling between the papilla and the endoscope, ultimately risking misdeployment. To facilitate forward movement of the stent, the endoscopy assistant must provide traction on the inner guiding catheter (or guidewire if there is no inner guiding catheter). Once optimal stent position is achieved, the inner guiding catheter and guidewire are removed while the endoscopist maintains forward pressure with the pusher tube against the stent to prevent distal stent dislodgement. If additional contrast is needed to assess drainage or intrahepatic anatomy above the stent, the guidewire can be removed before removing the inner guiding catheter to allow contrast injection (this is possible only when long-wire systems are used). The process is repeated for additional stent placement.
In patients with short, distal bile strictures (e.g., chronic pancreatitis, postsphincterotomy ampullary strictures), three to four 10-Fr, 5-cm-long stents can be mounted on the inner guiding catheter at one time. Once the first stent is placed ( Fig. 22.8 ) the inner guiding catheter and guidewire are withdrawn just enough to release this first stent; the duct is then recannulated alongside the first stent with the second stent, guidewire, and inner guiding catheter. The process is continued until all stents are deployed. Alternatively, the stents can be placed one by one alongside each other ( Fig. 22.9 ).
Stents for Irretrievable Bile Duct Stones
In the absence of a stricture, pigtail stents (see Fig. 22.1, B ) may be preferable to straight stents when placed into a dilated biliary tree in patients with irretrievable bile duct stones (see Chapter 19 ) because they are less likely to migrate distally . Pigtail stents are placed slightly differently from straight stents because the duodenoscope has to be partially withdrawn during final deployment to allow the pigtail to form in the duodenum. The stent should be advanced until the distal portion of the stent just proximal to the distal pigtail is identified endoscopically. The latter is identified by applying an indelible marker before placement (if a visible marker is not already on the stent) at the junction of the straight portion and distal pigtail. The stent is then advanced while simultaneously withdrawing the duodenoscope so that the pigtail is deployed into the duodenum, or by allowing the elevator of the duodenoscope to remain open while advancing the pusher tube and allowing the pigtail to form distally.
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