Joseph Leung, MD and Peter Cotton, MD

Dr. Leung at live demonstration ERCP workshop

Dr. Peter Cotton and the late Mr. Don Wilson

Joseph Leung, MD, FRCP, FACP, FACG, FHKCP, FHKAM
Mr. & Mrs. C. W. Law Professor of Medicine, University of California, Davis School of Medicine, Chief, Section of Gastroenterology, VA Northern California Health Care System, Sacramento, CA

Peter Cotton, MD, FRCP, FRCS, FASGE
Professor of Medicine, Director, Digestive Disease Center, Medical University of South Carolina, Charleston, SC

Introduction
In the 1970s, there were not many options for the palliation of malignant obstructive jaundice. Palliative biliary bypass surgery carried significant morbidity and mortality, and percutaneous transhepatic drainage was associated with considerable morbidity because of pain and external bile loss. Internal drainage with an endoscopically placed prosthesis in the bile duct or stenting was considered one of the major breakthroughs in therapeutic endoscopy in the late 1970s.

In 1978, Dr. Nib Soehendra in Hamburg fashioned a single pigtail stent for biliary drainage using the cut end of an angiographic catheter. In 1979, Dr. Peter Cotton in London reported the double pigtail stent design to prevent stent migration. In 1981, Dr. Kees Huibregtse from Amsterdam described the use of side flaps created in the wall of a straight stent in place of pigtails to prevent stent migration. Dr. Michel Cremer from Brussels designed a stent with a snake-shaped proximal tip and a distal C-loop in the duodenum for the same reason.

Design of the Cotton-Leung Stent
In 1984, in collaboration with Cook Endoscopy, the Cotton-Leung stent was designed to overcome the shortcomings and limitations of these earlier stents. The pigtail stent has restricted flow because of the small side holes at the tip. Despite the pigtail end and anchoring flaps, the single pigtail stent and the subsequent Amsterdam stent were more prone to migration because of the straight shaft. The small end hole at the tip of a Cremer stent limited the flow and drainage of bile. The proximal tip of the Amsterdam stent could get stuck at the lower level of a tight or angulated stricture or tumor because of the gap between the guide wire and the stent lumen (shoulder effect), which creates resistance to stent insertion. The curved ends of a double pigtail stent made it difficult to place through a stricture.

The unique feature of the Cotton-Leung stent is the coaxial tapered tip design, which eliminates the gap between the guide wire, inner catheter and tip of the stent, offering a tight fit to facilitate passage of the stent through a tight stricture. In vitro flow studies demonstrated that drainage through a tube depends on the diameter of the end hole (Table 1). A tapered tip could significantly reduce the flow of bile through the stent [1, 2]. To overcome this problem, we created a 5 mm side hole, which improves drainage through the proximal end of the stent with a resultant side flap similar to the design of the Amsterdam stent which offers resistance to stent migration (Figure). However, the side flap can be collapsed if it is being pushed against the bile duct wall or a tumor (or a failure to open up because of incomplete passage through a tumor), thus closing off the opening and reducing flow. To avoid this complication, we created another 5 mm side hole (without flap) on the opposite side of the side flap to ensure drainage of the obstructed system above the stricture. The tip of stent above the proximal side flap is about 1.5 cm with the side hole and side flap properly spaced to avoid weakening the stent and to prevent buckling in the normal deployed position. In order to prevent upward stent migration, we created another 5 mm side flap on the same side at the distal end which is positioned at the level of the papilla in the final deployed position. This distal flap opens up almost at a right angle to the shaft to provide maximum resistance to stent migration. The side hole allows continuous drainage from the stent in the event of downward stent migration when the distal end hole is blocked by the duodenal wall (a problem that affects straight stents without distal side hole). Assuming a perfect stent deployment and no subsequent stent migration, this side hole will be placed practically at the pancreatic orifice, thus avoiding any local pressure effect on the pancreatic opening. We have not observed a significant increase in post-stenting pancreatitis when a single 10 FR stent is used, even though the stent position is not guaranteed. On the other hand, a collapsed distal flap not only fails to resist upward migration (especially in the presence of a papillotomy) but could also possibly irritate the pancreatic opening and cause pancreatitis.

Theoretically, there is a risk of duodenal irritation and perforation associated with downward stent migration. In order to minimize potential irritation to the opposite duodenal wall, the stent has only a 1 cm tip extending beyond the distal flap. The stent is designed to conform to the shape of the bile duct, which in most cases has an inherent curvature rather than being straight. We created a gentle C-curve in the mid-shaft of the stent. When the stent is deployed, the curvature of the stent follows the contour of the bile duct and also provides a spring-like action holding the stent in place, further reducing the risk of stent migration. We did not put any side holes in the shaft of the stent (which traverses the tumor) between the side flaps to avoid the theoretical risk of tumor in-growth. This Cotton-Leung stent has been shown to provide more effective drainage than double pigtail stents in laboratory studies (Table 2) as well as in a clinical study [3].

Why Cotton-Leung Stents are Made of Polyethylene
In the early 1980s, homemade stents were popular and we often had to tailor the stents for patients. Therefore, it was crucial to find a material that could be easily shaped, manipulated or cut. After experimenting with different materials, we chose to use polyethylene instead of Teflon or polyurethane – the other materials available at the time. Polyethylene was chosen for its low melting point and because it becomes soft and malleable at 87°C compared to the much higher temperature required to soften Teflon. A polyethylene stent can be shaped and molded easily using boiling water or steam and subsequently set by holding it and immersing it in cold water. It is also softer than Teflon, making the cutting of side holes or side flaps much easier.

Stent Length
By definition, the stent length for the Cotton-Leung design is the distance between the proximal and distal flaps. In order to accommodate various strictures, stents are available in lengths ranging from 5 cm for distal CBD obstruction to 15 cm for hilar obstruction. Ideally, the proximal flap of a deployed stent should extend about 1 cm above the upper level of the stricture or tumor (to avoid tumor overgrowth), while the distal flap should be at the level of the papilla. In this case, even though there may be a risk of downward migration, only 2 cm of the stent may protrude from the papilla into the duodenum. However, this only holds true with a significant stricture holding the stent in position and may not apply when the stent is placed for stone obstruction or when the stricture has been dilated. In general, an 8 cm stent will fit most lesions, either a stricture or large obstructing CBD stones in the common bile duct. Stents are available in various diameters: 7, 8.5, 10 and 11.5 FR. Although a larger stent provides a faster flow, there was no significant difference observed in the flow rate and reported stent patency rate between the 10 FR and 11.5 FR stents because of similar internal diameters. Because of the thicker wall material, the larger 11.5 FR stent is more difficult to remove. We prefer to use 10 FR because they can be easily removed through a large 4.2 mm channel therapeutic scope.

Distal Tip of Stent in Duodenum
There have been discussions about the proper position of the stent, whether the tip should be placed entirely within the bile duct to avoid ascending infections and contamination leading to stent blockage by bacterial biofilm. The original design of the Cotton-Leung stent allowed the distal tip to be placed within the duodenum with the distal flap preventing upward migration. The 1 cm distal tip allows the stent to be captured easily and removed with a snare in case of stent change or removal. It is recognized that considerable effort is required to retrieve an upwardly migrated stent.

The Stent Introducer Mechanism
The early stent introducer mechanism consisted of three layers – a regular Teflon coated .035” guide wire, a 6 FR Teflon guiding catheter with radiopaque markers and a 10 FR Teflon pusher. This three-in-one co-axial layered system was in use for over 10 years before the simplified One Action Stent Introducer System (OASIS) was launched in the early 1990s. Early stenting required deep cannulation of the bile duct and negotiation of the stricture with the guide wire, followed by exchange and inserting the guiding catheter across the obstruction. The guiding catheter provided a stiff “railroad track” for the passage of the stent. The length of the stent could be estimated by reference to the radiopaque markers, set 7 cm apart. A suitable length stent was then chosen and loaded onto the guiding catheter and subsequently deployed using the pusher tube. The more convenient OASIS system combines the guiding catheter and pusher into a single unit using a Luer lock mechanism. Once the guide wire is inserted across the stricture, a suitable length stent is chosen and loaded onto the guiding catheter/pusher system before inserting over the guide wire. Keep in mind the stent length must be determined using other methods as the radiopaque markers set 5 cm apart on the guiding catheter are now used for guiding deployment and the final position of the stent. The stent is advanced over the guiding catheter and deployed by unlocking the guiding catheter from the pusher. With the stent in the final position, the pusher tube is held in position while the guide wire and guiding catheter are withdrawn leaving the stent in place.

The new Fusion OASIS has proven to be helpful in placing multiple stents in the bile duct for the management of benign strictures. Prior to final deployment of a stent, the guide wire can be separated from the guiding catheter and left in the bile duct across the stricture with the intra-ductal exchange (IDE) feature. The next stent can be delivered over the same guide wire eliminating the need to recannulate the stricture thereby cutting down on procedure time.

Shaping the Stent
Because of the varying contour of different bile ducts, as a personal preference, it may be necessary to alter the C-curve on the stent to conform to the curvature of the bile duct. Also, the side flaps may sometimes be collapsed when the stent is removed from the packaging. It is easy to use hot water from a kettle (contained in a plastic kidney tray) to open the flaps and shape the stent and then placing it in cold sterile water. (Use double gloves to avoid scalding one’s fingers in hot water).

Conclusion
Over the three decades since the development of the Cotton-Leung stent, many new designs and materials have been developed, used and evaluated. Expandable metal stents have played an important role in patients with unresectable malignancies. Despite all of these changes, the original Cotton-Leung stent has remained the most popular biliary stent in ERCP practice throughout the world.

References

1. Leung JW. Endoscopy and Malignant Obstructive Jaundice, MD Thesis. The Chinese University of Hong Kong, 1986.
2. Leung JW, Del Favero G, Cotton PB. Endoscopic biliary prosthesis: a comparison of materials. Gastrointest Endosc 1985;31:93-95.
3. Speer AG, Cotton PB, MacRae KD. Endoscopic management of malignant biliary obstruction: stents of 10 French gauge are preferable to stents of 8 French gauge. Gastrointest Endosc 1988;35:412-7