Stents are hollow tubes used to hold open strictured areas in various parts of the body, usually due to malignancy. There are two main types - simple plastic stents and self-expanding metal stents (SEMS). Plastic stents are used in the biliary tree and pancreas while SEMS can be placed in various areas using a guidewire. Stents are used to relieve obstructive symptoms from cancer and as a bridge to surgery. Complications include perforation, tumour overgrowth, and migration.

1. Stents in surgery
DR CARUNYA MANNAN

2.  Hollow tubes
 To hold open strictured areas in the oesophagus, the biliary tree, the
colon and the gastroduodenal region
 Usually positioned in order to overcome stricturing associated with
malignancy
 Bridge to surgery
 Palliation of obstructive symptoms

3. Basic Principle
 Initial placement of a guidewire and sometimes an overrunning
introducing catheter across the region to be stented, using endoscopic
vision /fluoroscopic guidance too
 The stent is advanced over the guidewire until it traverses the area to
be stented
 In the case of self-expanding stents, the restraining mechanism is then
released to deploy the stent

4. Types
 Simple plastic stents
 Self-expanding stents

5. Simple plastic stents
 Confined to use in the biliary tree and pancreas
 Composed of one of three polymers - polyethylene, polyurethane
orTeflon
 Plastic stents used in the biliary tree and pancreas
 Straight with anchoring side-flaps to prevent migration
 Pigtail stents - curled end of a pigtail stent is straightened over the
guidewire during positioning and the pigtail resumes its shape once the
guidewire has been removed

6. Plastic stents
Straight plastic stents Pigtail stent

7. Self-expanding stents
 Positioned while collapsed, using a
small calibre introducer
 Easier, safer, with a reduced risk of
perforation, and much reduced need
for prior stricture dilatation
 Metals - need to be biocompatible
biologically innocuous when
functioning in patients
 Shape memory alloys are
‘intelligent’, possessing the ability to
recover a previously defined length
or shape when deployed in the
patient

8. Self-expanding stents
 Each has its own characteristics in terms of radial forces exerted,
foreshortening on deployment, and flexibility
 SEMS can be made from stainless steel
 Alloys
 Nitinol is an alloy of nickel and titanium used in Ultraflex stent (Boston
Scientific, Natick, MA, USA) and Alimaxx E stent (Alveolus, Charlotte,
NC, USA)
 Elgiloy, a cobalt /chromium /nickel alloy, is used in Wallstent (Boston
Scientific)

9.  Fluoroscopically opaque to aid positioning
 Easily deployable via a small calibre introducer
 Introduced in a collapsed position, being run over a guidewire
positioned through the region to be stented
 Constraining mechanism is released and the stent expands, exerting
radial forces on any stricturing lesion thus increasing the lumen of the
area being stented

10.  SEMS - designed to expand to a diameter of more than 20mm.
 The bare metal strands of an uncovered stent may embed in the
underlying tumour and serve to anchor the stent in position
 Through pressure necrosis, the struts of the stent migrate into the
mucosa and submucosa of the gut wall.
 Fibrous reaction with chronic lymphocytic infiltration occurs, as the stent
becomes embedded in collagen and fibrous tissue
 A chronic lymphocytic reaction occurs in the normal tissue underlying
the proximal and distal ends of the stent
 MRI compatible

11. Uncovered Self-Expanding Metal Stent used in biliary
stenting

12. Covered metal stents
 SEMS may be covered with a silicone membrane to reduce the risk of
tumour in-growth and to seal fistulas
 Less likely to embed in the underlying tissues, and have an increased
risk of stent migration compared to uncovered stents
 Partially covered stents have been developed with flared uncovered
segments at both ends to anchor on to the tissue
 Fully covered SEMS are also increasingly used in benign oesophageal
disease, such as non-malignant strictures and anastomotic leaks
 Biodegradable stents have been developed which slowly break down
over time made from the biodegradable polymer poly-dioxanon, and
poly-L-lactic acid monofilaments

13.  Perforation, tumour overgrowth or ingrowth, and stent migration
 Areas of development -- radioactive or drug-eluting stents for malignant
disease

14. Oesophageal Stents

15. Malignant oesophageal obstruction
 Progressive dysphagia and weight loss
 Inoperable tumours
 Oesophageal stents - excellent option for the palliation of dysphagia
 In contrast to other treatment modalities like endoscopic laser or
brachytherapy, stents are widely available and are not restricted to
specialised centres

16. Malignant oesophageal obstruction
 First stents used in malignant dysphagia - rigid plastic stents
 Substantial risk of perforation
 SEMS were developed in the early 1990s. Their design allows them to be
preloaded onto a delivery mechanism typically measuring 5-10mm in
diameter
 Oesophageal SEMS are deployed over a guidewire after delineating the
margins of the stricture endoscopically.
 Diameter varies between 16 and 24 mm and their length varies between 7
and 15 cm
 SEMS are usually partially or fully covered with a membrane to prevent
tumour ingrowth through the metal mesh

17. Malignant oesophageal obstruction

18. Stents for benign oesophageal peptic strictures

19. Malignant tracheo-oesophageal fistulas
 Infiltration of oesophageal cancers into the respiratory tract, or cancers
of the trachea and bronchi infiltrating into the oesophagus
 Difficult to treat and are associated with poor prognosis
 Several case series have demonstrated that covered SEMS can lead to
fistula occlusion in 70-100% of patients

20. Oesophageal perforations and leaks
 Spontaneous and iatrogenic perforations - very high mortality and morbidity
 Iatrogenic perforations - more common
 Endoscopy, - malignant stricture dilatation
 Iatrogenic oesophageal perforation is life-threatening  contamination of the
mediastinum and pleural
 space with stomach contents is less problematic compared to spontaneous
perforation since
 the patient is fasted
 Insertion of a covered SEMS, together with thoracostomy tube drainage of the
pleural space and antibiotic administration - successful strategy in sealing off
iatrogenic perforations (Siersema et al., 2003)
 Prompt stent insertion (average delay 45 minutes) after iatrogenic oesophageal
perforation leads to minimal morbidity compared to delayed treatment, and produces
results similar to surgical treatment (Fischer et al., 2006)

21. Oesophageal anastomotic leaks
 Post-operative anastomotic leaks are another area where oesophageal stents
are increasingly used
 Case series of anastomotic leaks following upper gastrointestinal surgery
have demonstrated high success and low complications rates, with patients
returning to eating 2 days after stent insertion

22. Bleeding oesophageal varices
 Bleeding from oesophageal varices - high mortality
 Advanced liver disease with portal hypertension
 Endoscopic band ligation of the varices, vasopressor medication to decrease
portal
 pressure.
 Insertion of a Sengstaken-Blakemore tube which tamponades the varices
 Balloon tamponade is a temporary measure often used as a bridge to
treatment with a transjugular intrahepatic portosystemic stent shunt (TIPSS)

23. Sengstaken-Blakemore tube

24.  A Sengstaken–Blakemore tube is a medical device inserted through the nose or mouth and used occasionally in
the management of upper gastrointestinal hemorrhage due to esophageal varices (distended and fragile veins in the
esophageal wall, usually a result of cirrhosis). The use of the tube was originally described in 1950,[1] although similar
approaches to bleeding varices were described by Westphal in 1930.[2] With the advent of modern endoscopic
techniques which can rapidly and definitively control variceal bleeding, Sengstaken–Blakemore tubes are rarely used
at present.[3]
 The device consists of a flexible plastic tube containing several internal channels and two inflatable balloons. Apart
from the balloons, the tube has an opening at the bottom (gastric tip) of the device. More modern models also have
an opening near the upper esophagus; such devices are properly termed Minnesota tubes.[3][4] The tube is passed
down into the oesophagus and the gastric balloon is inflated inside the stomach. A traction of 1 kg is applied to the
tube so that the gastric balloon will compress the gastroesophageal junction and reduce the blood flow to
esophageal varices. If the use of traction alone cannot stop the bleeding, the esophageal balloon is also inflated to
help stop the bleeding. The esophageal balloon should not remain inflated for more than six hours, to avoid necrosis.
The gastric lumen is used to aspirate stomach contents.
 Generally, Sengstaken-Blakemore tubes are used only in emergencies where bleeding from presumed varices is
impossible to control with medication alone. The tube may be difficult to position, particularly in an unwell patient, and
may inadvertently be inserted in the trachea, hence endotracheal intubation before the procedure is strongly advised
to secure the airway. The tube is often kept in the refrigerator in the hospital's emergency department, intensive care
unit and gastroenterology ward. It is a temporary measure: ulceration and rupture of the esophagus and stomach are
recognized complications.[4][5]
 A related device with a larger gastric balloon capacity (about 500 ml), the Linton–Nachlas tube, is used for bleeding
gastric varices. It does not have an esophageal balloon.

25. Gastroduodenal stents
 Gastric outlet obstruction - pancreatic cancer, distal gastric cancer,
duodenal cancer, metastatic cancers
 Surgical gastroenterostomy to bypass the antro-pyloroduodenal region
 Gastroduodenal stent insertion offers a noninvasive means of palliating
vomiting without surgery

26.  SEMS variety and are positioned under direct endoscopic vision, and with fluoroscopic
guidance
 Before stent placement is attempted, a period of gastric drainage using a wide-bore
nasogastric tube is recommended
 Drainage of gastric contents will improve endoscopic views and reduce the risk of vomiting
and aspiration
 during the procedure. At endoscopy, the stricture’s proximal anatomy is assessed but
 usually the endoscope’s diameter is too large to allow safe negotiation through the stricture.
 The stricture can be outlined by fluoroscopy after the injection of a contrast agent. A
 guidewire is then passed down the operating channel of a therapeutic endoscope and
 advanced through the stricture. The stent assembly is then passed over the wire and
 positioned so that its ends overlap the ends of the stricture. Once fluoroscopy confirms a
 satisfactory position, the SEMS is deployed. An alternative method of gastroduodenal stent
 insertion involves a radiologist placing the stent via the oral route using fluoroscopy alone.