I.2.4. Self-Expandable Stents

Dra. Ana Echarri Piudo
Complejo Hospitalario Universitario de Ferrol
Dra. Carme Loras Alastruey
Hospital Universitari MútuaTerrassa. Barcelona

 

DESCRIPTION

Self-expandable metal stents (SEMS) are made of a cylindrical, laser-cut metal mesh that exerts its self-expanding force until it achieves its maximum diameter (Fig. 1) when released from a device where they are compressed for the purpose of recovering the intestinal lumen of a stenosed area (benign or malignant obstruction)1,2.
 

 
FIGURA 1. Dispositivo para la colocación y liberación de prótesis autoexpandible.
 

Presently, most stents currently used are composed of nitinol, a nickel and titanium alloy that increases flexibility, enabling placement in angulated regions, although they have less radial expansion force than other alloys like elgiloy (cobalt and nickel alloy) or Wallstent steel (Boston). In addition, the edges are softer than alloys previously utilised, reducing bowel trauma.

All stents are sold in a variety of lengths and diameters or with wider ends (cup) to help anchor the stent and avoid migration (Table I).
There are non-covered stents and covered stents (totally or partially), in which the spaces in the metal mesh are covered by a silicone membrane. Selection of a stent depends on the location, nature and extension of the lesion1-3 (Fig.2).

 
Tabla_SEC1_02_04_T01
 
FIGURA 2. A. Prótesis de distintos diámetros y longuitudes. B. Prótesis total y parcialmente cubiertas.
 

In general, when treating stenoses associated with Crohn’s Disease (CD), totally or partially covered SEMS are generally used. When treating a benign pathology, removal after an average time of 4 weeks is recommended, the most simple removal being via the use of covered stents (although the possibility for migration is greater)4-6.

Stents, such as UltraflexTM Precision stents, can be inserted through the working channel ((through-the-scope [TTS]) or through a guide (OTW) (Fig. 3) once the endoscope is removed. In these cases, the release devise is larger than the working channel (22F), and is only available at a length of 100 cm (distal colon and oesophagus), which allows the precise adjustment of the stent at the edge of the lesion, since they do not shorten when expanding1-3.

 
FIGURA 3. A. Sistema de colocación de prótesis a través del canal de trabajo del endoscopio. B. Sistema de colocación de prótesis por medio de guía (en paralelo).
 

Wallflex self-expandable stents (TTS) usually have a marking system (three radiopaque marks) that help in releasing the stent (Fig. 4):

1.st mark: External distal mark of the stent. The distal edge must exceed 4 cm from the stenosis (one must take into consideration the shortening of the stent, sometimes up to 45%) (Duodenal Wallflex).

2.nd mark: The post-deployment mark must be located at the proximal edge of the stenosis (the end closest to the endoscope); once the stent is released, the proximal end of
the stent will be located 2 cm over this mark. It is important to hold it still at the proximal edge of the stenosis.

3.rd mark: There is a mark above the post-deployment mark that indicates the point of no return for the release. Up to this point, the stent can fold over; once at this point it cannot: you will have to release it (approximately 70% of the stent).

 
FIGURA 4. Control fluoroscopico de colocación de la prótesis mediante el sistema de marcas radiopacas de las prótesis wallflex.

 

STENT PLACEMENT. TECHNIQUE

Before performing endoscopic stent placement in a stenosis associated with CD, it is essential to perform a proper test of the activity of the disease and the stenosis.

It is recommended that the technique be performed under conscious sedation, although in cases of high stenosis with significant gastric retention, the airway must be protected, and sometimes intubation is needed.

• The endoscope must be positioned proximal to the lesion.

• It is important to identify the margins (proximal and distal) of the lesion and they can be marked, if necessary, by markers in the skin, clips or intramucosal contrast injection (lipiodol). Moreover, the patient has their own marks, such as bone structures (ribs, vertebrae), air in the gastric chamber and previously placed staples that can be used as points of reference.

• Insert a rigid guide (0.035) as distal as possible (bends less than a regular guide and enables the passage of the stent, especially in stents that do not go through the channel), controlling the passage of the guide by direct view or fluoroscopic control.

• In the event that the lesion is not passable, a contrast injection will be used through a catheter in order to determine the length and appearance of the lesion. In some cases, the use of a Fogarty balloon catheter through a guide may be useful; once the stenosis is passed through, the balloon is inflated and pulled back until it impacts the stenosis: a below balloon can be used or the lesion can be contrasted when pulling back the balloon. This technique will help us to mark the edges of the stenosis, assess the extent and shape, and calculate the length of the stent.

• Theoretically, any endoscope with a proper working channel (therapeutic endoscope) can be used. Selecting a tube depends on the location of the lesion: proximal lesions can be treated with a therapeutic gastroscope (3.7 mm working channel) or a duodenoscope (4.2 mm); lesions located in the colon and terminal ileum, depending on their location, may be treated with a gastroscope or colonoscope, while enteral lesions distal to the second part of the duodenum will require a therapeutic colonoscope or an enteroscope with an overtube. In the latter case, a modified technique is used, in which the stent will be placed via a guide, removing the enteroscope but leaving the overtube that holds the folded intestine and deploying the stent via fluoroscopic control1-3,7.

• There are generally two methods for stent placement:

– The stent is introduced through a working channel (TTS), via a guide that passes through the stenosis, and is deployed by way of a direct endoscopic view.

– The stent is placed via the guide (OTW) without passing through the working channel. The stent is place endoscopically, then the endoscope is removed (leaving the overtube if using a enteroscope). The stent is introduced via the guide and deployment is controlled by fluoroscopy or under direct control with the parallel endoscope in case of accessible stenoses (Fig. 3).

When selecting the stent, one should keep in mind that each end must be at least 2 cm longer than the stenosis (4 cm of safety margin), since metal enteral stents shorten during the deployment and expansion of the stent. To prevent migration, is not recommended that the endoscope be passed through the stent once the stent is placed, although endoscopic/fluoroscopic control can be used to rule out early complications2,7,8.

Stents placed in the last 10 cm of the rectum must be considered carefully, given the pain and tenesmus associated with their placement.

 

GUIDES AND CATHETERS

There are no universal recommendations, and many times recommendations are determined according to the clinical scenario, but from a overall point-of-view, they would be the following:

• It is recommended that standard guides be used (those used in biliary cannulation).

• In the event of tortuous stenosis, the use of soft or hydrophilic guides is preferred.

• The standard catheter is recommended since it can help in exchanging the guide for a metal one that facilitates stent deployment.

• In some cases, it can be helpful to use a Fogarty balloon catheter.

 

COMPLICATIONS

 

Early or procedure-related

Generally, they are uncommon, they usually occur in 5–7% of the cases.

• Bleeding and perforation.

• Early migration of the stent or dysfunction of thestent.

• Bronchoaspiration.

• Rectal tenesmus in relation to the release of the stent very close to the anal pectinate line.

Late

Occur more often, up to 20%, according to the revised series.

• Migration: is a common complication, especially with the use of covered stents. This can be retrograde or anterograde (more common) and may lead to bowel obstruction.

• Stenosis: particularly common with the use of uncovered stents in malignant stenoses. This is the result of the occlusion of the stent due
to increased tissue inside or at the ends or due to tumour invasion. In these cases, it is advised that a second stent be used via the first.

• Inability to remove the stent, generally in relation to a burial of the edges.

 

REFERENCES

1. Classen M, Tytgat G, Lightdale C, editors. Gastrointestinal stenting. In: Gastroenterological Endoscopy. 2nd ed. 9. Stuttgart: Thieme; 2010.
2. ASGE Technology Committee, Varadarajulu S, Banerjee S, Barth B, Desilets D, Kaul V, et al. Enteral stents. Gastrointest Endosc. 2011; 74: 455-64
3. Kochar R, Shah N. Enteral stents: from esophagus to colon. Gastrointest Endosc. 2013; 78: 913-8.
4. Attar A, Maunoury V, Vahedi K, Vernier- Massouille G, Vida S, Bulois P, et al; the GETAID. Safety and efficacy of extractible self-expandable metal stents in the treatment of Crohn’s disease intestinal strictures: A prospective pilot study. Inflamm Bowel Dis. 2012; 18: 1849-54.
5. Loras C, Pérez-Roldan F, Gornals JB, Barrio J, Igea F, González-Huix F, et al. Endoscopic treatment with self-expanding metal stents for Crohn’s disease strictures. Aliment Pharmacol Ther. 2012; 36: 833-9.
6. Kwon YH, Jeon SW, Lee YK. Endoscopic management of refractory benign colorectal strictures. Clin Endosc. 2013; 46: 472-475.
7. Tierney W, Chuttani R, Croffie J, DiSario J, Liu J, Mishkin DS, et al. Enteral stents. Gastrointest Endosc. 2006; 63: 920-6.
8. Baron TH, Harewood GC. Enteral self-expandable stents. Gastrointest Endosc. 2003; 58: 421-33.

 

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