Self-expandable metallic stent

Self-expandable metallic stents (SEMS) are tubular devices made from a metal mesh that can be expanded, either by the body's own temperature or through mechanical means, to hold open a bodily passage. They are commonly used in the medical field to treat a variety of conditions that cause narrowing or blockage of body passages, such as in the arteries (Atherosclerosis), bile ducts (Cholestasis), esophagus (Esophageal cancer), and others. The primary function of SEMS is to provide a scaffold that keeps the affected passage open, thereby improving or enabling the flow of bodily fluids or, in the case of arteries, blood.

Indications

SEMS are indicated for use in several conditions, including but not limited to:

• Peripheral artery disease (PAD) where they are used to open narrowed arteries.
• Coronary artery disease (CAD) for the same purpose as in PAD.
• Esophageal cancer or benign esophageal strictures, where they help in keeping the esophagus open.
• Biliary obstruction, either malignant or benign, to ensure bile flow.
• Colorectal cancer or other conditions causing obstruction of the colon, to maintain bowel patency.

Types

There are two main types of self-expandable metallic stents:

• Balloon-expandable stents: These are expanded to their full size using a balloon catheter at the time of placement.
• Self-expanding stents: These automatically expand once deployed, often using the body's own temperature.

Materials

The materials used in the manufacture of SEMS include stainless steel, cobalt chromium, and nickel-titanium alloy (Nitinol). Nitinol is particularly favored for its shape-memory and superelastic properties, allowing the stent to expand to its predetermined shape at body temperature.

Procedure

The placement of a SEMS is typically performed under imaging guidance, such as fluoroscopy, to ensure accurate positioning. The procedure involves the following steps: 1. Insertion of a catheter through a small incision to the site of the blockage. 2. Deployment of the stent at the blockage site, where it expands to hold the passage open. 3. Removal of the catheter, leaving the stent in place.

Complications

While SEMS are generally safe, they can be associated with certain complications, including:

• Stent migration, where the stent moves from its original position.
• In-stent restenosis, the re-narrowing of the passage within the stent.
• Stent fracture, which is more common in certain types of stents or locations.
• Infection, although rare, can occur at the stent site.

Future Directions

Research in the field of SEMS is focused on improving the biocompatibility of stents, reducing complications, and enhancing their functional lifespan. Innovations such as drug-eluting stents (DES), which release medication to prevent restenosis, and bioabsorbable stents, which gradually dissolve after serving their purpose, are examples of advancements in this area.