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Endoscopic stenting is increasingly being used in the management of gastrointestinal luminal obstruction.
The current treatment of choice for the palliation of blockage caused by malignant or benign growths.
GI stents were originally designed as rigid, cylinder-like prostheses which had poor efficacy and high adverse event rates, such as migration, obstruction, and perforation of the GI tract.
In recent years, considerable advances have been made in the design of these stents, and several types of high-quality devices have been developed.
Stents have been used as safe and effective alternatives to surgery or repetitive endoscopic procedures, for patients with various gastrointestinal disorders.
Indications for the use of stenting include: malignant strictures, obstructions, external compressions of the GI tract, malignant GI perforations and fistulae, and selected cases of benign stricture that are resistant to repeated balloon dilation or surgical bougienage.
Stenting has been used as an excellent palliative therapeutic modality by providing the patient immediate relief of symptoms.
Rigid polyvinyl plastic stent placement has been used to alleviate obstruction of the GI tract.
Although efficacious, plastic stents were associated with complications, such as migration, food impaction, and perforation in up to 10% of patients.
With the use of plastic stents the lumen of the alimentary tract often required dilation prior to stent placement because the plastic stent was of a fixed diameter.
Because of tumor location, friability, angulation, and tightness, insertions were often traumatic and the procedural complication rates were high.
Self-expandable metallic stents (SEMS) consist of woven, knitted, or laser-cut metal mesh cylinders that exert self-expansive forces until they reach their maximum fixed diameter.
Can be inserted into a narrower opening, making dilation unnecessary and reducing the risks of perforation, obstruction, or migration, as can occur with plastic stents.
Nickel titanium alloy with shape memory and super-elastic characteristics, greatly improved their utility.
The use of SEMS is associated with significantly reduced stent-related adverse events compared to plastic prostheses in the palliative treatment of esophageal cancer
SEMS have a longer patency compared to plastic stents.
SEMS also have larger luminal diameters, and
the larger SEMS diameter leads to a lower incidence of bacterial growth in biliary stents, which is considered the main reason of biliary stent obstruction.
The maximum diameter of plastic stents is limited to 12 Fr, because a plastic stent larger than 12 Fr cannot be inserted through the endoscope.
Narrow lumens predispose plastic stents to occlusion by biliary sludge and/or bacterial biofilm formation, resulting in an average of 3 months of stent patency.
Partially covered SEMSs, which have a membrane to prevent tissue ingrowth into the lumen of the stent.
Compared to plastic prostheses in the palliative treatment of esophageal cancer, patients who receive a SEMS have better palliation of dysphagia, shorter hospital days, and longer survival.
Tumor ingrowth through the open mesh architecture is known to occur in 13% of uncovered SEMS cases.
Epithelialization of uncovered stents arises within 3 to 6 weeks.
Partially covered SEMSs, have a membrane for the purpose of preventing tissue ingrowth into the lumen.
SEMS have a longer patency compared to plastic stents because of their larger luminal diameters.
GI stent failures frequently occur due to the ingrowth and overgrowth of tumor cells or benign granulation tissue, despite the clinical improvement provided by the stent.
The ingrowth and overgrowth could cause delayed stent occlusion and restricted patency, and result in shortened patient survival.
Occlusion is inevitable over time in most cases, because the polyurethane used is biodegraded.
The combination of stent insertion and brachytherapy is likely to be a feasible and safe palliative treatment strategy in patients with unresectable esophageal cancer.
Biodegradable stents have been used in recurrent benign strictures after ingestion of corrosive agents or iatrogenic endoscopic submucosal dissection.
Indications for the use of stenting have gradually expanded to include a variety of malignant strictures, obstructions, external compressions of the GI tract, malignant GI perforations and fistulae, and selected cases of benign stricture that are resistant to repeated balloon dilation or surgical bougienage.
SEMS have a longer patency compared to plastic stents because of their larger luminal diameters.
In biliary stenting, the diameter of a SEMS can be extended to 24 to 36 Fr through a relatively smaller (7 to 10 Fr) delivery system, and the larger SEMS diameter leads to a lower incidence of bacterial growth.
Bacterial overgrowth in the stent, is considered the main reason of biliary stent obstruction.
Narrow lumens predispose plastic stents to occlusion by biliary sludge and/or bacterial biofilm formation, resulting in an average of 3 months of stent patency.
Self-expandable metal stents can be effective in preventing tumor ingrowth, migration occurs frequently, compared to uncovered stents, because the cover on the outside prevents the embedding of the mesh in the tissue, thus reducing stent anchorage.
A significant number of patients require re-intervention for stent malfunctions, including obstruction, migration, and other related complications.
Approximately 0.5 to 2 percent of patients who undergo placement procedure die as a result.
Several newly designed stents aimed at preventing migration have been developed.
Covered SEMSs are designed to withstand tumor growth, however, occlusion is inevitable over time in most cases, because the polyurethane used is biodegraded in vivo by hydrolysis, oxidation, and continuous contact with GI tract content.
Efforts to develop drug-eluting stents are ongoing.
Radioactive stents combine the advantage of immediate relief of GI tract obstruction by stent insertion, with the longer-term benefits achieved through brachytherapy.
Most studies on radioactive stents have been conducted on esophageal or biliary malignant obstruction.
Refluxed content through the SEMS can cause various diseases, including ascending cholangitis or gastroesophageal reflux; this could also cause stent obstruction, by inducing biofilm formation or introducing undigested food.
Biodegradable stents have been shown to be effective promising results in benign strictures after ingestion of corrosive agents or iatrogenic endoscopic submucosal dissection.
Biodegradable stents are made of absorbable polylactic acid polymers, and are degradable.
Degradable stents do not require removal, and can reduce hyperplastic tissue reactions and adverse events associated with stent removal