INTRODUCTION — Enteral stents are used as a nonsurgical alternative for the palliation of luminal gastrointestinal neoplasms, particularly in the esophagus and biliary tract [1]. They are commonly used in the treatment of obstruction in other areas of the gastrointestinal tract, such as the stomach, proximal small bowel, and colon.
This topic will review the use of self-expanding metal stents (SEMS) in the management of malignant colonic obstruction. The surgical management of malignant colonic obstruction and colon cancer is discussed separately.
●(See "Large bowel obstruction".)
●(See "Surgical resection of primary colon cancer".)
The use of stents for other portions of the gastrointestinal tract is discussed separately:
●(See "Endoscopic stenting for palliation of malignant esophageal obstruction".)
●(See "Enteral stents for the palliation of malignant gastroduodenal obstruction".)
●(See "Endoscopic stenting for malignant biliary obstruction".)
INDICATIONS — The indications for stent placement in patients with malignant colonic obstruction include [2-9]:
●Palliation of surgically incurable colorectal cancer. (See "Locoregional methods for management of metastatic colorectal cancer", section on 'Nonsurgical palliative options'.)
●Stenting as a bridge to surgery to avoid an emergent, two-step procedure and to allow for optimization of medical status and for preoperative staging including colonoscopy. (See "Clinical presentation, diagnosis, and staging of colorectal cancer" and "Large bowel obstruction", section on 'Malignant obstruction'.)
●Management of some patients with extracolonic pelvic tumors (eg, ovarian cancer). (See "Cancer of the ovary, fallopian tube, and peritoneum: Surgical cytoreduction", section on 'Bowel resection'.)
CONTRAINDICATIONS — Colonic stenting is contraindicated if there are signs of systemic toxicity. Emergency surgery is recommended in patients with complete colonic obstruction with evidence of systemic toxicity, as these patients may have already developed colonic ischemia and/or perforation. (See "Overview of the management of primary colon cancer" and "Large bowel obstruction", section on 'Clinical presentations'.)
Stent placement is also contraindicated in patients with intra-abdominal abscess and relatively contraindicated in patients with persistent coagulopathy despite treatment [10].
Stent placement to treat distal rectal lesions (ie, within 5 cm of the anal verge) is usually avoided because a stent in this location can induce severe pain, tenesmus, and rectal bleeding. However, some patients who wish to avoid an ostomy can undergo stent placement very low in the rectum with good tolerance.
Stenting in the setting of adjunctive therapy — High perforation rates have been reported in patients receiving the antiangiogenic agent bevacizumab [9,11,12]. We agree with the guidelines that suggest that colonic stenting should be avoided, if possible, in patients who are or who will be receiving antiangiogenic agents (eg, bevacizumab), especially if the obstruction is subtotal. (See "Locoregional methods for management of metastatic colorectal cancer", section on 'Intraluminal stent placement'.)
The data supporting the avoidance of self-expanding metal stents (SEMS) in patients who are candidates for antiangiogenic therapy include:
●In a study of 233 patients, 26 received bevacizumab after SEMS insertion (23 for palliation, 3 as a bridge to surgery) [13]. Colonic perforation occurred more often in patients who received bevacizumab after stent placement compared with patients who did not, though the result did not reach statistical significance (15 versus 7 percent). None of the six patients who received bevacizumab prior to stent insertion had a perforation.
●In a retrospective series of 201 patients who received SEMS for palliation, stents were successfully placed in 184 patients (92 percent) [14]. There were 12 perforations (6 percent). However, four of the eight patients who received bevacizumab experienced a perforation, a rate significantly higher than seen in those who did not receive bevacizumab (odds ratio 20; 95% CI 5.9-65).
In addition to the risk of perforation, many patients will respond to chemotherapy with improved luminal diameter and thus may not require stent placement or surgery to relieve colonic obstruction.
EQUIPMENT
Types of stents — Colorectal self-expanding metal stents (SEMS) may be uncovered (meshwork is bare wire) or covered (meshwork is covered to decrease tissue growth into the stent). All colorectal SEMS function very similarly.
●Only uncovered stents are available for the treatment of colonic obstruction in the United States, and include the following:
●Through-the-scope (TTS) stents:
•WallFlex Colonic Stent (Boston Scientific) – This uncovered nitinol TTS stent expands to mid-body diameter of either 22 or 25 mm and proximal flange of 27 or 30 mm. It is available in lengths of 6, 9, and 12 cm. Foreshortening, which is the reduction in stent length from the crimped to the expanded condition, occurs up to 30 to 40 percent during deployment.
•Evolution Colonic Controlled-Release Stent (Cook Medical) – This uncovered nitinol TTS stent has a mid-body diameter of 25 mm and proximal and distal flanges of 30 mm. It comes in lengths of 6, 8, and 10 cm. Foreshortening occurs during deployment.
•HANAROSTENT LowAx Colonic Stent (Olympus) – This uncovered nitinol TTS stent has a patented "hook and cross" design to promote ideal radial and axial force at the site of obstruction [15]. It is available in lengths of 6, 9, and 12 cm, with mid-body diameters of 22 and 25 mm. This stent demonstrates limited foreshortening during expansion in comparison to other commercially available colon stents.
●Non-TTS deliverable stent:
•Ultraflex Precision Colonic Stent (Boston Scientific) – This nitinol stent has a proximal flange of 30 mm and body diameter of 25 mm. It is available in lengths of 5.7, 8.7, and 11.7 cm [16,17]. It differs in that the delivery system is too large to be passed through the channel of the endoscope (non-TTS deliverable), it cannot be re-constrained during deployment, has a string release mechanism, and opens from the distal end (closest to the endoscopist, below the tumor, unlike the other stents that open from the proximal end, above the tumor). It also has less foreshortening than the previously mentioned stents.
Covered versus uncovered stents — Covered stents that are available outside the United States have been used mainly in the setting of malignant colo-vesical, colo-enteric, and colo-vaginal fistulas [18-20]. While a theoretical advantage of covered SEMS is the decreased risk of tumor ingrowth, they also have a greater tendency to migrate compared with uncovered SEMS.
Studies have not shown a significant advantage for covered stents:
●In a randomized trial of 151 patients with malignant colonic obstruction, there was no difference in clinical success rate for the placement of covered compared with uncovered stents (96 versus 92 percent) [21]. There was a higher rate of stent migration among patients with covered stents (21 versus 2 percent) and there was a trend toward a lower rate of cancer infiltration into the covered stents (4 versus 15 percent). There were no differences with regard to adverse events or stent obstruction from debris.
●In a nonrandomized study of 80 patients, there were no differences in technical or clinical success rates comparing uncovered with covered stents (100 versus 95 percent and 100 versus 97 percent, respectively) [22]. There was a lower rate of loss of stent function in the patients who received uncovered stents (60 versus 19 percent).
PREPROCEDURE TESTING — Although the diagnosis of colonic obstruction is often made based on presenting symptoms and imaging (ie, plain radiography and/or computed tomography [CT] scan), additional testing (eg, endoscopy, imaging) is often performed prior to stent placement.
●Direct endoscopic visualization of the site of the obstruction can provide the following information:
•Tissue biopsy for histologic diagnosis of the tumor.
•Assessment of the site for potential stent placement (ie, is the tumor in an area of angulation).
•Origin of the tumor (extrinsic versus intrinsic).
•Degree of colon obstruction by noting if and how easily the colonoscope can be advanced through the tumor. However, advancing the colonoscope through the tumor is not required prior to stent placement.
●Radiographic imaging
•Water-soluble enema examination or a rectal contrast CT scan may be helpful, though not absolutely necessary, to obtain a roadmap of the relevant anatomy, stricture length, and degree of obstruction. A barium contrast may also be used. Radiographic evaluation can also identify additional sites of obstruction that may mitigate the effect of a successful stent placement.
PREPROCEDURE PREPARATION
Bowel preparation — Our approach to bowel preparation prior to endoscopic stent placement depends on the location and degree of obstruction.
●For patients with partial obstruction in the distal colon, two cleansing tap water enemas are generally sufficient preparation for stent placement.
●For patients with partial obstruction from a proximal lesion, an oral bowel prep can be attempted and discontinued if symptoms (ie, abdominal pain, abdominal distension, nausea, or emesis) develop. (See "Bowel preparation before colonoscopy in adults".)
●For patients with complete colonic obstruction, oral preparations are not tolerated and could theoretically precipitate perforation. Tap water enemas may still be given to evacuate stool below the level of obstruction.
Antibiotics — Antibiotic prophylaxis is unnecessary for most patients undergoing stent placement. However, prophylactic antibiotics are suggested in completely obstructed patients who have a markedly dilated colon because insufflation during the procedure may lead to microperforation and bacteremia [6]. (See "Antibiotic prophylaxis for gastrointestinal endoscopic procedures".)
PROCEDURE
General considerations — Colorectal self-expanding metal stents (SEMS) are usually placed under endoscopic guidance, preferably with the aid of fluoroscopy. The endoscopic placement of SEMS is especially advantageous compared with radiologic placement when the obstruction is proximal to the recto-sigmoid region or in the presence of a tortuous colon [23].
During colonoscopy, judicious insufflation should be used to minimize the risk of perforation due to a closed-loop phenomenon between the obstructing lesion and the ileocecal valve. Carbon dioxide insufflation has largely supplanted room air insufflation for all endoscopic procedures, especially high-risk cases such as these. Water immersion colonoscopy is another technique which could be utilized to minimize bowel distention when colonoscopy with carbon dioxide insufflation is unsuccessful. (See "Overview of colonoscopy in adults", section on 'Colonoscope advancement and mucosal inspection'.)
Approach to evaluating the obstruction — Upon reaching the lesion (picture 1), a gentle attempt can be made to traverse the stricture with the colonoscope. However, if the colonoscope cannot be passed easily through the obstruction, a guidewire (ie, flexible tip, stiff shaft, 0.035 inch, long-length biliary guidewire preloaded in a biliary catheter) can be passed through the stricture under fluoroscopic guidance.
Balloon dilation of the stricture should be avoided since it is usually unnecessary, is unlikely to be of durable benefit, and increases the risk of perforation [24].
Placing the stent — After confirming the length of the lesion either by passage of the endoscope or with contrast injection under fluoroscopic guidance with contrast (image 1), the process of stent placement depends on the delivery system (ie, through-the scope [TTS] or non-TTS):
●TTS delivery system – The majority of colonic stents are deployed using a TTS delivery system that requires a therapeutic channel endoscope with a diameter large enough to pass the stent through the working channel. The guidewire is placed through the stricture and advanced beyond the level of the stricture. Guidewire placement is confirmed with fluoroscopy by injecting contrast through a biliary catheter over the wire. The stent is then passed over the guidewire until the tip is proximal to (ie, above) the tumor. The stent is then deployed under fluoroscopic guidance and with endoscopic visualization of the stent’s distal position (picture 2). The stent should be deployed with at least 2 cm exposed distal and proximal to the obstructing lesion.
●Non-TTS delivery system – Also referred to as over-the wire delivery, this system differs in that the endoscope is withdrawn after placement of the guidewire [10]. The stent is inserted over the guidewire and deployed under fluoroscopic guidance. The distal position of the stent can be assessed with endoscopic visualization after the endoscope is reinserted.
Ideal stent placement reveals a "waist" in the stent region traversing the tumor with a flare of the proximal and distal ends of the stent (image 2). If either end of the stent is not flared or expanded to produce a waist, the stent may be too short to traverse the stricture. In such cases, a second or third stent can be used in an overlapping fashion with the first to completely traverse the stricture [25].
Postprocedure dietary recommendations — Following stent placement in the left colon, stools should ideally be maintained at a soft consistency to avoid fecal impaction within the stent. This can usually be accomplished by advising patients to consume a low residue diet and to take polyethylene glycol at a dose and frequency that will result in soft stools for that individual patient. Titration of the laxative dose may be necessary. Patients should be instructed to avoid foods that are high in fiber, such as fruits, vegetables, and whole grains (table 1).
Patients with stents in the transverse or right colon can resume normal diets, as the stool in these portions of the colon is typically still liquid.
EFFICACY — The efficacy of surgery for the management of mechanical bowel obstruction compared with self-expanding metal stents (SEMS) placement is discussed separately. (See "Large bowel obstruction".)
Overall success rates — The greatest experience with stenting has been for treatment of colonic obstruction from left-sided lesions. A systematic review focusing on 88 studies (mainly case series, small comparative trials, and retrospective studies) that included 1785 patients and employed SEMS found the following [26]:
●Technical success was achieved in a median of 96 percent of patients (range 66 to 100 percent) and clinical success was achieved in 92 percent (range 46 to 100 percent).
●There was little difference in technical or clinical success rates based upon indication (palliation versus bridge to surgery) or based upon the etiology of the primary obstruction (eg, primary/recurrent colorectal, urogenital, or pancreatic cancer).
●The median duration of patency was 106 days (range 68 to 288 days), though it was only reported in 14 of the studies.
●The median rate of re-intervention (eg, need for unplanned surgery, placement of a second or subsequent stent, or other interventions to maintain stent patency) was 20 percent (range 0 to 100 percent).
●The median stent migration rate was 11 percent (range 0 to 50 percent).
●The median perforation rate was 4.5 percent (range 0 to 83 percent).
●The median rate of re-obstruction was 12 percent (range 1 to 92 percent).
●Other adverse events (such as rectal bleeding, anal/abdominal pain, and tenesmus) were rare and generally mild.
Higher clinical success rates of SEMS in some of the individual trials may be related to more experienced endoscopists or an academic medical center setting [27,28]. As an example, in a trial comparing colonic stenting versus emergency surgery that enrolled patients from 25 centers (21 of these centers were non-university settings), the technical success rate for stent placement was 70 percent, which was lower than that seen in other series (at least 90 percent) [28].
Stenting for palliation — The efficacy of long-term SEMS placement for palliation in patients who are not operative candidates or who have surgically incurable advanced disease is discussed separately. (See "Large bowel obstruction", section on 'Malignant obstruction'.)
Stenting as a bridge to surgery — The efficacy of preoperative SEMS placement that prevents emergency surgery and allows for colonic decompression, bowel preparation and staging is discussed separately. (See "Large bowel obstruction", section on 'Malignant obstruction'.)
ADVERSE EVENTS — A systematic review of showed that self-expanding metal stents (SEMS) placement was associated with an overall complication rate near 25 percent [29]. The most common adverse events following stent placement in a total of 1198 patients were stent migration (12 percent), recurrent obstruction (7 percent), and perforation (4 percent). Less common adverse events include abdominal pain and bleeding.
Perforation — The most serious complication following SEMS placement is perforation. Perforation can be immediate or delayed, and is more likely in the distal colon where sharp angulation and redundancy make stent deployment challenging. Furthermore, the anatomy of the left colon predisposes the colonic folds to drape over the two ends of the stent, which can cause excessive tension at the points of contact, and subsequent pressure necrosis [30].
In a systematic review of SEMS for malignant colonic obstruction, the median perforation rate was 4.5 percent with a range from 0 to 83 percent [26]. In subsequent reports, perforation rates ranged from 4 to 5 percent [31,32].
Additional concerns about perforation in relation to peritoneal seeding and worse oncologic outcomes have been raised [33]. Both chemotherapy and radiotherapy may increase the risk of perforation following SEMS placement, although the majority of perforations occur in patients without these potential risk factors [34]. (See 'Stenting in the setting of adjunctive therapy' above.)
Stent migration — Two systematic reviews found that rate of colorectal stent migration was approximately 10 percent [26,35]. Stent migration is usually detected within one week of insertion, but can occur later. The main settings where migration occurs are [24]:
●Stent is too narrow or small
●Stent is too short
●Colonic stricture is nonobstructive
●Tumor shrinks after radiotherapy or chemotherapy
Additional factors that predispose to stent migration include extrinsic lesion, stricture dilation, or use of covered stents [36].
Stent occlusion — Stent occlusion may be due to tumor ingrowth through the stent interstices or overgrowth at either end of the stent. This may require placement of an additional stent within the original stent. Alternatives include endoscopic treatment with laser ablation (uncommonly used and not readily available in most endoscopy units), or argon plasma coagulation [36]. Recurrent colonic obstruction due to stent occlusion has a reported incidence of up to 15 percent [37].
Bleeding — Immediate postprocedure bleeding is usually minor and probably due to tumor friability, superficial tearing of stented tissue, or mucosal irritation from stent flanges. Minor rectal bleeding generally requires no treatment. Delayed bleeding may be due to ulcerations or erosions in the colonic mucosa [10].
Pain — Transient and mild abdominal pain is common and may be felt up to five days after stenting. Mild abdominal pain generally requires no specific treatment other than the judicious use of analgesics. We prescribe non-narcotic analgesics, as needed. However, stent expansion occurs over 48 to 72 hours, which can be painful, and may require narcotic analgesics.
Although SEMS placement most often treats obstruction due to left-sided lesions that are at least 5 cm proximal to the anal verge, successful stent placement within 5 cm of the anal verge has been reported [38]. For these low-lying rectal lesions, care must be taken to avoid stent-induced irritation of the nerve endings near the squamocolumnar junction, which can lead to severe tenesmus [39].
FAILURE TO ACHIEVE COLONIC DECOMPRESSION — In some patients, stenting does not result in colonic decompression despite successful stent deployment. There are several potential reasons for treatment failure [6]:
●Additional sites of intestinal obstruction (eg, from synchronous lesions or extrinsic compression from peritoneal carcinomatosis)
●Incomplete stenting of the entire length of the stricture
●Early stent migration
●Underlying motility disorder
●Fecal impaction within a newly inserted stent
●Poor stent positioning
●Incomplete stent expansion
A retrograde radiographic contrast study (eg, a water soluble enema) can assess the anatomy, length of stricture, degree, and various sites of obstruction prior to stent placement and potentially reduce the stent failure rate [25]. (See 'Preprocedure testing' above.)
SOCIETY GUIDELINE LINKS — Links to society and government-sponsored guidelines from selected countries and regions around the world are provided separately. (See "Society guideline links: Colorectal cancer".)
SUMMARY AND RECOMMENDATIONS
●The indications for stent placement in patients with malignant colonic obstruction include (see 'Indications' above):
•Palliation of surgically incurable colorectal cancer.
•Stenting as a bridge to surgery to avoid an emergent, two-step procedure and to allow for optimization of medical status and for preoperative staging including colonoscopy.
•Management of some patients with extracolonic pelvic tumors (eg, ovarian cancer).
●High perforation rates have been reported in patients receiving bevacizumab as a component of chemotherapy. We agree with the guidelines that suggest that colonic stenting should be avoided in patients who are or will be receiving anti-angiogenic agents (eg, bevacizumab), especially if the obstruction is subtotal. (See 'Stenting in the setting of adjunctive therapy' above.)
●Covered stents that are available outside the United States have been used mainly in the setting of malignant colo-vesical, colo-enteric, and colo-vaginal fistulas. While a theoretical advantage of covered SEMS is the decreased risk of tumor ingrowth, they also have a greater tendency to migrate compared with uncovered SEMS. (See 'Covered versus uncovered stents' above.)
●Radiographic imaging may be helpful prior to colonic stent placement if more information is needed regarding relevant anatomy, stricture length, and degree of obstruction. (See 'Preprocedure testing' above.).
●Our approach to bowel preparation prior to endoscopic stent placement depends on the location and degree of obstruction. For patients with partial obstruction in the distal colon, two cleansing tap water enemas are generally sufficient. For patients with partial obstruction from a proximal lesion, an oral bowel prep can be attempted and discontinued if symptoms such as abdominal pain, abdominal distension, nausea, or emesis develop. (See 'Bowel preparation' above.)
●Colorectal self-expanding metal stents are usually placed under endoscopic guidance, preferably with the aid of fluoroscopy. During colonoscopy, judicious insufflation using carbon dioxide should be used to minimize the risk of perforation due to a closed-loop phenomenon between the obstructing lesion and the ileocecal valve. (See 'Procedure' above.).
●The most common adverse events following stent placement are stent migration, recurrent obstruction, and perforation. Less common adverse events include abdominal pain and bleeding. (See 'Adverse events' above.)
●In some patients, stenting does not result in colonic decompression despite successful stent deployment. Reasons for treatment failure may include additional sites of intestinal obstruction (eg, synchronous lesions), early stent migration, or fecal impaction within the stent. (See 'Failure to achieve colonic decompression' above.)
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