The surgical management of malignant colorectal obstruction is still controversial and has higher associated mortality and complication rates compared with elective surgery. Placement of self-expanding metallic stents (SEMS) has been proposed as an alternative therapeutic approach for colonic decompression of patients with acute malignant obstruction. SEMS placement may be used both as a bridge to surgery in patients who are good candidates for curative resection and for palliation of those patients presenting with advanced stage disease or with severe comorbid medical illnesses.
Malignant large-bowel obstruction can present as a life-threatening medical and surgical condition. The role of endoscopic management of this condition has significantly changed in the last 15 years. In the early 1990s luminal recanalization by laser debulking was the only available endoscopic option with high success rates in the treatment of primary malignant colonic obstruction. In the largest retrospective study of 272 patients treated with a neodymium-yttrium aluminum garnet laser for obstructing rectosigmoid tumors, successful relief of the obstruction was achieved in 85% of patients. Unfortunately, this technique was challenging to apply in patients with acute clinical obstruction, and required several sessions to successfully relieve the obstruction, with large mass lesions being less likely to respond to treatment.
Lelcuk and colleagues first described colon decompression by transanal insertion of a nasogastric tube in 1986. In 1991, Dohmoto and colleagues pioneered the placement of the first expandable metal stent for palliation of malignant rectal obstruction. Subsequently Spinelli and colleagues reported palliation of left-sided colonic strictures in a series of patients treated by placement of a modified Gianturco-Rosch stent. Several years later, Tejero and colleagues were the first to report 2 cases of colonic stent placement preoperatively to allow elective surgery. Since those preliminary experiences, successful management of malignant large-bowel obstruction using self-expanding metallic stents (SEMS) has been increasingly reported by several groups of investigators. With the introduction of dedicated enteral stents, this technique has gained more popularity and has been progressively incorporated in clinical practice, thus becoming the most effective alternative to surgery in management of patients with malignant large-bowel obstruction.
Surgery for malignant large-bowel obstruction
Malignant obstruction is the most common cause of emergency colorectal surgery. Among patients with primary colorectal cancer, 15% to 20% present with obstructive symptoms.
Most patients presenting with obstructive colorectal cancer have advanced stage disease, are often elderly, and are overall in poor medical condition. All of these factors adversely affect the operative risk, prognosis, and mortality. In addition, emergent surgery in a patient with an unprepared colon leads to significant morbidity and mortality. To date, there is no consensus regarding the optimal surgical approach for the management of patients seen on an emergency basis with obstruction from colorectal cancer.
In the past, the standard treatment of malignant left-sided colonic obstruction was a 3-stage approach that involved creation of a colostomy to relieve the obstruction, followed by a second surgery to resect the tumor, and then a third one for colostomy closure. Unfortunately, this approach resulted in a prolonged hospital stay and worse long-term prognosis and thus has been almost completely abandoned. During the 1970s, a 2-stage approach with primary resection of tumor, closure of the rectal stump, and proximal-end colostomy (Hartmann procedure) became increasingly popular. Still, mortality and morbidity figures for emergency surgical decompression remained high, up to 10% and 60%, respectively. Furthermore, reversal of the colostomy was not possible in 40%–60% of patients because of advanced disease or the presence of significant comorbid conditions. It is well known that a stoma itself can have a profound adverse effect on the quality of life of these patients. Therefore, it is not surprising that, in recent years, 1-stage surgical procedures, with and without intraoperative colonic lavage have been advocated in selected patients as an alternative to a Hartmann procedure. Although 1-stage resection and anastomosis is considered to be a better option than primary resection with end colostomy in left-sided colonic obstruction, this is not true for all patients. Several important predictors of outcome in patients with large-bowel obstruction caused by colorectal cancer have been identified and can be used to decide the best surgical approach. These include age, American Society of Anesthesiologists (ASA) score, operative urgency, and Dukes stage. Based on these factors it would be more appropriate to choose a simpler and safer procedure such as the Hartmann operation or even a diverting colostomy for patients deemed to be at high risk. This approach was reflected in a 2001 survey of American gastrointestinal surgeons. Sixty-seven percent would perform a Hartmann operation and 26% a simple colostomy in high-risk patients. Moreover, even in good operative candidates, only 53% of gastrointestinal surgeons would perform a resection with primary anastomosis. The surgical subspecialty and experience seems to be a primary factor in the choice of operation and its final outcome. It has been shown that a primary anastomosis is more likely to be performed by colorectal consultants than general surgeons, and consultants generally than unsupervised trainees.
In a study by The Association of Coloproctology of Great Britain and Ireland (ACPGBI) the mortality after surgery was similar between ACPGBI and non-ACPGBI members, although the data submitted were voluntary. The Large Bowel Cancer Project showed that registrars had a higher mortality rate than consultants after primary resection for obstruction in the late 1970s, and this did not changed 20 years later. Other studies have clearly shown that surgery by unsupervised trainees has significantly greater morbidity, mortality, and anastomotic dehiscence rates.
Given these considerations, the use of colorectal stents to manage patients with acute bowel obstruction has became popular and gained acceptance even by the surgical community who consider the endoscopic approach to be a safe and viable approach in an attempt toward a safer and more effective surgical resection of obstructing neoplasia.
Indications for colorectal stenting
Acute large-bowel obstruction caused by colorectal cancer is a common major surgical emergency, usually afflicting the left colon. If untreated, bowel obstruction causes rapid distension of enteral loops with a progression from abdominal pain, nausea, and vomiting to ischemia, bowel rupture, sepsis, and eventual death. In this setting, the use of SEMS has been proposed to provide a persisting opening of the neoplastic stricture and relieve acute obstruction. Indications for colorectal stent placement should be defined after a thorough evaluation of baseline clinical and radiologic data, with a multidisciplinary team of radiologists, surgeons, and endoscopists. Considerations for stent placement include the patient’s laboratory examination, medical history, and imaging studies in conjunction with the individual scenario. Images from a thin-section computed tomography (CT) scan with multiplanar reformatted reconstructions ( Fig. 1 ) can allow accurate delineation of relevant anatomy and morphology of the obstruction, as well as detection of any extraluminal spread or metastasis of the disease.
Once the evaluation is completed, the 2 main indications for colonic stenting in malignant colorectal obstruction are: (1) preoperative colonic decompression before colonic resection, the so-called bridge to surgery and (2) palliation of obstructing tumors not suitable for curative surgical resection.
SEMS placement allows colonic decompression with relief of acute obstruction, stabilization of the acute illness, preoperative bowel preparation, and preoperative colonoscopy to assess for synchronous cancers. If definitive surgery is indicated, patients may then undergo a 1-stage surgical procedure, even with a laparoscopic approach, with a primary anastomosis in a more elective setting and a better-prepared patient.
However, in the presence of metastatic disease or in patients with prohibitive operative risk, endoscopic decompression with stent placement may become the definitive palliative procedure.
Absolute contraindications to colorectal stenting are: (1) perforation documented with free intraperitoneal gas, (2) very distal rectal lesions with a healthy margin of tissue less than 3 to 4 cm from the anal sphincter, and (3) peritoneal carcinomatosis. Uncorrectable coagulopathy is a relative contraindication for SEMS placement, and in case of prolonged bleeding times, stenting can be performed after administration of fresh frozen plasma and platelets, as necessary.
Colonic obstruction may also arise from advanced extracolonic malignancy, including metastatic gynecologic, pancreatic, bladder, prostatic or small-bowel tumors. In these cases, extrinsic compression or invasion into the colon may lead to partial or complete obstruction of the lumen. In contrast to primary colonic cancer, these patients often have complex stricturing of the gut, potentially at more than 1 location, related to the underlying malignancy. They may also have underlying adhesions from previous debulking surgery and/or chemoradiotherapy. The combination of these multiple factors, including radiation therapy and peritoneal carcinomatosis, which can result in bowel immobilization, may contribute to decreased success and increased complication rate of colon stent placement in patients with extracolonic malignancies. Therefore it seems to be reasonable that endoscopic placement of a colon stent in this setting should only be undertaken in a limited subgroup of patients in whom either decompressive surgery is not feasible or alternative therapies have already failed. Patients and their family members should be made aware of the lower success rate and the potential for serious complications before attempting stent placement for a bowel obstruction caused by extracolonic malignancies.
Indications for colorectal stenting
Acute large-bowel obstruction caused by colorectal cancer is a common major surgical emergency, usually afflicting the left colon. If untreated, bowel obstruction causes rapid distension of enteral loops with a progression from abdominal pain, nausea, and vomiting to ischemia, bowel rupture, sepsis, and eventual death. In this setting, the use of SEMS has been proposed to provide a persisting opening of the neoplastic stricture and relieve acute obstruction. Indications for colorectal stent placement should be defined after a thorough evaluation of baseline clinical and radiologic data, with a multidisciplinary team of radiologists, surgeons, and endoscopists. Considerations for stent placement include the patient’s laboratory examination, medical history, and imaging studies in conjunction with the individual scenario. Images from a thin-section computed tomography (CT) scan with multiplanar reformatted reconstructions ( Fig. 1 ) can allow accurate delineation of relevant anatomy and morphology of the obstruction, as well as detection of any extraluminal spread or metastasis of the disease.
Once the evaluation is completed, the 2 main indications for colonic stenting in malignant colorectal obstruction are: (1) preoperative colonic decompression before colonic resection, the so-called bridge to surgery and (2) palliation of obstructing tumors not suitable for curative surgical resection.
SEMS placement allows colonic decompression with relief of acute obstruction, stabilization of the acute illness, preoperative bowel preparation, and preoperative colonoscopy to assess for synchronous cancers. If definitive surgery is indicated, patients may then undergo a 1-stage surgical procedure, even with a laparoscopic approach, with a primary anastomosis in a more elective setting and a better-prepared patient.
However, in the presence of metastatic disease or in patients with prohibitive operative risk, endoscopic decompression with stent placement may become the definitive palliative procedure.
Absolute contraindications to colorectal stenting are: (1) perforation documented with free intraperitoneal gas, (2) very distal rectal lesions with a healthy margin of tissue less than 3 to 4 cm from the anal sphincter, and (3) peritoneal carcinomatosis. Uncorrectable coagulopathy is a relative contraindication for SEMS placement, and in case of prolonged bleeding times, stenting can be performed after administration of fresh frozen plasma and platelets, as necessary.
Colonic obstruction may also arise from advanced extracolonic malignancy, including metastatic gynecologic, pancreatic, bladder, prostatic or small-bowel tumors. In these cases, extrinsic compression or invasion into the colon may lead to partial or complete obstruction of the lumen. In contrast to primary colonic cancer, these patients often have complex stricturing of the gut, potentially at more than 1 location, related to the underlying malignancy. They may also have underlying adhesions from previous debulking surgery and/or chemoradiotherapy. The combination of these multiple factors, including radiation therapy and peritoneal carcinomatosis, which can result in bowel immobilization, may contribute to decreased success and increased complication rate of colon stent placement in patients with extracolonic malignancies. Therefore it seems to be reasonable that endoscopic placement of a colon stent in this setting should only be undertaken in a limited subgroup of patients in whom either decompressive surgery is not feasible or alternative therapies have already failed. Patients and their family members should be made aware of the lower success rate and the potential for serious complications before attempting stent placement for a bowel obstruction caused by extracolonic malignancies.
Colorectal stents
The early experience of colorectal stent placement involved use of stents designed for other locations, such as esophageal stents ( Fig. 2 ). In 1998 a prototype nitinol stent specifically designed for colonic lesions was developed and tested in a prospective trial by the Leuven group. In the following years, many stents have been designed specifically for use in the lower gastrointestinal tract and are available in a variety of lengths and diameters, so that the appropriate stent can be selected based on factors such as the length of the obstructed section of bowel and anatomic location of the obstruction. Various SEMS are composed of metals such as stainless steel, Elgiloy, or nitinol and may be uncovered or covered with a polyurethane, polyethylene, or silicone coating to resist tumor ingrowth and tissue hyperplasia. Stainless steel and Elgiloy stents have been almost completely abandoned and replaced by nitinol stents, which are nonferromagnetic and are magnetic resonance imaging compatible. Nonetheless, they may produce imaging artifacts such as mild local field inhomogeneities on magnetic resonance imaging and beam-hardening on CT depending on stent shape and alloy composition.
A recent study has shown that CT colonography may be used safely for preoperative examination of the proximal colon after metallic stent placement in patients with acute colon obstruction caused by cancer. According to the size of the stent deployment system, 2 different classes of stents can be distinguished: the so-called TTS (through the scope), which is mounted on a small size catheter that can pass through an endoscope with a working channel of at least 3.7 mm ( Fig. 3 ); and the so-called OTW or (over the wire), which is mounted on a larger delivery system and cannot pass through the working channel of the endoscope ( Fig. 4 ). With the development of very flexible nitinol SEMS ( Fig. 5 ) mounted on a small diameter delivery system that can pass through the working channel of an adult colonoscope, therapeutic gastroscope, or duodenoscope, almost all intestinal obstructions that are within the reach of an endoscope are amenable to endoscopic decompression, including those in the ascending colon. Theoretically, the larger diameter stents are better suited to accommodate solid stool in the left colon and according to a recent study a larger diameter stent is not associated with an increased risk of complications even in patients undergoing chemotherapy. US Food and Drug Administration (FDA) approved and CE marked (Conformité Européene, available for European market) colorectal stents are listed in Table 1 .
| Stent Colonic | Manufacturer | Expanded Length (mm) | Diameter (mm) | TTS/OTW | Introduction System Fr Size | Working Length (cm) |
|---|---|---|---|---|---|---|
| Evolution colonic stent | Cook Medical | 60, 80, 100 | 30, 25 | TTS | 10 | 230 |
| Ultraflex Precision colonic stent a | Boston Scientific/Microvasive, Natick, MA, USA | 57, 87, 117 | 30, 25 | OTW | 16 | 105 |
| Wallstent a colonic and duodenal endoprosthesis | Boston Scientific/Microvasive, Natick, MA, USA | 60, 90 | 18, 20, 22 | TTS | 10 | 135 |
| WallFlex a colonic stent | Boston Scientific/Microvasive, Natick, MA, USA | 60, 90, 120 | 30, 25 27, 22 | TTS | 10 | 135 230 |
| Colonic Z-Stent a | Cook Medical, Winston-Salem, NC, USA | 40, 60, 80, 100, 120 | 35, 25 | OTW | 31 | 40 |
| Silky colorectal stent | Stentech, Seoul, South Korea | Covered/uncovered 50, 60, 70; 80, 90, 100, 120, 140, 160 | 30 | TTS | 10 | 70 80 |
| Niti-S colorectal stent | Taewoong Medical Co, Ltd, Seoul, South Korea | Uncovered 60, 80, 100 | 28, 20 30, 22 30, 24 28, 20 | OTW | 16 18 | 70 150 |
| Niti-S colorectal stent | Taewoong Medical Co, Ltd, Seoul, South Korea | Covered 60, 80, 100 | 30, 22 30, 24 | OTW | 20 22 | 70 150 |
| Bonastent colorectal stent | Standard Sci.Tech Inc | Uncovered 60, 80, 100 | 22, 24, 26 | TTS / OTW | 10 12 | 140 230 |
| Bonastent colorectal stent | Standard Sci.Tech Inc | Covered 60, 80, 100 30/50/80 | 22, 24, 26 | TTS / OTW | 10 12 | 140 230 |
| Hanaro colorectal stent | M.I TECH Co Ltd | 40, 70, 100 | 22 | TTS | 10.5 | 210 |
| ECO stent | Leufen Medizintechnik OHG | Uncovered 80, 100 | 30, 36 | OTW | 24 | 70 110 |
| SX-ELLA stent colorectal | ELLA-CS, Prague, Czech Republic | 82, 90, 113, 135 75, 88, 112, 123, 136 | 20, 25, 30 | OTW | 13 | 95 |
| Micro-Tech colon and rectum stent | Micro-tech Europe, Dusseldorf, Germany | Uncovered 80, 100, 120 Covered 80, 100, 120 50, 70, 90 | 30, 36 25, 30 | TTS | 10, 24 | 110, 230 |
Available studies comparing the performance of different stents suggest that there is no clear-cut advantage in the use of covered SEMS compared with uncovered SEMS in patients with malignant colonic obstruction either in the preoperative or palliative setting. An uncovered stent provides adequate and effective decompression when placed as a bridge to surgery and when resection is performed within a short period of time after placement. When used for definitive palliation, covered stents might have the potential advantage of preventing tumor ingrowth and reobstruction thus reducing the need for further intervention. However, comparative studies and retrospective analysis of published data seem to indicate that this potential advantage is offset by the tendency of covered stents to migrate more commonly. In an older study of 20 patients who presented with malignant colonic obstruction, 8 had SEMS placed for palliative decompression. Four patients had covered stents, all of which migrated within 3 to 4 days. The other 4 patients had partially covered stents, and these remained patent and in place until the time of death. In another nonrandomized study, 33 patients underwent successful SEMS placement for definitive palliation of malignant colonic obstruction. Three types of stents were used: fully covered, partially covered, and uncovered. Stent migration occurred in 11 of 33 patients (33%), none of which were uncovered.
In a pooled analysis of colonic SEMS by Sebastian and colleagues that included 54 studies, 170 covered SEMS were placed and 52 (30.5%) were reported to migrate on subsequent follow-up.
More recently, Lee and colleagues reported their experience comparing uncovered and covered SEMS in 80 patients with malignant colonic obstruction. The investigators used SEMS made of a mesh of single-strand wire of a nickel-titanium alloy (Niti-S, Colon TTS; Taewoong Medical Co, Seoul, South Korea). The uncovered stents were cylindrical, but the covered stents had a dumbbell shape with flange ends that were partially covered with a polyurethane membrane. In the covered stent group, there were 9 late complications, including 6 episodes of stent migration, 1 reported tumor overgrowth, and 2 cases of stool impaction. Tumor ingrowth was reported in only 3 patients in the uncovered stent group thus confirming that there is no obvious advantage in using covered stents compared with uncovered stents in the treatment of patients with malignant colonic obstruction either in the preoperative or palliative setting.
The increased risk of migration of covered stents in colorectal strictures could be mainly related to local factors, inherent to the colon’s anatomy, including its wide caliber and motility, which may facilitate stent migration. The lower risk of migration of uncovered stents is because these stents progressively incorporate deeply into the wall of the tumor and surrounding tissues by pressure necrosis, firmly anchoring the stent.
Placement techniques
Since its original description by Dohmoto and colleagues in the early 1990s, the technique of preoperative colonic stenting has remained substantially unchanged in its general principles. Prophylactic antibiotics should be considered in patients with complete obstruction as the introduction of air may induce microperforation and bacteremia. Because patients who have complete obstruction usually have evacuated most feces below the lesion, colonic bowel preparation is unnecessary or even dangerous because it may promote worsening of the obstruction. The use of 1 or 2 generous cleansing enemas is usually suggested to improve endoscopic visibility in the segments below the stricture. If the stricture is located in the rectosigmoid the patient is placed in the supine position which favors radiologic definition of anatomic landmarks. If the stricture is located proximal to the sigmoid, the patient is initially placed in the left lateral position to better negotiate the left colon and afterwards turned to the supine position once the stricture has been reached with the endoscope.
In most cases, colorectal stenting is a well-tolerated procedure with minimal patient pain and discomfort especially if the lesion is located in the distal part of the colon. The use of moderate sedation with a combination of an opiate (eg, fentanyl) and a benzodiazepine (eg, midazolam) is commonly used.
From a technical standpoint, placement of an OTW stent differs in the final steps from placement of a TTS stent.
The OTW stents, because of their catheter length and diameter, are best reserved for those patients whose strictures are located in the rectum or in the distal part of the sigmoid within 20 to 30 cm from the anal verge. The advancement of the OTW stent catheter beyond this limit is challenging because the force to move the stent forward is applied outside the anus, far from the stricture and this normally causes looping of the catheter in the mobile sigmoid instead of a true advancement of the stent across the stricture. The technique of SEMS placement in the rectum and distal sigmoid using an OTW stent is analogous to esophageal stent placement.
First the scope is advanced until the anal (distal) end of the stricture is identified. If an adult or therapeutic endoscope can be easily passed through the lesion, the authors suggest that stent placement is not undertaken because of the high risk of migration. However, no data are available to support this recommendation, which is based on personal experience. Conversely, there are data that strongly discourage dilation of the stricture either before or after stent placement because this significantly increases the risk of colonic perforation. A recent ex vivo experimental study on freshly excised human colon cancer specimens has confirmed that dilation of colorectal cancer strictures is associated with a high risk of perforation. According to the results of this elegant study, histopathologic and morphologic factors that cause a decrease in the elastic compliance of the lumen correlated with perforation risk more than dilation parameters such as balloon pressure. The best predictor for perforation was a combination of severe stricture and pronounced proliferation of peritumoral collagen fibers. Annular growth and fewer residual smooth muscle cells in the muscularis propria exhibiting tumor encroachment were also associated with an increased risk. because these factors are not known at the time of placement. Perforation is quite unpredictable and can occur regardless of the type of dilation performed.
After reaching the stricture, a guidewire is gently advanced under fluoroscopic guidance across the stricture. Air insufflation usually creates a contrast effect that may help to define fluoroscopically the bowel anatomy beyond the stricture and allow tracking of guidewire advancement above the stricture. If this contrast effect is not well defined or if doubts remain about anatomy and/or stricture morphology, a water soluble (meglumine diatrizoate, Gastrografin) contrast medium can be injected through the working channel of the endoscope. In addition, a hydrophilic or hybrid biliary guidewire preloaded through a biliary double or triple lumen occlusion balloon or catheter is used to inject contrast and cannulate under endoscopic and fluoroscopic guidance as is done during endoscopic retrograde cholangiography (ERCP). Once the wire has passed through the stricture, the catheter is advanced over the guidewire as far as possible and the standard guidewire is exchanged for a stiffer one. In cases of high-grade obstructions or sharply angulated strictures or eccentric position of the residual lumen, it may be challenging to introduce the guidewire in the correct orientation and safely advance it through the strictures. In such a case the use of a sphincterotome, which can be rotated and the tip flexed, is extremely useful in negotiating the correct direction to allow advancement of the guidewire. Alternatively, side-viewing endoscopes can also be used to allow access to sharply angulated strictures located at the distal sigmoid that cannot be approached with frontal view scope because of their eccentric position.
The length of the stent chosen should be about 4 to 6 cm longer than the estimated length of the stricture to allow an adequate margin of stent on either side of the obstruction.
At this point if an OTW stent is used, the scope is withdrawn leaving the guide wire in place well above the stricture. The endoscope is reinserted alongside the guide wire to monitor (together with fluoroscopy) the advancement of the predeployed stent and to precisely position the distal end during deployment. If a TTS stent is chosen, the stent is advanced through the working channel of the endoscope across the stricture ( Fig. 6 ) and then deployed under fluoroscopic and endoscopic guidance. During TTS stent deployment the physician handling the endoscope should gently but firmly pull back the external catheter of the stent to balance the tendency of the stent to move forward (away from the tip of the endoscope) because of advancement of the internal pushing catheter. Most TTS stents have a point of no return marker on the external portion of the delivery catheter that correlates with a radiologic marker on the constraining sheath at the level of the stent, indicating the point at which the stent cannot be reconstrained in case of improper positioning. Once the stent is deployed fully, the ends of the stent should be inspected carefully by fluoroscopy and contrast injected into the stent to assess complete patency and exclude perforation. Definition of technical success includes correct opening of the stent across the stricture with passage of fecal material and absence of perforation. The definition of clinical success varies, but is most frequently colonic decompression with resolution of obstructive symptoms within 72 hours of stent placement.
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Self-Expandable Metal Stents for Malignant Distal Biliary Strictures
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