Several colonic SEMS of varying lengths and diameters are commercially available for the management of ACO. Stents also differ by coating (uncovered vs. covered) and mechanism of delivery (through the scope (TTS) vs. non-TTS). Uncovered stents have a small risk of migration, but are susceptible to occlusion by tumor ingrowth and/or tissue hyperplasia. Conversely, covered stents help prevent tumor ingrowth but have a higher incidence of stent migration [31, 32]. Currently, only uncovered stents are available in the United States.

The colonic TTS WallFlex stent (Boston Scientific Inc., Natick, MA), the Ultraflex Precision stent (Boston Scientific Inc., Natick, MA), the colonic Z-Stent (Cook Endoscopy, Winston-Salem, NC), and the colonic Evolution stent (Cook Endoscopy, Winston-Salem, NC) are the most commonly used stents in North America [33]. Several other colonic SEMS are available worldwide, many of which are not available on the US market for clinical use.

In most patients, prior cross-sectional imaging study (e.g., CT) is available before endoscopy. If not, it is generally recommended to obtain such a study to assess the etiology, location, and severity of obstruction, as well as determining whether or not perforation has occurred. Most patients with malignant colonic obstruction have left-sided disease, although right-sided obstruction can be treated via stent placement with similar efficacy and safety [34, 35]. There are few absolute contraindications to colonic stent placement, although patients with perforation, hemodynamic instability, and inability to undergo endoscopy are generally treated surgically.

In general, passage of the endoscope through the site of obstruction is not feasible, but this is not required for successful stent placement (Fig. 17.3). If the endoscope cannot pass through the stricture, a guidewire (passed through a biliary occlusion balloon catheter) is advanced across the stricture under combined endoscopic and fluoroscopic guidance to allow access to the large bowel proximal to the obstruction (Video 17.2). Balloon dilation of the stricture is discouraged due to the increased risk of tumor perforation [36]. Once guidewire access across the obstruction is obtained, the catheter is advanced over the wire and used to inject contrast. Injection of contrast allows confirmation of access to the proximal colon, evaluation for any extravasation that would suggest perforation, and assessment of the configuration, length, and severity of the stricture. Fluoroscopic markers can be placed at the proximal and distal ends of the obstruction as an aid to deployment, although in practice these are rarely required. After contrast injection has been performed and guidewire positioning is adequate, a stent of proper dimensions is selected. The stent should generally exceed the length of the obstruction by 2–3 cm on either side of the tumor, and a long stenosis can be treated via multiple stents placed in an overlapping (stent-within-stent) manner. If a TTS stent is selected, the catheter is removed over the wire and exchanged for the stent through the therapeutic working channel of the endoscope. If a non-TTS stent is selected, the catheter and endoscope are removed, leaving the guidewire in place for stent insertion. TTS stents are deployed under combined endoscopic and fluoroscopic guidance (Fig. 17.3). Non-TTS stents may be deployed under fluoroscopic guidance alone or an endoscope can be advanced next to the stent’s delivery catheter to provide endoscopic guidance as well. After deployment, the patient should be evaluated for AEs and to assess adequacy of colonic decompression and satisfactory stent positioning. Most patients experience prompt relief with passage of gas and stool material through the stent.

Since Dohmoto et al. first described the use of colonic metallic stents in 1991, SEMS have been used frequently as palliative therapy in patients who are nonsurgical candidates with advanced colon cancer [37, 38]. Colonic stent placement allows for rapid decompression of the bowel, as well as time for medical stabilization and complete oncologic staging [23]. SEMS have been shown to significantly reduce medical complications, need for stoma formation, length of hospital stay, and mortality [39, 40].

SEMS placement has a high success rate in relieving obstructive symptoms in patients receiving palliative therapy. In one retrospective study, stent placement was technically successful in 94 % of the patients [41]. The duration of stent patency ranged from 2 to 64 weeks, with a mean of 17.3 weeks. The overall clinical effectiveness of SEMS for relief of obstruction in patients on palliative therapy was 82 % [41].

In a retrospective study of 144 patients, the long-term outcome of palliative stent placement vs. surgery was examined [42]. There was no statistical difference in the early success rates between the stent and surgery groups (95.8 % vs. 100 %, p = 0.12). In the first 30 days after stent placement, SEMS patients had less complications than surgical patients (15.5 % vs. 32.9 %, p = 0.015). The duration of initial stent patency was shorter than the luminal patency in the surgical group (average 137 days vs. 268 days, p < 0.001). However, the duration of overall luminal patency in the SEMS group was similar to the surgical group when a second stent was placed (average 229 days vs. 268 days, p = 0.239). The SEMS group was found to have a higher rate of AEs than the surgical group at 30 days after stent placement (33.8 % vs. 17.8 %, p = 0.028). However, the rates of major AEs did not significantly differ between the 2 groups (18.3 % vs. 8.2 %, p = 0.074). American Society of Anesthesiologists Physical Status (ASA PS) classification, stent diameter, and palliative chemotherapy were independent risk factors for the development of late events. Overall long-term efficacy and complications of SEMS were comparable to surgery [42].

ACO patients often present with a number of medical comorbidities, such as metabolic disturbances and dehydration, rendering them suboptimal surgical candidates. Accordingly, emergent surgery for ACO is associated with a mortality rate as high as 30 % [28]. One-stage surgical resection with primary anastomosis is sometimes performed in ACO patients. However, due to concern for anastomotic dehiscence, surgeons often perform a two-stage Hartmann’s procedure, which involves surgical decompression by formation of a diverting colostomy plus tumor resection with creation of a distal stump [27]. These patients often have to wait at least 8 weeks before reanastomosis can be safely attempted [27, 43, 44].

Colonic stent placement as a bridge to surgery allows for decompression, staging, bowel preparation, and optimization of the patient’s medical status prior to surgery [27, 41, 45]. The colonic malignancy can then be surgically resected electively, decreasing the risk of morbidity and mortality [27, 46]. Additionally, bowel preparation and decompression increase the likelihood of primary anastomosis, minimizing the need for colostomy and stoma formation [27].

In the largest review to date, 88 studies were examined assessing the safety and efficacy of SEMS placement vs. surgical intervention in malignant colonic obstruction [47]. The overall technical and clinical success rates for SEMS placement were 96 % and 92 %, respectively. There were no differences in the technical and clinical success rates between the stent and surgery groups. The average time from colonic stent placement to subsequent elective surgery in the bridge to surgery group was 7 days (range 2–12 days). Primary colonic anastomosis rates in the bridge to surgery group were at least twice those of the emergency surgery group. Moreover, the length of hospital stay was greater in those who underwent emergency surgery when compared to those who underwent stent placement. The 3- and 5-year prognosis (overall survival) did not differ between the two groups [47]. Colonic stent placement was, thus, deemed to be safe and effective for the relief of acute malignant colonic obstruction.

Stent placement is not limited to patients who have primary colorectal cancer. Patients may also present with colonic obstruction that arises from invasion or extrinsic compression of the bowel due to an extracolonic malignancy (ECM) [12]. ECM that causes colonic obstruction includes metastatic gynecologic, bladder, pancreatic, gastric, and small bowel malignancies [48, 49]. Several retrospective studies have showed variable technical success (20–87 %) in this setting [48–50]. In addition, higher AE rates (33–65 %) from SEMS placement for management of obstruction due to ECM have been reported, most notably increased migration [48–50]. Still, colonic SEMS are widely employed in this setting since many of these patients are poor surgical candidates and/or would undergo ostomy construction.

The data on AEs related to colonic SEMS are conflicting [51]. When all major and minor AEs are taken into account, SEMS placement carries an AE rate up to 25 %, although the rate is usually far lower in tertiary referral centers [51, 52]. Several factors have been linked to a higher incidence of AEs following SEMS placement, including the type of stent, etiology of stricture, operator experience, and whether the patient has received chemotherapy or radiation therapy [51, 53].

Colonic perforation is the most concerning AE following SEMS placement. In a review encompassing 82 studies, the median colonic stent perforation rate was 4.9 %, with an associated mortality rate of 16 % [54]. Perforation can be immediate as a result of the procedure itself or delayed due pressure necrosis or trauma related to stent pressure in the tumor area or adjacent uninvolved bowel wall [51]. Patients receiving chemotherapy have a higher risk of perforation, often in a delayed manner [54]. In particular, the chemotherapy agent bevacizumab administered to patients with colonic stents significantly increases the risk of perforation. Bevacizumab is not absolutely contraindicated, but recognition of its potential to increase the perforation risk is warranted [53, 55]. Other factors shown to increase the risk of perforation include anatomical factors, corticosteroids, and radiotherapy [53, 54]. Stent location may play a factor in the AE rate. In one study, stents placed in the left colon had a higher rate of AEs than those placed in the right colon (27.2 % vs. 12.5 %, p = 0.06) [53].

Another AE of colonic SEMS placement is stent migration. The median rate of stent migration after colonic SEMS placement is 11 % (range 0–50 %) [47]. Factors that predispose to stent migration include extrinsic lesions, stricture dilation, benign strictures, small stent caliber, post-stent radiotherapy, and the use of covered stents [56].

Tumor overgrowth and/or ingrowth can be seen in the long term following colonic stent placement and result in re-obstruction. This is often treated via placement of another stent inside the first stent (Fig. 17.4). Stent fracture, tenesmus, incontinence, fecal impaction, infection, post-procedure bleeding, and abdominal and rectal pain can also occur [51, 57].