Endoscopic stenting of malignant, benign and iatrogenic colorectal disorders: a primer for radiologists.

Self-expanding metal stents safely allow both palliative and bridge-to-surgery treatment of obstructing colorectal carcinomas Stenting of benign colorectal disorders is mostly reserved for selected refractory anastomotic strictures and post-surgical leaks With appropriate reconstructions, CT provides a comprehensive high-resolution visualisation of the stent, the treated colonic disease and surrounding structures CT is the technique of choice to comprehensively investigate patients with clinical suspicion of stent-related complications The commonest stent-related complications include misplacement, haemorrhage, perforation, migration and re-obstruction Self-expanding metal stents safely allow both palliative and bridge-to-surgery treatment of obstructing colorectal carcinomas Stenting of benign colorectal disorders is mostly reserved for selected refractory anastomotic strictures and post-surgical leaks With appropriate reconstructions, CT provides a comprehensive high-resolution visualisation of the stent, the treated colonic disease and surrounding structures CT is the technique of choice to comprehensively investigate patients with clinical suspicion of stent-related complications The commonest stent-related complications include misplacement, haemorrhage, perforation, migration and re-obstruction

Despite advances in modern colorectal surgery, postoperative anastomotic complications (leakage, dehiscence, fistulisation) represent a significant cause of prolonged hospitalisation, morbidity and mortality. The risk of a colonic anastomotic leak (AL) is highest in coloanal and low colorectal anastomoses. Surgical reintervention for complications is associated with additional morbidity and frequent need for faecal diversion: the classic treatment for colorectal or coloanal AL involves removal of the failed anastomosis and creation of a proximal end colostomy (Hartmann’s procedure). Several alternative approaches have been investigated, including endoluminal injection of fibrin sealant, endoscopic clips and transanal closure [ 27 , 28 ]. The use of endoscopic stenting is increasing in the management of colorectal AL, in patients both with and without a stoma and in combination with percutaneous drainage of abscesses. Covered SEMS (Figs. 11 and 12 ) or biodegradable stents (Fig. 13 ) are left in place for 2 months, and the former may be removed once the anastomosis heals. The technical success of stent placement approaches 100%, with a satisfactory clinical success 80–100%. This technique is not an option for very low anastomoses, since the distal end of the stent should be at least 5 cm above the anal verge to limit the risk of migration [ 23 – 26 , 29 ]. Additionally, interesting results have been reported in the management of postoperative rectovaginal fistula after CRC resection [ 30 ]. Fig. 11 Successful stent management of anastomotic leak (AL). After the CT diagnosis of CRC at the distal sigmoid colon (arrowhead in a ), an elderly male underwent surgical resection with primary anastomosis. Early postoperative CT ( b ) showed inhomogeneous collection (thin arrows) containing gas bubbles, located between the anterior aspect of the sacrum and the colorectal anastomosis site, consistent with clinical suspicion of AL. The patient ultimately recovered after having a SEMS (thick arrow in c ) placed through the anastomosis for 3 months Fig. 12 Successful stent management of postoperative AL. Preoperative water enema CT ( a ) showed stricturing CRC of the rectosigmoid junction (arrowhead). Days after anterior rectal resection with an ileostomy, CT ( b ) was requested because of fever and faecaloid material from drainage tube. Gas bubbles (thin arrow) and mild effusion abutting the site of coloanal anastomosis were consistent with the clinical and endoscopic diagnosis of AL, which was treated by placing a covered SEMS through the anastomosis (inset image in c ). A week later, follow-up CT ( c , d ) showed SEMS (thick arrow) in place, minimal residual perianastomotic fluid collection (thin arrows) and the patient ultimately did well. Fig. 13 Use of bioabsorbable stent to manage a chronic anastomotic fistula following anterior rectal resection. After drainage of a perianastomotic abscess (not shown), CT ( a ) showed the persistence of perianastomotic inflammation (thin arrows) with gas bubbles (note the close similarity to Fig. 11 b). Repeated CT ( b – d ) showed decreased perianastomotic inflammation (thin arrows) compared to a and confirmed correct placement of the bioabsorbable stent (thick arrows) which appears as a tubular structure with soft-tissue attenuation, best visible using MIP reconstructions ( b ). Successful stent management of anastomotic leak (AL). After the CT diagnosis of CRC at the distal sigmoid colon (arrowhead in a ), an elderly male underwent surgical resection with primary anastomosis. Early postoperative CT ( b ) showed inhomogeneous collection (thin arrows) containing gas bubbles, located between the anterior aspect of the sacrum and the colorectal anastomosis site, consistent with clinical suspicion of AL. The patient ultimately recovered after having a SEMS (thick arrow in c ) placed through the anastomosis for 3 months Successful stent management of postoperative AL. Preoperative water enema CT ( a ) showed stricturing CRC of the rectosigmoid junction (arrowhead). Days after anterior rectal resection with an ileostomy, CT ( b ) was requested because of fever and faecaloid material from drainage tube. Gas bubbles (thin arrow) and mild effusion abutting the site of coloanal anastomosis were consistent with the clinical and endoscopic diagnosis of AL, which was treated by placing a covered SEMS through the anastomosis (inset image in c ). A week later, follow-up CT ( c , d ) showed SEMS (thick arrow) in place, minimal residual perianastomotic fluid collection (thin arrows) and the patient ultimately did well. Use of bioabsorbable stent to manage a chronic anastomotic fistula following anterior rectal resection. After drainage of a perianastomotic abscess (not shown), CT ( a ) showed the persistence of perianastomotic inflammation (thin arrows) with gas bubbles (note the close similarity to Fig. 11 b). Repeated CT ( b – d ) showed decreased perianastomotic inflammation (thin arrows) compared to a and confirmed correct placement of the bioabsorbable stent (thick arrows) which appears as a tubular structure with soft-tissue attenuation, best visible using MIP reconstructions ( b ).

LBO is not uncommon in emergency departments and is caused by CRC in almost two thirds of cases [ 8 ]. Historically, the first indication for colonic stenting has been minimally invasive management of malignant LBO in non-operative candidates and in patients with non-resectable, fistulising or disseminated disease (Figs. 3 and 4 ). Currently, according to the European Society of Gastrointestinal Endoscopy (ESGE), SEMS placement is the preferred palliative treatment for malignant LBO, with the exception of patients treated with or who will receive antiangiogenic drugs such as bevacizumab, since the presence of the stent determines a threefold increase in the risk (10–20%) of either clinically overt and silent perforations [ 5 ]. Fig. 3 Palliation of unresectable CRC and dedicated CT reconstruction techniques. In an elderly male, sagittal contrast-enhanced CT ( a ) shows a 6-cm-long segment with enhancing, non-stratified increased mural thickness (arrowhead) at the rectosigmoid junction, causing luminal stricture and upstream large bowel obstruction (LBO*) complicated by fistulisation (thin arrow) to the prostate and urinary bladder. After endoscopic stenting, repeated CT ( b , c ) including focused oblique images (note obliquity in c insets) effectively depicted the correct position of the SEMS (thick arrows) at the site of CRC (arrowheads), filled with faecal fluid with partial persistence of upstream colonic dilatation (*). Additional thick-slab ( d ) and maximum-intensity projection (MIP) reconstructions depict the tubular shape and reticular “mesh” structure of the well-expanded SEMS ( e ) Fig. 4 Usual MRI appearance of a SEMS-treated CRC. At diagnosis, sagittal CT image ( a ) shows an endoscopically impassable, ulcerated CRC of the sigmoid colon as segmental mural thickening (arrowhead). After stent placement, sagittal T2- ( b ) and coronal fat-saturated T1-weighted after intravenous gadolinium contrast ( c ) MRI images show well-expanded SEMS (thick arrows) with patent lumen devoid of signal, and mural thickening (arrowheads) with T2-hypersignal ( b ) and positive enhancement ( b ) corresponding to the treated tumour Palliation of unresectable CRC and dedicated CT reconstruction techniques. In an elderly male, sagittal contrast-enhanced CT ( a ) shows a 6-cm-long segment with enhancing, non-stratified increased mural thickness (arrowhead) at the rectosigmoid junction, causing luminal stricture and upstream large bowel obstruction (LBO*) complicated by fistulisation (thin arrow) to the prostate and urinary bladder. After endoscopic stenting, repeated CT ( b , c ) including focused oblique images (note obliquity in c insets) effectively depicted the correct position of the SEMS (thick arrows) at the site of CRC (arrowheads), filled with faecal fluid with partial persistence of upstream colonic dilatation (*). Additional thick-slab ( d ) and maximum-intensity projection (MIP) reconstructions depict the tubular shape and reticular “mesh” structure of the well-expanded SEMS ( e ) Usual MRI appearance of a SEMS-treated CRC. At diagnosis, sagittal CT image ( a ) shows an endoscopically impassable, ulcerated CRC of the sigmoid colon as segmental mural thickening (arrowhead). After stent placement, sagittal T2- ( b ) and coronal fat-saturated T1-weighted after intravenous gadolinium contrast ( c ) MRI images show well-expanded SEMS (thick arrows) with patent lumen devoid of signal, and mural thickening (arrowheads) with T2-hypersignal ( b ) and positive enhancement ( b ) corresponding to the treated tumour In CRC patients with very poor lifetime expectancy, SEMS placement improves the quality of life and generally obviates unnecessary surgery and further morbidity. On the other hand, in patients with advanced stage CRC, SEMS placement can avoid a permanent stoma and result in lower morbidity, shorter hospitalisation, earlier start of chemotherapy and similar survival compared to surgery. In the palliative setting, when the expansion is satisfactory after 48 h, 80% and 72% of SEMS remain patent after 6 and 12 months, respectively [ 9 – 14 ]. Traditionally, immediate surgical resection of obstructing CRC was burdened with high morbidity (40–60%) and substantial postoperative mortality (8–20%). Furthermore, one-stage surgery without a colostomy is technically difficult in the emergency setting, resulting in a high risk of a temporary or permanent stoma. Nowadays, SEMS have emerged as an effective alternative option to manage malignant LBO that facilitates subsequent elective surgery with primary anastomosis. Early colonic decompression by SEMS placement allows time to optimise the patient’s medical conditions, to take biopsies and stage the CRC (Fig. 5 ), to obtain preoperative bowel cleansing and sometimes even to administer neoadjuvant chemotherapy. During elective one-stage surgery (usually performed 8 to 10 days after stent placement), the SEMS is surgically removed en bloc with the colon specimen [ 14 ]. Fig. 5 Comprehensive staging of SEMS-treated CRC using water enema CT. Multiplanar contrast-enhanced images ( a – c ) show sufficiently expanded SEMS (thick arrows) at a stricturing tumour of the descending colon, seen as circumferential enhancing mural thickening (arrowheads). The upstream large bowel is adequately distended by water and does not show additional suspicious changes Comprehensive staging of SEMS-treated CRC using water enema CT. Multiplanar contrast-enhanced images ( a – c ) show sufficiently expanded SEMS (thick arrows) at a stricturing tumour of the descending colon, seen as circumferential enhancing mural thickening (arrowheads). The upstream large bowel is adequately distended by water and does not show additional suspicious changes Indications for this “bridge-to-surgery” approach include patients with potentially curable left-sided CRC with symptoms, clinical and imaging signs of LBO, particularly those with an increased risk of postoperative mortality according to age and American Society of Anesthesiologists (ASA) Physical Status classification system. Exclusion criteria include poor life expectancy, bowel perforation and haemorrhage. Stenting of rectal carcinomas is generally avoided because of the higher risk of complications such as pain, tenesmus, incontinence and stent migration [ 1 , 2 , 5 , 14 ]. Bridge-to-surgery management of obstructing CRC (Figs. 6 , 7 and 8 ) has proven to be highly effective and safe, with limited procedure-related complications. Technical success (corresponding to appropriate insertion of the SEMS across the entire length of the stenosis) is achieved in 90% of CRC-related obstructions. Failure most commonly results from the inability to pass the guidewire across a tortuous or severe stricture. Clinical success, defined as effective resolution of LBO with symptomatic relief, is achieved in over 70% of patients within the first days after SEMS placement. Compared to surgery alone, bridge-to-surgery SEMS result in lower operative time, lower overall complication rates (33.9–37.8% versus 51.2–54.8%) including less wound infections, shorter or equal intensive care unit stay, similar early mortality, lower rates of temporary (28.8–33.9% versus 46–51.4%) and permanent (22.2% versus 35.3%) stoma [ 15 – 17 ]. Fig. 6 “Bridge-to-surgery” stenting of obstructing CRC. Upright ( a ) and supine ( b ) plain abdominal radiographs show marked dilatation of the large bowel (*) with fluid-faecaloid material consistent with mechanical LBO (note air-fluid levels in a ). Coronal CT image ( c ) confirm colonic dilatation (*) above a 4-cm-long, solid mural thickening at the distal descending colon (arrowhead). After biopsy, fluoroscopic images documented the endoscopic positioning of a SEMS (thick arrow in e ) along the guidewire (thick arrow in d ) through the tumour. The patient then underwent left hemicolectomy with primary anastomosis to remove pT3N1G2 carcinoma Fig. 7 Effective relief of LBO during bridge-to-surgery stenting of CRC. Initial supine ( a ) radiograph shows marked gaseous dilatation of the large bowel (*) consistent with LBO. Sagittal post-contrast CT image ( b ) confirm air-fluid colonic dilatation (*) above a short stricturing sigmoid tumour (arrowheads). Forty-eight hours after endoscopic positioning of a SEMS (thick arrow), a plain radiograph ( c ) shows near-complete resolution of LBO. Three weeks later, the patient successfully underwent sigmoid resection with termino-terminal anastomosis Fig. 8 Delayed relief of LBO during bridge-to-surgery stenting of CRC. Initial CT ( a ) shows luminal dilatation (*) above a stricturing tumour of the sigmoid colon (arrowhead, note shouldering). Early radiograph ( b ) shows persistent colonic dilatation despite correct placement of the SEMS (thick arrow) at the site of CRC. The patient experienced slow clinical and radiographic improvement and had neoadjuvant chemotherapy followed by resection of pT3N2 cancer with primary anastomosis. Note suture on early postoperative CT ( c ) performed to exclude anastomotic dehiscence “Bridge-to-surgery” stenting of obstructing CRC. Upright ( a ) and supine ( b ) plain abdominal radiographs show marked dilatation of the large bowel (*) with fluid-faecaloid material consistent with mechanical LBO (note air-fluid levels in a ). Coronal CT image ( c ) confirm colonic dilatation (*) above a 4-cm-long, solid mural thickening at the distal descending colon (arrowhead). After biopsy, fluoroscopic images documented the endoscopic positioning of a SEMS (thick arrow in e ) along the guidewire (thick arrow in d ) through the tumour. The patient then underwent left hemicolectomy with primary anastomosis to remove pT3N1G2 carcinoma Effective relief of LBO during bridge-to-surgery stenting of CRC. Initial supine ( a ) radiograph shows marked gaseous dilatation of the large bowel (*) consistent with LBO. Sagittal post-contrast CT image ( b ) confirm air-fluid colonic dilatation (*) above a short stricturing sigmoid tumour (arrowheads). Forty-eight hours after endoscopic positioning of a SEMS (thick arrow), a plain radiograph ( c ) shows near-complete resolution of LBO. Three weeks later, the patient successfully underwent sigmoid resection with termino-terminal anastomosis Delayed relief of LBO during bridge-to-surgery stenting of CRC. Initial CT ( a ) shows luminal dilatation (*) above a stricturing tumour of the sigmoid colon (arrowhead, note shouldering). Early radiograph ( b ) shows persistent colonic dilatation despite correct placement of the SEMS (thick arrow) at the site of CRC. The patient experienced slow clinical and radiographic improvement and had neoadjuvant chemotherapy followed by resection of pT3N2 cancer with primary anastomosis. Note suture on early postoperative CT ( c ) performed to exclude anastomotic dehiscence The long-term outcome is similar between patients undergoing emergency surgery and those who receive preoperative SEMS, regarding recurrence rates, overall and disease-free survival [ 18 , 19 ].

Stents for use in the large bowel (Fig. 1 ) are available in variable diameter, length and mural structure, in order to adapt to the colonic lesion or injury to be treated. When opened, SEMS appear as hollow cylindrical devices with a reticular “mesh” pattern, made of stainless steel or metal alloy such as nitinol (Fig. 1 a, b). Initially, SEMS are provided tightly compressed along a delivery guidewire (Fig. 1 c) that may pass through the operative channel of the endoscope. Fig. 1 Some common self-expandable metal stents (SEMS) available for use in colorectal disorders. a Two opened uncovered WallFlex TM (Boston Scientific, Massachusetts, USA) stents measuring 25 × 60 mm (left side) and 22 × 90 mm (right side), respectively. b Fully covered Niti-S stent (Taewoong Medical, South Korea) 22 × 100 mm. c Uncovered WallFlex TM stent, closed along its introducer sheath Some common self-expandable metal stents (SEMS) available for use in colorectal disorders. a Two opened uncovered WallFlex TM (Boston Scientific, Massachusetts, USA) stents measuring 25 × 60 mm (left side) and 22 × 90 mm (right side), respectively. b Fully covered Niti-S stent (Taewoong Medical, South Korea) 22 × 100 mm. c Uncovered WallFlex TM stent, closed along its introducer sheath Technically, SEMS are categorised as bare, partially (at the centre) or fully covered, depending on the absence or presence of a non-porous chemical “membrane” that prevents tumour growth through the mesh. In the management of obstructing CRC, no significant differences were found between covered and uncovered SEMS in terms of technical and clinical success, perforation and overall complication rates. Compared to covered ones, uncovered SEMS suffer from significantly higher obstruction rates from tumour ingrowth, but are less prone to migration. Conversely, fully covered SEMS allow prolonged stent patency and have a higher likelihood of retrieval due to the limited local tissue reaction [ 2 , 5 ]. Recently, biodegradable stents made of polydioxanone have been developed, but their use remains controversial [ 6 , 7 ]. Stents are positioned in the colonic lumen during endoscopy, generally under fluoroscopic guidance since the metal mesh is radio-opaque (Fig. 2 ). After the guidewire is passed through the stricture, the SEMS is released using the deployment device at its end and begins expanding. Complete expansion of the SEMS in place usually occurs within 24–48 h and may sometimes require a few days to be completed [ 2 ]. Fig. 2 Endoscopic placement of a SEMS through an obstructing tumour of the sigmoid colon. a Distal endoscopic view of colorectal carcinoma (CRC) impassable with the endoscope. b Under fluoroscopic guidance, the guidewire is passed through the stricture. c The SEMS is advanced along the guidewire. d After deployment and initial expansion of the SEMS, prompt outflow of faecal content is seen Endoscopic placement of a SEMS through an obstructing tumour of the sigmoid colon. a Distal endoscopic view of colorectal carcinoma (CRC) impassable with the endoscope. b Under fluoroscopic guidance, the guidewire is passed through the stricture. c The SEMS is advanced along the guidewire. d After deployment and initial expansion of the SEMS, prompt outflow of faecal content is seen

Colonic stenting is generally considered a low-risk procedure, with a 20% overall morbidity rate, mortality below 1% and occasional need for surgery and stoma. Listed in Table 2 , complications associated with colonic SEMS can be categorised as either early or late and may develop in both palliative and bridge-to-surgery settings. Risk factors for post-procedural complications include small SEMS caliber (≤ 22 mm), complete LBO, proximally located (right colon) CRC, extracolonic lesions, concurrent stricture dilation, history of radiation and chemotherapy [ 10 , 12 , 15 , 35 ]. Table 2 Complications after stent placement in the management of colorectal disorders Early complications Late complications Technical failure Stent migration Stent misplacement/failed relief of obstruction Re-obstruction Haemorrhage (Chemotherapy-related) perforation Stent migration Fistulisation Perforation Complications after stent placement in the management of colorectal disorders Patients with colonic SEMS commonly complain of symptoms such as pelvic or rectal pain. In the majority of cases, CT is the technique of choice to comprehensively investigate patients with clinical suspicion of stent-related complications [ 3 , 4 ]. Shortly after stent placement, the lack of clinical improvement and persistent imaging evidence of colonic dilatation and air-fluid levels may result from either malpositioning or incomplete expansion of the SEMS. The imaging diagnosis of misplacement (Fig. 14 ) should rely on the discrepancy between the position of the SEMS and the site and length of the treated tumour as shown in previous cross-sectional studies. Sometimes, the SEMS is positioned too distally and does not cover the entire length of the structure. On the other hand, failed expansion (Fig. 15 ) is easily assessed on both radiographs and CT, when the SEMS remains “hourglass-shaped.” In situations, endoscopic reintervention or emergency surgery is required to manage obstruction [ 3 , 4 ]. Self-limited bleeding occurs in 5% of cases and is generally minor, without the need for specific treatment. The CT hallmark is the identification of hyperattenuating material consistent with fresh blood in the bowel lumen (Fig. 16 ) on precontrast scans [ 3 , 4 ]. Fig. 16 Haemorrhage and impending stent-related perforation. Initial radiograph ( a ) showing marked colonic dilatation (*). After early clinical improvement, the patient experienced haematochezia. MIP CT image ( b ) confirmed correctly placed and expanded SEMS (thick arrows) at the descending colon. CT images showed some hyperattenuating fresh blood (thin arrow in c ) in the bowel lumen and a gas bubble (arrows in d and e ) piercing through the colonic wall at the distal end of the SEMS. Emergency laparotomic surgery (left hemicolectomy with primary anastomosis) was required Haemorrhage and impending stent-related perforation. Initial radiograph ( a ) showing marked colonic dilatation (*). After early clinical improvement, the patient experienced haematochezia. MIP CT image ( b ) confirmed correctly placed and expanded SEMS (thick arrows) at the descending colon. CT images showed some hyperattenuating fresh blood (thin arrow in c ) in the bowel lumen and a gas bubble (arrows in d and e ) piercing through the colonic wall at the distal end of the SEMS. Emergency laparotomic surgery (left hemicolectomy with primary anastomosis) was required Although uncommon, perforation is the most feared SEMS-related complication with non-negligible mortality (approximately 10%). Albeit incidence figures are highly variable among different studies and settings, the reported frequency is below 5% of all patients. Specific risk factors for early perforation following SEMS placement include previous irradiation, balloon dilation prior to stent insertion and excessive manipulation of guidewires, especially in the presence of diverticular disease or colonic wall ischaemia [ 36 ]. On the other hand, late perforations developing 3 to 6 months after stent insertion are generally associated with systemic (mostly bevacizumab) chemotherapy. Surgery should always be considered in patients with SEMS-related perforation [ 5 ]. Often clinically silent, colonic perforation is almost invariably diagnosed by CT. Imaging findings to be reported as consistent with perforation include nondependent pneumoperitoneum, free peritoneal effusion, pericolonic gas bubbles or fluid collections. However, in most cases, the amount of extraintestinal air is very limited (Fig. 16 ) [ 3 , 4 ]. Migration represents the commonest complication (overall incidence 10–11%, up to 50% of patients in some series) and may occur at any time following the SEMS insertion. Migration tends to develop with stents which are too small in diameter and/or too short compared to the stricture, is much more likely with fully covered compared with uncovered SEMS and can be favoured by chemotherapy-induced tumour shrinkage. Other factors that predispose to stent migration include treatment of partial LBO, extracolonic masses and tumours of the distal rectum. It may either remain asymptomatic or lead to further complications such as recurrent obstruction or perforation. Most usually, displaced stents generally migrate distally and are expelled through the anus. In these cases, repeated radiographs fail to detect the presence of the SEMS (Fig. 17 ). Alternatively, stent displacement (Fig. 10 e, f) is judged on the basis of accurate comparison of the SEMS position and orientation compared to previous studies: without a baseline image, the diagnosis may be missed. Symptomatic occurrences may require endoscopic repositioning, removal or replacement [ 2 , 10 , 12 , 35 , 37 ]. Fig. 17 Spontaneous stent migration. In a patient with endoscopically impassable sigmoid CRC (arrowhead in initial water enema CT, a ) with liver metastases (not shown) at diagnosis, multidisciplinary consultation opted to postpone surgical resection after neoadjuvant chemotherapy. A SEMS (thick arrow) was positioned endoscopically under radiologic guidance ( b ) and allowed relief of LBO, clinical improvement and start of chemotherapy. A month later, the patient experienced evacuation of the SEMS with stools and radiographs ( c ) confirmed SEMS loss [adapted from Open Access Ref. [ 38 ] Spontaneous stent migration. In a patient with endoscopically impassable sigmoid CRC (arrowhead in initial water enema CT, a ) with liver metastases (not shown) at diagnosis, multidisciplinary consultation opted to postpone surgical resection after neoadjuvant chemotherapy. A SEMS (thick arrow) was positioned endoscopically under radiologic guidance ( b ) and allowed relief of LBO, clinical improvement and start of chemotherapy. A month later, the patient experienced evacuation of the SEMS with stools and radiographs ( c ) confirmed SEMS loss [adapted from Open Access Ref. [ 38 ] The use of CT is crucial to differentiate between possible causes of recurrent LBO. Mostly observed in the palliative setting, re-obstruction is heralded at imaging by an increased amount of air-fluid bowel dilatation above the SEMS. In descending order of frequency, causes include tumour ingrowth or outgrowth, stent migration (Fig. 10 ), luminal impaction with stools and occasional SEMS fracture or angulation. Ingrowth (i.e. neoplastic tissue crossing through the “mesh” of an uncovered SEMS, Fig. 18 ) is diagnosed when CT or MRI detects the presence of solid enhancing tumour within the stent lumen and may be managed using laser/argon therapy, additional “stent-in-stent” placement or surgery. Conversely, outgrowth (Fig. 9 ) refers to the progression of neoplastic tissue surrounding or at the extremities of the stent. Faecal occlusion can be prevented using a dedicated low-residue diet and osmotic laxatives, appears at CT as SEMS lumen is filled with more or less thick faecal material with intermixed gas bubbles (Fig. 3 b, c) and may require medical or endoscopic desobstruction. Mechanical malfunction requires removal or replacement of the SEMS [ 2 – 4 ]. Fig. 18 Tumour ingrowth causing stent malfunctioning. In the same patient, compared to initial MRI (Fig. 5 ), focused multiplanar reconstructions ( a - c ) of follow-up CT showed enhancing neoplastic tissue (arrowheads) growing within the SEMS (thick arrows), leading to recurrent LBO Tumour ingrowth causing stent malfunctioning. In the same patient, compared to initial MRI (Fig. 5 ), focused multiplanar reconstructions ( a - c ) of follow-up CT showed enhancing neoplastic tissue (arrowheads) growing within the SEMS (thick arrows), leading to recurrent LBO

Nowadays, SEMS represent an established alternative to surgery for palliation of unresectable CRC and are widely used as a bridge-to-surgery to relieve LBO before elective oncologic resection. Additionally, intraluminal stents represent an appealing therapeutic option to manage selected benign colorectal disorders, particularly post-surgical strictures and leaks. At hospitals performing advanced multidisciplinary, radiologists should be aware of the technical basics and usual imaging appearances of colorectal stenting, in order to provide appropriate pre- and post-procedural studies and detect possible stent-related complications.

During the past two decades, growing experience and technical advancements progressively widened the indications and increased the use of intraluminal stents in the management of colorectal disorders. Specifically, endoscopic decompression of malignant large bowel obstruction (LBO) by means of self-expanding metal stents (SEMS) progressively gained acceptance as an alternative to surgical resection or diversion, particularly in metastatic tumours and in poor surgical candidates. Initially considered a palliative treatment, SEMS are nowadays used as a “bridge” to elective surgical management of colorectal carcinoma (CRC). Furthermore, endoscopists progressively perform stenting of benign colorectal disorders in selected patients. Finally, the use of stents represents an appealing option in the challenging management of iatrogenic complications following colorectal surgery. The current indications for stent placement to manage different colorectal disorders are summarised in Table 1 and discussed in detail in the following paragraphs [ 1 , 2 ]. Table 1 Indications for stent management of colorectal disorders Indication Palliation of colorectal carcinoma (CRC)-related bowel obstruction  In non-operative candidates  Non-resectable malignant stricture  Local postoperative neoplastic recurrence Preoperative decompression in obstructing resectable CRC (bridge-to-surgery) Relief of large bowel obstruction from extracolonic malignancy, pelvic mass or peritoneal carcinomatosis Malignant colorectal fistula, e.g. to the urinary bladder or vagina Postoperative anastomotic leakage/fistula Indications for stent management of colorectal disorders Palliation of colorectal carcinoma (CRC)-related bowel obstruction In non-operative candidates Non-resectable malignant stricture Local postoperative neoplastic recurrence Aimed at radiologists practicing emergency and oncologic imaging, this pictorial essay reviews the technical features and current indications of colorectal stenting and presents with examples the expected and abnormal radiographic and cross-sectional imaging appearances observed during endoscopic management of malignant, benign and iatrogenic colonic disorders using intraluminal stents [ 3 , 4 ].