Gastrointestinal bleeding (GIB) is a common clinical condition that can lead to significant morbidity and mortality without appropriate management.¹ It may exhibit different clinical presentations, including massive life-threatening bleeding, overt bleeding with hematemesis, melena, or hematochezia, or obscure blood loss, with iron deficiency anemia or positive results on a fecal blood test.^2–5 The diagnostic and therapeutic approach to GIB depends on its location, severity, and etiology. An upper GIB is one that is proximal to the ligament of Treitz, which includes the esophagus, stomach, and duodenum. A lower GIB is one that is distal to the ligament of Treitz, which includes the small bowel, colon, and rectum.^1,6 Among GIBs, an obscure GIB is defined as one that persists or recurs without an obvious etiology after standard endoscopic or radiological imaging.⁷ The diagnosis and management of patients with GIB are challenging and sometimes require extensive and expensive workups. The primary objective of interventional radiological approaches is to determine the etiology and identify the site of bleeding to establish the most appropriate treatment strategy. Radiology affords diagnostic capability to facilitate interventional management and can be performed promptly and effectively with successful outcomes. The role of interventional radiology is vital among patients in whom GIB remains resistant to medical and endoscopic treatment.¹ The introduction of capsule endoscopy, double-balloon enteroscopy, and recent improvements in computed tomography (CT) and magnetic resonance imaging (MRI) techniques have revolutionized the approach to patients with GIB, enabling visualization of the entire gastrointestinal (GI) tract, particularly the small bowel.⁸ Radiological imaging can be used to localize the source of bleeding and provide essential information to interventional radiologists and guide therapeutic management using conventional angiography and transarterial embolization. The present review highlights the essential role of interventional radiology in the management of GIB.

Small bowel series and conventional enteroclysis

The development of capsule endoscopy has dramatically reduced the role of conventional small bowel series and enteroclysis for the evaluation of GIB.⁹ Recent data suggest that small bowel series and conventional enteroclysis have limited yield in the evaluation of GIB, unless Crohn disease, small bowel stricture or obstruction, or nonsteroidal anti-inflammatory drug-induced enteropathy is suspected.^5,10,11

Technetium-labeled radionuclide scintigraphy

Two types of nuclear scans can be used for the diagnosis of active GIB: technetium 99m-labeled red blood cell scan; and technetium 99m-labeled sulfur colloid scan. However, a red blood cell scan is more commonly performed. It can detect active bleeding at a rate of 0.05–0.01 mL/min with a sensitivity of 93% and specificity of 95%.^5,6 The positive predictive value has also been reported to be as high as 84%; however, radionuclide scintigraphy has a false localization rate of approximately 22%, which limits its value as a diagnostic test.^7,12 In addition, when definitive lesions are verified using other means, the accuracy of a positive scan for lesion localization may be as poor as 41%.^7,13,14 Moreover, because nuclear-based scans are not therapeutic, other modalities, such as conventional angiography or endoscopy, must be followed.

Computed tomography angiography

Computed tomography angiography (CTA) is rapid and easy to perform compared with conventional angiography. Usually, a triphasic multidetector CTA protocol is used that includes unenhanced and arterial and venous phase imaging to detect acute GI bleeding. Recent advances in CT technology have significantly expanded the diagnostic utility of CTA. CTA can detect flow rates as low as 0.3–0.5 mL/min and has a sensitivity of 50% to 86% and specificity of 92% to 95% for GIB lesions.^1,6 CTA diagnosis of active GIB is made when hyperattenuating extravasated contrast material is visualized within the bowel lumen (Fig. 1).^10,15 Evaluation of GIB using CTA can often determine its etiology, which may be useful in further management. Furthermore, the morphology of extravasated contrast material varies according to etiology. “Jet-like” extravasation may reflect a high rate of GIB or bleeding from the anterior aspect of the bowel lumen, whereas “cloud-like” extravasation may indicate a low rate of bleeding or bleeding from the posterior source.^6,15 However, if bleeding has stopped or does not reach the threshold of CTA, an intraluminal high-density clot could be the only finding.⁶ Although CTA is only a diagnostic tool, it can provide important information about the arterial anatomy to inform interventional management or surgical treatment.

Figure 1. Arterial phase multidetector computed tomography revealing active contrast extravasation in the terminal ileum (arrow).

Conventional angiography

Conventional angiography involves the administration of intra-arterial contrast agent through an angiographic catheter. Angiography is the only radiological tool that can be used in both the diagnosis and treatment of both upper and lower GIB. Among patients with non-diagnostic endoscopic results or those who remain refractory to medical and endoscopic treatment, radiological imaging and intervention are the next treatment of choice. Conventional angiography is more likely to identify the exact location of the bleeding, provided the rate is > 0.5 mL/min.^10,16 Localization of contrast extravasation into the bowel lumen is considered to be a direct angiographic sign of active GIB (Fig. 2). Although active bleeding may occur, an angiographic study would be negative if the hemorrhage is below the threshold rate for visibility. Commonly encountered indirect angiographic signs of GIB include visualization of an aneurysm/pseudoaneurysm, abnormal vessel irregularity or spasm, vessel cutoff sign, pseudo-vein sign or a submucosal vessel, and early venous drainage of angiodysplasia (Fig. 3).^1,15,17,18 Angiodysplasia is often diagnosed by early and persistent filling of a draining vein and by abnormal clusters of vessels within the bowel wall. Visualization of varices at non-suspected sites may indicate the site of pathology. However, patients may not cooperate with breath-holding, which can negate the benefits of digital subtraction angiography and render the study less sensitive. There are several artifacts that mimic active bleeding, including bowel motion artifact, hypervascular mucosa, parts of the renal collecting system, and adrenal gland opacification.¹ When a site of active extravasation is visualized during an angiographic study, attempts at embolization can be performed for definitive management. If signs of direct or indirect bleeding are not visualized on angiography, an interventional radiologist may choose to examine other vessels or catheterize the smaller arteries likely supplying the suspected site of bleeding—possibly indicated by previous endoscopy or other imaging studies—to reduce the number of false-negative results.^1,19,20

Figure 2. Celiac angiography revealing active contrast extravasation in the duodenum (arrow).

Figure 3. Celiac angiography revealing small pseudoaneurysm at the right gastric artery (arrow).

Obscure GIB is defined as bleeding from the GI tract that persists or recurs in the absence of a positive diagnostic study.^5,6,10,21 The diagnosis and management of patients with obscure GIB are challenging and often require many imaging studies. Occult GIB may be attributable to several different causes, and any lesion located in the GI tract may be a source of obscure GIB. Frequently missed lesions include small gastric erosions, gastric fundic varices, peptic ulcer disease, angioectasia, Dieulafoy lesion (a large artery that impinges on the mucosa while pursuing its tortuous course through the submucosa), and bowel tumors.^5,7 Obscure GIB may be categorized into two subtypes: obscure silent bleeding and obscure overt bleeding. Obscure silent bleeding is bleeding in which the site is unknown because the bleeding occurs at such a slow rate that detection is challenging or impossible with diagnostic studies. Obscure overt bleeding is high-volume bleeding manifesting as hematemesis, melena, or hematochezia without an identified bleeding source.^5,7,10 Approximately 10% to 20% GIB cases are of the obscure type, thus requiring more extensive diagnostic studies.^10,22 These patients typically undergo many endoscopic and radiological examinations; however, depending on study timing, all examinations may be negative, and the patient may be discharged once stabilized or may experience additional bleeding episodes in the future. Therefore, the primary objective is to determine the etiology and identify the site of bleeding, which should be accomplished as rapidly as possible to establish the most appropriate treatment strategy.

Most patients who experience acute upper and lower GIB respond to conservative management or endoscopic intervention; however, patients with failed conservative or endoscopic therapy require other intervention(s) to control bleeding.^20,23 Therapeutic options include surgery, endoscopic management, and transcatheter arterial interventions (Fig. 4).^1,19 Surgery is associated with mortality rates as high as 15%–30% in emergent situations.^19,20 Transcatheter intervention to control GIB takes two forms: infusion of a vasoconstricting drug (i.e., vasopressin infusion); and direct occlusion of the blood supply responsible for the bleeding.²³

Figure 4. Flow-diagram illustrating treatment for acute gastrointestinal bleeding. CT, computed tomography.

Intra-arterial infusion of vasopressin

Vasopressin, a posterior pituitary hormone, constricts the arteries and decreases blood flow to the target site. Vasopressin infusion is easy to perform, most often by inserting a 5-Fr angiographic catheter into the target artery.^1,24 When GIB is caused by diffuse lesions, or super-selective catheterization is not possible, vasopressin infusion may be a therapeutic option before surgical intervention for endoscopically uncontrollable GIB. Typical vasopressin therapy involves an initial 20 minutes infusion at a rate of 0.2 U/min, followed by repeated arteriography to confirm whether bleeding has stopped and the artery is not over-constricted (Fig. 5). If bleeding continues, the infusion rate can be incrementally increased to 0.3 and then 0.4 U/min; however, each change in infusion rate must be followed by a waiting period for the increased drug dose to take effect, followed by another arteriogram to assess the effect. When the appropriate dose is determined, it requires continued intra-arterial infusion for 12 to 48 hours and intensive care monitoring during the procedure. Vasopressin infusion is reported to be more effective when applied to lower GIB. The higher failure rate of vasopressin in upper GIB is thought to be due to the rich collateral supply. General series of lower GIB report success rates ranging from 59% to 90%.^1,18,24 However, there are high rate of rebleeding rate of up to 36%–43%. It was more commonly used before the advancement and improvement of transcatheter technique, and it is a less frequently used treatment for acute GIB because it can cause systemic side effects, and super-selective embolization can be performed nowadays.^1,17,23,24

Figure 5. Protocol for transcatheter infusion of vasopressin.

Transcatheter arterial embolization

Transcatheter arterial embolization (TAE) is effective in controlling acute GIB. The aim of TAE is super-selective embolization of the source of bleeding to reduce arterial perfusion pressure while maintaining adequate collateral blood flow to maintain intestinal viability and minimize the risk for bowel infarction(s). TAE is associated with an initial bleeding control rate of 89%–98%. Clinical success rates range from 52% to 98%, with most studies reporting success rates of 70%–80%.^1,17,24 In cases of active bleeding, the bleeding artery is typically identified by selective catheterization and embolized using various embolic materials. Super-selection and embolization of short segments of visceral arteries can be performed using more recently advanced hydrophilic wires, microcatheters, and embolic agents. Many embolization agents have been used successfully, including metal coils and particulate materials such as resorbable gelatin sponge, non-resorbable polyvinyl alcohol (PVA), or tris-acryl gelatin particles. Liquid agents, such as n-butyl 2-cyanoacrylate glue, can also be used (Fig. 6). However, to date, there is no consensus regarding the best embolic agents, with each possessing advantages and disadvantages.^1,23,25

Figure 6. Treatment of small bowel bleeding using n-butyl cyanoacrylate (NBCA). (A) Super-selective angiography using a microcatheter revealing contrast extravasation in the ileal artery (arrow). (B) NBCA mixture embolization is performed.

Upper GIB arises in locations that are generally accessible to endoscopy. Therefore, endoscopic management is the best treatment option for most patients. However, for patients in whom endoscopy has not been successful, interventional management should be the next option considered. Because patients with acute massive GIB may experience episodes of intermittent bleeding, some interventional radiologists have adopted “blind embolization” based on endoscopic findings even in situations in which no extravasation is observed angiographically (Fig. 7).^20,23 The following criteria can serve as indications for interventional management of GIB: systolic blood pressure < 100 mmHg; heart rate > 100 beats/min; and > 4 units packed red blood cells transfused in < 24 hours.^2,10,23

Figure 7. Left gastric artery embolization for recurrent obscure gastrointestinal bleeding. (A) Angiography depicting no definitive active bleeding. (B) After super-selective gelfoam embolization of left gastric artery, obscure bleeding was stopped.

GIB visualized in the gastric fundus is managed by embolization of the left gastric artery, whereas GIB in the distal stomach or proximal duodenum is managed using gastroduodenal artery (GDA) embolization. When embolizing the GDA, embolization of both sides of the bleeding point is essential to avoid “backdoor” bleeding. During embolization, catheters are flushed with non-heparinized saline. A stable catheter position must be confirmed before TAE by test passage of a coil-pushing wire or test injection of contrast media for particulate agents. Non-radiopaque particulate embolic material (e.g., gelatin sponge and PVA particles) must be mixed with contrast media and injected under continuous high-quality fluoroscopy on a small field size to prevent or minimize reflux of the embolic agent into nontarget arteries. In hemodynamically unstable patients, volume depletion results in reduced vessel size. Coil embolization in this setting can result in undersized coils with recanalization once the intravascular volume is restored. A degree of coil oversizing is recommended in this setting. The temptation to pack the sac of a pseudoaneurysm with coils must be avoided because it is usually ineffective, with recurrence virtually inevitable, and it may promote the rupture of the pseudoaneurysm.

Lower GIB is much less common than upper GIB, and accounts for approximately 20%–25% of all GIB, with a reported annual incidence of 21–27 per 100,000 population.^24,26 However, it is associated with a 10% mortality rate and, although less common than upper GIB, it more often demands the special skills and techniques of an interventional radiologist. The first step is to determine whether the patient is bleeding actively enough to make it likely that an arteriogram will be positive. Due to the large holding capacity of the colon, the patient may not exhibit hematochezia despite active bleeding. Conventional treatment options for lower GIB include endoscopic management, TAE, and surgery. Endoscopic management is considered to be the best treatment option for patients with chronic and intermittent lower GIB, but is less reliable when treating patients with massive hematochezia due to inadequate visualization caused by inadequate bowel preparation or active hemorrhage.^1,24,26 The lower GI tract does not have a dual blood supply; therefore, the risk for ischemic bowel changes is greater.^1,10,19,27 In the past, bowel ischemic changes or infarctions occurred at an unacceptably high frequency, as high as 20%–33%.^24,28 The high rate of ischemic changes in older studies was probably a result of the relatively larger angiographic catheters (5–6.5 Fr) used and limited embolic materials. However, the development of technologies, such as coaxial microcatheters, new embolic materials, and super-selective embolization, have made TAE a feasible option for managing lower GIB.^24,26 The best embolic material is, however, controversial. Although micro-coils are commonly used agents, PVA or gelfoam are often used. N-butyl cyanoacrylate (NBCA) has been used in a small series with acceptable results.^27,29,30 Another point of debate is at what level to embolize—at the marginal artery or beyond—because safety is also a concern. Usually, for lower GIB, the microcatheter should be positioned as close to the bleeding site as possible to reduce ischemic complications. In most of the reported series in the literature, the target artery of embolization was the vasa recta and, in technically difficult cases, the marginal artery of Drummond or more proximally.^1,24,26 Jae et al³ reported that superselective embolization involving three or fewer vasa recta of the SMA was relatively tolerable, and embolization involving four or more vasa recta carried an increased risk of substantial ischemic bowel damage. However, larger clinical studies are needed to clarify the optimal level of embolization and choice of embolic agents.

Although many cases of acute GIB respond to medical and endoscopic management, massive or obscure GIB remains a challenge. Advances in interventional tools and embolic agents have made interventional radiological management an important treatment option for the diagnosis and treatment of patients refractory to endoscopic treatment. Nevertheless, a multidisciplinary team approach, including endoscopists, gastrointestinal surgeons, and interventional radiologists, is required for the optimal management of patients with GIB.

None.

No potential conflict of interest relevant to this article was reported.