Gastrointestinal Intervention 2018; 7(3): 106-111
Role of computed tomography angiography for acute gastrointestinal bleeding
Chul-min Lee1, Jong Keon Jang2, Ji Hoon Shin2, Soon-Young Song3, and Bo-kyeong Kang3,*
1Department of Radiology, Armed Forces Capital Hospital, Seongnam, Korea, 2Department of Radiology and Research Institute of Radiology, Asan Medical Center, University of Ulsan College of Medicine, Seoul, Korea, 3Department of Radiology, Hanyang University Medical Center, Hanyang University College of Medicine, Seoul, Korea
*Department of Radiology, Hanyang University Medical Center, Hanyang University College of Medicine, 222-1 Wangsimni-ro, Seongdong-gu, Seoul 04763, Korea. E-mail address: (B.-k. Kang). ORCID:
Received: July 16, 2018; Revised: September 20, 2018; Accepted: September 20, 2018; Published online: October 31, 2018.
© Society of Gastrointestinal Intervention. All rights reserved.

cc This is an open-access article distributed under the terms of the Creative Commons Attribution Non-Commercial License ( which permits unrestricted noncommercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

Acute gastrointestinal (GI) bleeding is a common cause of emergency department admission and hospitalization. Diagnosis and treatment requires promptly with a multidisciplinary approach to reduce morbidity and mortality of acute GI bleeding. Many diagnostic modalities are being used in the evaluation of GI bleeding, each with its own strengths and weaknesses. With the recent advances in technology, computed tomography (CT) angiography has become an effective first-line method for imaging the cause of GI bleeding to guide management. The purpose of this review is to discuss diagnostic modalities of GI bleeding, with a focus on the emerging role of CT angiography.

Keywords: Computed tomography angiography, Computed tomography enterography, Gastrointestinal bleeding, Hematemesis, Melena

Gastrointestinal (GI) bleeding is a common cause of hospitalization (1%–2% of the hospitalization), morbidity, and mortality (mortality rate of 8%–16%).1 Patient with GI bleeding usually present with hematemesis (vomiting of blood or coffee-ground-like material), and/or melena (black, tarry stools), and/or hematochezia (red blood per rectum). Massive GI bleeding is defined as bleeding causing hemodynamic instability with systolic blood pressure < 90 mmHg, heart rate > 100 beats/min, hematocrit decrease > 20%, or hemoglobin < 100 g/L, requiring at least 4 units of blood within 24 hours.2

GI bleeding is usually categorized according to the site of bleeding as upper GI bleeding (UGIB) and lower GI bleeding (LGIB). UGIB is a bleeding above the ligament of Treitz, which includes esophagus, stomach and duodenum. Main causes of UGIB are peptic ulcer disease, esophageal and gastric varices, Malory-Weiss syndrome, esophagitis and gastritis, arteriovenous malformation.3,4 Contrary to UGIB, LGIB refers to the GI bleeding below the ligament of Treitz, which includes small bowel, colon, and rectum. Major causes of LGIB are diverticular disease, angiodysplasia, colitis and inflammatory bowel disease, neoplasm, and coagulopathy.5,6 Most of patients with GI bleeding has upper GI tract source (75%).7 Differentiation between UGIB and LGIB is important in daily clinical practice, but that is not so easy solely based on clinical presentation and physical examination.

Many useful diagnostic modalities could assist in the diagnostic evaluation of GI bleeding, which include endoscopy (upper endoscopy and colonoscopy), radionuclide imaging, catheter angiography, and computed tomography (CT) angiography. With the recent advances in technology, CT angiography has become an effective method for imaging the cause of GI bleeding.

In this review, we are going to discuss the emerging role of CT angiography in GI bleeding as promising modality for the time-efficient, sensitive, and accurate diagnosis of GI bleeding, after discussing properties of other modalities for the evaluation of GI bleeding.

Endoscopy (Upper Endoscopy and Colonoscopy)

Endoscopy is highly sensitive and specific for upper GI bleeding with sensitivity and specificity up to 98% and 100%, respectively.7 It is considered the first-line modality of choice for evaluation of upper GI bleeding as it allows us to locate and treat the bleeding lesions. Upper endoscopy and colonoscopy can treat GI bleeding if the lesion is detected and can sample tissue if suspected malignancy is detected. But endoscopy may not be universally available in many clinical settings, and may be difficult to perform in hemodynamically unstable patient. Active massive hemorrhage could limit the visualization of source of bleeding. Although emergent colonoscopy can be performed without bowel preparation, colonoscopy usually needs bowel preparation which makes the utilization in urgent clinical setting difficult.8,9 Upper endoscopy cannot visualize the majority of the small bowel. However, the recent advent of capsule endoscopy makes it possible the evaluation of small bowel, which requires time and cost.5,9

Radionuclide Scintigraphy

Technetium-99m tagged red blood cell scan is usually performed for the evaluation of GI bleeding, and technetium-99m pertechnetate is used for evaluation of Meckel’s diverticulum. Radionuclide study is highly sensitive and can detect very low rate of bleeding of 0.05 to 0.1 mL/min with sensitivity of 93% and specificity of 95%.10,11 Radionuclide study can also detect both arterial and venous bleeding.5 Because of the time-consuming nature of the study, the radionuclide study may not be available in acute clinical setting. The radionuclide imaging also lacks precise localization of the site of bleeding (22% false localization rate), which could be aided by the combination of single-photon emission CT/CT (SPECT/CT) (Fig. 1).12,13

Catheter Angiography

Catheter angiography is the only radiographic modality that can be used in both diagnosis and treatment of both upper and lower GI bleeding. It can be used for the unstable patients with lower GI bleeding, and with failed upper endoscopy and colonoscopy.5 Catheter angiography shows high spatial resolution, detecting rates of bleeding as low as 0.5 mL/min.14 Diagnostic direct sign of active GI bleeding is extravasation of contrast into bowel lumen (Fig. 1D). Pseudoaneurysm, arteriovenous fistula, hyperemia, neovascularity, extravasation of contrast into confined space could be the indirect signs.7,15 The development of micro-catheters and embolic materials with super-selective embolization has made the catheter angiography as the first-line modality for acute UGIB and LGIB that cannot be controlled by endoscopy or surgery.3 The major disadvantages of catheter angiography are its invasive nature and time-consuming property, and the risk of radiation exposure during procedure. Catheter angiography could show false negative result for the slow rate or obscure bleeding.9 For these reasons, the role of catheter angiography as a diagnostic tool has decreased.

CT Angiography

CT angiography has become the ideal initial diagnostic test for GI bleeding because it is nearly universally available in many medical institutions. Recent advances CT technology allowed faster scanning time, greater spatial resolution and anatomic coverage, and thinner collimation. CT angiography can be performed rapidly in acute GI bleeding patients without specific preparation. CT angiography can also be performed prior to the catheter angiography and endoscopy, providing precise anatomic localization for the source of GI bleeding before other diagnostic or therapeutic procedures.5,16 Overall location-based sensitivity, specificity, accuracy, and positive and negative predictive values of CT angiography for detection of acute massive GI bleeding (defined as requirement of transfusion of at least 4 units of blood during 24 hours in the hospital or as hypotension with systolic blood pressure < 90 mmHg) were 90.9%, 99%, 97.6%, 95%, and 98%, respectively.17 Unlike the other diagnostic modalities, CT angiography can evaluate the wall of the entire GI tract and other structures that may cause of GI bleeding such as hemobilia (Fig. 2).

There are some disadvantages of CT angiography such as need for intravenous (IV) contrast and radiation exposure, which could be reduced by recent dose reduction CT technique such as iterative reconstruction. In addition, CT angiography is less sensitive compared to the radionuclide imaging, detecting active bleeding with a rate that exceeds 0.3 to 0.5 mL/min.17,18 Because CT angiography can detect GI bleeding more sensitively than catheter angiography, negative CT angiography result could defer catheter angiography. Unlike catheter angiography or endoscopy, CT angiography is just a diagnostic modality, but can help further guide optional treatment (endoscopic intervention, angiographic embolization, and surgery).


Intraluminal extravasation of contrast material is the diagnostic finding of GI bleeding which means the leakage of contrast-enhanced blood from the bleeding source. The morphology of the extravasated contrast material could vary according to the etiology. ‘Jet-like’ extravasation could mean high rate of bleeding or bleeding from the anterior aspect of the bowel lumen (Fig. 3). ‘Cloud-like’ extravasation could mean low rate of bleeding or bleeding from the posterior source.6,19 Changing appearance of the extravasated contrast material over time with peristalsis (at least during two phases of CT scan) is also an important finding suggestive of active GI bleeding (Fig. 4).6,20 If bleeding has stopped or does not reach the threshold of CT angiography, intraluminal high-density clot could be the only finding.19,21 Because of the usual water density of the intestinal content, intraluminal clot should reach the threshold of 60 Hounsfield units (HU).22,23 ‘Sentinel clot’ is the clot with highest attenuation, which means the closest site of bleeding.24

Common diagnostic pitfall in the diagnosis of GI bleeding is high density material within the bowel lumen such as metallic clips, suture material, oral contrast, fecalith, etc. (Fig. 5A, 5B). They could be mistaken for extravasated contrast material without non-contrast image. Cone-beam artifact near bowel wall could also be mistaken for the extravasated contrast material (Fig. 5C, 5D). Abundant fluid within bowel loops could dilute extravasated contrast material, which could hide the source of bleeding.5,6,25


CT protocols for GI bleeding could vary according to the medical institutions. But, at least of three phases including non-contrast, arterial, and venous phase are necessary in the GI bleeding CT angiography protocol. Arterial phase is acquired with bolus tracking technique for abdominal aorta (threshold of 150 HU). Venous phase is acquired after 70 to 90 seconds after contrast injection. About 100 to 125 mL of IV contrast is injected at the rate of 4 to 5 mL/sec.5 Image reconstruction thickness is varied according to the institution, but 1 to 2 mm section thickness are usually recommended.5,6,15 Multiplanar reformation image and maximal intensity projection image in both coronal and sagittal plane could provide more detailed information about bleeding pathology and vascular anatomy. Oral contrast is not recommended, because positive contrast could hinder contrast extravasation, and negative or neutral contrast could dilute the contrast material.3,5,15

Dual energy CT (DECT)

DECT is a new technology that uses both the normal x-ray and also a second less powerful x-ray to make images. DECT could offers the potential to analyze material composition through image acquisition through two different energy levels.26 DECT could generate virtual non-contrast image which could be the possible candidate for the true non-contrast image, resulting in radiation dose reduction.27 DECT could also provide iodine map to depict iodine content, which could aid in the evaluation of GI bleeding.5

CT enterography

CT enterography is a non-invasive imaging technique that offers superior bowel visualization compared to the standard abdomen-pelvic CT using positive or neutral contrast agents.28 Obscure GI bleeding is defined as GI bleeding without an obvious etiology after standard upper endoscopy and colonoscopy.29 According to Lee et al,9 CT enterography has a potential role in the evaluation of obscure GI bleeding. Positive CT enterographic findings could indicate the true source of obscure GI bleeding, particularly in patients with massive bleeding history.


Imaging is playing a pivotal role for the diagnosis and treatment for GI bleeding. Among them, CT angiography has become the initial and important diagnostic modality, as it is universally available and can be performed rapidly with the recent advances in technology. Radiologist should be aware of the appropriate use of CT angiography with its image findings and imaging pitfalls for upper and lower GI bleeding. By doing so, we could help guide the appropriate treatment for GI bleeding to be implemented at optimal timing.

Conflicts of Interest

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

Fig. 1. Lower gastrointestinal bleeding in a 68-year-old female in whom the findings from initial colonoscopy had been unrevealing. (A) Tagged red blood cell image shows abnormal accumulation of radiotracer within right lower abdomen (arrow). (B) Single-photon emission computed tomography/computed tomography (SPECT/CT) image shows migration and accumulation of radiotracer along the ileum in right lower abdomen (arrow). (C) Coronal arterial phase CT image show nodular extravasation of contrast material in the distal ileum (arrow). (D) Selective catheter angiography of a distal ileal branch shows intermittent contrast extravasation into the lumen of the ileum, which was subsequently treated with gelfoam embolization (arrow).
Fig. 2. Hemobilia cause by a pseudoaneurysm of hepatic artery in a 63-year-old female who presented with melena and severe epigastric pain. (A) Axial arterial phase computed tomography (CT) image shows a large pseudoaneurysm in hepatic segment VII (arrow). (B) Coronal arterial phase CT image shows a dilated common bile duct with internal high attenuation material (hemobilia) (arrow). (C) Coronal maximal intensity projection reformatted image depicts a pseudoaneurysm originating from right hepatic artery. (D) Celiac axis arteriography confirms the pseudoaneurysm.
Fig. 3. Upper gastrointestinal bleeding caused by gastric ulcer in a 79-year-old female who presented with hematemesis and melena. Coronal arterial phase computed tomography image (A) and coronal arterial phase volume-rendered reformatted image (B) shows contrast extravasation within the stomach (arrows). (C) Coronal maximal intensity projection reformatted image shows projection of contrast media into lumen (arrow). (D) Left gastric arteriography confirms the active bleeding to the lumen (arrow).
Fig. 4. Lower gastrointestinal bleeding in a 62-year-old male who presented with hematochezia. (A, B) There is active extravasation of contrast into the lumen of ileum in the arterial phase, which changes in size and morphology with peristalsis in the portal phase (arrows). (C) Superior mesenteric artery angiography shows no active bleeding. (D) Selective catheter angiography of an ileal artery branch shows active bleeding into the lumen (arrow).
Fig. 5. Potential pitfalls and image artifacts. (A, B) Axial arterial phase computed tomography (CT) image show high-density material within the ascending colon. Ingested material or fecaliths can be mistaken for hemorrhage without unenhanced CT image (arrows). (C, D) Axial unenhanced and arterial phase CT image show cone-beam artifact, a finding that mimics extravasation of contrast material (arrow).
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