Role of computed tomography angiography for acute gastrointestinal bleeding
Chul-min Lee, Jong Keon Jang, Ji Hoon Shin, Soon-Young Song
Abstract
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.
Introduction
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
Finding
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
Technique
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.
Conclusion
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.
Article information
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