From the Guidelines
CT angiography (CTA) of the abdomen is highly useful for diagnosing occult gastrointestinal (GI) bleeding, with a sensitivity and specificity of 85% and 92%, respectively, as reported in a meta-analysis of 22 studies evaluating accuracy of CTA for the diagnosis of active GIB 1. This diagnostic tool can detect bleeding rates as slow as 0.3 mL/min, making it a valuable asset in the diagnostic workup for patients with suspected occult bleeding, especially those with hemodynamic instability or ongoing blood loss. The procedure involves intravenous contrast administration followed by rapid CT scanning of the abdomen and pelvis, with noncontrast images useful for the detection of intraluminal high-attenuation material that may mimic intraluminal blood on contrast-enhanced images 1. Some key points to consider when using CTA for diagnosing occult GI bleeding include:
- The use of multiphase acquisition, with a portal venous or a delayed phase, in addition to the angiographic phase, which can increase the sensitivity of the test 1
- The avoidance of oral contrast, as it can render the examination nondiagnostic 1
- The potential for CTA to lead to faster triage of patients toward definitive treatment by angiography, compared to other diagnostic tests such as Tc-99m–labeled RBC scintigraphy 1
- The importance of considering CTA early in the diagnostic workup, particularly in patients with suspected occult bleeding and hemodynamic instability or ongoing blood loss.
From the Research
Computed Tomography Angiography in Diagnosing Occult GI Bleeding
- CT angiography is a feasible and reliable diagnostic imaging modality for overt GI bleeding, especially when standard endoscopy is negative 2.
- In cases of occult GI bleeding, video capsule endoscopy or double balloon endoscopy can be considered after normal upper and lower endoscopy 2.
- The sensitivity and specificity of CT scan in detecting ongoing internal bleeding are around 74.5% and 100%, respectively 3.
- CT angiography can aid in identifying the location and cause of bleeding and is an important complementary tool to endoscopy, nuclear medicine, and angiography in evaluating patients with GI bleeding 4.
Role of CT-Angiography in Acute Gastrointestinal Bleeding
- CT angiography is useful in the acute setting of gastrointestinal bleeding, especially in identifying the source of bleeding and guiding management 5.
- The learning objective of using CT angiography in acute GI bleeding is to illustrate the technique, including the potential role of dual-energy CT angiography, and to highlight tips and tricks to identify common and uncommon features of acute GI bleeding 5.
- CT angiography can detect active bleeding, suspicious for bleeding, or no bleeding, and can be used to guide transcatheter arterial embolization to control bleeding 6.
Limitations and Considerations
- The choice of investigation for GI bleeding is subject to timing of presentation and accessibility to investigations 2.
- CT scan and angiography may not detect all cases of ongoing internal bleeding, with a negative predictive value of around 84.6% and 85.7%, respectively 3.
- Radiologists should be aware of the appropriate uses of CT angiography and other imaging modalities in patients with acute GI bleeding, as well as the semiotics of bleeding and diagnostic pitfalls 5.