The Role of Computed Tomography in GIB
Computed tomography (CT) is used when initial endoscopy is inconclusive or cannot be performed. This method not only points to the exact site of bleeding but also helps detect associated abnormalities, such as metastatic lesions.
In emergency cases, CT angiography (CTA) is preferred. The examination is performed in three phases: non-contrast, arterial, and delayed phases. The primary sign of ongoing bleeding is the extravasation of contrast material into the bowel lumen. It is important to remember that patients must not be given oral iodinated contrast, as this will make it impossible to identify the source of bleeding within the lumen.
Multiphasic CT Enterography and Dual-Energy CT
If the patient is stable but endoscopy is negative (often when small bowel pathology is suspected), CT enterography is used. It also includes arterial and delayed phases, supplemented by the enteral phase. To optimize visualization, the bowel loops are distended using a neutral oral contrast agent.
Additionally, dual-energy CT (DECT) may be used. This method is indispensable when it is necessary to differentiate active bleeding from other causes of high-density areas in the bowel.
Capabilities of Scintigraphy
Radioisotope scanning is performed using technetium-99m (99mTc), which is bound to sulfur colloid or patient erythrocytes.
- Advantages: The method is extremely sensitive and can detect even minor (from 0.1 mL/min) or intermittent occult bleeding.
- Disadvantages: The procedure is time-consuming, has limited availability in emergency settings, and does not provide precise anatomical localization of the source.
Prognostic Value of CT Angiography
A positive CT angiography result indicates that the patient will very likely benefit from digital subtraction angiography (DSA). CTA is superior to scintigraphy in localizing the source.
Conversely, if CT angiography is negative, emergency surgery or angiography is rarely required. The majority of such patients (approximately 81%) show no recurrence over the subsequent two years.
Briefly: answers to topical questions
What endovascular treatment methods are used when a GIB source is identified on angiography?
When the source of gastrointestinal bleeding is identified on angiography, endovascular embolization is performed.
This method can be used in the following ways:
- Primary therapeutic method (therapeutic) — used for definitive cessation of active bleeding.
- Patient stabilization — used as a temporary measure prior to surgical intervention.
- Prophylactic embolization — performed in the absence of active bleeding if the source is known or clinically suspected.
The choice of a specific embolic agent and the scope of the procedure depend on the anatomical location of the source, which is necessary to prevent ischemia or infarction of surrounding tissues.
What neutral oral contrast agents are used for bowel distension during CT enterography?
Neutral oral contrast is used to distend the bowel during multiphasic CT enterography.
The cited sources list the following as neutral luminal/oral contrast agents for bowel CT examinations:
- water;
- methylcellulose solution;
- diluted polyethylene glycol (PEG).
It is also noted that neutral oral contrast is used to distend the bowel wall.
Class and exam questions
Why is oral iodinated contrast not used in CT angiography for GIB?
It creates high density within the bowel lumen that blends with the appearance of intravenous contrast extravasation, making result interpretation impossible.
Which method localizes the bleeding source more accurately: CTA or scintigraphy?
CT angiography provides much more precise anatomical localization of the bleeding source compared to scintigraphy.
What is the main advantage of scintigraphy over CT in GIB?
Scintigraphy is capable of detecting bleeding at very low rates (0.1–0.5 mL/min) and capturing intermittent occult bleeding.
What else to study on this topic
- Digital Subtraction Angiography (DSA) in GIB
- Dual-Energy CT (DECT): Physical Principles
- Management Algorithm for Patients with Negative Endoscopy
- Differential Diagnosis of High-Density Lesions in the Bowel
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