Lower gastrointestinal bleeding CT scan
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Lower gastrointestinal bleeding Microchapters |
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Differentiating Lower gastrointestinal bleeding from other Diseases |
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Aditya Ganti M.B.B.S. [2]
Overview
CT scan
Helical CT scanning of the abdomen and pelvis is employed used when a routine workup fails to determine the cause of active gastrointestinal bleeding. Helical CT scanning is a safe, convenient, and an accurate diagnostic tool relative to mesenteric angiography and colonoscopy in diagnosing acute lower GI bleeding (LGIB). Findings of helical CT scan in lower gastrointestinal bleeding include:
- Vascular extravasation of the contrast medium
- Contrast enhancement of the bowel wall
- Thickening of the bowel wall
- Spontaneous hyperdensity of the peri-bowel fat, and vascular dilatations.
Multidetector-row CT (MDCT) scanning is also useful in the evaluation of LGIB but its rarely used.
| Sensitivity | MDCT | Endoscopy |
|---|---|---|
| Site | 100% | 88.2% |
| Etiology | 52.9% | 52.9% |
CT Angiography
- CTA is a multidetector CT scan performed in the arterial phase. Contrast (100 mL) is given via peripheral venous access and a CT scan is performed 30 seconds following injection. The scan is then repeated in the portal phase (70 seconds following injection)
- CTA can detect bleeding with a rate of 0.5 mL/min or less whereas catheter angiography detects bleeding with a rate of 0.5 to 1 mL/min. Therefore, CTA is performed before catheter angiography.
Indications
- In patients who are actively bleeding but who are relatively hemodynamically stable
Advantages
- Noninvasive
- CT Angiography can pick up findings in the solid organs and soft tissue structures that would not be seen on catheter angiography.
- CT Angiography can potentially detect bleeding from any point in the gastrointestinal tract and may reveal an upper gastrointestinal source of bleeding in a patient thought to have LGIB.
- CT Angiography can also help with planning embolization by revealing any iliac artery or mesenteric ostial atherosclerotic disease that may hamper access.
- CTA also has the advantage that it is widely available 24 hours a day, unlike colonoscopy services in many areas.
- If a patient then becomes unstable and an initial bleeding point is localized on CTA, then the choice has to be made between urgent colonoscopy, angiographic embolization, or surgery
Findings/Interpretation
- Arterial phase CTA may show thrombus in the superior or inferior mesenteric artery.
- CTA has a sensitivity of 93% to 100% and specificity of 100% in detecting mesenteric ischemia.
- Advances made in CT with respect to greater resolution and shorter scanning times allow for improved identification of extravasated contrast material into the intestinal lumen
- If CTA fails to show a source of bleeding, then catheter angiography is generally not performed.
- If a bleeding point is seen on CTA, then catheter angiography and embolization can be undertaken
Disadvantage
- Poor sensitivity
Contraindications
- Contraindicated in patients with renal failure as the contrast agent may potentially worsen renal function.