Lower gastrointestinal bleeding CT scan

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Aditya Ganti M.B.B.S. [2]

Helical CT scanning of the abdomen and pelvis is recommended when a routine workup fails to determine the cause of active gastrointestinal bleeding. 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, hyperdensity of the peri-bowel fat, and vascular dilatations.

Helical CT scanning of the abdomen and pelvis is recommended 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:^[1][2]

• Vascular extravasation of the contrast medium
• Contrast enhancement of the bowel wall
• Thickening of the bowel wall
• 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.

• CT Angiography is a multidetector CT scan performed in the arterial phase.^{[3][4][5][6][7]}

• Contrast (100 mL) is given via peripheral venous access and a CT scan is performed 30 seconds following injection.
• CT scan is then repeated in the portal phase (70 seconds following injection).
• CT Angiography 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.
• Access into the arterial system is normally via a common femoral artery approach.
• If this is not possible, the brachial artery can be used, although this carries a small risk of stroke.
• A wide range of catheters can be used to access the mesenteric arteries (majority of bleeds due to diverticula or angiodysplasia receive their blood supply from the superior mesenteric artery).
• In practice, the inferior mesenteric artery is selectively catheterized before the superior mesenteric artery to avoid a bladder full of contrast obscuring the inferior mesenteric branches.
• If no bleeding source is identified from these two vessels (SMA, IMA) the celiac axis is catheterized and assessed, as bleeding points may be discovered from the gastroduodenal artery.

• In patients who are actively bleeding but who are relatively hemodynamically stable

• 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.
• 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.

• 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.
• 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.

• Poor sensitivity

• Contraindicated in patients with renal failure as the contrast agent may potentially worsen renal function.

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