What are the indications for a CT (Computed Tomography) angiogram of the abdomen?

Indications for CT Angiogram of the Abdomen

CT angiography (CTA) of the abdomen is the first-line imaging modality for evaluating suspected vascular pathology including abdominal aortic aneurysms, acute mesenteric ischemia, renal artery stenosis in transplants, active retroperitoneal bleeding, and visceral artery abnormalities. 1, 2

Primary Clinical Indications

Abdominal Aortic Aneurysm (AAA)

• CTA is the best diagnostic and pre-intervention planning study for AAA, providing near 100% sensitivity and specificity while accurately delineating location, size, extent, and branch vessel involvement with quantitative 3-D measurements 1, 2
• Order CTA for patients presenting with pulsatile abdominal mass, with or without clinical suspicion of contained aortic rupture 1
• Essential for planning endovascular or surgical intervention in AAAs ≥5.5 cm in external anteroposterior diameter 1
• CTA detects critical complications including thrombus (which affects hemodynamic properties and is associated with rapid enlargement), dissection flaps, and signs of imminent or contained rupture 1, 2
• The "run-off" component extending to iliofemoral vessels is crucial because approximately 5% of AAAs involve the iliac arteries 2

Acute Mesenteric Ischemia

• CTA is the first-line imaging approach for suspected acute bowel ischemia, with sensitivity and specificity as high as 93-100% and potential to improve patient survival 1
• CTA rapidly evaluates both arterial and venous patency, bowel wall enhancement, and identifies vascular findings (arterial stenosis, embolism, thrombosis, dissection, mesenteric vein thrombosis) 1
• Both arterial and portal venous phases should be included to assess arterial and venous patency 1
• CTA is preferred even in patients with renal insufficiency (GFR <30) when acute ischemia is suspected, as benefits of fast and accurate diagnosis outweigh risks of contrast-induced nephropathy 1
• CTA helps stratify patients to identify those who would benefit from angiography versus emergent surgery 1

Renal Transplant Vascular Complications

• CTA provides detailed anatomic depiction before percutaneous angiography for suspected renal artery thrombosis, renal artery stenosis, pseudoaneurysm, or arteriovenous fistula 1
• High spatial resolution provides high sensitivity and specificity for diagnosing renal artery stenosis in transplants 1
• European Association of Urology guidelines recommend CTA following unremarkable or indeterminate renal ultrasound in patients with suspected renal artery stenosis 1

Suspected Retroperitoneal Bleeding

• CTA is appropriate for initial evaluation of suspected retroperitoneal bleeding, detecting active bleeding rates as low as 0.3 mL/min 1
• CTA has better sensitivity than invasive angiography for detecting active bleeding, with sensitivity of 59.5% and positive predictive value of 62.9-71.0% for active extravasation 1
• Provides exact hematoma location and can identify bleeding sources including groin access complications, pelvic fractures, or masses 1
• In patients with suspected aortic aneurysm rupture, CTA provides confirmation and valuable preoperative information for endovascular or surgical repair 1

Chronic Mesenteric Ischemia (Abdominal Angina)

• Multi-detector row CTA is a primary tool for evaluating suspected steno-occlusive diseases of celiac trunk, superior mesenteric artery, and inferior mesenteric artery 3
• CTA evaluates presence and degree of stenosis, demonstrates collateral circulation, and excludes other causes of vascular obstruction 3
• Allows visualization of small vessels and vessel wall abnormalities even in absence of significant stenosis 3

Technical Requirements for Optimal CTA

Essential Protocol Elements

• Thin-section CT acquisition timed to coincide with peak arterial enhancement 1, 2
• Multiplanar reformations and 3D renderings are required elements—timing, reconstructions/reformats, and 3D renderings distinguish CTA from standard contrast CT 1, 2
• For AAA evaluation, measure outer-to-outer aortic diameter perpendicular to the long axis using angle-corrected multiplanar reformatted images, especially in tortuous aneurysms 1, 2

Contrast Phases

• Arterial phase is essential for evaluating arterial stenosis, embolism, and active bleeding 1
• Portal venous phase provides information about mesenteric veins and extra-aortic pathology 1
• Noncontrast phase may be added for suspected contained AAA rupture to identify dissecting hematoma (crescent sign), draped aorta, and adjacent vertebral erosion 1

Critical Pitfalls to Avoid

Don't Substitute Standard CT for CTA

• Standard CT with IV contrast during venous phase alone leads to suboptimal evaluation of mesenteric arteries, with diagnostic errors occurring when relying on portal venous phase only 1
• Arterial phase influenced care in 19% of patients compared to portal venous phase alone 1
• CT without contrast cannot assess for dissection, thrombus characteristics, or branch vessel involvement critical for management decisions 2

Don't Delay with Alternative Imaging First

• In symptomatic patients with suspected AAA, don't start with ultrasound—while excellent for screening asymptomatic patients, US underestimates aneurysm size by 4mm and cannot adequately assess for rupture or iliac involvement 2
• MRA has limited role in acute mesenteric ischemia due to long examination time, which may delay therapeutic options 1
• MRA is less likely to show ischemic bowel findings (pneumatosis, portal venous gas) compared to CTA 1

Recognize When Angiography is Needed

• While CTA has supplanted conventional angiography as first-line imaging, angiography provides complementary diagnostic role with option for endovascular treatment 1
• Early angiography is associated with increased survival in mesenteric ischemia and allows therapeutic maneuvers 1
• However, angiography should not delay surgery in patients with peritoneal signs suggesting infarcted bowel 1