When should I order a routine contrast‑enhanced abdominal computed tomography (CT) versus a computed tomography angiography (CTA) versus a CT aortic dissection protocol?

When to Order CT Abdomen vs CTA vs CT Dissection Protocol

For suspected vascular pathology (active bleeding, dissection, aneurysm, or vascular injury), order CTA; for non-vascular acute abdominal processes (infection, inflammation, solid organ injury without active bleeding), order routine contrast-enhanced CT; and for suspected aortic dissection specifically, use a dedicated CTA protocol with arterial and delayed phases covering chest through pelvis.

Clinical Decision Algorithm

Order CTA (CT Angiography) when you suspect:

• Active hemorrhage or vascular injury – CTA detects bleeding rates as low as 0.3 mL/min and identifies arterial extravasation, pseudoaneurysms, and vascular trauma 1, 2
• Aortic dissection – Requires dedicated CTA protocol with arterial phase timing and ECG-gating for ascending aorta; should include chest, abdomen, and pelvis to assess full extent 2
• Aortic aneurysm evaluation – CTA provides near 100% sensitivity and specificity for sizing, characterizing extent, and presurgical planning with outer-wall-to-outer-wall measurements 2
• Arterial stenosis or thrombosis – CTA is the standard for evaluating mesenteric or peripheral arterial occlusive disease 1
• Penetrating trauma in hemodynamically stable patients – Portal venous phase CTA provides optimal information for surgical planning 2

Key technical points for CTA:

• Arterial phase bolus timing is essential for vascular pathology 2
• ECG-gating improves temporal resolution in ascending aorta where cardiac motion causes artifacts 2
• Extend coverage to include iliofemoral arteries when planning endovascular interventions 2
• Multiphase acquisition (arterial + delayed) helps differentiate active bleeding from contained hematoma 2

Order Routine Contrast-Enhanced CT (portal venous phase) when evaluating:

• Non-vascular acute abdominal processes – Infection, abscess, inflammatory conditions, solid organ pathology without suspected active bleeding 1
• Blunt solid organ trauma – Standard contrast-enhanced CT is sufficient for detecting liver, spleen, and kidney lacerations in hemodynamically stable patients 2
• Bowel pathology – Perforation, obstruction, ischemia (though mesenteric ischemia may warrant CTA if arterial occlusion suspected) 3
• Incidental findings – Many AAAs and other vascular abnormalities are detected on routine contrast CT performed for other indications 2

Important considerations:

• Portal venous phase provides excellent parenchymal enhancement and is the workhorse phase for most abdominal pathology 2
• IV contrast is generally necessary for accurate diagnosis; unenhanced CT has similar accuracy only in select scenarios but misses vascular detail 3
• Oral contrast is often unnecessary and may obscure active bleeding or delay imaging 2

Order Dedicated Aortic Dissection Protocol when:

• Clinical suspicion for aortic dissection – Acute chest/back/abdominal pain with risk factors (hypertension, connective tissue disorders, known aneurysm) 2
• Pulsatile abdominal mass with acute symptoms – May represent ruptured or symptomatic AAA requiring immediate characterization 2

Dissection protocol specifications:

• Coverage: Chest through pelvis to assess full aortic extent and branch vessel involvement 2
• Phases: Noncontrast (to detect intramural hematoma), arterial phase (to visualize intimal flap and true/false lumens), and delayed phase (to assess organ perfusion) 2
• ECG-gating: Particularly important for ascending aorta to reduce motion artifact 2
• Thin-section acquisition: Submillimeter isotropic imaging for 3D reconstructions 2

Common Pitfalls to Avoid

Don't order CTA when routine CT suffices:

• CTA exposes patients to higher radiation and contrast doses 2
• For screening or surveillance of known AAA <5.0-5.5 cm, ultrasound or noncontrast CT may be adequate 2
• Solid organ trauma without suspected vascular injury doesn't require arterial phase imaging 2

Don't skip arterial phase when vascular pathology is suspected:

• Portal venous phase alone may miss active arterial bleeding, dissection flaps, or arterial injuries 2
• Standard "CT abdomen with contrast" protocols typically use portal venous phase only 2

Don't use oral contrast when bleeding or dissection suspected:

• Oral contrast obscures active hemorrhage and interferes with subsequent angiography 2
• Delays imaging acquisition when time-critical diagnosis needed 2

Recognize when hemodynamic instability precludes CT:

• Unstable penetrating trauma patients should go directly to OR, not CT scanner 2
• Distance to CT scanner and ability to continue resuscitation during imaging must be considered 2

Special Populations

Hemodynamically stable trauma patients:

• CTA with portal venous phase provides comprehensive evaluation of both vascular and solid organ injuries 2
• Single contrast bolus with multiphase acquisition minimizes contrast dose 2

Suspected vascular infection or inflammatory aortitis:

• CTA with delayed phase shows rim enhancement and perivascular changes 2
• Noncontrast phase helps identify wall thickening, calcification, and periaortic gas 2