CT Aortogram for Suspected Aortic Aneurysm: Contrast is Essential
For patients with suspected aortic aneurysm, contrast-enhanced CT angiography (CTA) is the reference standard and should be performed with intravenous contrast to accurately diagnose, measure, and characterize the aneurysm and assess for life-threatening complications. 1, 2
Why Contrast is Necessary
Contrast enhancement is essential because it allows visualization of the aortic lumen, mural thrombus, dissection flaps, and branch vessel involvement—critical information that cannot be adequately assessed with non-contrast studies alone. 1, 2
Key Diagnostic Advantages of Contrast-Enhanced CTA:
- Near 100% sensitivity and specificity for AAA diagnosis, far superior to non-contrast imaging 2
- Detects critical complications including intramural thrombus, dissection flaps, and signs of imminent or contained rupture that would be missed on non-contrast studies 1, 2
- Provides accurate outer-to-outer (OTO) wall measurements perpendicular to the long axis of the aorta, which is the recommended measurement technique for management decisions 1, 2
- Visualizes branch vessel involvement including renal, mesenteric, and iliac arteries—approximately 5% of AAAs involve iliac arteries, information essential for surgical planning 2, 3
- Enables 3D rendering, which is a required element of CTA and allows for precise pre-operative planning for endovascular or open surgical repair 1
Technical Requirements for Proper CTA
The American College of Radiology defines CTA as requiring three essential elements 1:
- Timing: Thin-section CT acquisition timed to coincide with peak arterial enhancement 1
- Reconstructions: Multiplanar reformations to ensure accurate measurements in tortuous vessels 1, 2
- 3D renderings: Required element that distinguishes CTA from standard contrast-enhanced CT 1
When Non-Contrast CT Falls Short
While non-contrast CT can detect the presence of an AAA and may show displaced calcifications suggesting dissection, it has critical limitations 1:
- Cannot distinguish aortic wall from lumen, making it impossible to assess mural thrombus characteristics 1
- Cannot detect dissection flaps unless there is displaced intimal calcification 4
- Cannot evaluate branch vessel involvement or patency 1, 2
- Provides no information about complications such as inflammatory changes or impending rupture 1
Clinical Algorithm
For symptomatic patients (acute abdominal/back pain with pulsatile mass):
- Order CTA abdomen/pelvis with IV contrast immediately, including run-off to iliofemoral vessels 1, 2
- Do not delay with ultrasound first—US underestimates size by 4mm and cannot assess for rupture 2
For asymptomatic screening in high-risk patients:
- Ultrasound is appropriate as first-line 1, 3
- If US is inadequate or shows AAA requiring intervention planning, proceed to CTA with contrast 1, 3
Special Circumstances
If contrast is contraindicated (severe renal insufficiency, contrast allergy):
- MR angiography (MRA) with or without gadolinium is an acceptable alternative with similar accuracy 1, 3, 5
- Non-contrast CT is a distant third option that provides limited information 1
Dual-energy CTA can reduce contrast dose by 50% while maintaining diagnostic quality in patients with borderline renal function 1, 6
Critical Pitfalls to Avoid
- Do not order "CT abdomen with contrast" instead of CTA—standard contrast-enhanced CT lacks the required 3D rendering and arterial-phase timing that are essential for accurate measurements and surgical planning 1
- Do not rely on non-contrast CT for suspected AAA—while it can detect the aneurysm, it cannot provide the critical information needed for management decisions about thrombus, dissection, or branch vessel involvement 1, 2
- Do not forget to include iliofemoral run-off in the scan range—this is essential for endovascular repair planning 2, 3
- Do not use inner-to-inner wall measurements—current guidelines recommend outer-to-outer wall diameter perpendicular to the aortic long axis 1