Imaging Workup for Suspected Abdominal Aortic Aneurysm
Yes, ordering an abdominal CT angiography (CTA) with run-off and contrast is absolutely appropriate and represents the optimal imaging strategy for this patient presenting with pain and right-sided mid-abdominal bulging in the setting of known abdominal aortic atherosclerosis. 1
Primary Imaging Recommendation
CTA abdomen and pelvis with IV contrast (including run-off to iliofemoral vessels) is the gold standard and should be your first-line imaging study in this symptomatic patient. 1, 2
Why CTA is Essential Here:
Contrast-enhanced multidetector CTA is the best diagnostic and pre-intervention planning study, accurately delineating the location, size, and extent of any aneurysm and the involvement of branch vessels, allowing for accurate quantitative 3-D measurements 1
Your patient's presentation—pain plus palpable bulging—raises concern for possible AAA with potential contained rupture or rapid expansion, which requires urgent definitive imaging 1
CTA provides near 100% sensitivity and specificity for AAA diagnosis and can detect critical complications including thrombus, dissection flap, and signs of imminent or contained rupture 1
The "run-off" component (extending to iliofemoral vessels) is crucial because approximately 5% of AAAs involve the iliac arteries, and this information is essential for surgical or endovascular planning 2
Technical Specifications:
- Use thin-section CT acquisition timed to coincide with peak arterial enhancement 1
- Ensure multiplanar reformations and 3D renderings are performed—these are required elements of CTA 1
- Measure the outer-to-outer (OTO) aortic diameter perpendicular to the long axis of the aorta using angle-corrected multiplanar reformatted images, especially if the aorta is tortuous 1, 2
Role of Additional Non-Invasive Studies
ABI (Ankle-Brachial Index):
- ABI is reasonable to obtain as it provides functional assessment of peripheral arterial disease, which commonly coexists with aortic atherosclerosis 3
- However, ABI does not diagnose or characterize AAA and should not delay definitive imaging 4
Arterial Duplex:
- Arterial duplex of lower extremities can be deferred until after CTA results are available 2
- If CTA demonstrates significant iliac or femoral disease affecting potential endovascular access, then targeted arterial duplex may provide additional hemodynamic information 2
Venous Duplex:
- Venous studies are generally not indicated for evaluating suspected AAA unless there is a separate clinical indication (e.g., leg swelling, suspected DVT) 1
Clinical Algorithm for This Patient:
Immediate: Order CTA abdomen/pelvis with IV contrast including run-off to iliofemoral vessels 1, 2
If CTA confirms AAA:
After CTA results: Consider ABI and selective arterial duplex based on CTA findings and treatment planning needs 2, 3
Critical Pitfalls to Avoid:
Do not start with ultrasound in this symptomatic patient—while US is excellent for screening asymptomatic patients, it underestimates aneurysm size by 4 mm compared to CTA and cannot adequately assess for rupture or iliac involvement 1
Do not delay CTA to obtain ABI or duplex studies first—the combination of pain and bulging requires urgent definitive anatomic imaging 1, 4
Do not order CT without contrast—while non-contrast CT can detect AAA, it cannot assess for dissection, thrombus characteristics, or branch vessel involvement that are critical for management decisions 1
Ensure the scan includes iliofemoral vessels—failing to image the full extent of potential disease can miss critical information for endovascular access planning 2
Special Consideration:
If the patient has renal insufficiency precluding IV contrast, then MR angiography (MRA) with IV contrast is an acceptable alternative, though non-contrast MRA techniques have limitations including longer acquisition times 2, 5