Imaging of Iliac Arteries in Patients with Abdominal Aortic Aneurysm

Rationale for Iliac Artery Imaging

A faint femoral pulse in a patient with known abdominal aortic aneurysm (AAA) suggests possible extension of aneurysmal disease or stenotic/occlusive disease in the iliac arteries, which could significantly impact treatment planning and patient outcomes 1
Approximately 5% of AAAs are juxtarenal or suprarenal, and iliac artery involvement is common in AAA patients, making comprehensive imaging essential 2
The American College of Radiology recommends that imaging of the iliac arteries should be included when evaluating AAA patients due to the close correlation between aortic and iliac pathology 3

The American College of Radiology considers CT angiography (CTA) the optimal choice for pre-intervention studies and the reference standard for AAA diagnosis and management decision-making 4
CTA provides high-resolution imaging of the aorta and its branch vessels with submillimeter, isotropic, 3-D datasets that allow for accurate assessment of both the AAA and iliac arteries 4
The scan range should include the iliofemoral arteries to evaluate access vessels, which is particularly important given the faint femoral pulse finding 4
CTA allows for proper measurement of the outer-to-outer (OTO) aortic diameter perpendicular to the long axis of the aorta, which is the recommended measurement technique 4

If CTA is contraindicated, MR angiography (MRA) with IV contrast is an acceptable alternative for evaluating iliac arteries and AAA 2
Non-contrast MRA techniques are available for patients with renal insufficiency, though they have limitations including longer acquisition times and increased motion artifacts 4
Catheter arteriography has very limited utility and should only be considered when both CTA and MRA are contraindicated 1

Relying solely on ultrasound may lead to underestimation of aneurysm size and inadequate visualization of iliac arteries 1
Failing to use multiplanar reformatted images for tortuous aneurysms can result in artifactual accentuation of a single dimension 2
Not including the full extent of the iliofemoral system in imaging studies can miss critical information about access vessels for potential endovascular repair 4

The American College of Radiology recommends ultrasound as the first-line imaging modality for diagnosing AAA in asymptomatic patients, while CT angiography (CTA) is the gold standard for pre-operative assessment and evaluation of symptomatic patients with suspected AAA 5, 6
Transabdominal US is the mainstay for AAA screening and surveillance with sensitivity and specificity approaching 100% 6
The American Institute of Ultrasound in Medicine recommends measuring the greatest diameter from outer-to-outer (OTO) edges of the aortic wall 6
US measurements typically underestimate AAA diameter compared to CT by 1-3 mm 6

CTA is considered the reference standard for AAA diagnosis and management decision-making 7
Indications for CTA include symptomatic patients with acute onset abdominal or back pain, pre-operative assessment before endovascular or open surgical repair, and when US evaluation is inadequate 7, 8
Outer-to-outer (OTO) aortic diameter perpendicular to the long axis of the aorta is recommended for measurement 7, 9
MR Angiography (MRA) is an alternative to CTA for diagnosis and pre-intervention evaluation, particularly for patients with contraindications to CTA 7, 10

For asymptomatic patients with risk factors, start with transabdominal US, and if US is inadequate, proceed to non-contrast CT 6, 7
For symptomatic patients, CTA is the preferred initial imaging modality, and if contrast is contraindicated, consider non-contrast CT or MRA 7, 10

The American College of Radiology recommends surveillance intervals based on AAA size: every 6 months for AAAs 4.5-5.4 cm, every 12 months for AAAs 3.5-4.4 cm, every 3 years for AAAs 3.0-3.4 cm, and every 5 years for AAAs 2.6-2.9 cm 11

Ensure proper measurement technique to avoid overestimation due to oblique measurements 7
Be aware that 5% of AAAs are juxtarenal or suprarenal, which may not be adequately visualized by US 8
For tortuous aneurysms, use multiplanar reformatted images to avoid artificial accentuation of a single dimension 8