Diagnosing Thoracic Aortic Aneurysm with CT Angiography

Rationale for CT with Contrast

The American College of Radiology recommends CT angiography (CTA) with intravenous contrast as the preferred imaging modality for diagnosing thoracic aortic aneurysm, providing critical information about the aortic lumen, wall, and surrounding structures 1, 2
CTA is considered the reference standard for aortic aneurysm diagnosis and management decision-making, providing high-resolution images that allow for accurate measurement and characterization 2, 3
Contrast enhancement is essential as it allows visualization of the aortic lumen, which cannot be adequately assessed with non-contrast studies 3
CTA provides a 3D dataset that can be reconstructed in multiple planes, allowing for precise measurement of the aneurysm perpendicular to the flow lumen 3

Electrocardiogram (ECG) gating is particularly valuable for imaging the ascending aorta to minimize cardiac motion artifacts and ensure accurate measurements 5, 6
CTA protocols for aortic pathology typically include arterial and delayed contrast phases for comprehensive evaluation 6
The scan range should include the entire thoracic aorta and may be extended to include the abdomen and pelvis if there is concern for extension of disease 5, 7
3D rendering is a required element of CTA, allowing for detailed visualization of the aneurysm and its relationship to branch vessels 1

In patients with renal insufficiency where contrast is contraindicated, MR angiography (MRA) is an alternative with similar sensitivity and specificity to CTA 1, 4
For patients with known intramural hematoma (IMH), a dual-phase protocol including both non-contrast and contrast-enhanced images may improve diagnostic accuracy 5, 6
Dual-energy CT allows for virtual non-contrast images that can help visualize intramural hematoma while reducing overall radiation exposure 5

CTA not only diagnoses the aneurysm but also provides critical information for treatment planning, including relationship to branch vessels and suitability for endovascular repair 3, 7
Measurements should be made perpendicular to the long axis of the aorta (outer-to-outer wall) for standardized evaluation 8
CTA allows for assessment of complications such as rupture, dissection, or thrombus formation that may affect management decisions 2, 3