Thoracic Aortic Aneurysms Are Readily Detected on Chest CT
Yes, thoracic aortic aneurysms will show up on chest CT scans, and they are commonly detected as incidental findings on imaging performed for other indications. 1
Detection Rates and Diagnostic Performance
Aortic disease is incidentally detected on chest CT in up to 3.4% of cases, with 21 of 22 incidentally detected aortic findings being aneurysms in one large series. 1
CT demonstrates 92% accuracy for diagnosing thoracic aortic abnormalities, including aneurysms, ruptured aneurysms, penetrating ulcers, dissections, and pseudoaneurysms. 1
Even non-contrast CT can identify the size and extent of aortic aneurysms, though it has limitations compared to contrast-enhanced studies. 1
What CT Shows
Aneurysmal dilation is the most common abnormality detected, particularly on non-contrast CT. 1 The imaging reveals:
Aortic diameter measurements - An aneurysm is defined as approximately 5.0 cm for the ascending aorta and 4.0 cm for the descending aorta (150% of normal diameter). 1
Anatomic location - Whether the aneurysm involves the ascending aorta, aortic arch, or descending thoracic aorta. 1
Mural thrombus - CT's advantage over traditional angiography is that it visualizes the aortic wall and any thrombus, not just the contrast-filled lumen. 2
Aortic wall calcification - Helpful for identifying the vessel and assessing disease chronicity. 2
Important Limitations to Recognize
Without intravenous contrast, aortic dissections and significant ulcerations are usually undetectable. 1 This is a critical pitfall:
Non-contrast CT will show the aneurysm size but cannot adequately assess the aortic lumen or detect acute complications like dissection. 1
For comprehensive evaluation including treatment planning, CT angiography (CTA) with IV contrast is the reference standard, providing near 100% sensitivity and 98% specificity for thoracic aortic pathology. 3, 4
CTA allows for 3D reconstruction and precise measurements perpendicular to the flow lumen, which is essential for surgical or endovascular planning. 1, 3, 4
Clinical Significance
Aneurysms measuring 5.5 cm or larger place patients at high risk for rupture and should be considered for intervention. 1 For patients with connective tissue disorders like Marfan or Ehlers-Danlos syndrome, intervention is considered at 5.0 cm. 1
If an aneurysm is detected incidentally on routine chest CT, the radiologist should report the anatomic location and precise diameter measurements to guide clinical management. 1 Diameters between normal and aneurysmal are termed "dilated" or "ectatic" and also warrant reporting. 1
When to Upgrade Imaging
If a chest CT (with or without contrast) detects an aortic aneurysm, order a dedicated CTA chest with ECG-gating for definitive characterization, particularly for the ascending aorta where cardiac motion can affect measurements. 3, 4 This provides the detailed anatomic information needed for surveillance intervals and treatment decisions. 1, 3, 4