What is the best initial imaging test to rule out aortic dissection?

Computed Tomography (CT) is the Best Initial Imaging Test for Aortic Dissection

Computed tomography (CT) angiography is the recommended first-line imaging modality for suspected aortic dissection due to its wide availability, rapid acquisition, and excellent diagnostic accuracy with sensitivity of 100% and specificity of 98%. 1

Rationale for CT as First-Line Test

• CT provides comprehensive anatomic detail with rapid image acquisition and processing, allowing for quick diagnosis and treatment in emergency settings 1
• CT demonstrates the full extent of dissection, entry tear sites, and branch vessel involvement, which is crucial for planning surgical or endovascular repair 1
• Modern multidetector CT scanners can image the entire aorta, including lumen, wall, and periaortic regions, with exceptional diagnostic performance 2
• In the International Registry of Aortic Dissection (IRAD), CT was the most commonly used first diagnostic step (61% of cases) 3
• CT can detect complications including malperfusion syndromes, pericardial effusion, hemopericardium, periaortic or mediastinal hematoma, and pleural effusion 1

Optimal CT Protocol

• ECG-gated acquisition is recommended to reduce motion artifacts of the aortic root and thoracic aorta 1
• Non-enhanced CT followed by contrast-enhanced angiography is the recommended protocol, particularly for suspected intramural hematoma (IMH) or aortic dissection 1
• Multidetector CT allows early recognition and characterization of aortic dissection as well as determination of associated complications 4

Alternative Imaging Options

Transesophageal Echocardiography (TEE)

• TEE is a reasonable alternative when CT is contraindicated or unavailable, particularly in unstable patients who cannot be transported to radiology 1
• TEE combines high sensitivity and specificity with high practicality, especially in hemodynamically unstable patients requiring rapid bedside imaging 5
• However, TEE has limitations in visualizing the distal ascending aorta and proximal arch due to the "blind spot" created by interposition of the trachea and left main stem bronchus 2

Magnetic Resonance Angiography (MRA)

• MRA demonstrates excellent sensitivity (92-98%) and specificity (100%) for diagnosing aortic dissection 6
• MRA clearly demonstrates the extent of aortic dissection and depicts the distal ascending aorta and aortic arch in more detail than TEE 6
• MRA can accurately assess adverse signs such as pericardial effusion and aortic regurgitation 6
• However, MRA is often not available on an emergency basis, limiting its use in acute settings 6
• MRA should be considered when a patient is stable but has a contraindication to iodinated contrast, or when follow-up imaging is needed to reduce radiation exposure 1

Clinical Considerations and Pitfalls

• The decision for a specific technique depends on availability in emergency situations and experience of the emergency room and imaging staff 3
• Using multiple imaging techniques (2-3) to diagnose aortic dissection is excessive and can lead to unnecessary time loss 3
• CT requires administration of iodinated contrast, which may cause allergic reactions or renal failure 1
• Radiation exposure from CT limits its use in young patients, especially women, and for serial follow-up 1
• When the probability of dissection is high, physicians must consider delays in obtaining specific diagnostic tests and order those that will be most quickly available 7

Diagnostic Goals in Aortic Dissection Imaging

• Confirm diagnosis and classify the dissection/delineate the extent 3
• Differentiate true and false lumen 3
• Localize intimal tears 3
• Distinguish between communicating and non-communicating dissection 3
• Assess side branch involvement (including coronary arteries) 3
• Detect and grade aortic regurgitation 3
• Detect extravasation (periaortic or mediastinal hematoma, pleural or pericardial effusion) 3