What is the recommended imaging modality for suspected aortic dissection?

Recommended Imaging for Suspected Aortic Dissection

Computed tomography (CT) is the recommended first-line imaging modality for suspected aortic dissection due to its wide availability, accuracy, speed, and comprehensive anatomic detail. 1

Primary Imaging Options

• CT angiography (CTA) is the preferred initial diagnostic test for suspected aortic dissection with excellent diagnostic accuracy (pooled sensitivity 100%, specificity 98%) 1
• Transesophageal echocardiography (TEE) is a reasonable alternative when CT is contraindicated or unavailable, particularly in unstable patients who cannot be transported to radiology 1
• Magnetic resonance imaging (MRI) is another reasonable alternative with high accuracy but is limited by longer acquisition times and challenges in monitoring unstable patients 1

Advantages of CT for Aortic Dissection

• Provides rapid image acquisition and processing with widespread 24/7 availability in emergency settings 1
• Shows the full extent of dissection, entry tear sites, and branch vessel involvement 1
• Detects complications including:
  • Malperfusion syndromes 1
  • Pericardial effusion and hemopericardium 1
  • Periaortic or mediastinal hematoma 1
  • Pleural effusion 1
• Allows visualization of the entire aorta and branch vessels in a single examination 1
• Can identify alternative diagnoses in patients without aortic pathology 1

Optimal CT Protocol

• ECG-gated acquisition is crucial 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
• High-end multidetector CT scanners (16 detectors or higher) are preferred for better spatial and temporal resolution 1
• Scan field should extend from thoracic inlet to femoral arteries to assist in planning surgical or endovascular repair 1

When to Consider Alternative Imaging

• TEE should be considered when:

  • Patient has contraindication to iodinated contrast 1
  • Patient is too unstable to transport to radiology 1
  • Rapid bedside assessment is needed 1
  • Additional information about cardiac and aortic valve function is required 1

• MRI should be considered when:

  • Patient is stable but has contraindication to iodinated contrast 1
  • Follow-up imaging is needed (reduces radiation exposure) 1
  • Diagnostic uncertainty exists after initial imaging 1

Pitfalls and Limitations

• CT requires administration of iodinated contrast, which may cause allergic reactions or renal failure 1
• Radiation exposure (10-15 mSv range) limits use in young patients, especially women, and for serial follow-up 1
• Motion artifacts can create false positives, particularly in the ascending aorta 1, 2
• TEE has a "blind spot" in the distal ascending aorta due to interposition of the right bronchus and trachea 1
• Plain chest x-ray is neither sufficiently sensitive nor specific for definitive diagnosis of aortic dissection 1

Diagnostic Accuracy Comparison

• All three modalities (CT, TEE, MRI) have comparable high sensitivity and specificity 3
• CT: sensitivity 93-100%, specificity 95-98% 1, 3
• TEE: sensitivity 88-98%, specificity 95-98% 1, 3
• MRI: sensitivity 98-100%, specificity 95-98% 3

The choice of imaging modality should ultimately be guided by patient stability, institutional availability, and specific clinical questions, but CT remains the first-line recommendation for most patients with suspected aortic dissection 1.