What is the best way to confirm a diagnosis of aortic dissection?

Confirming Diagnosis of Aortic Dissection

CT Angiography (CTA) with IV contrast is the recommended first-line imaging modality for confirming aortic dissection due to its high sensitivity (>95%) and specificity (>95%), wide availability, and rapid acquisition time. 1

Imaging Modalities for Aortic Dissection Diagnosis

CT Angiography (CTA)

• First-line recommendation: CTA chest with IV contrast
• Sensitivity: 93-100%
• Specificity: 98-100% 2
• Key diagnostic findings:
  • Visualization of intimal flap separating true and false lumen
  • Internal displacement of intimal calcifications
  • Delayed enhancement of false lumen
  • Aortic widening 2
• Advantages:
  • Rapid acquisition (critical in time-sensitive condition)
  • Widely available in emergency settings
  • Can assess branch vessel involvement
  • Can evaluate complications (pericardial effusion, mediastinal hematoma)
• Considerations:
  • For complete evaluation, CTA of chest, abdomen, and pelvis allows assessment of thoracic and abdominal aorta in a single acquisition 2
  • Adding non-contrast CT improves detection of intramural hematoma (IMH) 2

Transesophageal Echocardiography (TEE)

• Sensitivity: 99%
• Specificity: 89% 2, 1
• Best use case:
  • Hemodynamically unstable patients
  • When rapid bedside diagnosis is needed
  • In operating room for immediate surgical intervention
• Limitations:
  • "Blind spot" in distal ascending aorta and anterior arch due to trachea/bronchus interference
  • Requires experienced operators to avoid misinterpretation of artifacts 2

Magnetic Resonance Imaging (MRI)

• Sensitivity and Specificity: Approaching 100% 1
• Best use case:
  • Stable patients
  • Follow-up imaging
  • Patients with contrast allergy
• Limitations:
  • Limited availability in emergency settings
  • Longer acquisition time
  • Challenges with monitoring unstable patients 2

Transthoracic Echocardiography (TTE)

• Sensitivity: 59-80% 1
• Best use case:
  • Initial screening in unstable patients
  • Assessment of complications (aortic regurgitation, pericardial effusion)
• Limitations:
  • Limited sensitivity, especially for descending aorta
  • Should not be used to exclude aortic dissection 1

Diagnostic Algorithm

1. For stable patients with suspected aortic dissection:

   • Proceed directly to CTA chest with IV contrast (consider adding abdomen/pelvis)
   • If CTA is negative but clinical suspicion remains high, consider TEE or MRI as second-line test 3

2. For unstable patients with suspected aortic dissection:

   • Bedside TTE to assess for obvious dissection, pericardial effusion, or aortic regurgitation
   • If available quickly, proceed to TEE for definitive diagnosis
   • If TEE unavailable, proceed to CTA if patient can be stabilized for transport

3. For patients with contraindication to contrast:

   • MRI is preferred if patient is stable
   • Non-contrast CT combined with TEE if MRI unavailable

Important Diagnostic Considerations

• Time is critical: Mortality increases by 1-2% per hour in untreated aortic dissection 4
• False negatives can occur: Even with negative CTA, maintain high suspicion in patients with:
  • Ascending aortic aneurysm and acute chest pain
  • Pericardial effusion
  • Aortic regurgitation 5
• Differentiating true from false lumen:
  • True lumen: Typically smaller, with systolic expansion
  • False lumen: Often larger, may contain thrombus, delayed contrast enhancement 2
• Identifying intimal tears: Critical for planning intervention, visible in 61% of cases on TEE 2

Pitfalls to Avoid

1. Relying solely on TTE to exclude aortic dissection - insufficient sensitivity
2. Misinterpreting artifacts on TEE - reverberation artifacts in ascending aorta can mimic dissection flap
3. Overlooking intramural hematoma - may not show classic intimal flap
4. Delaying diagnosis for multiple imaging studies - choose the most rapidly available appropriate test
5. Missing branch vessel involvement - assess for malperfusion syndromes

In summary, CTA with IV contrast represents the optimal balance of accuracy, availability, and speed for diagnosing aortic dissection in most clinical scenarios, with TEE and MRI serving as valuable alternatives depending on specific clinical circumstances.