What is the recommended MRI for a patient with a left aortic arch and an aberrant right subclavian artery?

MRI Recommendation for Left Aortic Arch with Aberrant Right Subclavian Artery

For patients with a left aortic arch and an aberrant right subclavian artery, a dedicated cardiovascular magnetic resonance (CMR) study is recommended to evaluate for associated thoracic aortic aneurysm and to assess the presence and size of any Kommerell's diverticulum. 1, 2

Rationale for CMR Imaging

CMR offers several advantages for evaluating this aortic arch anomaly:

• Provides comprehensive assessment of vascular anatomy without ionizing radiation
• Allows visualization of potential Kommerell's diverticulum (present in 20-60% of cases)
• Enables measurement of critical diameters that guide treatment decisions:
  • Diverticulum orifice diameter
  • Combined diameter of diverticulum and adjacent descending aorta
• Permits evaluation of tracheal and esophageal compression
• Allows assessment of flow dynamics to both lungs

Key Measurements and Findings to Assess

When performing CMR for a patient with left aortic arch and aberrant right subclavian artery, the following should be specifically evaluated:

1. Presence and size of Kommerell's diverticulum - critical for determining need for intervention 1, 2

   • Measure diverticulum orifice diameter (radially and longitudinally at the aortic wall)
   • Measure combined diameter of diverticulum and adjacent descending aorta

2. Evidence of thoracic aortic aneurysm - left aortic arch with aberrant right subclavian artery is significantly associated with thoracic aortic dissection in 2-8% of patients 1

3. Compression of adjacent structures:

   • Tracheal compression
   • Esophageal compression (which may cause dysphagia)

4. Course of the aberrant vessel - typically retroesophageal 1

Clinical Implications and Management

The findings from CMR directly guide management decisions:

• No intervention needed if:

  • No Kommerell's diverticulum present
  • Diverticulum orifice <3.0 cm
  • Combined diameter of diverticulum and adjacent descending aorta <5.0 cm
  • Patient is asymptomatic

• Surgical intervention recommended when:

  • Diverticulum orifice >3.0 cm
  • Combined diameter of diverticulum and adjacent descending aorta >5.0 cm
  • Significant symptoms present (dysphagia, respiratory symptoms)

Important Considerations

• CMR is preferred over CT in younger patients to avoid radiation exposure 1
• 3D reconstruction capabilities of CMR are valuable for surgical planning 1
• Regular follow-up imaging is recommended to monitor for development or enlargement of Kommerell's diverticulum 2
• Patients with aberrant subclavian arteries should be referred to a cardiovascular surgeon or interventional radiologist for evaluation if symptomatic or if associated with Kommerell's diverticulum 2

Pitfalls to Avoid

• Failure to obtain adequate imaging of the entire thoracic aorta when an aberrant subclavian artery is discovered
• Inadequate measurement technique for Kommerell's diverticulum
• Missing associated congenital cardiac anomalies that may be present
• Overlooking compression of adjacent structures that may cause symptoms