What is the test of choice for diagnosing an aberrant right subclavian artery (ARSA) coursing posterior to the esophagus?

CT Angiography is the Test of Choice for Diagnosing Aberrant Right Subclavian Artery Coursing Posterior to the Esophagus

CT angiography (CTA) is the test of choice for diagnosing an aberrant right subclavian artery (ARSA) coursing posterior to the esophagus, as it provides excellent anatomic detail of vascular structures and their relationship to surrounding tissues. 1, 2

Diagnostic Approach

Primary Imaging Modality

• CTA offers superior visualization of the aberrant vessel, its origin from the aortic arch, and its retroesophageal course 1, 3
• CTA allows for multiplanar reformations (sagittal, coronal) which are crucial for accurate assessment of the degree of stenosis and compression of surrounding structures 1
• Volume-rendered 3D reconstructions from CTA provide optimal simultaneous analysis of both vascular and bony structures 1

Alternative Imaging Options

• MRI/MRA is an excellent alternative when:
  • Radiation exposure is a concern
  • Detailed soft tissue evaluation is needed
  • The patient has contraindications to iodinated contrast 1
• MRA with contrast provides comprehensive assessment of both soft tissues and vascular structures, making it particularly valuable for evaluating compression of adjacent structures 1

Imaging Protocol Considerations

• For CTA:
  • Both axial images and multiplanar reformations should be evaluated, as reliance on axial slices alone can lead to misrepresentation of stenosis severity 1
  • Studies should be evaluated on dedicated vascular workstations for optimal assessment 1
• For MRA:
  • Imaging should be performed in both neutral and arms-abducted positions to assess for dynamic compression 1
  • T1-weighted imaging in sagittal and axial planes helps demonstrate causative lesions 1

Clinical Implications and Management

Diagnostic Yield

• CTA has been shown to have excellent correlation with operative findings in arterial compression syndromes 1
• CTA can accurately identify the presence of Kommerell's diverticulum, which occurs in 20-60% of patients with ARSA 1, 2

Management Considerations

• Once diagnosed, measurement of key diameters is essential for management decisions:
  • Diverticulum orifice (measured radially and longitudinally at the aortic wall)
  • Combined diameter of the diverticulum and adjacent descending thoracic aorta 2
• Intervention is recommended when:
  • The Kommerell's diverticulum orifice is >3.0 cm
  • The combined diameter of the diverticulum and adjacent descending aorta is >5.0 cm
  • The patient is symptomatic with dysphagia, respiratory symptoms, or recurrent laryngeal nerve palsy 1, 2

Important Anatomical Considerations

• ARSA is the most common aortic arch anomaly, occurring in approximately 0.5-2% of the population 4, 5
• In patients with ARSA, the aberrant vessel typically originates as the last branch of the aortic arch and courses behind the esophagus 5, 6
• Associated anomalies may include a common origin of the carotid arteries, right-sided thoracic duct, and non-recurrent right inferior laryngeal nerve 4

Clinical Correlation

• The distance between the ARSA and trachea correlates with symptoms - patients with dysphagia typically have a smaller distance (median 4mm vs 7.5mm in asymptomatic patients) 3
• The lumen area of the ARSA at the level of the esophagus is typically larger in symptomatic patients (median 208mm² vs 108mm² in asymptomatic patients) 3

In conclusion, while multiple imaging modalities can detect ARSA, CT angiography provides the optimal combination of anatomic detail, multiplanar capabilities, and 3D reconstruction that makes it the test of choice for diagnosing this vascular anomaly and planning appropriate management.