What part of the body is imaged with MRI for thoracic outlet syndrome evaluation?

MRI Evaluation of Thoracic Outlet Syndrome

For thoracic outlet syndrome evaluation, MRI should include the brachial plexus, thoracic outlet, and subclavian vessels in both neutral and arms-abducted positions. 1

Anatomical Coverage for TOS MRI

MRI evaluation of thoracic outlet syndrome requires comprehensive imaging of:

• Brachial plexus - from cervical spine to axilla
• Thoracic outlet spaces:
  • Interscalene triangle
  • Costoclavicular space
  • Retropectoralis minor space
• Subclavian vessels (artery and vein)
• Cervical spine (to rule out cervical radiculopathy)

MRI Protocol Components

The American College of Radiology recommends the following protocol elements 1, 2:

• High-resolution T1-weighted and T2-weighted sequences in sagittal and axial planes
• Images obtained in both neutral and arms-abducted positions
• T2-weighted or STIR sequences to evaluate for alternative diagnoses
• Contrast-enhanced 3D MR angiography (MRA) and MR venography (MRV) in cases of suspected vascular TOS

Key Imaging Findings

• T1-weighted imaging in abducted position may show effacement of fat adjacent to brachial plexus components
• Sagittal and axial T1-weighted images can demonstrate causative lesions including:
  • Cervical ribs
  • Congenital fibromuscular anomalies
  • Muscular hypertrophy 1

Diagnostic Approach by TOS Type

Different types of TOS require specific focus during MRI evaluation:

1. Neurogenic TOS (most common, 69%) 3:

   • Focus on brachial plexus compression (particularly lower trunk)
   • Evaluate for anatomic anomalies affecting the brachial plexus

2. Venous TOS (66%) 3:

   • MR venography in neutral and abducted positions
   • Assess for subclavian vein compression or thrombosis

3. Arterial TOS (39%) 3:

   • MR angiography in neutral and abducted positions
   • Evaluate for subclavian artery compression

Clinical Relevance

MRI with dynamic positioning is essential because:

• Compression may only be evident during arm abduction
• It allows visualization of all potential sites of compression
• It helps differentiate TOS from other conditions with similar symptoms 2

Common Pitfalls to Avoid

• Inadequate positioning: Failure to image in both neutral and stressed positions may miss dynamic compression
• Limited field of view: Not including the entire course from cervical spine to axilla
• Overlooking cervical spine pathology: Cervical spondylosis may contribute to TOS symptoms in 14% of cases 3
• Not performing vascular sequences: When vascular TOS is suspected, dedicated MRA/MRV is necessary

Comparison with Other Imaging Modalities

While chest radiography and ultrasound have roles in TOS evaluation, MRI provides comprehensive assessment of all neurovascular structures and potential sites of compression 2. For definitive vascular evaluation, catheter venography remains the gold standard for venous TOS, though it is more invasive than MRI 2.