What is the most advisable position in arterial thoracic outlet syndrome (TOS)?

Imaging Position for Arterial Thoracic Outlet Syndrome

For arterial thoracic outlet syndrome (aTOS), imaging must be performed in both neutral and elevated arm (abducted) positions to demonstrate dynamic arterial compression, as this dual-position approach is essential for accurate diagnosis. 1

Specific Positioning Protocol

Neutral Position

• Obtain baseline images with the arm at the patient's side in anatomic position to assess for fixed stenosis, aneurysm, or mural thrombus 1
• This position establishes whether there is intrinsic arterial pathology independent of dynamic compression 1

Elevated/Abducted Arm Position

• Position the arm in abduction (typically 90 degrees or greater) to provoke and demonstrate dynamic arterial compression 1
• This stressed position reveals compression of the subclavian artery as it passes through the thoracic outlet, particularly around the anterior scalene muscle 1
• If no compression is evident on abducted images, imaging in the neutral position may be deferred 1

Critical Technical Considerations

Imaging Modality-Specific Positioning

For CTA (CT Angiography):

• Perform separate acquisitions in neutral and elevated arm positions 1
• Use sagittal reformations rather than relying solely on axial slices, as axial views underestimate stenosis in 43% of cases versus only 10% with sagittal reformations 1, 2
• Inject contrast in the contralateral arm to avoid artifact 3

For MRA (MR Angiography):

• Acquire images in both neutral and arms-abducted positions 1
• Combine T1-weighted imaging in sagittal and axial planes with contrast-enhanced MRA for optimal assessment 1
• Longer acquisition times may prove difficult for highly symptomatic patients during provocative positioning 1

For Catheter Arteriography:

• Perform injections and digital subtraction angiographic acquisitions in both neutral and abducted positions to assess dynamic changes 1
• This approach locates the exact point of vascular compression 1

Diagnostic Findings by Position

What to Look For in Each Position

• Neutral position findings: Fixed stenosis, complete occlusion, aneurysmal dilation, mural thrombus, or distal emboli 1
• Abducted position findings: Dynamic compression with indentation of the anterior wall of the subclavian artery, displacement of subclavian vessels, and percentage reduction in cross-sectional area or diameter 1
• A statistically significant difference in measured distances between neutral and abducted positions distinguishes patients with arterial stenosis from those without 1

Common Pitfalls to Avoid

• Do not rely on axial slices alone - this leads to underestimation of stenosis in 43% of cases 1, 2
• Do not skip the provocative positioning - compression may only be evident during arm elevation, and missing this dynamic component can result in false-negative studies 1
• Avoid evaluating studies without vascular workstations - volume-rendered images and sagittal reformations are essential for accurate assessment 1
• Do not use noncontrast time-of-flight MRA techniques - these suffer from flow artifacts causing false-positive stenosis 3