What imaging modalities are recommended to rule out Thoracic Outlet Syndrome (TOS)?

Imaging to Rule Out Thoracic Outlet Syndrome

Initial Imaging Approach

Begin with chest radiography to identify osseous abnormalities such as cervical ribs, first rib anomalies, or congenital bone malformations, which are present in approximately 36% of TOS cases. 1, 2

• Chest X-ray serves as the essential first screening test but has limited sensitivity for definitive diagnosis 2, 3
• This identifies structural causes that may require surgical correction 1

Type-Specific Imaging Protocols

Neurogenic TOS (Most Common - 69% of Cases)

MRI of the chest without IV contrast is sufficient for diagnosing neurogenic TOS and should be performed in both neutral and arm-abducted positions. 1, 4

• High-resolution T1-weighted and T2-weighted sequences in sagittal and axial planes delineate the brachial plexus, muscular attachments, and compression sites 1
• Look for effacement of fat adjacent to brachial plexus roots, trunks, or cords within the interscalene triangle or costoclavicular space 1
• T1-weighted imaging identifies causative lesions including cervical ribs, congenital fibromuscular anomalies (11% of cases), and muscular hypertrophy 1, 4
• Turbo spin-echo T2-weighted or short tau inversion recovery sequences help exclude alternative diagnoses like brachial plexitis or spinal cord lesions 1
• Critical pitfall: Always evaluate the cervical spine, as severe cervical spondylosis contributes to TOS symptoms in 14% of cases and may mimic or exacerbate symptoms 1, 4

Venous TOS (66% of Cases)

Duplex ultrasound is the first-line imaging test for venous TOS due to its non-invasive nature and ability to perform dynamic maneuvers. 2

• Perform ultrasound in both neutral position and with provocative maneuvers (arm abduction), looking for flow acceleration, turbulence, and arrest in signal propagation 2
• Major pitfall: Venous compression during arm abduction occurs in 71% of asymptomatic individuals, so imaging findings must be correlated with clinical symptoms to avoid misdiagnosis 1, 2
• True venous TOS is confirmed by finding venous thrombosis and collateral circulation in both neutral and stressed positions 2

For definitive diagnosis when intervention is considered, catheter venography is the gold standard. 2

• Perform with contrast injection during digital subtraction acquisition in both neutral and stressed positions 2
• Contrast must be injected in the contralateral arm to avoid artifact 1

CT venography (CTV) provides excellent anatomical evaluation when ultrasound is inconclusive. 1, 2

• Obtain CTV 120-180 seconds after IV contrast injection in each arm position separately (neutral and elevated) 1
• Multiplanar reformations evaluate the thoracic space and demonstrate true axial vessel compression 1
• Look for venous compression, thrombosis, and collateral circulation 2

MR venography (MRV) offers superior soft tissue contrast compared to CT. 1, 2

• Use contrast-enhanced 3D MRV at 1.5T or 3T with breath-hold arterial and equilibrium phase imaging 1
• A coronal oblique 3D slab covers bilateral subclavian and axillary vessels 1
• Perform unenhanced mask imaging followed by multiphase contrast-enhanced dynamic acquisition 1
• Avoid noncontrast time-of-flight techniques as they suffer from flow artifacts causing false-positive stenosis or thrombosis and require prohibitively long acquisition times during postural maneuvers 1

Arterial TOS (39% of Cases)

CTA with IV contrast, MRA, or ultrasound duplex Doppler are appropriate for arterial TOS diagnosis. 1

• Look for fixed or dynamic stenosis, aneurysm, mural thrombus, or distal emboli 1
• Arterial changes include intimal damage and thrombosis with risk of distal embolization and aneurysm formation 1
• Digital ischemia or gangrene in severe cases can occur from distal emboli 1

For CTA, perform imaging in both neutral and stressed positions to demonstrate dynamic compression. 1

• Center-line and volume-rendered images aid visualization of compression points 1
• Studies must be tailored specifically to the thoracic outlet, distinct from upper extremity protocols that extend to the wrist 1

Critical Anatomical Spaces to Evaluate

All imaging protocols must assess three distinct anatomical spaces where compression occurs: 1, 4

• Costoclavicular space (most common compression site - positional in 53% of cases) 1, 4
• Interscalene triangle 1, 4
• Pectoralis minor space (subpectoral tunnel) - rarely compressed but relevant for chest and axillary symptoms 1, 4

Essential Technical Requirements

Dynamic imaging in both neutral and stressed (arm abducted 90 degrees) positions is mandatory to demonstrate compression. 1, 2, 4

• Static imaging alone is insufficient as compression is often positional 1
• Quantify changes in costoclavicular or interscalene spaces with provocative maneuvers 5

Common Diagnostic Pitfalls

• Do not rely on dynamic vascular compression alone as a diagnostic criterion - it can be seen in asymptomatic individuals and requires clinical correlation 1, 2, 6
• Do not overlook concomitant cervical spine pathology that may mimic or exacerbate TOS symptoms 1, 4
• Do not use CT or ultrasound alone for neurogenic TOS - these modalities lack resolution of neural structures 5, 1
• Ensure imaging confirmation of the etiology such as bony tubercle, clavicle fracture, congenital cervical rib, or first rib abnormality to establish true pathology 1