What is the best imaging choice for diagnosing thoracic outlet obstruction?

Imaging Choice for Thoracic Outlet Obstruction

The best initial imaging for thoracic outlet syndrome is chest radiography to identify osseous abnormalities, followed by modality-specific advanced imaging: CTA/MRA for arterial TOS, CTV/MRV for venous TOS, and MRI without contrast for neurogenic TOS. 1

Initial Imaging Approach

• Chest radiography should be performed first to identify cervical ribs, first rib anomalies, or other congenital osseous malformations that account for approximately 36% of TOS cases 1
• This simple initial study establishes whether a bony etiology exists before proceeding to more complex vascular or neurogenic imaging 1

Advanced Imaging Based on TOS Subtype

Arterial TOS (aTOS)

• CTA with IV contrast is the preferred modality for evaluating subclavian artery compression 1
• MRA serves as an alternative, particularly when iodinated contrast is contraindicated 1
• Imaging must be performed in both neutral and stressed (arm abducted) positions to demonstrate dynamic compression 2
• Contrast injection should be performed in the contralateral arm to avoid artifact 2
• Multiplanar reformations evaluate the thoracic space and demonstrate true axial vessel compression 2

Venous TOS (vTOS)

• CTV with IV contrast or MRV are the primary choices for evaluating subclavian vein compression 1
• US duplex Doppler provides real-time assessment and can demonstrate compression during provocative maneuvers 1
• CTV is obtained 120-180 seconds after IV contrast injection in each arm position separately 2
• Critical caveat: Venous compression during arm abduction occurs in both asymptomatic and symptomatic individuals, making clinical correlation absolutely essential to avoid overdiagnosis 1

Neurogenic TOS (nTOS)

• MRI without IV contrast is sufficient for diagnosing neurogenic TOS and is the preferred modality 1
• High-resolution T1-weighted and T2-weighted sequences in sagittal and axial planes delineate the brachial plexus, muscular attachments, and compression sites 2
• Imaging in both neutral and arms-abducted positions demonstrates effacement of fat adjacent to brachial plexus roots, trunks, or cords within the interscalene triangle or costoclavicular space 2
• T1-weighted imaging identifies causative lesions including cervical ribs, congenital fibromuscular anomalies, and muscular hypertrophy 2
• Turbo spin-echo T2-weighted or short tau inversion recovery sequences help exclude alternative diagnoses like brachial plexitis or spinal cord lesions 2

Dynamic Imaging Protocols

MRA/MRV Technique

• Contrast-enhanced 3D MRA/MRV can be performed at 1.5T or 3T with breath-hold arterial and equilibrium phase imaging 2
• A coronal oblique 3D slab covers bilateral subclavian and axillary vessels 2
• Unenhanced mask imaging is followed by multiphase contrast-enhanced dynamic acquisition 2
• 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 2

CTA/CTV Technique

• Studies must be tailored specifically to the thoracic outlet, distinct from upper extremity protocols that extend to the wrist 2
• Center-line and volume-rendered images aid visualization of compression points 2

Common Pitfalls to Avoid

• Do not diagnose vTOS based solely on imaging compression during arm abduction, as this finding is common in asymptomatic individuals 1
• Imaging confirmation of a specific anatomical etiology (bony tubercle, clavicle fracture, cervical rib, first rib abnormality) is necessary to establish true pathology 1
• Dynamic compression showing increased velocity or monophasic flow during provocative maneuvers is common and does not necessarily indicate pathology requiring intervention 1
• Do not overlook concomitant cervical spine pathology that may mimic or exacerbate TOS symptoms 1
• Recognize that MRI sensitivity and specificity for TOS are limited (41% and 33% respectively in one surgical correlation study), emphasizing that imaging must support rather than replace clinical diagnosis 3

Anatomical Spaces to Evaluate

All imaging protocols should assess the three key compression sites:

• Interscalene triangle: Between anterior and middle scalene muscles 1
• Costoclavicular space: Between clavicle, first rib, and subclavius muscle 1
• Pectoralis minor space (subpectoral tunnel): Though rare, this can cause chest and axillary symptoms 1