What is the diagnostic workup for thoracic outlet syndrome?

Diagnostic Workup for Thoracic Outlet Syndrome

The diagnostic workup for thoracic outlet syndrome should begin with chest radiography as the initial imaging modality, followed by MRI of the chest for neurogenic TOS, or appropriate vascular studies (duplex ultrasound, CTA/MRA) for vascular forms of TOS. 1

Initial Evaluation

• Chest radiography should be performed first to identify osseous abnormalities associated with TOS, including first rib anomalies, cervical ribs, congenital osseous malformations, and focal bone lesions 2
• Radiographs can identify bony abnormalities but have low negative predictive value, making cross-sectional imaging necessary for complete evaluation 2
• TOS can be classified into three main types that require different diagnostic approaches 1:
  • Neurogenic TOS (nTOS) - 95% of cases 3
  • Venous TOS (vTOS) - 4-5% of cases 3
  • Arterial TOS (aTOS) - 1% of cases 3

Neurogenic TOS Workup

• MRI of the chest is the preferred imaging modality for neurogenic TOS due to its superior ability to delineate extravascular anatomy and differentiate soft tissues 2
• MRI should include:
  • Evaluation of the brachial plexus and cervical spine 2
  • Dynamic assessment with neutral and provocative positions to evaluate neurovascular bundles in the costoclavicular, interscalene, and pectoralis minor spaces 2, 1
• CT with IV contrast can be used if MRI is contraindicated, allowing visualization of anatomical narrowing and quantification of changes in costoclavicular or interscalene spaces with provocative maneuvers 2
• Ultrasound can evaluate the cross-sectional area of the costocervical space with and without provocative maneuvers but has limitations in directly assessing neurological involvement 2

Venous TOS Workup

• Duplex ultrasound is recommended as the first-line imaging test for vTOS 4
• Ultrasound should be performed in both neutral position and with provocative maneuvers to assess for flow acceleration, turbulence, and signal arrest 4
• CT venography (CTV) provides excellent anatomical evaluation and should be performed in neutral and elevated arm positions 4
• MR venography (MRV) offers superior soft tissue contrast and should be performed in both neutral and arms-abducted positions 4
• Catheter venography is the gold standard for definitive diagnosis when intervention is being considered 4

Arterial TOS Workup

• CTA with IV contrast, MRA, or duplex Doppler ultrasound are recommended for arterial TOS diagnosis 1
• Dynamic CT angiography can assess the degree of arterial stenosis with the following grading system: grade 1 (0-<25%), grade 2 (25-<50%), grade 3 (50-<75%), grade 4 (75-100%) 5

Diagnostic Pitfalls and Considerations

• Imaging findings must be correlated with clinical symptoms, as venous compression during arm abduction is common in asymptomatic individuals 4, 6
• TOS is not a diagnosis of exclusion - there should be evidence for a physical anomaly that can be corrected 7
• Consider deeper pathology such as Pancoast tumor or cervical spondylopathy that may mimic TOS symptoms 2, 4
• In neurogenic TOS, the neurovascular bundle is most commonly compressed in the costoclavicular space (63%), followed by the interscalene triangle (37%) 5

Algorithmic Approach to TOS Diagnosis

1. Start with chest radiography to identify osseous abnormalities 2
2. Based on predominant symptoms, proceed with:
   • For neurogenic symptoms: MRI chest (without and with contrast) 2, 1
   • For venous symptoms: Duplex ultrasound followed by CTV/MRV if needed 4
   • For arterial symptoms: CTA, MRA, or duplex Doppler ultrasound 1
3. Perform imaging in both neutral and provocative positions to assess dynamic compression 1, 4
4. Correlate imaging findings with clinical symptoms before making definitive diagnosis 4, 6