What is the best US (ultrasound) order to rule out thoracic outlet obstruction?

Best Ultrasound Order to Rule Out Thoracic Outlet Obstruction

Order a duplex Doppler ultrasound of the subclavian artery and vein with dynamic provocative maneuvers (neutral and arm abduction positions). This is the recommended first-line imaging test for evaluating thoracic outlet syndrome, as it is non-invasive, allows real-time assessment of vascular compression, and can effectively identify both arterial and venous pathology 1, 2, 3.

Initial Imaging Strategy

Chest Radiography First

• Always begin with plain chest radiography to identify osseous abnormalities that commonly cause TOS, including cervical ribs, first rib anomalies, congenital osseous malformations, and focal bone lesions 1, 2, 3.
• Chest X-rays are particularly valuable because osseous structures are frequently the underlying cause and are easily diagnosed with this simple test 1.

Duplex Doppler Ultrasound Protocol

• The ultrasound must be performed in both neutral position and with provocative maneuvers (typically arm abduction to 90-180 degrees) to demonstrate dynamic compression 2, 3, 4.
• For venous TOS, look for flow acceleration, turbulence, arrest in signal propagation, complete cessation of blood flow, or loss of atrial and respiratory dynamics in the subclavian vein waveform with hyperabduction 3, 4.
• For arterial TOS, diagnostic findings include at least a doubling of peak systolic velocity, complete cessation of flow with hyperabduction, decrease in arterial diameter, or changes in peak velocity 1, 4.
• The subclavian and axillary vessels can be directly visualized for aneurysmal change, arterial stenosis, and thrombosis 1.

Diagnostic Accuracy and Limitations

Sensitivity and Specificity

• When using criteria of subclavian vein clot or compression causing complete loss of normal venous phasicity with arm abduction, duplex sonography is 92% sensitive and 95% specific for diagnosing TOS 4.
• Ultrasound allows evaluation of the cross-sectional area of the costocervical space and can assess real-time changes in blood flow during provocative maneuvers 1, 2.

Critical Pitfalls to Avoid

• Venous compression during arm abduction is commonly seen in asymptomatic individuals (10% for veins, 20% for arteries in one study), making clinical correlation absolutely essential 2, 4.
• One study found 71% of patients with unilateral venous compression had significant bilateral compression on imaging, but only 21% had bilateral symptoms 3.
• Do not diagnose TOS based on imaging findings alone—symptoms must correlate with the imaging abnormalities 2, 3.
• Ultrasound may miss deeper pathology such as cervical spondylopathy, Pancoast tumor, or compression in the pectoralis minor space, which require further imaging 1, 2.

When to Proceed to Advanced Imaging

For Arterial TOS (aTOS)

• If ultrasound demonstrates arterial compression, proceed to CTA with IV contrast, MRA without and with IV contrast, or catheter arteriography for definitive anatomical evaluation and surgical planning 1, 2.
• These modalities are considered equivalent alternatives for aTOS evaluation 1.

For Venous TOS (vTOS)

• If ultrasound shows venous thrombosis or significant compression, consider catheter venography (gold standard when intervention is planned), CT venography, or MR venography 1, 3.
• Catheter venography should be performed with contrast injection during digital subtraction acquisition in both neutral and stressed positions 3.
• True vTOS is confirmed by finding venous thrombosis and collateral circulation in both neutral and stressed positions, representing objective findings of clinically significant compression 3.

For Neurogenic TOS (nTOS)

• Ultrasound is not the primary modality for neurogenic TOS 1.
• MRI without IV contrast is sufficient to diagnose nTOS and can demonstrate compression of neurovascular bundles in the costoclavicular, interscalene, and pectoralis minor spaces 2.

Algorithmic Approach

1. Start with chest radiography to identify bony abnormalities 1, 2, 3
2. Perform duplex Doppler ultrasound of subclavian artery and vein with dynamic maneuvers 1, 2, 3
3. If ultrasound is positive and correlates with symptoms:
   • For arterial findings: proceed to CTA, MRA, or arteriography 1, 2
   • For venous findings: proceed to catheter venography, CTV, or MRV 1, 3
   • For suspected neurogenic TOS: proceed to MRI without contrast 2
4. If ultrasound is negative but clinical suspicion remains high, consider MRI to evaluate for deeper pathology or neurogenic causes 1, 2