Neurologic Imaging

What Imaging Is Best for Suspected Arterial Thoracic Outlet Syndrome? An ACR Workflow

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What Imaging Is Best for Suspected Arterial Thoracic Outlet Syndrome? An ACR Workflow

A 24-year-old collegiate baseball pitcher presents to your clinic with right arm pain and fatigue that worsens during his wind-up and throwing motion. He reports his hand feels cold and looks pale after practice, and he’s noticed a diminished pulse at his right wrist compared to his left. You suspect extrinsic compression of the subclavian artery at the thoracic outlet, but you need to confirm the diagnosis, identify the cause, and assess for complications like aneurysm or thrombosis. What is the most appropriate initial imaging study to order?

This article provides a detailed clinical workflow for imaging suspected arterial thoracic outlet syndrome (aTOS), including follow-up after intervention, based on the American College of Radiology (ACR) Appropriateness Criteria. For this specific scenario, the ACR rates US duplex Doppler of the subclavian artery and vein as Usually Appropriate.

Who Fits the Clinical Scenario for Arterial Thoracic Outlet Syndrome?

This workflow applies to patients presenting with signs and symptoms of upper extremity arterial insufficiency, particularly when exacerbated by specific arm positions or activities. The classic presentation involves a young, athletic individual, but it can occur in anyone with anatomic predisposition.

Inclusion criteria for this scenario:

  • Symptoms of arm ischemia: exertional arm pain or claudication, pallor, coolness, paresthesias.
  • Physical exam findings suggesting arterial compromise: diminished or absent distal pulses (radial, ulnar), a bruit over the supraclavicular fossa, or reproduction of symptoms with provocative maneuvers (e.g., the Adson or Wright test).
  • Known or suspected aTOS requiring postoperative or post-interventional surveillance to assess graft patency or identify residual compression.

Exclusion criteria (route to a different workflow):

  • Purely Neurologic Symptoms: If the patient presents with pain, paresthesias, and weakness in a C8/T1 distribution without any signs of vascular compromise (normal pulses, color, and temperature), the primary concern is neurogenic thoracic outlet syndrome. This is the most common form of TOS and follows a different imaging pathway.
  • Arm Swelling and Cyanosis: If the dominant symptoms are arm swelling, cyanosis, and a feeling of heaviness, especially with activity, this points toward venous thoracic outlet syndrome (Paget-Schroetter syndrome), caused by subclavian vein compression and potential thrombosis.

What Diagnoses Are You Working Up in This Scenario?

When ordering imaging for suspected aTOS, you are evaluating a specific differential diagnosis centered on subclavian artery pathology. The goal is to confirm compression and rule out other serious vascular conditions.

Arterial Thoracic Outlet Syndrome (aTOS)
This is the primary diagnosis. It is the least common form of TOS but carries the most significant risk of limb-threatening complications. The subclavian artery is compressed as it passes through the thoracic outlet, typically between the anterior and middle scalene muscles, or between the clavicle and first rib. Chronic compression can lead to vessel wall damage, resulting in stenosis, post-stenotic dilatation, aneurysm formation, intraluminal thrombus, and distal embolization to the hand and digits. A common underlying cause is a congenital bony anomaly, such as a cervical rib.

Subclavian Artery Stenosis from Other Causes
While aTOS is due to extrinsic compression, intrinsic stenosis must be considered. In older patients, atherosclerosis is a primary concern. In younger patients, consider less common etiologies like large-vessel vasculitis (e.g., Takayasu arteritis) or fibromuscular dysplasia (FMD), which can affect the subclavian artery and its branches.

Proximal Embolic Source
Symptoms of acute limb ischemia in the arm could originate from a more proximal source. This includes emboli from the heart (e.g., in atrial fibrillation) or from atherosclerotic plaque in the aortic arch or brachiocephalic artery. Imaging helps differentiate this from a thrombus formed locally within a subclavian aneurysm caused by aTOS.

Why Is US Duplex Doppler the Recommended Initial Study for Arterial TOS?

The ACR designates US duplex Doppler of the subclavian artery and vein as Usually Appropriate for the initial evaluation of suspected aTOS. This non-invasive study provides a powerful combination of anatomic and functional information, making it the ideal first step.

The strength of duplex ultrasound lies in its dynamic capability. A sonographer can visualize the subclavian artery in real-time while the patient performs provocative maneuvers, such as abducting the arm. This allows for direct observation of arterial compression and measurement of blood flow velocity changes that indicate a hemodynamically significant stenosis. The study is highly effective at identifying key pathologic findings, including focal stenosis, post-stenotic dilatation, and aneurysm formation. It is non-invasive, widely available, and involves no ionizing radiation (0 mSv).

Why are other studies rated lower for initial evaluation?

  • CTA chest with IV contrast is also rated Usually Appropriate but is often reserved as a second-line or pre-operative planning tool. While it provides excellent anatomic detail of bony structures (like a cervical rib) and the vessel lumen, it is a static test and involves significant radiation (ACR RRL ☢☢☢ 1-10 mSv). It is less effective at demonstrating the dynamic, position-dependent nature of the compression.
  • Arteriography upper extremity, the traditional gold standard, is also Usually Appropriate but is an invasive procedure with risks of vessel injury and contrast-induced nephropathy. It is typically reserved for cases where intervention is planned or when non-invasive tests are inconclusive.

For a detailed overview of the technical performance of duplex imaging, including waveform analysis and diagnostic criteria, see our protocol guide. While the target vessel differs, the principles of duplex Doppler evaluation are similar to those detailed in our US Carotid Doppler protocol guide.

What’s Next After US Duplex Doppler? Downstream Workflow

The results of the initial ultrasound guide the subsequent clinical and imaging pathway. The decision tree branches based on whether the study is positive, negative, or indeterminate.

  • If the study is positive for aTOS: A positive result (e.g., demonstrating focal stenosis with provocative maneuvers, post-stenotic dilatation, or an aneurysm) confirms the diagnosis. The next step is typically a high-resolution, cross-sectional imaging study to delineate the anatomy for surgical planning. CTA chest with IV contrast is Usually Appropriate and is excellent for visualizing the bony anatomy (e.g., cervical rib, anomalous first rib) and the vascular tree in detail. This allows the surgical team to plan for decompression (e.g., first rib resection, scalenectomy) and any necessary vascular reconstruction (e.g., aneurysm repair, bypass grafting).
  • If the study is negative: A technically adequate and completely normal duplex ultrasound, including with provocative maneuvers, makes hemodynamically significant aTOS less likely. At this point, the clinical picture should be reassessed. If suspicion remains high, or if symptoms are primarily neurologic, consider a workup for neurogenic TOS. If another vascular etiology like vasculitis is suspected, further investigation with MRA or CTA may be warranted.
  • If the study is indeterminate: In cases where the ultrasound is technically limited (e.g., due to patient body habitus) or the findings are equivocal, a follow-up study is necessary. MRA chest without and with IV contrast or CTA chest with IV contrast are both Usually Appropriate options to clarify the anatomy and pathology.

For postoperative surveillance, duplex ultrasound is again the preferred modality to assess the patency of a vascular reconstruction and confirm the resolution of any dynamic compression.

Pitfalls to Avoid (and When to Get Help)

Navigating the workup for aTOS requires careful attention to clinical and imaging details. Here are common pitfalls to avoid:

  • Not requesting dynamic maneuvers: A standard subclavian ultrasound performed only with the arm in a neutral position may miss the diagnosis entirely. The order must specify provocative maneuvers to assess for positional compression.
  • Stopping at a negative ultrasound despite high suspicion: If a patient has a classic history and compelling physical exam findings (e.g., a supraclavicular bruit and pulse changes with abduction), a single negative non-invasive study may not be sufficient.
  • Overlooking bony anatomy: Always obtain a Radiography chest, which is Usually Appropriate, early in the workup. It is a simple, low-dose study that can quickly identify a cervical rib or other bony anomaly contributing to the compression.
  • Delaying workup in acute ischemia: If a patient presents with signs of acute limb ischemia (the “six P’s”), the workup must be expedited. This is a vascular emergency.

If you identify an aneurysm, thrombus, or signs of distal embolization, immediate escalation to a vascular surgeon is critical.

Related ACR Topics and Tools

For a comprehensive overview of all clinical variants and imaging modalities related to this condition, please consult our parent guide. It provides a broader context that complements this deep-dive article.

To explore adjacent clinical scenarios, compare imaging techniques, or discuss radiation dose with your patients, the following GigHz resources are available:

Frequently Asked Questions

Why is a chest radiograph also rated ‘Usually Appropriate’ for arterial TOS?

A chest radiograph is a simple, low-radiation first step that can identify underlying bony abnormalities responsible for the arterial compression. The most common finding is a cervical rib, which is present in a significant percentage of patients with arterial TOS. Identifying this early can help confirm the diagnosis and guide further imaging and surgical planning.

Can I use MRA instead of CTA for pre-operative planning in arterial TOS?

Yes, MRA of the chest with and without IV contrast is also rated ‘Usually Appropriate’ by the ACR. It provides excellent soft tissue and vascular detail without using ionizing radiation. The choice between CTA and MRA often depends on institutional preference, scanner availability, and patient factors, such as renal function or contraindications to MRI (e.g., incompatible hardware).

What is the role of imaging after surgical decompression for arterial TOS?

Post-operative imaging is crucial for surveillance. US duplex Doppler is the primary modality used to confirm the resolution of dynamic compression and to assess the patency of any arterial reconstruction, such as a bypass graft or patch angioplasty. It is typically performed at scheduled intervals to detect any potential late complications like graft stenosis.

If the US Doppler is negative but the patient has a cervical rib, what is the next step?

The presence of a cervical rib does not automatically mean a patient has arterial TOS, as many are asymptomatic. If the dynamic US Doppler is definitively negative for arterial compression but the patient has clear symptoms, you should reconsider the diagnosis. The symptoms may be neurogenic in origin, in which case an MRI of the brachial plexus might be a more appropriate next step to evaluate for nerve compression.

Is catheter arteriography still used for diagnosing arterial TOS?

Conventional catheter arteriography is rated ‘Usually Appropriate’ but is now rarely used for initial diagnosis due to the quality of non-invasive alternatives like duplex US, CTA, and MRA. Its primary role is now therapeutic. If a patient has significant thrombosis or stenosis requiring treatment, arteriography is performed at the same time as the endovascular intervention (e.g., thrombolysis, angioplasty, or stenting).

Reviewed by Pouyan Golshani, MD, Interventional Radiologist — May 29, 2026