Brachial Plexus MRI for Arterial or Venous Thoracic Outlet Syndrome

Version 1.0 — August 2026

1. Executive Summary

1.1 Added Value over the Generic Protocol

Arterial (aTOS) and venous (vTOS) thoracic outlet syndrome share the same anatomic compression sites as neurogenic TOS — documented in the companion Neurogenic Thoracic Outlet Syndrome child page — but require a fundamentally different acquisition strategy centred on contrast-enhanced MR angiography in the provocative position, rather than the fluid-sensitive nerve-signal-focused sequences central to the neurogenic protocol. This child page documents that vascular-specific acquisition, the arterial-vs-venous distinction, and the recognition of acute complications (effort thrombosis/Paget-Schroetter syndrome, subclavian artery aneurysm/thrombosis) that carry their own urgent management pathway.

1.2 Limits of the Dedicated Protocol

Some degree of positional vascular compression — narrowing or even transient occlusion of the subclavian vein or artery on provocative arm positioning — can be demonstrated in a proportion of asymptomatic individuals, exactly as described for the neurogenic subtype; imaging findings must therefore be interpreted in conjunction with clinical presentation, and an isolated positional compression finding, without a compatible clinical picture or a fixed/structural abnormality, does not by itself establish a diagnosis of vascular TOS requiring intervention.

2. Clinical Context

2.1 Clinical Presentation

Venous TOS classically presents as effort-induced arm swelling, cyanosis, and venous distension — Paget-Schroetter syndrome (effort thrombosis of the axillosubclavian vein) is the acute, urgent presentation of this subtype, typically in young, active patients after strenuous or repetitive overhead arm activity. Arterial TOS presents with arm claudication, coldness, pallor, or, in more advanced cases, digital ischaemia or embolic phenomena from a poststenotic subclavian artery aneurysm — a comparatively rare but clinically serious presentation.

2.2 Anatomic Basis Shared with Neurogenic TOS

As detailed in the companion Neurogenic Thoracic Outlet Syndrome child page, the same three anatomic compartments (interscalene triangle, costoclavicular space, retropectoralis minor space) are the relevant compression sites; vascular TOS, however, localises predominantly to the costoclavicular space, in contrast to neurogenic TOS, which can occur at any of the three sites — a distinction worth bearing in mind when correlating imaging findings with the specific TOS subtype under clinical consideration.

2.3 Differential Diagnosis (Clinical)

Venous TOS/Paget-Schroetter must be distinguished from other causes of upper-limb deep vein thrombosis (central venous catheter-associated, malignancy-associated, or idiopathic), while arterial TOS must be distinguished from other causes of upper-limb ischaemia (embolism from a cardiac source, primary atherosclerotic disease, vasospastic disorders) — the anatomic, positional nature of TOS-related vascular compromise, and its association with an identifiable anatomic compression site, is the key distinguishing feature this protocol is designed to demonstrate.

3. Indications, Timing, and Patient Selection

3.1 When the Dedicated Protocol Is Indicated

Suspected effort thrombosis (Paget-Schroetter), suspected arterial compression/aneurysm with claudication or embolic symptoms, and clinical or examination findings suggesting a vascular contribution alongside neurogenic symptoms (differential pulses, arm swelling) are indications for this dedicated vascular protocol, per the ACR Appropriateness Criteria’s consideration of TOS as encompassing distinct neurogenic, venous, and arterial variants requiring differently targeted imaging.

3.2 Acute vs Elective Timing

Suspected acute effort thrombosis or acute arterial compromise (Section 3.4) requires urgent imaging, generally via the most immediately available and appropriate modality (which may be duplex ultrasound or CT venography/angiography as the first-line urgent test in many pathways) — this dedicated MRI/MRA protocol is more typically employed for elective/subacute evaluation, surgical planning, and follow-up assessment (Section 3.3) rather than as the primary acute-presentation imaging test in every centre.

3.3 Post-Treatment and Surveillance Imaging

Following thrombolysis, angioplasty, or surgical decompression (first-rib resection) for vascular TOS, follow-up imaging — for which this dedicated MRA protocol is well suited — assesses vessel patency, residual or recurrent compression, and post-surgical anatomy, providing a noninvasive alternative to repeat catheter angiography for this purpose.

3.4 Red Flags Modifying Urgency

Acute arm swelling with pain and venous distension (suspected acute effort thrombosis) and acute digital ischaemia, pallor, or absent pulses (suspected acute arterial thrombosis/embolism) are both urgent presentations warranting immediate vascular imaging via the most rapidly available appropriate modality, ahead of the elective-timed dedicated MRA protocol described in the remainder of this child page.

4. Dedicated Protocol Design

4.1 Mandatory Core Sequences

The table below lists the complete mandatory protocol for arterial or venous thoracic outlet syndrome — the five generic-protocol core sequences (1-5) plus the three vascular-TOS-specific contrast-enhanced MRA additions (6-8) detailed in Section 4.3. See Section 4.2 for the full three-way comparison against both the generic protocol and the neurogenic TOS protocol.

4.2 Protocol Delta vs the Generic Brachial Plexus Protocol and vs the Neurogenic TOS Protocol

4.3 Mandatory Dedicated Sequences

• Contrast-enhanced 3D MR angiography, acquired with the arm in the provocative (abducted) position, timed to separately capture arterial and venous phases — the core acquisition of this protocol, distinct from anything in the generic or neurogenic-TOS protocols.
• A matched neutral-position acquisition, for direct comparison, exactly as the dual-position principle established in the companion neurogenic TOS child page requires — positional change relative to a neutral baseline, not a single-position finding, is central to interpretation here as well.
• Coronal T1, per the generic protocol, for baseline osseous and soft-tissue anatomy, including assessment for a cervical rib or other anatomic substrate shared with the neurogenic subtype.

4.4 Conditional and Advanced Sequences

• Separate, dedicated arterial-phase and venous-phase acquisitions (rather than a single combined-phase acquisition) improve the ability to independently characterise arterial and venous compromise when both are clinically relevant, at the cost of a longer overall protocol.
• Non-contrast MRA techniques may be considered in patients with contraindications to gadolinium, accepting a trade-off in diagnostic confidence relative to the contrast-enhanced technique that is the primary recommended approach in the reviewed literature.
• Standard STIR/T2 fluid-sensitive sequences, as in the neurogenic protocol, may be added where a neurogenic component is also suspected, since vascular and neurogenic TOS can coexist.

4.5 Rationale per Disease-Specific Sequence

Contrast-enhanced 3D MRA in the provocative position (the core vascular-TOS-specific acquisition) The rationale is that vascular compression in TOS, exactly as for the neurogenic subtype, is frequently positional and can be minimal or absent in the neutral position — a dedicated technical description in the literature specifically validated contrast-enhanced 3D MRA with provocative arm positioning as an efficient, reproducible, noninvasive alternative to digital subtraction angiography for this purpose, also noting its value for post-surgical follow-up in identifying restenosis or residual compression.

Separate arterial and venous phase timing The rationale for deliberately separating arterial and venous phase acquisition, rather than a single combined acquisition, is that venous and arterial compromise can occur independently or together, and clinical presentation at referral does not always reliably predict which vessel(s) will show the abnormality on imaging — meaning both circulations warrant deliberate, separate interrogation rather than assuming the clinically-suspected vessel alone.

Matched neutral-position comparison The rationale is identical in principle to the neurogenic TOS protocol’s bilateral/comparative interpretation requirement: because some degree of positional vascular narrowing can be demonstrated even in individuals without clinically significant TOS, a genuine neutral-to-provocative comparison — not an isolated provocative-position finding — is required to support a clinically meaningful interpretation.

4.6 Dedicated Planes and Field of View

Coverage should extend from the subclavian vessels’ origin through the axillary vessels bilaterally, in both the neutral and provocative positions, with a field of view specifically designed around vascular anatomy (rather than the nerve-centred coronal oblique plexus plane that anchors the neurogenic protocol) — a genuinely distinct planning approach reflecting the different anatomical target of this protocol.

4.7 Contrast Strategy

Contrast-enhanced 3D MRA, using standard macrocyclic GBCA dosing with a technique optimised for first-pass arterial and separately-timed venous phase acquisition, is the core technique in this protocol — a materially different, more contrast-timing-critical approach than the largely non-contrast neurogenic TOS protocol or the conditional contrast use in the generic protocol. Bolus timing and injection technique should follow standard site-wide MRA practice, adapted specifically for the provocative-position acquisition constraints.

4.8 Sequence Matching to Clinical Question

5. MRI Semiotics of Vascular Thoracic Outlet Syndrome

5.1 Direct Signs

Direct signs are demonstrable narrowing, compression, or occlusion of the subclavian artery or vein, specifically or predominantly in the provocative position, most consistently localised to the costoclavicular space, with relative preservation of normal calibre in the neutral position — closely paralleling the positional-compression pattern described for the neurogenic subtype but assessed on angiographic rather than nerve-signal sequences.

5.2 Indirect and Secondary Signs

For venous TOS, secondary signs include collateral venous channels (indicating chronic or subacute venous compromise), residual filling defect after thrombolysis, and perivenous soft-tissue change. For arterial TOS, secondary signs include poststenotic dilatation/aneurysm formation distal to the compression site, mural thrombus within an aneurysm (a source of distal embolisation), and, on occasion, evidence of distal embolic occlusion in the hand/digital vessels.

5.3 Severity, Extent, and Site Localisation

Reporting should specify the affected vessel (artery, vein, or both), the specific compartment of compression (predominantly costoclavicular for vascular TOS, per Section 2.2), the degree of narrowing/occlusion in each position, and — where present — the presence and size of any poststenotic aneurysm or the extent of venous thrombus.

5.4 Relevant Classification and Reporting Frameworks

As for the neurogenic subtype, the Society for Vascular Surgery reporting standards for TOS (Illig et al.) provide the current consensus framework for arterial (aTOS) and venous (vTOS) case definition and reporting terminology, distinct from but complementary to the neurogenic (nTOS) framework referenced in the companion child page — using consistent, standards-based terminology across all three subtypes supports the multidisciplinary decision-making this reporting is intended to inform.

5.5 Differential Diagnosis on Imaging

The principal imaging differential for venous findings is distinguishing TOS-related positional/anatomic venous compression from a central venous catheter-related or otherwise non-anatomic cause of thrombosis; for arterial findings, distinguishing TOS-related extrinsic compression from primary atherosclerotic or embolic arterial disease — in both cases, the presence of a clear positional component and/or an identifiable anatomic compressive structure (cervical rib, anomalous band) favours a genuine TOS-related mechanism.

5.6 Mimickers and Pitfalls

As with the neurogenic subtype, some degree of positional vascular narrowing — even transient venous compression on abduction — can be demonstrated in asymptomatic individuals; a positive provocative-position finding should therefore always be interpreted alongside the neutral-position comparison and the clinical presentation, not reported as diagnostic of clinically significant vascular TOS in isolation.

6. Reporting Framework

6.1 Structured Reporting Template

Vessel(s) assessed: subclavian/axillary artery, subclavian/axillary vein (bilateral, neutral and provocative position). Positional compression identified: vessel, site, side(s), degree. Thrombus/occlusion: present/absent, vessel, extent, acute vs chronic appearance where determinable. Aneurysm: present/absent, vessel, size, presence of mural thrombus. Collateral venous channels: present/absent (relevant to chronicity assessment). Anatomic substrate: cervical rib / anomalous band / none identified.

6.2 Mandatory Reporting Elements

Every report should explicitly state whether the provocative-position acquisition was successfully obtained and diagnostic, exactly as required in the neurogenic TOS protocol, and should explicitly distinguish acute findings (fresh thrombus, active compromise) from chronic/adaptive findings (collateral channels, chronic occlusion) given the different management urgency each implies.

6.3 Critical/Actionable Findings

Acute thrombus, a large or symptomatic poststenotic aneurysm, and evidence of distal embolisation are the most directly actionable findings in this protocol and should be communicated with appropriate urgency, distinct from the elective-timed reporting appropriate for stable, chronic, or purely positional findings.

6.4 Common Reporting Errors

Reporting positional vascular narrowing on the provocative position alone without a stated neutral-position comparison; failing to distinguish acute from chronic thrombus appearance when this distinction is determinable and clinically important; and omitting explicit comment on the presence or absence of an anatomic substrate (cervical rib, anomalous band) that carries direct surgical planning relevance.

7. Technical Pitfalls

7.1 Contrast Bolus Timing

Because this protocol depends on correctly timed arterial and venous phase acquisition, suboptimal bolus timing is a genuine and consequential technical failure mode specific to this protocol, distinct from the largely non-contrast neurogenic TOS protocol — careful attention to injection rate, timing, and phase-specific acquisition triggering is more critical here than in most other brachial plexus protocols on this site.

7.2 Positioning Failure

As in the neurogenic TOS protocol, the provocative position must reproduce genuine, sufficient abduction/external rotation; an inadequately provoked position undermines this protocol’s core diagnostic rationale exactly as it does for the neurogenic subtype.

7.3 When the Generic or Neurogenic-TOS Protocol Alone Is Insufficient

A brachial plexus MRI performed using either the generic protocol or the neurogenic TOS protocol alone, without the dedicated contrast-enhanced MRA technique described in this child page, will not adequately assess a suspected vascular component of TOS — the two protocols address genuinely different anatomical targets (nerve vs vessel) using genuinely different sequence strategies, and one cannot substitute for the other.

8. MRI Technologist Pearls

8.1 Sequence Order Logic

Given the contrast-timing sensitivity of this protocol (Section 7.1), careful pre-planning of injection timing relative to the provocative-position acquisition — rather than treating contrast timing as a routine, generic step — is a specific technical priority for this indication.

8.2 Positioning Tricks

As in the neurogenic TOS protocol, achieving genuine, reproducible provocative-position abduction requires deliberate coaching and coil/patient setup planning before the patient enters the bore.

8.3 Fast Salvage Protocol

If contrast timing or positioning genuinely fails for one phase (e.g. venous phase compromised by timing error), prioritise salvaging the phase most consistent with the leading clinical suspicion (venous phase for suspected effort thrombosis, arterial phase for suspected arterial compromise) rather than treating both phases as having equal salvage priority.

8.4 Disease-Specific Common Avoidable Errors

Using a non-contrast or poorly-timed contrast technique for suspected vascular TOS when a properly-timed contrast-enhanced MRA is required; omitting the provocative-position acquisition; and failing to obtain both arterial and venous phase imaging when the clinical presentation does not clearly point to only one circulation.

9. Quality Control Checklist

• Both neutral and genuine provocative position acquisitions successfully obtained and diagnostic quality confirmed.
• Both arterial and venous phase acquisitions confirmed adequately timed and diagnostic, unless clinical context clearly justifies a single-phase-only protocol.
• Bilateral coverage confirmed for comparison.
• Osseous/fibrous anatomic survey (cervical rib, anomalous band) explicitly reviewed.
• Clinical indication (specifically “vascular TOS” / “suspected effort thrombosis” / “suspected arterial TOS”) confirmed as correctly communicated to protocol against, distinguishing this request from the neurogenic-TOS-specific or generic plexus MRI order.

11. Evidence Gaps and Ongoing Debate

• Optimal contrast timing and phase-separation technique for provocative-position MRA is not fully standardised, with different centres reported to use somewhat different bolus-timing and phase-triggering approaches, reflecting genuinely different practical trade-offs rather than a single settled optimal technique.
• The specificity of positional vascular narrowing, exactly as for the neurogenic subtype, is incompletely characterised, since some degree of positional compression is demonstrable in asymptomatic individuals — the precise diagnostic threshold distinguishing clinically significant compression from a normal variant remains an active area of investigation.
• First-line imaging modality selection for acute presentations (duplex ultrasound vs CT vs MRA) varies by centre and clinical scenario, and the reviewed literature does not describe a single universally adopted acute-imaging-pathway standard, distinct from this protocol’s more clearly defined role in elective and follow-up assessment.

12. Evidence-Based References

A. Guidelines / Consensus / Society Recommendations

C. Important Prospective / Original Studies

D. Technical MRI Papers

E. Landmark Historical References

No landmark historical reference specific to vascular thoracic outlet syndrome MRI, distinct from the original studies already listed in Category C, was identified as warranting separate citation. Category E is therefore not populated for this child page.

End of document — Brachial Plexus MRI for Arterial or Venous Thoracic Outlet Syndrome — Child Protocol under the MRIninja Neck / Brachial Plexus master page — v1.0 — August 2026 Parent page: Brachial Plexus MRI — Generic Standard Protocol