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Aug. 20, 2026

Thoracic outlet syndrome (TOS) is a clinically significant neurovascular compression disorder with a dynamic pathophysiology that complicates diagnosis and management. Symptom manifestations are highly position-dependent and influenced by muscle activation, scapulothoracic mechanics and postural alignment. Ongoing efforts at Mayo Clinic focus on refining diagnostic protocols and implementing treatment strategies that account for anatomic variability and position-dependent compression.

"TOS is a 'position-provoked' condition," says Sam Farres, M.D., a vascular surgeon serving as division chair for Vascular Surgery and associate program director of the General Surgery Residency Program at Mayo Clinic in Jacksonville, Florida. "What looks normal at rest can become pathologic when the patient raises their arm or loads their shoulder. If we treat it as a static problem, we may miss the diagnosis or misclassify the type of TOS."

Diagnostic challenges related to the dynamic nature of TOS

Static anatomic factors may predispose an individual to thoracic outlet narrowing. But TOS symptom onset is often determined by dynamic changes in posture, muscle tone and movement. Reproducing the neurovascular compromise associated with these position changes remains challenging due to:

• Heterogeneity in clinical presentation.
• Limited sensitivity of standard diagnostic imaging.
• Absence of standardized MRI protocols.

Variability in clinical presentation of TOS

Clinical presentation of TOS is often heterogeneous and may not provide a straightforward diagnostic pathway. Accurate assessment requires consideration of:

• Baseline thoracic outlet dimensions determined by congenital anatomical structure or repetitive trauma.
• Distinct and overlapping features of neurogenic, arterial and venous TOS.
• Severity of vascular involvement, which dictates whether symptoms present as hemodynamic.
• Specific structures involved in compression, possibly including the subclavian artery, subclavian vein, brachial plexus or a combination.
• Symptom overlap with musculoskeletal or neurogenic conditions, such as peripheral neuropathy, cervical radiculopathy and rotator cuff injuries.

This variability underscores the need for a structured, multidisciplinary evaluation strategy.

Limitations of static imaging tests for dynamic disorders

TOS symptoms are often triggered by specific arm positions or dynamic loading, reflecting the dynamic nature of neurovascular compromise. Standard imaging performed at rest typically fails to reproduce clinically relevant compression.

"Demonstrating anatomic compression alone is insufficient," Dr. Farres says. "The critical task is correlating imaging findings with presenting symptoms to exclude alternative causes."

Capturing dynamic compression requires integration of detailed history, targeted physical examination and imaging performed with positional and provocative maneuvers. If imaging sensitivity is inadequate, even with provocative maneuvers, an anterior scalene block test may be employed.

"Temporarily paralyzing the anterior scalene muscle opens up the thoracic outlet," Dr. Farres says. "Placing the individual in a symptom-triggering position during that muscle paralysis can clarify whether dynamic compression is clinically meaningful."

Need for standardized MRI protocols for TOS

Mayo Clinic's patient-facing guidance for TOS notes that MRI can help determine the location and cause of compression and identify anatomic contributors. However, there is no protocolized, clinically deployed measurement for TOS that can guide clinicians and foster interpreter consistency. A 2023 review published in Frontiers in Physiology highlighted insufficient documentation and standardization of MRI protocols as a barrier to validating MRI for neurogenic TOS.

To address this gap, Dr. Farres and colleagues have developed and are testing a dedicated TOS MRI/MRA protocol designed to capture the dynamic features of TOS by:

• Combining high-resolution anatomic evaluation of the thoracic outlet and surrounding structures with vascular imaging sequences.
• Quantifying changes in the thoracic outlet space across arm positions by imaging in neutral/adduction and again in abduction/elevation to reproduce symptoms and known compression.

"At a high level, the new MRI/MRA protocol is designed to standardize what we image and when we image it, while explicitly accounting for the dynamic nature of the disease," Dr. Farres says. "The goal is to improve consistency and reproducibility across studies and interpreters."

The new MRI/MRA protocol is intended as an adjunct, rather than a replacement, for established diagnostic pathways, which include:

• Comprehensive health history and physical exam.
• Conventional imaging and electrodiagnostic studies.
• Consultations with a multidisciplinary team of experts, including peripheral neurology and physical medicine and rehabilitation specialists.

"We start with the fundamentals," Dr. Farres says. "The dedicated MRI/MRA protocol is used selectively to answer questions that static tests do not resolve. We want to determine if there is evidence for compression and substantial space reduction, in what position it occurs and what structures are involved."

Evolving surgical strategies for TOS as a dynamic disorder

TOS management is conceptually centered on precise decompression of structures that become compressed with motion. Surgical intervention is indicated if symptoms persist despite conservative therapy or if there is objective evidence of neurovascular compromise.

While traditional surgical approaches have relied on open techniques, robotic-assisted first-rib resection offers technical advantages particularly suited to dynamic disease. Data published in Seminars in Vascular Surgery support robotic first-rib resection as a safe and reliable approach associated with favorable outcomes and low morbidity.

Mayo Clinic surgeons are further advancing this approach through single-port robotic first-rib excisions in appropriately selected patients. Although outcome reporting is ongoing, principle-based benefits parallel those reported for multiport robotic first-rib resection and include the following:

• Enhanced visualization in a tight space provides magnification and helps identify the neurovascular structures and the boundaries of the first rib.
• Instrument precision and controlled dissection reduce traction on sensitive structures compared with more constrained approaches.
• Minimally invasive access through small incisions offers faster functional recovery and improved cosmesis.
• Reproducible exposure of the first rib does not require direct harmful retraction of the neurovascular bundle to achieve successful outcomes.

"The 'dynamic' component of TOS is why surgical precision is critical," Dr. Farres states. "If decompression is incomplete, symptoms often persist when the individual returns to activity. The robotic platform helps us perform that decompression with excellent visualization and fine control in a very confined space."

For more information

Szaro P, et al. Magnetic resonance imaging for diagnosis of suspected neurogenic thoracic outlet syndrome-a systematic scoping review. Frontiers in Physiology. 2023;14;1198165.

Sutton W, et al. Video-assisted thoracic surgery and robotic-assisted first-rib excision and thoracic outlet syndrome decompression. Seminars in Vascular Surgery. 2024;37:82.

Refer a patient to Mayo Clinic.