What are the steps to diagnose thoracic outlet syndrome?

Diagnosing Thoracic Outlet Syndrome

Diagnosis of thoracic outlet syndrome requires a systematic approach starting with chest radiography to identify bony abnormalities, followed by type-specific imaging (duplex ultrasound for venous TOS, CTA/MRA for arterial TOS, or MRI for neurogenic TOS), with all imaging findings requiring careful clinical correlation since compression can occur in asymptomatic individuals. 1, 2

Initial Clinical Assessment

History and Physical Examination

• Identify the TOS subtype based on presenting symptoms: 1

  • Neurogenic TOS (most common): Arm pain, paresthesias, weakness, and fatigue 3
  • Venous TOS: Arm swelling, discoloration, and symptoms of venous congestion 3
  • Arterial TOS: Digital ischemia, hand discoloration, or in severe cases gangrene from distal emboli 1

• Perform provocative maneuvers to reproduce symptoms through compression and positional testing, which are positive in 94% of TOS cases 4

• Look for precipitating factors: neck trauma, repetitive work stress, postural changes with arm elevation/abduction, or occupations involving manual labor, throwing, or weightlifting 1, 3, 5

Critical Caveat

TOS is not a diagnosis of exclusion—there should be evidence of a physical anomaly that can be corrected 3. However, recognize that clinical testing has poor sensitivity and specificity, making definitive diagnosis challenging 5.

Step 1: Initial Imaging - Chest Radiography

Obtain chest radiography first to identify osseous abnormalities that may cause compression 1, 2:

• Cervical ribs (present in 36% of congenital cases) 1
• First rib anomalies 1, 2
• Congenital osseous malformations 1, 2
• Focal bone lesions 2

Step 2: Type-Specific Advanced Imaging

For Venous TOS (vTOS)

Duplex ultrasound is the first-line imaging test due to its non-invasive nature and ability to perform dynamic maneuvers 2:

• Perform in both neutral position and with provocative maneuvers (arm abduction) 2
• Look for flow acceleration, turbulence, and arrest in signal propagation during maneuvers 2
• Assess for venous compression, thrombosis, and collateral circulation 2

If intervention is being considered, catheter venography is the gold standard for definitive diagnosis 2:

• Perform with contrast injection during digital subtraction acquisition in both neutral and stressed positions 2

Alternative advanced imaging options: 1, 2

• CT Venography (CTV): Excellent for anatomical evaluation; obtain 120-180 seconds after IV contrast in each arm position separately 1, 2
• MR Venography (MRV): Superior soft tissue contrast; perform in both neutral and arms-abducted positions 1, 2

For Arterial TOS (aTOS)

Use CTA with IV contrast, MRA, or US duplex Doppler to identify 1:

• Fixed or dynamic stenosis 1
• Aneurysm formation 1
• Mural thrombus 1
• Distal emboli 1

For Neurogenic TOS (nTOS)

MRI without and with IV contrast of the chest is the preferred modality 1:

• Use high-resolution T1-weighted and T2-weighted sequences in sagittal and axial planes to delineate the brachial plexus, muscular attachments, and compression sites 1
• Perform imaging in both neutral and arms-abducted positions to demonstrate effacement of fat adjacent to brachial plexus roots, trunks, or cords 1
• T1-weighted imaging identifies causative lesions including cervical ribs, congenital fibromuscular anomalies, and muscular hypertrophy 1
• Use turbo spin-echo T2-weighted or short tau inversion recovery sequences to exclude alternative diagnoses like brachial plexitis or spinal cord lesions 1

Avoid CT or ultrasound alone for neurogenic TOS as these modalities lack resolution of neural structures 1

Step 3: Identify Compression Sites

Evaluate the three distinct anatomical spaces where compression occurs: 1

• Interscalene triangle 1
• Costoclavicular space (most common site, formed by clavicle superiorly, anterior scalene muscle posteriorly, and first rib inferiorly) 1
• Pectoralis minor space (subpectoral tunnel) (rare but relevant for chest and axillary symptoms) 1

Quantify changes in costoclavicular or interscalene spaces with provocative maneuvers 1

Step 4: Confirm Anatomical Abnormalities

Look for specific anatomical variations that predispose to TOS: 1, 6

• Variations in anterior scalene muscle insertion or scalenus minimus muscle 6
• Cervical ribs or fibrous bands originating from cervical ribs 3, 6
• Variations in pectoralis minor insertion 6
• Congenital fibromuscular anomalies (11% of cases) 1
• Positional compression (53% of cases) 1

Step 5: Clinical Correlation - Essential Pitfall Avoidance

Critical warning: Venous compression during arm abduction is commonly seen in both asymptomatic and symptomatic individuals, making clinical correlation essential 1, 2, 7:

• One study found 71% of patients with unilateral venous compression had significant bilateral compression on imaging, but only 21% had bilateral symptoms 2
• True vTOS is confirmed by finding venous thrombosis and collateral circulation in both neutral and stressed positions, representing objective findings of clinically significant venous compression 2

Do not overlook concomitant cervical spine pathology that may mimic or exacerbate TOS symptoms 1

Consider deeper pathology such as Pancoast tumor or cervical spondylopathy if clinical presentation is atypical 2

Adjunctive Diagnostic Tests

Electrophysiological studies have limited utility: 3, 4

• Only 1-2% of patients have positive nerve conduction studies/electromyography at the brachial plexus level 4
• These studies may be useful in cases of suspected neurogenic TOS to screen for patients likely to benefit from surgical decompression 6

Sensory testing (vibration thresholds, two-point discrimination) is typically normal in 98% of cases 4

Imaging Protocol Specifications

For dynamic imaging studies, ensure proper technique: 1

• Contrast injection should be performed in the contralateral arm to avoid artifact 1
• Use multiplanar reformations to evaluate the thoracic space and demonstrate true axial vessel compression 1
• Avoid noncontrast time-of-flight MRA techniques as they suffer from flow artifacts causing false-positive stenosis or thrombosis 1
• Studies must be tailored specifically to the thoracic outlet, distinct from upper extremity protocols 1