What is the difference between thoracic outlet syndrome and thoracic inlet syndrome?

Thoracic Outlet Syndrome vs. Thoracic Inlet Syndrome

Thoracic outlet syndrome (TOS) refers specifically to compression of neurovascular structures at the superior thoracic outlet, while thoracic inlet syndrome is not a recognized clinical entity in current medical literature. 1, 2

Thoracic Outlet Syndrome: Definition and Classification

• TOS is a condition caused by compression of neurovascular structures (brachial plexus, subclavian artery, or subclavian vein) as they pass from the thoracic outlet to the axilla 1, 3
• TOS is classified into three main types based on the compressed structure:
  • Neurogenic TOS (nTOS): Compression of the brachial plexus (95% of cases) 1, 4
  • Venous TOS (vTOS): Compression of the subclavian vein (3% of cases) 1, 4
  • Arterial TOS (aTOS): Compression of the subclavian artery (1% of cases) 1, 4

Anatomical Considerations

• The thoracic outlet refers to the region where neurovascular structures pass from the neck to the axilla 1, 3
• Key anatomical spaces involved in TOS include:
  • Costoclavicular triangle (between clavicle, first rib, and anterior scalene muscle) 1, 5
  • Interscalene triangle (between anterior and middle scalene muscles) 1, 6
  • Pectoralis minor space (beneath the pectoralis minor muscle) 1, 6

Clinical Presentation of TOS

• Symptoms vary based on the type of TOS:
  • Neurogenic TOS: Upper limb pain, numbness, tingling, and weakness 2, 7
  • Venous TOS: Arm swelling, discoloration, and development of collateral veins 6, 1
  • Arterial TOS: Distal ischemia, claudication, and potentially thromboembolism 1, 3
• Symptoms are typically exacerbated by arm elevation or abduction 1, 7

Diagnostic Approaches

• Initial evaluation includes chest radiography to identify osseous abnormalities such as cervical ribs or first rib anomalies 1, 6
• Advanced imaging is selected based on the suspected type of TOS:
  • Neurogenic TOS: MRI without and with IV contrast 1, 6
  • Venous TOS: CTV, venography, or duplex ultrasound 6, 1
  • Arterial TOS: CTA, MRA, or duplex ultrasound 1, 6
• Dynamic imaging with arms in neutral and stressed positions is crucial to demonstrate neurovascular compression 1, 6

Treatment Options

• Conservative management includes physical therapy, anti-inflammatory medications, and weight loss 2, 7
• Surgical intervention is considered when conservative management fails after 3-6 months or when there are progressive symptoms or vascular complications 1, 8
• Surgical approaches include:
  • Transaxillary approach for first rib excision 4, 8
  • Supraclavicular approach for scalenectomy 3, 4
  • Combined approaches for complex cases 3, 4

Common Pitfalls and Caveats

• Venous compression during arm abduction is common in asymptomatic individuals, making clinical correlation essential 1, 6
• TOS is not a diagnosis of exclusion; there should be evidence for a physical anomaly that can be corrected 2, 1
• Reliance on axial imaging alone can lead to misrepresentation of the degree of stenosis; multiplanar reformations are necessary 6, 1
• Postoperative complications can include injury to subclavian vessels, brachial plexus injury, hemothorax, and pneumothorax 2, 8

Thoracic Inlet Syndrome: Clarification

• "Thoracic inlet syndrome" is not a recognized clinical entity in current medical literature and guidelines 1, 2
• The term "thoracic inlet" anatomically refers to the superior opening of the thoracic cage, bounded by the first thoracic vertebra posteriorly, the first ribs laterally, and the manubrium anteriorly 3
• Any symptoms attributed to "thoracic inlet syndrome" would likely fall under the classification of thoracic outlet syndrome based on current medical understanding 1, 2