Two separates entities:

1. 
   

   Neurogenic thoracic outlet syndrome (nTOS)

   
   
2. 
   

   Vascular thoracic outlet syndrome (vTOS).

Caused by anatomical sites of compression of nervous structures/brachial plexus (nTOS) or shoulder girdle vessels (vTOS)

Incidence is 1 to 2% of general population:

1. 
   

   nTOS is more common (19:1).

More common in women than men (3.5:1):

1. 
   

   Theoretical risk factors are long neck and drooping shoulders.

Clinical symptoms include upper extremity pain, paresthesias, numbness, weakness, fatigability, heaviness, swelling, discoloration, and Raynaud phenomenon:

1. 
   

   Pain and paresthesias most common.

Treatment:

1. 
   

   Operative versus nonoperative management depending on cause.

Nervous tissue:

1. 
   

   Brachial plexus:

   
   
   
   
   1. 
      

      Five roots: C5, C6, C7, C8, T1

      
      
   2. 
      

      Three trunks: Superior, middle, and inferior

      
      
   3. 
      

      Six divisions: Anterior and posterior divisions of three trunks

      
      
   4. 
      

      Three cords: Posterior, lateral, and medial

      
      
   5. 
      

      Five branches: Median, axillary, radial, musculocutaneous, and ulnar nerves

      
      
   6. 
      

      Lower trunk (C8–T1) > upper trunk (C5–C7) involvement in nTOS.

Vasculature:

1. 
   

   Subclavian vein:

   
   
   
   
   1. 
      

      Runs anterior to interscalene triangle proximally

      
      
   2. 
      

      Becomes axillary vein after crossing first rib

      
      
   3. 
      

      Joins artery and brachial plexus in costoclavicular and retropectoralis minor space.

   
   
2. 
   

   Subclavian artery:

   
   
   
   
   1. 
      

      Branches off brachiocephalic trunk

      
      
   2. 
      

      Becomes axillary artery after crossing first rib.

   
   
3. 
   

   Axillary artery (▶ Fig. 21.1 ):

   
   
   
   
   1. 
      

      Divided into three parts:

      
      
      
      
      • 
        

        i. First: Lateral border of first rib to superior border of pectoralis minor muscle

        
        
      • 
        

        ii. Second: Lies deep to the pectoralis minor muscle

        
        
      • 
        

        iii. Third: Extends from inferior border of the pectoralis minor muscle to the inferior border of the teres major muscle.

        

Sites of compression from proximal to distal (▶ Fig. 21.2 ):

1. 
   

   Interscalene triangle:

   
   
   
   
   1. 
      

      Anterior scalene muscle: Anterior border

      
      
   2. 
      

      Middle scalene muscle: Posterior border

      
      
   3. 
      

      First rib: Inferior border.

   
   
2. 
   

   Costoclavicular space:

   
   
   
   
   1. 
      

      Clavicle: Anterior border

      
      
   2. 
      

      First rib: Posteromedial border

      
      
   3. 
      

      Costoclavicular ligament/scapula: Posterolateral border.

   
   
3. 
   

   Retropectoralis minor space:

   
   
   
   
   1. 
      

      Pectoralis minor: Anterior border

      
      
   2. 
      

      Ribs 2 to 4: Posterior border

      
      
   3. 
      

      Coracoid: Superior border.

Anatomical anomalies causing TOS:

1. 
   

   Congenital:

   
   
   
   
   1. 
      

      Soft tissue:

      
      
      
      
      • 
        

        i. Variation in scalene muscle origin or insertion

        
        
      • 
        

        ii. Presence of scalenus minimus

        
        
      • 
        

        iii. Fibromuscular bands constricting inlet spaces.

        

      
      
   2. 
      

      Osseous:

      
      
      
      
      • 
        

        i. Presence of cervical ribs

        
        
      • 
        

        ii. Prominent C7 vertebrae transverse processes

        
        
      • 
        

        iii. First rib anomalies

        
        
      • 
        

        iv. Vertebral anomalies.

      
      
   3. 
      

      Vascular:

      
      
      
      
      • 
        

        i. Atypical vessel course and branching.

   
   
2. 
   

   Acquired:

   
   
   
   
   1. 
      

      Osseous:

      
      
      
      
      • 
        

        i. Osteochondroma of first rib/clavicle

        
        
      • 
        

        ii. Malunion after fracture of first rib/clavicle

        
        
      • 
        

        iii. Hyperostosis

        
        
      • 
        

        iv. Posterior sternoclavicular dislocation.

      
      
   2. 
      

      Occupational:

      
      
      
      
      • 
        

        i. Repetitive overhead activity produces cumulative effects of micro trauma.

      
      
   3. 
      

      Hypertrophy:

      
      
      
      
      • 
        

        i. Hypertrophic scalene muscles.