THORACIC OUTLET SYNDROME

T

horacic outlet syndrome is a group of disorders that involves the nerves and blood vessels of the thoracic outlet.

This occurs at the area of thoracic inlet, i.e. superior most part of the thoracic cavity (as discussed in the Lungs blog).

But that area is mentioned as “inlet” and here it is called as outlet because of the structures that leave the thorax, i.e. the subclavian artery. Other structures in relation to this are Subclavian vein, 1^st rib, clavicle and brachial plexus.

Fig 1.0 structures involved in thoracic outlet syndrome (Source: Mayo-clinic)

The term Thoracic outlet syndrome/TOS was coined by R. M. Peet in 1956.

Three main anatomic compartments of this syndrome –

1.    Interscalene triangle.

2.    Costoclavicular area.

3.    Retro-pectoralis minor spaces.

Interscalene triangle is formed by - anteriorly the anterior scalene muscle, posteriorly by the middle scalene muscle and inferiorly by the1^st rib. It contains the Subclavian artery which later on continues in the arm as the axillary and brachial artery; this is accompanied by the brachial plexus (a group of nerves that give the innervation to the upper limb).

Costoclavicular – as the name suggests, lies between the Clavicle and the 1^st rib. A part of scapula (posterolateral) is also included and this completes the space.

Retropectoralis muscle – area beneath the coracoid process of scapula and behind the pectoralis minor muscle.

Fig 1.1 Retropectoralis minor space.

Aetiology –

Anatomical defects –

1.    Cervical rib

2.    Long C7 transverse process

3.    Fracture of the clavicle or 1^st rib

4.    Abnormal bands or ligaments

Soft tissue defects –

1.    Variation in the origin and insertion of scalene muscles

2.    Hypertrophy of scalene muscles

3.    Trauma

4.    Accessory scalenus minimus muscle

5.    Tumours

Classification –

1.    True neurogenic (nTOS)

2.    Arterial TOS (aTOS)

3.    Venous TOS (vTOS)

4.    Traumatic Neurovascular

Neurogenic TOS accounts of 80 – 90% of the disease but vascular occurs in non-athletic men and women.

Neurogenic TOS –

Presents as Loss of dexterity, muscle spasm and heaviness in the upper limb. Pain in the dermatomes of C8 and T1 root compression, may be associated with weakness. Weakness in the whole arm, shoulders or partly in the neck may also be seen. Raynaud’s phenomenon may be seen due to the sympathetic overactivity for prevention of ischaemia.

Venous TOS (vTOS) –

Also called as the Paget Schroetter syndrome; is caused by spontaneous thrombosis of subclavian vein due to heavy lifting, swimming or playing tennis. Limbs become heavy, oedematous, and sometimes cyanotic. Patients might feel the neurologic symptoms like pain, paraesthesia not because of any neuronal injury but because of the vascular compromise. This is usually resulted because of hypertrophy of pectoral muscle, or because of damage to intima of the vessel wall that leads to the fibrosis and sometimes thrombus.

Arteria TOS (aTOS) –

Least common form of the TOS but very severe. Most commonly scene due to compression of the artery in between the scalene muscles or because of trauma to the rib or cervical rib presence. Kee et al. reported on the ischaemia of the throwing hand of professional baseball pitchers because of embolic occlusion of axillary artery and thus creating axillary aneurysm. Pallor, and coldness of the peripheries is seen with no oedema. Neurologic symptoms may also be seen.

DD’s (Differential diagnosis) –

Carpal tunnel syndrome

Horner’s syndrome

deQuverians tenosynovitis

Lateral epicondylitis (tennis elbow)

Medial epicondylitis (golfers’ elbow)

Complex regional Pain syndrome (CRPS)

Rotator cuff pathology

Glenohumeral joint instability

Investigations/Tests –

It is better to investigate and rule out all the other diseases so as to achieve a proper diagnosis. A proper history of the patient with his/her work and stress. Electromyography can be done; X ray, CT, MRI to rule out any abnormal anatomical structures like cervical rib or fractures.

EAST or Elevated Arm Stress Test can be performed, which is the most sensitive and apt test for diagnosis of TOS.

It is also called as ROOS test. It is performed by holding the “surrender” position for 3 minutes while opening and closing the hands.

Treatment –

Mild TOS is treated conservatively and sometimes no treatment is required in itself. Moderate TOS is treated by reduction in the aggressive activities and pain medications are given along with some physical therapy to prevent further damages.

Severe TOS is surgically treated where there is decompression of the neurovascular bundle, or removal of the underlying pathology like tumours. One such decompressive surgery is Trans axillary 1^st rib resection. In this surgery the patient is made to lie on one of his/her side and the arm is stretched over head, a small semi-circular incision of size 1.5 – 2.0 cm is made and the 1^st rib is approached. The subclavius muscle is cut, a part of the 1^st rib is removed and any accessory structures impairing the area are also removed. Post operatively, the patient is not allowed to do heavy work for 3-4 months, physiotherapy is started after 3-4 days of operation and then normal life is resumed after 4 months of surgery (video on Instagram page @creativesparkblogs).