Thoracic outlet syndrome is a group of disorders involving compression of neurovascular bundle passing between the anterior scalene and middle scalene muscles as they pass between the chest and upper extremity. The structures that could be affected are the brachial plexus, the subclavian artery, and, rarely, the subclavian vein.
Note: Subclavian vein, normally, does not pass between scalene muscles.
Potential site for compression are
- Interscalene space [Space between the anterior scalene and middle scalene muscles]
- Costoclavicular space [between first rib and clavicle]
- space below pecotralis minor
Causes of Thoracic Outlet Syndrome
Thoracic outlet syndrome may result from
- Dynamic compression such as abnormal compression from the clavicle and shoulder girdle on arm movement.
- Static compression caused by abnormalities such as cervical rib
- Enlargement or spasm of the surrounding muscles
- Pancoast tumor (cancer in the apex of the lung) in the progressive stages of the disease.
- Physical trauma – accidents, repetitive strain injury, sports-related activities
- Pregnancy- Joints loosen during pregnancy, leading to bad posture. Any preexisting narrow thoracic outlet may become symptomatic.
- Congenital abnormalities – cervical rib, prolonged C7 transverse process, and muscular anomalies in the scalenus anterior or scalenus medius muscle, fibrous connective tissue anomalies.
Cervical rib syndrome, scalenus anterior syndrome, costoclavicular syndrome, hyperabduction syndrome are types of thoracic outlet syndrome named by the condition that causes it.
Scalenus Anterior Syndrome
The compression on brachial plexus and/or subclavian artery caused by muscle growth.
Cervical Rib Syndrome
The compression on brachial plexus and/or subclavian artery is caused by bone growth termed as cervical rib