Thoracic Outlet Syndrome Flashcards
What is Thoracic Outlet Syndrome (TOS)?
Thoracic outlet syndrome (TOS) refers to the clinical features that arise from compression of the neurovascular bundle within the thoracic outlet.
The signs and symptoms that arise can be divided into neurological (nTOS, most common), venous (vTOS) and arterial (aTOS). Most people affected are between 20-50 years old.
What can cause TOS?
It usually occurs in the setting of hyperextension injuries, repetitive stress injuries (e.g. work-related, particularly when working over the head), or external compressing factors (e.g. poor posture), but can also be secondary to anatomical abnormalities, including that of the 1st rib, an anomalous cervical rib, or bands within the thoracic outlet.
Briefly describe the pathophysiology of TOS
The brachial plexus and subclavian artery pass through the scalene triangle, and the subclavian vein passes anterior to anterior scalene. The brachial plexus can be compressed between the anterior and middle scalene muscles, or against the 1st rib or a cervical rib; typically, it is the lower cord which becomes irritated (resulting in symptoms affecting the ulnar distribution).
As such, hypertrophy of the scalene muscles, abnormality in the first rib, or the presence of a cervical rib can all lead to compression on the brachial plexus or subclavian artery. Previous clavicle fracture can cause abnormal bony healing that compresses on the thoracic outlet. The presence of a costoclavicular ligament can reduce the costoclavicular space, leading to vTOS, due to positional venous obstruction.
What is a cervial rib? And how is it linked to TOS?
A cervical rib is an extra rib that arises from the seventh cervical vertebra. It occurs in 0.2-0.5% of the population and can be partial or complete.
Whilst this increases the risk of thoracic outlet syndrome, the majority of patients with a cervical rib are unaware of it and causes no symptoms. Identification of a cervical rib in an otherwise asymptomatic patient does not warrant any intervention.
What are the risk factors for TOS?
Recent trauma, repetitive motion occupations, athletes or anatomical variations are potential risk factors for TOS.
What are the clinical features of TOS?
The specific clinical features present will be dependent on neurological, arterial, or venous involvement. Symptoms may also worsen with certain movements, e.g. shoulder abduction or extension.
- Compression of the brachial plexus can cause paraesthesia and/or motor weakness, which is often in the ulnar distribution; there may be muscle wasting, and pain can radiate to the neck and upper part of the back
- Venous compression can lead to deep vein thrombosis and extremity swelling (termed Paget-Schrötter syndrome); in untreated severe cases, there can be prominent veins over the shoulder due to collateralisation
- Arterial compression can cause claudication symptoms or acute limb ischaemia through either occlusion, distal embolisation, or aneurysm formation
On examination, assess for areas of weakness or numbness, for swelling or tenderness, and any features of limb ischaemia. Tenderness over the scalene muscles is often present.
