1

What is thoracic outlet syndrome (Figure 1)?

Thoracic outlet syndrome (TOS) represents the presence of upper extremity symptoms caused by compression of the neurovascular bundle in the posterior triangle of the neck at the level of the 1st rib.

It has previously been described as scalenus anticus syndrome, costoclavicular syndrome, hyperabduction, cervical rib or 1st rib syndrome.

2

Describe the anatomy of the thoracic outlet (Figure 2)

Anatomically, the thoracic outlet extends from the supraclavicular fossa to the axilla and includes the area between the clavicle and the 1st rib.

The thoracic outlet consists of three compartments, each of which is a potential site of neurovascular compression:

a)

interscalene triangle;

b)

costoclavicular space;

c)

subcoracoid space (deep to the pectoralis minor tendon).

Technically, as the neurovascular bundle traverses down through the chest, the superior aspect of the thoracic cage should be known as the thoracic inlet and the inferior aspect of the thoracic cage (covered by the diaphragm) should be known as the thoracic outlet. To maintain consistency with the medical literature, however, this chapter uses the term ‘thoracic outlet’ to describe the superior aspect of the thoracic cage.

3

What is the pathophysiology of thoracic outlet syndrome?

Compression of the neurovascular structures of the thoracic outlet can be caused by a variety of bony and soft tissue abnormalities, including:

a)

cervical rib – which is a supernumerary rib originating from the 7th cervical vertebra and occurs in <1% of the general population, with only 10% of those patients experiencing symptoms (Figure 3);

b)

elongated C7 transverse process;

c)

abnormal 1st rib or clavicle – which can cause compression through exostosis, tumour, callus or fracture (trauma);

d)

anatomic variations of the scalene muscles;

e)

anomalous fibrous bands – including those from the C7 transverse process to the upper surface of the 1st rib.

4

What is the classification of thoracic outlet syndrome?

TOS is traditionally classified according to the anatomical structure being compressed:

a)

neurogenic (NTOS) – which is caused by compression of the brachial plexus nerves;

b)

arterial (ATOS) – which is caused by compression of the subclavian artery;

c)

venous (VTOS) – which is caused by compression of the subclavian vein. It may result in thrombosis of the subclavian vein (Paget-Schroetter syndrome).

The classification of TOS can be also based on aetiology, symptoms or clinical presentation.

Another classification, which mixes anatomy with aetiology, describes five types of TOS, including true neurogenic, disputed neurogenic, venous, arterial and traumatic.

5

What is the epidemiology of thoracic outlet syndrome?

TOS is usually diagnosed in patients aged 20-50 years and rarely occurs in paediatric patients.

The most common form of TOS is NTOS (95% of cases), followed by VTOS and ATOS.

Women are 3-4 times more likely to develop NTOS.

The incidence of VTOS is increased in competitive athletic men, secondary to hypertrophy of the subclavius muscle, a small triangular muscle that lies between the clavicle and the 1st rib.

6

What are the characteristic features of neurogenic thoracic outlet syndrome?

Aetiology may involve cervical ribs, anomalous 1st ribs and congenitally narrow scalene triangles.

Aggravating factors include:

a)

hyperextension neck injury, from a whiplash injury following a road traffic accident or a fall on ice;

b)

repetitive injury at work, most often from sitting at a keyboard for long hours.

Symptoms include pain, paraesthesia and weakness in the arm and hand. Paraesthesia most often involves all five fingers but is usually most noticeable in the 4th and 5th fingers and the ulnar forearm.

In addition to upper extremity symptoms, NTOS usually includes pain in the neck, over the trapezius and anterior chest wall, and occipital headaches.

7

What are the characteristic features of venous thoracic outlet syndrome?

Aetiology involves either thrombotic or non-thrombotic obstruction of the subclavian vein, caused by congenital anatomic narrowing at the point where the subclavian and internal jugular veins join to form the innominate vein. Thrombosis may be precipitated by excessive inactivity of the arm or an underlying coagulopathy.

Symptoms may include pain and sometimes mild paraesthesia. Neck pain and headaches are seldom seen.

Physical findings include swelling of the arm, forearm and hand, as well as discoloration, cyanosis, and visible subcutaneous veins over the involved shoulder and chest wall.

8

What are the characteristic features of arterial thoracic outlet syndrome?

Aetiology involves compression of the subclavian artery, which gives rise to the development of an aneurysm, with the potential for thrombus formation and distal embolisation. The aneurysm and stenosis are usually asymptomatic until embolisation occurs.

Symptoms include changes in the hands and fingers, including pain, paraesthesia and cold fingers. Shoulder pain, neck pain or paraesthesia is rare.

Physical findings typically include loss of pulses with the arm by the side and pulled downward or by elevating the arm above the head. It is occasionally associated with colour changes or ischaemic fingertips. In the supraclavicular area, there may be a tender lump, bony prominence or even pulsation of the subclavian artery, which may indicate aneurysm formation.

Although ATOS has the most serious symptoms and limb-threatening implications including digital gangrene, it is very rare.

9

What are the compression and release phenomena?

The compression phenomenon represents the presence of symptoms while using prolonged postures, such as protracted and depressed shoulder girdles with the head forward, or activities, such as working overhead with elevated arms, that increase the tension or compression of the neurovascular bundle.

The release phenomenon represents return of normal sensation following release of tension or compression of the perineural blood supply to the brachial plexus. It is a prognostic indicator of a favourable outcome.

10

Which provocative clinical tests are used to aid the diagnosis of thoracic outlet syndrome?

Supraclavicular pressure test – which addresses compromise to the brachial plexus through the interscalene triangles. The patient is seated with arms at the side and the examiner places fingers on the upper trapezius and thumb on the anterior scalene muscle near the 1st rib. The examiner then squeezes the fingers and thumb together for 30 seconds, with a positive test represented by reproduction of the pain or paraesthesia.

Adson’s test – which addresses compromise to the brachial plexus through the interscalene triangles (both ipsilateral and contralateral). The patient is seated upright with arms at the side and the radial pulse is palpated. The patient then inhales deeply and holds their breath for up to 30 seconds while extending and rotating their neck toward the tested side. A positive test is represented by a change in the radial pulse or the presence of pain or paraesthesia.

Costoclavicular manoeuvre – which addresses provocation from narrowing of the costoclavicular space, with subclavian artery, subclavian vein or brachial plexus entrapment. The patient is seated with arms at the side with the examiner assisting the patient in performing scapular retraction, depression, elevation and protraction, holding each position between 30-60 seconds. The patient then rests their forearms on their thighs while the examiner monitors for changes in pulse and symptom onset. A positive test is represented by a change in the radial pulse, pain, paraesthesia or symptom provocation.

Wright’s test – where the patient, from a sitting position, holds their arm upwards and backwards (hyperabduction), rotating it outward. This examines neural tissue compromise through the thoraco-coraco-pectoral space, with changes in the radial pulse indicating compression.

Elevated arm stress test (Roos stress test) – which examines the result of loading the brachial plexus throughout the thoracic outlet. It is the most sensitive and specific test for neurological TOS. The patient is seated with their arms above 90° of abduction, full external rotation, elbows flexed to 90° and the head in a neutral position. The patient then opens and closes their hands, making a fist, while holding their arms in the elevated position for 3 minutes. A positive test is represented by the inability to maintain the position for 3 minutes, pain, paraesthesia or discontinuation by dropping their arms for pain relief.

Cyriax release test – which examines the result of unloading of the brachial plexus throughout the thoracic outlet. The patient is seated or standing, with the examiner standing behind the patient, grasping under the forearms, holding the elbows at 80° of flexion, and the forearms and wrists in neutral. The patient then leans posteriorly and passively elevates the shoulder girdle, holding this position for up to 3 minutes. A positive test is represented by a return of normal sensation (release phenomenon).

Upper limb neural tension test – which examines provocation to the neural tissue passing through the thoracic outlet under a tension load. The patient is assessed for symptoms whilst lying supine; with downward pressure on the shoulder girdle; shoulder abducted to ~110°; forearm into maximal supination; digit extension; ulnar deviation; wrist extension; full external rotation of the shoulder; full elbow extension; and lateral flexion of the head away from the upper extremity being tested. A positive test is represented by the presence of radicular symptoms during the execution of these manoeuvres.

It is important to note, however, that provocative clinical testing for TOS has been reported to display high false-positive and false-negative rates.

11

What are the differential diagnoses of thoracic outlet syndrome?

Cervical disc disease (protrusion/compression).

Cervical vertebral facet disease.

Malignancies, including Pancoast tumour, nerve sheath tumours and spinal cord tumours.

Peripheral nerve entrapment, including the ulnar or median nerve.

Neuropathic syndromes of the upper extremity, including complex regional pain syndrome I and II.

Neurologic disorders, including multiple sclerosis.

Brachial plexitis.

Shoulder pathology, including rotator cuff injuries.

Muscular spasm.

Fibromyalgia.

Vascular disease, including Raynaud’s disease or vasculitis.

Angina.

12

Describe the radiographical findings in a patient with suspected thoracic outlet syndrome (Figure 4)

A cervical and chest radiograph should be performed in all patients with suspected TOS to identify the presence of a cervical rib, anomalous 1st rib or previous clavicular trauma.