The thoracic outlet is an anatomical region located between the neck and the shoulder. It extends from the anterior scalenus muscle anteriorly to the posterior scalenus muscle dorsally, and is limited by the first rib.

The outlet contains the nerves of the brachial plexus as well as the subclavian artery. The subclavian vein runs volar to the thoracic outlet.

The thoracic outlet syndrome encomapsses all clinical manifestations related to the intermittent or permanent compression of the brachial plexus (nerves) and/or of the upper limb vessels (subclavian artery and vein).

As they travel from the cervical region to the upper limb, the neuro-vascular bundles (brachial plexus nerves, subclavian artery and vein) are surrounded by muscular, bony, tendinous and ligament structures. During certain movements of the arm, or in certain positions, these rigid structures may cause compression.

• Between the scalenus muscles
• At the level of the costo-clavicular outlet (below the clavicle)
• Art the level of the axilla (below the pectoralis minor tendon)

• A bone anomaly: supernumerary rib, C7 transverse mega-apophysis, bone callus resulting from a clavicle fracture
• Muscle structures : supernumerary muscle, scalenus muscle hypertrophy (bodybuilders)
• Tendon or ligament anomalies : fibrous bands at the level of the pleural dome or the first rib

Such bone, muscle, and ligament anomalies are common and don?t necessarily lead to TOS. In 40% of cases, the syndrome is the result of trauma in patients with an anatomical predisposition to compression.

The symptoms are numerous and vary widely :

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• tingling sensation (paresthesia) most often located in the C8-D1 territory (i.e. ring and little finger)
• Burning sensation, swelling, discomfort, pain, heaviness
• Occasional finger swelling (the ring sign)
• Vessel dilatation around the shoulder (collateral venous circulation) may also be observed.

During the clinical exam, a complete examination of the cervical region and a neurological examination must be performed.

A number of tests are specific to the TOS, such as:
- Roos test (hands up test)
- Adson's maneuver

EMG Test
X-rays of the chest and cervical spine to check for bone malformation
Dynamic ultrasonography
Arteriogram or angio-CT scan
Brachial plexus MRI
Lab tests including hemostasis

Most of the time, the TOS produces only minor symptoms, and the first step should be a prolonged rehabilitation program based on the PEET protocol, which aims at increasing the subclavian space.

If the symptomatology is too bothersome, or if rehabilitation fails, a surgical option may be considered. Such procedure must be thoroughly discussed with the patient beforehand.

The procedure consists in decompressing the brachial plexus, performing a scalenectomy and, occasionally, removing a transversal apophysis or the first rib. At times, the arteries may need a specific procedure.