Thoracic outlet syndrome (TOS) is a broad term that refers to compression of the neurovascular structures in the area just above the first rib and behind the clavicle that results in upper extremity symptoms. It represents a constellation of symptoms. The cause, diagnosis, and treatment are controversial. The brachial plexus (95%), subclavian vein (4%), and subclavian artery (1%) are affected such that TOS is usually classified into neurogenic, venous, and arterial forms.  Most presentations to the emergency department (ED) are nonemergent and require only symptomatic treatment and referral.
The brachial plexus trunks and subclavian vessels are subject to compression or irritation as they course through 3 narrow passageways from the base of the neck toward the axilla and the proximal arm. The most important of these passageways is the interscalene triangle, which is also the most proximal. This triangle is bordered by the anterior scalene muscle anteriorly, the middle scalene muscle posteriorly, and the medial surface of the first rib inferiorly. This area may be small at rest and may become even smaller with certain provocative maneuvers. Anomalous structures, such as fibrous bands, cervical ribs, and anomalous muscles, may constrict this triangle further. Repetitive trauma to the plexus elements, particularly the lower trunk and C8-T1 spinal nerves, is thought to play an important role in the pathogenesis of thoracic outlet syndrome (TOS).
The second passageway is the costoclavicular triangle, which is bordered anteriorly by the middle third of the clavicle, posteromedially by the first rib, and posterolaterally by the upper border of the scapula.
The last passageway is the subcoracoid space beneath the coracoid process just deep to the pectoralis minor tendon.
Because no objective confirmatory test is available for thoracic outlet syndrome (TOS), there is much disagreement with regards to its true incidence, with reported figures ranging from 3-80 cases per 1000 people.
Neurologic TOS is generally neither progressive nor likely to resolve spontaneously.
Arterial or venous TOS usually results in a good outcome with adequate treatment.
Neurologic complications include chronic pain.
Arterial complications include thrombosis, thromboembolism, acute ischemia, and poststenotic aneurysm formation.
Venous thrombosis may develop.
Overall, the entity is approximately 3 times more common in women than in men. However, the sex ratio varies depending on the type of thoracic outlet syndrome (TOS) (eg, neurologic, venous, arterial), as follows:
Neurologic - Female-to-male ratio approximately 3.5:1
Venous - More common in males than in females
Arterial - No gender predilection
The onset of symptoms usually occurs in persons aged 20-50 years.
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