Thoracic outlet syndrome is not the name of a single entity but rather a collective title for a variety of conditions attributed to the compression of neurovascular structures as they traverse the thoracic outlet. [1, 2, 3, 4, 5, 6] The thoracic outlet is bordered by the scalene muscles, first rib, and clavicle. Neurovascular structures pass from the neck and thorax into the axilla through this space. Thoracic outlet syndrome remains one of the most controversial clinical entities in medicine. [7, 8, 9] See the image below.
Diagnosis and management
To exclude systemic disease and inflammation, a few simple blood tests may refine the differential diagnosis for thoracic outlet syndrome, including a blood glucose level, complete blood cell (CBC) count, erythrocyte sedimentation rate (ESR), basic metabolic panel, thyrotropin level, and rheumatologic workup, if indicated.
Imaging studies that can be used in the diagnosis of thoracic outlet syndrome include the following:
Computed tomography (CT) scanning and magnetic resonance imaging (MRI) - Useful for identifying other conditions that might cause similar symptoms
Magnetic resonance angiography (MRA)
Venography and duplex scanning
Electrodiagnostic studies can be helpful in classic cases of neurogenic thoracic outlet syndrome. However, many symptoms are intermittent in this disorder; therefore, negative test results do not rule out the diagnosis.
Surgery in cases of thoracic outlet syndrome is indicated for acute vascular insufficiency and progressive neurologic dysfunction. Other patients should receive nonoperative treatment that, in the acute phase, includes relative rest, nonsteroidal anti-inflammatory medications (NSAIDs), cervicoscapular strengthening exercises, and modalities such as ultrasound, transcutaneous nerve stimulation, and biofeedback. Physiotherapy in the acute phase focuses on pain control and range of motion with specific stretching exercises.
The wide variability of symptoms and signs in patients with thoracic outlet syndrome and the lack of an objective confirmatory test for the diagnosis makes correctly identifying patients with thoracic outlet syndrome difficult.  Therefore, determining its exact incidence remains elusive; estimates range from 3-80 cases per 1000 population.  Thoracic outlet syndrome is more common in women, particularly those with poor muscular development, poor posture, or both. 
The neurovascular bundle courses through 3 spaces, or triangles, as it exits the neck to reach the axilla and proximal arm. All 3 spaces can be the source of compression of the various components of the neurovascular bundle, including the brachial plexus and the subclavian vessels.  These spaces are small at rest and become even smaller with certain arm maneuvers, such as abduction and external rotation. [14, 15] This can aid in the diagnosis of thoracic outlet syndrome and forms the basis for provocative testing, which is discussed later (see Clinical, Physical).
The first space is the interscalene triangle. It is bordered by the anterior scalene muscle, the middle scalene muscle, and the upper border of the first rib. This space contains the trunks of the brachial plexus and subclavian artery. The interscalene triangle is the most common site for neural compression, vascular compression, or both. 
The second space is the costoclavicular triangle, which is bordered by the clavicle, first rib, and scapula and contains the subclavian artery and vein and the brachial nerves.
The third and final space is beneath the coracoid process just deep to the pectoralis minor tendon; it is referred to as the subcoracoid space.
Thoracic outlet syndrome is most often seen in patients who engage in repetitive motions that place the shoulder at the extreme of abduction and external rotation. An example of such activity is swimming, especially with the freestyle stroke, butterfly stroke, and backstroke. When a swimmer reports tightness and pain around the shoulder, neck, and clavicle as his or her hand enters the water, thoracic outlet syndrome should be suspected.
In addition to swimmers, other athletes affected by thoracic outlet syndrome include water polo, baseball, and tennis players and athletes in any other activity that places repetitive stress on the shoulder at the extremes of abduction and external rotation. These individuals may present with neurologic and arterial or venous symptoms. Venous thoracic outlet syndrome most commonly develops in young male athletes in whom the upper extremity musculature is overdeveloped as a result of work or physical conditioning. Baseball players, whose sport requires repetitive throwing motions, are at increased risk for arterial thoracic outlet syndrome in their dominant arm.
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