There can be many causes of compression of the neurovascular bundle. Congenital abnormalities such as the cervical or rudimentary first rib and prolonged transverse processes are asymptomatic in most people, but have been shown to be a predisposing factor. Fibrous bands or anomalies in the trasversocostal, costocostal area are reported along with muscular anomalies such as a scalenus anticus muscle or sickle shaped scalene medius muscle (2). Fibromuscular abnormalities are more likely to cause symptoms (3). Post-traumatic is another cause with either isolated or repeated trauma. This can be due to soft tissue abnormalities in the scalenes and is common is whiplash injuries or other motor vehicle accidents. Some fractures such as clavicle fractures can fall under this category. Diagnostic criteria of post-traumatic TOS are the pathogenic mechanism and the onset of symptoms within the first two years. Functional or acquired cases can also occur. Upper limb dysfunction or muscle imbalance of the neck and shoulder region can cause hypertrophic or abnormal scalene muscles. The factors involved in the pathogenesis of these cases include overuse and physical and mental stress phenomena (4). One final cause would be malignancy or mass causing compression. Pancoast tumors, or superior pulmonary sulcus tumors, can invade and compress the brachial plexus (5). Others may be due to benign tumors or osteochondromas (6).

The vascular forms of TOS present in different ways and prompt recognition of the presenting signs can be critical in preventing long term sequelae such as chronic pain and disability. Venous TOS tends to be more common in young men and associated with repetitive upper extremity activity and more commonly affects the dominant arm (1). In the athletic population, it seems to be more common with overhead athletes. It can present in an acute form with phlebitis or in a more chronic form exacerbated by arm position. An occlusion or thrombosis caused by repetitive or strenuous activity with the arms is named Paget-Schroetter syndrome or effort thrombosis. This occurs within the costoclavicular space with the subclavian vein being compressed. Mechanical compression and repetitive injury of the vein below the clavicle and first rib can lead to stagnation and effort thrombosis (7). This typically presents with acute upper extremity swelling, cyanosis, heaviness and pain. Intermittent claudication without thrombosis or due to positional obstruction is called McCleery syndrome. It can present with similar symptoms with periodic arm swelling and discomfort. In the largest series of vascular TOS to date with 626 extremities, Ursehel and Patel reported patients most commonly present with visible collateral veins around the shoulder (99%), followed by arm swelling (96%), bluish discoloration (94%), aching pain with exercise (33%), and cervical ribs (10%). Only 4% of the patients presented with minimal symptoms (8).

Arterial TOS typically occurs within the scalene triangle, but also can occur under the pectoralis minor. The compression incites intimal damage in the arteries, causes turbulent blood flow and vessel dilation. This damage eventually leads to thrombosis and distal embolization that may result in acute upper extremity ischemia. Arterial signs consist of ischemia on effort of the upper limb or positional vasomotor disorders (1). Patients may present initially with a dull ache, numbness or discomfort in the upper extremity that tends to be worse with activity and improves with rest. It is similar to claudication most people associate with lower extremity pain during walking. As this issue progresses, cyanosis, pallor and coolness can occur in upper extremity. Patients may also complain of easy fatigue or a “dead arm” sensation. It is rare to have weakness or sensory deficit (9). More serious presenting symptoms include cerebrovascular accident, acute hand and or digital ischemia.

Physical examination can be helpful with diagnosis. The cervical spine, shoulder and upper extremity should be thoroughly examined. Head and neck posture should be noted and extremities should be compared. Some signs of observation include skin color, temperature and hair distribution. Blood pressure reading in arms can be affected and have large differences of more than 20 mm Hg. The shoulder and chest may have edema in vascular TOS, while there may be signs of pallor with arterial TOS. There may also be supraclavicular fullness or aneurismal pulsations (10).

Use of provocative maneuvers can also be beneficial. Adson test is performed by abducting the patient’s arm to 30 degrees at the shoulder while maximally extended and having the patient extend their neck towards the ipsilateral shoulder. The provider palpates the radial pulse and a positive test is a decrease or absence of the radial pulse of the ipsilateral arm. Adson test was shown to have a specificity of 72 percent and 53 specific (11). East or Roos test is done by placing the arms placed in a “surrender” position with shoulder abducted to 90 degrees while in external rotation, elbows flexed to 90 degrees. The patient slowly opens and closes hand for 3 minutes and a positive test precipitates pain, paresthesias, heaviness of weakness. The upper limb tension test or Elvey test occurs in three positions. Position one occurs with the arms abducted to 90 degrees with elbows flexed, position two has the patient actively dorsiflex both wrists and position three has the patient tilt their head ear to shoulder in both directions. A positive test occurs when positions one and two elicit symptoms on the ipsilateral side, while position 3 can elicit symptoms on the contralateral side. One study compared the Adson and Roos test and showed a specificity of 76 and 30 percent, respectively, when used alone. The specificity was increased to 82 percent when both were positive (11).

Many providers start with a cervical x-ray to rule out cervical first ribs, prominent ribs or transverse processes, fracture calluses and compressive tumors can sometimes be seen. The prior gold standard for thoracic TOS was arteriography and venography (catheter based), but these have been replaced by less invasive methods and methods that assess the surrounding structures (1). Ultrasound maintains high sensitivity and specificity and is noninvasive and inexpensive. It is typically the first test used for imaging of suspected thoracic TOS. Moreover, DUS has the advantage of assessing dynamic blood flow during compression maneuvers (hyperabduction), with a decrease in arterial diameter, changes in peak velocity or reproducible symptoms considered to be diagnostic of TOS. CT or MR angiography can differentiate equivocal cases or provide additional anatomical detail (12). It can be performed in different positions as well, such as neutral and arm abduction.

The natural history of acute venous TOS with subclavian-axillary vein thrombosis is associated with high long-term morbidity and disability. Treatment involves consideration of 3 therapies in addition to anticoagulation: thrombolysis, decompression and venoplasty. The therapy selected is dependent on the stage of presentation and provider knowledge. For patients with acute symptoms (<6 weeks), prompt catheter-directed thrombolysis with early surgical decompression of the thoracic outlet by first rib resection has been reported with greater than 90 percent clinical success. Anticoagulation is normally given for 3-6 months until venous patency is confirmed on imaging and follow up. In patients with symptoms greater than 6 weeks (chronic) with evidence of stenosis or occlusion, surgical decompression is typically performed with preoperative thrombolysis in patients with total occlusion. Venoplasty may be performed for residual subclavian stenosis. In patients with intermittent obstruction, patient may try conservative measures such as limiting provocative positions. In many patients, surgical decompression without anticoagulation or venoplasty is performed. More recently, less invasive options such as robotic and thoracoscopic assisted approaches are being used with minimal brachial plexus manipulation (1,13).