Thoracic Outlet Syndrome (Obstruction) 

Updated: Sep 17, 2020
Author: Mark K Eskandari, MD; Chief Editor: Vincent Lopez Rowe, MD 


Practice Essentials

Thoracic outlet syndrome (TOS) is a collective term for a constellation of compressive problems that occur at the thoracic outlet. It has been an important clinical entity for more than a century.

In 1821, Cooper described axillary-subclavian artery symptoms due to compression from a cervical rib. In 1875, Paget described clinical symptoms resulting from subclavian vein thrombosis (eg, arm swelling, pain). In 1884, von Schroetter correctly attributed these upper-extremity symptoms to thrombosis or compression of the subclavian vein at the thoracic outlet. Consequently, venous thrombosis at the thoracic outlet is known as venous TOS or Paget-Schroetter syndrome.[1]

TOS has distinct clinical pictures (ie, neurogenic, arterial, and venous) caused by compression of the neurovascular structures at the thoracic outlet. The classification is based on which structure is primarily involved.

The indication for surgical treatment of neurogenic TOS is the failure of conservative treatment in a patient with disability so severe that the patient is unable to work or live comfortably. The indication for surgical treatment of venous TOS is controversial but is based on symptomatology and venographic evidence of compression at the thoracic outlet. Arterial TOS, however, in most circumstances should be treated surgically with first-rib resection and arterial repair.


The relevant anatomy of TOS focuses on the scalene triangle and the costoclavicular space. Reports of compression of the neurovascular bundle at the area of the pectoralis minor space exist, but this is very uncommon and will not be discussed further.

Neurogenic and arterial TOS result from compression that occurs in the scalene triangle, which is defined by the first rib, the anterior scalene muscle, and the middle scalene muscle. The subclavian artery and the branches of the brachial plexus pass through the borders of this triangle (see the image below).

Thoracic outlet obstruction. Scalene triangle. Thoracic outlet obstruction. Scalene triangle.

Venous TOS occurs secondary to compression that occurs in the costoclavicular space. The borders of the costoclavicular space are the first rib, the costoclavicular ligament, the subclavius, and the anterior scalene muscle. As the subclavian vein passes through this space, it is susceptible to compression by these structures, as depicted in the image below.

Thoracic outlet obstruction. Costoclavicular space Thoracic outlet obstruction. Costoclavicular space.

Other important local structures are the phrenic nerve, the lateral thoracic nerve, and the thoracic duct. The phrenic nerve passes from lateral to medial along the anterior border of the anterior scalene muscle, and the lateral thoracic nerve passes through the body of the middle scalene muscle. The thoracic duct joins cervical lymphatics and drains into the superior aspect of the jugulosubclavian vein confluence behind the left sternocleidomastoid muscle. Care must be taken to avoid injury to these structures during surgery.

A search for cervical, rudimentary, or broad first ribs should be done. These structures should be resected during surgical therapy. Rudimentary ribs usually arise higher in the neck than normal first ribs and typically articulate with the second rib rather than with the sternum. Cervical ribs and rudimentary first ribs occur in less than 0.5% of the population.

Abnormal scalene muscle anatomy also has been identified and may be a cause of some symptoms. For example, these muscles have been noted to interdigitate around the cords of the brachial plexus and, thus, have been implicated in the irritation of the cords of the brachial plexus.

In a study of 98 meticulously dissected cadavers, the authors noted a number of abnormalities of the thoracic outlet fibrous bands and cervical ribs, and other abnormalities were found in most of the patients. Only 10% of the dissected cadavers were found to have normal anatomy bilaterally.


Neurogenic TOS most commonly is associated with a history of neck trauma. Swollen and scarred muscles or aberrant scalene anatomy can irritate cords of the brachial plexus locally and lead to the neurologic symptoms.

Arterial TOS often is associated with cervical ribs or a rudimentary first rib.[2, 3] This aberrant anatomy leads to repeated intermittent arterial compression coinciding with arm movement. This repetitive localized trauma leads to intimal lesions, focal arterial stenosis, poststenotic dilatation, aneurysmal change, and subsequent thromboembolic complications. The second portion of the subclavian artery, which has a retroscalene position, often is the site of positional compression and stricture.

Venous TOS usually results from compression of the subclavian vein by the subclavius and the costoclavicular ligament.[4] When local structures are placed in abnormal or unaccustomed positions by extremes of activity or injury, vein compression and subsequent vein thrombosis can result. Venous TOS tends to occur in the more active dominant extremity.

Arterial and venous TOS usually are associated with certain predisposing anatomic abnormalities, whereas neurogenic TOS is more likely to result after traumatic injury.


The potential for either neurologic or vascular compression exists at the thoracic outlet. When compression occurs, one of the TOSs may develop. Neurogenic and arterial TOS result from compression that occurs in the scalene triangle (see the first image below), and venous TOS results from compression in the costoclavicular space (see the second image below).[5]

Thoracic outlet obstruction. Scalene triangle. Thoracic outlet obstruction. Scalene triangle.
Thoracic outlet obstruction. Costoclavicular space Thoracic outlet obstruction. Costoclavicular space.


Neurogenic TOS is the most common presentation, reported to occur in approximately 95% of patients. Arterial TOS is the next most common presentation, reported to occur in about 2-3% of patients who are affected. Venous TOS is the least common presentation, accounting for about 1-2% of patients with TOS.

In a single-institution study by Illig et al, the annual incidence of neurogenic TOS was cited as 2-3 cases per 100,000 population, whereas that of venous TOS was 0.5-1.0 per 100,000 population; arterial TOS was sporadic.[6]

Approximately 70% of patients with neurogenic TOS are females aged 20-50 years. Venous TOS occurs with a male-to-female ratio of 2:1.


Most patients do not experience full relief of symptoms after surgery for neurogenic TOS. A good result occurs when partial relief is achieved and symptoms do not progress. Approximately 40-80% of patients who undergo surgical treatment have some relief of symptoms. Approximately 10-15% of patients who initially experience symptomatic relief have recurrence of symptoms.

If only first-rib resection was performed, these patients may benefit from anterior and middle scalenectomy along with neurolysis. If only scalenectomy was performed, a second operation with first-rib resection and neurolysis may be considered. Only 40% of patients experience long-term symptomatic relief after reoperation for TOS.

Patients with arterial and venous TOS usually do well if workup and treatment have been appropriate.

In a study that used data from the American College of Surgeons (ACS) National Surgical Quality Improvement Program (NSQIP) to evaluate 30-day outcomes of brachial plexus surgical decompression for TOS (N = 225), first and/or cervical rib resection (± scalenectomy; n = 205) was compared with rib-sparing scalenectomy (n = 20).[7] Rib resection was associated with longer operating times and hospital stays. Only eight patients experienced complications at 30 days of whom seven were in the rib-resection group.

A review of outcomes for 538 patients who underwent 594 first-rib resections for neurogenic (n = 308), venous (n = 261), or arterial (n = 25) TOS reported excellent results, attributed to appropriate selection of neurogenic TOS patients, use of a standard protocol for venous TOS patients, and expeditious intervention in arterial TOS patients.[8]

A systematic review of outcomes for transaxillary first-rib excision (TAFRE), supraclavicular first-rib excision with scalenectomy (SCFRE), and supraclavicular release leaving the first rib intact (SCR) in patients with neurogenic TOS found that SCR had a high probability of a success rate greater than 80%, whereas both TAFRE and SCFRE had a low probability of a success rate greater than 80% but a high probability of a success rate greater than 70%.[9]  The complication rates were 22.5% for TAFRE, 25.9% for SCFRE, and 12.6% for SCR.



History and Physical Examination

Neurogenic thoracic outlet syndrome

Neurogenic thoracic outlet syndrome (TOS) is a clinical diagnosis that only is made when objective findings are supported by subjective symptoms and physical findings. Other diagnoses that should be considered include tendinitis, fibromyalgia, cervical disc herniation, spinal stenosis, carpal tunnel syndrome, repetitive motion syndrome, and epicondylitis.

A history of a motor vehicle collision (MVC) or other neck trauma is usually elicited, and patients may report a variety of symptoms, such as neck, shoulder, and arm pain. Symptoms of compression from all cords of the brachial plexus are the most common neurologic pattern noted with TOS.

It has often been maintained that ulnar nerve involvement is the typical pattern of symptoms related to neurogenic TOS, but this is not the case. Paresthesias and weakness in an arm, occipital headaches, and paraspinal muscle pain are common. The paraspinal muscle pain and occipital headaches are secondary to referred nerve pain.

As expected, specific symptoms coincide with the area of the brachial plexus that is compressed. On physical examination, symptoms usually can be reproduced with pressure on the scalenes and with abduction/external rotation (AER) of the arms. Coldness and color changes in the hand usually are secondary to sympathetic nerve involvement rather than arterial involvement.

The examination should focus on the neurologic and vascular findings. The scalene muscles and supraclavicular fossa should be carefully examined for abnormal pulsations, bruits, and pain with palpation. All upper-extremity pulses should be assessed, and provocative positioning should be performed during the vascular examination. Petechiae and other evidence of embolic events should also be sought.

Arterial thoracic outlet syndrome

The mean age of patients with arterial TOS at presentation is approximately 10 years older than that of patients with neurogenic TOS. Occasionally, arterial TOS is recognized during workup for other pathologies. An incidental pulsatile mass or a supraclavicular bruit may be noted during thorough physical examination. Unfortunately, arterial TOS usually remains unrecognized until a thromboembolic complication occurs. Patients who embolize may present with hand claudication, gangrene, and other embolic stigmata.

Venous thoracic outlet syndrome

In 80% of cases of venous TOS, the dominant extremity is involved. The diagnosis is based on the clinical presentation of upper-extremity swelling, venous engorgement, and pain. These signs and symptoms, in association with radiologic documentation of venous compression at the thoracic outlet, confirm the diagnosis of Paget-Schroetter syndrome. Sometimes, venous compression cannot be demonstrated, and the diagnosis is made clinically and by the pattern of venous thrombosis.

Pulmonary embolism has been reported in patients with primary venous thrombosis, but this more commonly occurs in patients presenting with secondary venous thrombosis. Secondary venous thrombosis occurs due to processes such as malignancy, polycythemia vera, heart failure, infection, drug abuse, thrombocytosis, estrogens, and, most commonly, central venous catheters and indwelling cardiac pacing wires.

Upper-extremity deep venous thrombosis (DVT) accounts for 1-4% of all DVTs, and primary venous thrombosis accounts for 25% of these cases. Catheter-related DVTs account for most upper-extremity DVTs.



Laboratory Studies

No laboratory studies are required for the workup of thoracic outlet syndrome (TOS), because no laboratory study aids in the diagnosis of this condition. However, laboratory studies are useful for ruling out other diseases, such as a hypercoagulable state in venous thrombosis, and they also may be useful in preparing a patient for general anesthesia.

Chest Radiography

Chest radiography may be helpful in evaluating patients with neurogenic or arterial TOS. Cervical ribs or rudimentary first ribs often can be identified on chest radiography.

Computed Tomography

Standard computed tomography (CT) may help rule out other pathologic conditions that might cause symptoms mimicking TOS. For example, a herniated cervical disk or spinal stenosis is diagnosed by means of CT.

CT with three-dimensional (3D) reconstruction has become popular for evaluating the thoracic outlet. With the use of 3D CT scanning, compression of the structures at the thoracic outlet can be demonstrated clearly by using dynamic positioning (see the images below).

Thoracic outlet obstruction. Three-dimensional CT Thoracic outlet obstruction. Three-dimensional CT scan showing subclavian artery at the thoracic outlet.
Thoracic outlet obstruction. Three-dimensional CT Thoracic outlet obstruction. Three-dimensional CT scan showing subclavian artery with the arm abducted.

CT arteriography (see the first and second images below) and venography (see the third and fourth images below) can produce excellent images by using maximal intensity projection (MIP).

Thoracic outlet obstruction. CT scan, maximal inte Thoracic outlet obstruction. CT scan, maximal intensity projection (MIP), showing subclavian artery in the neutral position.
Thoracic outlet obstruction. CT scan, maximal inte Thoracic outlet obstruction. CT scan, maximal intensity projection (MIP), showing subclavian artery when arm is abducted.
Thoracic outlet obstruction. CT scan, maximal inte Thoracic outlet obstruction. CT scan, maximal intensity projection (MIP), showing subclavian vein in neutral position.
Thoracic outlet obstruction. CT scan, maximal inte Thoracic outlet obstruction. CT scan, maximal intensity projection (MIP), showing subclavian vein in abducted position.

Magnetic Resonance Imaging

Standard magnetic resonance imaging (MRI) also can be used to rule out alternative diagnoses. It may be the noninvasive imaging modality of choice for suspected TOS.[10]  Dynamic MRI with gadolinium infusion provides detail of the thoracic outlet and may be helpful when evaluating for compression. Gadolinium-enhanced magnetic resonance angiography (MRA) is thought to hold significant potential for imaging the thoracic outlet.

Poretti et al described an MRA protocol for evaluation of TOS that permitted separate assessment of veins and arteries through the use of a single, simultaneous and bilateral (SB-MRA) contrast injection that was valid for both abduction and adduction.[11]  The investigators found this protocol to be safe and reliable and to be helpful for the diagnosis of TOS of arterial or venous origin.

Arteriography and Venography

Arteriography with dynamic positioning is used to demonstrate compression of the subclavian artery. Angiography may identify axillary-subclavian aneurysm (see the image below), and if an aneurysm is present, it is useful in planning surgery. Arterial stenosis with poststenotic dilatation also may be identified angiographically.

Thoracic outlet obstruction. Angiogram showing sub Thoracic outlet obstruction. Angiogram showing subclavian artery aneurysm in abduction/external rotation (AER).

Venography with dynamic positioning demonstrates abnormalities of the subclavian vein in patients with Paget-Schroetter syndrome (see the image below). Interestingly, venography of the contralateral arm of patients with venous TOS identifies compression with dynamic positioning in as many as 80% of patients. Despite the compression that occurs in the contralateral extremity, the incidence of contralateral DVT is only 15%.

Thoracic outlet obstruction. Venogram showing veno Thoracic outlet obstruction. Venogram showing venous stenosis.

During venography, abduct patients' arms to only 30° to avoid an erroneous diagnosis of complete vein occlusion. Always perform provocative maneuvers under fluoroscopy to document venous compression in patients with presumed Paget-Schroetter syndrome. If compression of the vein is not identified at 30º of abduction, then rotation of the neck, flexion or extension of the neck, or further abduction may be useful.


In venous TOS, ultrasonography (US) is useful as a noninvasive test to search for collateral circulation and evaluate the extent of thrombosis. Identification of significant collaterals may help with operative planning and may determine the type of exposure used in order to limit damage to these collaterals. Intravascular US (IVUS) has also been used to evaluate residual subclavian vein stenosis in patients who have undergone first-rib resection with anterior scalenectomy for venous TOS.[12]

In arterial TOS, US can document stenosis, poststenotic dilatation or aneurysm of the subclavian artery, and mural thrombus.

In neurogenic TOS, the finding of compression of the subclavian vein or artery on duplex US can facilitate diagnosis.[13]

Other Tests

Electromyography (EMG) and nerve conduction studies are useful in the workup of patients suspected of having neurogenic TOS. EMG usually yields normal findings in patients with TOS, but it is helpful in ruling out other neuromuscular problems. Nerve conduction velocity studies usually are more helpful than EMG is. A reduction in nerve conduction velocity of less than 85 m/s in either ulnar or median nerves across the thoracic outlet corroborates the diagnosis of neurogenic TOS. These studies also can be used as baseline values before treatment.

In evaluating a patient with neurogenic TOS, careful examinination of the scalene muscles and supraclavicular fossa is important. Scalene muscle block with local anesthetic has a 94% correlation with good early results of surgery.

The Adson sign is the loss of the radial pulse upon rotation of the head to the ipsilateral side and inspiration. A positive test result was considered pathognomonic for TOS, but the Adson test no longer is considered reliable, because these findings occur in as many as 53% of subjects without TOS.

Histologic Findings

Muscle biopsy specimens from patients with neurogenic TOS show that type I fibers predominate and type II fibers atrophy. Increased fibrosis also has been noted in the scalene muscles of these patients. These findings suggest that repetitive trauma may have a role in the development of neurogenic symptoms.



Approach Considerations

The indication for surgical treatment of neurogenic thoracic outlet syndrome (TOS) is the failure of conservative treatment in a patient with disability so severe that the patient is unable to work or live comfortably. The indication for surgical treatment of venous TOS is controversial but is based on symptomatology and venographic evidence of compression at the thoracic outlet. Arterial TOS, however, in most circumstances should be treated surgically with first-rib resection and arterial repair.

No absolute contraindication for the surgical treatment of patients with TOS exists. An individual patient may have significant comorbidities that outweigh the benefits of surgical repair and thus may have a relative contraindication for surgery.

Continued clinical investigation may help better define the timing of thoracic outlet decompression after thrombolytic therapy for Paget-Schroetter syndrome. In addition, better patient selection may improve the results for neurogenic TOS. A randomized prospective study would be helpful in determining optimal treatment for patients with neurogenic TOS; however, because of the relative rarity of this condition, multi-institutional participation would be required.

Medical Therapy

Neurogenic thoracic outlet syndrome

Physical therapy has an important role in the initial treatment of neurogenic TOS. Postural exercises, stretching, abdominal breathing, and medications used to relieve muscular tension and pain are beneficial. Abdominal breathing and postural exercises relax the neck musculature, which helps to relieve symptoms.

Approximately 60% of patients improve significantly with conservative treatment alone. The indication for surgical treatment of neurogenic TOS is the failure of conservative treatment in a patient with disability so severe that the patient is unable to work or live comfortably. Most physicians prescribe 3-12 months of physical therapy before considering surgical decompression of the thoracic outlet.

Arterial thoracic outlet syndrome

No satisfactory medical treatment for arterial TOS exists. These patients usually present with a history of thromboembolic complications and require surgical repair. Arterial TOS requires prompt surgical intervention to treat or prevent acute thromboembolic events.

Confusion may occur when a patient presents with an upper-extremity thromboembolic event and no identifiable source. If a cervical rib or an aberrant first rib is identified under these circumstances, opening the artery and examining for intimal lesions has been proposed. If an intimal lesion is found, then the patient should undergo thoracic outlet decompression and repair of the artery.

Endovascular repair of subclavian arterial aneurysms has been described, but this treatment modality does not abolish the need for surgical decompression. Aneurysm resection and arterial replacement remains the preferred treatment. Endovascular treatment of large arterial aneurysms may be useful when a difficult exposure is anticipated.[14]

Venous thoracic outlet syndrome

Treatment for venous TOS–related effort thrombosis that relies on anticoagulation and arm elevation leaves 74% of patients with residual disability and 12% with a significant complication. Thrombolytic therapy generally is preferred to venous thrombectomy; however, thrombectomy still may play a role in some cases with low surgical risk and contraindication to thrombolytic therapy.

Although thrombolytic therapy alone is superior to simple anticoagulation in patients who present with venous TOS, the patients who achieve the best results are those who are treated with thrombolytics and surgical decompression. Unfortunately, most primary care and emergency department (ED) physicians do not appreciate or share this view, and as a result, most patients with venous TOS are not treated aggressively.

Surgical Therapy

Venous thoracic outlet obstruction

Surgical treatment of venous TOS consists of releasing the extrinsic compression and restoring luminal patency. The traditional view was that a staged approach would be more beneficial, with surgical decompression deferred until several weeks after thrombolytic intervention. The presumed advantage allowed for resolution of the inflammatory response before embarking on the surgical procedure. Subsequent data suggested that a more uniform approach, with treatment completed during a single hospitalization, might be a better option.[15, 16]

If a residual lesion is less than 2 cm long, an option is to perform a thrombectomy with vein patch angioplasty and venolysis during decompression surgery. An alternative option is to perform vein angioplasty in a staggered fashion after decompressive surgery or, as Schneider et al suggested, at the same time as open decompressive surgery.[17] Other authors have cautioned against vein angioplasty at the time of decompressive surgery out of concern that a bleeding complication is more likely.

A lesion longer than 2 cm may require venous bypass or a jugular vein turndown procedure. A consensus statement favored conservative treatment with anticoagulation under these circumstances and concluded that venous bypass should be reserved for only those patients with disabling symptoms and serious complications.

Neurogenic/arterial thoracic outlet obstruction

Thoracic outlet decompression can be performed through an axillary, supraclavicular, or posterior approach, and the choice usually is based on the surgeon's preference.

In neurogenic TOS, results are equal, and the approach or operation performed for TOS may be selected irrespective of the presenting neurologic symptoms.

For arterial TOS, the operation can be performed using the axillary, supraclavicular, or combined supraclavicular-infraclavicular approach. If the supraclavicular approach is utilized, an infraclavicular counterincision always can be performed for added exposure. The supraclavicular approach is becoming more popular and may be superior for total surgical decompression of the thoracic outlet. The supraclavicular approach also allows for adjunct procedures and vascular reconstructions.[18]

Thoracic outlet decompression may entail anterior and middle scalenectomy, first-rib resection, or scalenectomy plus first-rib resection. Reports of scalenectomy versus first-rib resection have noted similar results for the two procedures, irrespective of the procedure performed. Sanders et al noted no difference in results whether the procedure was rib resection only, anterior and middle scalenectomy, or combined first-rib resection plus scalenectomy.[19]

Video-assisted minimally invasive approaches to transaxillary first-rib resection for TOS have been described.[20, 21, 22]  Experience is being gained with a minimally invasive transthoracic robotic approach to first-rib resection for TOS.[23, 24]

A transclavicular approach via resection of the midclavicle or the medial two thirds of the clavicle also has been reported for repair of arterial pathology. An alternative approach utilizes both supraclavicular and infraclavicular incisions to achieve the necessary exposure.

Plan arterial reconstruction when an arterial aneurysm or mural thrombus is identified; either autogenous or prosthetic repair can be performed, though autogenous repair with the saphenous vein usually is preferred. Vein graft aneurysms in the subclavian position may occur over time and with greater frequency than in other positions.

Embolic events causing ischemia should be treated with embolectomy and reconstruction as necessary. Clinical results are good if initial surgical management has been appropriate.


Nerve injuries, lymph leak, and bleeding are the most common postoperative complications. Phrenic, long thoracic, and sympathetic nerves are at risk of injury during this procedure. Injury to the sympathetic nerves results in Horner syndrome. Persistent lymph leak may follow injury to the thoracic duct and is more common following operations on the left side. Fewer than 1% of lymph leaks require reoperation for treatment. Postoperative hemorrhage may be difficult to control, especially after transaxillary decompression, because of poor exposure of vascular structures.