eMedicine Specialties > Radiology > Vascular/Interventional

Thoracic Outlet Syndrome

Author: Meghal Antani, MD, Consulting Staff, Department of Interventional Radiology, Washington Hospital Center
Coauthor(s): Gary P Siskin, MD, Associate Professor, Department of Radiology, Albany Medical College; Chief, Division of Vascular and Interventional Radiology, Department of Radiology, Albany Medical Center
Contributor Information and Disclosures

Updated: Jun 10, 2008

Introduction

Background

Thoracic outlet syndromes are caused by compression of the neurovascular structures passing through the thoracic outlet. These syndromes can be classified into 3 subgroups, based on the neurologic or vascular structures involved. The specific clinical presentations, demographics, treatments, and outcomes vary among the subgroups. The 3 subgroups are as follows:

• Subgroup 1, also called the neurologic type, is the most common. It is responsible for approximately 95% of cases of thoracic outlet syndrome. This type is secondary to compression of the brachial plexus caused by various soft tissue and bony abnormalities at the point where the nerves pass between the anterior and middle scalene muscles. For a discussion of the neurology of this syndrome, see Thoracic Outlet Syndrome in the Neurology section of eMedicine.
• Subgroup 2, also called the venous type, is the more common of the 2 vascular causes of thoracic outlet syndrome (which are the venous and arterial types); it is seen in approximately 3-4% of cases. Venous thrombosis may be categorized into primary and secondary thrombosis based on the etiology. Primary venous thoracic outlet syndrome, or primary venous thrombosis, is also called Paget-Schrötter syndrome. The disease is named after the 2 individuals who first described this entity: Paget, who described it in 1875, and von Schrötter, in 1884. Other terms for this condition include effort thrombosis, spontaneous thrombosis, and traumatic thrombosis.¹
• Subgroup 3, also called the arterial type, is the least common form of thoracic outlet syndrome. It is seen in approximately 1-2% of cases. This type is associated with the most serious complications, including limb ischemia (which may result in the loss of the affected upper extremity).

Rarely, compression of a combination of structures may be responsible for the symptoms. This article is limited to the vascular causes of thoracic outlet syndrome.^2,3,4,5,6

Related Medscape topics:
Resource Center Vascular Surgery
Specialty Site Radiology
CME  Progressive Angina Pectoris of Uncertain Etiology

Related eMedicine topics:
Thoracic Outlet Syndrome: Emergency Medicine
Thoracic Outlet Syndrome: Neurology
Thoracic Outlet Obstruction

Pathophysiology

Compression of the vascular structures passing through the thoracic outlet may occur at several anatomic sites, including the following:

• compression of arteries or veins medial to the scalene triangle in the costoclavicular space or beneath the pectoralis minor tendon in the axilla
• arterial compression within the scalene triangle itself
• venous compression between the anterior scalene muscle and the clavicle

Arterial causes

The essential mechanism of subclavian artery thoracic outlet syndrome is chronic compression that results in intimal injury with fibrosis, thickening of the wall, and, eventually, luminal narrowing. Poststenotic dilation develops as a result of hemodynamic turbulence distal to the site of narrowing. Distal thromboembolism is a severe complication that may result either from mural thrombus originating within the area of poststenotic dilation or from an intimal lesion at the site of compression with resultant formation of platelet aggregates. These platelet aggregates may microembolize distal to the small vessels of the hands and fingers, resulting in ischemia with eventual tissue necrosis.

Mural thrombi typically result in the occlusion of more proximal arteries with larger collateral supplies; therefore, mural thrombi are less likely to produce severe ischemic changes than other types. Rarely, occlusion of the subclavian artery may occur. The most common cause of subclavian artery compression is a cervical rib, which is seen in 50% of cases. A cervical rib can posteriorly compress the subclavian artery against the anterior scalene muscle and first rib at the scalene triangle.

Other etiologies include congenital first-rib anomalies, first-rib exostoses, and malunited fractures of the clavicle. Rare causes include congenital fibromuscular bands and anterior scalene muscle anomalies.

Venous causes

Primary venous thrombosis is usually related to a multifactorial etiology, including extrinsic compression or trauma with a congenitally narrow thoracic inlet. Chronic extrinsic compression may be caused by anatomic anomalies, such as a cervical rib or abnormality of the first rib; hypertrophied subclavius or anterior scalene muscles; or a malunited clavicle fracture with abundant callous formation. Compression may be exaggerated when the upper extremity is in certain positions, such as in the rigid military style of sitting with the back straight and the shoulders placed posteriorly and inferiorly.

With chronic irritation of the vessel walls, these anomalies may predispose an individual to stasis, intimal damage, and hypercoagulability, which form a constellation of pathophysiologic events called the Virchow triad. At least 2 of these 3 factors are typically found in patients with primary venous thrombosis. The eventual result is the formation of an intraluminal thrombus, which causes the lumen to become narrowed and, possibly, entirely occluded. Most authors classify the anatomic causes of axillosubclavian vein thrombosis as primary; however, the etiology is investigated in all patients, and as the body of knowledge about the causes of venous thrombosis improves, the label of primary venous thrombosis is slowly falling out of favor.

Secondary venous thrombosis has a number of causes, including the following:

• Injury to the venous intima
  • Venous foreign bodies
    • Central venous catheters (most common cause)
    • Pacemaker wires
  • Traumatic injury
    • Fractured rib or clavicle
    • Blunt or penetrating injury
• External compressive force
  • Tumors (thoracic, cervical, axillary)
  • Substernal goiter
• Inflammatory diseases
  • Thrombophlebitis of ipsilateral upper extremity
  • Infections in the chest or neck
  • Fibrosing mediastinitis
  • Radiation therapy
  • Periphlebitis
• Systemic disorders
  • Nephrotic syndrome
  • Extreme dehydration or shock
  • Congestive heart failure
  • Hypercoagulable states (polycythemia vera)
  • Dysplastic valve

The most common cause of secondary venous thoracic outlet syndrome is central venous catheter placement.

Other causes

Intraluminal foreign bodies often result in intimal injury; the incidence increases with the size of the foreign object. As in primary venous thrombosis, this predisposes an individual to the formation of a thrombus.

Radiation therapy is known to cause arterial occlusion, and several studies have been performed to investigate the occurrence of venous thrombosis after radiation therapy. Wilson reported findings in 2 patients with breast cancer who were treated with tamoxifen and radiation therapy, with ipsilateral arm swelling 3 or 4 years after therapy. Venography revealed subclavian vein thrombosis in both patients.⁷

Schreiber and Kapp reviewed findings in 225 patients who underwent combined chemotherapy and mantle radiation therapy for mediastinal lymphoma. They identified 4 patients with posttreatment subclavian vein thrombosis, of whom 3 received chemotherapy in the same arm as the venous thrombosis. Their observation suggests that the chemotherapeutic agent is a potential factor.⁸

Malignant tumors have also been associated with venous thrombosis, and at least 2 mechanisms (direct venous compression and transitory migratory thrombophlebitis) have been postulated; the 2 mechanisms may exist simultaneously.^9,10

Frequency

United States

Of the vascular causes of thoracic outlet syndrome, the venous type is more common and occurs in approximately 3-4% of patients, whereas the arterial type is seen in approximately 1-2% of patients.

International

Although the international demographic data regarding thoracic outlet syndrome are limited, data from Europe indicate that the incidence of arterial and venous thoracic outlet syndrome is similar to that of the United States.

Mortality/Morbidity

• Arterial thoracic outlet syndrome may result in ischemic signs and symptoms ranging from Raynaud phenomenon to gross digital ischemia.
• The venous variant, if left untreated, usually results in swelling and a bluish discoloration of the entire affected arm.

Race

No racial predilection exists.

Sex

Thoracic outlet syndrome is traditionally more common in women than in men, with a female-to-male ratio as high as 3:1.⁶

Age

Thoracic outlet syndrome is most common in people aged 10-50 years.

Anatomy

Arteries

The right subclavian artery arises from the innominate artery, which is the first major branch of the aortic arch. The left subclavian artery arises directly from the aortic arch as the final major branch. After leaving the thoracic cavity posterior to the sternoclavicular joint and arching over the pleural cupola, the subclavian artery passes through the scalene triangle (which is bounded by the first rib inferiorly, the anterior scalene muscle anterolaterally, and the medial scalene muscle posteromedially). The artery then continues under the clavicle and the subclavius muscle and enters the axilla, where it is renamed the axillary artery.

After passing inferior to the pectoralis minor muscle tendon, the artery is called the brachial artery, which continues distally along the medial aspect of the humerus. After occlusion of the subclavian artery, the blood supply to the peripheral arm is maintained by the collateral vessels present among the suprascapular, circumflex scapular, subscapular, and posterior circumflex humeral arteries, as well as between the transverse cervical and posterior circumflex humeral arteries.

Veins

Superficial veins along the ulnar aspect of the arm drain into the median antebrachial and median antecubital veins, which in turn drain into the basilic vein. The basilic vein becomes the axillary vein after joining with the brachial vein. The radial aspect of the arm is drained by the cephalic vein, which passes along the deltopectoral groove lateral to the clavicle and joins the azygous vein. At the outer border of the first rib, the axillary vein becomes the subclavian vein, which passes through the costoclavicular space. The first rib and anterior scalene muscles are positioned posteriorly, and the clavicle and subclavius muscle are positioned anteriorly. This path is unlike that of the subclavian artery, which is posterior to the anterior scalene muscle.

Presentation

Arterial thoracic outlet syndrome

The most common initial clinical sign of arterial thoracic outlet syndrome is ischemia of the affected arm resulting from distal embolization. The site of ischemia depends on the size of the emboli. Microembolization of the arteries of the fingers and digital arch may result in ischemic signs and symptoms ranging from Raynaud phenomenon to gross digital ischemia.

Arterial thoracic outlet syndrome infrequently appears prior to the onset of acute upper extremity ischemia. Occasionally, neurologic symptoms resulting from a bony abnormality, such as a cervical rib, may occur before the onset of signs and symptoms secondary to arterial ischemia.

A subclavian artery aneurysm may be detected as a palpable mass during a routine physical examination, or a cervical rib may result in anterior and superior displacement, leading to prominence of the subclavian artery.

All patients with upper extremity ischemic symptoms require a thorough evaluation for possible embolic sources, including a complete vascular examination. During the examination, the contralateral arm should be checked because evidence of bilateral upper extremity ischemia supports a central thromboembolic source, such as the heart. In particular, arterial thoracic outlet syndrome should be considered in a young patient with upper extremity ischemic symptoms. The patient should be asked about a history of trauma to the upper body with a healed fracture of the clavicle or upper ribs. Previous chest radiographs or other radiologic studies of the upper body should be reviewed to search for a cervical rib or other bony abnormality.

Venous thoracic outlet syndrome

With primary venous thoracic outlet syndrome, male patients are typically affected more often than female patients, with a ratio of 3:2 or 4:1, depending on various studies.

The right upper extremity is affected more often than the left upper extremity.

Symptoms commonly begin within the first 24 hours in primary venous thrombosis, although in some patients the symptoms may be insidious at the onset of thrombosis. Patients are usually aged 20-50 years and otherwise healthy.

Secondary venous thrombosis, unlike the primary variant, typically occurs in older patients and has a more uniform sex distribution. The most common symptoms of subclavian or axillary venous thrombosis include swelling, discoloration, collateral vein dilatation, and aching. Secondary venous thrombosis tends to develop gradually, with a relative delay in the clinical presentation and, therefore, in treatment. Initial symptoms may range from minor discomfort to aching or weakness to severe pain. Over time, the hand and forearm become cold to the touch, with diminished finger movements. Untreated, this condition eventually results in swelling and bluish discoloration of the entire affected arm.

Signs of secondary venous thrombosis during physical examination are typically more prominent in the distal structure, with the fingers and dorsal aspect of the hand having the most severe findings. Pitting edema, bluish discoloration, and coolness to the touch may be present. Distension of the venous system of the arm is also common, with the basilic and cephalic vein distention occurring first, followed by generalized distention of the remaining veins and venules.

On examination, the distended veins feel tense and do not collapse with abduction of the arm to above the level of the right atrium. In approximately one half of patients, the axillary vein is palpable as a cordlike mass in the lateral aspect of the axilla. In addition, supraclavicular tenderness may indicate extension of thrombus into the subclavian vein, which is a common finding. Further extension into the internal jugular vein or superior vena cava may result in swelling of the face and neck, which is similar to the findings of superior vena cava syndrome. During the following weeks, as further collateral pathways form between the axillary and cephalic veins to the mediastinal and intercostal veins, collateral veins may become visible over the upper part of the chest and the shoulder. These veins may allow adequate drainage of the affected extremity and, thus, improvement or resolution of the symptoms.

Preferred Examination

The findings of the Allen maneuver, the hyperabduction maneuver, are considered positive when the radial pulse disappears during extreme abduction of the arm. This finding, however, is also present in individuals who do not have thoracic outlet syndrome and in individuals with asymptomatic cervical ribs; therefore, this finding is not diagnostic.

A positive Adson finding occurs when the radial pulse is reduced or disappears or when the blood pressure changes with the patient (1) in a sitting position, (2) holding a deep inspiration, (3) fully extending the neck, or (4) turning the head toward the ipsilateral and contralateral sides. Some investigators believe that the cause of these findings is compression by the anterior scalene muscle. A supraclavicular bruit may be audible with this maneuver, and it is believed to result from an associated subclavian stenosis.

The costoclavicular maneuver is performed when the patient assumes an exaggerated military posture and positions his or her shoulders back and downward; this positioning induces compression between the clavicle and the first rib.

Ultrasonography is readily available and relatively inexpensive, and it can be performed in both arterial and venous thoracic outlet syndrome. Magnetic resonance (MR) angiography and computed tomographic (CT) angiography of the thoracic inlet, especially with recently devised techniques and protocols, are promising noninvasive modalities that may soon provide image quality comparable to that of angiography and venography. Angiography and venography remain the criterion standards for the radiologic diagnosis of these conditions, and they have the added benefit of enabling potential endovascular treatment.^11,12

Limitations of Techniques

Despite considerable investigation into identifying a clinical maneuver for the accurate diagnosis of vascular thoracic outlet syndrome, no clinical test has been shown to have a consistently high degree of accuracy. The same positive findings are occasionally found in individuals without vascular thoracic outlet syndrome; therefore, the clinicians should consider a positive result at clinical examination in context with the clinical history and the results of other diagnostic tests. The final diagnosis often depends on invasive procedures such as arteriography. MR angiography and CT angiography techniques are evolving, and in the near future, they may be able to replace many of today's invasive diagnostic angiographic examinations.

Differential Diagnoses

Aorta, Coarctation
Coronary Artery Disease
Pancoast Tumor
Superior Vena Cava Syndrome

Other Problems to Be Considered

Lung, abscess

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