What is Thoracic Outlet Syndrome?

What is Thoracic Outlet Syndrome?

What is TOS?

Thoracic outlet syndrome is a pain syndrome of the upper extremities. Doctors use the abbreviation ‘TOS’ instead of the full name of the disease, ‘Thoracic Outlet Syndrome.’ TOS patients suffer pain, tingling, numbness, weakness, or abnormal blood flow in one or both upper extremities. TOS can range from an emergent surgical condition to a progressive, chronic pain syndrome that alters the lives of TOS patients.

Three vital structures pass from the neck and chest to reach each upper extremity. When compression of these vital structures causes symptoms, TOS is present. 

TOS stands for Thoracic Outlet Syndrome. The thoracic outlet is the hollow space between your neck and shoulder on each side, above the collar bone. Three vital structures pass through the thoracic outlet on each side: an artery, a vein, and a nerve plexus. If compression of one or more of these structures causes symptoms, thoracic outlet syndrome is present.

Compression may be caused by abnormal fibrous bands or muscles, or an extra rib, present from birth. Alternately, acquired abnormalities, such as muscle enlargement or injury, or a fractured bone, may cause compression. In addition, patients may develop abnormal movement of the arms and shoulders from work, injury, or athletics. Abnormal shoulder movement may cause compression when using the arms for typical activities, when using a computer, or during athletic activity.

Doctors define three types of thoracic outlet syndrome, based on the primary structure being compressed:

  • Venous TOS-compression of the subclavian vein

  • Arterial TOS-compression of the subclavian artery

  • Neurogenic TOS-compression of the brachial plexus

Symptoms of TOS are different in each type of TOS. Patients with venous TOS suffer swelling of the arm from decreased blood flow returning to the heart. Patients with arterial TOS suffer loss of blood flow to all or part of the arm. Patients with neurogenic TOS suffer a broad range of sensory and motor disturbances of the affected arm and hand

Thoracic outlet syndrome occurs in women more than men, usually between the ages of 20 to 40. We currently recognize an increased risk of developing thoracic outlet syndrome in the following situations:

  • Neck injuries resulting from motor vehicle accidents

  • Work environments with repetitive stress injures

  • Extensive computer use

  • Overhead athletic activities

Recently, thoracic outlet syndrome has been diagnosed in a number of elite athletes, including NBA basketball players and MLB pitchers.

What are the three types of TOS?

Costoclavicular Interval Brachial Plexus

Neurogenic TOS

Compression of the brachial plexus, a complex nerve network, causes sensory and motor symptoms and signs.

Venous TOS Retropectoralis Space

Venous TOS

Compression of a large vein allows the formation of blood clot, which blocks blood flow from the arm to the heart. 

Arterial TOS Scalene Triangle

Arterial TOS

Compression of a large artery damages the artery, and leads to blood clot formation, which can block blood flow to the arm.

A large, branching network of nerves, the brachial plexus, passes through each thoracic outlet. Compression or tension on one or more of these nerves can occur in the thoracic outlet. This process can cause damage to these nerves. When the damage results in symptoms, neurogenic TOS is present. Neurogenic TOS patients may experience pain, tingling, abnormal sensations, weakness, or muscle atrophy. Neurogenic TOS is the most common type of TOS, 95 to 98% of all TOS cases. Neurogenic TOS is also the most difficult type of TOS to diagnose.

Venous TOS

A single, large subclavian vein passes through each thoracic outlet. Compression of this vein can occur in the thoracic outlet, especially due to arm movement. Repeated compression may eventually damage the vein, resulting in scarring and narrowing. Blood clot may form in this damaged vein segment, and can then grow in size, or break off and travel to the lungs or brain. When blood clot forms, venous TOS is present. Venous TOS is very uncommon, accounting for 2 to 5 % of TOS cases. Patients with venous TOS often present with swelling and discoloration of the arm and upper chest. Doctors should diagnose and treat venous TOS urgently by resolving the blood clot, and then relieving the compression of the vein.

Arterial TOS

A single, large subclavian artery passes through each thoracic outlet. Compression of this artery can occur in the thoracic outlet, more likely if a cervical rib is present. Repeated compression may damage the artery, resulting in scarring and narrowing, or focal dilation. Blood clot may form in the damaged arterial segment. This clot can break off and block arteries in the arm. When this occurs, arterial TOS is present. Arterial TOS is rare, only 1% of TOS cases. Arterial TOS patients may have a pulsatile neck mass, with weakness, pale color, coldness or gangrene of the arm. This sudden blockage of blood flow is a surgical emergency, treated by removal or dissolving of the clot. After this emergent treatment, doctors usually relieve the structures compressing the artery, and repair the damaged arterial segment.

Anatomy of the Thoracic Outlet

The anatomy of the thoracic outlet appears incredibly complex. Besides the native anatomy, a number of anatomic variants and anomalies create more complexity. These variants can compress the nerves, artery or veins, resulting in TOS. Moreover, motion of the arms causes complex changes in the anatomic tunnels of the thoracic outlet. When you understand the anatomy of the thoracic outlet, you have taken the first step in understanding thoracic outlet syndrome.

You can feel the thoracic outlet on each side of your neck. Specifically, the thoracic outlet is the hollow space above your collarbone, between your shoulder and your neck. Slide your hand down either side of your neck to find the thoracic outlet.

Three vital structures pass from the neck and chest through each thoracic outlet to enter each arm. Specifically, the subclavian artery, subclavian vein, and brachial plexus pass through the thoracic outlet on each side.

Each structure must pass through a series of narrow tunnels to reach the arm. These tunnels have bony or soft tissue structures that define their walls. Any abnormality of these walls can narrow one of the critical tunnels. In this way, an abnormal tunnel can compress one or more of  the vital structures.

In addition, the thoracic outlet will change when the shoulder is moved. Since the shoulder has a very broad range of motion, additional narrowing of one or more tunnels may take place.

As you can see, each thoracic outlet is quite complex, both at baseline and with motion. You can learn more about this complex anatomy by clicking this button.

What causes TOS?

Laptop Causes TOS Pain

The nerves, artery and vein must be free to pass through the thoracic outlet. However, anatomic variants, acquired abnormalities, and abnormal arm motion may cause compression of these vital structures. In that case, patients may experience the symptoms of thoracic outlet syndrome. People with neck injuries, occupational injuries or overuse, and overhead athletes are all at risk for developing thoracic outlet syndrome.

Doctors are aware of factors that increase the risk of developing TOS:

  • Motor vehicle accidents: People who suffer neck injuries in motor vehicle accidents may develop TOS. Most people have heard the term, ‘whiplash,’ which is non-specific. Many whiplash cases actually represent TOS.

  • Repetitive stress injuries: Often related to non-ergonomic work environments, repetitive stress injuries include a broad group of painful disorders. Thoracic outlet syndrome falls within this group of disorders.

  • Computer use: As computer use has exploded over the past few decades, we believe that more cases of thoracic outlet syndrome have appeared as a result. Whether occupational or recreational, people often use computers, phones, or tablets in a number of non-ergonomic ways, for long hours each day. The resulting abnormal posture of neck, shoulders, arms and neck contributes to abnormalities in the thoracic outlet.

  • Overhead athletics: Sports physicians have known for some time that overhead athletes may suffer from a unique set of pain syndromes. In particular, volleyball players, baseball pitchers, and swimmers are at increased risk for developing thoracic outlet syndrome. Recently, elite athletes in the NBA and MLB have been diagnosed and treated for TOS.

  • Manual laborers: From UPS drivers to painters and constructions workers, those people who use their arms in front or overhead for extended periods of work are at increase risk of developing thoracic outlet syndrome.

  • Cervical rib: Since 1895, when Roentgen created the first medical x-ray, doctors have known that some patients with TOS have a cervical rib. A cervical rib is an extra rib above the first rib, and can range in size from small to quite large. For this reason, some TOS authorities suggest a chest or neck x-ray be used for the diagnosis of thoracic outlet syndrome. However, about 0.5% of the population has a cervical rib, and the vast majority of these people do not have TOS. In addition, AA Law demonstrated numerous soft tissue anomalies in the thoracic outlet in 1920. We know that the vast majority of TOS patients do not have cervical ribs. On the contrary, these TOS patients have soft tissue anomalies or abnormal arm motion. Neither of these factors is seen on x-rays. For these reasons, the presence of a cervical rib, or diagnosis based on x-rays, does not adequately diagnose thoracic outlet syndrome.


History of TOS

Like many other scientific pursuits, the history of TOS takes many twists and turns. In essence, The history revolves around human nature, curiosity and discovery. Here you can enjoy a wild and fascinating ride of dead ends and discoveries, egos and errors, personalities and politics. Learn about the history of TOS, starting from a simple English housemaid to modern robotic surgeons.