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Causes of TOS2019-04-20T02:30:37+00:00

What causes TOS?

There are three types of TOS

Doctors classify TOS into one of three types.The causes of TOS are different for each type of TOS, depending on which vital structure suffers compression.

To clarify, three vital structures pass through the thoracic outlet on each side:

  • Brachial plexus

  • Subclavian artery

  • Subclavian vein

Causes of TOS-Brachial Plexus, Subclavian Vein, Subclavian Artery

In each thoracic outlet, compression or injury of any of these vital structures may occur. As a result of compression or injury of different structures, one type of TOS can occur . In addition to the primary type of TOS, patients may suffer symptoms from lesser compression of the other vital structures.

Introduction to the causes of TOS

Causes of Neurogenic TOS

Five nerve roots arise from the spinal cord on each side of the neck. Then, these nerve roots travel out of the spine to the thoracic outlet. In each thoracic outlet, the roots form a complex branching network, called the brachial plexus. Compression of the brachial plexus or tension on the brachial plexus results in neurogenic TOS. Given the complexity of the structure of the brachial plexus, patients can suffer a broad range of symptoms.

Thus, doctors see a complex clinical presentation, since compression may involve different parts of the brachial plexus. Symptoms include pain, numbness, tingling, coldness and weakness of the affected upper extremity.

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Causes of Venous TOS

A single, large subclavian vein drains almost all of the blood from each arm. Compression of this vein can cause impaired venous drainage of the arm. When compression is severe or prolonged, it can cause damage to the inner vein wall. As a result, blood clot can form within the vein. Signs and symptoms include swelling, heaviness and cyanosis (abnormal blue color) of the affected arm. Blood clots can break off and travel to the lungs or, rarely, to the brain, resulting in a stroke.

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Causes of Arterial TOS

A single, large subclavian artery provides most of the blood flow to each arm. Compression of this artery causes damage to the arterial wall. Damage to the inner wall can cause scar tissue and stenosis (narrowing of the artery). In contrast, damage to the full thickness of the wall can result in an aneurysm (focal ballooning of the artery). As a result of this aneurysm, a doctor may feel a pulsatile mass in the thoracic outlet. When arterial damage occurs, blood clots may form. These clots can break off and travel to distal arteries.  As a result, blood flow stops, and gangrene of the affected area may develop.

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Causes of TOS

TOS results from many causes

What causes my TOS?

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Can multiple types of TOS occur in the same patient?

Yes, one patient can have multiple types of TOS at the same time. As shown above, the artery, vein, and brachial plexus pass through each thoracic outlet together. Furthermore, the mechanism of compression is similar for all types of TOS. Thus, a patient can have compression of 1, 2, or all 3 of these vital structures. In fact, many patients with neurogenic TOS have significant compression of the subclavian vein, but without a blood clot. Since this compression impairs venous drainage of the arm, swelling or edema of the arm can result. As a result, compression of the brachial plexus is magnified. In that case, treatment to relieve the venous compression helps relieve compression on the brachial plexus.

It is often difficult for a physician to distinguish these multiple compression effects. Therefore, modern imaging quite often provides this important additional information prior to treatment.