Causes of TOS

Causes of Venous TOS2019-03-24T05:41:47+00:00

Causes of Venous TOS

Venous TOS occurs quite uncommonly, but has potentially serious complications. Middle-aged people can develop venous TOS, but patients are often young and athletic. At the present time, physicians do not fully understand the causes of venous TOS. As a result, treatment choices continue to evolve.

Venous TOS occurs as a result of three interwoven processes. Initially, arm motion creates compression of the subclavian vein between the subclavius muscle tendon and the first costal (rib) cartilage. If compression persists, it eventually damages the wall of the vein, with resulting scar and stenosis (narrowing) of the vein. Finally, blood clot forms at the damaged area of the vein.

Ultimately, it is the formation of blood clot that creates the dramatic clinical presentation of venous TOS. Venous compression by itself is necessary but inadequate to create venous TOS. Damage to the wall of the vein is necessary but inadequate to create venous TOS. As the final step in the process, the formation of blood clot causes partial or complete blockage of venous drainage from the arm. This is the cause of symptoms in venous TOS.

Blood clot in the subclavian vein can break loose and travel through the heart to the pulmonary (lung) arteries. This pulmonary embolism is rare but potentially life-threatening. To be sure, blood clots in leg veins are more likely to cause pulmonary embolism than blood clots in the subclavian vein. Nonetheless, blood clot in the subclavian vein may cause serious complications if not promptly diagnosed and treated.

Venous TOS Anatomy

In venous TOS, compression of the subclavian artery occurs in the prescalene space. To understand venous TOS, it is important to first understand the key anatomic structures of the prescalene space:

  • The first rib and its cartilage (costal cartilage) form the floor of this space. The costal cartilage sits at the anterior aspect of the rib, and attaches to the sternum (breastbone).
  • The clavicle (collarbone) forms the roof of the prescalene space.
  • The anterior scalene muscle forms the posterior wall of the prescalene space.
  • The costoclavicular ligament forms the anterior wall of the prescalene space. This ligament links the costal cartilage to the undersurface of the clavicle (collarbone).
  • The tendon of the subclavius muscle contributes to the anterior wall and roof of the prescalene space. This muscle arises from the first costal cartilage and extends along the undersurface of the clavicle, towards the shoulder

Tap on any number below to open the venous TOS anatomy exhibit

Symptoms of Venous TOS

Venous blood clot and occlusion causes symptoms including swelling, tightness and blue or purple discoloration of the affected arm. Learn more about the symptoms of venous TOS here.

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Diagnosis of Venous TOS

Your doctor may observe secondary signs of venous clot, such as distended veins and swelling of the chest or arm. Modern medical imaging tests including ultrasound, CT scan and MRI scan are accurate in finding a blood clot. Learn more about the diagnosis of venous TOS here.

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Treatment of Venous TOS

Critical treatment decisions center around removal of the blood clot causing venous occlusion. Severe or total venous occlusion demands urgent treatment. After doctors treat the blood clot, they address the underlying vein damage. Learn more about the treatment of venous TOS here.

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