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.