Causes of Venous Thoracic Outlet Syndrome

Venous thoracic outlet syndrome occurs quite uncommonly, but has potentially serious complications. Of all cases of thoracic outlet syndrome, only about 5% are the type of thoracic outlet syndrome known as venous thoracic outlet syndrome. Middle-aged people can develop venous TOS, while other patients are young athletes. Some patients with venous thoracic outlet syndrome have a history of an episode of significant exertion. Others practice at their athletic specialty on a regular basis, with no specific inciting event. As a result, the causes of venous thoracic outlet syndrome result in different syndromes with different names.

The causes of venous thoracic outlet syndrome comprise three possible 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 or recurs, it may cause damage of the wall of the subclavian vein, with resulting scar and stenosis (narrowing) of the vein. Eventually, depending on the severity and frequency of vein compression, blood clot may form at the damaged area of the subclavian vein.

The clinical presentation of patients with venous thoracic outlet syndrome depends on the underlying mechanisms of vein compression and narrowing. Some patients may experience symptoms of venous thoracic outlet syndrome caused only by extrinsic compression of the subclavian vein. In this case, the subclavian vein is structurally normal and no blood clot is present. Other patients may develop scarring and stenosis of the subclavian vein, which causes a fixed and non-positional narrowing of the subclavian vein. This stenosis limits venous return of blood to the heart, causing swelling of the affected arm.

Ultimately, it is the formation of blood clot that creates the most dramatic clinical presentation of venous TOS. These patients will frequently present to an emergency room with swelling and bluish color of the arm, along with the appearance of new superficial veins over the chest on the same side. These patients already have the underlying compression of the subclavian vein, with a damaged vein wall, but it is the relatively rapid blood clot formation that creates the dramatic clinical picture.

Venous compression by itself is necessary but not sufficient to create this blood clot. Damage to the wall of the vein by itself is necessary but not sufficient to create the blood clot. While these mechanisms create the opportunity for blood clot, the final step that causes blood clot is currently unknown. Nonetheless, in these patients, it is the formation of blood clot that causes partial or complete blockage of venous drainage from the arm and results in the most severe form of venous thoracic outlet syndrome.

In addition, blood clot in the subclavian vein can break loose and travel through the heart to the pulmonary arteries in the lungs. 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.

In 1875, Sir James Paget in London published the first description of venous thoracic outlet syndrome, caused by a blood clot in the subclavian vein. Paget felt this blood clot arose spontaneously. Interestingly, Leopold von Schrotter in Vienna recorded a very similar case in Berlin at the same time, but did not publish the case until 1884. Von Schrotter felt the blood clot had formed due to muscular contractions surrounding the subclavian vein. Both Paget and Von Schrotter are credited with the first description of venous thoracic outlet syndrome, which is now frequently referred to as ‘Paget-Schrotter syndrome.’

Paget-Schrotter syndrome includes cases with spontaneous blood clot formation and those thought to be due to activity. The name ‘effort thrombosis’ or ‘primary effort thrombosis’ is used by many physicians to refer to those latter cases where blood clot formation associated with active use of the upper extremity. The distinction may be of little real performance, and is unlikely to affect diagnosis or treatment.

The causes of venous thoracic outlet syndrome are widely-accepted to result from venous blood clot in the arm. However, some patients experience similar symptoms, but in the absence of a venous blood clot in the arm. In these patients, the cause of venous thoracic outlet syndrome results from positional changes of the arm that create intermittent obstruction of the subclavian vein. Symptoms are quite similar to those patients with a subclavian vein blood clot, although no clot is present. This is known as McCleery syndrome. In fact, the syndrome was first described by McLaughlin and Popma in 1939, then described in detail by McCleery in 1951.

Venous thoracic outlet syndrome occurs as a result of three possible 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 or recurs, it may cause damage of the wall of the vein, with resulting scar and stenosis (narrowing) of the vein. Blood clot may form at the damaged area of the vein.

Ultimately, it is the formation of blood clot that creates the most dramatic clinical presentation of venous TOS. Venous compression by itself is necessary but not sufficient to create this dramatic. Damage to the wall of the vein by itself is necessary but not sufficient 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 arteries in the lungs. 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.

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 (first 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.

The prescalene space is outlined in lavender. 

The prescalene space is outlined in lavender. 

Venous blood clot in the arm delays venous blood returning from the arm to the heart. This is the most common cause of venous thoracic outlet syndrome. The venous blood clot creates symptoms of venous thoracic outlet syndrome including arm swelling, tightness, blue or purple discoloration of the affected arm, and new prominent veins of the chest wall. Click through to learn more about the symptoms of venous thoracic outlet syndrome.

Your doctor cannot directly see the venous blood clot in the arm causing venous thoracic outlet syndrome. However, she can observe secondary signs of the venous blood clot, such as distended veins and swelling of the chest or arm. Modern medical imaging tests including ultrasound, CT scan and MRI scan are quite accurate in finding a venous blood clot. Click through to learn more about the diagnosis of venous thoracic outlet syndrome.

Critical treatment decisions center around removal of the venous blood clot in the arm. Severe or total venous occlusion demands urgent treatment. After doctors remove the venous blood clot in the arm, they are able to address the underlying causes of vein compression and damage. Click through to learn more about the treatment of venous thoracic outlet syndrome.