Venous Thoracic Outlet Syndrome: Understanding Subclavian Vein Compression

Medically reviewed by Dr. Baraa Alnahhal, MD · Last reviewed: October 2026

Venous thoracic outlet syndrome (VTOS), also called Paget-Schroetter syndrome, is a rare condition in which the subclavian vein is compressed as it passes through the thoracic outlet behind the collarbone. It can cause arm swelling, discoloration and heaviness, and it can lead to blood clots. [1] Treatment usually includes medications to treat blood clots and, if needed, surgery, and starting treatment within the first 14 days of symptoms significantly improves the chance of a successful outcome. [1]

Quick Answer

Venous thoracic outlet syndrome (VTOS) is a condition in which the subclavian vein is squeezed between the collarbone and the first rib, causing a heavy, aching, swollen or blue-tinted arm, usually on one side. [1] It is more likely with sports or repetitive arm motion. [1] Imaging confirms it, and treatment addresses blood clots and sometimes widens the space surgically.

What the research says

• Combining treatments gives the highest symptom-free rates. A meta-analysis of 60 reports (2,653 patients) found that the proportion of patients who were symptom free at last follow-up was 0.54 with anticoagulation alone, 0.71 with catheter-directed thrombolysis plus anticoagulation, 0.80 with anticoagulation plus first rib resection and 0.96 with thrombolysis plus first rib resection, although the certainty of the evidence was very low (Hoexum et al., European Journal of Vascular and Endovascular Surgery, 2023) [2].

• Thrombolysis clears clots more often than anticoagulation alone. In a meta-analysis of 25 studies (1,511 patients), complete thrombus resolution was estimated at 78.11% after thrombolysis versus 40.70% after anticoagulation, and first rib resection improved vein patency and symptom resolution compared with thrombolysis alone, although no randomized trials were available (Karaolanis et al., Journal of Vascular Surgery: Venous and Lymphatic Disorders, 2021) [3].

• Surgery can still help when the problem has become chronic. In a retrospective review of 83 patients with chronic VTOS who had first rib resection, 83% reported substantial improvement in symptoms, the postoperative complication rate was 8%, and patients in two of the three recanalization groups were able to stop anticoagulants (Mangiameli et al., Annals of Vascular Surgery, 2025) [4].

What Is Venous Thoracic Outlet Syndrome?

Veins take blood from your tissues back to your heart and lungs to collect oxygen. The subclavian vein runs from the arm behind the collarbone (clavicle), and the space where it runs is the thoracic outlet. In VTOS, the vein is squeezed in this space, which restricts blood flow and often causes arm soreness, swelling or discoloration. [1] Another name for VTOS is Paget-Schroetter syndrome (PSS).

All types of thoracic outlet syndrome are rare, and VTOS is one of the least common types. [1] About 2 in 50 people with thoracic outlet syndrome have it.

What Causes VTOS and Who Is at Risk?

Most people have plenty of space for the subclavian vein to run from the arm to the heart. Some people have a naturally narrow passageway, and in them overusing the arm and shoulder can compress or aggravate the vein, block blood flow and lead to clots. [1]

Category	Contributing Factors
Demographics	Women ages 20 to 50 are more likely to get any type of thoracic outlet syndrome
Anatomy	A naturally narrow passageway for the subclavian vein [1]
Activity	Sports or jobs with repetitive arm and shoulder movements, such as throwing a ball, lifting boxes overhead or swinging a baseball bat [1]
Trauma	Injuries from a car accident or fall [1]
Weight and posture	Carrying extra weight (obesity), which puts extra pressure on the joints, and posture
Pregnancy	Pregnancy can contribute

Recognizing the Symptoms

Most people with VTOS have symptoms that affect one arm and hand. [1] You may have:

• Aching

• Blue or purple discoloration

• Heaviness

• Swelling

• Visible veins in one shoulder, arm or on one side of the chest [1]

Potential Complications

VTOS can be dangerous without treatment. [1] The compression can cause blood clots to form in the subclavian vein, and these clots can block blood flow in the arm or hand or travel to the lungs. A blood clot that moves to the lungs is a pulmonary embolism. [1]

Seek emergency care for chest pain, cough or shortness of breath. [1] These can be signs of a pulmonary embolism, which is a life-threatening emergency.

How Is VTOS Diagnosed?

Your provider will visually examine your shoulder, neck and arm, may ask you to move your arms in specific ways to check your range of motion, will ask about your symptoms and will take your blood pressure. [1] If VTOS is suspected, you may have imaging tests to examine the thoracic outlet and view blood flow in your veins:

• CT scan: multiple X-rays create detailed images

• MRI: radio waves and magnets create a detailed picture

• Ultrasound: sound waves show structures inside the body, including blood flow

• Venogram: a small hollow tube (catheter) and contrast dye are placed in your veins before an X-ray [1]

• X-ray: targeted, safe doses of radiation produce images

How Is VTOS Treated?

Treatment can include nonsurgical and surgical options.

Medical Management

Typically, your provider prescribes medications to treat the blood clots. You may take anticoagulants (blood thinners) such as warfarin (Coumadin) or direct oral anticoagulants (Xarelto or Eliquis). [1] In some cases, clot-dissolving treatment delivered through a catheter (thrombolysis) is also used. [1] [2]

Surgery

After the clot breaks up, you may need surgery to prevent blood clots from happening again. During surgery, your provider may remove extra tissue or ligaments around the subclavian vein, which can include part of the first rib, or redirect blood flow to avoid damaged veins and restore circulation.

Outlook

Without treatment, VTOS can cause complications such as blood clots, and early treatment helps. Research shows that getting treatment within the first 14 days of symptoms significantly increases your chances of a successful outcome. [1] If you have any signs of VTOS, see a healthcare provider right away.

Prevention

There is no guaranteed way to avoid VTOS [1], but you can lower your risk of compression injuries by:

• Achieving and maintaining a healthy weight for your age, sex and body type

• Avoiding carrying heavy bags on one shoulder

• Limiting repetitive overhead movements [1]

• Strengthening your shoulders with resistance training or weight lifting

• Stretching your neck, shoulders and chest daily

Questions to Ask Your Healthcare Provider

• What is the most likely cause of my symptoms?

• What tests do I need for diagnosis?

• What are the treatment options?

• Will nonsurgical treatments improve my symptoms?

• What lifestyle changes can I make to improve my symptoms?

Conclusion

Venous thoracic outlet syndrome is a rare but serious vascular condition that needs prompt medical attention. Recognizing arm swelling, discoloration and heaviness early gives you the best chance of treatment before complications such as a pulmonary embolism develop. Treatment combines medications to treat blood clots with surgery to relieve the compression when needed, and daily shoulder care and healthy habits can help lower your risk of compression injuries.

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Frequently Asked Questions

What is venous thoracic outlet syndrome?

VTOS is a compressed subclavian vein, the vein that carries blood from your arm to your heart, in the thoracic outlet behind the collarbone. It often causes arm soreness, swelling, discoloration or heaviness.

What is Paget-Schroetter syndrome?

Paget-Schroetter syndrome (PSS) is another name for venous thoracic outlet syndrome.

How common is VTOS?

All types of thoracic outlet syndrome are rare, and VTOS is one of the least common types. About 2 in 50 people with thoracic outlet syndrome have it.

Who is most at risk for VTOS?

Women ages 20 to 50 are more likely to get any type of thoracic outlet syndrome. You are also more likely to develop VTOS if you play sports or have a job that involves repetitive arm and shoulder motion, or if you have a naturally narrow passageway for the subclavian vein.

What do blue or purple discoloration and swelling mean?

Blue or purple discoloration and swelling are signs that blood is not draining normally from the arm because the vein is compressed. See a healthcare provider promptly if you notice them.

Can VTOS cause a pulmonary embolism?

Yes. Compression can cause clots to form in the subclavian vein, and a clot that travels to the lungs is a pulmonary embolism. Chest pain, cough and shortness of breath are emergency symptoms, so seek emergency care.

Can VTOS be treated without surgery?

Treatment usually starts with medications to treat blood clots, such as anticoagulants. After the clot breaks up, surgery may be needed to prevent clots from happening again.

How soon should treatment start?

Research shows that treatment within the first 14 days of symptoms significantly increases the chance of a successful outcome, so see a healthcare provider right away if you notice signs of VTOS.

Does posture matter for VTOS?

Posture is listed as one of the factors that can contribute to compression of the subclavian vein, along with obesity, injury, pregnancy and repetitive arm movements.

Can VTOS be prevented?

There is no guaranteed way to avoid VTOS, but you can lower your risk of compression injuries by keeping a healthy weight, avoiding carrying heavy bags on one shoulder, limiting repetitive overhead movements, strengthening your shoulders and stretching your neck, shoulders and chest daily.

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Related Reading

Axillo-Subclavian Vein Thrombosis: The Blood Clot Condition That Strikes Active People — and How It's Treated explains the arm vein clot that compression of the subclavian vein can cause.

What Is Arterial Thoracic Outlet Syndrome? A Plain-Language Guide to the Arm Blood Flow Problem That Rarely Gets Spotted Early explains the rarer form of thoracic outlet syndrome that squeezes the artery.

Subclavian Vein: Anatomy, Essential Functions, and Care explains where the subclavian vein runs and what it does.

Venogram (Venography): Why It's Done, What to Expect and Risks explains the dye X-ray test that shows blocked or narrowed veins.

References

1. Cleveland Clinic. Venous Thoracic Outlet Syndrome. Cleveland Clinic. Last updated August 18, 2026. https://my.clevelandclinic.org/health/diseases/22317-venous-thoracic-outlet-syndrome

2. Hoexum F, Hoebink M, Coveliers HME, et al. Management of Paget-Schroetter Syndrome: a Systematic Review and Meta-Analysis. European Journal of Vascular and Endovascular Surgery. 2023;66(6):866-875. PMID 37678659. https://doi.org/10.1016/j.ejvs.2023.08.065

3. Karaolanis G, Antonopoulos CN, Koutsias SG, et al. A systematic review and meta-analysis for the management of Paget-Schroetter syndrome. Journal of Vascular Surgery: Venous and Lymphatic Disorders. 2021;9(3):801-810.e5. PMID 33540134. https://doi.org/10.1016/j.jvsv.2021.01.011

4. Mangiameli G, Italiani A, Rizzardi G, et al. Venous Thoracic Outlet Syndrome (vTOS): May Surgery be a Solution in Chronic Form? Annals of Vascular Surgery. 2025;121:1-13. PMID 40414534. https://doi.org/10.1016/j.avsg.2025.05.025

Medical disclaimer

The information provided in this article is for educational purposes only and should not be used as a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of your physician or other qualified health provider with any questions you may have regarding a medical condition.