---
title: Thoracic outlet syndrome
description: What thoracic outlet syndrome is, why nerves, an artery or a vein can be compressed in the passage from the neck to the arm, how it is recognised, which treatment approaches the sources describe and when to call an ambulance.
type: disease
aliases:
  - thoracic outlet syndromes
  - TOS
  - thoracic outlet compression syndrome
    - thoracic outlet compression syndromes
  - superior thoracic aperture syndrome
  - Paget–Schroetter syndrome
  - effort thrombosis

sources:
  - tier: guideline
    org: minzdrav-rf
    title: Тромбоз глубоких вен конечностей
    year: 2025
    url: https://cr.minzdrav.gov.ru/view-cr/960_1
  - tier: guideline
    org: minzdrav-rf
    title: Острая ишемия конечностей
    year: 2025
    url: https://cr.minzdrav.gov.ru/view-cr/1006_1
  - tier: reference
    org: msd-manuals
    title: Thoracic Outlet Compression Syndromes (TOS) (MSD Manual Professional Version)
    year: 2026
    url: https://www.msdmanuals.com/professional/neurologic-disorders/peripheral-nervous-system-and-motor-unit-disorders/thoracic-outlet-compression-syndromes-tos
  - tier: reference
    org: msd-manuals
    title: Thoracic Outlet Syndromes (TOS) (MSD Manual Consumer Version)
    year: 2026
    url: https://www.msdmanuals.com/home/brain-spinal-cord-and-nerve-disorders/peripheral-nerve-and-related-disorders/thoracic-outlet-syndromes-tos
sources_checked: 2026-10-14
review: null
---

Thoracic outlet syndrome is a group of conditions in which nerves, arteries or large veins are compressed where they pass from the neck into the chest and on to the arm.<Cite n={[1, 4]} /> The Russian Ministry of Health guideline calls it superior thoracic aperture syndrome, and the professional version of the MSD Manual calls them thoracic outlet compression syndromes.<Cite n={[1, 3]} />

The Russian Ministry of Health has no separate clinical guideline on this syndrome: its venous form is covered in the guideline on deep vein thrombosis, and this article describes the nerve and arterial forms from the MSD Manual.

<Diagram name="thoracic-outlet-syndrome">
  <p slot="normal">
    The diagram shows the passage from the neck to the arm on one side of the body, from the front,
    simplified. Large blood vessels and many nerves pass through it to the arm; the space is
    crowded, with a rib, the collarbone and muscles close by.<Cite n={4} /> According to MSD, the
    lower trunk of the brachial plexus passes below the scalene muscles and over the first
    rib.<Cite n={3} />
  </p>
  <p slot="disease">
    The form of the syndrome depends on what exactly is compressed; for clarity the diagram shows
    all three at once.<Cite n={3} /> When the nerves are compressed, pain and tingling run from the
    neck or shoulder along the inside of the arm to the hand.<Cite n={4} /> When the subclavian
    artery is compressed, less blood reaches the arm, and it becomes pale and cool.<Cite n={4} /> The
    subclavian vein can be squeezed between the collarbone and the first rib<Cite n={1} />; the arm
    then swells, and the skin may look bluish.<Cite n={4} />
  </p>
</Diagram>

## Why it happens

<Patient>

The passage from the neck to the arm is crowded, so blood vessels or nerves can be squeezed between a rib, the collarbone or a muscle.<Cite n={4} /> According to the MSD Manual, the exact cause is often unclear, and an obvious anatomical abnormality is found only very rarely: for example, a small extra rib in the neck (cervical rib), an abnormal rib in the chest or a badly healed broken collarbone.<Cite n={4} /> Women are affected more often.<Cite n={[1, 3, 4]} />

There are three forms, depending on what is compressed: neurogenic (the nerves of the brachial plexus), venous (the subclavian vein) and arterial (the subclavian artery).<Cite n={[1, 3]} /> According to MSD, the vast majority of cases are neurogenic.<Cite n={3} />

In the venous form, a clot can form in the compressed vein after intense exertion of the shoulder girdle muscles: this is Paget–Schroetter syndrome, or effort thrombosis, one form of deep vein thrombosis of the arm.<Cite n={1} /> More in the article on [deep vein thrombosis](../deep-vein-thrombosis/).

Another disease of the subclavian artery, its narrowing, is described in the article on [subclavian artery stenosis](../subclavian-artery-stenosis/).

</Patient>

<Student>

The Russian Ministry of Health guideline defines superior thoracic aperture syndrome as a group of clinical syndromes caused by congenital or acquired compression of the brachial plexus or subclavian vessels as they pass through the superior thoracic aperture.<Cite n={1} /> According to the same guideline, the neurogenic form accounts for 95% of cases, the venous form for 4% and the arterial form for 1%.<Cite n={1} /> Causes of subclavian vein compression: the junction of the clavicle and the first rib, an accessory cervical rib, hypertrophy of the anterior scalene or subclavius muscle, an elongated C7 transverse process.<Cite n={1} />

According to MSD, the neurogenic form involves compression of the lower trunk of the brachial plexus, although the nature of this involvement is unclear; causes of compression include abnormal attachment or position of the scalene muscles.<Cite n={3} /> The sources give different ages: MSD Professional 25–55 years, MSD Consumer 35–55 years, the Russian Ministry of Health guideline most often 25 to 50 years.<Cite n={[1, 3, 4]} />

</Student>

## Symptoms

<Patient>

The symptoms depend on what is compressed:<Cite n={4} />

- **nerves**: pain and tingling that usually start in the neck or shoulder and run along the inside of the arm to the hand;<Cite n={4} /> occasionally the whole hand becomes weak;<Cite n={3} />
- **artery**: less blood reaches the arm, and it becomes pale and cool;<Cite n={4} />
- **vein**: the hand, arm and shoulder on the affected side may swell, and the skin may look bluish.<Cite n={4} />

Rare complications, according to MSD, are Raynaud syndrome in the affected arm, in which the fingers turn pale or blue and numb in the cold, and tissue death (gangrene) in the far parts of the arm.<Cite n={[3, 4]} /> More in the article on [Raynaud phenomenon](../raynaud-phenomenon/).

If a clot has formed in a vein of the arm, the veins under the skin of the arm and the front of the chest become more visible, the arm swells and turns bluish, and the pain gets worse with exertion.<Cite n={1} /> Sometimes the first sign is a [pulmonary embolism](../pulmonary-embolism/) (PE).<Cite n={1} />

</Patient>

<Student>

MSD: many patients have mild to moderate sensory impairment in the C8–T1 distribution on the painful side; a few have prominent vascular-autonomic changes in the hand (cyanosis, swelling).<Cite n={3} />

</Student>

## How it is diagnosed

<Patient>

There is no single test that confirms or rules out this syndrome: the doctor relies on the symptoms, the examination and the results of several tests.<Cite n={[3, 4]} /> According to the MSD Manual, nerve conduction studies and electromyography are usually done, an MRI scan to look for anatomical abnormalities and a neck X-ray to look for a cervical rib; sometimes angiography of the arteries of the arm.<Cite n={4} />

If thrombosis of an arm vein is suspected, the first test is an ultrasound (duplex) scan of the veins.<Cite n={1} /> If blood flow in an arm artery has suddenly been disrupted and compression is suspected, for example by a cervical rib, the Russian Ministry of Health guideline considers imaging of the arteries mandatory.<Cite n={2} />

</Patient>

<Student>

MSD: electrodiagnostic testing is warranted in all patients with suggestive symptoms, and MRI of the brachial plexus and/or cervical spine is usually also indicated; provocative tests (for example, raising the arm above the head) have low sensitivity and specificity; angiographic findings are not incontrovertible evidence of disease.<Cite n={3} />

Russian Ministry of Health guideline, upper extremity DVT: initial imaging is duplex ultrasound of the veins (level of evidence 1, grade of recommendation A); to clarify the source of compression, phlebography or CT angiography (level of evidence 5, grade of recommendation C).<Cite n={1} /> Russian Ministry of Health guideline, acute limb ischaemia: when atypical ischaemia of the arm is suspected (compression syndrome, cervical rib), imaging is mandatory; if the artery is patent, duplex ultrasound or DSA is recommended to confirm the compression syndrome.<Cite n={2} />

</Student>

## How it is treated

<Patient>

According to the MSD Manual, most people are helped by physiotherapy and exercise; the doctor may add painkillers.<Cite n={[3, 4]} /> Not everyone needs surgery: it is considered if an anatomical abnormality or compression of large blood vessels is confirmed, or if the symptoms keep getting worse.<Cite n={4} /> A definite diagnosis is difficult to make and symptoms often persist after surgery, so the question of surgery is usually decided with an experienced specialist.<Cite n={4} />

Thrombosis of the subclavian vein is treated with medicines that prevent blood from clotting.<Cite n={1} /> The Russian Ministry of Health guideline suggests considering dissolving the clot through a catheter followed by relieving the compression of the vein, and, after the clot has been removed, considering removal of the first rib if there is evidence of compression of the vein at the thoracic outlet; at the same time it acknowledges that approaches to treating thrombosis of the arm veins are not uniform.<Cite n={1} /> The doctor decides which treatment is needed.

</Patient>

<Student>

MSD: most patients without objective neurological deficits respond to physiotherapy and drug treatment; with few exceptions, surgery is reserved for patients with significant or progressive neurovascular deficits who do not respond to conservative treatment.<Cite n={3} />

Russian Ministry of Health guideline, upper extremity DVT: in primary DVT, treatment that prevents blood clotting is recommended (level of evidence 4, grade of recommendation C); in primary axillary-subclavian thrombosis in patients with superior thoracic aperture syndrome, thrombolysis followed by decompression of the thoracic outlet should be considered (level of evidence 2, grade of recommendation B); in patients who have undergone early clot removal, first rib resection should be considered if there is evidence of venous thoracic outlet syndrome (level of evidence 3, grade of recommendation C).<Cite n={1} />

</Student>

## When to call an ambulance

Pain and tingling from the neck to the hand are a reason to see a doctor. Urgent help is needed for complications.

Call your local emergency number (112 in the EU, 911 in the US and Canada, 999 in the UK) if you suddenly develop shortness of breath, chest pain, feeling faint or fainting, or coughing up blood: these may be signs of PE.<Cite n={1} /> More in the article on [pulmonary embolism](../pulmonary-embolism/).

Also call for emergency help if the arm has suddenly become cold, pale and painful, numb or weak: this may be acute ischaemia, a sudden loss of blood flow in an artery that needs urgent diagnosis and treatment.<Cite n={2} /> More in the article on [acute limb ischaemia](../acute-limb-ischemia/).

If the arm has swollen and turned bluish, and the veins under the skin of the shoulder and chest have become more visible, do not put off seeing a doctor: this may be thrombosis of an arm vein, which can only be confirmed by tests, and timely diagnosis helps prevent complications.<Cite n={1} /> More in the article on [deep vein thrombosis](../deep-vein-thrombosis/).

As with any heart or blood vessel condition, call an ambulance for fainting, chest pain or severe shortness of breath: this is the site's general safety rule, repeated at the bottom of every page.

<Quiz />