Thoracic Outlet Syndrome

Thoracic outlet syndrome (TOS) is a broad term used for a spectrum of syndromes related to the general region of the thoracic outlet, which involves the compression or irritation of elements of the brachial plexus, subclavian artery, or subclavian vein. The most common etiology involves structural abnormalities. Thoracic outlet syndrome can present as the neurogenic, arterial, or venous type. The neurogenic type is the most common among the 3 variants and mainly involves the inferior trunk of the brachial plexus (C8–T1). Signs and symptoms vary based on the structure that is involved. The diagnosis of TOS is clinical and supported by radiography and a number of provocation maneuvers. Untreated TOS can lead to various complications such as a frozen shoulder. Management of TOS is using pharmacological and surgical methods.

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Thoracic outlet syndrome (TOS) refers to a spectrum of signs and symptoms that arise from the compression of the neurovascular bundle by any of the various structures within the confined space of the thoracic outlet, usually within the scalene triangle.


  • Neurogenic: 
    • Accounts for 95% of cases
    • Due to compression of the trunks of the brachial plexus
  • Arterial:
    • Accounts for 4% of cases, but rarely causes symptoms
    • Due to compression of the subclavian artery
  • Venous:
    • Accounts for 1% of cases, but causes symptoms more commonly than the arterial type
    • Due to compression of the subclavian vein


  • More common in women:
    • Usually occurs in women who are 20–50 years old
    • Presents most commonly as neurogenic TOS
  • Men most commonly present with venous TOS.


Structural causes:

  • Cervical ribs
  • Fibrous bands running within this region
  • Hypertrophy or abnormal insertion of the scalene muscles (reduces the size of the scalene triangle)
  • Anomalous muscles (e.g., supernumerary scalenes) in the region of the thoracic outlet

Other causes:

  • Injuries: sports-related injuries and motions (e.g., clavicle fracture, repetitive throwing motions)
  • Fractured clavicle
  • Repetitive stress: abnormal pressure on the shoulder
  • Poor posture: a condition called forward head posture (FHP) seen in people who, for example, read on the computer for long periods of time
  • Pancoast tumor (tumor of the lung apex)
Ossified cervical ribs

X-ray of the cervical ribs

Image: “Cervical Ribs” by Huntsville Hospital Imaging. License: Public Domain

Anatomy and Pathophysiology


Thoracic outlet:

  • Passageway of the neurovasculature between the base of the neck, through the axilla, and into the upper limb
  • The thoracic outlet is made up of: 
    • Thoracic vertebra (T1) posteriorly
    • 1st pair of ribs laterally
    • Clavicle, sternoclavicular joint, and manubrium of the sternum anteriorly

The structures of significance in TOS are:

  • Inferior trunk of the brachial plexus (C8–T1)
  • Subclavian arteries
  • Subclavian veins
Thoracic outlet

The thoracic outlet featuring the brachial plexus, subclavian vessels, scalene triangle, and costoclavicular angle

Image by BioDigital, edited by Lecturio


There are 3 main sites where the compression of structures occurs in TOS:

  • Scalene triangle; borders:
    • Anterior scalene muscle anteriorly 
    • Middle scalene muscle posteriorly
    • 1st rib inferiorly
  • Costoclavicular angle or space: the angle made between the clavicle and 1st rib
  • Subcoracoid space: the space behind and below the coracoid process of the scapula
Sites of thoracic outlet syndrome

The 3 most common sites of compression leading to thoracic outlet syndrome: scalene triangle, costoclavicular angle, and subcoracoid space

Image by BioDigital, edited by Lecturio

Clinical Presentation

Neurogenic TOS

  • Paresthesia of the medial side of the arm and hand (can also affect the anterolateral aspect of the chest wall)
  • Pain in the neck, shoulder, arm, forearm, and fingers (especially the medial side)
  • Symptoms are aggravated by:
    • Arm elevation above shoulder level (reaching, lifting)
    • Sustained use of arms and hands (e.g., typing)
  • Occipital headache
  • Progressively weakened grip and difficulty in completing daily activities 
  • Gilliatt-Sumner hand: wasting (atrophy) of the muscles of the hand, especially of the thumb, and thenar eminence (advanced manifestation, rare)

Arterial TOS

  • Fatigue and weakness of the arm and forearm
  • Sensation of coldness in the arm and forearm, also cold upon palpation
  • Upper limb claudication
  • Low BP in the affected arm in comparison to the contralateral side
  • Symptoms of hand ischemia secondary to embolization from subclavian thrombus:
    • Paraesthesia
    • Pallor
    • Pain
    • Coldness

Venous TOS

  • Swelling of the arm
  • Cyanosis
  • Pain
  • Forearm fatigue
  • Sensation of heaviness or numbness of the arm
  • Collateral venous patterning in ipsilateral neck, chest, and shoulder
  • Paget-Schroetter syndrome (see Complications)


History and physical exam

  • Typical symptoms of pain, swelling, and paresthesias aggravated by certain activities or positions
  • Unilateral upper-extremity swelling
  • Pulse difference between the upper extremities
  • Weak hand grip
  • Hand muscle atrophy

Provocative tests

Adson’s test:

  • Procedure:
    1. Fully extend and abduct the patient’s arm at approximately 30 degrees.
    2. Palpate the radial pulse during the exam (should be compared to the contralateral side and ipsilateral side in a relaxed position).
    3. Ask the patient to extend their neck, rotate it toward the affected shoulder, take a deep breath, and hold the position.
  • Positive result: significant reduction or loss of radial pulse, or aggravated paresthesia
  • Prone to false-positive results; limited clinical value

Roos or elevated-arm test:

  • Procedure:
    1. Hold the patient’s arms at 90 degrees of abduction and external rotation, with the elbows flexed and in the frontal plane.
    2. Ask the patient to hold the position and open and close their fists for a few minutes.
  • Positive results:
    • Gradual increase in pain or paresthesia at the neck, shoulder, and/or arm 
    • Pallor, cyanosis, and swelling of the arm
    • Aggravation of usual symptoms
    • The patient drops their arms in distress before completing the test.

Wright’s hyperabduction test:

  • Procedure:
    1. Passively bring the patient’s arm to 90 degrees of abduction and external rotation, with the elbow flexed at 45 degrees.
    2. Palpate the radial pulse while the position is held for 1 minute.
    3. Then, repeat the test with the patient’s arm in hyperabduction.
  • Positive result: significant reduction or loss of radial pulse, or aggravated paresthesia

Costoclavicular maneuver:

  • Procedure:
    1. While the patient is standing, passively move their shoulder down and back while they lift their chest. 
    2. Palpate the radial pulse during the motion. 
  • Positive result: significant reduction or loss of the radial pulse, or aggravated paresthesia

Lidocaine scalene block test:

  • Procedure: Lidocaine is injected into the anterior scalene muscle under imaging guidance.
  • Positive results: significant reduction or complete relief of symptoms


  • Can confirm neurogenic TOS and localize the area of compression
  • Can rule out/differentiate from carpal tunnel syndrome


  • Chest X-ray: can confirm the presence of abnormal structures in the thoracic outlet causing compression on the neurovascular bundle
    • Cervical ribs
    • Elongated C7 transverse processes
    • Pancoast tumor 
  • Ultrasound:
    • Good initial test when a vascular TOS is suspected
    • Will reveal vessel stenosis or occlusion
    • Can be performed with positional changes and provocative maneuvers
  • CT angiography:
    • Yields high-quality images
    • Delineates the anatomical relationship of vessels to the surrounding structures
  • MRI or cervical myelography: can rule out narrowing of the intervertebral foramen, disc compression, and intraspinal space-occupying lesions
  • Angiogram or venogram: 
    • Can rule out aneurysm and thrombosis of the vessels being studied
    • Not always necessary for diagnosis, but can be important for surgical planning

Management and Complications


The management and care of TOS are approached via 2 different methods:

  • Medical management:
    • Posture improvement
    • Stretching
    • Physiotherapy
    • IM steroid injection
    • Analgesics and/or muscle relaxants
    • Avoiding aggravating activities
    • Use of systemic anticoagulants if venous or arterial thrombosis is present
  • Surgical management indicated for:
    • Vascular symptoms in patients at low risk for surgery
    • Severe/progressive neurological symptoms that do not improve with medical therapy
    • Surgical approaches:
      • 1st rib resection
      • Cervical rib resection
      • Anterior scalenectomy: The anterior and middle scalene muscles are resected. 
      • Angioplasty (with resection of the muscle and rib), if an aneurysm is present
      • Catheter-directed thrombolysis for venous or arterial thrombi


  • Frozen shoulder: 
    • If left untreated, TOS can cause increased pain on the affected side, resulting in the inability to move the upper limb. 
    • Long periods of immobility lead to a frozen shoulder, which is characterized by chronic stiffness and shoulder pain.
  • Paget-Schroetter syndrome:
    • Known as effort thrombosis or effort axillary-subclavian vein thrombosis
    • Excess strenuous movement of the upper limb can lead to thrombosis of the subclavian vein (deep vein thrombosis).
  • Cerebrovascular arterial insufficiency:
    • The carotid artery is also present in the thoracic outlet, and distal compression of the subclavian artery can lead to carotid artery compression and stroke.
    • If the vertebral artery is affected, vision abnormalities, embolic stroke, and hypoperfusion of the brainstem and brain are possible.

Differential Diagnosis

  • Carpal tunnel syndrome: a type of peripheral neuropathy caused by compression of the median nerve. Symptoms include numbness, the sensation of heaviness, and decreased grip strength in the hands owing to sensory loss in the palmar aspect, the 1st–3rd digits, and the radial half of the 4th digit. Diagnosis is made based on a compression test, Tinel’s sign, and Phalen’s sign. Management includes occupational therapy, neutral positioning of a wrist splint, steroid injection, or surgery.
  • De Quervain tenosynovitis: inflammation of the 1st extensor compartment of the wrist, which results in radial pain and swelling. Diagnosis is made based on positive Finkelstein’s test and an ultrasound, which shows synovial thickening. Management includes physiotherapy, splinting of the affected joint, steroid injection, or surgery.
  • Horner syndrome: a neurological disorder resulting from the interruption of the sympathetic innervation of the head, eye, and neck. Horner syndrome is characterized by a triad of miosis, partial ptosis, and absence of facial sweating, but can also present with pain in the face and neck, and atrophy of the hand and forearm muscles. Diagnosis is clinical and supported by findings from imaging studies. Treatment involves resolving the underlying cause.
  • Raynaud’s disease: an exaggerated vascular response of the digits to cold temperatures or emotional stress, which typically results in sequential digital blanching, cyanosis, and rubor. Diagnosis of primary Raynaud’s disease relies on the Allen test and laboratory workup for secondary causes. Management includes treatment of the underlying cause or therapy with vasodilators.
  • Pectoralis minor syndrome: a rare syndrome that causes pain, numbness, and tingling in the hand and arm, and pain or tenderness in the chest wall below the clavicle and axilla. Pectoralis minor syndrome occurs due to compression of the neurovascular structures under the pectoralis minor muscle. Diagnosis is clinical and supported by imaging. Management includes physiotherapy, pectoralis minor muscle block, and surgery.


  1. Mohammad Ali Hosseinian, Ali Gharibi Loron, and Yalda Soleimanifard (2017). Evaluation of complications after surgical treatment of thoracic outlet syndrome, NCBI.,plexus%2C%20severe%20sequelae%20such%20as
  2. Kaoru Goshima (2020). Overview of thoracic outlet syndromes. Retrieved April 8, 2021, from
  3. Riki Duncan. Thoracic Outlet Syndrome or Carpal Tunnel Syndrome. KCBJ. Retrieved April 8, 2021, from
  4. Sian Smale (2013). Thoracic Outlet Syndrome; Rayner and Smale.

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