condition Thoracic outlet syndrome (TOS) is an uncommon disorder that results from compression or irritation of the nerves and/or blood vessels in the base of the neck underneath the collarbone. t

Thoracic outlet syndrome (TOS) is an uncommon disorder that results from compression or irritation of the nerves and/or blood vessels in the base of the neck underneath the collarbone.

What is Thoracic Outlet Syndrome?

Thoracic outlet syndrome (TOS) is an uncommon disorder that results from compression or irritation of the nerves and/or blood vessels at the base of the neck and front of the chest underneath the collarbone. This area is known as the thoracic outlet. This compression can cause a variety of symptoms depending upon which area is affected. The symptoms resulting from this compression are called TOS.

There are three types of TOS: neurogenic, venous and arterial. Approximately 90% of all TOS patients suffer from the neurogenic type. The remaining 10% may have symptoms from compression of the subclavian vein (a large vein leading to each arm that brings blood to the heart) or the subclavian artery (an artery leading to each arm that delivers blood from the heart). Some patients have symptoms that are caused by compression of both the nerves and blood vessels.

What Causes TOS?

TOS usually is caused by a combination of two factors:

  • Having abnormal anatomy that creates compression in the thoracic outlet
  • Having some form of injury to the thoracic outlet area 

Anatomic abnormalities may be obvious, such as the presence of an additional rib in the neck (cervical rib) or an abnormality in the spine at the base of the neck. Some abnormalities may be subtle and difficult to detect, such as abnormalities within the scalene muscles (a group of muscles in the neck, located in the front on either side of the throat) or ligaments within this region. The injuries required to trigger symptoms may also be severe, such as a car accident, or subtle, such as a mild injury from arm activity.

What are the Symptoms for TOS?

The symptoms of TOS depend upon which areas are compressed within the thoracic outlet.

Neurogenic TOS (NTOS)

NTOS results from compression of the nerves in the area known as the brachial plexus (a group of nerves that run from the spine and into the neck, armpit region and the arm). Symptoms of NTOS can be painful, confusing and frustrating for patients. NTOS often dramatically affects the quality of life for both the patient and his/her family. Symptoms can vary greatly from patient to patient and can range from mild to severe with changes from day to day.

For patients with NTOS, pain is the most common symptom. This pain may involve the neck, the front and/or back of the upper chest, as well as the shoulder and arm. Specific symptoms may include:

  • Headaches or pain that extends to the ear, jaw or face. This pain can be constant or only occur occasionally
  • A pins-and-needles sensation or a feeling of numbness in the neck, chest or arm
  • Mild weakness or decreased coordination of the hand. Patients may drop objects that they are holding
  • Cold sensation or changes in the skin color of the arm or hand

Patients’ symptoms may worsen with activity. Any combination of these symptoms may be present, and not all are required to have a diagnosis of NTOS.

Venous TOS (VTOS)

VTOS is caused by compression of the subclavian vein, which returns blood from the arms back into the chest and to the heart. This vein passes under the collarbone through the thoracic outlet region. Chronic compression of this area damages the vein, causing scarring and narrowing. This can result in a blood clot within the vein that produces a swelling of the affected arm, although not all patients have a blood clot present. Other symptoms of VTOS may include:

  • Changes in the color of the skin in the arm and shoulder area, with a mild blue, purple or red color
  • Enlarged blood vessels seen under the skin in the front of the shoulder or chest area
  • Feeling of a heavy sensation or a mild ache in the arm

Arterial TOS (ATOS)

ATOS is rare and occurs when compression within the thoracic outlet—usually from a bone abnormality—damages the artery, resulting in expansion of the artery (aneurysm) or blockage of the artery from a blood clot. Aneurysms of the subclavian artery may not initially produce symptoms, but create risk for developing blood clots. These clots may either block the blood flow to the arm or break away and travel further down the arm. Either situation can cause:

  • Immediate pain
  • A pins-and-needles sensation
  • A pale arm that is cold to the touch

How is TOS Diagnosed?

The diagnosis of all forms of TOS begins with a careful and detailed history and physical examination.


NTOS can be extremely difficult to diagnose, as other conditions of the neck or shoulder can cause symptoms nearly identical to TOS.

There is no national consensus regarding the role of diagnostic testing for NTOS, but detailed anatomic information of a patient’s thoracic outlet region can be obtained through imaging studies, including:

  • A computed tomography (CT) angiogram that takes images using contrast dye to better visualize the blood vessels and blood flow within them
  • A high-resolution magnetic resonance imaging (MRI) scan that takes images from various angles to get a more complete picture of the patient’s condition

Nerve conduction studies and electromyography (EMG) are occasionally helpful in evaluating for other potential causes that can mimic TOS, although they are not commonly used. Some patients require an MRI evaluation of the spine or shoulder to evaluate these areas as potential causes of their symptoms.


VTOS is typically diagnosed with a venogram (an X-ray that uses contrast dye to visualize the veins), as noninvasive studies using ultrasound are often unable to diagnose the condition.


The CT angiogram used in evaluating NTOS patients is also extremely helpful in diagnosing ATOS patients.

Treatment for TOS

Both physical therapy and medications are possible treatments for TOS. For some patients, surgery may be a recommended approach. All surgical cases are different, and each surgery is tailored to each patient. Regardless of the cause, thoracic outlet surgery can be performed through different incisions. The two most common are incisions in the armpit (2 inches) or above the collarbone (2.5-3 inches). More complex VTOS cases, and almost all cases of ATOS, typically require an incision above and below the collarbone, which allows for reconstruction of the damaged blood vessel.

Generally, surgery for TOS typically involves removing parts of the scalene muscles (a group of muscles in the neck, located in the front on either side of the throat), as well as the first thoracic rib. Bone abnormalities, such as an additional rib in the neck or an abnormality in the spine at the base of the neck, are often removed along with the first thoracic rib. Any other tissues that may be affecting the nerves of the shoulder and brachial plexus (a network of nerves that sends signals from the spine to the shoulder, arm and hand) are also removed to achieve a complete decompression.

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