Thoracic Outlet Syndrome

Thoracic outlet syndrome (TOS) is a condition caused by compression of the neurovascular bundle as it exits the chest to supply the upper extremities. This triangular region, bordered by the scalene muscles, upper border of the first rib and clavicle is referred to as the thoracic outlet. The constellation of symptoms depending on the specific region of compression is referred to as Thoracic Outlet Syndrome.

There are three main types: Neurogenic (nTOS), Venous (vTOS), and Arterial (aTOS). Neurogenic is the most common (95%) and presents with pain, weakness, and occasionally muscle wasting. Venous (4%) results in swelling, pain, and cyanosis of the arm. Arterial (1%) results in pain, coldness, and progressive ischaemia.

Risk Factors

• CONGENITAL: Anatomical anomalies (e.g. cervical rib, scalene muscle attachments, ligamentous variation)
• POST-TRAUMATIC: Isolated or repetitive trauma to thoracic outlet (e.g. clavicular fracture, "whiplash”, shoulder trauma or scalene fibrosis)
• FUNCTIONAL: Repetitive abduction and external rotation of the shoulder (e.g swimming, weight lifting, painting).Typically acquired due to hypertrophy of these muscles and associated fibrosis
• SEX: Female > Male
• OTHER: Less common systemic conditions (e.g. tumours)

Any condition that causes encroachment of the space for the brachial plexus at the thoracic outlet can lead to thoracic outlet syndrome, including poor posture.

Presentation

TOS symptoms are dependent of the region of neurovascular compression. Neurogenic pain is the most common presentation and occurs predominantly in women aged 20-40years. It is more controversial as the diagnosis is largely clinical. Guidelines recommend symptoms must extend beyond the distribution of a single nerve, be present continuously for more then 3months and no other cause be identified. Venous and arterial TOS diagnosis is more objective.

Certain manoeuvres of the arm and neck can produce symptoms of the compression. Adson's manoeuvre, whereby the examiner moves the shoulder joint into certain positions can elicit symptoms. Roos test asks the patient to abduct and externally rotate both shoulders and elbows to 90 degrees and exercise the hands. This is diagnostic if symptoms occur in less than one minute.

Investigations

Further investigations can include electrical tests, such as Electromyography (EMG) and somatosensory evoked responses. These tests are often negative until late stages of nTOS but serve to exclude other possible neurogenic causes. Plain Xray can help identify a complete or partial cervical rib, however, only 5-10% of cervical ribs are associated with TOS. MRI is of limited value except when a tumour is suspected. It may also assist in locating fibromuscular variations. The use of vascular ultrasonography in static and dynamic manoeuvres can be diagnostic, particularly when a post-stenotic aneurysm is identified.

Cervical Rib (Partial)

Another diagnostic modality recommended by the Society for Vascular Surgery is a scalene muscle injection test which can be diagnostic when performed properly. An anterior scalene block with 1% lignocaine can provide useful information and increase functional motor capacity. The subjective nature of the validity of investigations for nTOS cause controversy in its diagnosis.

Treatment

SURGICAL: Patient selection remains the constant in successful outcomes. Open surgical treatment with resection of the first rib (or cervical rib when present) and anterior scalene muscle remains the operation of choice, with some authors reporting success in more then 90% patients at one year. Various approaches are used including transaxillary, supra and infra-clavicular. Neurogenic TOS has a high rate of recurrence and better outcomes are achieved in patients who are younger, respond well to a course of physical therapy and scalene block.

MEDICAL: Anterior scalene muscle injection not only serves as a both diagnostic and prognostic tool; it also plays a role as a therapeutic tool in patients with nTOS. Trauma patients who receive this treatment, particular those treated soon after onset of symptoms, experience better results.

First Rib Resection and Scalenectomy

REHABILITATION: Despite the high rate of success with minimal complications associated with surgical decompression, medical management may be the most appropriate option for certain patients. These measures are effective in up to 70% of patients presenting with nTOS. Physical therapy, modifications to daily activities and pharmacologic agents are all medical options in the treatment of nTOS.

Thoracic Outlet Syndrome remains a challenging entity to diagnose but treatment outcomes can be very successful and long-lasting given the correct patient selection. The Society of Vascular Surgery continues to develop treatment guidelines and diagnostic criteria for Neurogenic Thoracic Outlet Syndrome to improve outcomes. First rib resection with scalenectomy to surgically decompress the thoracic outlet remains the treatment of choice as minimally invasive techniques advance.

Dr Andrew Bullen
Vascular Surgeon
Circulation Health
101/62 Harbour Street
Wollongong NSW 2500
Phone: 02 4243 8050