- 0.3 – 0.8% of the population
- 60% remain asymptomatic
- Bilateral in 70% of cases
- More common in women
- 10% develop thoracic outlet syndrome
It is mainly considered as a congenital anomaly, but there have been reports suggestive of acquired cases following trauma.
Cervical ribs can cause compression on the neurovascular structures that lies within the thoracic outlet leading to thoracic outlet syndrome.
Anatomy Of The Thoracic Outlet
It is the space where subclavian artery, subclavian vein and brachial plexus exit from the thorax to enter into the arm.
These neurovascular structures pass above the first rib, but below the clavicle.
At the level of the first rib, lower roots of brachial plexus combine to form the trunks of brachial plexus.
The lowermost trunk formed by the union of C8 and T1 lies in contact with the superior surface of the first rib.
Pathogenesis Of Cervical Rib
In the presence of a cervical rib, subclavian artery, subclavian vein and brachial plexus have to go above the cervical rib but below the clavicle to enter into the arm
There is kinking of subclavian artery and compression of lowermost trunk of brachial plexus (C8 – T1) leading to….
- Poststenotic dilatation of the subclavian artery (Aneurysm)
Murmur, best heard in the infraclavicular region
- Pain, paraesthesia, wasting along the medial side of the hand and forearm (C8, T1 distribution)
- Emboli – Can cause gangrene and necrosis of digits
- Venous congestion – Swollen, warm tender arm
These consequences are called as thoracic outlet syndrome.
Causes Of Thoracic Outlet Syndrome
- Cervical rib
- Hypertrophy of muscles
- Abnormal fibrous muscular bands
- Neck trauma – Haematoma, callus, scar formation, malunion of clavical fracture can lead to TOS
Clinical Presentation Of Thoracic Outlet Syndrome
- Venous obstruction (obstruction of subclavian vein)
- Upper limb swelling
- Warm, tender arm
- Venous distention
- Arterial obstruction (Obstruction of subclavian artery)
- Pallor, cold
- Tender arm
- Absent of pulse
- Gangrene, necrosis
- Neurological features (Compression of brachial plexus)
- Paraesthesia (Ulnar nerve distribution)
- Painless atrophy of the intrinsic muscles of the hand (APB, hypothenar muscles, interossei)
- Adson test
- It is performed by asking the patient to extend and rotate the patient’s head towards the examining side, while holding the radial pulse of the slightly abducted symptomatic limb
- If positive – There will be a reduction or an absence of radial pulse
- Bilateral blood pressure measurement
- > 20 mmHg difference is suggestive of an arterial obstruction
- Roos’ test
- Abduct and externally rotate the arm
- If positive – It will aggravate the symptoms
Differential Diagnosis Of Thoracic Outlet Syndrome
- Carpal tunnel syndrome
- Cervical spondylosis
- Raynaud syndrome
- Subclavian aneurysm
- Trauma (Whiplash injury, clavicle fracture)
- TIA / Stroke
Investigations Of Thoracic Outlet Syndrome
- Chest X-ray and thoracic outlet views
- Cervical ribs may not be visible
- Nerve conduction studies
- Reduced velocity in neurogenic thoracic outlet syndrome
- Duplex ultrasonography
- Can be used to detect obstruction of subclavian vein
- CT angiography / MR angiography
- Can be used to detect obstruction of subclavian artery
Treatment Of Thoracic Outlet Syndrome
- Surgical decompression
- Resection of first part of first rib / cervical rib or divide anterior scalene muscle