Arterial Thoracic Outlet Syndrome

Arterial thoracic outlet syndrome is compression of the subclavian artery in the thoracic outlet, usually by a cervical rib or an abnormal first rib. It causes arterial stenosis, post-stenotic aneurysm, thrombus and distal embolisation, and can threaten the hand.

It is the rarest form of thoracic outlet syndrome, accounting for about 1 to 2% of cases. The neurogenic form accounts for about 90 to 95% and the venous form for 3 to 5%. Arterial disease occurs mostly in young adults, with a bony abnormality in nearly all cases.

Cervical ribs occur in about 0.5 to 1% of people, and only a small minority develop arterial complications. Other causes are an anomalous or fractured first rib, a clavicular fracture with callus, an exostosis, and scalene muscle variants. Overhead athletes and repetitive work increase risk.

Disease is bilateral in about half of patients with cervical ribs. Early diagnosis matters because repeated embolisation can destroy the digital arteries.

Pathophysiology.

The subclavian artery crosses the first rib between the scalene muscles. A bony abnormality narrows the space, and repeated arm elevation compresses and traumatises the artery.

Chronic injury causes intimal damage, stenosis, post-stenotic dilatation and aneurysm formation, with mural thrombus. Thrombus and debris embolise into the brachial, forearm and digital arteries, or the artery thromboses and occludes.

Distal emboli cause digital ischaemia, ulceration and gangrene. Disease is localised to the subclavian artery in the outlet, so the proximal and distal vessels are often normal until embolism occurs.

Arm fatigue and pain with use, cold intolerance, pallor, coolness and numbness of the hand, claudication of the arm, digital ulceration, blue fingers, Raynaud type symptoms, and sometimes acute hand ischaemia. Neurological symptoms (pain, tingling, weakness) may coexist.

Examination:

• Supraclavicular fullness, a bruit, or a pulsatile mass (aneurysm).
• Reduced or absent radial pulse, a systolic blood pressure difference of 20 mmHg or more between arms, and loss of the pulse with arm abduction and external rotation.
• Splinter haemorrhages, digital ulcers and gangrene.
• A bony prominence in the supraclavicular fossa (cervical rib).

• Blood pressure in both arms, and digital pressures with photoplethysmography.
• Duplex ultrasound of the subclavian, axillary and brachial arteries with the arm in neutral and provocative positions (abduction, external rotation), showing compression, stenosis, aneurysm and thrombus.
• Chest and cervical spine radiographs for cervical rib, first rib abnormality, and clavicular fracture.
• CT angiography with the arm in neutral and abducted positions: the key test for the arterial lesion, the bony anatomy and distal run off. MR angiography is an alternative. Catheter angiography is used before intervention to show distal embolic disease.
• Echocardiography and ambulatory ECG to exclude a cardiac source of emboli.
• Blood tests for other causes of digital ischaemia: full blood count, ESR, C-reactive protein, antinuclear antibody, antiphospholipid antibodies, cryoglobulins, thrombophilia screen.

Differential diagnosis.

• Neurogenic and venous thoracic outlet syndrome.
• Subclavian atherosclerosis, Takayasu arteritis and giant cell arteritis.
• Cardiac embolism and other causes of digital ischaemia (vasculitis, connective tissue disease, thrombophilia).
• Raynaud disease, Buerger disease and traumatic arterial injury.

Surgical decompression is the definitive treatment because the compression persists and drives complications.

• Resection of the first rib, with resection of the cervical rib when present, and scalenectomy, via a supraclavicular, transaxillary or combined approach. Neurolysis of the brachial plexus is added when nerve compression coexists.
• Arterial reconstruction when there is stenosis, aneurysm, thrombus or occlusion: resection and interposition graft using reversed saphenous vein or prosthetic graft, or bypass, in the same operation or after decompression. Thrombectomy of the distal arteries with a Fogarty catheter.
• Cefazolin 2 g intravenously within 60 minutes before incision (3 g when weight is over 120 kg); heparin 70 to 100 units/kg intravenously before clamping, reversed with protamine 1 mg for each 100 units given in the previous 2 to 3 hours (maximum 50 mg, given slowly).
• Stent placement across the outlet is avoided because of compression, fracture and thrombosis.
• Cervicothoracic sympathectomy is added in selected patients with refractory digital ischaemia.

Acute hand ischaemia (thrombosis or embolism).

• Unfractionated heparin 80 units/kg intravenous bolus (usual 5000 units), then 18 units/kg/h, aPTT 1.5 to 2.5 times control. Analgesia and warmth.
• Catheter directed thrombolysis for a viable or marginally threatened hand: alteplase 0.5 to 1 mg/h (usual total up to about 40 mg) with low dose heparin 500 units/h, with fibrinogen and clinical review every 6 hours. Contraindications are previous intracranial haemorrhage, ischaemic stroke in the last 6 months, intracranial neoplasm, active bleeding, and major surgery or trauma in the last 3 weeks.
• Surgical thrombectomy for an immediately threatened hand, followed by decompression and reconstruction.

Antithrombotic therapy.

• Aspirin 75 to 100 mg orally once daily lifelong after reconstruction.
• Anticoagulation for 3 months after thrombosis or embolism, or for aneurysm with thrombus: apixaban 5 mg twice daily (2.5 mg twice daily if two of age 80 or over, weight 60 kg or under, creatinine 133 micromol/L or over), or warfarin to INR 2.0 to 3.0.

Digital ischaemia.

• Smoking cessation, keeping the hand warm, and amlodipine 5 to 10 mg once daily for vasospasm.
• Iloprost 0.5 to 2 ng/kg/min intravenously over 6 hours daily for 3 to 5 days for severe digital ischaemia (limited evidence; monitor blood pressure and heart rate).
• Wound care for ulcers, and amputation only after demarcation.

Physiotherapy. Not effective for arterial compression, so it does not replace surgery.

Monitoring. Duplex at 1 month, 6 months and 12 months after surgery, then yearly for graft surveillance. Digital perfusion at each visit. Imaging of the other side.

Referral and escalation. Refer every suspected case to a vascular surgeon with thoracic outlet experience. Same day referral for acute hand ischaemia, a pulsatile mass, or digital gangrene.

Special groups.

• Pregnancy: use enoxaparin 1 mg/kg subcutaneously every 12 hours when anticoagulation is needed, with aspirin 75 mg; avoid warfarin and direct oral anticoagulants; defer elective surgery.
• Athletes: stop overhead activity and return only after surgery and healing, usually at 3 to 6 months.
• Kidney impairment: limit contrast volume; give enoxaparin 1 mg/kg once daily when creatinine clearance is under 30 mL/min; adjust apixaban by criteria.
• Region specific: where CT angiography is unavailable, positional duplex and chest radiography can establish the diagnosis.