Subclavian Artery Aneurysm

Subclavian artery aneurysm is focal dilatation or false aneurysm of the subclavian artery. It causes embolisation to the hand and arm, thrombosis, compression of the brachial plexus, vein, trachea or oesophagus, and, rarely, rupture.

It is rare, accounting for about 1% of peripheral aneurysms. The right side is more often affected. Aberrant right subclavian artery with Kommerell diverticulum is a recognised variant.

Causes: atherosclerosis, post-stenotic dilatation distal to a cervical rib, first rib or fibrous band in thoracic outlet syndrome, trauma (penetrating, clavicle fracture, shoulder dislocation), iatrogenic injury (central line, cardiac catheterisation, pacemaker implantation, surgical), arteritis (Takayasu, giant cell arteritis), connective tissue disease, infection (tuberculosis, syphilis, bacterial), and congenital abnormalities.

Embolic complications are frequent in thoracic outlet syndrome and are a main indication for repair.

Pathophysiology.

Repeated compression and arterial wall injury in thoracic outlet syndrome cause post-stenotic dilatation and mural thrombus. Atherosclerotic degeneration affects the proximal artery. Wall disruption from trauma or lines leads to pseudoaneurysm.

Mural thrombus embolises into the brachial, radial and ulnar arteries and the digital arteries (blue finger, digital ulceration). Thrombosis may occlude the subclavian artery and lead to arm claudication and subclavian steal.

Large aneurysms compress the brachial plexus (pain, weakness, paraesthesia), the subclavian vein, the trachea and recurrent laryngeal nerve.

Pulsatile supraclavicular or infraclavicular mass, bruit, arm pain, claudication, cold, pale or blue fingers with digital ulceration, Raynaud type symptoms, neurological symptoms in the arm, a difference in arm blood pressures, and dyspnoea, dysphagia or hoarseness from compression. Some patients have no symptoms. Vertebrobasilar symptoms occur with proximal lesions involving the vertebral artery origin.

• Duplex ultrasound of the subclavian, axillary and brachial arteries, with digital pressures and photoplethysmography in embolic disease.
• CT angiography of the chest, neck and arm: size, relation to the first rib, clavicle and vertebral artery origin, thrombus, run off and arch anatomy. MR angiography as an alternative. Dynamic imaging with arm abduction to assess compression.
• Plain radiograph for cervical rib. Upper limb blood pressure in both arms.
• Echocardiography for cardiac embolic source and aortic arch assessment.
• Workup for inflammation and infection: ESR, C-reactive protein, blood cultures, syphilis serology, tuberculosis tests.
• Genetic assessment when connective tissue disease is suspected.

Differential diagnosis.

• Aortic arch aneurysm and Kommerell diverticulum.
• Pancoast tumour, carotid body tumour, lymph nodes and apical lung mass.
• Subclavian artery stenosis or occlusion without aneurysm, and thoracic outlet syndrome without arterial dilatation.
• Raynaud disease and other causes of digital embolisation (cardiac).

Medical therapy.

• Aspirin 75 to 100 mg orally once daily for all patients.
• Acute embolic digital ischaemia: unfractionated heparin 80 units/kg intravenous bolus then 18 units/kg/h (aPTT 1.5 to 2.5 times control), then warfarin to INR 2.0 to 3.0 or 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) for at least 3 months. Keep the hand warm, give analgesia, and stop smoking.
• Atorvastatin 40 to 80 mg daily for atherosclerotic disease, with blood pressure control.
• Digital vasospasm: amlodipine 5 to 10 mg once daily.

Indications for repair. Symptomatic aneurysm, embolisation, thrombosis, compression of adjacent structures, pseudoaneurysm, infection, rupture, associated thoracic outlet compression, and size of 2 cm or more (or more than twice the normal diameter). Small asymptomatic atherosclerotic aneurysms can be observed with duplex every 6 months.

Procedures.

• Open repair: resection and interposition graft or bypass (prosthetic graft, or vein in small arteries), through supraclavicular, infraclavicular, or combined approaches, with median sternotomy or thoracotomy for proximal right or left lesions. Include decompression of the thoracic outlet (first rib resection with or without cervical rib resection and scalenectomy) when compression is the cause. Preserve or reconstruct the vertebral artery. 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.
• Endovascular repair: covered stent graft for proximal, atherosclerotic, traumatic and iatrogenic lesions, particularly at high surgical risk. Cover the vertebral origin only after confirming a dominant opposite vertebral artery or with bypass. Avoid stenting where the artery crosses the thoracic outlet because of fracture and compression. After stenting: aspirin 75 to 100 mg and clopidogrel 75 mg daily for 3 months, then aspirin alone.
• Embolic occlusion of distal arteries: catheter directed thrombolysis with alteplase 0.5 to 1 mg/h (usual total up to about 40 mg) with low dose heparin, or surgical thrombectomy, after proximal repair. Contraindications are previous intracranial haemorrhage, recent stroke, active bleeding, recent major surgery.
• Infected aneurysm: vancomycin 25 mg/kg intravenously as a loading dose then 15 to 20 mg/kg every 8 to 12 hours (trough 15 to 20 mg/L) with piperacillin and tazobactam 4.5 g intravenously every 6 hours, adjusted to cultures, with resection and extra-anatomical reconstruction; at least 6 weeks of antibiotics.
• Arteritis: prednisolone 0.5 to 1 mg/kg daily (usual 40 to 60 mg) for 4 weeks, tapered over 6 to 12 months, with methotrexate 10 to 25 mg weekly and folic acid 5 mg weekly or tocilizumab 162 mg subcutaneously weekly; delay elective repair until inflammation is controlled.

Monitoring. Duplex at 1 month, 6 months and 12 months after repair, then yearly. CT angiography at 12 months after stenting, then every 2 to 3 years. Digital perfusion and neurological review at each visit. Full blood count and liver tests during methotrexate.

Referral and escalation. Refer to a vascular surgeon and, when thoracic outlet compression is present, to a thoracic outlet service. Urgent referral for acute hand ischaemia, expanding mass, haemoptysis or haematemesis (rupture into airway or oesophagus), stroke, or tracheal compression.

Special groups.

• Pregnancy: rare; use aspirin 75 mg and low molecular weight heparin when anticoagulation is needed (enoxaparin 1 mg/kg subcutaneously every 12 hours with anti-Xa monitoring); avoid warfarin and direct oral anticoagulants.
• Young adults: thoracic outlet syndrome and trauma predominate; remove the compressing structure at the time of repair.
• Kidney impairment: limit contrast volume and adjust apixaban by creatinine clearance.
• Region specific: tuberculous and syphilitic aneurysms occur where these infections are prevalent, so test for both.