Axillary Artery Aneurysm

Axillary artery aneurysm is dilatation or false aneurysm of the axillary artery. It is rare, and its main danger is embolisation of thrombus to the hand, with limb threatening ischaemia, together with compression of the brachial plexus and axillary vein.

It accounts for well under 1% of peripheral aneurysms. Most are false aneurysms from blunt or penetrating trauma, or iatrogenic injury. True aneurysms are very rare.

Causes:

• repeated crutch use (axillary crutch compression)
• blunt trauma including anterior shoulder dislocation and fracture of the humeral neck
• penetrating injury
• iatrogenic injury (axillary access for transcatheter valve and mechanical support devices, brachial plexus nerve blocks, arterial lines, surgery)
• thoracic outlet syndrome
• throwing and overhead athletes (injury to the posterior circumflex humeral artery or the axillary artery)
• atherosclerosis
• arteritis (Takayasu, giant cell arteritis, Kawasaki disease in childhood)
• connective tissue disease and infection

Distal embolisation is frequent. Rupture is rare but possible with infection or anticoagulation.

Pathophysiology.

Repeated mechanical stress, direct injury, or wall inflammation weaken the vessel wall. A tear in the intima or media forms a contained haematoma (pseudoaneurysm) that communicates with the lumen.

Turbulence in the sac promotes thrombus formation. Thrombus embolises into the brachial, radial, ulnar and digital arteries, and may occlude the axillary artery.

Expansion within the confined axillary sheath compresses the brachial plexus (pain, weakness, paraesthesia) and the axillary vein (arm swelling).

Pulsatile axillary or upper arm mass, pain, paraesthesia, weakness, arm swelling, cold pale hand, blue fingers, digital ulceration, rest pain and absent distal pulses. Throwing athletes have exertional arm fatigue, pain and coldness. Haematoma and bruising follow trauma or procedures. Some patients are asymptomatic.

• Duplex ultrasound of the axillary, brachial and forearm arteries, with digital pressures.
• CT angiography or MR angiography of the arm and arch: size, neck, thrombus, relation to the brachial plexus, distal run off, and the status of the subclavian artery. Catheter angiography before intervention in embolic disease.
• Inflammatory markers (ESR, C-reactive protein), blood cultures when infection is possible, and echocardiography for cardiac embolic source.
• Nerve conduction studies when neurological deficit is present.
• History of crutch use, athletic activity, trauma and procedures.

Differential diagnosis.

• Axillary haematoma, abscess and lymph node mass.
• Brachial plexus tumour and lipoma.
• Axillary artery occlusion or stenosis, and thoracic outlet syndrome.
• Other causes of digital embolisation (cardiac, subclavian aneurysm).

Medical therapy.

• Aspirin 75 to 100 mg orally once daily.
• Acute embolic 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. Analgesia and warmth.
• Atorvastatin 40 to 80 mg daily in atherosclerotic disease.
• Stop crutch use or the provoking activity, and use forearm or platform crutches.

Indications for repair. Any symptomatic aneurysm, embolisation, expanding or large pseudoaneurysm, neurological compression, infection, and rupture. Small asymptomatic atherosclerotic aneurysms under 2 cm can be observed with duplex every 6 months.

Procedures.

• Open repair is the usual treatment: exposure through an infraclavicular or axillary incision, resection of the aneurysm with an interposition graft (reversed saphenous vein is preferred, with prosthetic graft as an alternative), with thrombectomy of the distal arteries using Fogarty catheters. 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. Decompress the brachial plexus.
• Endovascular repair with a covered stent is an option for suitable trauma and iatrogenic lesions in high risk patients, but is limited by arm mobility (kinking and fracture) and nerve compression, which stent grafts do not relieve. After stenting: aspirin 75 to 100 mg and clopidogrel 75 mg daily for 3 months, then aspirin alone.
• Distal embolic occlusion: 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, and recent major surgery.
• Infected false 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 reconstruction using autologous vein; at least 6 weeks of antibiotics.
• Arteritis: prednisolone 0.5 to 1 mg/kg daily, 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. Kawasaki disease aneurysms in children are managed by paediatric cardiology with aspirin 3 to 5 mg/kg daily.

Monitoring. Duplex at 1 month, 6 months and 12 months after repair, then yearly. Digital perfusion, pulses and neurology at each visit. Observed aneurysms every 6 months.

Referral and escalation. Refer every confirmed aneurysm to a vascular surgeon. Urgent referral for acute hand ischaemia, expanding mass, neurological deficit or haemorrhage.

Special groups.

• Pregnancy: rare; use aspirin 75 mg and low molecular weight heparin if anticoagulation is needed (enoxaparin 1 mg/kg subcutaneously every 12 hours with anti-Xa monitoring); avoid warfarin and direct oral anticoagulants.
• Athletes: avoid provoking activity and repair the aneurysm when indicated, with return to throwing after healing, usually 3 to 6 months, decided by the treating specialist.
• Children: Kawasaki disease aneurysm needs paediatric specialist care.
• Kidney impairment: limit contrast volume and adjust apixaban by creatinine clearance.