Carotid Artery Aneurysm

Carotid artery aneurysm is focal dilatation of the extracranial carotid artery to over 1.5 times the normal diameter (true aneurysm), or a contained arterial wall defect (pseudoaneurysm). It matters because of embolic stroke, thrombosis, compression of adjacent structures and rupture.

It is rare, accounting for under 1% of all arterial aneurysms and under 1% of carotid operations. The common carotid bifurcation and internal carotid artery are most often involved.

Causes:

• Atherosclerosis (the commonest cause of true aneurysm in older adults).
• Trauma (blunt or penetrating).
• Iatrogenic injury (after carotid endarterectomy patch angioplasty, carotid stenting, central line placement).
• Infection (mycotic, syphilitic, tuberculous, from adjacent abscess).
• Dissection, fibromuscular dysplasia, and connective tissue disorders (vascular Ehlers-Danlos, Marfan and Loeys-Dietz syndromes).
• Arteritis (Takayasu, Behçet) and radiotherapy.

Without treatment, stroke or transient ischaemic attack complicates 30 to 50% in older series, and mortality was high. Rupture is uncommon.

Pathophysiology.

Atherosclerotic medial degeneration and loss of elastin dilate the wall and promote mural thrombus. Pseudoaneurysms form after wall disruption contained by adventitia and haematoma.

Thrombus embolises into the intracranial circulation, or the aneurysm thromboses, causing carotid occlusion and ischaemic stroke. Large aneurysms compress the cranial nerves (IX to XII), the sympathetic chain and the airway.

Infected aneurysms enlarge rapidly and rupture into the pharynx or neck, with life threatening haemorrhage.

• Pulsatile neck mass (often at the angle of the jaw), bruit, neck pain, and dysphagia.
• Transient ischaemic attack, stroke, amaurosis fugax, and Horner syndrome.
• Cranial nerve palsies (hoarseness, dysphagia, tongue deviation).
• In extracranial intrapharyngeal aneurysms, a pulsatile tonsillar mass.

Bleeding from the mouth or ear (sentinel bleed) after trauma or infection is an emergency. Some are found incidentally.

• Duplex ultrasound: diameter, wall, thrombus, flow and bilateral carotid assessment.
• CT angiography of the head and neck is the key test: size, neck width, relation to the skull base, thrombus, and the circle of Willis. MR angiography is an alternative, particularly in the young and in dissection. Catheter angiography is used for treatment planning.
• Brain MRI with diffusion imaging for silent infarcts.
• Infection assessment when suspected: blood cultures (three sets before antibiotics), C-reactive protein, white cell count, syphilis serology, tuberculosis tests, and PET-CT.
• Connective tissue and vasculitis workup: examination, genetic testing (COL3A1, FBN1, TGFBR1, TGFBR2, SMAD3), ESR, C-reactive protein, ANCA.
• ECG and echocardiography for cardiac embolic source and associated aneurysms.

Differential diagnosis.

• Carotid body tumour, branchial cyst, lymph node and neck abscess.
• Tortuous or kinked carotid artery.
• Thyroid mass and salivary gland tumour.
• Carotid dissection with pseudoaneurysm, and extracranial intracranial aneurysm.

Medical therapy for all patients.

• Aspirin 75 to 100 mg orally once daily (clopidogrel 75 mg daily if intolerant).
• Atorvastatin 40 to 80 mg daily (LDL cholesterol under 1.4 mmol/L after stroke), blood pressure control (under 130/80 mmHg), and smoking cessation.
• Anticoagulation for dissecting pseudoaneurysm or thrombus containing aneurysm for 3 to 6 months, with repeat imaging:
  • 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).

Indications for repair. Symptomatic aneurysm (stroke, transient ischaemic attack, compression, pain), enlarging aneurysm, diameter of 2 cm or more (or over 1.5 times the normal artery), thrombus within the sac, pseudoaneurysm, infection, and rupture. Small asymptomatic aneurysms under 2 cm that are stable can be observed with duplex every 6 months.

Procedures.

• Open repair:
  • Resection with interposition graft (reversed saphenous vein, or prosthetic graft when vein is unsuitable), or patch repair.
  • Ligation only when collateral flow and back pressure are adequate (stump pressure over 70 mmHg is typical).
  • Operate with shunting, careful cranial nerve protection, and 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 (activated clotting time 250 to 300 seconds), reversed with protamine 1 mg for each 100 units given in the previous 2 to 3 hours.
  • Stroke rate is about 3 to 8%, and cranial nerve injury is common but usually temporary.
• Endovascular repair:
  • Covered stent placement (often for pseudoaneurysm and trauma, and in high surgical risk, previous neck surgery or radiation, and skull base lesions), embolisation with coils after bypass, or flow diversion.
  • Loading with aspirin 300 mg and clopidogrel 300 to 600 mg before the procedure, then aspirin 75 to 100 mg and clopidogrel 75 mg daily for 3 months, then aspirin alone.
  • Heparin 70 to 100 units/kg intravenously during the procedure.
  • Long term durability of covered stents is limited by kinking and thrombosis.
• Infected aneurysm:
  • Draw cultures, then 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.
  • Surgical excision with autologous reconstruction is the definitive treatment, and antibiotics continue for at least 6 weeks after source control.
• Syphilitic aneurysm: benzathine benzylpenicillin 2.4 million units intramuscularly weekly for 3 weeks (with neurological assessment), with surgery.
• Rupture or sentinel bleed: airway protection (early intubation), direct pressure, and immediate endovascular or surgical control.

Associated disease. Treat vasculitis with prednisolone 0.5 to 1 mg/kg daily and an immunosuppressant, delaying elective repair until inflammation is controlled. Vascular Ehlers-Danlos syndrome needs gentle handling and specialist surgery.

Monitoring. Duplex or CT angiography at 1 month, 6 months and 12 months after repair, then yearly. Observed aneurysms every 6 months. Brain imaging for new neurological symptoms. Lipids at 4 to 12 weeks after statin start.

Referral and escalation. Refer every carotid aneurysm to a vascular surgeon. Urgent referral for transient ischaemic attack, stroke, enlarging mass, bleeding from the mouth or neck, or airway compromise (same day). Stroke services for any new deficit.

Special groups.

• Pregnancy: rare; use endovascular options when possible, with low dose aspirin 75 mg; avoid warfarin and direct oral anticoagulants.
• Children and young adults: look for connective tissue disease, infection and trauma.
• Older adults: stenting is favoured at high surgical risk; assess frailty.
• Kidney impairment: limit contrast volume, adjust apixaban by creatinine clearance, and dose vancomycin by levels.