For a patient presenting with amaurosis fugax, what is the preferred initial imaging investigation?

Management of Amaurosis Fugax: Diagnostic Approach

For a patient presenting with amaurosis fugax (transient monocular blindness), magnetic resonance angiography (MRA) is the preferred initial imaging investigation after carotid duplex ultrasound. 1, 2

Initial Evaluation

Amaurosis fugax represents a medical emergency requiring prompt evaluation due to its association with carotid artery disease and risk of subsequent stroke. The diagnostic approach should follow this algorithm:

1. First-line imaging: Carotid Duplex Ultrasound

   • Indicated as the initial test for patients with amaurosis fugax 1
   • Provides assessment of carotid stenosis severity through blood flow velocity measurements
   • Non-invasive, widely available, and cost-effective

2. Second-line imaging: Magnetic Resonance Angiography (MRA)

   • Preferred follow-up imaging when carotid pathology is suspected 1
   • Provides accurate anatomic imaging of the aortic arch, cervical and cerebral arteries 1
   • Advantages over other modalities:
     • Relative insensitivity to arterial calcification
     • No exposure to ionizing radiation
     • Lower incidence of nephrotoxicity compared to CTA

3. Alternative if MRA contraindicated: CT Angiography (CTA)

   • Consider when MRA is unavailable or contraindicated (claustrophobia, incompatible implanted devices) 1
   • Provides direct imaging of the arterial lumen
   • Limitations include exposure to ionizing radiation and need for iodinated contrast

Clinical Context and Rationale

The 75-year-old patient presenting with recurrent attacks of loss of consciousness with blurred vision likely has amaurosis fugax, which is characterized by:

• Transient monocular blindness often described as a "curtain" or "shadow" moving across the visual field 2
• High association with ipsilateral carotid artery stenosis 3, 4
• Significant risk factor for subsequent stroke 5, 6

According to guidelines, amaurosis fugax requires urgent evaluation as it represents a form of transient ischemic attack (TIA) 1, 2. The American College of Cardiology Foundation/American Heart Association guidelines specifically mention amaurosis fugax as an indication for vascular imaging 1.

Important Considerations

• Carotid stenosis detection: In patients over 50 years, atherosclerotic lesions are found in approximately 63% of relevant precerebral internal carotid arteries, with over half causing >75% diameter reduction 4

• Risk stratification: The risk of stroke after amaurosis fugax varies based on vascular risk factors, with 3-year stroke risks ranging from 1.8% (0-1 risk factors) to 24.2% (3-4 risk factors) 2

• Pitfall to avoid: Relying solely on carotid duplex ultrasound may miss tandem lesions or other vascular pathologies, which is why MRA is recommended as the next step 1

• Giant Cell Arteritis consideration: In elderly patients, always consider giant cell arteritis as a potential cause, which would require different management (high-dose glucocorticoids) 1, 2

While carotid duplex ultrasound provides excellent initial assessment, MRA offers comprehensive evaluation of both the extracranial and intracranial vasculature, which is crucial for complete assessment of patients with amaurosis fugax and determination of appropriate management.