What is the best initial imaging investigation for a patient presenting with symptoms suggestive of amaurosis fugax?

Diagnostic Approach for Amaurosis Fugax

Magnetic Resonance Angiography (MRA) is the preferred initial imaging investigation for a 75-year-old lady with recurrent attacks of loss of consciousness with blurred vision suggestive of amaurosis fugax. 1

Initial Assessment and Diagnostic Algorithm

1. Urgent Evaluation Required:

   • Amaurosis fugax should be treated as a medical emergency requiring immediate evaluation due to high risk of concurrent cerebral infarction and future stroke 2, 1
   • Patients with transient visual loss should be evaluated within 24 hours of symptom onset 2

2. Imaging Pathway:

   • First-line imaging: Carotid duplex ultrasound to assess carotid stenosis severity 1
   • Second-line imaging: MRA from aortic arch to vertex 2, 1
   • Alternative if MRA unavailable/contraindicated: CT Angiography (CTA) 1

Rationale for MRA as Preferred Imaging

MRA is superior to other modalities for this clinical scenario because:

• Provides comprehensive visualization of both extracranial and intracranial vasculature from aortic arch to vertex 2, 1
• Relatively insensitive to arterial calcification compared to CTA 1
• No exposure to ionizing radiation 1
• Lower incidence of nephrotoxicity compared to CTA, important in elderly patients 1
• Can detect both vascular stenosis and evidence of cerebral infarction in a single study 2

Clinical Context for Amaurosis Fugax

Amaurosis fugax in this 75-year-old patient represents a form of transient ischemic attack (TIA) that requires urgent evaluation 2:

• Characterized by sudden, transient monocular vision loss, often described as a "curtain" or "shadow" moving across the visual field 1
• Associated with high risk of stroke - up to 24% of patients have concurrent cerebral infarcts detectable on diffusion-weighted MRI 1
• Often caused by atherosclerotic stenosis of the ipsilateral carotid artery with emboli causing retinal ischemia 3, 4

Additional Investigations

After initial vascular imaging:

• Brain imaging (MRI preferred over CT) to evaluate for silent infarcts 2
• 12-lead ECG to assess for atrial fibrillation or other cardiac sources of emboli 2
• Laboratory investigations: CBC, electrolytes, coagulation studies, renal function, glucose/HbA1c 2
• Consider erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP) to screen for giant cell arteritis, particularly important in this 75-year-old patient 2

Management Implications of Imaging Findings

• If significant carotid stenosis (>70% by noninvasive imaging or >50% by catheter angiography) is identified, carotid revascularization may be indicated 2
• Antiplatelet therapy is recommended for all patients with carotid artery disease 2
• High-dose statin therapy is recommended regardless of initial cholesterol levels 1

Common Pitfalls to Avoid

1. Delay in evaluation: Amaurosis fugax should not be dismissed as benign; it represents a medical emergency requiring prompt evaluation 2, 1

2. Missing giant cell arteritis: In elderly patients, always consider giant cell arteritis as a potential cause, which would require immediate high-dose glucocorticoid therapy 2, 1

3. Incomplete vascular assessment: Evaluating only the carotid arteries without assessing the complete cerebrovascular system may miss important pathology 2

4. Misdiagnosis: Amaurosis fugax can be confused with retinal migraine; vascular imaging is essential for accurate diagnosis 5

5. Underestimating risk: Studies show that untreated patients with amaurosis fugax and carotid disease have significantly higher rates of stroke and permanent visual loss compared to those who receive appropriate intervention 6