Can TIA (Transient Ischemic Attack) and CVA (Cerebrovascular Accident) be distinguished by their visibility on MRI (Magnetic Resonance Imaging)?

Distinguishing TIA from CVA on MRI

The key difference between TIA and CVA is that CVA (stroke) shows permanent infarction on MRI, while TIA typically does not show infarction despite similar symptoms. 1

Definitions and Imaging Characteristics

TIA (Transient Ischemic Attack)

• Modern tissue-based definition: "a transient episode of neurological dysfunction caused by focal brain, spinal cord, or retinal ischemia, without acute infarction" 2
• Typically does not show infarction on MRI, though up to 40% of TIA patients may have positive findings on diffusion-weighted imaging (DWI) 3
• Symptoms resolve completely, usually within minutes (though the traditional definition allowed up to 24 hours)

CVA (Cerebrovascular Accident/Stroke)

• Shows evidence of infarction on MRI, particularly on DWI sequences
• Represents permanent tissue damage
• Symptoms may persist beyond 24 hours or leave residual deficits

Imaging Recommendations

For Suspected TIA:

• MRI with DWI is preferred over CT for evaluation 3, 1
• Should be performed within 24 hours of symptom onset 2
• CT has limited utility for TIA evaluation as its sensitivity for detecting early ischemic changes is only 25-30% 1
• DWI positivity in TIA patients is associated with higher risk of recurrent ischemic events 3

For Suspected Stroke:

• Either non-contrast CT or MRI should be performed immediately to exclude hemorrhage 1
• MRI with DWI is more sensitive than CT for detecting early ischemic changes 3
• Vascular imaging (CTA, MRA) should be performed to assess for large vessel occlusion 3

Clinical Implications

• The presence of an infarct on MRI may reclassify what was clinically thought to be a TIA as a stroke, regardless of symptom duration 2
• Up to 25% of patients with TIA symptoms will show evidence of infarction on MRI 3
• The distribution of DWI lesions can help determine stroke etiology:
  • Scattered emboli in multiple territories suggest a proximal embolic source (e.g., cardiac)
  • Watershed distribution suggests hypoperfusion from carotid disease 3

Common Pitfalls

• Relying solely on symptom duration: The traditional time-based definition of TIA (symptoms resolving within 24 hours) is outdated. The tissue-based definition using imaging is now preferred 2
• Delaying imaging: TIA patients should undergo neuroimaging within 24 hours of symptom onset 2
• Using only CT for TIA evaluation: CT has limited sensitivity for early ischemic changes and may miss small infarcts 1
• Overlooking TIA as a medical emergency: TIA should be considered part of the "acute cerebrovascular syndrome" spectrum, requiring urgent evaluation 4

Algorithm for Evaluation

1. For any patient with transient neurological symptoms suggestive of cerebral ischemia:

   • Perform MRI with DWI within 24 hours 2
   • If MRI shows infarction → Diagnosis is stroke (CVA)
   • If MRI shows no infarction → Diagnosis is TIA

2. If MRI is unavailable:

   • Perform CT to exclude hemorrhage and other mimics 1
   • Recognize that a negative CT does not rule out small infarcts
   • Consider clinical features and duration of symptoms

3. For both TIA and stroke patients:

   • Perform vascular imaging (CTA, MRA, or carotid ultrasound) within 24-48 hours 3
   • Complete cardiac evaluation including ECG 1

Remember that both TIA and stroke represent medical emergencies requiring rapid assessment and treatment to prevent recurrent events and permanent disability.