What is the best way to diagnose a posterior cerebral vascular accident (CVA)?

Best Diagnostic Approach for Posterior CVA

MRI with diffusion-weighted imaging (DWI) is the gold standard for diagnosing posterior circulation strokes due to its superior sensitivity compared to CT, particularly for detecting acute ischemic changes in the posterior fossa. 1

Primary Diagnostic Algorithm

Initial Imaging

1. MRI Brain with DWI sequence

   • Highest sensitivity for acute posterior circulation infarcts
   • Can detect small brainstem and cerebellar infarcts often missed on CT
   • Particularly important given the challenging nature of posterior circulation stroke diagnosis

2. MR Angiography (MRA) of head and neck

   • Should be performed concurrently with MRI
   • Evaluates vascular occlusions and stenosis
   • Preferred combination includes noncontrast head MRA and contrast-enhanced neck MRA 1

If MRI is contraindicated or unavailable

1. CT Head without contrast

   • First-line emergency imaging to exclude hemorrhage
   • Limited sensitivity (~10%) for posterior fossa infarcts 1
   • Can rapidly identify large infarcts or hemorrhage

2. CT Angiography (CTA) of head and neck

   • Should follow noncontrast CT
   • High sensitivity and specificity for large vessel occlusions
   • Essential for evaluating potential thrombectomy candidates 1

3. CT Perfusion (CTP)

   • Adds significant diagnostic value for posterior circulation strokes
   • Substantially improves detection compared to noncontrast CT alone
   • AUC of 0.86 for posterior circulation infarct detection (vs. 0.64 for noncontrast CT) 2

Special Considerations

Susceptibility-Weighted Imaging (SWI)

• Highly sensitive for detecting intraluminal thrombus in posterior cerebral artery infarctions
• 92% detection rate for thrombi in posterior circulation strokes
• Superior to MRA for detecting peripheral thrombi in distal PCA branches 3

Time Considerations

• For patients within 3 hours of symptom onset eligible for thrombolysis:
  • Either CT or MRI is acceptable to exclude hemorrhage
  • MRI with DWI preferred if it doesn't delay treatment 1
• For patients beyond 3 hours:
  • MRI with DWI or CTA-SI should be performed along with vascular imaging 1

Diagnostic Pitfalls to Avoid

1. Relying solely on CT for posterior circulation strokes

   • Posterior fossa ischemic strokes are difficult to detect on CT with sensitivity as low as 10% 1
   • Overall diagnostic yield for head CT in acute dizziness is only 2.2% 1

2. Overlooking vascular imaging

   • Vascular imaging is essential during initial evaluation even within 3 hours of symptom onset 1
   • Helps determine the site of occlusion and guides treatment decisions

3. Misinterpreting clinical presentations

   • Posterior circulation strokes may present with atypical symptoms like isolated dizziness, visual disturbances, or ataxia
   • Clinical exam alone (even HINTS testing) may not be sufficiently sensitive to exclude posterior circulation stroke 1

4. Delaying diagnosis

   • Posterior circulation strokes are frequently misdiagnosed initially
   • MRI changes diagnosis in up to 16% of cases initially evaluated with CT 1

In summary, while CT remains important for initial hemorrhage exclusion, MRI with DWI is clearly superior for detecting posterior circulation infarcts and should be the preferred diagnostic modality when available and not contraindicated.