Prevalence of Posterior Circulation TIA
Posterior circulation TIAs are relatively uncommon, representing approximately 20% of all TIAs and strokes, though true posterior circulation emergent large vessel occlusions (pc-ELVO) are rare at only 1% of all ischemic strokes and 5% of all emergent large vessel occlusions. 1
Epidemiological Context
- Posterior circulation strokes account for approximately 20% of all strokes, making them a meaningful minority of cerebrovascular events 1
- True posterior circulation emergent large vessel occlusions represent only 1% of all ischemic strokes and 5% of all ELVOs, making them genuinely rare events 1
- The overall prevalence of TIA itself is difficult to gauge accurately because a large proportion of patients who experience a TIA fail to report it to a healthcare provider 1
Clinical Significance Despite Lower Frequency
Posterior circulation TIAs carry particularly poor prognosis compared to anterior circulation events, with good clinical outcomes occurring in only approximately 20% of cases despite advanced care 1. This makes recognition critical despite their relative rarity.
Key Prognostic Factors
The recurrence risk after posterior circulation ischemic stroke varies significantly based on specific clinical features:
- Patients with repeated TIAs within 3 months before the stroke have dramatically elevated risk (hazard ratio 15.4) for recurrent events within one year 2
- Chief complaint of dysphagia increases recurrence risk (hazard ratio 4.16) 2
- Responsible artery stenosis ≥70% substantially increases risk (hazard ratio 7.91) 2
- Multisector infarcts carry higher recurrence risk (hazard ratio 5.38) 2
Diagnostic Challenges Contributing to Perceived Rarity
Unlike hemispheric ischemia, posterior circulation events can mimic other clinical conditions, resulting in delays to clinical neurological evaluation and identification 1. This diagnostic difficulty may lead to underreporting and underestimation of true prevalence.
Non-specific Presentations Include:
- Loss of consciousness, headache, nausea, vomiting, dizziness 1
- Double vision, hearing loss, slurred speech, vertigo, imbalance 1
- Unilateral extremity weakness, ataxia, nystagmus, visual field defects 1
- Pure or predominantly sensory symptoms are particularly uncommon presentations that strongly suggest posterior cerebral artery disease 3
Common Pitfall to Avoid
Do not dismiss transient neurological symptoms referable to the posterior circulation as benign simply because they are less common than anterior circulation events—the 20% rate of good outcomes despite treatment underscores the serious nature of these events 1. Urgent assessment and preventive treatment should be offered immediately, particularly in patients with repeated TIAs or severe arterial stenosis 2.