Definition of Large Vessel Occlusion
Large vessel occlusion (LVO) refers to acute occlusion of major intracranial arteries including the internal carotid artery terminus, middle cerebral artery (M1 and M2 segments), anterior cerebral artery, vertebral artery, and basilar artery 1.
Specific Intracranial Vessels Qualifying as LVO
For your 67-year-old patient with left vertebral artery occlusion, the following intracranial arteries constitute large vessel occlusions:
Anterior Circulation LVO:
- Internal carotid artery (ICA) terminus
- M1 segment of middle cerebral artery (MCA)
- M2 segment of middle cerebral artery
- Anterior cerebral artery (ACA) 2, 1
Posterior Circulation LVO:
Clinical Significance in Your Patient's Case
The left vertebral artery occlusion in your patient qualifies as a posterior circulation LVO. This carries important prognostic implications:
Posterior circulation LVOs have significantly worse outcomes compared to anterior circulation occlusions, with lower odds of achieving good functional outcome (modified Rankin Scale 0-2) and higher mortality rates (adjusted hazard ratio: 2.97) 2.
LVO accounts for approximately 46% of acute ischemic strokes in unselected patients presenting to academic centers 1.
The presence of basilar or internal carotid terminus occlusions independently predicts 6-month outcome, beyond age and stroke severity 1.
Key Clinical Pitfall
Do not rely solely on NIHSS score to predict LVO presence - the correlation between NIHSS and LVO is relatively poor due to variability in collateral circulation, stroke mimics, and effects of prehospital recumbency 3. This means even patients with lower NIHSS scores may harbor significant LVOs requiring urgent vascular imaging.
Diagnostic Confirmation
LVO diagnosis requires confirmation by CT angiography (CTA), MR angiography (MRA), or conventional catheter angiography 4. Transcranial Doppler alone is insufficient for LVO diagnosis in clinical decision-making 4.