Association between the degree of vertebrobasilar stenosis, location, infarction pattern, and QMRA flow state.

Severe stenosis of ≥70% may mark the minimal threshold required to cause hemodynamic insufficiency in the posterior circulation, but nearly half of these patients may remain hemodynamically sufficient. Bilateral vertebral stenosis resulted in a fivefold increase in QMRA low distal flow status compared to unilateral vertebral disease. These results may have implications in the design of future treatment trials of intracranial atherosclerotic disease.