Medium vessel occlusion (MeVO), also termed distal medium vessel occlusion (DMVO), describes occlusion of a medium-sized intracranial artery resulting in impending acute ischemic stroke.
Definition
One consensus definition of ‘medium vessel’ suggests intracranial arteries with a luminal diameter of 0.75-2.0 mm 1. Thus, arteries included in the definition of medium vessel occlusion include 1-3:
M3 and M4 segments of the middle cerebral arteries
A2, A3, A4, and A5 segments of the anterior cerebral arteries
P2, P3, P4 and P5 segments of the posterior cerebral arteries
The M2 segments of the middle cerebral arteries, A1 segments of the anterior cerebral arteries and the P1 segment of the posterior cerebral arteries have heterogenous angioarchitecture among patients and as a result, may be variably defined as either sites of medium vessel occlusion or large vessel occlusion (LVO) 1-3. Please see the article on large vessel occlusion (LVO) for further discussion.
Clinical importance
medium vessel occlusion accounts for 25-40% of acute ischemic stroke 8
multi-phase CT angiography with CT perfusion is more sensitive than single-phase CT angiography to detect medium vessel occlusions 6
in CT perfusion, the traditional Tmax delay cut-off of >6 seconds may not detect perfusion defects due to medium vessel occlusion in 10% of cases, and in those cases milder Tmax delay (e.g. >4 seconds) may be present 9
there is no robust randomized control data to support routine endovascular clot retrieval in patients with acute ischemic stroke due to medium vessel occlusion 4,5,8, although one meta-analysis of available data suggested benefit of endovascular clot retrieval over best medical therapy 7
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