Table 1

Proposed definition of medium vessel occlusion (both A and B have to apply)*

A) Occlusion in one of the following vessel segments
AnatomicalM2 segment (from the main MCA bifurcation/trifurcation to the circular sulcus of the insula)12
M3 segment (from the circular sulcus of the insula to the external/superior surface of the Sylvian fissure)12
A2 segment (from the origin of the anterior communicating artery to the origin of the callosomarginal artery)13
A3 segment (from the origin of the callosomarginal artery to the artery’s posterior turn above the corpus callosum)13
P2 segment (from the origin of the posterior communicating artery to the point of entrance in the quadrigeminal cistern)14
P3 segment (segment within the quadrigeminal cistern)14
B) Substantial clinical deficit (one of the following)
FunctionalNIHSS ≥ 5
NIHSS < 5 with disabling deficit†
  • *Vessel size allows for safe endovascular thrombectomy based on available technology and techniques (typical vessel size in MeVOs ranges from 1 to 3 mm15).

  • †Particularly important for P2/3 segment occlusions, since the NIHSS score does not accurately capture clinical deficits caused by posterior circulation occlusions.16

  • MCA, middle cerebral artery; MeVO, medium vessel occlusion ; NIHSS, National Institutes of Health Stroke Scale.