Table 1:

Anatomic definition of MCA segments

MCA Segment	Anatomic Definition
M1	Horizontal segment of the proximal MCA from the bifurcation of the ICA into the anterior and middle cerebral arteries to the genu of the MCA branch or branches at the entrance to the insula
M2	Vertical MCA branches in the Sylvian fissure originating at the genu and extending to the next genu at the level of the operculum; if the anterior temporal artery arises from the horizontal M1 segment, it will not be considered an M2 branch
M3	Branches that continue when the M2 branches change course again to a more lateral/horizontal course in the Sylvian fissure away from the insula and below the operculum
M4	Branch vessels primarily extend vertically over the frontal and parietal lobes and inferiorly over the temporal lobe