The internal carotid artery terminates in a larger MCA and smaller anterior cerebral artery. The MCA runs horizontally to the Sylvian fissure, giving off the lenticulostriate vessels. These small perforating vessels supply the basal ganglia and internal capsule. The MCA then typically bifurcates into a superior and inferior division. The superior division supplies the lateral frontal and superior parietal lobes, whereas the inferior division predominantly supplies the lateral temporal and inferior parietal lobes.

Occlusions of the proximal stem of the MCA affect both the superior and inferior divisions, as well as the lenticulostriates. Complete infarctions on the distal MCA stem result in a contralateral hemiplegia (face, arm AND leg); contralateral hemisensory loss; and a contralateral visual field deficit. With an infarct in the dominant hemisphere, there is often an associated global aphasia (expressive and receptive); with a non-dominant infarct, there is often a neglect syndrome and impairment of visuospatial skills (e.g., drawing, copying, dressing). The major clinical difference between a proximal and distal MCA stem occlusion is that with a proximal lesion the leg is plegic as well. This occurs because the lenticulostriates are involved, which results in infarction of the internal capsule, which contains fibers to the leg, arm and face.