Middle Cerebral Artery: Stem
The middle cerebral artery (MCA) has a large diameter and branches at an acute angle from the internal carotid. The MCA passes laterally just underneath the frontal lobe, ultimately taking up a position between the temporal and frontal lobes in the Sylvian fissure. The initial part of the MCA is a single vessel called the stem or M1 segment. As it passes laterally, the stem gives off a series of six to twelve long, small diameter, penetrating vessels that travel directly upward to supply the basal ganglia and much of the internal capsule. These are called the lenticulostriate arteries.
| Clinical Note: The lenticulostriate vessels are small diameter arteries that originate as right angle branches from the MCA stem (a large diameter vessel with a brisk, high pressure blood flow). These small arteries are particularly susceptible to damage from hypertension.[More about hypertension: http://www.umassmed.edu/strokestop/module_two/hypertension.html.] They may either rupture (producing an intracerebral hemorrhage that is initially centered in the region they supply) or become occluded (producing a lacunar infarct in the tissue they supply). The lenticulostriate arteries are 'end arteries' and regions that they supply do not have significant collateral blood supply. Therefore occlusion of these vessels leads to stereotyped stroke syndromes. |
| Clinical Note: In the case of the lenticulostriate vessels, hemorrhage may remain localized to the putamen (and caudate), may involve neighboring structures like the internal capsule and other more distant white matter of the hemisphere, or may even rupture into the ventricular system [Examples:Specimens CT Scans]. Lacunar infarcts may have serious functional consequences if they involve motor or sensory fibers in the internal capsule, but may be 'silent' if they involve other small regions of white matter or the basal ganglia. [Example: Specimens] Once in the Sylvian fissure itself, the MCA stem divides into two or, in a small number of cases, three main cortical branches that supply almost the entire lateral surface of the brain as well as the insula. |
| Clinical Note: Large emboli carried up the carotid tend to be swept into the MCA, and are prone to getting stuck at this branch point in the Sylvian fissure. |