Middle cerebral artery
The middle cerebral artery (MCA) is a terminal branch of the internal carotid artery and is part of the anterior cerebral circulation. The MCA supplies many deep brain structures, the majority of the lateral surface of the cerebral hemispheres, and the temporal pole of the brain. It travels from the base of the brain through the lateral sulcus (of Sylvius), before terminating on the lateral surface of the brain.
The surgical classification divides the middle cerebral artery into four segments (M1-M4), which give rise to a total of 10 branches.
This article will discuss the anatomy and function of the middle cerebral artery.
|Origin||Internal carotid artery|
|Branches||Lateral lenticulostriate, anterior temporal, orbitofrontal, prefrontal, precentral, central, postcentral, parietal, angular, middle temporal arteries|
|Supply||Anterior commissure, internal capsule, caudate nucleus, putamen, globus pallidus, substantia innominata, temporal pole, insula, lateral aspect of orbital surface of frontal lobe, opercular surfaces of frontal, parietal, and temporal lobes, inferior and middle frontal gyri, precentral and postcentral gyri, superior and inferior parietal lobules, superior, lateral surface of temporal lobe, superior part of lateral surface of occipital lobe|
- Course and segments
- Branches and supply
- Anatomical variations
- Clinical relations
Course and segments
The middle cerebral artery arises within the interpeduncular fossa, from the internal carotid artery from the lateral angle of the circle of Willis. It courses laterally between the frontal and temporal lobes, traversing the Sylvian fissure. It then passes over the posterosuperior surface of the insula, where it bifurcates into the superior and inferior trunks. The trunks travel together through the Sylvian fissure towards the lateral surface of the brain.
Dividing the middle cerebral artery into four segments helps to further define its course;
- M1 (sphenoidal/horizontal) segment travels in an almost horizontal fashion from the internal carotid artery to a point of MCA bifurcation between temporal and frontal lobes. It is situated within the sphenoidal part of the Sylvian fissure, through which it courses as far as to the junction of the sphenoidal and operculoinsular segment of the Sylvian fissure. At the site of termination of M1 segment, the trunks of the middle cerebral artery take a 90° turn in the posterosuperior direction, which is demarcated as the genu (lat. “knee”) of MCA. Here, the MCA divides into the superior and inferior trunks.
- M2 (insular) segment begins at the point of MCA bifurcation and consists of a superior and inferior trunk. This segment starts with the genu of MCA at the level of limen insulae and then travels along the surface of the insula. It terminates at the level of the circular sulcus of insula.
- M3 (opercular) segment begins to ascend from the circular sulcus of insula towards the surface of the brain. This segment courses over the inner surfaces of the parietal and temporal portion of the insular operculum.
- M4 (terminal, cortical) segment continues onto the M3 segment once it emerges through the lateral fissure to reach the surface of the brain and travels over the surface of the cerebral hemisphere.
Branches and supply
The middle cerebral artery has 10 branches, which are classified into the central and cortical.
The numerous central branches arise from the middle cerebral artery as it enters the Sylvian fissure. They are also called striate or lateral lenticulostriate arteries, and their main function is to supply the deep structures of the brain.
The cortical branches ramify from the middle cerebral artery once it emerges on the surface of the brain. The main function of the cortical branches is to supply most of the lateral surface of the brain, i.e. the orbital, frontal, parietal and temporal parts of the cerebral cortex.
The central branches of the middle cerebral artery arise within the Sylvian fissure, from the M1 and M2 segments of the MCA. They are all collectively called the lateral striate (lenticulostriate) arteries.
The lateral lenticulostriate arteries pierce the floor of the Sylvian fissure and course as deep as to the external surface of the thalamus. They supply the basal ganglia, i.e. the striatum, much of the head and body of the caudate nucleus, and large portions of the lenticular nucleus and of the external and internal capsules.
The cortical branches of the middle cerebral artery arise from all of its segments. They gradually increase in size, with those originating from M1 being the shortest, while those that originate from M4 are the longest. It is noteworthy that the cortical branches which arise before the bifurcation of the MCA are often termed as the early central branches for the sake of the neurosurgical distinction.
The cortical branches are named according to the region of the brain that they supply;
- Anterior temporal arteries vascularize the temporal pole of the brain, which is the most anterior aspect of the temporal lobe. They arise from the M1 segment of MCA.
- Lateral frontobasal artery supplies the lateral part of the orbital surface of the frontal lobe, as well as the inferior frontal gyrus. It arises from the M2 segment of the MCA.
The remainder of the cortical branches arises from the M4 segment of the MCA;
- Artery of prefrontal sulcus supplies the anterior aspects of the inferior and middle frontal gyri
- Artery of precentral sulcus travels in the precentral sulcus to supply the posterior aspect of the inferior and middle frontal gyri, Broca’s area and the precentral gyrus, which contains the primary motor cortex for the head, upper limb, and trunk.
- Artery of central sulcus travels within the central sulcus and contributes to the blood supply of the pre- and postcentral gyri
- Artery of postcentral sulcus travels in the postcentral sulcus to supply the anterior aspect of parietal lobe and the postcentral gyrus which contains the primary somatosensory cortex for the head, upper limbs, and trunk
- A variety of parietal branches supply the lateral aspect of the parietal lobe, including the superior and inferior paracentral lobules.
- Angular artery supplies the angular and supramarginal gyri of the parietal lobe, the posterior part of the superior temporal gyrus, and the superior part of the lateral surface of the occipital lobe
- Middle temporal branches supply the middle aspect of the superior and middle temporal gyri, as well as the primary auditory cortex and Wernicke’s area
Review the topography of the brain to help understand the structures that are supplied by the middle cerebral artery.
The middle cerebral artery can be variable in its origin. A duplicated middle cerebral artery is only seen in less than 3% of individuals but would be seen arising from the internal carotid artery, paralleling the main MCA and traveling towards the anterior temporal lobe to supply it.
Up to 4% of people have an accessory middle cerebral artery which typically supplies the orbitofrontal aspect of the brain. It can be seen arising from either the internal carotid (Type 1), A1 segment of anterior cerebral (Type 2), or A2 segment of the anterior cerebral (Type 3).
Middle cerebral artery stroke
The MCA is the cerebral artery that is most often occluded, and its large area of supply means that a stroke to this artery can be devastating. If the branches to the precentral gyrus are affected, this would cause a loss of motor innervation for the head, upper limbs or trunk in the opposite side of the body. If instead the branches to the postcentral gyrus are affected, a loss of sensation from the head, upper limb, and trunk would be observed. An MCA stroke involving Broca’s or Wernicke’s area would greatly affect speech, leading to a condition known as “aphasia”.