Middle cerebral artery

The middle cerebral artery (MCA) is one of the three major paired arteries that supply blood to the brain. The MCA arises from the internal carotid artery as the larger of the two main terminal branches (the other being the anterior cerebral artery), coursing laterally into the lateral sulcus where it branches to perfuse the cerebral cortex.

Gross anatomy

Segments

The MCA is divided into four segments:

• M1: sphenoidal or horizontal segment

  • originates at the terminal bifurcation of the internal carotid artery

  • courses laterally parallel to the sphenoid ridge

  • terminates at one of two points (controversial; see below note*):

    • at the genu adjacent to the limen insulae

    • at the main bifurcation

• M2: insular segment

  • originates at the genu/limen insulae or the main bifurcation (see above)

  • courses posterosuperiorly in the insular cleft

  • terminates at the circular sulcus of insula, where it makes a right angle to hairpin turn

• M3: opercular segment

  • originates at the circular sulcus of the insula

  • courses laterally along the frontoparietal operculum

  • terminates at the external/superior surface of the Sylvian fissure

• M4: cortical segment

  • originates at the external/top surface of the Sylvian fissure

  • courses superiorly on the lateral convexity

  • terminates at their final cortical territory

*The point where the M1 (sphenoidal) segment becomes the M2 (insular) segment is not agreed upon. As originally described by Fischer in 1938, the M1 segment ends where the artery turns ⁵. Although the bifurcation coincides with the genu in the classically described anatomy, most patients have a nonclassical bifurcation that occurs proximal or distal to the genu ⁶. Thus, the M1 could include rather than necessarily end at the main bifurcation. This landmark-based nomenclature was adopted in Gibo and Rhoton's microsurgical descriptions ^7,8. In contrast, in the era of endovascular intervention, stroke expert groups have recommended the designation that the M1 ends at the main bifurcation ^9,10. Different studies still variably define the M1-M2 distinction ^11-14.

Branches

M1

• medial lenticulostriate penetrating arteries

• lateral lenticulostriate penetrating arteries

• anterior temporal artery (largest branch)

• polar temporal artery

• uncal artery (which may branch from the anterior choroidal artery)

• orbitofrontal branch (same territory as orbitofrontal artery)

M2

Division of the MCA is variable after the horizontal segment, although most commonly, it divides into two trunks, superior and inferior:

• 78% bifurcate into superior and inferior divisions

  • the inferior division is dominant in 32% and the superior is dominant in 28% ¹⁵

  • superior and inferior divisions are codominant in the remaining 18%

• 12% trifurcate into superior, middle and inferior divisions giving frontal branches, parietal branches and temporal branches respectively ¹⁶

• 10% branch into many smaller branches

Superior terminal branch

• lateral frontobasal artery

• prefrontal sulcal artery

• pre-Rolandic (precentral) and Rolandic (central) sulcal arteries

Inferior terminal branch

• three temporal branches: anterior, middle, posterior

• angular artery

• two parietal branches: anterior, posterior

Supply

The middle cerebral arteries supply the majority of the lateral surface of the hemisphere, except the superior portion of the parietal lobe (via the anterior cerebral artery) and the inferior portion of the temporal lobe and occipital lobe (via the posterior cerebral artery). In addition, the middle cerebral arteries supply part of the internal capsule and basal ganglia.

The superior division M2 supplies the lateral inferior frontal lobe, which on the dominant (usually left) hemisphere includes the Broca area. The inferior division M2 supplies the lateral superior temporal lobe, which includes the auditory cortex in Heschl's gyrus and the dominant hemisphere includes the Wernicke area. The supply of the central and parietal region, including the primary motor and somatosensory cortices, is variable, depending on which division is dominant. The sensorimotor homunculus supplied covers the upper body including face, arm, and hand, but not the legs.

Variant anatomy

• MCA duplication: reported incidence of ~1.5% (range 0.2-2.9%); parallels the main MCA and supplies the anterior temporal lobe

• accessory MCA

• MCA fenestration is rare with a reported incidence of <1%

• early branching of the MCA-bifurcation/trifurcation occurs within 1 cm of its origin