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, manymost 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, which was also the nomenclature adopted byin Gibo and Rhoton's microsurgical descriptions ^67,8. However, in the current era of endovascular intervention, stroke expert groups have recommended the designation that the M1 ends at the main bifurcation ⁸⁹.

Branches

M1

• medial lenticulostriate penetrating arteries
• lateral lenticulostriate penetrating arteries
• anterior temporal artery
• 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
• 12% trifurcate into superior, middle and inferior divisions
• 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 ACA) and the inferior portion of the temporal lobe and occipital lobe (via the PCA). In addition, they supply part of the internal capsule and basal ganglia.

In its territory lie the motor and sensory areas excluding leg and perineum and auditory and speech areas.

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