Branches
The middle cerebral artery can be classified into 4 parts:
- M1: The sphenoidal segment, so named due to its origin and loose lateral tracking of the sphenoid bone. Although known also as the horizontal segment, this may be misleading since the segment may descend, remain flat, or extend posteriorly the anterior (dorsad) in different individuals. The M1 segment perforates the brain with numerous anterolateral central (lateral lenticulostriate) arteries, which irrigate the basal ganglia.
- M2: Extending anteriorly on the insula, this segment in known as the insular segment. It is also known as the Sylvian segment when the opercular segments are included. The MCA branches may bifurcate or sometimes trifurcate into trunks in this segment which then extend into branches that terminate towards the cortex.
- M3: The opercular segments and extends laterally exteriorly from the insula towards the cortex. This segment is sometimes grouped as part of M2.
- M4: These finer terminal or cortical segments irrigate the cortex. They begin at the external of the Sylvian fissure and extend distally away on the cortex of the brain.
Although the M2-M3 segments may split into 2 or 3 main trunks (terminal branches) with an upper trunk, lower trunk and occasionally a middle trunk. Bifurcations and trifurcations occurs in 50% and 25% of the cases respectively. Other cases include duplication of the MCA at the internal carotid artery (ICA) or an accessory MCA (AccMCA) which arise not from the ICA but as a branch from the anterior cerebral artery. The middle trunk that exist in parts of the population, when present provides the pre-Rolandic, Rolandic, anterior parietal, posterior parietal and the angular artery for irrigation instead of the upper and lower trunks.
The branches (ramus) of the MCA can be described by the areas that they irrigate.
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