The middle cerebral artery (MCA) is one of the three major paired cerebral arteries that supply blood to the cerebrum. The MCA arises from the internal carotid artery and continues into the lateral sulcus where it then branches and projects to many parts of the lateral cerebral cortex. It also supplies blood to the anterior temporal lobes and the insular cortices. The left and right MCAs rise from trifurcations of the internal carotid arteries and thus are connected to the anterior cerebral arteries and the posterior communicating arteries, which connect to the posterior cerebral arteries. The MCAs are not considered a part of the Circle of Willis. Structure The middle cerebral artery divides into four segments, named by the region they supply as opposed to order of branching as the latter can be somewhat variable: M1: The sphenoidal segment (stem), receiving its name due to its course along the adjacent sphenoid bone. It is also referred to as the horizontal segment, though 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 supply the basal ganglia. M2: Extending anteriorly on the insula, this segment is 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 segment, extending laterally and exteriorly from the insula towards the cortex. This segment is sometimes grouped with M2. M4: These finer terminal or cortical segments irrigate the cortex. They begin at the external margins of the Sylvian fissure and extend distally away on the cortex of the brain. The M2 and M3 segments may each 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