Which MCA segment corresponds to the cortical branches that are the most distal and extend across the lateral surfaces of the brain?

• A. M1
• B. M2
• C. M3
• D. M4

Answer: (D)

Think of the MCA as a trunk that tapers into smaller branches as it travels from its origin to the brain’s surface. The most distal, surface-reaching branches are the final cortical arteries that spread over the lateral convexity of the hemisphere. These tiny terminal arteries form the M4 segment, reaching across the outer aspects of the lateral cortex to supply the gyri there. The earlier segments—M1 being the main trunk before major branching, M2 branches within the Sylvian fissure, and M3 branches along the opercular regions—are more proximal or deeper and do not represent the distal, surface-distributing arteries. So, the most distal cortical branches that extend across the lateral surfaces correspond to the final cortical segment.