Diagrams

Ischemia in the ACA-MCA Cortical Border Zone
When blood flow in the carotid artery is suddenly reduced secondary to severe global hypotension or dissection, structures in the cortical border zone that lies between distal branches of the ACA and MCA can be at risk for ischemia. Vessels in the ACA-MCA border zone supply superior parts of the frontal lobe, including primary motor cortex concerned with the proximal limb girdle of the arm or leg or both. However, the exact position of the border zone varies between individuals and depends on factors such as whether there is carotid stenosis. One patient with border zone infarction suffered primarily paralysis of the contralateral hip while the rest of the leg was spared. Another patient had a paralyzed shoulder and was initially worked up for a brachial plexus injury until other neurologic deficits made it clear that his problem was inside the CNS.