If the middle cerebral artery is occluded, the collateral circulation can replace it for blood supply to a certain extent, but the occurrence of this situation depends mainly on whether the middle cerebral artery is acutely occluded or chronically occluded. Generally, acute occlusion is commonly seen in cerebral embolism, and the embolus is mostly originated from the heart, or dislodged from the atherosclerotic plaques of other large blood vessels. In this case, the collateral circulation is too late to open and generate, and large cerebral infarction often occurs leading to severe neurological deficits, with patients experiencing paralysis of the limbs, and may be left with significant disability after treatment. In the case of chronic occlusion, such as chronic atherosclerosis of the middle cerebral artery, where plaques gradually form leading to stenosis as well as occlusion of the blood vessel, there will be enough time to form collateral circulation and guide the opening of the collateral circulation, and the compensatory effect will be better. During angiography, it can be found that although the middle cerebral artery is occluded, there are still many collateral blood vessels in the area of its blood supply, which can ensure the adequate supply of blood to the brain.