Foggy disease is the formation of an abnormal vascular network at the base of the brain. It is generally believed that after the narrowing or occlusion of the main trunk of the cerebral floor artery ring, each deep penetrating branch proliferates and expands, anastomosing each other and forming a vascular network, thus establishing a rich collateral circulation. This abnormal vascular network, when shown in cerebral angiography, shows a smoke-like image, hence the name. As to whether the narrowing or occlusion of the lumen of the main trunk of the basilar artery is congenitally caused or occurs later in life, there are two views: (1) The abnormal vascular network is a congenital vascular development disorder. This is because it resembles the early embryonic cerebral vascular development. (2) The anomalous capillary network is secondary to cerebral artery occlusion. This is because pathologically, the internal carotid artery is significantly narrowed at the end and even occluded. There is a dilated anomalous capillary network in the base of the brain and in the lateral fissure. The collateral circulation is derived from the external carotid artery system and the proximal branches of the internal carotid artery. Smoker’s disease is a widely affected cerebrovascular disease with a long course. In the early stage when the collateral circulation is not fully established on both sides due to vascular stenosis or occlusion, the clinical manifestations are mostly transient or persistent cerebral ischemia, such as hemiparesis, aphasia and tamponade. In the late stage, because the collateral circulation has been fully established, the small vessels of the abnormal vascular network dilate and the vessel wall becomes thin, followed by rupture and bleeding. If combined with hypertensive disease, cerebral hemorrhage is more likely to occur. Since the main manifestations triggered by smog disease are cerebral infarction and cerebral hemorrhage, the relationship between it and cerebrovascular disease is obvious, and it is one of the causes of cerebrovascular disease. There is no effective treatment for smog, and the efficacy of medical treatment is not satisfactory. The more effective treatment is extracranial and intracranial vascular bypass surgery, most often performed with superficial temporal artery and cortical artery anastomosis.