First of all, smog is neither a disease caused by smoke coming out of the brain nor by smoking. It is a group of cerebrovascular diseases characterized by chronic progressive stenosis or occlusion of the main branches of the Willis ring (the siphon section of the internal carotid artery and the anterior and middle cerebral arteries, and sometimes also the beginning of the posterior cerebral artery), followed by a network of small vessels with abnormal side branches. It was first described by Japanese doctors Takeuchi and Shimizu in 1957 and is characterized by spontaneous progressive infarction of the internal carotid artery above the bed process and the ring of Willis, with a large number of collateral compensating vessels at the base of the skull. Suzuki and Takaku named the disease Moyamoya disease (Japanese for “smoke”) in 1967 because these abnormal vessels looked like “smoke” on angiography. The cause of the disease is still unclear, but it is generally believed that Moyamoya disease is associated with chronic inflammation of the central nervous system. In young patients, the main symptoms are cerebral ischemia, such as transient ischemic attack (TIA), ischemic stroke and cerebrovascular dementia, but also headache or epilepsy. The treatment of Moyamoya disease can be divided into two categories: pharmacological treatment and surgical treatment. The efficacy of pharmacological treatment has not yet been confirmed. In contrast, although there are no prospective randomized controlled clinical trials, some large sample case studies have shown that surgery is effective in reducing the incidence of stroke and TIA. The main surgical treatment is bypass surgery, including direct bypass, indirect bypass and combined bypass. Direct bypass refers to the anastomosis of the intracranial and extracranial arteries. The donor artery is the superficial temporal artery (STA) and the recipient artery is the middle cerebral artery (MCA), sometimes the anterior cerebral artery (ACA) is also used. Direct bypass can rapidly and effectively improve cerebral perfusion and reduce the abnormal Moyamoy vessels at the skull base, but it is more difficult to perform.