1. Etiology Among intracranial aneurysms, cystic aneurysms are the most common, and the mechanism of their occurrence, enlargement and rupture is one of the hot spots of research in recent years. The congenital or mesenteric defect theory of saccular aneurysm suggests that the mesenteric defect at the bifurcation of intracranial arteries is congenital and is the basis of aneurysm formation. However, it has been found that 80% of intracranial arterial bifurcations in both patients with aneurysms and normal subjects have intima-media defects; the internal elastic membrane of the arterial wall can withstand intraluminal pressures of up to 600 mmHg whether the defect is naturally present or caused by probe injury; and studies in animal models of aneurysms have confirmed that early changes in aneurysms do not occur at the intima-media defect at the tip of the Willis ring bifurcation As a result, the concept of “congenital aneurysm” is rarely mentioned in the foreign literature. The degenerative changes and endoelastic membrane defect theory suggest that endoelastic membrane is the main structure to maintain the strength of arterial wall, and its degenerative changes are the most important factor for the formation of cystic aneurysm, which is an acquired disease caused by the damage of endoelastic membrane caused by pathogenic factors. 2.Epidemiological study Currently, intracranial aneurysm is still a very dangerous disease. One-third of patients with aneurysms die before they have time to reach a medical unit for treatment after bleeding. Half of the patients who are hospitalized also die or are left with neurological deficits. In recent years, the medical community has placed great emphasis on the dissemination of knowledge about SAH and intracranial aneurysms so that patients with aneurysms can be diagnosed and treated in a timely manner and misdiagnosis can be reduced so that more patients can be identified and saved as early as possible. Particular emphasis is being placed on the emergency management of patients with SAH due to aneurysm rupture, especially in the first few hours after SAH. This includes placing the patient in ICU immediately and performing cerebral angiography in time to clarify the cause of bleeding as soon as possible and strive for the timing of surgery. 3.Diagnostic value of 3D-CT angiography on cerebrovascular 3D-CT angiography is a computer processing of the signal obtained from CT, which shows the color image of cerebrovascular in three dimensions, and can observe the morphology, size and relationship of blood supplying arteries of AVM and aneurysm from different angles on the monitor. 3D-CT angiography has been clinically applied to make the diagnosis of cerebrovascular disease more detailed and three-dimensional, especially for determining The clinical application of 3D-CT imaging makes the diagnosis of cerebrovascular disease more detailed and three-dimensional, especially for determining the tip site and width of aneurysms, and provides detailed information for surgical clamping of aneurysms and removal of giant aneurysms. Recently, it has been reported that the angular analysis of the C1-2 segment aneurysm and the aneurysm-carrying artery using 3D-CT angiography can ensure the accurate clamping of the aneurysm during surgery. 4. Surgical treatment of aneurysm In recent years, the number of foreign scholars who advocate emergency surgery after aneurysm rupture has gradually increased. Surgery within a few hours after aneurysm bleeding has been carried out in many units. Deciding whether to operate and choosing the timing of surgery no longer rely on clinical grading alone. It is believed that with adequate surgical skill and experience, the risk of early surgery is the same as late surgery. Early surgery reduces the incidence of rebleeding and the sequelae caused by delayed surgery. For the treatment of cerebral vasospasm, in addition to the continued use of Nimodipin, a new drug, Fasudil hydrochloride, has been developed in Japan and has been used clinically for more than 5 years with satisfactory results. In addition to preoperative continuous TCD monitoring of cerebral arteries, there are also studies on intraoperative detection of tumor-bearing arteries using TCD to find measures to prevent complications caused by vasospasm. However, basic research on cerebral vasospasm has still not progressed surprisingly in recent years. In recent years, a multicenter analysis of 772 patients with early and late surgery was performed in North America. 0-3 days for early surgery and 11-32 days for late surgery, and the results were observed for 6 months after surgery, and those with good postoperative recovery were better off with early surgery than with late surgery. The mortality rate of rebleeding from unoperated aneurysms was 70-90%, mostly occurring 24-48 hours after the first bleeding, of which 20-30% rebleed due to untimely surgery within 2 weeks. Operative mortality and postoperative complications. At surgery 0-1 days after SAH, half of the patients had high brain tone, and only 20% of the patients had high brain tone after 10 days, but no increase in postoperative complications due to brain contusion from high brain tone was seen. Within two weeks after hemorrhage, the incidence of vasospasm was as high as 70-90%, and mortality due to spasm decreased from 40% in 1960, to 15% in 1980, and 8% in recent years. Early surgical removal of SAH can reduce the incidence of vasospasm. According to incomplete statistics, in the past 10 years, there were 3246 cases of intracranial aneurysm treated by neurosurgery in more than 50 hospitals in China, which achieved good results. 5.Surgical treatment of giant aneurysm Aneurysm with a diameter greater than 2.5cm is a giant aneurysm, accounting for 5-7% of intracranial aneurysm, which is still a challenging topic for neurosurgery. The difficulties of treatment are: (1) to protect the patency of blood vessel and its main branches; (2) to remove the aneurysm to relieve the occupying effect; (3) to reconstruct the aneurysm-carrying artery; Beijing Tiantan Hospital Neurosurgery Department carries out surgical resection of huge aneurysm and reconstruction of the aneurysm-carrying artery to treat 75 cases of aneurysm. (3) reconstruction of the aneurysm-carrying artery by applying window aneurysm clips; (4) chronic ligation of the internal carotid artery and isolation of the aneurysm.