A limited cystic dilatation of the cerebral arterial wall. The etiology is mostly congenital malformations, followed by infections and atherosclerosis. The peak age of onset is between 50 and 54 years, with a slightly higher proportion of females and males. The location of the aneurysm is mostly in the intracranial segment of the internal carotid artery, followed by the anterior and middle cerebral arteries, with the posterior cerebral artery being less common. Spontaneous subarachnoid hemorrhage is the first symptom, accounting for about 80% to 90% of cases. Sudden headache, nausea, vomiting, cervical tonicity or partial impairment of consciousness are often seen during exertion or excitement, and cerebrospinal fluid is seen to be bloody by lumbar puncture. Depending on the amount of hemorrhage and the location of the aneurysm, there may be specific neurological signs, such as internal carotid artery-posterior communicating artery aneurysm hemorrhage, there may be ipsilateral actinic nerve palsy (eyelid ptosis, limited eye movement, dilated pupil); if the hemorrhage is large enough to form a huge hematoma, the patient may die within a short time. In typical cases, the clinical diagnosis is not difficult, and the diagnosis can be confirmed by CT scan to determine the side and angiography. In the examination, it should be active and steady, and early angiography should be performed in mild cases. Mostly, aneurysm neck clamping is performed before the rupture of the second hemangioma. The operative mortality rate has decreased to 5% or 0. Most of the critically ill patients are treated conservatively and have poor prognosis.