Intracranial aneurysm is a kind of aneurysmal protrusion of the arterial wall caused by the restricted abnormal enlargement of the lumen of the cerebral artery. Intracranial aneurysms are mostly caused by congenital defects of the cerebral arterial wall canal localization and cystic bulge based on the increased pressure in the lumen, which is the first cause of subarachnoid hemorrhage. In the past, they were called congenital cerebral aneurysms, but in fact congenital cerebral aneurysms account for 70% to 80% of cerebral aneurysms. The cause of aneurysms is not well understood. The causes of aneurysms are not well understood. The causes of aneurysm formation are summarized as follows: (1) congenital factors; (2) atherosclerosis; (3) infection; and (4) trauma. In addition, some rare causes such as tumor can also cause aneurysm, skull base anomalous vascular network disease, cerebral arteriovenous malformation, intracranial vascular development anomaly and cerebral artery occlusion can also be accompanied by aneurysm. Clinical manifestations (1) Intracranial hemorrhage: Most patients have simple subretinal space hemorrhage, manifested as sudden headache, vomiting, impaired consciousness, epileptic-like seizures and meningeal irritation signs. (2) Focal symptoms: large aneurysms often produce compression symptoms, hemiparesis, actinic nerve palsy and obstructive hydrocephalus. (3) Cerebral ischemia and cerebral artery spasm: patients may have different degrees of neurological dysfunction, hemiparesis, aphasia, profound and superficial sensory loss, blindness, and psychiatric symptoms.