1, cerebral aneurysm: It occurs in patients aged 40-60 years, with acute onset, severe headache, positive neck strength and Kirsch’s sign, and some patients may have impaired consciousness or even coma, and CT head shows high-density shadow of cerebral sulcus and cerebral pool, and also cerebral (ventricular) hematoma, hydrocephalus, cerebral infarction and cerebral edema. 2. Cerebral arteriovenous malformation: It is more likely to occur in patients over 35 years old, and the bleeding mostly occurs in the brain, accounting for 9% of subarachnoid hemorrhage, often with a history of seizures and headaches. Vascular malformation can be seen on head CT enhancement or MRI, and cerebral angiography can clarify the diagnosis. The size and extent of the vascular malformation group, blood supply artery, drainage vein and blood flow rate can be understood. 3.Smoke disease: It is common in children and adolescents, and may manifest as congenital or ischemic stroke. Ischemic manifestations are transient ischemic attack aura, repeated attacks, gradual appearance of limb paralysis, aphasia, mental retardation and other symptoms, rapid onset, headache, vomiting, impaired consciousness and focal neurological signs, head MRA suggests vascular abnormalities, and smoky abnormal skull base vascular shadow is seen. 4, angiography negative subarachnoid hemorrhage: about 7%-30% of subarachnoid hemorrhage cerebral angiography without abnormal performance, the reasons may be: (1) undetected aneurysm, generated by cerebral vasospasm after bleeding aneurysm destruction or spontaneous thrombosis, aneurysm neck stenosis or improper imaging techniques, reading errors, etc. (2) Non-aneurysmal subarachnoid hemorrhage includes occult AVM, cavernous hemangioma, hypertensive atherosclerosis, vascular amyloidosis, hematologic disease, immunologic disease, etc. (3) Periaqueductal subarachnoid hemorrhage in the midbrain. Some of the above patients need further investigation. 5, traumatic subarachnoid hemorrhage: there is often a clear history of head trauma, some patients can be combined with cerebral contusions, intracerebral hematoma, etc. When the medical history is not clear and it is difficult to identify traumatic or spontaneous, cerebrovascular CTA examination is feasible to exclude cerebrovascular aneurysm.