Subarachnoid hemorrhage (SAH) refers to a clinical syndrome caused by the rupture of diseased blood vessels at the base or surface of the brain and the direct flow of blood into the subarachnoid space, also known as primary subarachnoid hemorrhage, accounting for about 10% of acute strokes. I. Spontaneous SAH (9 categories): 1. Vascular lesions: Aneurysm, cerebrovascular malformation especially AVM, hypertensive atherosclerotic vascular rupture, giant cell arteritis, polyarteritis nodosa, adult smoker’s disease, capillary dilation, vascular amyloidosis, etc. 2, venous thrombosis (intracranial vein and dural sinus thrombosis): pregnancy, contraceptive pills, trauma, infection, wasting, dehydration, coagulation system diseases, etc. 3.Hematological diseases: leukemia, lymphatic gonorrhea, Hodgkin’s disease, hemophilia, DIC, use of anticoagulant drugs, anemia and coagulation disorders caused by various reasons, etc. 4, allergic diseases: allergic purpura, hemorrhagic nephritis, Xu Lan – Henao syndrome tablets, etc. 5, infection: bacterial meningitis, tuberculous meningitis, syphilitic meningitis, fungal meningitis, parasitic diseases, etc. 6, poisoning: carbon monoxide, morphine, nicotine, cocaine, epinephrine, alcohol, ether, etc. 7, tumor: glioma, meningioma, hemangioblastoma, pituitary tumor, ventricular meningioma, choroid plexus papilloma, etc. 8, systemic lesions: RA, SLE, liver disease, kidney disease, etc. 9, other: vitamin K deficiency, electrolyte disorders, heat stroke, etc. Traumatic SAH: often complicated by other craniocerebral trauma manifestations. Diagnosis: CT, digital subtraction angiography (DSA), MRI. 1, DSA negative is seen in: occult cerebrovascular malformation, micro A tumor, micro AVM, AVM rupture disappears on its own, spasm of aneurysm-carrying artery, etc. Occult cerebrovascular malformation: refers to vascular malformation such as thrombosed AVM, small AVM, cavernous hemangioma, capillary dilatation, venous vascular malformation, etc. that are not seen abnormally in DSA. 2.DSA-negative SAH: The incidence varies, averaging around 20%+-10%, with PNSH being more common. 3, pericentral cerebral SAH: DSA negative, probably caused by venous hemorrhage, CT shows that the hemorrhage is only located in the front of the brainstem, not involving the cerebral sulcus and ventricles, the prognosis is better. However, ruptured aneurysm of the vertebrobasilar system may also have similar head CT manifestations, so this disease cannot be easily diagnosed. 4. Terson syndrome: i.e. fundus hemorrhage can be retinal, subvitreous or intravitreal. It is mostly seen in ruptured anterior communicating artery aneurysm, which causes central retinal V hemorrhage due to increased intracranial pressure and clot compression of the optic nerve sheath. This film has special significance because it still exists after the CSF is restored to normal, which is one of the important bases for diagnosing subarachnoid hemorrhage and is also the main cause of blindness in patients.