Knowledge about subarachnoid hemorrhage Subarachnoid hemorrhage is divided into primary and secondary. Primary subarachnoid hemorrhage is a type of stroke in which blood flows into the subarachnoid space after a rupture of a blood vessel at the base of the brain or on the surface of the brain, causing the corresponding clinical symptoms. Among cerebrovascular accidents, it ranks third after cerebral thrombosis and hypertensive cerebral hemorrhage. Intracranial aneurysms are the most common cause of subarachnoid hemorrhage, accounting for about 50% to 85% of cases. Intracranial aneurysms are generally insidious in course, but have a sudden onset, and once they develop, the death and disability rates are extremely high, so they are called “untimely bombs” in the skull and are one of the most dangerous cerebrovascular diseases. Intracranial aneurysm is the most common major disease that threatens human life and health. How can an aneurysm cause an aneurysm to rupture and bleed? Intracranial aneurysms may be caused by congenital myelomeningocele defects in the arterial wall or acquired degeneration of the internal elastic lamina, or a combination of both. There is a degree of genetic predisposition and familial aggregation for the development of aneurysms, such as an increased prevalence of aneurysms in patients with a family history of atherosclerosis, aneurysms, and polycystic kidneys. However, intracranial aneurysms are not entirely congenital; a significant proportion develop later in life over a long period of time. With age, the elasticity of the arterial wall gradually decreases and the weak wall protrudes outward to form a saccular aneurysm under the influence of blood flow impact and other factors. The diseased vessel may rupture spontaneously or as a result of a sudden increase in blood pressure or other obscure triggers, and blood enters the subarachnoid space and spreads rapidly through the cerebrospinal fluid surrounding the brain and spinal cord, irritating the meninges and causing headache and neck tonicity. Long-term smoking, uncontrolled hypertension, and excessive alcohol consumption are the main risk factors for intracranial aneurysm rupture and bleeding. Therefore, it is possible to reduce the occurrence of aneurysm to some extent by controlling the risk factors in general. The presence of unruptured aneurysms can also be detected early by imaging means of cerebral angiography so that appropriate treatment can be given before the aneurysm ruptures and bleeds.