What is a subarachnoid hemorrhage? A subarachnoid hemorrhage is when a blood vessel at the base of the brain or superficial part of the brain ruptures and blood enters the subarachnoid space directly. What causes a subarachnoid hemorrhage? Any cause that can cause cerebral hemorrhage can also cause this disease, but intracranial aneurysm, arteriovenous malformation, hypertensive arteriosclerosis, anomalous vascular network at the base of the brain and blood disorders are the most common. The onset of the disease usually occurs during emotional stress or excessive exertion. Arteriovenous aneurysms are usually found in the branches of the large arteries of the cerebral base arterial ring, with the anterior half of the ring being the most common. Arteriovenous malformations are mostly located in the middle cerebral artery distribution area of the cerebral hemisphere. When blood flows into the cerebral subarachnoid space from a ruptured vessel, the contents of the cranial cavity increase, pressure increases, and cerebral vasospasm ensues. The latter is due to extensive ischemic damage and edema of the neuromuscular junction formed between the smooth muscle cells of the vessel wall as a result of the traction of the blood clot and the fibrous cords surrounding the vessel wall after hemorrhage (mechanical factors). In addition, a large amount of blood or clots deposited at the base of the skull and some agglutinated red blood cells can block the small sulcus between the arachnoid villi, blocking the reabsorption of cerebrospinal fluid, which can lead to acute traffic hydrocephalus and a rapid increase in intracranial pressure, further reducing cerebral blood flow, aggravating cerebral edema, and even leading to brain herniation. All of the above can cause patients to reappear with impaired consciousness or limited neurological symptoms after their condition has stabilized and improved. What are the symptoms of subarachnoid hemorrhage? It can occur at all ages, but is more common in young adults. They occur acutely in emotional or exertional situations, and some patients may have a history of recurrent headaches. (a) Headache and vomiting: Sudden onset of severe headache, vomiting, pale face and cold sweat. If the headache is confined to a certain place, it has localization significance, such as anterior headache suggesting supratentorial and cerebral hemispheres (unilateral pain), and posterior headache indicating posterior cranial recess lesion. (b) Disorders of consciousness and psychiatric symptoms: Most patients have no disorders of consciousness, but they may have irritability. In critical cases, delirium, varying degrees of unconsciousness and coma may be present.