What is the most common cause of subarachnoid hemorrhage?

Subarachnoid hemorrhage is mostly caused by congenital factors, the most common of which are vascular malformations or intracranial aneurysms. In addition, studies have found that smoking and drinking are also common causes of subarachnoid hemorrhage. Relevant prevention measures should be taken for secondary causes.

1. The most common causes of subarachnoid hemorrhage are congenital intracranial aneurysms and vascular malformations, followed by hypertensive cerebral atherosclerosis, intracranial tumors, blood diseases, arteritis caused by various infections, tumor destruction of blood vessels, and abnormal vascular network at the base of the skull (moyamoya disease). There are also some cases of unexplained subarachnoid hemorrhage, which refers to those for which no cause can be found through whole-brain angiography and brain CT scan.

2. Among the causes, miliary aneurysms account for about 75%, with an annual incidence of 6/100,000; arteriovenous malformations account for about 10%, which are more common in young people, and more than 90% are located above the tentorium; abnormal vascular network at the base of the brain (Moyamoya disease) accounts for 20% of SAH in children; and unknown causes account for 10%. It is generally believed that those who develop the disease before the age of 30 are mostly suffering from vascular malformations, those who develop the disease after the age of 40 are mostly suffering from ruptured intracranial aneurysms, and those who develop the disease over the age of 50 are often caused by hypertension, cerebral arteriosclerosis and brain tumors.

3. In addition, smoking and drinking are closely related to subarachnoid hemorrhage. Foreign animal experiments have shown that there are three factors that contribute to the formation of aneurysms: Willis circle pressure, hypertension, and increased vascular fragility. Smoking can affect these three factors, causing an acute increase in blood pressure, which then gradually falls back after 3 hours, which is consistent with the clinical observation that the incidence of subarachnoid hemorrhage is highest within 3 hours after smoking. Smoking can also activate the activity of lung macrophages, promote the release of hydrolytic enzymes, cause lung damage and increase cerebral vascular fragility, thereby increasing the risk of subarachnoid hemorrhage. Drinking large amounts of alcohol may cause high blood pressure or other changes including blood coagulation mechanisms and cerebral blood flow, which can accelerate the onset of subarachnoid hemorrhage. It has been reported that the incidence of subarachnoid hemorrhage in heavy drinkers is twice that of non-drinkers.