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Subarachnoid hemorrhage
Definition:
Subarachnoid hemorrhage is bleeding between the middle membrane covering of the brain and the brain itself. Specifically it occurs within the cerebrospinal fluid-filled spaces surrounding the brain (also known as the subarachnoid space). Patients with subarachnoid hemorrhage usually complain of the "the worst headache of their lives." Alternative Names:
Hemorrhage - subarachnoid Text Continues Below
Causes, incidence, and risk factors:
Subarachnoid hemorrhage occurs in approximately 1 out of 10,000 people. About 5 to 10% of strokes are caused by subarachnoid hemorrhage. It is most common in people 20 to 60 years old. It is slightly more common in women than men. The most common cause of any form of subarachnoid hemorrhage is trauma. The most common cause of subarachnoid hemorrhage in young adults is a ruptured cerebral aneurysm. A small percentage of subarachnoid hemorrhages have a nonaneurysmal pattern to them. They occur spontaneously, and are usually localized to the area in the brain called the perimesencephalic cisterns. The usual outcome for this type of hemorrhage is excellent. Unlike the majority of hemorrhages that are caused by arterial ruptures, this type is thought to be caused by a ruptured vein or capillary. Subarachnoid hemorrhage occurs when there is bleeding into the space between the brain and the arachnoid membrane (the middle membrane covering the brain). This may occur from a ruptured cerebral aneurysm or arteriovenous malformation, but some result from unidentified causes. Risks include: disorders associated with aneurysm or weakened blood vessels, including a history of polycystic kidney disease, fibromuscular dysplasia (FMD), other connective tissue disorders, aneurysms in other blood vessels, high blood pressure, and smoking.
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