Definition and Incidence

Subarachnoid hemorrhage (SAH) refers to bleeding that occurs within the subarachnoid space of the brain. SAH can be caused by trauma (traumatic SAH), or by spontaneous rupture of a cerebral vessel. Non-traumatic, spontaneous rupture of vessels is most frequently caused by cerebral aneurysms (95%), but can also be due to arteriovenous malformations (AVM) (<5%). The initial presentation, treatment, and management of patients with SAH may vary based on the cause of SAH (trauma vs spontaneous). The focus of this course is on aneurysmal subarachnoid hemorrhage, aSAH, as it is the most frequent type of spontaneous SAH.