RT Book, Section A1 Hemphill, III, J. Claude A1 Smith, Wade S. A1 Gress, Daryl R. A2 Loscalzo, Joseph A2 Fauci, Anthony A2 Kasper, Dennis A2 Hauser, Stephen A2 Longo, Dan A2 Jameson, J. Larry SR Print(0) ID 1201833124 T1 Subarachnoid Hemorrhage T2 Harrison's Principles of Internal Medicine, 21e YR 2022 FD 2022 PB McGraw-Hill Education PP New York, NY SN 9781264268504 LK accessmedicine.mhmedical.com/content.aspx?aid=1201833124 RD 2024/11/08 AB Subarachnoid hemorrhage (SAH) renders the brain critically ill from both primary and secondary brain insults. Excluding head trauma, the most common cause of SAH is rupture of a saccular aneurysm. Other causes include bleeding from a vascular malformation (arteriovenous malformation or dural arteriovenous fistula) and extension into the subarachnoid space from a primary intracerebral hemorrhage. Some idiopathic SAHs are localized to the perimesencephalic cisterns and are benign; they probably have a venous or capillary source, and angiography is unrevealing.