What is the most common cause of spontaneous subarachnoid hemorrhage?
Saccular aneurysm rupture is the cause in 85% of spontaneous cases. Other causes of subarachnoid hemorrhage include arteriovenous malformation (AVM) rupture, vasculitis, trauma, or dissection. In approximately 10% of cases of spontaneous subarachnoid hemorrhage, no aneurysm or AVM is found and the diagnosis of perimesencephalic subarachnoid hemorrhage is made. The cause of perimesencephalic subarachnoid hemorrhage is generally a diagnosis of exclusion and thought to be secondary to a venous bleed.
