Subarachnoid Hemorrhage

Life-sustaining blood is supplied to the brain by blood vessels, many of which run within the arachnoid layer covering the external surface before plunging into the deeper brain tissue.  If the vessels are disturbed, either by trauma, infection, or other insults, blood may exit the vessel and collect in the subarachnoid space in a process called subarachnoid hemorrhage (pictured here).