Traumatic subarachnoid hemorrhage occurs when an acceleration force

such as the impact of a motor vehicle accident or blunt force trauma

causes the brain to move inside the skull.

Rapid movement of the brain puts stress on blood vessels in the subarachnoid space,

which causes them to rupture.

The subarachnoid space, which is normally filled with cerebrospinal fluid, fills with blood.

Compared to a subdural hematoma, bleeding in a subarachnoid hemorrhage

is spread diffusely through the subarachnoid space,

so it does not produce massive pressure on the brain tissue as rapidly.

Complications can arise if the subarachnoid hemorrhage

produces cerebral vasospasms, which can lead to permanent brain damage.