It is common for both focal and diffuse damage to occur as a result of the same event; many traumatic brain injuries have aspects of both focal and diffuse injury.

A focal traumatic injury results from direct mechanical forces (such as occur when the head strikes a windshield in a vehicle accident) and is usually associated with brain tissue damage visible to the naked eye.

[3] A common cause of focal injury is penetrating head injury, in which the skull is perforated, as frequently occurs in auto accidents, blows, and gunshot wounds.

[3] Focal injuries typically have symptoms that are related to the damaged area of the brain.

[2] Unlike focal injuries, which are usually easy to detect using imaging, diffuse injuries may be difficult to detect and define; often, much of the damage is microscopic.