Focal and diffuse brain injury are ways to classify brain injury: focal injury occurs in a specific location, while diffuse injury occurs over a more widespread area. 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. Focal injuries are commonly associated with an injury in which the head strikes or is struck by an object; diffuse injuries are more often found in acceleration/deceleration injuries, in which the head does not necessarily contact anything, but brain tissue is damaged because tissue types with varying densities accelerate at different rates. In addition to physical trauma, other types of brain injury, such as stroke, can also produce focal and diffuse injuries. There may be primary and secondary brain injury processes. Focal
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. 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. Focal injuries typically have symptoms that are related to the damaged area of the brain. Stroke can produce focal damage that is associated with signs and symptoms that correspond to the part of the brain that was damaged.
Ischemic brain injury resulting from an insufficient blood supply to the brain, is one of the leading causes of secondary brain damage after head trauma. Vascular injury usually causes death shortly after an injury. Although it is a diffuse type of brain injury itself, diffuse vascular injury is generally more likely to be caused by focal than diffuse injury. Swelling, commonly seen after TBI, can lead to dangerous increases in intracranial pressure. Though swelling itself is a diffuse type of injury, it can result from either focal or diffuse injury. See also
Focal neurologic deficit

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