Focal and diffuse brain injury

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 the result of the same event; many traumatic brain injuries have aspects of both focal and diffuse injury.^[1] 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.^[2] In addition to physical trauma, other types of brain injury, such as stroke, can also produce focal and diffuse injuries.^[1] 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.^[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.^[3] Stroke can produce focal damage that is associated with signs and symptoms that correspond to the part of the brain that was damaged.^[1] For example, if a speech center of the brain such as Broca's area is damaged, problems with speech are common.

Focal injuries include the following:

• Cerebral contusion is a bruise of brain tissue that commonly results from contact of the brain with the inside of the skull.^[4]
• Cerebral laceration is a brain injury in which the pia-arachnoid is torn.^[4]
• Epidural hemorrhage is bleeding between the dura mater and the skull.^[4] It is commonly associated with damage to the middle meningeal artery, often resulting from a skull fracture.
• Subdural hemorrhage is bleeding between the dura mater and the arachnoid.^[4]
• Intracerebral hemorrhage is bleeding within the brain tissue itself.^[4]
• Intraventricular hemorrhage is bleeding within the ventricles of the brain.^[4]

Diffuse

Diffuse injuries, also called multifocal injuries, include brain injury due to hypoxia, meningitis, and damage to blood vessels.^[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.^[4] Diffuse injuries can result from acceleration/deceleration injuries.^[2] Rotational forces are a common cause of diffuse injuries;^[5] these forces are common in diffuse injuries such as concussion and diffuse axonal injury. The term "diffuse" has been called a misnomer, since injury is often actually multifocal, with multiple locations of injury.^[2]

Diffuse injuries include the following:

• Diffuse axonal injury is widespread damage to the white matter of the brain that usually results from acceleration/deceleration types of injury.^[4]
• 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.^[4]
• Vascular injury usually causes death shortly after an injury.^[4] Although it is diffuse type of brain injury itself, diffuse vascular injury is generally more likely to be caused by focal than diffuse injury.^[4]
• Swelling, commonly seen after TBI, can lead to dangerous increases in intracranial pressure.^[4] Though swelling itself is a diffuse type of injury, it can result from either focal or diffuse injury.^[4]

See also

• Focal neurologic deficit

References