Traumatic brain injuries may be classified as closed head injuries or penetrating head injuries. Closed head injuries usually occur as a result of a blow to the head, or from being struck in the head by an object. A closed head injury may result from a motor vehicle accident when you strike your head on the windshield. A penetrating head injury occurs when an object penetrates the skull, which may drive small bits of bone or tissue into the brain. A gunshot wound is a good example of a penetrating head trauma.

TBI’s may also be classified as diffuse or focal. Diffuse injuries involve damage to multiple microscopic areas of the brain. Diffuse injuries cause damage to the axons, or the connections that allow nerve cells to communicate with each other.

Focal injuries are confined to a specific area of the brain. These injuries cause localized damage that can often be detected by x-rays or CT scans.

Diffuse Injuries

Diffuse Axonal Injury (DAI)-This type of injury causes shearing (tearing) of large nerve fibers and stretching of blood vessels in many areas of the brain. This type of injury may cause hemorrhage (bleeding) as well as a buildup of toxic substances in the brain in the days following the injury. Frontal and temporal lobes are very susceptible to this type of injury.

The patient may experience visual loss or weakness on one side of the body if small nerve centers are affected. They may also experience disorganization, loss of memory, and inability to focus on certain tasks.

Hypoxic-Ischemic Injury (HII)-This type of injury causes swelling in the brain, which in turn restricts the flow of blood, oxygen, and glucose, and other nutrients.

Patients with diffuse injuries typically have a poorer prognosis and usually experience some loss of memory as well as decreased cognitive function.

Focal Injuries

Contusions-A contusion is the medical term for bruising. Contusions may cause swelling, bleeding, and destruction of brain tissue. Contusions generally occur in the frontal and temporal lobes, which house the memory and behaviour centers of the brain. Contusions may also occur in the parietal and occipital lobes of the brain, although these injuries occur less commonly. Symptoms that a patient with a contusion of the brain might experience are abnormal sensations, changes in behaviour, loss of part or all of the vision, loss of coordination, weakness, and memory loss. Contusions shrink as swelling subsides, but may leave residual scar tissue. This may leave the patient with lasting neurological impairment.

Hemorrhage-Intracranial (within the brain) hemorrhage occurs when blood leaks from a damaged vessel into brain tissue. The size of a hemorrhage may range from tiny to large. Symptoms that the patient will experience with a hemorrhage depend on the size and location of the damage. Hemorrhage may occur in minutes, or may not occur for hours or days.

Infarction-Infarction is the term used for stroke. Infarctions that occur as a result of TBI occur when an artery to the brain is compressed by the swelling of surrounding tissues. This prevents the flow of blood and oxygen to the brain cells. Most strokes that occur as a result of TBI affect the occipital and temporal lobes and cause vision loss or speech and language problems.

Hematoma-Hematomas involve bleeding on the outside of the brain.

Subdural hematomas- slow bleeding outside the brain. They are caused by damage to a blood vessel carrying deoxygenated blood. They may develop slowly. If they become large enough, they can exert pressure on the brain, creating the need for surgery to drain the accumulated blood and relieve the pressure.

Epidural hematoma- occurs outside the brain. They are caused by a leaking artery. A large EDH can cause pressure to build up very rapidly because arteries carry blood under pressure. An EDH requires immediate surgery to relieve pressure and prevent death or permanent neurological damage.

Subarachnoid Hematoma-This type of injury involves a small amount of bleeding spread over the surface of the brain. This small amount of bleeding may have little significance and will likely cause no damage.