The term brain injury is often used synonymously with traumatic brain injury (TBI), however, it is important to note that not all types of injury to the brain tissue is associated with trauma. Similarly, head trauma will not always result in brain injury. Therefore brain injury should never be assumed by the degree of head injury, although it should be suspected, investigated and monitored following trauma to the head.
There are various mechanisms by which the brain tissue may be injured, each with a host of causes and associated risk factors. The brain tissue is fairly delicate – oxygen ‘hungry’, demanding of glucose and sensitive to chemical toxins. More importantly though, it is unable to elicit any pain responses when undergoing damage unless the meninges, blood vessels and ventricles are affected.The warning signal of injury is therefore not present until associated symptoms arise as a result of damage, often to a significant area of the brain.
Types of Injury to the Brain
All injury involves the process of inflammation. The inflammatory process is the body’s response to injury. It aims to protect the affected area and leads to swelling, pain, redness and heat – the cardinal features of inflammation.
Acquired Brain Injury
Acquired brain injury is any damage to the brain tissue that occurs after birth. It is a broad term that encompasses traumatic brain injury, ischemic injury, cancer, encephalitis and encephalopathy. Encephalitis is inflammation of the brain usually associated with an infection. Encephalopathy is a neurodegenerative disease which may be due to a number of causes including autoimmune disorders, alcohol, drugs, toxins, liver disease, metabolic disorders, hypertension, oxygen deficiency and infections.
Traumatic Brain Injury
Inflammation of the brain tissue associated with external mechanical trauma to the head. This may be seen in motor vehicle accidents, where the sudden jerking of the head causes a cerebral contusion (brain injury), or penetrating injuries where the brain is pierced (cerebral laceration). This may damage the cells only in one part of the brain or the entire brain (diffuse axonal injury).
This occurs when the supply of oxygen is insufficient to maintain the needs of the brain tissue. Inflammation follows which often exacerbates the condition due to the swelling of the brain further impairing blood flow and hence oxygen supply. Ischemia is not always a result of reduced oxygen intake or problems with gas exchange in the lungs. Blood clots, hemorrhages (bleeding in the brain) and even cerebral edema may be some of the mechanisms that compromise the blood flow and oxygen supply to the brain. This type of brain injury is seen with a stroke.
Raised Intracranial Pressure
Also known as pressure on the brain, it occurs when there is compression of the brain tissue. Apart from the direct damage of tissue compression, it also disrupts the blood flow to the brain thereby contributing to ischemia to some degree. Raised intracranial pressure may occur for a number of reasons, including trauma, cerebral edema, hemorrhage and intracranial masses, and cannot be seen entirely as a separate entity from brain ischemia and traumatic injury.