Introduction to Brain Injury - Fact Sheet

Acquired brain injury is often called the hidden disability because its long term problems are usually in the areas of thinking and behaviour, and are not as easy to see and recognise as many other physical disabilities.

As a consequence, the difficulties people with brain injuries face are easily ignored or misunderstood. Even family members and friends may regard a person with acquired brain injury who exhibits cognitive problems or changed behaviour, as lazy or hard to get along with.

The term acquired brain injury (ABI) is used to describe all types of brain injury that occur after birth. There is very little understanding or knowledge in the community about brain injury and the impact it has on individuals and families.

Acquired brain injury is not to be confused with intellectual disability. People with an acquired brain injury do not necessarily experience a decline in their overall level of general intellectual functioning. Rather, they are more likely to experience specific cognitive changes that lead to difficulty in areas such as memory, concentration and communication.

Acquired brain injury is also not a mental illness. Mental illness is an observable abnormality in the functioning of the brain. Brain injury, although it does alter the functioning of the brain, is an observable abnormality in the structure of the brain – a physical condition that causes a change in function. Mental illness does not, by definition, arise from a physical condition.

Effects

People with ABI may experience long term effects such as medical difficulties, impaired physical and sensory abilities, and changes in cognition, behaviour, personality and communication. Long term effects will be different for each person, but some of the more common ones are:

Some of the more common physical effects may be:

Causes

The brain can be injured as a result of an accident, a stroke, alcohol or drug abuse, tumours, poisoning, infection and disease, near drowning, haemorrhage, AIDS, and a number of other disorders such as Parkinson’s disease, Multiple Sclerosis, and Alzheimer’s disease.

Traumatic Brain Injury

Traumatic brain injury (TBI) is an acquired brain injury caused by a blow to the head or by the head being forced to move rapidly forward or backward, usually with some loss of consciousness. As a result of this blow or rapid movement, brain tissue may be torn, stretched, penetrated, bruised or become swollen. Oxygen may not be able to get through to the brain cells and there may be bleeding.

The effects of traumatic brain injury can be temporary or permanent and range from mild injury, such as being momentarily stunned while playing football, to a very severe injury that may cause prolonged loss of consciousness. Concussion for any period of time, however slight, may result in acquired brain injury. In fact, the Centre for Disease Control in America defines concussion as “mild traumatic brain injury”. While most people make a good recovery, many are left with lasting effects that, even if mild, may have significant consequences for everyday living.

Open and Closed Head Injuries

A brain injury can be the result of either an open or closed injury to the head. People can have injuries to their head without acquiring a brain injury. Alternatively, the brain can be injured with little or no visible injury to the head.

After the impact of either an open or closed head injury, brain swelling and bleeding can cause further damage. Injuries to other parts of the body frequently result in a loss of blood or lack of oxygen to the brain, also causing damage. The frontal lobes, due to their position beneath the sharp bony ridges of the skull, and the temporal lobes, which are closer to the skull than are other regions of the brain, are most often affected after high impact injuries.

Closed Head Injury

Closed head injury is the most common cause of brain injury. It occurs when the head is struck or moved violently but the skull and/or membrane lining of the brain is not broken or penetrated. Such damage often involves “Diffuse Brain Injury” via widespread shearing, twisting and stretching of nerve fibres and bleeding due to the tearing of arteries and veins throughout the brain. The forward motion and rotation of the brain on the relatively fixed brain stem is a common cause of loss of consciousness and coma.

In addition to diffuse brain injury, focal lesions and bruising may occur as the brain collides with the sharp bony inner surface of the skull. Focal lesions can occur at the site of impact inside the skull (coup injury) or at a different site (contrecoup injury) which is typically, although not limited to, the opposite side of the skull.

A closed head injury may not be obvious to medical staff in an emergency department, and may not receive appropriate treatment until symptoms become worse over several days.

Open Head Injury

An open head injury occurs when the skull and membrane lining of the brain have been fractured, cracked or broken so that the brain is exposed or penetrated. When an open head injury occurs, pieces of bone or cerebrospinal fluid may enter the substance of the brain. Considerable local damage can occur in the area of the brain immediately below the impact area, as well as more widespread damage.

An open head injury is more likely to receive immediate treatment, but also poses a high risk of infection through the wound.

Primary versus Secondary Effects

The direct application of physical forces damaging nerve fibres, blood vessels and other brain tissue are commonly referred to as the “primary” mechanisms of traumatic brain injury. Further complications are often called “secondary” mechanisms of brain injury. A large number of secondary complications may occur including: haemorrhage (bleeding), haematoma or blood clot, raised intracranial pressure, hypoxia (loss of oxygen), brain swelling and post-traumatic epilepsy. Such complications require close monitoring and medical management.

In a closed head injury which may only appear to be a case of mild concussion, secondary effects such as a build up of pressure inside the skull are often the biggest causes for concern.

Mild Brain Injury

Sometimes, when the head is struck or moved violently there will be no loss of consciousness and the person may appear not to need medical attention. Even so, there may be some mild damage to the brain that can interfere with the person’s everyday living. The injury may not be diagnosed but the person may be observed responding more slowly than usual or complaining about physical and mental problems. Symptoms of mild brain injury may include fatigue, headache, and dizziness, hearing loss, ringing in the ears, memory problems, sleep difficulties, irritability and short attention span.

Even though termed “mild”, this type of injury can lead to long-term cognitive problems that severely impact on the individual’s life.

How the brain is injured

Three separate processes work to injure the brain in a traumatic event: bruising (bleeding), tearing, and swelling. In a traumatic brain injury, the soft tissue of the brain is propelled against the very hard bone of the skull and then bounced backwards. Blood vessels may tear which releases blood into areas of the brain. The skull does not expand so the blood begins to press on softer things like brain tissue. Brain tissue is very delicate and will stop working properly or may even die off.

The movement of the brain can result in tearing of brain tissue which breaks the connections between neurons. This happens on a microscopic level and may not show on standard medical tests.

The brain can swell in the same way a damaged muscle does. This pressure pushes down on the brain and damages structures in the brain. If there is too much pressure, this can stop important structures that control breathing or the heart rate. Sometimes, doctors will install a “relief valve” to let off the excess pressure.

Non-traumatic brain injury

Non-traumatic injury any cause that does not injure the brain using physical forces. Causes include lack of oxygen, glucose or blood, which can occur through stroke, heart attack, near-drowning, strangulation or a diabetic coma, poisoning or other chemical causes such as alcohol abuse or drug overdose, infections or tumours and degenerative conditions such as Alzheimer’s disease and Parkinson’s disease.

How the brain is injured

In a non-traumatic injury nerve calls may die from the direct action of a toxic substance or through being starved of oxygen, glucose or the blood which supplies both of those substances. Tumours, by taking up space, may restrict blood supply to other cells or may, through exerting physical pressure upon cells, squash them. Infectious substances may cause cell death through exerting pressure if the brain swells (encephalitis) or the tissue surrounding the brain swells (meningitis), or may kill cells through direct infection. Viral infections may result in diffuse injury which can manifest as fatigue disorders such as chronic fatigue syndrome.

There are several mechanisms which may be at work with degenerative conditions. In multiple sclerosis, nerve cells die when the fatty lining which protects them is removed. In many diseases such as Alzheimer’s and Parkinson’s, there is a generalised or localised death of cells but the cause is not known, or very poorly understood.

Differences between traumatic and non-traumatic injury

In a traumatic injury, damage to nerve tissue is usually focused in one or more areas of the brain, although tearing can result in diffuse injury. With a non-traumatic injury, damage is usually spread throughout the brain. Exceptions to this include tumours and an infection that remains localised or that spreads evenly from one starting point. This can make diagnosis difficult because small, scattered areas of damaged tissue may not show up on a CAT scan. An MRI scan will usually show diffuse injury, but is not often used to the increased cost of the scan. Some cognitive abilities, particularly short term memory, are commonly affected. Fatigue is also extremely common, due to the brain having to work harder to work around diffuse areas of injury.

There are many fact sheets available at www.braininjury.org.au that explore the issues raised in more depth.