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Types of brain injury

There are two methods of classifying a brain injury:

1. How the injury is sustained

2. The severity of the injury

How the injury is sustained

How a brain injury is sustained can be broken down into three main categories: traumatic brain injury, acquired brain injury, and congenital brain injury.

Traumatic brain injury

Traumatic brain injury (TBI) is an injury to the head or brain caused by some form of external trauma. For example, this may be the result of an assault, fall or a car accident. Such trauma causes the brain to move around inside the skull (or damages the skull itself), in turn causing damage to the brain.

In addition to any damage caused by the initial injury, the trauma causes something called a ‘secondary injury’. Examples of this include a change in blood flow to the brain, or a change of pressure within the skull.

Acquired brain injury

Acquired brain injury (ABI) is the term used to describe any brain injury (including those that are traumatic brain injuries) that occur after birth.

The most common cause of an ABI is from a build-up of pressure on the brain. Examples of what may cause this include a tumour (unwanted cell growth associated with cancer), or a neurological illness such as a stroke (a blood clot in the brain).

Congenital brain injury

Both traumatic and acquired brain injuries refer to an injury that is sustained during or after birth. A congenital brain injury (CBI) is the term used to describe a brain injury that occurs while a baby is still in the womb.

It can be caused by disorders, genetic defects, or as a result of something happening to the mother during pregnancy.

The three levels of severity

The severity of an injury is very dependent on its type and location, and must be considered on a case-by-case basis by a medical professional. They will be categorised as minor, moderate, or severe.

Minor brain injury - cerebral concussion

A minor brain injury is commonly referred to as concussion (or cerebral concussion), and common symptoms include brief unconsciousness, nausea, dizziness, mild confusion and headaches.

It is the most common type of head injury, yet the least dangerous. Around 80% of all head injuries are concussions, with the majority of them occurring in children and youths ages between 5 and 14.

Even with mild head injuries, it's important to go to your local hospital and see a medical professional to ensure that the injury is not serious. This is because even mild head injuries can lead to complications. Even if you are initially discharged, be on the lookout over the next few days for the following symptoms.

  • Falling unconscious
  • Worsening disorientation
  • Difficulty in walking
  • Problems with communication
  • Weakness in the arms or legs
  • Blurred vision
  • Vomiting
  • Inability to be woken or unusual drowsiness
  • Clear fluid coming from the ears or nose
  • Severe headache that is not relieved by painkillers

If you experience any of these symptoms, make sure to go back to the hospital, because whilst unlikely, mild brain injuries can sometimes develop into something worse.

Moderate brain injury

A moderate head injury is an injury that causes between 15 minutes and 6 hours of unconsciousness. If the person experiences amnesia up to 24 hours after the injury, it is also classed as a moderate brain injury. Hospital policy with moderate brain injury is to keep the patient overnight, in order to properly assess the damage and ensure that no serious secondary injuries take place.

Moderate head injury makes it very likely that the victim will suffer some of, but not limited to, the following effects:

  • Fatigue

  • Headaches

  • Dizziness

  • Low attention span and an inability to concentrate

  • Poor memory

  • Irritability

One of the issues that arise from a moderate brain injury is that victims often expect their symptoms to go away within a few days. This is unlikely to be the case, as it is typical for symptoms following a moderate brain injury to last between 6 to 9 months. After several weeks, patients who expect to be healthy within a few days can become very anxious that the problems will be permanent. This anxiety can lead to further problems, creating a vicious cycle.

Severe brain injury

A head injury is classed as severe if the sufferer is rendered unconscious for over 6 hours. It is also classed as a severe injury if they suffer amnesia for more than 24 hours.

With severe brain injury, the person will often need to be hospitalised and may suffer permanent and life changing disabilities. These disabilities can be cognitive, behavioural or physical and rehabilitation is required in order to minimise their severity as much as possible.

The extent of the disabilities sustained largely depends on how long the person is unconscious. The longer that this is, the more likely it is that the person will suffer a serious deficit. ‘Very serious injury’ is a further category for those who remain unconscious for 48 hours or more.

Please note this information is a generalisation. The complexity of severe brain injuries means that every case is unique, and only a medical professional who is familiar with the particular circumstances in question can give you in-depth advice. It is possible for someone with a mild brain injury to make limited recovery, just as it is possible for someone with a severe injury to make a complete recovery.

For more in-depth discussion of the aftermath of head injuries, visit our effects of brain injury page.