What Is an Acquired Brain Injury? An Australian Guide

What is an acquired brain injury? An Australian guide

Acquired brain injury is the most common disability nobody can name.

Roughly 2% of Australians have one. On the figures in Brain Injury Australia’s statistics fact sheet, drawing on AIHW survey data, 338,700 Australians had a disability related to ABI, of whom 160,200 were severely or profoundly affected and needed daily support. The fact sheet notes that this is almost certainly an underestimate, because it relies on people identifying themselves in a survey — and a great many people with a brain injury either do not know they have one or would not describe it that way.

And yet “acquired brain injury” is a term most Australians could not define, and the people who have one are routinely described as something else: difficult, unreliable, aggressive, lazy, drunk, or simply rude.

This guide explains what an ABI actually is, what causes it, and why it behaves so differently from the disabilities people are more used to thinking about.

The definition, and what it rules out

An acquired brain injury is damage to the brain that happens after birth. That is the whole of the definition, and the timing is the only thing it specifies.

Which means ABI is not one condition. It is a category containing dozens of causes with very different trajectories, united only by the fact that the brain was developing or developed normally and then something happened to it.

Three distinctions matter, because they determine what support looks like.

ABI is not intellectual disability. Intellectual disability is present from birth or early childhood and affects development. A person with an ABI developed typically — went to school, learned to drive, held a job, had a personality — and then sustained damage. That difference is not academic. Someone with an ABI remembers being the person they were before, which creates a grief that is specific to this group and is frequently mistaken for depression or denial.

ABI is generally not progressive. Unlike dementia, Parkinson’s disease or multiple sclerosis, most ABIs are a single event followed by a long recovery. The brain does not keep getting worse. Where a condition is progressive — some forms of alcohol-related brain injury, or a degenerative dementia — it sits outside the usual ABI framing.

ABI is not mental illness, although the two coexist constantly. Depression, anxiety and substance use are all more common after a brain injury, and brain injury is more common among people with mental illness. Treating one and ignoring the other produces poor outcomes in both.

What causes it

The causes divide into traumatic and non-traumatic, and the division matters because it determines which funding system a person ends up in.

Traumatic brain injury

External force to the head: a car crash, a fall, an assault, a sporting collision, a workplace accident.

The best current Australian data comes from the ATBIND study published in the Medical Journal of Australia, which counted moderate to severe TBI across 23 major trauma services from 2015 to 2020:

• 16,350 hospitalisations — about 3,270 a year, roughly nine admissions a day
• 2,437 in-hospital deaths, a mortality rate of 14.9%
• Mean age 50.5 years
• 71.2% were men
• Falls caused 49.4% of admissions; transport-related injuries 34.9%; being struck by a person, animal or object 9.9%
• 98.1% were blunt trauma

Two findings in that data are worth separating out, because together they explain why ABI services struggle to serve everybody.

Male admissions peaked in the 20s; female admissions peaked in the 80s. The population with moderate to severe TBI is really two populations: young men injured in vehicles, at work, in assaults and playing sport; and older people, disproportionately women, who fell. Among people aged 65 and over, falls caused 78.5% of admissions. Among those under 65, transport was the leading cause.

Those two groups need almost entirely different things, and they land in different funding systems.

Neither hospitalisations nor deaths changed significantly across the five years. The authors’ conclusion is blunt: more effective care strategies are required, particularly among younger men.

A note on concussion, which is mild TBI. Most people recover fully within weeks. A minority develop persisting symptoms, and repeated concussion — in contact sport, in domestic violence — carries risks that are now taken considerably more seriously than they were a decade ago.

Non-traumatic brain injury

Stroke, which is the largest single cause of ABI in Australia and has its own body of practice. We cover it separately and in depth in our stroke guides — everything there about aphasia, hemiplegia, neglect and rehabilitation applies, and this ABI series does not repeat it.

Hypoxic and anoxic injury, where the brain is starved of oxygen: cardiac arrest, drowning, overdose, strangulation, anaesthetic complications, severe asthma. These injuries are typically diffuse rather than focal, which means the effects are spread across memory, attention and coordination rather than concentrated in one function. Recovery tends to be less complete than from a focal injury of comparable severity.

Infection — meningitis, encephalitis — including autoimmune encephalitis, which is now recognised far more often than it used to be and which can produce profound psychiatric presentations before anybody looks for a neurological cause.

Brain tumours and their treatment. Damage can come from the tumour, from surgery, or from radiotherapy, and the effects may emerge years later.

Alcohol-related brain injury, which is substantially under-diagnosed in Australia and gets its own guide: alcohol-related brain injury.

Other causes including epilepsy-related damage, metabolic disorders, poisoning (carbon monoxide, solvents), and neurosurgical complications.

Why ABI is called the invisible disability

Because the things it damages are mostly not visible.

A person with a significant brain injury may walk normally, speak fluently, look well, and pass a casual conversation — while being unable to remember what was agreed yesterday, plan a week, judge a risk, recognise when they have offended someone, or stop themselves saying the first thing that occurs to them.

The commonest consequences of ABI are:

Memory, particularly forming new memories. Old memories are often intact, which produces the characteristic situation of a person who can describe their wedding in detail and cannot recall this morning’s appointment.

Executive function — planning, organising, initiating, sequencing, switching tasks, judging risk, monitoring their own performance. This is frequently the most disabling consequence and the least visible.

Attention and processing speed.

Fatigue, which is near-universal and is not ordinary tiredness.

Insight, which is the hardest of all, because a person who cannot perceive their own deficits cannot be reasoned into accepting support.

Behaviour and emotional regulation — disinhibition, impulsivity, irritability, aggression, apathy, emotional lability. These are the consequences that cost people their relationships, their housing and their liberty.

That last point is not rhetorical, which brings us to the statistic that should be much better known.

ABI in the justice system

Against a general population prevalence of about 2%, a Corrections Victoria study found acquired brain injury in 42% of male prisoners and 33% of female prisoners in Victorian prisons — roughly twenty-one and sixteen times the community rate, as the Enabling Justice project sets out.

Sit with that for a moment. Something approaching half of the men in Victorian prisons have a brain injury.

The pathway is not mysterious. A brain injury impairs impulse control, judgment, memory and the ability to read a situation. It makes a person more likely to react badly to a police officer, less able to follow bail conditions they cannot remember, less able to explain themselves in a courtroom, less able to comply with a program they cannot organise their week around. And because the disability is invisible, none of that gets recognised as disability. It gets recognised as a bad attitude.

The Enabling Justice project’s conclusion is that over-representation will only fall when the justice system recognises the disability and the people living with it are actually listened to.

The practical implication for families: where a relative with a brain injury is dealing with police or a court, put the injury on the record in writing at the earliest opportunity and request a disability advocate. Matters are handled differently once it is documented, and hardly anybody thinks to do it.

Severity, briefly

Brain injury severity is classified mainly by the Glasgow Coma Scale on arrival and the duration of post-traumatic amnesia, and the categories run from mild through to very severe.

It matters more than people expect, for one reason beyond prognosis: severity determines eligibility for the compensation schemes, which fund support at a level the NDIS often does not. The NSW Lifetime Care and Support Scheme, for instance, uses post-traumatic amnesia of more than one week as its brain injury threshold.

We have set this out in brain injury severity: PTA and GCS explained and the funding consequences in compensation schemes and brain injury.

The funding question, which is the thing to get right first

ABI is the one disability category where which system you end up in depends on how you were injured, and the differences are enormous.

• Injured in a motor vehicle accident? Depending on the state and the severity, a lifetime care scheme may fund you — NSW’s Lifetime Care, Queensland’s NIISQ, Victoria’s TAC — generally more generously than the NDIS, and regardless of fault.
• Injured at work? Workers compensation, with its own catastrophic injury provisions.
• Injured any other way — a fall at home, a cardiac arrest, meningitis, an assault, a tumour — the NDIS, if you are under 65 and meet the disability test.
• Over 65 at the time you apply? The aged care system, which is a materially different proposition.

Two people with identical injuries can therefore have entirely different support for the rest of their lives, decided by the circumstances of a single afternoon. That is not a defensible system, and it is the system we have. The practical response is to find out quickly which door you are standing in front of, because the time limits are real — three years for a NSW Lifetime Care interim application, for instance.

What recovery actually looks like

Families are given two incompatible stories: that the brain cannot repair itself, and that with enough determination anything is possible. Neither is useful.

What is true is that dead neurons are not replaced, and that the brain reorganises. Undamaged regions take over functions, pathways strengthen with use, and the person relearns. That process is driven by repetition and practice, which means recovery is something a person does rather than something that happens to them while they wait.

The rough shape:

The acute phase, measured in days to weeks, where the medical priority is survival and preventing secondary damage from swelling, pressure and oxygen deprivation.

Post-traumatic amnesia, in traumatic injury — a confused, disoriented, often agitated state that is a stage of recovery rather than a glimpse of the final outcome. Families who see a relative swearing, hitting out and failing to recognise them during PTA frequently conclude that this is who the person now is. It usually is not, and knowing that in advance prevents a great deal of unnecessary despair.

The fast phase, the first six to twelve months, where change is most rapid.

The long phase, which continues for years. Improvement slows and does not stop, and the gains in this period are almost entirely a function of whether anything structured is still happening.

Two honest caveats. The claim that recovery stops at two years is not supported by the evidence, and what usually stops at two years is the therapy. And equally, many people do not return to their previous function, and being pushed indefinitely toward an unreachable goal is its own harm. Good rehabilitation does both jobs: restoring what can be restored and building workarounds for what cannot. See rehabilitation after brain injury.

The part about families

ABI is unusual in how heavily the consequences fall on the people around the injured person, and it deserves naming.

Where a person’s memory, judgment, insight and emotional regulation have changed, their relationships change with them. Spouses describe being married to someone who looks identical and behaves like a stranger. Parents of adult children find themselves parenting again, decades after they stopped. Adult children find themselves managing a parent who does not accept management.

Several things about this are specific to brain injury rather than disability generally:

The grief has no ritual. The person is alive, so there is no funeral, no acknowledgment and no socially sanctioned mourning for the relationship that existed before. Families describe feeling that they are not allowed to grieve.

The behaviour is not personal and is experienced personally. Knowing intellectually that disinhibition is a frontal lobe injury does not make being insulted in front of your children feel neutral.

Insight problems put families in an impossible position. Someone who does not accept that they cannot drive, cannot manage money, or cannot be left alone with children forces their family into the role of the obstacle.

Separation rates are high, and the people who leave are frequently judged for it by people who have not lived it.

What helps, concretely: family counselling with someone who understands brain injury rather than generic relationship counselling; respite used before exhaustion rather than after; Carer Gateway on 1800 422 737, which is free and provides counselling, coaching and respite; and peer contact with other families, because the single most common thing families say is that nobody else understands.

Where to go next

If the injury is recent, read brain injury severity and compensation schemes first. Getting the funding question right in the first months shapes everything afterwards.

If behaviour is the issue, read insight and behaviour after brain injury and then behaviour support and restrictive practices.

If memory and organisation are the problem, cognition and memory after brain injury.

If the cause was a stroke, go to the stroke guides instead, which cover that ground specifically.

Synapse is the national ABI organisation and worth contacting — it runs information and advocacy services and understands this better than most. Brain Injury Australia is the national peak body for policy and advocacy. State brain injury associations exist in most states.