Brain injury means that the brain has been hurt in some way.  Many different things can hurt the brain.  For example, brain injuries can happen before a baby is even born.  These are called congenital brain injuries.

A physical injury (trauma) can also hurt the brain (for example, if a person hits their head in a car accident).  These types of brain injuries are called traumatic brain injuries.

Many medical problems can also injure the brain.  For example, the brain can get injured if it does not get enough oxygen (for example, during a stroke).

All brain injuries are different.  Some are mild (not very bad); some are severe (very bad).  Some are temporary (they get better); some get better slowly over time; and some never get better.  Also, since the brain controls every part of the body, the symptoms of brain injury can be very different for different people.  This depends partly on what part of the brain was injured, and how badly.

Types of brain injuries

Congenital brain injuries
Congenital brain injuries are caused by something that damages a fetus's brain during a woman's pregnancy.

For example, a fetus can get a congenital brain injury if:
 The mother drinks alcohol while pregnant (this can cause fetal alcohol syndrome)
 The mother takes illegal drugs, or medications that are poisonous to the fetus, while pregnant
 The mother has an infection like rubella, chickenpox, or toxoplasmosis while pregnant

Traumatic brain injuries

Traumatic brain injuries (TBI) are caused by a physical injury to the brain.  They can happen when the head suddenly hits an object very hard, like in a car accident.  They can also happen when something - like a bullet or knife - goes through the head and into the brain.

Traumatic brain injury is one of the most common causes of disability everywhere in the world.  It is more common in developing countries.  All over the world, about 10 million people are affected by TBI every year.

Experts estimate that the most common causes of TBI in the world are:p. 341
 Injuries from road traffic (they cause about 60% of all TBI)
 Falls (about 20%-30%)
 Violence (10%)
 Injuries from working or playing sports (10%)

War and violence are often much more common causes of TBI in certain parts of the world.  In the past, these places have included Sub-Saharan Africa, Latin America, and the Middle East.pp. 344–345

Traumatic brain injury has become one of the most common types of injuries in soldiers serving in Iraq and Afghanistan.  The United States Department of Defense says that 22% of all injuries from these wars are traumatic brain injuries.

Some traumatic brain injuries are mild and can get better with time, like a concussion.  Others are more serious, especially if they cause bleeding or swelling in the brain.

Other brain injuries
Another major type of brain injury is a hypoxic brain injury.  This happens when the brain does not get enough oxygen.  This can happen for many reasons, like:
 Cardiac arrest
 Drowning
 Stroke
 Shock

The brain can also be injured by many other things.  Some examples are:
 Infections like encephalitis and meningitis
 Seizures
 Brain cancer
 Use of illegal drugs or alcohol
 Poisons, like lead

Signs and symptoms
The signs and symptoms of a brain injury depend on many things.

Diffuse or focal

A diffuse injury hurts the entire brain.  For example, if a person is drowning, and cannot breathe, no part of their brain will get oxygen.  If this lasts long enough, the entire brain will be injured by not having enough oxygen.

A focal injury hurts just part of the brain.  For example, in some strokes, a person has a blood clot that blocks the blood flow to just part of their brain.  If the person gets good medical treatment, just that part of their brain may be injured.

This is important because different parts of the brain control different things.  When a person has a focal brain injury, their symptoms will depend on what part of the brain was injured.  For example, if a part of the brain that controls speech was injured, the person may have trouble speaking.

Severity
A brain injury's symptoms may also depend on how bad the injury was.

For example, brain injuries can cause changes or problems in a person's thinking, senses, feelings, or ability to move.  However, some people might have mild problems in these areas, while other people might have more serious problems:

 Thinking problems
 Mild symptoms: Getting distracted easily; feeling confused sometimes; forgetting things easily
 Severe symptoms: Unable to concentrate; getting very confused; unable to remember important things, people, or parts of life; intellectual disability
 Problems with the senses
 Mild symptoms: Being sensitive to bright lights and sounds
 Severe symptoms: Hearing loss; vision loss
 Changes in feelings
 Mild symptoms: Mood changes; depression; anxiety
 Severe symptoms: Long-lasting depression or anxiety; severe, sudden mood changes or aggression; changes in personality
 Trouble moving
 Mild symptoms: Feeling dizzy
 Severe symptoms: Trouble walking; weakness in the arms or legs; trouble with balance

Recovery
There are many different treatments that may help people with brain injuries.  For example:
 Physical therapy can help people re-learn how to move, walk, and balance themselves
 Occupational therapy can help people practice how to do everyday things, like getting dressed and making meals
 Speech therapy can help people who are having trouble speaking after their brain injury
 Psychotherapy can help with depression, anxiety, mood changes, and stress

References

Disability
Diseases and disorders of the brain