There are many types of acquired brain injury (ABI). It is a broad class of brain injuries that are neither genetic nor acquired during birth, and are typically identified as traumatic or non-traumatic. These injuries produce a wide variety of symptoms that range from moderate to severe. In most cases, the cause of the injury is readily apparent, with symptoms beginning shortly after the initial injury. For some ABI survivors, though, symptoms only appear months or years later, and may be intermittent and unpredictable.

Traumatic Brain Injuries

Traumatic brain injuries (TBI) are the leading cause of brain injuries, with at least 1.7 million people sustaining such injuries each year. About 52,000 people die of their injuries, which are commonly caused by car accidents, falls, blunt force trauma, and sporting injuries.

As the name implies, what differentiates a TBI from a non-traumatic brain injury is that TBIs are caused by trauma to the head—not diseases, cancer, or tumors. TBIs can lead to non-traumatic injuries, such as infections or dangerous swelling, but these injuries must be treated secondarily to the TBI itself.

*To learn more about specific types of TBI, visit our “Types of Traumatic Brain Injury” page.

Non-Traumatic Brain Injuries

The “trauma” in TBI refers to physical trauma, not psychological trauma. Non-traumatic brain injuries can be every bit as emotionally challenging as traumatic ones. They also demand prompt treatment. If you suspect you or someone you love has suffered a non-traumatic brain injury, or if you notice changes in mood, cognition, personality, or consciousness, prompt treatment could be life-saving.


Brain infections can occur through many processes. Sometimes a serious infection, such as staph, spreads through the blood to the brain, damaging brain tissue. In other cases, a brain injury makes it easier for bacteria to get into the brain, undermining brain function and health. One of the most common brain infections, meningitis, occurs in both a bacterial form and viral form. It produces high fevers, and is more common in childhood. A number of communities have faced meningitis outbreaks. 

A related condition, encephalitis, causes damage similar to that associated with a brain infection. Encephalitis is swelling of the brain tissue. The swelling itself can impede brain function until it goes down. Swelling may also damage surrounding brain tissue, or result in other problems, such as loss of oxygen to the brain or fluid on the brain. Brain swelling is often the product of an infection, but can also be due to an untreated autoimmune disorder, cancer, and even some allergic reactions.


Not all brain tumors are cancerous, but even benign tumors can cause brain damage. When a brain tumor pushes on a region of the brain or deprives it of oxygen, function may be impaired. Sometimes removing the tumor fixes the problem, but brain surgery is a risky undertaking. In some cases, the damage might already have been done. If the tumor is not growing, your doctor might elect to leave it in place and avoid the risk of surgery.

When a tumor is due to brain cancer, your doctor might remove it, recommend chemotherapy or radiation, or offer some combination of these treatments.


A stroke is a cardiovascular event that temporarily cuts off blood supply to the brain. In most cases, it's due to a blood clot that narrows a vein or artery or travels to a region that affects blood flow to the brain. Poor cardiovascular health is the most significant predictor of strokes, though anyone—including children—can suffer from a stroke.

A related occurrence, called a transient ischemic attack (TIA), is sometimes called a mini-stroke. These episodes, which sometimes occur multiple times, produces a temporary blockage that quickly resolves. If you have suffered a TIA, you are at risk of a stroke. Some people also experience minor brain damage as a result of TIA.

Locked-in Syndrome

Locked-in syndrome is often caused by a stroke, and results in brain damage so significant that the survivor cannot speak or move, but may be able to move the eyes. Consciousness remains fully in tact, so the victim of such an injury is quite literally locked into his or her brain. Doctors must be careful to differentiate between vegetative states and locked-in syndrome, since a cursory review may cause locked-in syndrome to appear as though the person has completely lost conscious awareness.

Arteriovenous Malformation (AVM)

In HBO's hit drama Six Feet Under, the specter of arteriovenous malformation (AVM) drove many of Nate's decisions. Surgery to correct the AVM ultimately claimed the character's life. AVM is a condition that causes blood vessels to malform. Sometimes the blood vessels are in the brain. Though the condition is often congenital, most people don't know they have it until the malformed blood vessels cause a problem—either by cutting off blood supply, rupturing, or pushing on part of the brain. When this occurs, injuries range from minor dizziness to catastrophic, including strokes and other life-threatening events.

Brain Hemorrhage

Bleeding in the brain is known as a brain hemorrhage. Hemorrhages are typically caused by some other problem, including a sudden blow to the head, a rupture blood vessel, a tumor pushing on the brain, or even a brain infection. The bleeding ranges from minor to life-threatening, and may temporarily impede brain function. When the bleeding spreads to other areas of the brain or deprives the brain of oxygen, the damage may be permanent.

Loss of Oxygen

Hypoxia is reduced oxygen to the brain, while anoxia refers to a total deprivation of oxygen. Anoxisia typically more dangerous, but both can spur catastrophic brain damage. Minor brain damage may begin as early as one minute into the oxygen deprivation, while lasting and severe damage requires only four minutes of oxygen deprivation. At the four to six minute mark, oxygen deprivation becomes fatal.

The brain can be deprived of oxygen in many ways, including:

  • Drowning
  • Choking
  • Anaphylactic shock
  • Allergic reactions to various substances 
  • Drug and alcohol overdoses 
  • Physical assaults 
  • Strokes

Surgical Complications

Sometimes surgery to remove a tumor or other growth in the brain produces a brain injury, such as a hemorrhage, stroke, or damage to surrounding brain tissue. This injury might be unanticipated. IN some cases, though, the risk of not performing surgery is greater than the risk associated with the surgery, so doctors opt to pursue treatment even though it poses a substantial risk of producing some form of brain damage.


Most forms of dementia, including Alzheimer's, are caused by deterioration in the brain tissue. Alzheimer's, for instance, is thought to be the product of brain plaques that steadily worsen over time. Occasionally dementia is the product of some other illness, such as when a stroke causes aphasic dementia—a type of dementia that impedes the ability to speak or understand words. More typically, dementia is an independent process that appears on its own.

Other Causes

The above concerns are not the only potential types of acquired brain injury (non-traumatic). Some other common sources of these injuries include:

  • Seizures, especially grand mal seizures that last longer than 60 seconds.
  • Diabetes and some other endocrine system disorders.
  • Reaction to a medical procedure or prescription drug.
  • Exposure to certain environmental toxins, or as the result of asphyxiation due to smoke inhalation.