Types of Traumatic Brain Injury

From mild to severe

Mild Traumatic Brain Injury

Mild traumatic brain injury and concussion are not exactly the same things.

"Mild" is a subjective term, but in the medical world, there are criteria that are accepted as reasonably objective measures of “mild.”

The Glasgow Coma Scale is a simple, but reliable clinical measure of responsiveness that is used at an accident scene, in the emergency department or in the intensive care unit (ICU) to define the severity of a patient’s injury.

The American Congress of Rehabilitation Medicine (ACRM) devised a more specific set of criteria to define “mild” that takes other factors into account: how long the patient was unconscious, how long the patient was confused or experienced memory loss and the type of brain injury seen on CT scan. 

To a non-medical person, these criteria probably do not seem very “mild,” but research has shown that they are roughly accurate predictors of long-term recovery.


Concussion is often used as a synonym for “mild traumatic brain injury,” but the medical community uses this term only for injuries at the most mild end of the mild traumatic brain injury spectrum. All of these medical definitions include a brief period of loss or alteration of consciousness and/or a brief lapse of memory following injury.

No medical test currently confirms or measures concussion. This may be available in the near future.

Here is a more clinically precise definition cited directly from the 3rd International Conference on Concussion in Sport (2008):

“Concussion is a complex pathophysiological process affecting the brain, induced by traumatic biomechanical forces … Concussion typically results in the rapid onset of short-lived impairment of neurological function that resolves spontaneously …a graded set of clinical symptoms that may or may not involve loss of consciousness.”

The implications of this definition provide clinical guidance:

  • Concussion “affects the brain,” not just the head; bleeding scalps and hurting heads are not concussions.
  • People recover from concussions
  • Only in a small percentage of cases are post-concussive symptoms prolonged

The conference report endorsed the conclusion that the symptoms of concussion fall into one of three general areas: Somatic (physical), cognitive (brain function), and emotional (psychological). Thinking of a patient’s symptoms in this manner can guide treatment better than collapsing all symptoms into “post concussion syndrome."

Moderate to Severe Brain Injury

In the acute phase after injury, severity is defined by the Glasgow Coma Scale. Patients with a certain Glasgow Coma Score number are not responsive except perhaps to pain – what a layperson would consider to be coma.

Coma in severe injury may be prolonged. Emergence from coma will almost always follow a path of low arousal to agitation to confusion to orientation but still impaired cognition, and finally slow improvement in cognition. There are several clinical scales that physicians and therapists use to follow this improvement. Although the focus of recovery is on cognitive and behavioral problems, more severe injury can also cause substantial problems with movement, speech and walking.

Subdural or epidural hemorrhages (bleeding) are outside the brain and do not directly cause brain damage. If large, either may cause brain damage by compression (herniation) and contribute to early severity. Epidural hematomas, in particular, may accumulate very quickly and cause death if removal is delayed when they are large. Once removed, however, there need not be any residual brain damage from these hemorrhages.

Focal cortical contusions (FCC) are bruises on the surface of the brain. These can be associated with “complicated” mild injuries. They can be caused by direct trauma often associated with skull fracture and subdural hematoma (bruising). In this case, the focal cortical contusions might be located anywhere over the surface of the brain. They can also be caused by momentum of the brain against the inner surface of the skull. 

Like stroke, which is another cause of injury to specific parts of the brain, focal cortical contusions do not cause coma. They do produce impairments based on the functions of the damaged parts of the brain.