What is a "Mild" Traumatic Brain Injury?

A traumatic brain injury (TBI) is an injury that disrupts the normal function of the brain.
TBIs are categorized as mild, moderate, or severe. Most TBIs fall into the “mild” category even though the consequences of these brain injuries may be devastating.
The American Congress of Rehabilitation Medicine (ACRM) established the following definition of a mild traumatic brain injury (mTBI):
A traumatically induced physiological disruption of brain function as manifested by at least one of the following:

Any loss of consciousness
Any loss of memory for event immediately before or after the accident (retrograde or post-traumatic amnesia)
Any alteration in mental state at the time of the accident (e.g., feeling dazed, disoriented, or confused) and
Focal neurological deficits that may or may not be transient (e.g., post-traumatic seizures, intracranial lesions, loss of the sense of smell, visual field deficits, double vision, difficulties with speech, and gait/balance problems).

But where the severity of the injury does not exceed the following:

Loss of consciousness of approximately 30 minutes or less
After 30 minutes, an initial Glasgow Coma Scale of 13-15, and
Post-traumatic amnesia not greater than 24 hours.

Other organizations including the American Academy of Neurology and the World Health Organization have also published definitions of a mTBI. The definition from the ACRM, however, remains the most widely-accepted definition among medical and psychological/neuropsychological experts in the United States..