A concussion is defined by the Berlin Consensus Guideline 2016 as a traumatic brain injury induced by biomechanical forces. It has a number of common features:
- It may be caused either by a direct blow to the head or elsewhere on the body.
- Onset is usually rapid. However, in some cases, signs and symptoms evolve over a number of minutes to hours.
- Signs and symptoms mostly reflect a functional disturbance rather than a structural injury.
- Most often no abnormality is seen on standard neuroimaging studies.
- It may or may not involve loss of consciousness.
- Recovery of the clinical and cognitive features usually follows a set course. However, in some cases symptoms may be prolonged.