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From Dr. Robert Cantu

Concussion Defined

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A concussion is defined as trauma (e.g. usually but not always a blow to the head, face or neck) which causes the brain - a jellylike structure which is normally protected from collisions with the skull by a tough, fluid-filled membrane - to collide with the skull. A "concussion" is derived from the Latin concutere, meaning to shake violently. It is also often referred to as an MTBI (mild traumatic brain injury). A concussion  typically results in the rapid onset of symptoms of impaired neurological function that, in most cases, gradually disappear spontaneously with rest, usually within a week to 10 days. CT or MRI scans are usually normal.
  • Brain function disrupted. A concussion may result in neuropathological changes but the acute clinical symptoms largely reflect a functional disturbance in the brain rather than structural injury.

  • Loss of consciousness not required. Concussions result in a graded set of clinical symptoms that may or may not involved loss of consciousness (LOC). Resolution of clinical and cognitive symptoms typically follow a sequential course, but in a small percentage of cases, post-concussive symptoms may be prolonged.

  • Normal MRI/CAT scans. Concussion is typically associated with grossly normal structural neuroimaging studies. In other words, unlike other injuries, concussions are usually injuries no one sees and, contrary to popular belief, don't show up on most magnetic resonance imaging (MRI) exams or CT scans. A brain CT - or, where available, MR brain scan - should, however, be conducted if symptoms of a more serious brain injury are present.