In layperson's terms, a concussion results from trauma (usally but not always a blow to the head) 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.
According to Dr. Robert Cantu, a concussion causes temporary metabolic changes in brain function, which one expert likens a concussion to a break in the local cables in a television network that results in lengthy re-routing of the call, so that when it finally gets through, it's delayed and full of static.
Five Common Features
While no two concussions are exactly the same, they share the following five characteristics:
- Direct blow to head not required. A concussion may be caused by a direct blow to the head, face, neck, or elsewhere on the body with a force transmitted to the head.
- Rapid onset and gradual resolution of symptoms. A concussion typically results in the rapid onset of symptoms of impaired neurological function that, in most cases, gradually disappear with rest, usually within a week to 10 days (so-called "simple" concussions). When post-concussions symptoms persist, the concussion is considered "complex" under the Prague consensus statement, requiring more specialized management.
- Brain function disrupted. A concussion may result in neuropathological changes but the acute clinical symptoms largely reflect a functional disturbance in brain activity rather than structural injury to the brain itself.
- Loss of consciousness not required. Concussions result in a graded set of clinical symptoms that may or may not involved loss of consciousness (LOC) which follow a sequential course to resolve.
- 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 CAT scans.