Concussion injuries are invisible.  No one can look at the inside of the brain to see evidence of the concussion.  In most cases, there are no imaging tests (Xrays, MRIs, CT scans) that can look inside the brain to see the injury. The concussion diagnosis must be made almost always made on the basis of the clinical evaluation with careful emphasis on the history and symptoms.

Concussions are invisible for yet another reason-the initial symptoms are not readily apparent.  Many of the immediate symptoms are gone by the time the victim gets to the emergency room.  On the other hand, many of the symptoms of a concussion do not develop until days, weeks, or months later.  (Mayo Clinic says most are manifest in 7-10 days after injury).  See the section on Delayed Symptoms of Concussion.)

A recent example is illustrative.  All of the 200 US soldiers in the military base in Iraq that was attacked by Iranian missile in January 2020 were declared “injury-free” the next day after the attack.  One month later, it was determined that more than 50% (107 of 200) had suffered a concussion injury.

A University of Minnesota football quarterback was hit in the 3rd quarter.  He finished the game, calling plays, passing and running the football with a high level of Division 1 skill.  It was not until 3 days later that he was diagnosed with a concussion.

Even after so-called “recovery” the residuals can be “invisible” but important.  A study at the University of Georgia tested students who had been diagnosed with a concussion and declared to be “recovered”.  When their ability to safely drive a motor vehicle was tested with driving simulator tests, the participant exhibited poor vehicle control, especially when negotiating curves-at times similar to someone driving under the influence of alcohol.

Concussions are also invisible for yet another reason. There are no symptoms that are unique to a concussion.  Almost all concussion symptoms are shared by other medical problems.  They can be present but don’t necessarily point to a concussion as opposed to some other medical condition.  (The one symptom that is common to all concussions is that of a period of “alteration of mental function” (i.e. “brain fog”) following a forceful blow to the head or to any part of the body with is transferred to the head causing a “whiplash” of the brain.)

Finally, the concussion is often “invisible” to the victims themselves.  Because of their altered mental function, they often cannot comprehend their own situation.

All of these factors contribute to making so many concussions “invisible”.