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What is concussion and what causes concussion?

Concussion describes a brain injury where, after an injury, there are functional changes that occur in how the brain works but no structural damage can be seen on standard imaging tests like CT scan.

Mild traumatic brain injury, or concussion, can be defined as a short-lived loss of brain function due to head trauma that resolves spontaneously. With concussion, function may be interrupted but there is no structural damage to the brain.

The brain floats in cerebrospinal fluid and is encased in the skull. These protections allow it to withstand many of the minor injuries that occur in day-to-day life. However, if there is sufficient force to cause the brain to bounce against the rigid bones of the skull, then there is potential for injury. It is the acceleration and deceleration of the brain against the inside of the skull that can cause the brain to be irritated and interrupt its function. The acceleration can come from a direct blow to the head or face, or from other body trauma that causes the head to shake. While temporary loss of consciousness due to injury means that a concussion has taken place, most concussions occur without the patient being knocked out. Studies of football players find that the most of those affected were not aware that they had sustained a head injury.

What are the types of concussion?

All injuries to the brain are potentially serious and devastating. Historically, attempts to decide what symptoms could define a concussion as more or less severe and serious have not been able to adequately describe potential risk or guide the care provider and patient as to when the brain is fully healed.

Concussions in sports are more easily studied than in the general public because of their frequency and the numerous studies on their evaluation and treatment. At present, it is reasonable to think of only one type of concussion, since the mechanism is to shake the brain. More importantly, it is important to recognize that there can be a broad spectrum of symptoms and severity for concussions and understand that most concussion symptoms will resolve themselves within a week or 10 days.

Picture of the brain and potential brain injury areas.
Picture of the brain and potential brain injury areas.

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Concussion Symptoms and Testing

Medical Author: Benjamin Wedro, MD, FACEP, FAAEM
Medical Editor: Melissa Conrad Stöppler, MD

When talking about Title IX, the discussion centers on the increased participation of girls in sports and that's a good thing, but there may be a statistic that is less exciting. While football is king in causing sports head injuries in young athletes, girls' soccer can proudly boast being in second place, beating out hockey, basketball, and wrestling. Regardless of the activity, it is estimated that there are more than 300,000 sports-related concussions every year in the U.S., and that number is likely on the low side. Regardless of whether it's a boy or girl, the number of concussions diagnosed in the past 10 years has increased by more than 50%.

Concussion can be an easy diagnosis when the athlete gets knocked out on the field or is slow to get up, but often, concussions are subtle and even the athlete isn't aware that the brain has been shaken. Being unconscious is not a requirement for diagnosis of a concussion, and symptoms can be delayed by many hours from the trauma that has irritated the brain. The symptoms of a head injury may be as subtle as a child having a hard time concentrating in school, having difficulty with homework, or being more irritable at the dinner table. Recurrent headaches, dizziness, and lethargy are more easily recognizable by parents or friends. While the medical literature uses the term minor head injury, there is nothing minor about a brain that has been concussed.

More typical symptoms of a concussion include:

  • headache,
  • dizziness,
  • nausea,
  • a dazed feeling,
  • irritability, and
  • visual problems.