September 20, 2019 at 6:08 am

Brain Injury 101: Second Impact Syndrome

The brain is a complex organ that controls numerous functions, including mobility, speech, and memory. When a brain is injured, the repercussions can be severe and, in some cases, deadly.

Sadly, concussions and other brain injuries happen frequently. It is estimated that as many as 3.8 million concussions per year occur in the U.S., and that number only includes those resulting from sports or recreational activities. Thankfully, many first-time concussions have minimal lasting effects.

When the brain receives repeated trauma, however, the severity of the consequences increases.

What Is a Concussion?

A concussion occurs when there is trauma to the head, often in the form of a jolt or blow. During this incident, the brain moves within the skull, harming the brain cells and, possibly, the organ itself.

It’s difficult to tell how long concussions last because the recovery rate depends on the injury. To measure the severity of a concussion, doctors separate them into grades 0 to 4.

Concussions generally take seven to 10 days to heal, but grade 3 or 4 concussions, which involve loss of consciousness and are the most severe types, can take weeks or even months.

What Is Second Impact Syndrome?

Second Impact Syndrome (SIS) occurs when someone receives another concussion to the head while the brain is still recovering from a previous one. The definition, frequency, and at-risk populations associated with SIS are widely disputed among researchers.

Cases of Second Impact Syndrome are rare, but the consequences are extreme.

After sustaining the first head injury, the brain protects itself by limiting cerebral blood flow, which researchers believe discourages swelling.

After a second injury occurs, the organ can no longer regulate cerebrospinal fluid pressure, and the brain swells.

In some cases, this results in fluids around the brain and brain herniation, a condition that moves brain tissues because of pressure buildup. Blood flow to the brain is cut off.

Should the injury lead to these consequences, it is likely the individual will die within minutes. Those that survive often face lifelong disabilities.

One health expert described it as “a rare and disastrous brain injury with terrible consequences.”

What Are the Symptoms?

Unfortunately, the onset of SIS occurs so quickly that symptoms may not be readily apparent until it is too late.

After the second trauma to the head, an individual may show no signs of distress until he or she collapses, although symptoms may include dilated eyes and respiratory failure. Individuals may continue their activities for a few minutes before falling unconscious.

What Are the Effects?

Death occurs in approximately 50% of individuals who suffer from SIS. For others, the injury may lead to lifelong complications, including:

  • Mental disability
  • Hallucinations
  • Epilepsy
  • Muscle spasms

The second injury can be mild, with even a light blow to the chest having enough force to lightly shake the brain and cause SIS.

Who Is at Risk?

Health professionals and researchers debate the populations most at risk for SIS. However, almost all agree that younger athletes appear to be the most vulnerable.

Because individuals involved in sports may experience regular jolts, a concussion can go undiagnosed for weeks. Further, it’s estimated athletes who have suffered from one concussion are three to six times more likely to experience another than those who have never had one.

How Is It Diagnosed?

Diagnosing a concussion or SIS involves a CAT scan to show injuries to the head. The CAT scan will reveal any structural brain damage, which a neurosurgeon can then analyze.

To date, few tests have been conducted on possible treatment opportunities directly after the injury occurs. Current treatment options are more lengthy therapies.


Second Impact Syndrome is a serious and life-threatening condition. As with many other health issues, the best defense against SIS is a good offense.

Focusing on prevention includes knowing the signs of a concussion and being vigilant about avoiding activity that could lead to additional injuries after a concussion. For athletes, this may require sitting on the sidelines until the brain fully heals.

Symptoms from a concussion may appear days or weeks after the initial injury. They may cause:

  • Unconsciousness
  • Dizziness
  • Irritability
  • An inability to concentrate
  • Fatigue

However, if individuals work together to identify and prevent concussions, especially within athletics, we take the first step toward eliminating this serious and deadly condition.

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