Mya Care Blogger 13 Mar 2024

Head injuries are fairly frequent in contact sports, such as football, hockey, and soccer. While most people are aware of the short-term effects of a concussion, there is a potentially life-threatening condition that can result from repeated head trauma: Second Impact Syndrome (SIS).

This article covers SIS's definition, causes, symptoms, and risk factors and the importance of early recognition and treatment.


  • Second Impact Syndrome is a rare condition with a high mortality rate that occurs when an individual acquires a second head injury prior to full recovery from an initial one.
  • Repeated head trauma is the most significant contributing factor to SIS.
  • Early intervention is necessary for a positive outcome.
  • Prevention is critical, and following guidelines can help reduce the risk of head injuries.

What is Second Impact Syndrome?

Second Impact Syndrome is a potentially deadly condition that occurs when an individual acquires a second head injury before completely recovering from a previous one.[1] This rapid progression of brain swelling can lead to severe brain damage, coma, and death. While the prevalence is unknown, studies suggest that mortality rates attributable to SIS are very high, averaging 50-100%.[2]

The concept of second impact syndrome was introduced in an article by Saunders and Harbaugh, published in 1984. They outlined a case study of a football player who tragically died after receiving a second head injury. This tragic event occurred four days after the initial head injury.

Contributing Factors and Causes

SIS is not an officially recognized condition, and the exact mechanism is not fully understood.

Researchers suspect that the initial head injury disrupts the brain's capacity to maintain adequate blood supply, making it more vulnerable to subsequent injury[3]. This disturbance can result in a rapid increase in intracranial pressure upon the second impact, leading to brain herniation and, ultimately, death.

SIS relates to a severe form of CTE. If repeated head trauma does not cause SIS, it can lead to a condition known as chronic traumatic encephalopathy (CTE)[4]. CTE is related to a buildup of damaged proteins in the brain that causes symptoms of brain damage.

The most significant contributing factor to SIS is repeated head trauma. Head injuries can occur in contact sports, such as football, hockey, and soccer, where athletes are at a higher risk of sustaining multiple head injuries. However, SIS can also occur in non-contact sports, such as cheerleading and gymnastics, where falls and collisions can result in head injuries.

Other factors that can increase the risk of SIS include:

  • Age: Younger athletes are more susceptible to SIS due to their developing brains and weaker neck muscles. The prime ages are 13-24 years old.
  • Gender: Males are more likely to acquire SIS than females.
  • Previous head injuries: Individuals who have had a previous concussion or head injury are at a higher risk of developing SIS. Indirect head injuries may also lead to SIS, such as chest injuries that result in whiplash.
  • Lack of proper rest and recovery: Not allowing enough time for the brain to heal after a head injury can increase the risk of SIS.

Symptoms and Diagnosis

The symptoms of SIS are similar to those of a concussion, but they tend to progress rapidly. Unfortunately, most people with SIS die within several minutes of sustaining the second injury.

Therefore, a diagnosis of a severe concussion or initial head injury is the most common way to diagnose and predict SIS susceptibility. The affected person needs to have sustained a second head injury up to several weeks after the initial injury for it to be considered relevant to SIS. The initial injury must be severe enough to leave the brain vulnerable.

SIS is likely to develop in those who experience long-term symptoms from the first injury. Chronic symptoms indicate brain injury and a higher vulnerability to SIS.

Some common symptoms of severe head injury include[5]:

  • Headache
  • Dizziness or loss of balance
  • Nausea and vomiting
  • Confusion
  • Loss of consciousness
  • Seizures
  • Difficulty speaking or understanding speech
  • Weakness or numbness in the limbs
  • Unequal pupil size
  • Trouble seeing clearly or hearing
  • Changes in behavior or personality

If an individual experiences any of these symptoms after withstanding a head injury, it is crucial to seek immediate medical attention.

A medical evaluation, including a neurological exam and imaging scans using a CT scanner or MRI, can help diagnose the extent of a head injury and can help track its progress[6]. Ensuring successful recovery of the initial impact is vital in avoiding or lessening the severity of potential SIS.

Importance of Early Recognition and Treatment

Early recognition and treatment of an initial head impact is crucial for a positive outcome. Successful recovery of the initial impact substantially reduces the chances of contracting SIS.

If an individual displays signs of SIS, it is a medical emergency in which every minute counts. They need to be removed from the activity immediately for urgent stabilization.

If the patient survives, the prognosis is often poor.

The first step in treating SIS is to reduce the swelling and pressure on the brain. Treatment may involve medication, such as diuretics, to decrease the amount of fluid in the brain. In extreme cases where the patient has been stabilized in time, surgery may relieve the pressure.

After the initial treatment, rehabilitation is essential to help the individual recover from any cognitive impairment or physical disabilities caused by the head injury or SIS. The patient may require any combination of physical therapy, occupational therapy, and speech therapy to recuperate properly.

Guidelines for Prevention

The best way to prevent SIS is to prevent head injuries in the first place. The following guidelines can minimize risks associated with contracting head trauma:

  • Proper equipment: Athletes should wear suitable protective headgear to lower the risk of head injuries.
  • Proper technique: Coaches should teach athletes adequate techniques to avoid head injuries, such as tackling in football.
  • Risk education: Athletes, coaches, and parents need to remain informed about the risks of repeated head trauma and the importance of rest and recovery after a head injury.
  • Brain health prioritization: Prioritizing the health and safety of athletes over winning games or returning to play too soon after a head injury is vital for protecting against SIS.
  • Concussion management: Athletes who have sustained a head injury should be closely monitored and receive proper medical attention before returning to play.


Second Impact Syndrome is a severe life-threatening condition that can result from repeated head trauma. It is vital to determine the warning signs and seek immediate medical attention if an individual experiences a traumatic head impact. By following guidelines for prevention and prioritizing brain health, we can reduce the risk of SIS and protect the well-being of athletes. Regarding head injuries, it is always better to steer on the side of caution. The best course of action involves seeking immediate medical attention to ensure a full recovery.

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