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Second-impact syndrome

second impact syndrome, second impact syndrome concussion
Second-impact syndrome SIS occurs when the brain swells rapidly, and catastrophically, after a person suffers a second concussion before symptoms from an earlier one have subsided This second blow may occur minutes, days or weeks after an initial concussion,1 and even the mildest grade of concussion can lead to SIS2 The condition is often fatal, and almost everyone who is not killed is severely disabled The cause of SIS is uncertain, but it is thought that the brain's arterioles lose their ability to regulate their diameter, and therefore lose control over cerebral blood flow, causing massive cerebral edema2

Most cases of SIS have occurred in young people, who are thought to be particularly vulnerable In order to prevent SIS, guidelines have been established to prohibit athletes from returning to a game prematurely For example, professionals recommend that athletes not return to play before symptoms of an initial head injury have resolved3

Due to the very small number of recorded cases of SIS, there is doubt about whether it is a valid diagnosis However, the syndrome is recognized by physicians4


  • 1 Epidemiology
    • 11 Risks
  • 2 Features
  • 3 Pathophysiology
  • 4 Prevention
  • 5 Diagnosis
  • 6 Treatment
  • 7 Prognosis
  • 8 History
  • 9 Controversy
  • 10 See also
  • 11 References


Though the incidence of second impact syndrome is unknown,5 the condition is rare; very few cases have been confirmed in medical literature1 In the 13-year period from 1980–1993, 35 American football related cases of SIS were recorded, but only 17 of these were confirmed by necropsy or surgery and magnetic resonance imaging to be due to SIS, and 18 cases were found to be probably SIS-related2 Additionally, the initial trauma commonly goes unreported, adding to the confusion about how often the syndrome occurs6

By one estimate, the syndrome kills four to six people under the age of 18 per year7 According to the Centers for Disease Control, about 15 people die each year from concussion in the US; in most of these cases, the person had received another concussion previously8

In part due to the poor documentation of the initial injury and continuing symptoms in recorded cases,9 some professionals think that the condition is over-diagnosed,1 and some doubt the validity of the diagnosis altogether10


Second-impact syndrome shares all the risk factors of concussion; that is, those who are at increased risk for concussion are also at higher risk for SIS Thus, people who participate in sports such as boxing, soccer, American football, baseball, rugby, basketball, ice hockey, pro wrestling, and skiing especially Alpine are at increased risk8 The condition most commonly occurs in American football11

Second-impact syndrome disproportionately affects teenagers All documented cases occurred in people younger than 20 except in boxing12 As of 2000, the syndrome had never been reported in the medical literature in children younger than adolescent age13 Young athletes have been found to be both more susceptible to concussions and more likely to get second-impact syndrome than their older counterparts14 However, SIS is also a concern for adult athletes15 Adolescent and young adult males who play American football or hockey, or who box or ski are the most common sufferers of the condition6 Every documented case of SIS has occurred in males, but it is not known whether this is due to a special vulnerability or to a greater exposure of males to second impacts16

Studies have found that people who have received one concussion are at a higher risk to receive a concussion in the future17


SIS is the most serious potential complication that could result from an athlete returning to a game before symptoms from a minor head injury have subsided18 Such symptoms include headache, cognitive difficulties, or visual changes1

The initial injury may be a concussion, or it may be another, more severe, type of head trauma, such as cerebral contusion19 However, the first concussion need not be severe for the second impact to cause SIS20 Also, the second impact may be very minor, even a blow such as an impact to the chest that causes the head to jerk, thereby transmitting forces of acceleration to the brain21 Loss of consciousness during the second injury is not necessary for SIS to occur2223 Both injuries may take place in the same game12

The athlete may continue playing in the game after the second concussion, and may walk off the field without assistance, but symptoms quickly progress and the condition can rapidly worsen24 Neurological collapse can occur within a short period,13 with rapid onset of dilating pupils, loss of eye movement, unconsciousness, and respiratory failure24 Failure of the brain stem frequently occurs between two and five minutes after the second impact,1224 and death can follow shortly22

SIS is sometimes associated with a small subdural hematoma12


Types of brain herniation25 1 Uncal 2 Central - The brainstem herniates caudally 3 Cingulate herniation - The brain squeezes under the falx cerebri 4 Transcalvarial herniation - through a skull fracture 5 Upward herniation of the cerebellum 6 Tonsillar herniation - the cerebellar tonsils herniate through the foramen magnum

Concussion temporarily changes the brain's function17 It is believed that the brain is left in a vulnerable state after concussion and that a second blow is linked to SIS26 The actual mechanism behind the catastrophic brain swelling is controversial927 A second injury during this time is thought to unleash a series of metabolic events within the brain28 Changes indicative of SIS may begin occurring in the injured brain within 15 seconds of the second concussion29 Pathophysiological changes in SIS can include a loss of autoregulation of the brain's blood vessels,133031 which causes them to become congested513 The vessels dilate, greatly increasing their diameter and leading to a large increase in cerebral blood flow1 Progressive cerebral edema may also occur3032 The increase of blood and brain volume within the skull causes a rapid and severe increase in intracranial pressure, which can in turn cause uncal and cerebellar brain herniation, a disastrous and potentially fatal condition in which the brain is squeezed past structures within the skull13

Studies on animals have shown that the brain may be more vulnerable to a second concussive injury administered shortly after a first33 In one such study, a mild impact administered within 24 hours of another one with minimal neurological impairment caused massive breakdown of the blood brain barrier and subsequent brain swelling26 Loss of this protective barrier could be responsible for the edema found in SIS26

Animal studies have shown that the immature brain may be more vulnerable to brain trauma; these findings may provide clues as to why SIS affects only people under age 1833


Measures that prevent head injuries in general also prevent SIS Thus athletes are advised to use protective gear such as helmets,1 though helmets do not entirely prevent the syndrome28

Experts advise that athletes who have suffered one concussion and still complain of concussion-related symptoms be prohibited from returning to the game due to the possibility of developing SIS234 Athletes are also discouraged from returning to play until after they have been evaluated and approved for resuming the sport by a healthcare provider skilled in evaluating concussion7 Some athletes may deny concussion symptoms because they do not wish to be prevented from rejoining the game Thus athletic trainers may prohibit return to play for any athlete who has suffered a concussion, regardless of the speed with which the symptoms reportedly resolve35 An initial head injury may impair an athlete's judgment and ability to decide to refrain from participating in risky activity, so some healthcare providers encourage family members and other acquaintances to pressure an athlete not to return to play29

Several different sets of return-to-play guidelines exist for athletes who have suffered minor head trauma These exist in part to prevent the player from developing SIS36 A variety of concussion grading systems have been devised, in part to aid in this determination Every return-to-play guideline recommends that an athlete not return to competition until all concussion symptoms are absent during both rest and exercise13 The American Academy of Neurology recommends that young athletes be prohibited from returning to play for at least a week in most cases of concussion37

The current return-to-play guidelines may not be strict enough to protect young athletes from SIS38 On the other hand, they may be too strict for professional football players; evidence that the syndrome exists in this population is lacking39


Magnetic resonance imaging and computed tomography are the most useful imaging tools for detecting SIS2 The congestion in the brain's blood vessels may be visible using CT scans30

SIS is distinct from repetitive head injury syndrome, in which a person suffers a series of minor head injuries over time and experiences a slow decline in functions such as cognitive abilities1 Unlike SIS, repetitive head injury syndrome may still occur even when symptoms from prior injuries have completely resolved1 SIS is thought to be more severe than repetitive head injury syndrome in both the short- and long-term1


Treatment of the loss of autoregulation of the brain's blood vessels may be difficult or impossible5 When SIS occurs, surgery does not help and there is little hope for recovery9 Treatment requires immediate recognition and includes administration of osmotic agents and hyperventilation9 in order to lower intracranial pressure


The mortality rate for SIS approaches 50%,35 and morbidity disability is almost 100%40 Since the condition is so rare, the connection between SIS and future disability has been difficult to establish and is therefore poorly understood1

When SIS is not fatal, the effects similar to those of severe traumatic brain injury can occur, including persistent muscle spasms and tenseness, emotional instability, hallucinations,22 post-traumatic epilepsy, mental disability, paralysis,6 coma, and brain death41


The condition was first described in 197318 by RC Schneider,11 and the term second-impact syndrome was coined in 19841 In 1984, RL Saunders described the death of a football player who had died after a second, unremarkable concussion42 and hypothesized that the second blow caused a catastrophic rise in ICP, possibly through loss of vasomotor tone, because the brain was in a vulnerable state43 Between 1984 and 1991, only four cases were documented5 Between 1992 and 1998, reports of the condition began to be made more frequently than they had before, a fact is thought to be due to wider recognition of the syndrome by clinicians1 In 1991, JP Kelly and others reported another football death after repeated concussions44 and coined the term "vascular congestion syndrome"43

In 2002, a high-school football player from Texas named Will Benson suffered two concussions within two weeks; he collapsed shortly after the second one and died six days later as the result28 He is thought to have died from SIS45 Will's Bill, a law for which the father of the player had advocated after his death, was passed in Texas in June 200728 The law mandates basic emergency and safety training for sports officials in high schools, including education about second-impact syndrome,28 with a special focus on concussion symptoms45

In 2005, Preston Plevretes, a football player for LaSalle University, had his life changed forever by second-impact syndrome After undergoing a head-to-head hit at football practice, a university doctor diagnosed Plevretes with a concussion and two days later was told he was allowed to resume play Three games after returning Plevretes sustained another concussion resulting in second-impact syndrome He was rushed to the hospital where doctors cut the right side of his skull Five years after the injury, he still struggles to do everyday activities Because of Plevretes, the NCAA revised concussion guidelines The NCAA strongly urges schools to have a concussion management plan They also require that an athlete have clearance by a team doctor before being allowed to return46

In 2006, Zachary Lystedt, a thirteen-year-old football player, suffered a concussion during one of his games He shrugged off the hit and went back in the game a few plays later At the end of the game, he collapsed on the field Lystedt had second-impact syndrome He was airlifted to a hospital where surgeons cut both sides of his skull so that the blood clot could be taken out He was in the hospital for months and he still has trouble doing everyday things, such as walking To prevent other families from going through what they went through, the Lystedt family made it their goal to make a law that athletes who are suspected of a concussion are not allowed to return to play unless he or she is cleared by a licensed physician The law is now effective in over thirty states47

By 2003, 21 cases of SIS had been reported in medical literature43


The existence of SIS is in question and is somewhat controversial33 The sudden collapse seen in sufferers may be due to a type of cerebral edema that can follow an initial impact in children and teenagers, rather than to SIS10 This type of edema, referred to as diffuse cerebral swelling, may be the real reason for the collapse which young people sometimes experience and which is commonly thought to be due to SIS48 Those who doubt the validity of the diagnosis cite the finding that diffuse cerebral swelling is more common in children and adolescents as an explanation for the greater frequency of SIS diagnoses in young people48 One group found that of 17 previously identified cases of SIS, only 5 met their diagnostic criteria for the syndrome,16 with some cases not clearly involving a second impact10 They found that diagnoses of SIS were frequently based on bystander accounts of previous injuries, which they showed to be unreliable11 Teammates of players who are thought to have SIS may over-report the initial concussion, giving the appearance of a greater number of second impacts than actually exist16 Thus critics argue that the small number of reported cases leaves the question of whether SIS really causes the brain to swell catastrophically unanswered23

Whether a second impact is really involved in the diffuse cerebral swelling that occurs on rare occasions after a mild traumatic brain injury is controversial, but some expertswho agree that such catastrophic brain swelling does occur after a very small number of mild brain injuries and that young age is associated with increased risk31 It is also agreed that some people may be particularly vulnerable to catastrophic brain swelling as the result of multiple head injuries11

See alsoedit

  • Brain damage
  • Dementia pugilistica punch-drunk syndrome
  • Post-concussion syndrome


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  3. ^ McLaren F1 "Fernando Alonso: A Medical Update" http://wwwmclarencom McLaren F1 Retrieved 13 March 2015  External link in |website= help
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  11. ^ a b c d MacReady N 2004 "Study leading some experts to question the existence of 'second-impact syndrome'" Clinical Psychiatry News 32 10: 55 
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