Second-impact syndrome
Encyclopedia
Second-impact syndrome is a condition in which the brain swells rapidly and catastrophically after a person suffers a second concussion before symptoms from an earlier one have subsided. This deadly second blow may occur days, weeks or minutes after an initial concussion, and even the mildest grade of concussion can lead to SIS. 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 arteriole
s lose their ability to regulate their diameter
, and therefore lose control over cerebral blood flow
, causing massive cerebral edema
.
Most cases of SIS have occurred in young people, who are thought to be particularly vulnerable. Young athletes are most at risk. 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 resolved.
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 physicians.
of second impact syndrome is unknown, the condition is rare; very few cases have been confirmed in medical literature. In the 13 year period from 1980–1993, 35 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-related. Additionally, the initial trauma commonly goes unreported, adding to the confusion about how often the syndrome occurs.
By one estimate, the syndrome kills four to six people under the age of 18 per year. According to the Centers for Disease Control, about 1.5 people die each year from concussion in the US; in most of these cases, the person had received another concussion previously.
In part due to the poor documentation of the initial injury and continuing symptoms in recorded cases, some professionals think that the condition is over-diagnosed, and some doubt the validity of the diagnosis altogether.
, soccer, grid iron
, baseball
, rugby
, basketball
, hockey
, and skiing
are at increased risk. The condition most commonly occurs in American football.
Second-impact syndrome disproportionately affects teenagers. All documented cases occurred in people younger than 20 except in boxing
. As of 2000, the syndrome had never been reported in the medical literature in children younger than adolescent age. Young athletes have been found to be both more susceptible to concussions and more likely to get second-impact syndrome than their older counterparts. However, SIS is also a concern for adult athletes. Adolescent and young adult males who play football or hockey, or who box or ski are the most common sufferers of the condition. 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 impacts.
Studies have found that people who have received one concussion are at a higher risk to receive a concussion in the future.
The initial injury may be a concussion, or it may be another, more severe, type of head trauma, such as cerebral contusion
. However, the first concussion need not be severe for the second impact to cause SIS. 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 brain
. Loss of consciousness
during the second injury is not necessary for SIS to occur. Both injuries may take place in the same game.
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 worsen. Neurological collapse can occur within a short period, with rapid onset of dilating pupils
, loss of eye movement, unconsciousness, and respiratory failure. Failure of the brain stem
frequently occurs between two and five minutes after the second impact, and death can follow shortly.
SIS is sometimes associated with a small subdural hematoma
.
Concussion temporarily changes the brain's function. It is believed that the brain is left in a vulnerable state after concussion and that a second blow is linked to SIS. The actual mechanism behind the catastrophic brain swelling
is controversial. A second injury during this time is thought to unleash a series of metabolic events within the brain.
Changes indicative of SIS may begin occurring in the injured brain within 15 seconds of the second concussion. Pathophysiological changes in SIS can include a loss of autoregulation
of the brain's blood vessel
s, which causes them to become congested. The vessels dilate, greatly increasing their diameter and leading to a large increase in cerebral blood flow
. Progressive cerebral edema may also occur. 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 skull.
Studies on animals
have shown that the brain may be more vulnerable to a second concussive injury administered shortly after a first. 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 swelling. Loss of this protective barrier could be responsible for the edema found in SIS.
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 18.
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 SIS. 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 concussion. 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 resolve. 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 play.
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 SIS. 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 exercise. The American Academy of Neurology recommends that young athletes be prohibited from returning to play for at least a week in most cases of concussion.
The current return-to-play guidelines may not be strict enough to protect young athletes from SIS. On the other hand, they may be too strict for professional football players; evidence that the syndrome exists in this population is lacking.
and computed tomography
are the most useful imaging tools for detecting SIS. The congestion in the brain's blood vessels may be visible using CT scans.
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 abilities. Unlike SIS, repetitive head injury syndrome may still occur even when symptoms from prior injuries have completely resolved. SIS is thought to be more severe than repetitive head injury syndrome in both the short- and long-term.
does not help and there is little hope for recovery. Treatment requires immediate recognition and includes administration of osmotic agents and hyperventilation
in order to lower intracranial pressure.
) is almost 100%. Since the condition is so rare, the connection between SIS and future disability has been difficult to establish and is therefore poorly understood.
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, hallucination
s, post-traumatic epilepsy
, mental disability, paralysis
, coma
, and brain death
.
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 result. He is thought to have died from SIS. Will's Bill, a law for which the father of the player had advocated after his death, was passed in Texas in June 2007. The law mandates basic emergency and safety training for sports officials in high schools, including education about second-impact syndrome, with a special focus on concussion symptoms.
By 2003, 21 cases of SIS had been reported in medical literature.
that can follow an initial impact in children and teenagers, rather than to SIS. 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 SIS. 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 people. One group found that of 17 previously identified cases of SIS, only 5 met their diagnostic criteria for the syndrome, with some cases not clearly involving a second impact. They found that diagnoses of SIS were frequently based on bystander accounts of previous injuries, which they showed to be unreliable. Teammates of players who are thought to have SIS may overreport the initial concussion, giving the appearance of a greater number of second impacts than actually exist. Thus critics argue that the small number of reported cases leaves the question of whether SIS really causes the brain to swell catastrophically unanswered.
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 experts agree that such catastrophic brain swelling does occur after a very a small number of mild brain injuries and that young age is associated with increased risk. It is also agreed that some people may be particularly vulnerable to catastrophic brain swelling as the result of multiple head injuries.
Arteriole
An arteriole is a small diameter blood vessel in the microcirculation that extends and branches out from an artery and leads to capillaries.Arterioles have muscular walls and are the primary site of vascular resistance...
s lose their ability to regulate their diameter
Diameter
In geometry, a diameter of a circle is any straight line segment that passes through the center of the circle and whose endpoints are on the circle. The diameters are the longest chords of the circle...
, and therefore lose control over cerebral blood flow
Cerebral blood flow
Cerebral blood flow, or CBF, is the blood supply to the brain in a given time. In an adult, CBF is typically 750 millitres per minute or 15% of the cardiac output. This equates to 50 to 54 millilitres of blood per 100 grams of brain tissue per minute. CBF is tightly regulated to meet the brain's...
, causing massive cerebral edema
Cerebral edema
Cerebral edema or cerebral œdema is an excess accumulation of water in the intracellular or extracellular spaces of the brain.-Vasogenic:Due to a breakdown of tight endothelial junctions which make up the blood-brain barrier...
.
Most cases of SIS have occurred in young people, who are thought to be particularly vulnerable. Young athletes are most at risk. 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 resolved.
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 physicians.
Epidemiology
Though the incidenceIncidence (epidemiology)
Incidence is a measure of the risk of developing some new condition within a specified period of time. Although sometimes loosely expressed simply as the number of new cases during some time period, it is better expressed as a proportion or a rate with a denominator.Incidence proportion is the...
of second impact syndrome is unknown, the condition is rare; very few cases have been confirmed in medical literature. In the 13 year period from 1980–1993, 35 football
American football
American football is a sport played between two teams of eleven with the objective of scoring points by advancing the ball into the opposing team's end zone. Known in the United States simply as football, it may also be referred to informally as gridiron football. The ball can be advanced by...
-related cases of SIS were recorded, but only 17 of these were confirmed by necropsy or surgery
Surgery
Surgery is an ancient medical specialty that uses operative manual and instrumental techniques on a patient to investigate and/or treat a pathological condition such as disease or injury, or to help improve bodily function or appearance.An act of performing surgery may be called a surgical...
and magnetic resonance imaging
Magnetic resonance imaging
Magnetic resonance imaging , nuclear magnetic resonance imaging , or magnetic resonance tomography is a medical imaging technique used in radiology to visualize detailed internal structures...
to be due to SIS, and 18 cases were found to be probably SIS-related. Additionally, the initial trauma commonly goes unreported, adding to the confusion about how often the syndrome occurs.
By one estimate, the syndrome kills four to six people under the age of 18 per year. According to the Centers for Disease Control, about 1.5 people die each year from concussion in the US; in most of these cases, the person had received another concussion previously.
In part due to the poor documentation of the initial injury and continuing symptoms in recorded cases, some professionals think that the condition is over-diagnosed, and some doubt the validity of the diagnosis altogether.
Risks
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 boxingBoxing
Boxing, also called pugilism, is a combat sport in which two people fight each other using their fists. Boxing is supervised by a referee over a series of between one to three minute intervals called rounds...
, soccer, grid iron
Gridiron football
Gridiron football , sometimes known as North American football, is an umbrella term for related codes of football primarily played in the United States and Canada. The predominant forms of gridiron football are American football and Canadian football...
, baseball
Baseball
Baseball is a bat-and-ball sport played between two teams of nine players each. The aim is to score runs by hitting a thrown ball with a bat and touching a series of four bases arranged at the corners of a ninety-foot diamond...
, rugby
Rugby football
Rugby football is a style of football named after Rugby School in the United Kingdom. It is seen most prominently in two current sports, rugby league and rugby union.-History:...
, basketball
Basketball
Basketball is a team sport in which two teams of five players try to score points by throwing or "shooting" a ball through the top of a basketball hoop while following a set of rules...
, hockey
Hockey
Hockey is a family of sports in which two teams play against each other by trying to maneuver a ball or a puck into the opponent's goal using a hockey stick.-Etymology:...
, and skiing
Skiing
Skiing is a recreational activity using skis as equipment for traveling over snow. Skis are used in conjunction with boots that connect to the ski with use of a binding....
are at increased risk. The condition most commonly occurs in American football.
Second-impact syndrome disproportionately affects teenagers. All documented cases occurred in people younger than 20 except in boxing
Boxing
Boxing, also called pugilism, is a combat sport in which two people fight each other using their fists. Boxing is supervised by a referee over a series of between one to three minute intervals called rounds...
. As of 2000, the syndrome had never been reported in the medical literature in children younger than adolescent age. Young athletes have been found to be both more susceptible to concussions and more likely to get second-impact syndrome than their older counterparts. However, SIS is also a concern for adult athletes. Adolescent and young adult males who play football or hockey, or who box or ski are the most common sufferers of the condition. 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 impacts.
Studies have found that people who have received one concussion are at a higher risk to receive a concussion in the future.
Features
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 subsided. Such symptoms include headache, cognitive difficulties, or visual changes.The initial injury may be a concussion, or it may be another, more severe, type of head trauma, such as cerebral contusion
Cerebral contusion
Cerebral contusion, Latin contusio cerebri, a form of traumatic brain injury, is a bruise of the brain tissue. Like bruises in other tissues, cerebral contusion can be associated with multiple microhemorrhages, small blood vessel leaks into brain tissue. Contusion occurs in 20–30% of severe head...
. However, the first concussion need not be severe for the second impact to cause SIS. 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
Acceleration
In physics, acceleration is the rate of change of velocity with time. In one dimension, acceleration is the rate at which something speeds up or slows down. However, since velocity is a vector, acceleration describes the rate of change of both the magnitude and the direction of velocity. ...
to the brain
Human brain
The human brain has the same general structure as the brains of other mammals, but is over three times larger than the brain of a typical mammal with an equivalent body size. Estimates for the number of neurons in the human brain range from 80 to 120 billion...
. Loss of consciousness
Unconsciousness
Unconsciousness is the condition of being not conscious—in a mental state that involves complete or near-complete lack of responsiveness to people and other environmental stimuli. Being in a comatose state or coma is a type of unconsciousness. Fainting due to a drop in blood pressure and a...
during the second injury is not necessary for SIS to occur. Both injuries may take place in the same game.
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 worsen. Neurological collapse can occur within a short period, with rapid onset of dilating pupils
Mydriasis
Mydriasis is a dilation of the pupil due to disease, trauma or the use of drugs. Normally, the pupil dilates in the dark and constricts in the light to respectively improve vividity at night and to protect the retina from sunlight damage during the day...
, loss of eye movement, unconsciousness, and respiratory failure. Failure of the brain stem
Brain stem
In vertebrate anatomy the brainstem is the posterior part of the brain, adjoining and structurally continuous with the spinal cord. The brain stem provides the main motor and sensory innervation to the face and neck via the cranial nerves...
frequently occurs between two and five minutes after the second impact, and death can follow shortly.
SIS is sometimes associated with a small subdural hematoma
Subdural hematoma
A subdural hematoma or subdural haematoma , also known as a subdural haemorrhage , is a type of haematoma, a form of traumatic brain injury. Blood gathers within the outermost meningeal layer, between the dura mater, which adheres to the skull, and the arachnoid mater, which envelops the brain...
.
Pathophysiology
Swelling (medical)
In medical parlance, swelling is the transient enlargement or protuberance in the body and may include tumors. According to cause, it may be congenital, traumatic, inflammatory, neoplastic or miscellaneous....
is controversial. A second injury during this time is thought to unleash a series of metabolic events within the brain.
Changes indicative of SIS may begin occurring in the injured brain within 15 seconds of the second concussion. Pathophysiological changes in SIS can include a loss of autoregulation
Autoregulation
Autoregulation is a process within many biological systems, resulting from some internal adaptive mechanism that works to adjust the systems response to stimuli. While most systems of the body show some degree of autoregulation, it is most clearly observed in the kidney, the heart, and the brain...
of the brain's blood vessel
Blood vessel
The blood vessels are the part of the circulatory system that transports blood throughout the body. There are three major types of blood vessels: the arteries, which carry the blood away from the heart; the capillaries, which enable the actual exchange of water and chemicals between the blood and...
s, which causes them to become congested. The vessels dilate, greatly increasing their diameter and leading to a large increase in cerebral blood flow
Cerebral blood flow
Cerebral blood flow, or CBF, is the blood supply to the brain in a given time. In an adult, CBF is typically 750 millitres per minute or 15% of the cardiac output. This equates to 50 to 54 millilitres of blood per 100 grams of brain tissue per minute. CBF is tightly regulated to meet the brain's...
. Progressive cerebral edema may also occur. The increase of blood and brain volume within the skull causes a rapid and severe increase in intracranial pressure
Intracranial pressure
Intracranial pressure is the pressure inside the skull and thus in the brain tissue and cerebrospinal fluid . The body has various mechanisms by which it keeps the ICP stable, with CSF pressures varying by about 1 mmHg in normal adults through shifts in production and absorption of CSF...
, which can in turn cause uncal and cerebellar brain herniation
Brain herniation
Brain herniation, also known as cistern obliteration, is a deadly side effect of very high intracranial pressure that occurs when the brain shifts across structures within the skull...
, a disastrous and potentially fatal condition in which the brain is squeezed past structures within the skull.
Studies on animals
Animal testing
Animal testing, also known as animal experimentation, animal research, and in vivo testing, is the use of non-human animals in experiments. Worldwide it is estimated that the number of vertebrate animals—from zebrafish to non-human primates—ranges from the tens of millions to more than 100 million...
have shown that the brain may be more vulnerable to a second concussive injury administered shortly after a first. 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 swelling. Loss of this protective barrier could be responsible for the edema found in SIS.
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 18.
Prevention
Measures that prevent head injuries in general also prevent SIS. Thus athletes are advised to use protective gear such as helmets, though helmets do not entirely prevent the syndrome.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 SIS. 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 concussion. 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 resolve. 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 play.
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 SIS. A variety of concussion grading systems
Concussion grading systems
Concussion grading systems are sets of criteria used in sports medicine to determine the severity, or grade, of a concussion, the mildest form of traumatic brain injury. At least 16 such systems exist, and there is little agreement among professionals about which is the best to use...
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 exercise. The American Academy of Neurology recommends that young athletes be prohibited from returning to play for at least a week in most cases of concussion.
The current return-to-play guidelines may not be strict enough to protect young athletes from SIS. On the other hand, they may be too strict for professional football players; evidence that the syndrome exists in this population is lacking.
Diagnosis
Magnetic resonance imagingMagnetic resonance imaging
Magnetic resonance imaging , nuclear magnetic resonance imaging , or magnetic resonance tomography is a medical imaging technique used in radiology to visualize detailed internal structures...
and computed tomography
Computed tomography
X-ray computed tomography or Computer tomography , is a medical imaging method employing tomography created by computer processing...
are the most useful imaging tools for detecting SIS. The congestion in the brain's blood vessels may be visible using CT scans.
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 abilities. Unlike SIS, repetitive head injury syndrome may still occur even when symptoms from prior injuries have completely resolved. SIS is thought to be more severe than repetitive head injury syndrome in both the short- and long-term.
Treatment
Treatment of the loss of autoregulation of the brain's blood vessels may be difficult or impossible. When SIS occurs, surgerySurgery
Surgery is an ancient medical specialty that uses operative manual and instrumental techniques on a patient to investigate and/or treat a pathological condition such as disease or injury, or to help improve bodily function or appearance.An act of performing surgery may be called a surgical...
does not help and there is little hope for recovery. Treatment requires immediate recognition and includes administration of osmotic agents and hyperventilation
Hyperventilation
Hyperventilation or overbreathing is the state of breathing faster or deeper than normal, causing excessive expulsion of circulating carbon dioxide. It can result from a psychological state such as a panic attack, from a physiological condition such as metabolic acidosis, can be brought about by...
in order to lower intracranial pressure.
Prognosis
The mortality rate for SIS approaches 50%, and morbidity (disabilityDisability
A disability may be physical, cognitive, mental, sensory, emotional, developmental or some combination of these.Many people would rather be referred to as a person with a disability instead of handicapped...
) is almost 100%. Since the condition is so rare, the connection between SIS and future disability has been difficult to establish and is therefore poorly understood.
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, hallucination
Hallucination
A hallucination, in the broadest sense of the word, is a perception in the absence of a stimulus. In a stricter sense, hallucinations are defined as perceptions in a conscious and awake state in the absence of external stimuli which have qualities of real perception, in that they are vivid,...
s, post-traumatic epilepsy
Post-traumatic epilepsy
Post-traumatic epilepsy is a form of epilepsy that results from brain damage caused by physical trauma to the brain . A person with PTE suffers repeated post-traumatic seizures more than a week after the initial injury...
, mental disability, paralysis
Paralysis
Paralysis is loss of muscle function for one or more muscles. Paralysis can be accompanied by a loss of feeling in the affected area if there is sensory damage as well as motor. A study conducted by the Christopher & Dana Reeve Foundation, suggests that about 1 in 50 people have been diagnosed...
, coma
Coma
In medicine, a coma is a state of unconsciousness, lasting more than 6 hours in which a person cannot be awakened, fails to respond normally to painful stimuli, light or sound, lacks a normal sleep-wake cycle and does not initiate voluntary actions. A person in a state of coma is described as...
, and brain death
Brain death
Brain death is the irreversible end of all brain activity due to total necrosis of the cerebral neurons following loss of brain oxygenation. It should not be confused with a persistent vegetative state...
.
History
The condition was first described in 1973 by R.C. Schneider, and the term second-impact syndrome was coined in 1984. In 1984, R.L. Saunders described the death of a football player who had died after a second, unremarkable concussion 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 state. Between 1984 and 1991, only four cases were documented. 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 clinicians. In 1991, J.P. Kelly and others reported another football death after repeated concussions and coined the term "vascular congestion syndrome".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 result. He is thought to have died from SIS. Will's Bill, a law for which the father of the player had advocated after his death, was passed in Texas in June 2007. The law mandates basic emergency and safety training for sports officials in high schools, including education about second-impact syndrome, with a special focus on concussion symptoms.
By 2003, 21 cases of SIS had been reported in medical literature.
Controversy
The existence of SIS is in question and is somewhat controversial. The sudden collapse seen in sufferers may be due to a type of cerebral edemaEdema
Edema or oedema ; both words from the Greek , oídēma "swelling"), formerly known as dropsy or hydropsy, is an abnormal accumulation of fluid beneath the skin or in one or more cavities of the body that produces swelling...
that can follow an initial impact in children and teenagers, rather than to SIS. 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 SIS. 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 people. One group found that of 17 previously identified cases of SIS, only 5 met their diagnostic criteria for the syndrome, with some cases not clearly involving a second impact. They found that diagnoses of SIS were frequently based on bystander accounts of previous injuries, which they showed to be unreliable. Teammates of players who are thought to have SIS may overreport the initial concussion, giving the appearance of a greater number of second impacts than actually exist. Thus critics argue that the small number of reported cases leaves the question of whether SIS really causes the brain to swell catastrophically unanswered.
Whether a second impact is really involved in the diffuse cerebral swelling that occurs on rare occasions after a mild traumatic brain injury
Traumatic brain injury
Traumatic brain injury , also known as intracranial injury, occurs when an external force traumatically injures the brain. TBI can be classified based on severity, mechanism , or other features...
is controversial, but experts agree that such catastrophic brain swelling does occur after a very a small number of mild brain injuries and that young age is associated with increased risk. It is also agreed that some people may be particularly vulnerable to catastrophic brain swelling as the result of multiple head injuries.
See also
- Brain damageBrain damage"Brain damage" or "brain injury" is the destruction or degeneration of brain cells. Brain injuries occur due to a wide range of internal and external factors...
- Dementia pugilisticaDementia pugilisticaDementia pugilistica is a type of neurodegenerative disease or dementia, which may affect amateur or professional boxers as well as athletes in other sports who suffer concussions...
(punch-drunk syndrome) - Post-concussion syndromePost-concussion syndromePost-concussion syndrome, also known as postconcussive syndrome or PCS, and historically called shell shock, is a set of symptoms that a person may experience for weeks, months, or occasionally up to a year or more after a concussion – a mild form of traumatic brain injury . PCS may also...