Second-impact syndrome

SIS is a potential complication 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. 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, and death can follow shortly. SIS is sometimes associated with a small subdural hematoma. ==Risk factors==

Second-impact syndrome shares all the risk factors of a concussion; that is, those who are at increased risk for a concussion are also at higher risk for SIS. Thus, people who participate in sports such as boxing, Association football, American football, baseball, rugby, basketball, ice hockey, pro wrestling, horse riding, and skiing (especially Alpine) are at increased risk. However, SIS is also a concern for adult athletes. Adolescent and young adult males who play American football or hockey, or who box or ski are the most common individuals with the condition. Studies have found that people who have received one concussion are at a higher risk to receive a concussion in the future. ==Pathophysiology==

. 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.'' A concussion temporarily changes the brain's function. 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 vessels, which causes them to become congested. 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. Loss of this protective barrier could be responsible for the edema found in SIS. ==Diagnosis==

Magnetic resonance imaging and computed tomography are the most useful imaging tools for detecting SIS. SIS is distinct from repetitive head injury syndrome, in which a person has 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. ==Prevention==

Measures that prevent head injuries in general also prevent SIS. Thus athletes are advised to use protective gear such as helmets, 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. 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 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. ==Treatment==

Treatment of the loss of auto regulation of the brain's blood vessels may be difficult or impossible. When SIS occurs, surgery 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. ==Prognosis==

The mortality rate for SIS approaches 50%, and morbidity (disability) 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. post-traumatic epilepsy, mental disability, paralysis, coma, and brain death. ==Epidemiology==

Though the incidence of second-impact syndrome is unknown, The United States seemingly has far more reported cases of second-impact syndrome than elsewhere. The adolescent brain is 60 times more sensitive to components of the metabolic chain reaction that occurs after trauma, resulting in more diffuse cerebral swelling. In the 13-year period from 1980 to 1993, 35 American football related cases of SIS were recorded; 17 of these were confirmed by autopsy or surgery and magnetic resonance imaging to be due to SIS, and 18 cases were found to be probably SIS-related. A study by Sullivan et al. found that 83% of male rugby athletes were aware of concussion signs and symptoms, but only 50% understood or were aware of the protocol to return to play after an injury. According to the Centers for Disease Control, about 1.5 people die each year from a concussion in the US; in most of these cases, the person had received another concussion previously. In the presence of second-impact syndrome, the mortality rate is at best 50% when diffuse cerebral swelling occurs. In part due to the poor documentation of the initial injury and continuing symptoms in recorded cases, Due to the nature of the impact, the validity may be in question as subdural hematomas or other structural anomalies may directly affect the outcome. Along with the short term effects that occur with second-impact syndrome, improper care for concussions can lead to longer term effects as well. These include early onset dementia or Alzheimer's, and early onset of Parkinson's disease. Increased loss of vision and risk of stroke can occur further on in their lives. ==History==

The condition was first described in 1973 and the term second-impact syndrome was coined in 1984. 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. and coined the term "vascular congestion syndrome". In 2006, Zachary Lystedt, a thirteen-year-old football player, sustained 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 reportedly still has trouble with physical tasks 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 states. By 2003, 21 cases of SIS had been reported in medical literature. ==Controversy==

The existence of SIS is in question and is somewhat controversial. 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. 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 some experts 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 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==