Concussion of the brain
Encyclopedia
Concussion, from the Latin
concutere ("to shake violently") or the Latin
concussus ("action of striking together"), is the most common type of traumatic brain injury
. The terms mild brain injury, mild traumatic brain injury (MTBI), mild head injury (MHI), minor head trauma, and concussion may be used interchangeably, although the latter is often treated as a narrower category. The term "concussion" has been used for centuries and is still commonly used in sports medicine
, while "MTBI" is a technical term used more commonly nowadays in general medical contexts. Frequently defined as a head injury
with a temporary loss of brain function, concussion can cause a variety of physical, cognitive
, and emotional symptoms.
Treatment of concussion involves monitoring and rest. Symptoms usually go away entirely within three weeks, though they may persist, or complications may occur. Repeated concussions can cause cumulative brain damage
such as dementia pugilistica
or severe complications such as second-impact syndrome
.
Due to factors such as widely varying definitions and possible underreporting of concussion, the rate at which it occurs annually is not known; however it may be more than 6 per 1,000 people. Common causes include sports injuries, bicycle accidents, car accidents, and falls; the latter two are the most frequent causes among adults. Concussion may be caused by a blow to the head, or by acceleration
forces without a direct impact. The forces involved disrupt cellular processes in the brain
for days or weeks. On the battlefield, MTBI is a potential consequence of nearby explosions.
It is not known whether the concussed brain is structurally damaged the way it is in other types of brain injury (albeit to a lesser extent) or whether concussion mainly entails a loss of function with physiological
but not structural changes. Cellular damage has reportedly been found in concussed brains, but it may have been due to artifacts from the studies. It is now thought that structural and psychiatric factors may both be responsible for the effects of concussion.
normally shows no gross structural changes to the brain as the result of the condition.
According to the classic definition, no structural brain damage occurs in concussion; it is a functional state, meaning that symptoms are caused primarily by temporary biochemical
changes in neuron
s, taking place for example at their cell membrane
s and synapse
s. However, in recent years researchers have included injuries
in which structural damage does occur under the rubric of concussion. According to the National Institute for Health and Clinical Excellence
definition, concussion may involve a physiological or physical disruption in the brain's synapse
s.
Definitions of mild traumatic brain injury (M.T.B.I) have been inconsistent since the 1970s, but the World Health Organization
's International Statistical Classification of Diseases and Related Health Problems
(ICD-10) described MTBI-related conditions in 1992, providing a consistent, authoritative definition across specialties. In 1993, the American Congress of Rehabilitation Medicine defined MTBI as 30 minutes or fewer of loss of consciousness (LOC), 24 hours or fewer of post-traumatic amnesia
(PTA), and a Glasgow Coma Scale
(GCS) score of at least 13. In 1994, the American Psychiatric Association
's Diagnostic and Statistical Manual of Mental Disorders
defined MTBI using PTA and LOC. Other definitions of MTBI incorporate focal neurological deficit and altered mental status, in addition to PTA and GCS.
Concussion falls under the classification of mild TBI. It is not clear whether concussion is implied in mild brain injury or mild head injury. "MTBI" and "concussion" are often treated as synonyms in medical literature. However, other injuries such as intracranial hemorrhage
s (e.g. intra-axial hematoma
, epidural hematoma
, and subdural hematoma
) are not necessarily precluded in MTBI or mild head injury, but they are in concussion. MTBI associated with abnormal neuroimaging may be considered "complicated MTBI". "Concussion" can be considered to imply a state in which brain function is temporarily impaired and "MTBI" to imply a pathophysiological
state, but in practice few researchers and clinicians distinguish between the terms. Descriptions of the condition, including the severity and the area of the brain affected, are now used more often than "concussion" in clinical neurology.
Although the term "concussion" is still used in sports literature as interchangeable with "MHI" or "MTBI", the general clinical medical literature now uses "MTBI" instead.
Controversy exists about whether the definition of concussion should include only those injuries in which loss of consciousness
occurs.
Historically, by definition, concussion involved a loss of consciousness. However, the definition has evolved over time to include a change in consciousness, such as amnesia. The best-known concussion grading scales count head injuries in which loss of consciousness does not occur to be mild concussions and those in which it does to be more severe.
In the past, the decision about when to allow athletes to return to contact sports was frequently based on the grade of concussion. However current research and recommendations by professional organizations such as the National Athletic Trainers Association recommend not using these grading systems for determination of severity of injury or for making return to play decisions. Injured athletes are prohibited from returning to play before they are symptom-free during rest and exertion and neuropsychological tests are normal again. This is to avoid cumulative effects.
Three grading systems were followed most widely: one was developed by Robert Cantu, one by the Colorado Medical Society
, and a third by the American Academy of Neurology
. Each divides concussion into three grades, as summarized in the following table:
is the most common MTBI symptom. Other symptoms include dizziness, vomiting, nausea, lack of motor coordination
, difficulty balancing
, or other problems with movement or sensation. Visual symptoms include light sensitivity
, seeing bright lights, blurred vision
, and double vision
. Tinnitus
, or a ringing in the ears, is also commonly reported. In one in about seventy concussions, concussive convulsion
s occur, but these seizures that take place during or immediately after the concussion are not the same as post-traumatic seizure
s, and they, unlike post-traumatic seizures, are not in themselves predictive of post-traumatic epilepsy
, which requires some form of structural brain damage, not just a momentary disruption in normal brain functioning. Concussive convulsions are thought to result from temporary loss or inhibition of motor function, and are not associated either with epilepsy or with more serious structural damage. They are not associated with any particular sequelae
and have the same high rate of favorable outcomes as concussions without convulsions.
. Loss of consciousness may occur but is not necessarily correlated with the severity of the concussion if it is brief. Post-traumatic amnesia
, in which the person cannot remember events leading up to the injury or after it, or both, is a hallmark of concussion. Confusion
, another concussion hallmark, may be present immediately or may develop over several minutes. A patient may, for example, repeatedly ask the same questions, be slow to respond to questions or directions, have a vacant stare, or have slurred or incoherent speech. Other MTBI symptoms include changes in sleeping patterns and difficulty with reasoning, concentrating, and performing everyday activities.
Affect
ive results of concussion include crankiness, loss of interest in favorite activities or items, tearfulness, and displays of emotion that are inappropriate to the situation. Common symptoms in concussed children include restlessness, lethargy, and irritability.
The brain
is surrounded by cerebrospinal fluid
, one of the functions of which is to protect it from light trauma, but more severe impacts or the forces associated with rapid acceleration may not be absorbed by this cushion. Concussion may be caused by impact force
s, in which the head strikes or is struck by something, or impulsive forces, in which the head moves without itself being subject to blunt trauma
(for example, when the chest hits something and the head snaps forward).
Forces may cause linear, rotational, or angular movement of the brain, or a combination of these types of motion. In rotational movement, the head turns around its center of gravity, and in angular movement it turns on an axis not through its center of gravity. The amount of rotational force is thought to be the major type of force to cause concussion and the largest component in its severity. Studies with athletes have shown that the amount of force and the location of the impact are not necessarily correlated to the severity of the concussion or its symptoms, and have called into question the threshold for concussion previously thought to exist at around 70–75g
.
The parts of the brain most affected by rotational forces are the midbrain and diencephalon
. It is thought that the forces from the injury disrupt the normal cell
ular activities in the reticular activating system
located in these areas, and that this disruption produces the loss of consciousness often seen in concussion. Other areas of the brain that may be affected include the upper part of the brain stem
, the fornix, the corpus callosum
, the temporal lobe
, and the frontal lobe
. Angular acceleration
s of 4600, 5900, or 7900 radian
/s2 are estimated to have 25, 50, or 80% risk of MTBI respectively.
events. Though these events are thought to interfere with neuronal and brain function, the metabolic
processes that follow concussion are reversed in a large majority of affected brain cell
s; however a few cells may die after the injury.
Included in the cascade of events unleashed in the brain by concussion is impaired neurotransmission
, loss of regulation of ion
s, deregulation of energy use and cellular metabolism, and a reduction in cerebral blood flow
. Excitatory neurotransmitter
s, chemicals such as glutamate that serve to stimulate nerve cells, are released in excessive amounts as the result of the injury. The resulting cellular excitation causes neurons to fire
excessively. This creates an imbalance of ions such as potassium
and calcium
across the cell membranes of neurons (a process like excitotoxicity
). Since the neuron firing involves a net influx of positively charged ions into the cell, the ionic imbalance causes cells to have a more positive membrane potential
(i.e. it leads to neuronal depolarization
). This depolarization in turn causes ion pumps that serve to restore resting potential
within cells to work more than they normally do. This increased need for energy leads cells to require greater-than-usual amounts of glucose
, which is made into ATP
, an important source of energy for cells. The brain may stay in this state of hypermetabolism for days or weeks. At the same time, cerebral blood flow is relatively reduced for unknown reasons, though the reduction in blood flow is not as severe as it is in ischemia
. Thus cells get less glucose than they normally do, which causes an "energy crisis".
Concurrently with these processes, the activity of mitochondria
may be reduced, which causes cells to rely on anaerobic metabolism to produce energy, which increases levels of the byproduct lactate
.
For a period of minutes to days after a concussion, the brain is especially vulnerable to changes in intracranial pressure
, blood flow, and anoxia
. According to studies performed on animals (which are not always applicable to humans), large numbers of neurons can die during this period in response to slight, normally innocuous changes in blood flow.
Concussion involves diffuse (as opposed to focal) brain injury
, meaning that the dysfunction occurs over a widespread area of the brain rather than in a particular spot. Concussion is thought to be a milder type of diffuse axonal injury
because axon
s may be injured to a minor extent due to stretching. Animal studies in which primates were concussed have revealed damage to brain tissues such as small petechial hemorrhages and axonal injury. Axonal damage has been found in the brains of concussion sufferers who died from other causes, but inadequate blood flow to the brain due to other injuries may have contributed to the damage. Findings from a study of the brains of dead NFL athletes who received concussions suggest there is lasting damage to the brain after experiencing one; this damage can lead to a variety of other health issues.
The debate over whether concussion is a functional or structural phenomenon is ongoing. Structural damage has been found in the mildly traumatically injured brains of animals, but it is not clear whether these changes would be applicable to humans. Such changes in brain structure could be responsible for certain symptoms such as visual disturbances, but other sets of symptoms, especially those of a psychological nature, are more likely to be caused by reversible pathophysiological changes in cellular function that occur after concussion, such as alterations in neurons' biochemistry. These reversible changes could also explain why dysfunction is frequently temporary. A task force of head injury experts called the Concussion In Sport Group met in 2001 and decided that "concussion may result in neuropathological changes but the acute clinical symptoms largely reflect a functional disturbance rather than structural injury."
Diagnosis of MTBI is based on physical and neurological exams, duration of unconsciousness (usually less than 30 minutes) and post-traumatic amnesia (PTA; usually less than 24 hours), and the Glasgow Coma Scale
(MTBI sufferers have scores of 13 to 15). Neuropsychological test
s exist to measure cognitive function, the international consensus meeting in Zurich recommend the use of the SCAT2.
The tests may be administered hours, days, or weeks after the injury, or at different times to determine whether there is a trend in the patient's condition. Athletes may be tested before a sports season begins to provide a baseline neurocognitive test for comparison in the event of an injury, though it may not reduce risk or effect return to play.
Health care providers examine head trauma survivors to ensure that the injury is not a more severe medical emergency
such as an intracranial hemorrhage. Indications that screening for more serious injury is needed include worsening of symptoms such as headache, persistent vomiting, increasing disorientation or a deteriorating level of consciousness, seizures, and unequal pupil size
. People with such symptoms, or who are at higher risk for a more serious brain injury, are CT scanned to detect brain lesions and are frequently observed for 24 – 48 hours.
If the Glasgow Coma Scale
is less than 15 at two hours or less than 14 at any time a CT recommended. In addition, they may be more likely to perform a CT scan on people who would be difficult to observe after discharge or those who are intoxicated, at risk for bleeding, older than 60, or younger than 16. Most concussions cannot be detected with MRI or CT scans. However, changes have been reported to show up on MRI and SPECT imaging in concussed people with normal CT scans, and post-concussion syndrome
may be associated with abnormalities visible on SPECT
and PET scan
s. Mild head injury may or may not produce abnormal EEG
readings.
Concussion may be under-diagnosed. The lack of the highly noticeable signs and symptoms that are frequently present in other forms of head injury could lead clinicians to miss the injury, and athletes may cover up their injuries to remain in the competition. A retrospective survey in 2005 found that more than 88% of concussions go unrecognized.
Diagnosis of concussion can be complicated because it shares symptoms with other conditions. For example, post-concussion symptoms such as cognitive problems may be misattributed to brain injury when they are in fact due to post-traumatic stress disorder
(PTSD).
In 2011, the Georgia Tech Research Institute
researchers are investigating the use of radar as a possible concussion detection tool. No clinic studies have been done to prove it is accurate, therefore currently not ready for use.
s and using airbag
s in cars. Older people are encouraged to try to prevent falls, for example by keeping floors free of clutter and wearing thin, flat, shoes with hard soles that do not interfere with balance.
Use of protective equipment such as headgear has been found to reduce the number of concussions in athletes. Improvements in the design of protective athletic gear such as helmets may decrease the number and severity of such injuries. New "Head Impact Telemetry System" technology is being placed in helmets to study injury mechanisms and potentially help reduce the risk of concussions among American Football players. Changes to the rules or the practices of enforcing existing rules in sports, such as those against "head-down tackling", or "spearing", which is associated with a high injury rate, may also prevent concussions.
Medications may be prescribed to treat symptoms such as sleep problems and depression. Analgesic
s such as ibuprofen
can be taken for the headaches that frequently occur after concussion, but paracetamol (acetaminophen)
is preferred to minimize the risk for complications such as intracranial hemorrhage. Concussed individuals are advised not to drink alcohol
or take drug
s that have not been approved by a doctor, as they could impede healing.
Observation to monitor for worsening condition is an important part of treatment. Health care
providers recommend that those suffering from concussion return for further medical care and evaluation 24 to 72 hours after the concussive event if the symptoms worsen. Athletes, especially intercollegiate or professional athletes
, are typically followed closely by team trainers during this period. But others may not have access to this level of health care and may be sent home with no medical person monitoring them unless the situation gets worse. Patients may be released from the hospital to the care of a trusted person with orders to return if they display worsening symptoms or those that might indicate an emergent condition, like unconsciousness or altered mental status; convulsions; severe, persistent headache; extremity weakness; vomiting; or new bleeding or deafness in either or both ears. Repeated observation for the first 24 hours after concussion is recommended; however it is not known whether it is necessary to wake the patient up every few hours.
or clinical depression
, poor health before the injury or additional injuries sustained during it, and life stress. Longer periods of amnesia or loss of consciousness immediately after the injury may indicate longer recovery times from residual symptoms. For unknown reasons, having had one concussion significantly increases a person's risk of having another. Having previously sustained a sports concussion has been found to be a strong factor increasing the likelihood of a concussion in the future. Other strong factors include participation in a contact sport and body mass size. The prognosis may differ between concussed adults and children; little research has been done on concussion in the pediatric population, but concern exists that severe concussions could interfere with brain development
in children.
A 2009 study published in Brain
found that individuals with a history of concussions might demonstrate a decline in both physical and mental performance for longer than 30 years. Compared to their peers with no history of brain trauma, sufferers of concussion exhibited effects including loss of episodic memory
and reduced muscle speed.
, memory and attention problems, sleep problems, and irritability. There is no scientifically established treatment, and rest, a recommended recovery technique, has limited effectiveness. Symptoms usually go away on their own within months. The question of whether the syndrome is due to structural damage or other factors such as psychological ones, or a combination of these, has long been the subject of debate.
can occur with the third and subsequent concussions. Studies have had conflicting findings on whether athletes have longer recovery times after repeat concussions and whether cumulative effects such as impairment in cognition and memory occur.
Cumulative effects may include psychiatric disorders and loss of long-term memory
. For example, the risk of developing clinical depression has been found to be significantly greater for retired American football
players with a history of three or more concussions than for those with no concussion history. Three or more concussions is also associated with a fivefold greater chance of developing Alzheimer's disease
earlier and a threefold greater chance of developing memory
deficits.
is an example of the cumulative damage that can occur as the result of multiple concussions or less severe blows to the head. The condition called dementia pugilistica, or "punch drunk" syndrome, which is associated with boxers, can result in cognitive and physical deficits such as parkinsonism
, speech and memory problems, slowed mental processing, tremor, and inappropriate behavior. It shares features with Alzheimer's disease.
s lose the ability to regulate their diameter, causing a loss of control over cerebral blood flow. As the brain swells
, intracranial pressure rapidly rises. The brain can herniate
, and the brain stem can fail within five minutes. Except in boxing, all cases have occurred in athletes under age 20. Due to the very small number of documented cases, the diagnosis is controversial, and doubt exists about its validity.
Young children have the highest concussion rate among all age groups. However, most people who suffer concussion are young adults. A Canadian study found that the yearly incidence
of MTBI is lower in older age groups (graph at right). Studies suggest males suffer MTBI at about twice the rate of their female counterparts. However, female athletes may be at a higher risk for suffering concussion than their male counterparts.
Up to five percent of sports injuries are concussions. The U.S. Centers for Disease Control and Prevention
estimates that 300,000 sports-related concussions occur yearly in the U.S., but that number includes only athletes who lost consciousness. Since loss of consciousness is thought to occur in less than 10% of concussions, the CDC estimate is likely lower than the real number. Sports in which concussion is particularly common include football and boxing (a boxer aims to "knock out
", i.e. give a mild traumatic brain injury to, the opponent). The injury is so common in the latter that several medical groups have called for a ban on the sport, including the American Academy of Neurology, the World Medical Association
, and the medical associations of the UK, the U.S., Australia, and Canada.
Due to the lack of a consistent definition, the economic costs of MTBI are not known, but they are estimated to be very high. These high costs are due in part to the large percentage of hospital admissions for head injury that are due to mild head trauma, but indirect costs such as lost work time and early retirement account for the bulk of the costs. These direct and indirect costs cause the expense of mild brain trauma to rival that of moderate and severe head injuries.
The Hippocratic Corpus, collection of medical works from ancient Greece, mentions concussion, later translated to commotio cerebri, and discusses loss of speech, hearing and sight that can result from "commotion of the brain". This idea of disruption of mental function by "shaking of the brain" remained the widely accepted understanding of concussion until the 19th century. The Persian physician Muhammad ibn Zakarīya Rāzi was the first to write about concussion as distinct from other types of head injury in the 10th century AD. He may have been the first to use the term "cerebral concussion", and his definition of the condition, a transient loss of function with no physical damage, set the stage for the medical understanding of the condition for centuries. In the 13th century, the physician Lanfranc of Milan
's Chiurgia Magna described concussion as brain "commotion", also recognizing a difference between concussion and other types of traumatic brain injury (though many of his contemporaries did not), and discussing the transience of post-concussion symptoms as a result of temporary loss of function from the injury. In the 14th century, the surgeon Guy de Chauliac
pointed out the relatively good prognosis of concussion as compared to more severe types of head trauma such as skull fracture
s and penetrating head trauma. In the 16th century, the term "concussion" came into use, and symptoms such as confusion, lethargy, and memory problems were described. The 16th century physician Ambroise Paré
used the term commotio cerebri, as well as "shaking of the brain", "commotion", and "concussion".
Until the 17th century, concussion was usually described by its clinical features, but after the invention of the microscope, more physicians began exploring underlying physical and structural mechanisms. However, the prevailing view in the 17th century was that the injury did not result from physical damage, and this view continued to be widely held throughout the 18th century. The word "concussion" was used at the time to describe the state of unconsciousness and other functional problems that resulted from the impact, rather than a physiological condition.
In 1839, Guillaume Dupuytren described brain contusions, which involve many small hemorrhages, as contusio cerebri and showed the difference between unconsciousness associated with damage to the brain parenchyma
and that due to concussion, without such injury. In 1941, animal experiments showed that no macroscopic
damage occurs in concussion.
Latin
Latin is an Italic language originally spoken in Latium and Ancient Rome. It, along with most European languages, is a descendant of the ancient Proto-Indo-European language. Although it is considered a dead language, a number of scholars and members of the Christian clergy speak it fluently, and...
concutere ("to shake violently") or the Latin
Latin
Latin is an Italic language originally spoken in Latium and Ancient Rome. It, along with most European languages, is a descendant of the ancient Proto-Indo-European language. Although it is considered a dead language, a number of scholars and members of the Christian clergy speak it fluently, and...
concussus ("action of striking together"), is the most common type of 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...
. The terms mild brain injury, mild traumatic brain injury (MTBI), mild head injury (MHI), minor head trauma, and concussion may be used interchangeably, although the latter is often treated as a narrower category. The term "concussion" has been used for centuries and is still commonly used in sports medicine
Sports medicine
Sports medicine is a branch of medicine that deals with physical fitness, treatment and prevention of injuries related to sports and exercise...
, while "MTBI" is a technical term used more commonly nowadays in general medical contexts. Frequently defined as a head injury
Head injury
Head injury refers to trauma of the head. This may or may not include injury to the brain. However, the terms traumatic brain injury and head injury are often used interchangeably in medical literature....
with a temporary loss of brain function, concussion can cause a variety of physical, cognitive
Cognition
In science, cognition refers to mental processes. These processes include attention, remembering, producing and understanding language, solving problems, and making decisions. Cognition is studied in various disciplines such as psychology, philosophy, linguistics, and computer science...
, and emotional symptoms.
Treatment of concussion involves monitoring and rest. Symptoms usually go away entirely within three weeks, though they may persist, or complications may occur. Repeated concussions can cause cumulative brain damage
Brain 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...
such as dementia pugilistica
Dementia pugilistica
Dementia 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...
or severe complications such as second-impact syndrome
Second-impact syndrome
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...
.
Due to factors such as widely varying definitions and possible underreporting of concussion, the rate at which it occurs annually is not known; however it may be more than 6 per 1,000 people. Common causes include sports injuries, bicycle accidents, car accidents, and falls; the latter two are the most frequent causes among adults. Concussion may be caused by a blow to the head, or by 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. ...
forces without a direct impact. The forces involved disrupt cellular processes in the brain
Brain
The brain is the center of the nervous system in all vertebrate and most invertebrate animals—only a few primitive invertebrates such as sponges, jellyfish, sea squirts and starfishes do not have one. It is located in the head, usually close to primary sensory apparatus such as vision, hearing,...
for days or weeks. On the battlefield, MTBI is a potential consequence of nearby explosions.
It is not known whether the concussed brain is structurally damaged the way it is in other types of brain injury (albeit to a lesser extent) or whether concussion mainly entails a loss of function with physiological
Physiology
Physiology is the science of the function of living systems. This includes how organisms, organ systems, organs, cells, and bio-molecules carry out the chemical or physical functions that exist in a living system. The highest honor awarded in physiology is the Nobel Prize in Physiology or...
but not structural changes. Cellular damage has reportedly been found in concussed brains, but it may have been due to artifacts from the studies. It is now thought that structural and psychiatric factors may both be responsible for the effects of concussion.
Classification
No single definition of concussion, minor head injury, or mild traumatic brain injury is universally accepted, though a variety of definitions have been offered. In 2001, the first International Symposium on Concussion in Sport was organized by the International Olympic Committee Medical Commission and other sports federations. A group of experts called the Concussion in Sport Group met there and defined concussion as "a complex pathophysiological process affecting the brain, induced by traumatic biomechanical forces." They agreed that concussion typically involves temporary impairment of neurological function that heals by itself within time, and that neuroimagingNeuroimaging
Neuroimaging includes the use of various techniques to either directly or indirectly image the structure, function/pharmacology of the brain...
normally shows no gross structural changes to the brain as the result of the condition.
According to the classic definition, no structural brain damage occurs in concussion; it is a functional state, meaning that symptoms are caused primarily by temporary biochemical
Biochemistry
Biochemistry, sometimes called biological chemistry, is the study of chemical processes in living organisms, including, but not limited to, living matter. Biochemistry governs all living organisms and living processes...
changes in neuron
Neuron
A neuron is an electrically excitable cell that processes and transmits information by electrical and chemical signaling. Chemical signaling occurs via synapses, specialized connections with other cells. Neurons connect to each other to form networks. Neurons are the core components of the nervous...
s, taking place for example at their cell membrane
Cell membrane
The cell membrane or plasma membrane is a biological membrane that separates the interior of all cells from the outside environment. The cell membrane is selectively permeable to ions and organic molecules and controls the movement of substances in and out of cells. It basically protects the cell...
s and synapse
Synapse
In the nervous system, a synapse is a structure that permits a neuron to pass an electrical or chemical signal to another cell...
s. However, in recent years researchers have included injuries
Injury
-By cause:*Traumatic injury, a body wound or shock produced by sudden physical injury, as from violence or accident*Other injuries from external physical causes, such as radiation injury, burn injury or frostbite*Injury from infection...
in which structural damage does occur under the rubric of concussion. According to the National Institute for Health and Clinical Excellence
National Institute for Health and Clinical Excellence
The National Institute for Health and Clinical Excellence is a special health authority of the English National Health Service , serving both English NHS and the Welsh NHS...
definition, concussion may involve a physiological or physical disruption in the brain's synapse
Chemical synapse
Chemical synapses are specialized junctions through which neurons signal to each other and to non-neuronal cells such as those in muscles or glands. Chemical synapses allow neurons to form circuits within the central nervous system. They are crucial to the biological computations that underlie...
s.
Definitions of mild traumatic brain injury (M.T.B.I) have been inconsistent since the 1970s, but the World Health Organization
World Health Organization
The World Health Organization is a specialized agency of the United Nations that acts as a coordinating authority on international public health. Established on 7 April 1948, with headquarters in Geneva, Switzerland, the agency inherited the mandate and resources of its predecessor, the Health...
's International Statistical Classification of Diseases and Related Health Problems
ICD-10
The International Statistical Classification of Diseases and Related Health Problems, 10th Revision is a medical classification list for the coding of diseases, signs and symptoms, abnormal findings, complaints, social circumstances, and external causes of injury or diseases, as maintained by the...
(ICD-10) described MTBI-related conditions in 1992, providing a consistent, authoritative definition across specialties. In 1993, the American Congress of Rehabilitation Medicine defined MTBI as 30 minutes or fewer of loss of consciousness (LOC), 24 hours or fewer of post-traumatic amnesia
Post-traumatic amnesia
Post-traumatic amnesia is a state of confusion that occurs immediately following a traumatic brain injury in which the injured person is disoriented and unable to remember events that occur after the injury. The person may be unable to state his or her name, where he or she is, and what time it...
(PTA), and a Glasgow Coma Scale
Glasgow Coma Scale
Glasgow Coma Scale or GCS is a neurological scale that aims to give a reliable, objective way of recording the conscious state of a person for initial as well as subsequent assessment...
(GCS) score of at least 13. In 1994, the American Psychiatric Association
American Psychiatric Association
The American Psychiatric Association is the main professional organization of psychiatrists and trainee psychiatrists in the United States, and the most influential worldwide. Its some 38,000 members are mainly American but some are international...
's Diagnostic and Statistical Manual of Mental Disorders
Diagnostic and Statistical Manual of Mental Disorders
The Diagnostic and Statistical Manual of Mental Disorders is published by the American Psychiatric Association and provides a common language and standard criteria for the classification of mental disorders...
defined MTBI using PTA and LOC. Other definitions of MTBI incorporate focal neurological deficit and altered mental status, in addition to PTA and GCS.
Concussion falls under the classification of mild TBI. It is not clear whether concussion is implied in mild brain injury or mild head injury. "MTBI" and "concussion" are often treated as synonyms in medical literature. However, other injuries such as intracranial hemorrhage
Intracranial hemorrhage
An intracranial hemorrhage is a hemorrhage, or bleeding, within the skull.-Causes:Intracranial bleeding occurs when a blood vessel within the skull is ruptured or leaks. It can result from physical trauma or nontraumatic causes such as a ruptured aneurysm...
s (e.g. intra-axial hematoma
Intra-axial hematoma
A cerebral hemorrhage or hemorrhage is a subtype of intracranial hemorrhage that occurs within the brain tissue itself. Intracerebral hemorrhage can be caused by brain trauma, or it can occur spontaneously in hemorrhagic stroke...
, epidural hematoma
Epidural hematoma
Epidural or extradural hematoma is a type of traumatic brain injury in which a buildup of blood occurs between the dura mater and the skull. The dura mater also covers the spine, so epidural bleeds may also occur in the spinal column...
, and 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...
) are not necessarily precluded in MTBI or mild head injury, but they are in concussion. MTBI associated with abnormal neuroimaging may be considered "complicated MTBI". "Concussion" can be considered to imply a state in which brain function is temporarily impaired and "MTBI" to imply a pathophysiological
Pathophysiology
Pathophysiology is the study of the changes of normal mechanical, physical, and biochemical functions, either caused by a disease, or resulting from an abnormal syndrome...
state, but in practice few researchers and clinicians distinguish between the terms. Descriptions of the condition, including the severity and the area of the brain affected, are now used more often than "concussion" in clinical neurology.
Although the term "concussion" is still used in sports literature as interchangeable with "MHI" or "MTBI", the general clinical medical literature now uses "MTBI" instead.
Controversy exists about whether the definition of concussion should include only those injuries in which 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...
occurs.
Historically, by definition, concussion involved a loss of consciousness. However, the definition has evolved over time to include a change in consciousness, such as amnesia. The best-known concussion grading scales count head injuries in which loss of consciousness does not occur to be mild concussions and those in which it does to be more severe.
Grading systems
At least 41 systems exist to measure the severity, or grade, of a mild head injury, and there is little agreement among professionals about which is the best. Several of the systems use loss of consciousness and amnesia as the primary determinants of the severity of the concussion.In the past, the decision about when to allow athletes to return to contact sports was frequently based on the grade of concussion. However current research and recommendations by professional organizations such as the National Athletic Trainers Association recommend not using these grading systems for determination of severity of injury or for making return to play decisions. Injured athletes are prohibited from returning to play before they are symptom-free during rest and exertion and neuropsychological tests are normal again. This is to avoid cumulative effects.
Three grading systems were followed most widely: one was developed by Robert Cantu, one by the Colorado Medical Society
Colorado Medical Society
The Colorado Medical Society is the largest group of organized physicians in Colorado.This nonprofit organization is composed of physicians, residents and medical students. It was founded in 1871 to promote the art and science of medicine and to improve public health...
, and a third by the American Academy of Neurology
American Academy of Neurology
The American Academy of Neurology is a professional society for neurologists and neuroscientists. As a medical specialty society it was established in 1949 by A.B. Baker of the University of Minnesota to advance the art and science of neurology, and thereby promote the best possible care for...
. Each divides concussion into three grades, as summarized in the following table:
| Grade I | Grade II | Grade III | |
|---|---|---|---|
| Cantu guidelines | Post-traumatic amnesia <30 minutes, no loss of consciousness | Loss of consciousness <5 minutes or amnesia lasting 30 minutes–24 hours | Loss of consciousness >5 minutes or amnesia >24 hours |
| Colorado Medical Society guidelines | Confusion, no loss of consciousness | Confusion, post-traumatic amnesia, no loss of consciousness | Any loss of consciousness |
| American Academy of Neurology guidelines | Confusion, symptoms last <15 minutes, no loss of consciousness | Symptoms last >15 minutes, no loss of consciousness | Loss of consciousness (IIIa, coma lasts seconds, IIIb for minutes) |
Signs and symptoms
Concussion can be associated with a variety of symptoms, which typically occur rapidly after the injury. Early symptoms usually subside within days or weeks. The number and type of symptoms a person suffers varies widely.Physical
HeadacheHeadache
A headache or cephalalgia is pain anywhere in the region of the head or neck. It can be a symptom of a number of different conditions of the head and neck. The brain tissue itself is not sensitive to pain because it lacks pain receptors. Rather, the pain is caused by disturbance of the...
is the most common MTBI symptom. Other symptoms include dizziness, vomiting, nausea, lack of motor coordination
Motor coordination
thumb|right|Motor coordination is shown in this animated sequence by [[Eadweard Muybridge]] of himself throwing a diskMotor coordination is the combination of body movements created with the kinematic and kinetic parameters that result in intended actions. Such movements usually smoothly and...
, difficulty balancing
Balance (ability)
In biomechanics, balance is an ability to maintain the center of gravity of a body within the base of support with minimal postural sway. When exercising the ability to balance, one is said to be balancing....
, or other problems with movement or sensation. Visual symptoms include light sensitivity
Photophobia
Photophobia is a symptom of abnormal intolerance to visual perception of light. As a medical symptom photophobia is not a morbid fear or phobia, but an experience of discomfort or pain to the eyes due to light exposure or by presence of actual physical photosensitivity of the eyes, though the term...
, seeing bright lights, blurred vision
Blurred vision
-Causes:There are many causes of blurred vision:* Use of atropine or other anticholinergics* Presbyopia -- Difficulty focusing on objects that are close. The elderly are common victims....
, and double vision
Diplopia
Diplopia, commonly known as double vision, is the simultaneous perception of two images of a single object that may be displaced horizontally, vertically, or diagonally in relation to each other...
. Tinnitus
Tinnitus
Tinnitus |ringing]]") is the perception of sound within the human ear in the absence of corresponding external sound.Tinnitus is not a disease, but a symptom that can result from a wide range of underlying causes: abnormally loud sounds in the ear canal for even the briefest period , ear...
, or a ringing in the ears, is also commonly reported. In one in about seventy concussions, concussive convulsion
Convulsion
A convulsion is a medical condition where body muscles contract and relax rapidly and repeatedly, resulting in an uncontrolled shaking of the body. Because a convulsion is often a symptom of an epileptic seizure, the term convulsion is sometimes used as a synonym for seizure...
s occur, but these seizures that take place during or immediately after the concussion are not the same as post-traumatic seizure
Post-traumatic seizure
Post-traumatic seizures are seizures that result from traumatic brain injury , brain damage caused by physical trauma. PTS may be a risk factor for post-traumatic epilepsy , but a person who has a seizure or seizures due to traumatic brain injury does not necessarily have PTE, which is a form of...
s, and they, unlike post-traumatic seizures, are not in themselves predictive of 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...
, which requires some form of structural brain damage, not just a momentary disruption in normal brain functioning. Concussive convulsions are thought to result from temporary loss or inhibition of motor function, and are not associated either with epilepsy or with more serious structural damage. They are not associated with any particular sequelae
Sequela
A sequela) is a pathological condition resulting from a disease, injury, or other trauma.Chronic kidney disease, for example, is sometimes a sequela of diabetes, and neck pain is a common sequela of whiplash or other trauma to the cervical vertebrae. Post-traumatic stress disorder may be a...
and have the same high rate of favorable outcomes as concussions without convulsions.
Cognitive and emotional
Cognitive symptoms include confusion, disorientation, and difficulty focusing attentionAttention
Attention is the cognitive process of paying attention to one aspect of the environment while ignoring others. Attention is one of the most intensely studied topics within psychology and cognitive neuroscience....
. Loss of consciousness may occur but is not necessarily correlated with the severity of the concussion if it is brief. Post-traumatic amnesia
Post-traumatic amnesia
Post-traumatic amnesia is a state of confusion that occurs immediately following a traumatic brain injury in which the injured person is disoriented and unable to remember events that occur after the injury. The person may be unable to state his or her name, where he or she is, and what time it...
, in which the person cannot remember events leading up to the injury or after it, or both, is a hallmark of concussion. Confusion
Mental confusion
Confusion of a pathological degree usually refers to loss of orientation sometimes accompanied by disordered consciousness and often memory Confusion (from Latin confusĭo, -ōnis, noun of action from confundere "to pour together", also "to confuse") of a pathological degree usually refers to loss...
, another concussion hallmark, may be present immediately or may develop over several minutes. A patient may, for example, repeatedly ask the same questions, be slow to respond to questions or directions, have a vacant stare, or have slurred or incoherent speech. Other MTBI symptoms include changes in sleeping patterns and difficulty with reasoning, concentrating, and performing everyday activities.
Affect
Affect (psychology)
Affect refers to the experience of feeling or emotion. Affect is a key part of the process of an organism's interaction with stimuli. The word also refers sometimes to affect display, which is "a facial, vocal, or gestural behavior that serves as an indicator of affect" .The affective domain...
ive results of concussion include crankiness, loss of interest in favorite activities or items, tearfulness, and displays of emotion that are inappropriate to the situation. Common symptoms in concussed children include restlessness, lethargy, and irritability.
Mechanism
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...
is surrounded by cerebrospinal fluid
Cerebrospinal fluid
Cerebrospinal fluid , Liquor cerebrospinalis, is a clear, colorless, bodily fluid, that occupies the subarachnoid space and the ventricular system around and inside the brain and spinal cord...
, one of the functions of which is to protect it from light trauma, but more severe impacts or the forces associated with rapid acceleration may not be absorbed by this cushion. Concussion may be caused by impact force
Force
In physics, a force is any influence that causes an object to undergo a change in speed, a change in direction, or a change in shape. In other words, a force is that which can cause an object with mass to change its velocity , i.e., to accelerate, or which can cause a flexible object to deform...
s, in which the head strikes or is struck by something, or impulsive forces, in which the head moves without itself being subject to blunt trauma
Blunt trauma
In medical terminology, blunt trauma, blunt injury, non-penetrating trauma or blunt force trauma refers to a type of physical trauma caused to a body part, either by impact, injury or physical attack; the latter usually being referred to as blunt force trauma...
(for example, when the chest hits something and the head snaps forward).
Forces may cause linear, rotational, or angular movement of the brain, or a combination of these types of motion. In rotational movement, the head turns around its center of gravity, and in angular movement it turns on an axis not through its center of gravity. The amount of rotational force is thought to be the major type of force to cause concussion and the largest component in its severity. Studies with athletes have shown that the amount of force and the location of the impact are not necessarily correlated to the severity of the concussion or its symptoms, and have called into question the threshold for concussion previously thought to exist at around 70–75g
G-force
The g-force associated with an object is its acceleration relative to free-fall. This acceleration experienced by an object is due to the vector sum of non-gravitational forces acting on an object free to move. The accelerations that are not produced by gravity are termed proper accelerations, and...
.
The parts of the brain most affected by rotational forces are the midbrain and diencephalon
Diencephalon
The diencephalon is the region of the vertebrate neural tube which gives rise to posterior forebrain structures. In development, the forebrain develops from the prosencephalon, the most anterior vesicle of the neural tube which later forms both the diencephalon and the...
. It is thought that the forces from the injury disrupt the normal cell
Cell (biology)
The cell is the basic structural and functional unit of all known living organisms. It is the smallest unit of life that is classified as a living thing, and is often called the building block of life. The Alberts text discusses how the "cellular building blocks" move to shape developing embryos....
ular activities in the reticular activating system
Reticular activating system
The reticular activating system is an area of the brain responsible for regulating arousal and sleep-wake transitions.- History and Etymology :...
located in these areas, and that this disruption produces the loss of consciousness often seen in concussion. Other areas of the brain that may be affected include the upper part 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...
, the fornix, the corpus callosum
Corpus callosum
The corpus callosum , also known as the colossal commissure, is a wide, flat bundle of neural fibers beneath the cortex in the eutherian brain at the longitudinal fissure. It connects the left and right cerebral hemispheres and facilitates interhemispheric communication...
, the temporal lobe
Temporal lobe
The temporal lobe is a region of the cerebral cortex that is located beneath the Sylvian fissure on both cerebral hemispheres of the mammalian brain....
, and the frontal lobe
Frontal lobe
The frontal lobe is an area in the brain of humans and other mammals, located at the front of each cerebral hemisphere and positioned anterior to the parietal lobe and superior and anterior to the temporal lobes...
. Angular acceleration
Angular acceleration
Angular acceleration is the rate of change of angular velocity over time. In SI units, it is measured in radians per second squared , and is usually denoted by the Greek letter alpha .- Mathematical definition :...
s of 4600, 5900, or 7900 radian
Radian
Radian is the ratio between the length of an arc and its radius. The radian is the standard unit of angular measure, used in many areas of mathematics. The unit was formerly a SI supplementary unit, but this category was abolished in 1995 and the radian is now considered a SI derived unit...
/s2 are estimated to have 25, 50, or 80% risk of MTBI respectively.
Pathophysiology
In both animals and humans, MTBI can alter the brain's physiology for hours to weeks, setting into motion a variety of pathologicalPathology
Pathology is the precise study and diagnosis of disease. The word pathology is from Ancient Greek , pathos, "feeling, suffering"; and , -logia, "the study of". Pathologization, to pathologize, refers to the process of defining a condition or behavior as pathological, e.g. pathological gambling....
events. Though these events are thought to interfere with neuronal and brain function, the metabolic
Metabolism
Metabolism is the set of chemical reactions that happen in the cells of living organisms to sustain life. These processes allow organisms to grow and reproduce, maintain their structures, and respond to their environments. Metabolism is usually divided into two categories...
processes that follow concussion are reversed in a large majority of affected brain cell
Brain Cell
Brain Cell is a mail art project begun by Ryosuke Cohen in June 1985. The project is basically a networked art project where individual artists create their own 30x42cm work of art with stamps, drawings, stickers and so forth. This is sent to Cohen, who prints each cell - 150 copies each - with a...
s; however a few cells may die after the injury.
Included in the cascade of events unleashed in the brain by concussion is impaired neurotransmission
Neurotransmission
Neurotransmission , also called synaptic transmission, is the process by which signaling molecules called neurotransmitters are released by a neuron , and bind to and activate the receptors of another neuron...
, loss of regulation of ion
Ion
An ion is an atom or molecule in which the total number of electrons is not equal to the total number of protons, giving it a net positive or negative electrical charge. The name was given by physicist Michael Faraday for the substances that allow a current to pass between electrodes in a...
s, deregulation of energy use and cellular metabolism, and a reduction 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...
. Excitatory neurotransmitter
Neurotransmitter
Neurotransmitters are endogenous chemicals that transmit signals from a neuron to a target cell across a synapse. Neurotransmitters are packaged into synaptic vesicles clustered beneath the membrane on the presynaptic side of a synapse, and are released into the synaptic cleft, where they bind to...
s, chemicals such as glutamate that serve to stimulate nerve cells, are released in excessive amounts as the result of the injury. The resulting cellular excitation causes neurons to fire
Action potential
In physiology, an action potential is a short-lasting event in which the electrical membrane potential of a cell rapidly rises and falls, following a consistent trajectory. Action potentials occur in several types of animal cells, called excitable cells, which include neurons, muscle cells, and...
excessively. This creates an imbalance of ions such as potassium
Potassium in biology
Potassium is an essential mineral macronutrient and is the main intracellular ion for all types of cells.It is important in maintaining fluid and electrolyte balance in the bodies of humans and animals....
and calcium
Calcium in biology
Calcium plays a pivotal role in the physiology and biochemistry of organisms and the cell. It plays an important role in signal transduction pathways, where it acts as a second messenger, in neurotransmitter release from neurons, contraction of all muscle cell types, and fertilization...
across the cell membranes of neurons (a process like excitotoxicity
Excitotoxicity
Excitotoxicity is the pathological process by which nerve cells are damaged and killed by excessive stimulation by neurotransmitters such as glutamate and similar substances. This occurs when receptors for the excitatory neurotransmitter glutamate such as the NMDA receptor and AMPA receptor are...
). Since the neuron firing involves a net influx of positively charged ions into the cell, the ionic imbalance causes cells to have a more positive membrane potential
Membrane potential
Membrane potential is the difference in electrical potential between the interior and exterior of a biological cell. All animal cells are surrounded by a plasma membrane composed of a lipid bilayer with a variety of types of proteins embedded in it...
(i.e. it leads to neuronal depolarization
Depolarization
In biology, depolarization is a change in a cell's membrane potential, making it more positive, or less negative. In neurons and some other cells, a large enough depolarization may result in an action potential...
). This depolarization in turn causes ion pumps that serve to restore resting potential
Resting potential
The relatively static membrane potential of quiescent cells is called the resting membrane potential , as opposed to the specific dynamic electrochemical phenomena called action potential and graded membrane potential....
within cells to work more than they normally do. This increased need for energy leads cells to require greater-than-usual amounts of glucose
Glucose
Glucose is a simple sugar and an important carbohydrate in biology. Cells use it as the primary source of energy and a metabolic intermediate...
, which is made into ATP
Adenosine triphosphate
Adenosine-5'-triphosphate is a multifunctional nucleoside triphosphate used in cells as a coenzyme. It is often called the "molecular unit of currency" of intracellular energy transfer. ATP transports chemical energy within cells for metabolism...
, an important source of energy for cells. The brain may stay in this state of hypermetabolism for days or weeks. At the same time, cerebral blood flow is relatively reduced for unknown reasons, though the reduction in blood flow is not as severe as it is in ischemia
Ischemia
In medicine, ischemia is a restriction in blood supply, generally due to factors in the blood vessels, with resultant damage or dysfunction of tissue. It may also be spelled ischaemia or ischæmia...
. Thus cells get less glucose than they normally do, which causes an "energy crisis".
Concurrently with these processes, the activity of mitochondria
Mitochondrion
In cell biology, a mitochondrion is a membrane-enclosed organelle found in most eukaryotic cells. These organelles range from 0.5 to 1.0 micrometers in diameter...
may be reduced, which causes cells to rely on anaerobic metabolism to produce energy, which increases levels of the byproduct lactate
Lactic acid
Lactic acid, also known as milk acid, is a chemical compound that plays a role in various biochemical processes and was first isolated in 1780 by the Swedish chemist Carl Wilhelm Scheele. Lactic acid is a carboxylic acid with the chemical formula C3H6O3...
.
For a period of minutes to days after a concussion, the brain is especially vulnerable to changes 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...
, blood flow, and anoxia
Hypoxia (medical)
Hypoxia, or hypoxiation, is a pathological condition in which the body as a whole or a region of the body is deprived of adequate oxygen supply. Variations in arterial oxygen concentrations can be part of the normal physiology, for example, during strenuous physical exercise...
. According to studies performed on animals (which are not always applicable to humans), large numbers of neurons can die during this period in response to slight, normally innocuous changes in blood flow.
Concussion involves diffuse (as opposed to focal) brain injury
Focal and diffuse brain injury
Focal and diffuse brain injury are ways to classify brain injury: focal injury occurs in a specific location, while diffuse injury occurs over a more widespread area. It is common for both focal and diffuse damage to occur as the result of the same event; many traumatic brain injuries have aspects...
, meaning that the dysfunction occurs over a widespread area of the brain rather than in a particular spot. Concussion is thought to be a milder type of diffuse axonal injury
Diffuse axonal injury
Diffuse axonal injury is one of the most common and devastating types of traumatic brain injury, meaning that damage occurs over a more widespread area than in focal brain injury. DAI, which refers to extensive lesions in white matter tracts, is one of the major causes of unconsciousness and...
because axon
Axon
An axon is a long, slender projection of a nerve cell, or neuron, that conducts electrical impulses away from the neuron's cell body or soma....
s may be injured to a minor extent due to stretching. Animal studies in which primates were concussed have revealed damage to brain tissues such as small petechial hemorrhages and axonal injury. Axonal damage has been found in the brains of concussion sufferers who died from other causes, but inadequate blood flow to the brain due to other injuries may have contributed to the damage. Findings from a study of the brains of dead NFL athletes who received concussions suggest there is lasting damage to the brain after experiencing one; this damage can lead to a variety of other health issues.
The debate over whether concussion is a functional or structural phenomenon is ongoing. Structural damage has been found in the mildly traumatically injured brains of animals, but it is not clear whether these changes would be applicable to humans. Such changes in brain structure could be responsible for certain symptoms such as visual disturbances, but other sets of symptoms, especially those of a psychological nature, are more likely to be caused by reversible pathophysiological changes in cellular function that occur after concussion, such as alterations in neurons' biochemistry. These reversible changes could also explain why dysfunction is frequently temporary. A task force of head injury experts called the Concussion In Sport Group met in 2001 and decided that "concussion may result in neuropathological changes but the acute clinical symptoms largely reflect a functional disturbance rather than structural injury."
Diagnosis
Glasgow Coma Scale
Glasgow Coma Scale or GCS is a neurological scale that aims to give a reliable, objective way of recording the conscious state of a person for initial as well as subsequent assessment...
(MTBI sufferers have scores of 13 to 15). Neuropsychological test
Neuropsychological test
Neuropsychological tests are specifically designed tasks used to measure a psychological function known to be linked to a particular brain structure or pathway. Tests are used for research into brain function and in a clinical setting for the diagnosis of deficits. They usually involve the...
s exist to measure cognitive function, the international consensus meeting in Zurich recommend the use of the SCAT2.
The tests may be administered hours, days, or weeks after the injury, or at different times to determine whether there is a trend in the patient's condition. Athletes may be tested before a sports season begins to provide a baseline neurocognitive test for comparison in the event of an injury, though it may not reduce risk or effect return to play.
Health care providers examine head trauma survivors to ensure that the injury is not a more severe medical emergency
Medical emergency
A medical emergency is an injury or illness that is acute and poses an immediate risk to a person's life or long term health. These emergencies may require assistance from another person, who should ideally be suitably qualified to do so, although some of these emergencies can be dealt with by the...
such as an intracranial hemorrhage. Indications that screening for more serious injury is needed include worsening of symptoms such as headache, persistent vomiting, increasing disorientation or a deteriorating level of consciousness, seizures, and unequal pupil size
Anisocoria
-Causes:In the absence of the iris or eyeball proper, anisocoria is usually the result of a defect in efferent nervous pathways controlling the pupil traveling in the oculomotor nerve or the sympathetic pathways...
. People with such symptoms, or who are at higher risk for a more serious brain injury, are CT scanned to detect brain lesions and are frequently observed for 24 – 48 hours.
If the Glasgow Coma Scale
Glasgow Coma Scale
Glasgow Coma Scale or GCS is a neurological scale that aims to give a reliable, objective way of recording the conscious state of a person for initial as well as subsequent assessment...
is less than 15 at two hours or less than 14 at any time a CT recommended. In addition, they may be more likely to perform a CT scan on people who would be difficult to observe after discharge or those who are intoxicated, at risk for bleeding, older than 60, or younger than 16. Most concussions cannot be detected with MRI or CT scans. However, changes have been reported to show up on MRI and SPECT imaging in concussed people with normal CT scans, and post-concussion syndrome
Post-concussion syndrome
Post-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...
may be associated with abnormalities visible on SPECT
Single photon emission computed tomography
Single-photon emission computed tomography is a nuclear medicine tomographic imaging technique using gamma rays. It is very similar to conventional nuclear medicine planar imaging using a gamma camera. However, it is able to provide true 3D information...
and PET scan
Positron emission tomography
Positron emission tomography is nuclear medicine imaging technique that produces a three-dimensional image or picture of functional processes in the body. The system detects pairs of gamma rays emitted indirectly by a positron-emitting radionuclide , which is introduced into the body on a...
s. Mild head injury may or may not produce abnormal EEG
Electroencephalography
Electroencephalography is the recording of electrical activity along the scalp. EEG measures voltage fluctuations resulting from ionic current flows within the neurons of the brain...
readings.
Concussion may be under-diagnosed. The lack of the highly noticeable signs and symptoms that are frequently present in other forms of head injury could lead clinicians to miss the injury, and athletes may cover up their injuries to remain in the competition. A retrospective survey in 2005 found that more than 88% of concussions go unrecognized.
Diagnosis of concussion can be complicated because it shares symptoms with other conditions. For example, post-concussion symptoms such as cognitive problems may be misattributed to brain injury when they are in fact due to post-traumatic stress disorder
Post-traumatic stress disorder
Posttraumaticstress disorder is a severe anxiety disorder that can develop after exposure to any event that results in psychological trauma. This event may involve the threat of death to oneself or to someone else, or to one's own or someone else's physical, sexual, or psychological integrity,...
(PTSD).
In 2011, the Georgia Tech Research Institute
Georgia Tech Research Institute
The Georgia Tech Research Institute is the nonprofit applied research arm of the Georgia Institute of Technology in Atlanta, Georgia, United States...
researchers are investigating the use of radar as a possible concussion detection tool. No clinic studies have been done to prove it is accurate, therefore currently not ready for use.
Prevention
Prevention of MTBI involves taking general measures to prevent traumatic brain injury, such as wearing seat beltSeat belt
A seat belt or seatbelt, sometimes called a safety belt, is a safety harness designed to secure the occupant of a vehicle against harmful movement that may result from a collision or a sudden stop...
s and using airbag
Airbag
An Airbag is a vehicle safety device. It is an occupant restraint consisting of a flexible envelope designed to inflate rapidly during an automobile collision, to prevent occupants from striking interior objects such as the steering wheel or a window...
s in cars. Older people are encouraged to try to prevent falls, for example by keeping floors free of clutter and wearing thin, flat, shoes with hard soles that do not interfere with balance.
Use of protective equipment such as headgear has been found to reduce the number of concussions in athletes. Improvements in the design of protective athletic gear such as helmets may decrease the number and severity of such injuries. New "Head Impact Telemetry System" technology is being placed in helmets to study injury mechanisms and potentially help reduce the risk of concussions among American Football players. Changes to the rules or the practices of enforcing existing rules in sports, such as those against "head-down tackling", or "spearing", which is associated with a high injury rate, may also prevent concussions.
Treatment
Usually concussion symptoms go away without treatment, and no specific treatment exists. About one percent of people who receive treatment for MTBI need surgery for a brain injury. Traditionally, concussion sufferers are prescribed rest, including plenty of sleep at night plus rest during the day. Health care providers recommend a gradual return to normal activities at a pace that does not cause symptoms to worsen. Education about symptoms, how to manage them, and their normal time course can lead to an improved outcome.Medications may be prescribed to treat symptoms such as sleep problems and depression. Analgesic
Analgesic
An analgesic is any member of the group of drugs used to relieve pain . The word analgesic derives from Greek an- and algos ....
s such as ibuprofen
Ibuprofen
Ibuprofen is a nonsteroidal anti-inflammatory drug used for relief of symptoms of arthritis, fever, as an analgesic , especially where there is an inflammatory component, and dysmenorrhea....
can be taken for the headaches that frequently occur after concussion, but paracetamol (acetaminophen)
Paracetamol
Paracetamol INN , or acetaminophen USAN , is a widely used over-the-counter analgesic and antipyretic . It is commonly used for the relief of headaches and other minor aches and pains and is a major ingredient in numerous cold and flu remedies...
is preferred to minimize the risk for complications such as intracranial hemorrhage. Concussed individuals are advised not to drink alcohol
Alcoholic beverage
An alcoholic beverage is a drink containing ethanol, commonly known as alcohol. Alcoholic beverages are divided into three general classes: beers, wines, and spirits. They are legally consumed in most countries, and over 100 countries have laws regulating their production, sale, and consumption...
or take drug
Drug
A drug, broadly speaking, is any substance that, when absorbed into the body of a living organism, alters normal bodily function. There is no single, precise definition, as there are different meanings in drug control law, government regulations, medicine, and colloquial usage.In pharmacology, a...
s that have not been approved by a doctor, as they could impede healing.
Observation to monitor for worsening condition is an important part of treatment. Health care
Health care
Health care is the diagnosis, treatment, and prevention of disease, illness, injury, and other physical and mental impairments in humans. Health care is delivered by practitioners in medicine, chiropractic, dentistry, nursing, pharmacy, allied health, and other care providers...
providers recommend that those suffering from concussion return for further medical care and evaluation 24 to 72 hours after the concussive event if the symptoms worsen. Athletes, especially intercollegiate or professional athletes
Professional sports
Professional sports, as opposed to amateur sports, are sports in which athletes receive payment for their performance. Professional athleticism has come to the fore through a combination of developments. Mass media and increased leisure have brought larger audiences, so that sports organizations...
, are typically followed closely by team trainers during this period. But others may not have access to this level of health care and may be sent home with no medical person monitoring them unless the situation gets worse. Patients may be released from the hospital to the care of a trusted person with orders to return if they display worsening symptoms or those that might indicate an emergent condition, like unconsciousness or altered mental status; convulsions; severe, persistent headache; extremity weakness; vomiting; or new bleeding or deafness in either or both ears. Repeated observation for the first 24 hours after concussion is recommended; however it is not known whether it is necessary to wake the patient up every few hours.
Prognosis
MTBI has a mortality rate of almost zero. The symptoms of most concussions resolve within weeks, but problems may persist. Problems are seldom permanent, and outcome is usually excellent. People over age 55 may take longer to heal from MTBI or may heal incompletely. Similarly, factors such as a previous head injury or a coexisting medical condition have been found to predict longer-lasting post-concussion symptoms. Other factors that may lengthen recovery time after MTBI include psychological problems such as substance abuseSubstance abuse
A substance-related disorder is an umbrella term used to describe several different conditions associated with several different substances .A substance related disorder is a condition in which an individual uses or abuses a...
or clinical depression
Clinical depression
Major depressive disorder is a mental disorder characterized by an all-encompassing low mood accompanied by low self-esteem, and by loss of interest or pleasure in normally enjoyable activities...
, poor health before the injury or additional injuries sustained during it, and life stress. Longer periods of amnesia or loss of consciousness immediately after the injury may indicate longer recovery times from residual symptoms. For unknown reasons, having had one concussion significantly increases a person's risk of having another. Having previously sustained a sports concussion has been found to be a strong factor increasing the likelihood of a concussion in the future. Other strong factors include participation in a contact sport and body mass size. The prognosis may differ between concussed adults and children; little research has been done on concussion in the pediatric population, but concern exists that severe concussions could interfere with brain development
Neural development
Neural development comprises the processes that generate, shape, and reshape the nervous system, from the earliest stages of embryogenesis to the final years of life. The study of neural development aims to describe the cellular basis of brain development and to address the underlying mechanisms...
in children.
A 2009 study published in Brain
Brain (journal)
Brain is a neurological journal published by Oxford University Press. It was edited by John Newsom-Davis from 1997 to 2004. Under his editorship it became one of the first scientific journals to go online. Since 2004 the journal is edited by Alastair Compston, Professor and Head of Department of...
found that individuals with a history of concussions might demonstrate a decline in both physical and mental performance for longer than 30 years. Compared to their peers with no history of brain trauma, sufferers of concussion exhibited effects including loss of episodic memory
Episodic memory
Episodic memory is the memory of autobiographical events that can be explicitly stated. Semantic and episodic memory together make up the category of declarative memory, which is one of the two major divisions in memory...
and reduced muscle speed.
Post-concussion syndrome
In post-concussion syndrome, symptoms do not resolve for weeks, months, or years after a concussion, and may occasionally be permanent. Symptoms may include headaches, dizziness, fatigue, anxietyAnxiety
Anxiety is a psychological and physiological state characterized by somatic, emotional, cognitive, and behavioral components. The root meaning of the word anxiety is 'to vex or trouble'; in either presence or absence of psychological stress, anxiety can create feelings of fear, worry, uneasiness,...
, memory and attention problems, sleep problems, and irritability. There is no scientifically established treatment, and rest, a recommended recovery technique, has limited effectiveness. Symptoms usually go away on their own within months. The question of whether the syndrome is due to structural damage or other factors such as psychological ones, or a combination of these, has long been the subject of debate.
Cumulative effects
Cumulative effects of concussions are poorly understood. The severity of concussions and their symptoms may worsen with successive injuries, even if a subsequent injury occurs months or years after an initial one. Symptoms may be more severe and changes in neurophysiologyNeurophysiology
Neurophysiology is a part of physiology. Neurophysiology is the study of nervous system function...
can occur with the third and subsequent concussions. Studies have had conflicting findings on whether athletes have longer recovery times after repeat concussions and whether cumulative effects such as impairment in cognition and memory occur.
Cumulative effects may include psychiatric disorders and loss of long-term memory
Long-term memory
Long-term memory is memory in which associations among items are stored, as part of the theory of a dual-store memory model. According to the theory, long term memory differs structurally and functionally from working memory or short-term memory, which ostensibly stores items for only around 20–30...
. For example, the risk of developing clinical depression has been found to be significantly greater for retired American 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...
players with a history of three or more concussions than for those with no concussion history. Three or more concussions is also associated with a fivefold greater chance of developing Alzheimer's disease
Alzheimer's disease
Alzheimer's disease also known in medical literature as Alzheimer disease is the most common form of dementia. There is no cure for the disease, which worsens as it progresses, and eventually leads to death...
earlier and a threefold greater chance of developing memory
Memory
In psychology, memory is an organism's ability to store, retain, and recall information and experiences. Traditional studies of memory began in the fields of philosophy, including techniques of artificially enhancing memory....
deficits.
Dementia pugilistica
Chronic encephalopathyEncephalopathy
Encephalopathy means disorder or disease of the brain. In modern usage, encephalopathy does not refer to a single disease, but rather to a syndrome of global brain dysfunction; this syndrome can be caused by many different illnesses.-Terminology:...
is an example of the cumulative damage that can occur as the result of multiple concussions or less severe blows to the head. The condition called dementia pugilistica, or "punch drunk" syndrome, which is associated with boxers, can result in cognitive and physical deficits such as parkinsonism
Parkinsonism
Parkinsonism is a neurological syndrome characterized by tremor, hypokinesia, rigidity, and postural instability. The underlying causes of parkinsonism are numerous, and diagnosis can be complex...
, speech and memory problems, slowed mental processing, tremor, and inappropriate behavior. It shares features with Alzheimer's disease.
Second-impact syndrome
Second-impact syndrome, in which the brain swells dangerously after a minor blow, may occur in very rare cases. The condition may develop in people who receive a second blow days or weeks after an initial concussion, before its symptoms have gone away. No one is certain of the cause of this often fatal complication, but it is commonly thought that the swelling occurs because the brain's arterioleArteriole
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 the ability to regulate their diameter, causing a loss of control over cerebral blood flow. As the brain swells
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....
, intracranial pressure rapidly rises. The brain can herniate
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...
, and the brain stem can fail within five minutes. Except in boxing, all cases have occurred in athletes under age 20. Due to the very small number of documented cases, the diagnosis is controversial, and doubt exists about its validity.
Epidemiology
Most cases of traumatic brain injury are concussions. A World Health Organization (WHO) study estimated that between 70 and 90% of head injuries that receive treatment are mild. However, due to underreporting and to the widely varying definitions of concussion and MTBI, it is difficult to estimate how common the condition is. Estimates of the incidence of concussion may be artificially low, for example due to underreporting. At least 25% of MTBI sufferers fail to get assessed by a medical professional. The WHO group reviewed studies on the epidemiology of MTBI and found a hospital treatment rate of 1–3 per 1000 people, but since not all concussions are treated in hospitals, they estimated that the rate per year in the general population is over 6 per 1000 people.Young children have the highest concussion rate among all age groups. However, most people who suffer concussion are young adults. A Canadian study found that the yearly incidence
Incidence (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 MTBI is lower in older age groups (graph at right). Studies suggest males suffer MTBI at about twice the rate of their female counterparts. However, female athletes may be at a higher risk for suffering concussion than their male counterparts.
Up to five percent of sports injuries are concussions. The U.S. Centers for Disease Control and Prevention
Centers for Disease Control and Prevention
The Centers for Disease Control and Prevention are a United States federal agency under the Department of Health and Human Services headquartered in Druid Hills, unincorporated DeKalb County, Georgia, in Greater Atlanta...
estimates that 300,000 sports-related concussions occur yearly in the U.S., but that number includes only athletes who lost consciousness. Since loss of consciousness is thought to occur in less than 10% of concussions, the CDC estimate is likely lower than the real number. Sports in which concussion is particularly common include football and boxing (a boxer aims to "knock out
Knockout
A knockout is a fight-ending, winning criterion in several full-contact combat sports, such as boxing, kickboxing, Muay Thai, mixed martial arts, Karate and others sports involving striking...
", i.e. give a mild traumatic brain injury to, the opponent). The injury is so common in the latter that several medical groups have called for a ban on the sport, including the American Academy of Neurology, the World Medical Association
World Medical Association
The World Medical Association is an international and independent confederation of free professional Medical Associations, therefore representing physicians worldwide...
, and the medical associations of the UK, the U.S., Australia, and Canada.
Due to the lack of a consistent definition, the economic costs of MTBI are not known, but they are estimated to be very high. These high costs are due in part to the large percentage of hospital admissions for head injury that are due to mild head trauma, but indirect costs such as lost work time and early retirement account for the bulk of the costs. These direct and indirect costs cause the expense of mild brain trauma to rival that of moderate and severe head injuries.
History
Lanfranc of Milan
The surgeon Lanfranc of Milan , variously called Guido Lanfranchi, Lanfranco, or Alanfrancus was a student of Guglielmo da Saliceto. Involved in the struggles of Guelphs and Ghibellines, he was exiled from Milan by Matteo I Visconti in 1290. He moved first to Lyons, then on to Paris...
's Chiurgia Magna described concussion as brain "commotion", also recognizing a difference between concussion and other types of traumatic brain injury (though many of his contemporaries did not), and discussing the transience of post-concussion symptoms as a result of temporary loss of function from the injury. In the 14th century, the surgeon Guy de Chauliac
Guy de Chauliac
Guy de Chauliac or Guigonis de Caulhaco was a French physician and surgeon who wrote a lengthy and influential treatise on surgery in Latin, titled Chirurgia Magna...
pointed out the relatively good prognosis of concussion as compared to more severe types of head trauma such as skull fracture
Skull fracture
A skull fracture is a break in one or more of the bones in the skull usually occurring as a result of blunt force trauma. If the force of the impact is excessive the bone may fracture at or near the site of the impact...
s and penetrating head trauma. In the 16th century, the term "concussion" came into use, and symptoms such as confusion, lethargy, and memory problems were described. The 16th century physician Ambroise Paré
Ambroise Paré
Ambroise Paré was a French surgeon. He was the great official royal surgeon for kings Henry II, Francis II, Charles IX and Henry III and is considered as one of the fathers of surgery and modern forensic pathology. He was a leader in surgical techniques and battlefield medicine, especially the...
used the term commotio cerebri, as well as "shaking of the brain", "commotion", and "concussion".
In 1839, Guillaume Dupuytren described brain contusions, which involve many small hemorrhages, as contusio cerebri and showed the difference between unconsciousness associated with damage to the brain parenchyma
Parenchyma
Parenchyma is a term used to describe a bulk of a substance. It is used in different ways in animals and in plants.The term is New Latin, f. Greek παρέγχυμα - parenkhuma, "visceral flesh", f. παρεγχεῖν - parenkhein, "to pour in" f. para-, "beside" + en-, "in" + khein, "to pour"...
and that due to concussion, without such injury. In 1941, animal experiments showed that no macroscopic
Macroscopic
The macroscopic scale is the length scale on which objects or processes are of a size which is measurable and observable by the naked eye.When applied to phenomena and abstract objects, the macroscopic scale describes existence in the world as we perceive it, often in contrast to experiences or...
damage occurs in concussion.
See also
- Concussion grading systemsConcussion grading systemsConcussion 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...
- Head injury criterionHead injury criterionThe Head Injury Criterion is a measure of the likelihood of head injury arising from an impact. The HIC can be used to assess safety related to vehicles, personal protective gear, and sport equipment....
- Chronic traumatic encephalopathyChronic traumatic encephalopathyChronic traumatic encephalopathy is a progressive degenerative disease found in individuals who have been subjected to multiple concussions and other forms of head injury. A variant of the condition, dementia pugilistica, is primarily associated with boxing...
External links
- "Facts about Concussion and Brain Injury and Where to Get Help" US Centers for Disease Control and Prevention
- "Concussion in High School Sports" US Centers for Disease Control and Prevention
- Headway - the brain injury association UK based charity providing information and support