Updated: Jan 06, 2023
  • Author: David T Bernhardt, MD; Chief Editor: Craig C Young, MD  more...
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Practice Essentials

Concussion, or mild traumatic brain injury (MTBI), is common among contact and collision sports participants. [1, 2, 3, 4, 5, 6, 7] One definition of concussion is a condition in which there is a traumatically induced alteration in mental status, with or without an associated loss of consciousness (LOC). [1] A broader definition is a traumatically induced physiologic disruption in brain function that is manifested by LOC, memory loss, alteration of mental state or personality, or focal neurologic deficits.

Signs and symptoms

An athlete suffering from an MTBI may demonstrate the following:

  • Confusion: Athletes with an MTBI often appear acutely with a confused or blank expression or blunted affect

  • Delayed responses and emotional changes: Delayed response to simple questioning may be demonstrated, along with emotional lability; the emotional lability may become more evident as the athlete attempts to cope with his or her confusion

  • Pain/dizziness: Many athletes report an associated headache and dizziness

  • Visual disturbances: Visual complaints may include seeing stars, blurry vision, or double vision

  • Amnesia: Pretraumatic (retrograde) and posttraumatic (antegrade) amnesia may be present; usually, the duration of retrograde amnesia is quite brief, while the duration of posttraumatic amnesia is more variable (lasting seconds to minutes), depending upon the injury

  • Signs of increased intracranial pressure: A history of persistent vomiting may suggest a significant brain injury with associated elevated intracranial pressure; other signs of increased intracranial pressure include worsening headache, increasing disorientation, and a changing level of consciousness

Physical examination

The physical examination should include assessment of the following:

  • Appearance: The initial clinical examination should include a careful inspection of the athlete's general appearance

  • Head and neck: Palpating the head and neck is important when looking for an associated skull or cervical injury

  • Facial bones: Palpate the facial bones and the periorbital, mandibular, and maxillary areas after any head trauma

  • Jaws: Open and close the mouth to help in the evaluation of possible temporomandibular joint (TMJ) pain, malocclusion, or mandibular fracture

  • Nose: Inspect the nose for deformity and tenderness, which may indicate a possible nasal fracture

  • Presence of discharge: Persistent rhinorrhea or otorrhea (clear) indicates a possible associated skull fracture.

  • Vision: Perform a careful, detailed neurologic examination that includes evaluation of the visual fields, extraocular movements, pupillary reflexes, and level of the eyes

  • Strength and sensation: Assess upper-extremity and lower-extremity strength and sensation

  • Coordination and balance: Concussed patients often have difficulty with the finger-nose-finger test and will use slow, purposeful movements to complete the task

Postconcussive syndrome

Postconcussive syndrome consists of prolonged symptoms that are related to the initial head injury. Symptoms usually consist of the following:

  • Persistent, recurrent headaches

  • Dizziness

  • Memory impairment

  • Loss of libido

  • Ataxia

  • Sensitivity to light and noise

  • Concentration and attention problems

  • Depression

  • Anxiety

See Clinical Presentation for more detail.



The following imaging studies can be used in the examination of head injury (Note: Although the following studies may be useful in the evaluation of head trauma, they will be negative for a concussion with no other injury.):

  • Computed tomography scanning: CT scanning continues to be the imaging study of choice for evaluating acute head injury

  • Magnetic resonance imaging: MRI is the imaging study of choice for patients who have prolonged symptoms (>7 days) or when a late change occurs in an individual's neurologic signs or symptoms

Although positron emission tomography (PET) scanning and functional MRI (fMRI) may be used in evaluating patients with concussion, their clinical application in most cases of MTBI is uncertain. [8, 9, 10]

Neuropsychological testing

Detailed neuropsychologic testing is employed more often at the professional level and in research in athletes with MTBI.

See Workup for more detail.


Most patients with MTBI recover in 48-72 hours, even with detailed neuropsychological testing, and are headache free within 2-4 weeks of the injury.

A clinical report by the American Academy of Pediatrics (AAP) on the diagnosis and management of sports-related concussions in adolescents and children noted the following [11] :

  • Cognitive and physical rest is the mainstay of management of patients with concussion

  • Ongoing neuropsychological testing is a helpful tool during management

Although several different guidelines regarding return to play have been established, the main criteria for an athlete's return to play after a concussion include the following:

  • Complete clearing of all symptoms

  • Complete return of all memory and concentration

  • No symptoms after provocative testing: Provocative testing includes jogging, sprinting, sit-ups, or pushups (ie, exercise that raises the athlete's blood pressure and heart rate)

Davis and Purcell have released an assessment of the evaluation and management of acute concussion in young children. [12]

In 2013, the American Academy of Neurology issued updated guidelines for the evaluation and management of sports concussion. [13]

See Treatment and Medication for more detail.



Concussion has many different meanings to patients, families, and physicians. [1, 14, 15, 16] One definition of concussion is a condition in which there is a traumatically induced alteration in mental status, with or without an associated loss of consciousness (LOC). [1] A broader definition for concussion is a traumatically induced physiologic disruption in brain function that is manifested by LOC, memory loss, alteration of mental state or personality, or focal neurologic deficits. [1] Concussions usually result in relatively temporary impairment of neurologic function. [8, 16, 17]

Concussion or mild traumatic brain injury (MTBI) is common among most contact and collision sports participants. [1, 2, 3, 4, 5, 6, 7] For many physicians, even those who specialize in MTBI, this area is confusing due to the paucity of scientific evidence to support much of the clinical decision making that is faced in the office. [4, 9, 14, 15, 18] The inconsiderable amount of good scientific research in the area of MTBI is due to problems with ambiguous definitions of concussion, inconsistent criteria when selecting patients to study, variability of injury mechanisms and locations, and differing means of measuring cognitive function. [19, 20] The purpose of this article is to review the epidemiology and diagnosis (but not necessarily the classification) of MTBI, as well as the role of imaging studies, issues regarding return to play, and complications surrounding MTBI.



United States statistics

The incidence of head injury varies with the sport and the age of the participants; many head injuries are likely unreported due to their supposed mild nature; mild concussions may go unnoticed by teammates, coaches, and even the athletes themselves. [1] An athlete's fear of medical disqualification may also lead to underreporting. Studies of high school athletes show the rate of concussions per 1000 exposures as follows: 0.59 for football (boys), 0.25 for wrestling (boys), 0.18 for soccer (boys; 0.23 for girls), 0.09 for field hockey (girls), and 0.11 for basketball (boys; 0.16 for girls). The data from one study noted that concussions account for nearly 15% of all sport-related injuries in high school athletes. [21]

Among National Collegiate Athletic Association (NCAA) soccer players, the rate of injury has been reported as 0.4-0.6 per 1000 athlete exposures [6] ; 72% of these injuries were described as mild and were almost always secondary to direct contact with an opponent. None of the injuries in this group of Atlantic Coast Conference (ACC) soccer players was noted to be a direct result of heading the ball. In contrast, boxing is the sport with the highest rate of head injuries and has more deaths than any other organized athletic activity. At the professional level, many of the boxing bouts end with a technical knockout (ie, brain injury).

Sports activities that place the athlete at high risk for a head injury include boxing, football, ice hockey, wrestling, rugby, and soccer. Physicians and other allied health providers who are responsible for the medical care of such contact or collision sports participants should be adept at evaluating, treating, and making playability decisions related to the short- and long-term consequences of an injury to the brain.


Sport-Specific Biomechanics

The mechanisms of brain injury may differ among sports activities. Possible mechanisms of injury include compressive forces, which may directly injure the brain at the point of contact (coup); tensile forces produce injury at the point opposite the injury (contrecoup) because the axons and nerves are stretched; finally, rotational forces may result in a shearing of axons. Therefore, the direct force at the point of contact may not be solely responsible for the severity of an injury if a high rotational component with a significant shear effect occurs.

All of the different mechanisms may result in biochemical changes related to perfusion, energy demand, and utilization at the site of injury that are not well understood. At this time, it is unclear whether any experimental animal model or human studies on more severe brain-injured patients accurately reflect the pathophysiology of the typical mild traumatic alteration in brain function.



A previous concussion is a significant risk factor for sustaining a concussion. [2, 3, 7, 22, 23, 24, 25]

One study reported that the risk of sustaining a concussion was 4-5 times higher in patients who had at least 1 concussion in the past. Another study reported that athletes with a history of 3 or more previous concussions were 3-fold more likely to have a concussion than players who had no history of concussion. [24]

Other risk factors for sustaining a concussion that have been suggested but not proven include not wearing mouth guards, poor fitting helmets, and genetic predisposition. [26, 27]  Research in all of these areas continues.



Most patients with an MTBI are able to return to full competition without complication. Because many patients may not report minor head injuries to the athletic trainer, emergency department (ED), or a primary care physician, the overall prognosis of many head injuries is unclear.

A study including male high school football players noted that dizziness at the time of injury is associated with an increased risk of protracted (≥21 d) recovery. Another study involving athletes aged 9-23 years with a diagnosed protracted concussion found that those who have vestibular symptoms after concussion may have slower reaction times than those who do not and thus may be at greater risk for new injury. [28]

A study by Ling and colleagues indicated that at least 4 months after an MTBI, the brain continues to display signs of damage, even if the clinical symptoms of injury have subsided. Evaluation of patients with mild brain injury, however, revealed no evidence of cortical or subcortical atrophy. The study involved 50 patients with MTBI and 50 matched controls. In the first 2 weeks following injury (the semiacute injury phase), patients with concussion complained of more cognitive, somatic, and emotional symptoms than did the controls. These symptoms, however, were significantly reduced at 4-month follow-up (at which time, 26 of the patients were evaluated). [29, 30]

In a prospective cohort study of 280 patients aged 11 to 22 years who presented to an emergency department with acute concussion, repeat concussions increased the risk for prolonged recovery. [31]  Patients with a history of previous concussions had symptoms that lasted twice as long (24 days) as those who did not have such a history (12 days).

An analysis of children presenting to the ED with concussion showed that the patients were still struggling with a significant burden of symptoms 1 week after injury. [32, 33]  Headache was the most common initial symptom; by day 7, 69.2% were still experiencing headaches. Fatigue persisted in 59.8% of children at day 7, and poor concentration persisted in 56.8% 1 week later. Emotional symptoms (eg, depression, frustration, irritability, and restlessness) also developed and increased by day 7 but were largely resolved by day 90.

A retrospective study by Kontos et al showed that adolescent athletes with concussion who received clinical care within 7 days of the injury recovered in a mean of 20 days more quickly than athletes who received care 8-20 days after the injury. The researchers suggest that the earlier initiation of active rehabilitation strategies may explain the more rapid recovery. [34]

Chronic postconcussive syndrome can be quite severe, with the most dramatic presentation including dementia pugilistica, which is associated with boxing. This Alzheimer-like condition has a reported incidence of 15% among professional boxers. Fortunately, this condition is rare in most other sports. Hopefully, more frequent, detailed neuropsychologic testing will decrease the frequency of postconcussive syndrome among elite and professional athletes by detecting more subtle injuries earlier. For further information on this topic, see Repetitive Head Injury Syndrome.


Chronic traumatic encephalopathy (CTE) 

Persons with a history of repetitive brain trauma, including boxers and football players, are at risk for developing chronic traumatic encephalopathy (CTE), a progressive degenerative disease. Degenerative changes, which can begin months to decades after the patient’s last brain trauma, include atrophy of the cerebral hemispheres, medial temporal lobe, thalamus, mammillary bodies, and brainstem. The condition is also characterized by ventricular dilatation and by fenestration of the cavum septum pellucidum, as well as the accumulation of phosphorylated tau in the brain, with deposits of the protein being found in the sulci and in perivascular areas of the cerebral cortex. Symptoms of CTE include memory loss, confusion, impaired judgment, reduced impulse control, aggression, explosive anger, depression, and progressive dementia. [35, 36, 37, 38]

According to a report from the US Department of Veterans Affairs and Boston University, 87 of 91 deceased former players for the National Football League (NFL) (96%) who donated their brains for study were found to have changes consistent with CTE. These finding need to be tempered by the fact the donors had, prior to death, expressed concern that they might have CTE and so may have had a higher proportion of the disease than does the overall population of former NFL players. In addition these individuals had not necessarily had clinical symptoms of CTE, but felt they might be at risk. [39, 40]

A study by Mez et al diagnosed CTE in 177 (78%) of 202 samples from deceased American football players. The samples included 111 former NFL players of which, 110 (99%) were diagnosed with CTE. The study also found that among the 26 participants diagnosed with mild CTE, 96% had behavioral or mood symptoms or both, 85% had cognitive symptoms, and 33% had signs of dementia. In the 84 participants diagnosed with severe CTE, 89% had behavioral or mood symptoms, 95% had cognitive symptoms, and 85% had signs of dementia. [41]

A study by Alosco et al showed that a distinct pattern of frontal-temporal atrophy on MRI may suggest CTE. Compared with persons with normal cognition, those with CTE had significantly greater atrophy in several brain regions, including the orbital-frontal cortex, dorsolateral frontal cortex, superior frontal cortex, anterior temporal lobes, and medial temporal lobe. [42]