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Mild traumatic brain injury (mTBI) is a trauma-induced disruption of brain function on the lowest end of the TBI severity spectrum, typically due to a fall, motor vehicle accident, or sports injury. Characteristic manifestations include a GCS ≥ 13–15, transient loss of consciousness, altered mental status at the time of injury, posttraumatic amnesia, and minor neurological abnormalities that do not require surgical intervention. Concussion, a term often used synonymously with mTBI, is difficult to define but typically refers to a heterogeneous subset of TBI with variable constellations of physical, cognitive, and neuropsychiatric features and variable recovery times. mTBI is primarily a clinical diagnosis. Neuroimaging is not routinely indicated, as it is frequently normal or reveals only minor findings that do not alter management. Clinical decision rules for neuroimaging should be used to identify patients at risk of intracranial lesions that require surgical intervention. Most patients with a reassuring clinical presentation can be treated as outpatients after a period of observation, while some benefit from hospital admission and monitoring. If at any point during the observation period the GCS deteriorates to < 13, the patient should be reclassified as or and managed accordingly. The mainstay of treatment of mTBI is physical and cognitive rest until patients are completely asymptomatic, followed by a gradual return to activity. Most patients recover completely within 1–2 weeks and better outcomes are associated with early diagnosis and treatment adherence. is the most common complication, causing symptoms lasting for weeks to months that usually require multidisciplinary care and follow-up.
Athletes with a possible sports-related concussion should be immediately removed from play and assessed by a healthcare professional trained in evaluating these injuries. Sports-specific assessment tools such as the Sport Concussion Assessment Tool (SCAT) may be used. Patients should not be permitted to return to play on the day of injury.
See also “severe TBI.” for information on moderate and
- There is a lack of consensus on the ideal terminology used to describe this entity.
- “Mild traumatic brain injury” (mTBI) is the preferred term of most specialists and guideline working groups , however, its precise definition remains debated. 
- Significant controversy surrounds the use of the terms “concussion” and “minor head injury”, as they are even more elusive to define and lack specificity. 
- Several authorities have proposed to retire these terms in favor of “mTBI”. 
- Nevertheless, “concussion” remains widely used in the literature 
- Many authors and institutions use “concussion” interchangeably with “mTBI” despite ambiguities and variability in their definitions. 
The working definitions provided here are based on the best available evidence and may change as this is an evolving area of research. 
Mild traumatic brain injury consists of a trauma-induced disruption of brain function associated with: 
- GCS ≥ 13–15 at least 30 minutes after the injury
- AND ≥ 1 of the following:
- Altered mental state (e.g., disorientation, confusion) at the time of the injury
- Brief loss of consciousness (i.e., < 30 minutes duration)
- Posttraumatic amnesia < 24 hours duration
- Minor neurological abnormalities: e.g., transient focal neurological signs/symptoms, self-limited seizure, small or benign traumatic intracranial lesion/bleeding that does not require surgical intervention.
Concussion: A heterogeneous subset of mTBI associated with complex pathophysiology, and variable clinical features and natural history 
- Symptoms should not be better explained by other injuries , toxic exposures , or comorbidities . 
- Typically associated with no visible abnormalities on standard neuroimaging (i.e., CT, MRI) 
- Can be categorized into the following concussion subtypes: 
- Can be associated with sleep disturbance and/or cervical strain 
- Incidence: mTBI accounts for approx. 75–90% of the estimated 1.7–2.5 million annual TBI cases. 
- Sex: ♂ > ♀ 
- Age: more common in children 0–4 years, teenagers and young adults 15–24 years, and adults > 65 years 
- Occupation: more common in athletes and military populations. 
Epidemiological data refers to the US, unless otherwise specified.
The pathophysiology of mTBI is complex and poorly understood. It is most likely an interplay of the following mechanisms of brain injury: 
- Prerequisite: GCS ≥ 13–15
- Variable onset, severity, and duration. 
- Most common symptoms: confusion and amnesia
- Can be associated with features of
|Clinical features of mTBI|
|Domain||Signs and symptoms|
Symptoms of mTBI may be transient or subtle and should be explicitly asked about to avoid missing the diagnosis. 
Loss of consciousness at the time of injury is not required for the diagnosis, and its absence does not rule out mTBI. 
The following features suggest a more serious brain injury (i.e., moderate or severe TBI) or associated complications (e.g., intracranial hemorrhage, elevated ICP) that require further evaluation (e.g., neuroimaging, laboratory studies). 
- History of prolonged loss of consciousness
- Focal neurological signs: e.g., sensory, motor, speech, balance, or vision disturbances
- Altered behavior: e.g., agitation, aggression without provocation, restlessness
- Progression of any physical, cognitive, or behavioral symptoms, including:
- Inability to recognize family or friends
- Current anticoagulant use
- Signs of basilar skull fracture 
- Signs of a neck injury, e.g., clinical features of vertebral fracture, clinical features of a 
All patients with suspected mTBI with or without loss of consciousness should be evaluated as early as possible by a trained clinician. Patients with an initially high GCS score can deteriorate rapidly if there is a significant intracranial lesion. Initial management of mTBI should be performed with the same urgency as patients with moderate TBI or severe TBI until the patient is stable and shows neurological improvement. 
In stable patients with suspected mTBI and no obvious significant additional injuries, there typically is little need for intervention during the primary survey.
- Approach: See ''Initial management of TBI” for general considerations and modifications to ATLS for head-injured patients.
- Urgent diagnostics: Determine the need for neuroimaging (see ''Criteria for neuroimaging in mTBI'').
- Urgent treatment
- Urgent consultation: Neurosurgery consult if are present and/or initial neuroimaging is abnormal.
Patients who have a loss of consciousness > 30 minutes, posttraumatic amnesia > 24 hours, or evidence of intracranial hemorrhage on neuroimaging likely have a more severe brain injury (see ''Management of moderate or severe TBI'' for details).
- Obtain collateral information from witnesses.
- Quantify mTBI symptom number and severity with a standardized assessment tool if appropriate.
- Adults: Consider use of a tool (e.g., the Acute Concussion Evaluation). 
- Children: Use of a tool is recommended (e.g., the Graded Symptom Checklist). 
- Assess occupational risk (e.g., athletes, military personnel) of subsequent mTBI.
- Identify lifestyle factors that may impact recovery (e.g., drug and alcohol consumption).
- See also “Sport-related concussion.”
- Physical examination
- Further care and disposition: See "Treatment".
If at any point the GCS deteriorates below 13, reclassify the patient as moderate TBI (GCS 9–12) or severe TBI (GCS ≤ 8) and manage accordingly (see "Treatment of moderate or severe TBI" for details). 
- mTBI is primarily a clinical diagnosis (See “Clinical features”)
Neuroimaging is not routinely required. 
- Patients fulfilling should undergo noncontrast CT head as an initial investigation to rule out more severe injuries.
- Follow clinical judgment and local protocols for neuroimaging in patients who do not fulfill the inclusion criteria for validated clinical decision rules (CDRs) for neuroimaging.
- See "Special patient groups” for the approach to patients on antithrombotic therapy.
- Patients with bleeding disorders (e.g., hemophilia): CT head is recommended even in patients with GCS 15 and a normal neurological examination. 
- Laboratory studies can be helpful to evaluate for differential diagnoses or determine bleeding risk (e.g., due to coagulopathy)
Indications for neuroimaging in mTBI
Various clinical decision rules (CDRs) have been developed to identify when neuroimaging is warranted in mTBI; the choice of CDR varies by institution and guidelines.
Although both of these CDRs have been validated for clinical use, the Canadian CT head rule is recommended. 
|Adult clinical decision rules for neuroimaging in mTBI|
|CDR||Criteria for neuroimaging: ≥ 1 of the following||Inclusion criteria: all of the following|
Canadian CT head rule (CCHR) 
New Orleans criteria 
The Canadian CT head rule is used for patients with an initial GCS of 13–15 with or without neurological deficits at presentation. The New Orleans criteria can only be used for patients with an initial GCS of 15 and no neurological deficits at presentation.
- The Pediatric Emergency Care Applied Research Network (PECARN) blunt head-trauma prediction rule is typically the preferred pediatric CDR in US institutions. 
- Inclusion criteria 
|Pediatric Emergency Care Applied Research Network (PECARN) blunt head-trauma prediction rule |
|Criterion||< 2 years||2–18 years|
|High-risk features||Evidence of skull fracture|| |
|GCS = 14 or other signs of AMS|
|Intermediate-risk features||Severe signs or symptoms|
|Severe mechanism of injury|| || |
Neuroimaging modalities 
CT head without IV contrast
- Indications: preferred initial imaging modality in patients that meet criteria for neuroimaging in mTBI 
- Findings are usually normal; in a minority of patients the following may be seen: 
- See also "Diagnostics in TBI" for findings of more severe TBIs and “Differential diagnosis of intracranial hemorrhage” for a comparison of CT findings of intracranial bleeds.
- Indication: second-line imaging modality in patients with clinical features unexplained by CT findings 
- Findings: subtle injuries missed on initial CT scan (e.g., microhemorrhages, axonal injury, infarctions) 
- Advanced imaging (e.g., susceptibility-weighted imaging, diffusion tensor imaging): may be considered in patients whose clinical features are unexplained by initial neuroimaging
Laboratory studies 
The following conditions may mimic mTBI (e.g., cause confusion and amnesia), but may also be the underlying precipitant of the injury that caused the mTBI. Careful clinical correlation and evaluation of the individual's pretest probability are recommended. 
- and/or drug intoxication (see " ")
- Seizures or postictal state
- Cardiac arrest
- See also “Critical causes of agitation.”
- See also “Causes of AMS and coma.”
The differential diagnoses listed here are not exhaustive.
Therapeutic measures for all patients 
Physical and cognitive rest: mainstay of therapy
- Patients should refrain from strenuous mental and physical work or activity.
- Individuals with suspected mTBI in the field (e.g., sports-related concussion) should be immediately removed from activity, evaluated by a trained clinician, and not be allowed to return on the same day. 
Supportive pharmacological therapy: should be used for as short a duration as possible as some medications can potentially worsen postconcussion syndrome. 
- OTC oral analgesics (e.g., acetaminophen or ibuprofen ) are usually sufficient for early treatment of headache.
- Consider antiemetics (e.g., ondansetron )
- Consider OTC melatonin for sleep disturbances.
- Other prescription medication (e.g., antidepressants, triptans, methylphenidate) should only be prescribed in consultation with a TBI specialist (see “ ”).
- Nonpharmacological therapy
These criteria are not strict and clinical judgment and local resources should be considered for individual disposition decisions.
Outpatient management after an initial period of observation is safe in most patients with the following characteristics:
- Clinical presentation: asymptomatic OR only mildly symptomatic
- Neuroimaging: normal OR not performed as were not met
- Normal examination after the initial period of observation
- Absent criteria for hospital admission
Hospital admission is suggested if any of the following are present:
- mTBI features
- Other patient or system factors
- Significant intoxication due to alcohol or drugs
- Associated injuries requiring admission
- Patients on anticoagulant/antiplatelet therapy with additional risk factors for bleeding (see "Special patient groups")
- Lack of social supports or appropriate caregiver outside of the hospital
- Inability to quickly return to the hospital if red flags for mTBI arise
- Age > 65 years 
Initial encounter 
Most patients with reassuring clinical features and either no neuroimaging (i.e., did not meet criteria for neuroimaging in mTBI) or normal neuroimaging can be managed safely as outpatients after an initial period of observation. 
- Neurosurgical consultation is not routinely required.
- Recommend follow-up with regular primary care provider within a few days.
- Consider referral to a specialized multidisciplinary neurotrauma team for complex cases or patients with risk factors for postconcussion syndrome.
Patient counseling 
Provide written instructions regarding the following to the patient and caregivers.
- Relative rest period: Limit physical and cognitive activities for a minimum of 24–48 hours. 
- Advise a stepwise and gradual return to regular physical and cognitive activity that is guided by symptoms.
- Return to activity protocols may be used for certain patients (e.g., students, atheletes, military); for athletes, a full return to sports should take at least 1 week. 
- Return precautions: Advise returning to seek care if any develop. 
- Possible complications: Discuss the risk of complications such as postconcussion syndrome. 
Follow up 
- Reassess regularly in the outpatient setting until symptoms resolve. 
- Assess for ongoing symptoms; consider using symptom checklists.
- Monitor progression through return to activity protocols, if relevant.
- Consider additional workup if symptoms don't resolve within: 
- 1–2 weeks for adults
- 2–4 weeks for children
- Persistent symptoms (typically, > 4 weeks): Consider referral to a specialized multidisciplinary neurotrauma team. 
Short hospital admission is typically recommended for patients with disabling symptoms, high-risk injuries, or other patient and system factors that render outpatient management unsafe. 
- Monitoring and referrals
- Follow-up neuroimaging (e.g., in 8–24 hours) should be considered in the following situations: 
- Treatment of complications
General principles 
- Return to activity protocols may be used for certain patients (e.g., students, athletes); see “Tips and Links” for the SCAT 6.
- Protocols start with an initial period of relative rest.
- If symptoms worsen with increased activity , slow the rate of progression through the protocol. 
- Pediatric patients may proceed simultaneously through the different protocols but should fully return to school before fully returning to play.
- See also “Tips and Links” for the SCAT6, which includes details on individualized protocols.
Return to school protocol 
- If symptoms are exacerbated, reduce the pace of progression to the next step.
- Accomodations to minimize symptoms may be needed, e.g.: 
- Reduced workload
- Extra time to complete tasks
- Cognitive breaks
- Supplemental written materials
- Low-stimulatory environment
Order of steps
- Initial period of relative rest for 24–48 hours: daily cognitive activities as tolerated 
- School-specific activities at home
- Part-time return to school
- Full-time return to school
Return to play protocol 
Full return to sports activities takes at least 1 week.
- No more than one step should be completed per 24 hours.
- Step 4 cannot be started until both of the following have occurred:
- Complete resolution of all concussion-related signs and symptoms 
- Medical clearance by a healthcare professional
- If symptoms worsen
- During steps 1–3: Stop activity until the next day.
- During steps 4–6: Return to step 3.
Order of steps
- Initial period of relative rest for 24–48 hours: daily physical activities as tolerated 
- Light to moderate aerobic exercise
- Sport-specific exercise individually, with no risk of head impact 
- Non-contact sports drills within the team
- Full contact practice
- Full return to sports activities
Premature return to competitive sport may increase the risk of second-impact syndrome. 
Special patient groups
Patients on antithrombotic therapy 
Management of mTBI in patients on anticoagulant and/or antiplatelet medication is a challenge due to the risk of immediate and delayed intracranial hemorrhage (DICH) . There is a paucity of evidence on the optimal management of these patients.
Neuroimaging at presentation
- Keep a low threshold to perform neuroimaging (even if patients do not meet standard ). 
- Consider routine neuroimaging at presentation if any of the following risk factors for bleeding are present: 
- Neurosurgery and hematology consultation recommended
- Anticoagulant reversal: not routinely required.
- Asymptomatic patients with normal initial neuroimaging
- No risk factors for bleeding
- Observe in the ER for 12–24 hours and then discharge to home care under supervision
- Provide written instructions to return if new symptoms or signs of neurologic deterioration occur.
- Risk factors for bleeding
- No risk factors for bleeding
- Symptomatic patients: Treatment is the same as mTBI patients requiring admission (see "Inpatient treatment").
Patients with bleeding disorders 
- Most (80–90%) patients make a full recovery within 1–2 weeks. 
- Outcomes are improved with early diagnosis and adherence to treatment. 
Immediate complications 
- Posttraumatic seizures: uncommon 
- Intracranial bleeding (e.g., ICH, SDH): uncommon
Postconcussion syndrome (PCS) 
- Epidemiology: most common consequence of mTBI
- Definition: clinical features of mild TBI that persist longer than expected, typically at least > 4 weeks post-injury 
- Risk factors for postconcussion syndrome include: 
- Diagnosis is primarily clinical.
- Consider neuroimaging. 
- Evaluate for other causes for symptoms. 
- Referral to multidisciplinary specialty care clinics specialized in neurotrauma
- Prolonged restriction of physical and cognitive activity
- Symptomatic pharmacotherapy (e.g., SSRIs, tricyclic antidepressants, stimulants, sleep aids)
- Advanced nonpharmacological therapy (e.g., biofeedback, physical therapy, psychotherapy)
- Prognosis: Most patients recover within 6 months.
Other delayed complications 
Second-impact syndrome (SIS)
- A very rare, but potentially devastating brain injury precipitated by a second injury that occurs prior to complete healing from an initial mTBI. 
- Postulated pathomechanism: reinjury to susceptible brain cells with incomplete recovery→ rapid development of diffuse cerebral edema→ ↑ ICP → brain herniation → death. 
Chronic traumatic encephalopathy 
- A condition of cumulative neuropsychologic symptoms attributed to repeated TBI (e.g., from sports-related mTBI, military trauma).
- Seen more commonly in professional athletes engaging in contact sports (e.g., boxing, football, hockey)
- Other neurodegenerative diseases (e.g., Alzheimer disease, Parkinson disease): Patients with mTBI have an increased long-term risk of developing these conditions. 
We list the most important complications. The selection is not exhaustive.
A direct physical impact to the head, neck, or body that both:
- Transmits an impulsive force to the brain, resulting in a traumatic brain injury
- Occurs during a sports-related or exercise-related activity
- Sports-related concussions account for ∼ 10% of all TBIs in the US. 
- Significant underreporting may occur. 
Risk factors 
- Competition settings (versus practice settings)
- Younger ages (i.e., middle school versus high school)
- High-impact sports
Initial management 
Follow these steps for any individual with possible sports-related concussion based on the presence of .
- Perform urgent on-field stabilization measures (see “Initial management of TBI”), if necessary.
- Remove from play immediately.
- Transfer to a higher level of care if there are either of the following:
- Ensure a person trained in evaluating sports-related concussions performs a thorough evaluation for mTBI.
- Determine the next steps based on the evaluation assessment.
Athletes often downplay or ignore symptoms to be allowed to keep playing. 
Athletes with a suspected should be removed from play and not permitted to return to play on the day of injury. 
Subsequent management 
- See .
- For symptom reevaluation > 72 hours after injury, consider using the Sport Concussion Office Assessment Tool-6 (SCOAT6). 
- Athletes must be cleared by a medical provider before resuming any activities with risk for a head injury, e.g., prior to step 3 or 4 in the return to play protocol.
- Refer for cervicovestibular rehabilitation if any of the following last > 10 days: 
- Educate school-based professionals, parents, and athletes about signs, symptoms, and risks of concussion.
- Recommend sport-specific protective gear (e.g., mouthgards for ice hockey players). 
- Primary survey including assessment of severity (see )
- AMPLE history and complete neurological examination
- Assessment for additional injuries (e.g., C-spine injury)
- Determine need for noncontrast CT head using criteria for neuroimaging in mTBI.
- Consider tranexamic acid if intracranial bleeding on neuroimaging and < 3 hours since injury.
- Neurosurgical consult if neuroimaging is abnormal are present and/or initial
- Observe in ER for at least 4–6 hours.
- Serial GCS and neurological examination
- Determine need for admission (see “Disposition”)
- Ensure physical and cognitive rest.
- Provide supportive therapy as needed (e.g., analgesics, antiemetics)
- Identify and treat immediate complications (e.g., posttraumatic seizures, delayed intracranial bleeding)
- For patients eligible for discharge:
- Emphasize the minimum duration of physical and cognitive rest (i.e., 24–48 hours).
- Ensure stepwise and gradual return to activity.
- Arrange follow-up (e.g., primary care provider, multidisciplinary mTBI specialty clinic).
- Provide written discharge instructions with explicit reasons to return and seek care.
- Counsel on lifestyle factors that affect recovery and delayed complications.