Introduction
Mild traumatic brain injury (mTBI), commonly known as concussion, is a clinical diagnosis that occupies a critical space at the intersection of neurology, emergency medicine, sports medicine, and rehabilitation. Though often labeled as “mild,” mTBI can result in significant morbidity if not recognized, appropriately evaluated, and carefully managed.
Every year, millions of individuals around the world experience a mild head injury. Most recover uneventfully. However, a significant subset suffers from lingering cognitive, emotional, and physical symptoms — an entity commonly referred to as post-concussion syndrome (PCS). Furthermore, repetitive concussions can predispose individuals to serious long-term neurodegenerative consequences, including chronic traumatic encephalopathy (CTE).
This article provides a comprehensive, narrative, and evidence-based exploration of mTBI — its definitions, pathophysiology, clinical manifestations, protocols for evaluation, management strategies, and guidance on safe return to activity.
Defining Mild Traumatic Brain Injury
Mild traumatic brain injury is classically defined as a traumatically induced disruption of brain function with a Glasgow Coma Scale (GCS) score of 13 to 15, evaluated approximately 30 minutes after injury.
The American Congress of Rehabilitation Medicine offers a refined definition, highlighting any one of the following:
- Any period of loss of consciousness (LOC),
- Any loss of memory for events immediately before or after the injury (amnesia),
- Any alteration in mental state at the time of the injury (e.g., feeling dazed, confused, or disoriented).
Importantly, structural imaging such as a CT scan may be normal in cases of mild TBI. Nevertheless, a minority of patients exhibit small intracranial hemorrhages, contusions, or edema that may significantly affect prognosis.
The term “concussion” is often used interchangeably with mild TBI, although some clinicians reserve “concussion” to describe the clinical syndrome of transient neurological dysfunction following biomechanical brain trauma.
Epidemiology: A Widespread Public Health Concern
Traumatic brain injuries affect approximately 2.5 million people annually in the United States alone, and about 75% to 95% of these injuries are classified as mild.
Risk factors and contexts vary across demographics:
- Young adults (ages 15–34) experience high rates, primarily from motor vehicle accidents and sports injuries.
- Elderly populations are particularly vulnerable to falls, leading to head injuries.
- Military personnel face a heightened risk due to blast injuries.
- Athletes, especially those in contact sports such as American football, rugby, soccer, and ice hockey, represent a substantial at-risk group. Studies estimate that up to 20% of athletes in these sports may sustain a concussion during a single season.
Males are statistically more likely to experience TBI, a reflection of both behavioral and occupational factors. Socioeconomic status, lower educational attainment, and a history of substance abuse also correlate with increased incidence.
Pathophysiology: More Than Meets the Eye
The pathophysiology of mild TBI extends beyond macroscopic brain injury visible on standard imaging.
Biomechanical Forces
Concussions occur when external forces — whether direct blows or acceleration-deceleration movements — cause the brain to move rapidly within the skull. The forces involved include:
- Linear acceleration/deceleration (front-to-back or side-to-side movements),
- Rotational forces, which are particularly damaging to axons.
Cellular and Molecular Events
The immediate aftermath of injury includes:
- Axonal stretching and disruption of axonal transport,
- Release of excitatory neurotransmitters such as glutamate and aspartate, leading to excitotoxicity,
- Generation of reactive oxygen species causing oxidative damage,
- Activation of inflammatory cascades that, although initially protective, may contribute to long-term neurodegeneration.
Microstructural damage can be observed in experimental models and, increasingly, in humans using diffusion tensor imaging (DTI) and functional MRI (fMRI). Subtle white matter abnormalities, alterations in connectivity, and perfusion deficits are often detected despite normal appearance on conventional CT.
This nuanced pathophysiological picture underpins why some patients with “mild” TBI develop profound and persistent symptoms.
Clinical Features: The Subtle and the Overt
Acute Presentation
The hallmark symptoms of concussion are:
- Confusion, often immediate or delayed,
- Amnesia surrounding the event (retrograde or anterograde).
Loss of consciousness, although common, is not required for a diagnosis of concussion.
Other typical features include:
- Headache (the most frequently reported symptom),
- Dizziness or vertigo,
- Nausea or vomiting,
- Photophobia and phonophobia,
- Disorientation,
- Vacant stare or “blank expression”,
- Incoordination,
- Slurred or incoherent speech,
- Emotional lability (crying or laughing inappropriately).
Athletes often present subtly, perhaps showing only slight sluggishness or confusion during gameplay.
Red Flags
Findings inconsistent with an uncomplicated mild TBI that should trigger immediate imaging and specialist evaluation include:
- Focal neurological deficits (e.g., limb weakness, hemiparesis),
- Pupillary asymmetry,
- Progressive drowsiness or confusion,
- Seizures,
- Persistent vomiting.
Such findings may herald intracranial hemorrhage, brain contusion, or evolving mass effect.
Evaluation: Structured Assessment is Key
Evaluation of suspected concussion must be thorough, systematic, and standardized when possible.
Sideline and Emergency Department Assessment
The initial evaluation includes:
- Symptom inventory,
- Neurological examination,
- Cognitive assessment (orientation, memory, concentration).
Importantly, simple orientation questions (e.g., “What day is it?”) are not sensitive enough to detect concussion.
Several structured tools have been developed:
Standardized Assessment of Concussion (SAC)
- Evaluates orientation, immediate memory, concentration, and delayed recall.
- Scores are compared to baseline (if available).
- Particularly useful on the sidelines of athletic events.
Example Components:
- Immediate recall of word lists,
- Serial 3 subtraction,
- Months of the year in reverse order.
Sport Concussion Assessment Tool (SCAT5)
- Endorsed internationally,
- Incorporates symptom scales, GCS, balance examination, and cognitive assessment,
- Provides a comprehensive picture but requires time (10–15 minutes).
Graded Symptom Checklist (Post-Concussion Symptom Scale)
- Symptom severity rated on a 0–6 scale,
- Tracks symptom resolution over time,
- Useful for monitoring recovery trajectory.
Imaging: When and What to Scan
Not all patients with mild TBI require imaging. Selective use of CT scanning is guided by clinical decision rules designed to maximize sensitivity while limiting unnecessary radiation.
Canadian CT Head Rule (CCHR)
Indications for head CT include:
- GCS <15 at 2 hours post-injury,
- Suspected open or depressed skull fracture,
- Signs of basilar skull fracture (Battle’s sign, CSF rhinorrhea),
- Vomiting >2 episodes,
- Age ≥65,
- Retrograde amnesia >30 minutes,
- Dangerous mechanisms (e.g., pedestrian struck, ejection from a vehicle, fall >3 feet).
New Orleans Criteria (NOC)
Criteria include:
- GCS = 15 with any of headache, vomiting, age >60, drug/alcohol intoxication, persistent anterograde amnesia, visible trauma above clavicle, seizure.
NEXUS II Criteria
CT indicated if there is:
- Significant skull fracture,
- Scalp hematoma,
- Neurological deficit,
- GCS ≤14,
- Coagulopathy,
- Persistent vomiting.
Management: Early Steps and Ongoing Care
Once a concussion is diagnosed, the first principle of management is prevention of further injury during the period of acute vulnerability. This principle underpins immediate recommendations for rest and close observation.
Observation After Injury
Patients should be observed closely during the first 24 hours after injury because of the small but real risk of evolving intracranial complications such as hematomas.
Settings for Observation:
- In-hospital observation is indicated for:
- GCS <15
- Intracranial hemorrhage detected on imaging
- Persistent vomiting
- Seizures
- Abnormal neurologic findings
- Coagulopathy (e.g., anticoagulant therapy)
- GCS <15
- At-home observation may be appropriate for patients who:
- Have normal mental status,
- A normal head CT (if indicated),
- No significant risk factors for deterioration,
- Have a reliable caregiver.
- Have normal mental status,
Caregiver Instructions:
Caregivers must monitor for signs of worsening neurological status, including:
- Increasing somnolence,
- Inability to awaken the patient,
- Severe or worsening headaches,
- Repeated vomiting,
- New focal neurological symptoms (e.g., weakness, speech difficulties).
Should any of these signs arise, immediate re-evaluation and imaging are warranted.
Seizures and Antiepileptic Management
Early posttraumatic seizures (within the first 7 days) occur in less than 5% of mild TBI cases. Most often, these seizures are self-limited and do not indicate a diagnosis of epilepsy.
Treatment considerations:
- Antiepileptic drugs (AEDs) are not recommended prophylactically in uncomplicated mTBI.
- If a seizure occurs, it is managed as an acute symptomatic seizure.
- Recurrent seizures or persistent focal deficits demand a detailed workup for structural injury.
Imaging Follow-Up: Is It Needed?
Routine repeat CT scanning in asymptomatic patients is generally not necessary.
Indications for repeat imaging include:
- Neurological deterioration,
- New-onset symptoms,
- Known risk factors such as anticoagulation.
MRI becomes more valuable in the subacute and chronic phases, particularly in patients with persistent cognitive, emotional, or physical symptoms, where conventional CT remains unrevealing.
MRI can detect:
- Small cortical contusions,
- Microhemorrhages (especially in diffuse axonal injury),
- White matter integrity loss (seen on DTI).
However, while imaging abnormalities are fascinating, current evidence does not support MRI findings alone guiding return-to-activity decisions or prognostication for mTBI.
Return to Activity: From Rest to Full Recovery
A pivotal question following any concussion revolves around when it is safe to return to work, school, or sport.
The guiding principles are:
- Physical and cognitive rest during the acute phase,
- Graduated return to activities, monitoring for symptom recurrence.
Return to Work
Most patients require:
- 24 to 48 hours of cognitive rest,
- Gradual reintroduction of tasks,
- Accommodation for reduced workload if symptoms persist.
Severe early restrictions (e.g., strict bed rest) are not beneficial and may prolong recovery.
Cognitive and physical stress should be increased slowly, ensuring symptoms do not worsen.
Return to Play (RTP) in Athletes
The management of athletes requires even greater caution, given the physical demands and risk of re-injury.
The internationally accepted six-stage RTP protocol is as follows:
| Stage | Activity | Goal |
| 1 | Symptom-limited activities (daily life) | Gradual reintroduction |
| 2 | Light aerobic exercise (walking, cycling) | Increase heart rate |
| 3 | Sport-specific exercise (no contact) | Add movement |
| 4 | Non-contact training drills (complex drills) | Exercise, coordination, thinking |
| 5 | Full-contact practice | Restore confidence, test skills |
| 6 | Return to competition | Normal game play |
Key Points:
- Each stage requires a minimum of 24 hours.
- If symptoms recur at any stage, the athlete should drop back to the previous level.
- Athletes must not return to play while symptomatic, even with mild symptoms.
Same-day return to play is prohibited.
This precaution prevents catastrophic complications such as second impact syndrome, a rare but potentially fatal condition resulting from a second concussion before the brain has fully recovered from the first.
Post-Concussion Syndrome (PCS)
While the majority of individuals recover fully within days to a few weeks, approximately 15% to 20% develop lingering symptoms — a constellation known as post-concussion syndrome.
Symptoms of PCS include:
- Persistent headache,
- Fatigue,
- Dizziness,
- Irritability,
- Depression or anxiety,
- Sleep disturbances,
- Memory impairment,
- Poor concentration.
PCS is more likely in individuals with:
- Previous concussions,
- Baseline psychiatric conditions,
- Older age,
- Female gender,
- High initial symptom burden.
Management strategies for PCS focus on symptom-targeted therapy, including:
- Cognitive behavioral therapy (CBT) for mood disturbances,
- Medications for headaches and sleep issues,
- Gradual re-engagement with activities under supervision.
Multidisciplinary care teams often include neurologists, psychologists, physiotherapists, and occupational therapists.
Long-Term Consequences: Repetitive Injuries and CTE
Emerging evidence suggests that repetitive concussions, even if individually mild, may contribute to long-term neurodegenerative diseases, notably chronic traumatic encephalopathy (CTE).
CTE is characterized by:
- Progressive cognitive decline,
- Behavioral changes (impulsivity, aggression),
- Mood disorders (depression, suicidality),
- Motor symptoms resembling Parkinsonism.
Pathological hallmarks include the accumulation of hyperphosphorylated tau protein in specific brain regions.
At present, CTE can only be definitively diagnosed postmortem.
Nonetheless, its devastating consequences have raised public awareness and prompted new safety initiatives in professional sports, military protocols, and public health guidelines.
Special Populations and High-Risk Groups
Anticoagulated Patients
Patients on anticoagulants (e.g., warfarin, direct oral anticoagulants) are at increased risk for:
- Delayed intracranial hemorrhage,
- Larger hematomas,
- Worse clinical outcomes.
Observation periods may be prolonged, and lower thresholds for imaging apply.
Emerging evidence suggests that patients on antiplatelet therapy alone (e.g., aspirin) may have less risk compared to those on anticoagulants, but vigilance remains essential.
Children and Adolescents
Children’s brains are still developing, making them more vulnerable to concussion effects and prolonged recovery.
Guidelines for return-to-sport in children emphasize:
- More conservative progression through RTP stages,
- Extended periods of rest if needed,
- Academic accommodations such as reduced homework, breaks during classes, and shortened school days.
Biomarkers and the Future of Diagnosis
Recent studies explore biomarkers such as plasma tau protein, neurofilament light chain (NfL), and glial fibrillary acidic protein (GFAP) as tools for diagnosing and monitoring mTBI.
While promising, these biomarkers are not yet ready for routine clinical use. Research continues into their potential to:
- Aid in rapid sideline diagnosis,
- Monitor recovery,
- Predict long-term outcomes.
Integration with advanced neuroimaging techniques and artificial intelligence (AI) analysis may, in the future, revolutionize concussion management.
Final Summary: Best Practice Approach
When faced with a patient presenting after a head injury, clinicians should:
- Conduct a systematic neurological assessment,
- Use standardized batteries (SAC, SCAT5) when available,
- Apply clinical decision rules for imaging (CCHR, NOC, NEXUS II),
- Ensure observation for at least 24 hours,
- Emphasize gradual return to activity,
- Recognize and manage PCS proactively,
- Counsel patients, athletes, and families on the risks of repeated injury,
- Collaborate across disciplines for persistent or complex cases.
Mild traumatic brain injury may be called “mild,” but its impact can be profound. Through vigilant evaluation, compassionate care, and evidence-based management, we can safeguard recovery today and protect brain health for tomorrow.
