Traumatic brain injury (TBI) occurs when an external mechanical force causes damage to the brain, disrupting its normal structure and function. It is a leading cause of death and long-term disability worldwide, affecting approximately 2.8 million Americans annually. TBI ranges in severity from a mild concussion with brief disorientation to a catastrophic injury with prolonged unconsciousness and permanent neurological impairment. Prompt evaluation and management are critical at every severity level.
TBI is associated with a range of secondary complications that require both acute and long-term neuroimaging surveillance. Acute complications include subdural hematoma — one of the most common surgical emergencies following head trauma — and hydrocephalus from post-traumatic CSF pathway disruption. Long-term consequences include progressive brain atrophy, post-traumatic epilepsy, and in athletes and military personnel with repeated injuries, chronic traumatic encephalopathy (CTE) — a neurodegenerative condition with features overlapping dementia. MRI, particularly with advanced sequences, is far more sensitive than CT for characterizing the full extent of injury beyond the acute phase.
Causes
Falls and motor vehicle accidents
Falls are the most common cause of TBI across all age groups — the leading cause in young children under 5 and adults over 65, in whom age-related brain atrophy stretches bridging veins and increases subdural hematoma risk even from minor falls. Motor vehicle accidents — including car crashes, motorcycle accidents, and pedestrian injuries — are the leading cause of severe and fatal TBI in young adults aged 15–44. Other significant causes include sports-related head injuries (the most common cause of mild TBI in young people), assaults, and blast injuries in military personnel, where the pressure wave mechanism produces diffuse axonal injury without external impact.
Mechanisms of brain injury
TBI causes harm through two distinct temporal phases. Primary injury is the direct mechanical damage occurring at the moment of impact — including cortical contusions (bruising of the brain surface), intracerebral hemorrhage, skull fractures, and diffuse axonal injury (DAI) from the rotational shear forces that stretch and tear axons throughout the white matter, particularly at the gray-white matter junction. DAI is the pathological substrate of concussion and the most common cause of prolonged unconsciousness after TBI.
Secondary injury develops in the hours to days following the initial trauma and can dramatically worsen outcomes — including cerebral edema, elevated intracranial pressure, excitotoxicity from glutamate release, oxidative stress, post-traumatic hemorrhage expansion, hypoxia, and hypotension. Preventing and actively managing secondary injury is the primary goal of neurocritical TBI care.
Symptoms
Symptoms vary widely with injury severity:
- Mild TBI (concussion): Headache, confusion, dizziness, nausea, retrograde and anterograde amnesia around the injury event, and sensitivity to light and noise. Loss of consciousness is brief (seconds to minutes) or absent. Symptoms typically resolve within days to weeks, though post-concussion syndrome with persistent symptoms lasting months affects a significant minority.
- Moderate TBI: Prolonged confusion or loss of consciousness (minutes to hours), post-traumatic amnesia lasting 1–7 days, focal neurological deficits, and behavioral changes. Structural brain injury is typically visible on CT.
- Severe TBI: Prolonged loss of consciousness or coma, abnormal posturing (decorticate or decerebrate), pupillary abnormalities, and signs of elevated intracranial pressure — including the Cushing triad (hypertension, bradycardia, irregular breathing), which signals imminent brain herniation and requires emergency neurosurgical intervention.
- Post-concussion syndrome: Persistent headache, cognitive difficulties, mood changes, sleep disturbance, and fatigue lasting beyond the expected recovery period — affecting up to 30% of mild TBI patients and requiring structured multidisciplinary management.
- Long-term consequences: Post-traumatic epilepsy (seizures developing weeks to years after TBI), progressive cognitive decline, and in those with repeated TBIs, features of chronic traumatic encephalopathy (CTE) — including mood disturbance, impulsivity, and dementia-like cognitive decline.
Diagnosis
Neurological assessment using the Glasgow Coma Scale (GCS) — scoring eye opening, verbal response, and motor response from 3 (deepest coma) to 15 (normal) — provides rapid, standardized grading of consciousness and is the basis for TBI severity classification.
CT scan (non-contrast) is the immediate first-line imaging study in the acute setting — rapidly available, highly sensitive for hemorrhage, skull fractures, contusions, and signs of raised intracranial pressure (midline shift, effaced cisterns). The Canadian CT Head Rule and NEXUS criteria guide appropriate CT use in mild TBI to avoid unnecessary radiation exposure while ensuring serious injuries are not missed.
MRI is significantly more sensitive than CT for detecting the full spectrum of TBI pathology and is the preferred study in the subacute and chronic phases. Susceptibility-weighted imaging (SWI) detects microhemorrhages and diffuse axonal injury hemorrhagic foci invisible on CT — a key marker of injury severity. Diffusion tensor imaging (DTI) quantifies white matter tract integrity and reveals diffuse axonal injury in patients with cognitive symptoms but normal conventional MRI — providing objective evidence of injury that CT and standard MRI miss. These advanced MRI techniques are increasingly important for prognosis, return-to-work and return-to-sport decisions, and medicolegal documentation of injury in mild TBI cases.
Severity Classification
TBI is classified by initial GCS score, duration of loss of consciousness, and duration of post-traumatic amnesia:
- Mild TBI (Concussion) — GCS 13–15: Brief or no loss of consciousness (under 30 minutes), post-traumatic amnesia less than 24 hours. The most common TBI severity — accounts for 80% of all TBI presentations.
- Moderate TBI — GCS 9–12: Loss of consciousness up to 24 hours, post-traumatic amnesia 1–7 days. Structural injury typically present on CT. Requires hospital admission and monitoring.
- Severe TBI — GCS 3–8: Loss of consciousness greater than 24 hours, often with major structural injury on imaging. Requires ICU-level neurocritical care and often surgical intervention. Associated with high mortality and significant long-term disability.
Treatments
Management is tailored to injury severity, specific injury type, and the presence of complications such as elevated intracranial pressure or intracranial hemorrhage.
Mild TBI / Concussion:
Initial cognitive and physical rest, followed by a structured, supervised graduated return-to-activity protocol — progressing from rest through light aerobic exercise, sport-specific exercise, and non-contact drills before return to full contact. Return to contact sports is governed by strict stepwise protocols to prevent second-impact syndrome — a rare but potentially fatal condition in which a second concussion occurs before the first has fully resolved. Symptom management for headache, sleep disturbance, and mood symptoms is provided as needed. Most patients recover fully within 4 weeks; those with persistent symptoms are referred for multidisciplinary post-concussion care.
Moderate to severe TBI — acute neurocritical care:
Severe TBI is managed in a dedicated neurocritical care unit with continuous intracranial pressure (ICP) monitoring — maintaining ICP below 22 mmHg and cerebral perfusion pressure (CPP) above 60–70 mmHg. Osmotherapy with mannitol or hypertonic saline reduces cerebral edema. Controlled hyperventilation temporarily reduces ICP in herniation emergencies. Surgical intervention is required for evacuation of significant subdural or epidural hematomas, elevation of depressed skull fractures, and decompressive craniectomy — surgical removal of a large skull flap to relieve uncontrollable intracranial hypertension when all medical measures have failed.
Rehabilitation:
Comprehensive neurorehabilitation — physical, occupational, speech, cognitive, and psychological therapy — is the foundation of recovery following moderate and severe TBI. Recovery follows an initially rapid trajectory that continues more gradually for 1–2 years or longer. Vocational rehabilitation and community reintegration support are important for long-term outcomes. Long-term neurological follow-up with serial neuropsychological testing and MRI monitoring tracks recovery, identifies complications including post-traumatic epilepsy and progressive brain atrophy, and guides ongoing management.
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