What is traumatic brain injury?

What is Traumatic Brain Injury?

Traumatic brain injury (TBI) is an alteration in brain function or other evidence of brain pathology caused by an external mechanical force to the head or body, resulting in a spectrum of injury severity from mild (brief mental status changes) to severe (prolonged unconsciousness), and represents a chronic disease process rather than a single event. 1, 2

Core Definition and Pathophysiology

TBI occurs when external physical forces impact the head with sufficient intensity to cause brain damage, disrupting normal brain function through mechanical energy transfer. 1, 3 The injury is not merely an isolated event but initiates an ongoing pathophysiological cascade that can persist for months to years, affecting multiple organ systems and potentially accelerating neurodegenerative processes. 2

Primary and Secondary Injury Mechanisms

• Primary injury refers to the immediate damage from the original physical impact, which triggers a destructive pathophysiological cascade. 1
• Secondary injury develops from processes extending beyond the initial trauma zone, including ischemia, cerebral edema, herniation, seizures, altered metabolism, inflammation, oxidative stress, calcium dysregulation, and apoptosis. 1, 4, 3
• Vascular damage, blood-brain barrier disruption, and persistent neuronal hyperexcitation contribute to progressive tissue destruction. 3

Clinical Classification by Severity

The Glasgow Coma Scale (GCS) provides the standard severity classification that directly predicts mortality, morbidity, and need for neurosurgical intervention: 1, 5

Mild TBI (GCS 13-15)

• Defined as GCS 13-15 after 30 minutes post-injury or on presentation. 1, 5
• Must include one or more of: confusion/disorientation, loss of consciousness ≤30 minutes, post-traumatic amnesia <24 hours, transient neurological abnormalities (focal signs, symptoms, or seizure). 1, 5
• Represents over 90% of patients presenting to hospital with TBI. 1
• Can occur with or without intracranial injury on neuroimaging. 1

Moderate TBI (GCS 9-12)

• Intermediate severity requiring close monitoring and often hospitalization. 5, 6

Severe TBI (GCS 3-8)

• Requires immediate intracranial pressure monitoring and intensive care management. 5
• Associated with highest mortality and morbidity rates. 5

Epidemiology and Public Health Impact

TBI represents a major global health burden with devastating effects on patients and families: 1

• Affects approximately 60 million people worldwide annually, making it the neurological disease with highest prevalence and incidence. 1
• In the United States, there were 223,135 TBI-related hospitalizations in 2019 and 64,362 TBI-related deaths in 2020. 1
• Adults aged 75 years and older account for approximately 32% of TBI-related hospitalizations and 28% of TBI-related deaths. 1
• In high-income countries, older patients injured by falls represent 30-40% of hospital admissions for TBI. 1
• In low- and middle-income countries, road traffic incidents cause most injuries, with substantial disparities in access to emergency and post-acute care. 1

Clinical Manifestations and Long-Term Consequences

TBI adversely affects quality of life through multiple domains: 6, 7

Acute Symptoms

• Altered consciousness, confusion, disorientation. 1
• Loss of consciousness (duration varies by severity). 1
• Post-traumatic amnesia. 1
• Focal neurological deficits. 5

Chronic Effects

• Cognitive impairments: Memory difficulties, attention deficits, executive dysfunction. 5, 6
• Physical symptoms: Headaches, balance disturbances, sleep disorders. 6, 3
• Visual sequelae: Wide range of visual complaints affecting daily function. 3
• Psychiatric manifestations: Depression, personality changes, behavioral alterations. 6, 2
• Post-concussive syndrome: Occurs in 15-20% of mild TBI patients beyond 2 weeks, with headaches and memory difficulties as most common symptoms. 5

Long-Term Disease Processes

• Increased incidence of seizures and post-traumatic epilepsy. 3, 2
• Neurodegenerative diseases. 2
• Neuroendocrine dysregulation. 2
• Non-neurological disorders including sexual dysfunction, bladder/bowel incontinence, and systemic metabolic dysregulation. 2
• Increased long-term mortality and reduced life expectancy. 2

Critical Clinical Pitfalls

Never dismiss TBI as merely an isolated event requiring only acute treatment. TBI is a chronic disease process fitting the World Health Organization definition of a chronic condition, requiring long-term observation, supervision, and care. 2 The perception that patients require little further treatment after initial management fundamentally misunderstands the ongoing pathophysiological processes that can persist indefinitely. 2

Recognize that even "good recovery" patients may demonstrate significant neuropsychological deficits on formal testing. 5 The absence of obvious clinical impairment does not indicate complete recovery or absence of ongoing disease processes. 2