Understanding Traumatic Brain Injury

Traumatic Brain Injury (TBI) is brain injury resulting from the application of an external physical force to the brain, including acceleration/deceleration and/or blast-related forces , that produce immediately apparent physiological disruption of brain function and/or structure, usually evidenced by an alteration of mental state and/or sensorimotor impairments, that result in at least transient functional disability. This definition of TBI excludes brain injuries due to perinatal trauma, hypoxia-ischemia, inflammation, toxic insults, metabolic insults, primary ischaemic and/or haemorrhagic strokes, seizures disorders and their consequences, intracranial surgery and cerebral neoplasms. Although clinical definitions narrow the clinical referents of TBI, there is still a large amount of within-diagnosis heterogeneity at all levels of injury severity, including:

•Penetrating vs. non-penetrating TBI
•Focal vs. diffuse vs. focal-diffuse
•Mild TBI with or without neuroimaging abnormalities.

Epidemiology of TBI

Among countries collecting and reporting head injury data, the annual incidence of TBI varies from 60-600/100,000 population. Estimates of total number of people affected each year by TBI  in different countries include 1.5 million in the United States, 1.5-2 million in India, 280,000 in Germany and Russia, 220,000 in England and Mexico, 180,000 in France, 110,000 in Japan, 80,000 in Spain and the lowest in Australia of approximately 70,000.

Children aged 0 to 4 years, older adolescents aged 15 to 19 years, and adults aged 65 years and older were most likely to sustain a TBI and almost half a million (473,947) emergency department visits for TBI were made annually by children aged 0 to 14 years. The highest rates of TBI-related hospitalization and death were seen in the over 75 year age group. In every age group, rates for men were higher than women. Male children between the ages of 0-4 years had the highest rates of TBI-related emergency department visits, hospitalizations and deaths combined.

Burden of TBI

TBI is a leading cause of coma, trauma-related disability, brain damage in children and young adults and death in the young and the old around the world. TBI has substantial health, economic and societal costs globally.

Every year, at least 80,000 people in the USA develop permanent functional disabilities as a result of TBI and 3.17 million Americans currently live with TBI-related disabilities. Beyond the first post-injury year, individuals with TBI are 2-4.5 times more likely to die compared to those of similar age, gender and race in the general population. Increased mortality in TBI is due to increased risk of seizures (37 times), septicaemia (12 times), respiratory infections (3-4 times), digestive conditions (3 times) and other external causes of injury (3 times).  Estimated average life expectancy is reduced by seven years when individuals with TBI require hospitalization and rehabilitation. Within the TBI population, the strongest independent risk factors for death beyond the first post-injury year are older age, unemployment at time of injury and greater post-rehabilitation disability.

Silver JM, McAllister TW, & Arciniegas DB (2009). Depression and cognitive complaints following mild traumatic brain injury. The American journal of psychiatry, 166 (6), 653-61 PMID: 19487401

Coronado VG, Xu L, Basavaraju SV, McGuire LC, Wald MM, Faul MD, Guzman BR, Hemphill JD, & Centers for Disease Control and Prevention (CDC) (2011). Surveillance for traumatic brain injury-related deaths–United States, 1997-2007. Morbidity and mortality weekly report. Surveillance summaries (Washington, D.C. : 2002), 60 (5), 1-32 PMID: 21544045