A World Health Organization study estimated that between 70 and 90% of head injuries that receive treatment are mild, and a US study found that moderate and severe injuries each account for 10% of TBIs, with the rest mild.The incidence of TBI varies by age, gender, region and other factors. Findings of incidence and prevalence in epidemiological studies vary based on such factors as which grades of severity are included, whether deaths are included, whether the study is restricted to hospitalized people, and the studys location. The annual incidence of mild TBI is difficult to determine but may be 100–600 people per 100,000. Mortality
In the US, the case fatality rate is estimated to be 21% by 30 days after TBI. A study on Iraq War soldiers found that severe TBI carries a mortality of 30–50%. Deaths have declined due to improved treatments and systems for managing trauma in societies wealthy enough to provide modern emergency and neurosurgical services. The fraction of those who die after being hospitalized with TBI fell from almost half in the 1970s to about a quarter at the beginning of the 21st century. This decline in mortality has led to a concomitant increase in the number of people living with disabilities that result from TBI.Biological, clinical, and demographic factors contribute to the likelihood that an injury will be fatal. In addition, outcome depends heavily on the cause of head injury. In the US, patients with fall-related TBIs have an 89% survival rate, while only 9% of patients with firearm-related TBIs survive.
The incidence of fall-related TBI in First-World countries is increasing as the population ages; thus the median age of people with head injuries has increased.Regardless of age, TBI rates are higher in males. Men have twice as many TBIs as women do and have a fourfold risk of fatal head injury, and males account for two thirds of childhood and adolescent head trauma. However, when matched for severity of injury, women appear to fare more poorly than men.Socioeconomic status also appears to affect TBI rates; people with lower levels of education and employment and lower socioeconomic status are at greater risk. Approximately half of those incarcerated in prisons and jails in the United States have had TBIs. History
Head injury is present in ancient myths that may date back before recorded history. Skulls found in battleground graves with holes drilled over fracture lines suggest that trepanation may have been used to treat TBI in ancient times. Ancient Mesopotamians knew of head injury and some of its effects, including seizures, paralysis, and loss of sight, hearing or speech. The Edwin Smith Papyrus, written around 1650–1550 BC, describes various head injuries and symptoms and classifies them based on their presentation and tractability. Ancient Greek physicians including Hippocrates understood the brain to be the center of thought, probably due to their experience observing the effects of head trauma.Medieval and Renaissance surgeons continued the practice of trepanation for head injury. In the Middle Ages, physicians further described head injury symptoms and the term concussion became more widespread.