Definition Traumatic brain injury (TBI) is a nondegenerative, noncongenital insult to the brain from an external mechanical force, possibly leading to permanent or temporary impairment of cognitive, physical, and psychosocial functions, with an associated diminished or altered state of consciousness. The definition of TBI has not been consistent and tends to vary according to specialties and circumstances. Often, the term brain injury is used synonymously with head injury, which may not be associated with neurologic deficits. The definition also has been problematic with variations in inclusion criteria.
TBI defined by the Head Injury Interdisciplinary Special Interest Group of the American Congress of Rehabilitation Medicine The Head Injury Interdisciplinary Special Interest Group of the American Congress of Rehabilitation Medicine defines mild head injury as “a traumatically induced physiologic disruption of brain function, as manifested by one of the following: Any period of loss of consciousness (LOC), * Any loss of memory for events immediately before or after the accident, Any alteration in mental state at the time of the accident, * Focal neurologic deficits, which may or may not be transient.
In the past, the use of roentgenograms to help diagnose skull fractures after head injury did not show much of any concurrent intracranial lesions. These lesions were difficult to diagnose until the advent of CT scanning, which is now the diagnostic imaging of choice in TBI cases. Other confounding variables in determining the epidemiology of TBI exist. The use of different definitions that may not clearly define the type of injury (see Synonyms, Key Words, and Related Terms) makes the epidemiology of TBI difficult to describe.
Another variable is the difference in findings from diagnostic imaging at different time intervals (eg, when early epidural hematoma is present, the CT scan may be normal, but if the scan is later repeated, it may show evidence of pathology). TBI accounts for approximately 40% of all deaths from acute injuries in the United States. Annually, 200,000 victims of TBI need hospitalization, and 1. 74 million persons sustain mild TBI requiring an office visit or temporary disability for at least 1 day. The financial cost is estimated at approximately $4 billion per year.
This estimate includes the loss of potential income of the patient and of relatives (who may need to become caregivers), the cost of acute care, and other medical expenses, such as continuous ambulatory and rehabilitation care. Mortality rate Approximately 52,000 US deaths per year result from TBI. Local factors in the United States may influence this mortality rate; it is lowest in the Midwest and Northeast and is highest in the South. The mortality rate for deaths outside of the hospital is approximately 17 per 100,000 people; it is approximately 6 per 100,000 people for patients who are hospitalized.
The initial GCS score and, therefore, the severity of the TBI help to predict the likelihood of death from the injury. The mortality rate is high in severe TBI and is low in moderate TBI. In a TCDB study, the mortality rate in severe TBI was about 33%; in another study, in Central Virginia, the mortality rate in moderate TBI was found to be 2. 5%. Among children aged 0-14 years, an estimated 475,000 TBIs occur each year. Rates are higher among children aged 0-4 years. Death and hospitalization rates are highest among black children aged 0-9 years, compared with whites, in TBIs related to motor vehicle accidents (MVAs).
Prevalence and incidence The prevalence (ie, the existing cases at any given time) of TBI is not well documented, because most cases (ie, mild TBI) are not fatal, and patients may not have been hospitalized. Estimates often are based on existing disabilities. Estimates by the National Institutes of Health Consensus Development Panel on Rehabilitation of Persons with TBI showed that 2. 5-6. 5 million Americans live with TBI-related disabilities. A National Health Interview Survey estimated that annually, 1. 9 million persons sustain a skull fracture or intracranial injury, with such trauma making up approximately 1% of all injuries.
That incidence of mild TBI is about 131 cases per 100,000 people, the incidence of moderate TBI is about 15 cases per 100,000 people, and the incidence of severe TBI is approximately 14 cases per 100,000 people. The inclusion of prehospital deaths increases the last figure to 21 cases per 100,000 people. Differences in rates in various parts of the United States may be attributable to differences in the methods of case verification and in the cause of injury.
Mechanism of injury Common causes of fatal injuries vary according to gender, age, race, and geographical location. Such causes are as follows: MVAs are the leading cause of TBI in the general population, especially among whites in the United States. MVAs account for approximately 50% of all TBIs. In the United Kingdom, MVAs are the third most common cause of TBI, after falls and assaults. Falls are the second leading cause of TBI. Falls account for 20-30% of all TBIs. In individuals aged 75 years or older, falls are the most common cause of TBI.
Very young persons also commonly sustain TBI due to falls. Firearms are the third leading cause of TBI (12% of all TBIs) and are a leading cause of TBI among individuals aged 25-34 years. Gunshot-related, fatal TBIs are higher among men than among women and are more prevalent among African Americans than they are among whites. Work-related TBIs constitute an estimated 45-50% of all TBIs. Incidence varies from 37 cases per 100,000 people for military employees (57% are related to transportation) to 15 cases per 100,000 people for civilians (50% are because of falls).
While the incidence of TBIs from major causes decreased significantly following the introduction of safety measures (eg, seatbelts, helmets), the rate of TBI from gunshots has increased. Alcohol is a major factor in many TBIs and often is associated with the leading causes of TBI. Prevention The use of helmets by cyclists has led to fewer TBIs, and the cases that do occur are less severe than they were in prehelmet days. Automobile seatbelts and child restraints also have been associated with reduced TBI morbidity and mortality rates. No data currently address the effects of air bag use on TBI mortality and morbidity rates.
Trends The incidence of TBI has been decreasing because of the introduction of preventive measures and as a result of better enforcement of drunk driving laws. The length of stay in acute hospitals and rehabilitation facilities has been declining because of the increased demand for facilities and because of the resources that are available in the community for patients who are discharged early. Update on mild TBI The National Hospital Ambulatory Medical Care Survey, published in February 2005, looked at mild TBI in the United States from 1998-2000.
[9] The survey found that the average rate of mild TBI was 503. 1 cases per 100,000 population, with peaks among males at 590 cases per 100,000 population, among Native Americans at 1026 cases per 100,000 population, among persons younger than 5 years at 1115. 2 cases per 100,000 population, and in the Midwest region of the United States at 578. 4 cases per 100,000 population. Sports and bicycles account for about 26. 4% of mild TBIs among children aged 5-14 years. Pathophysiology: Primary Injury Overview Traumatic brain injury (TBI) is the result of an external mechanical force applied to the cranium and the intracranial contents, leading to temporary or permanent impairments, functional disability, or psychosocial maladjustment.
TBI can manifest clinically from concussion to coma and death. Injuries are divided into 2 subcategories: primary injury, which occurs at the moment of trauma, and secondary injury, which occurs immediately after trauma and produces effects that may continue for a long time.
Hematoma, cranial nerve damage, and increased brain injury may be associated with skull fractures. Vault fractures tend to be linear and may extend into the sinuses. Injuries also can be stellate, closed, or open fractures. Closed fractures do not permit communication with the outside environment, while the open fractures do. Fractures are defined as depressed or nondepressed, depending on whether or not the fragments are displaced inwardly. A simple fracture is defined as having 1 bone fragment; a compound fracture exists when there are 2 or more bone fragments.
Basal skull fractures often are caused by dissipated force and may be associated with injuries to the cranial nerves and discharges from the ear, nose, and throat. Auditory/vestibular dysfunction Impact force to the temporal region may not cause a fracture but may lead to possible conductive or sensorineural hearing loss. Conductive hearing loss results from a defect in the conduction of sound, which may occur as a result of tympanic perforation, hemotympanum, or ossicular (ie, malleus, incus, stapes) disruption. Sensorineural hearing loss may be secondary to defect in the inner ear (eg, acute cochlear concussion, perilymphatic fistula).
Benign paroxysmal positional vertigo can occur when calcium carbonate crystals become dislodged from the macula of the utricle and move into the posterior semicircular canal. In such cases, vertigo can provoked by any sudden change in head position. The diagnostic test for this condition is the Dix-Hallpike maneuver. Intracranial hemorrhages Several types of intracranial hemorrhages can occur, including the following: Epidural hematoma occurs from impact loading to the skull with associated laceration of the dural arteries or veins, often by fractured bones and sometimes by diploic veins in the skull’s marrow.
More often, a tear in the middle meningeal artery causes this type of hematoma. When hematoma occurs from laceration of an artery, blood collection can cause rapid neurologic deterioration. Subdural hematoma tends to occur in patients with injuries to the cortical veins or pial artery in severe TBI. The associated mortality rate is high, approximately 60-80%. Intracerebral hemorrhages occur within the cerebral parenchyma secondary to lacerations or to contusion of the brain, with injury to larger, deeper cerebral vessels occurring with extensive cortical contusion.
Intraventricular hemorrhage tends to occur in the presence of very severe TBI and is, therefore, associated with an unfavorable prognosis. Subarachnoid hemorrhage may occur in cases of TBI in a manner other than secondary to ruptured aneurysms, being caused instead by lacerations of the superficial microvessels in the subarachnoid hemorrhage may occur in cases of TBI in a manner other than secondary to ruptured aneurysms, being caused instead by lacerations of the superficial microvessels in the subarachnoid space.
If not associated with another brain pathology, this type of hemorrhage could be benign. Traumatic subarachnoid hemorrhage may lead to a communicating hydrocephalus if blood products obstruct the arachnoid villi or in the event of a noncommunicating hydrocephalus secondary to a blood clot obstructing the third or fourth ventricle.
Coup contusions occur at the area of direct impact to the skull and occur because of the creation of negative pressure when the skull, distorted at the site of impact, returns to its normal shape. Contrecoup contusions are similar to coup contusions but are located opposite the site of direct impact. Cavitation in the brain, from negative pressure due to translational acceleration impacts from inertial loading, may cause contrecoup contusions as the skull and dura matter start to accelerate before the brain on initial impact.
