Overview

Traumatic brain injury (TBI) is a major public health issue globally and in the United States. The Centers for Disease Control (CDC) defines TBI as an insult (blow or bump to the head) or penetrating head injury affecting the normal function of the brain. TBI can vary in severity, and in the United States, the majority are mild and clinically often described as a “concussion.” Recent research over the past decade has demonstrated that there is a growing societal cost involved in the management of the long-term physical and psychosocial sequelae of TBI. Following a head injury, trauma may also occur to the lateral skull base, which is an area that includes critical neurovascular structures within the middle and posterior fossae and temporal bone, which, similar to TBI, may greatly affect quality of life. Given the rising incidence of TBI and growing public health concern, understanding the epidemiologic patterns of these types of injuries is important for identifying and managing populations at risk.

Incidence and epidemiology of traumatic brain injury in the United States

Each year in the United States, the overall incidence of TBI is 823.7 per 100,000 people. The overall incidence of TBI can be further subdivided in different settings: 403, 85, and 18 per 100,000 people for emergency department (ED) visits, hospitalizations, and deaths, respectively. Annually, these account for 2.5 million patients who are treated in the ED (87%), hospitalized (11%), or die from their injuries (2%). These annual estimates, however, likely underestimate the true incidence as they do not account for individuals who do not seek medical treatment or receive care in either an outpatient setting or federal facility (e.g., Veterans Affairs hospital).

Among individuals who experience a TBI in the United States, there are several etiologies that are major contributors to annual ED visits, hospitalizations, and death. The top three most common etiologies resulting in TBI-related ED visits are falls (658,668 individuals; 41%), being struck by or against an object (304,797 individuals; 19%), and being in a motor vehicle traffic accident (232,240; 15%). Among patients who were hospitalized, the leading etiologies resulting in TBI-related hospitalizations are falls (66,291 individuals; 24%) and motor vehicle traffic accidents (53,391 individuals; 19%). Major causes of TBI-related death are motor vehicle traffic accidents (14,795; 29%), self-inflicted/suicide (14,713; 29%), and falls (10,944; 21%).

Sports-related TBI is also a growing area of public health interest. At present, data from the National Electronic Injury Surveillance System—All Injury Program suggest that the majority of TBI-related ED visits are due to contact sports (football and soccer) as well as from basketball, bicycling, and playground activities. Recent studies suggest that within the past two decades, there has been a 62% increase in the treatment of pediatric sports-related TBI ^, ; this may, however, be driven by public health initiatives to raise awareness for sports-related concussions, such as the CDC’s HEADS UP campaign, which prompted more patients to recognize and seek care in the ED following a suspected TBI. A recent study examining a large epidemiologic sample of pediatric patients with TBI suggested that children were more likely to have auditory dysfunction. Further studies are needed to understand how head trauma management in this population can be improved to reduce the known long-term negative developmental sequelae of TBI, such as disrupted cognitive and social performance.

Prior studies have highlighted that specific populations are at increased risk for TBI, which include people within certain age groups and males. Individuals who are at the extremes of age ranges (0–4 years, 15–19 years, and ≥75 years) are at increased risk for TBI, leading to an ED visit or hospitalization whereas those ≥75 years old are at greatest risk for TBI-related hospitalizations and death. Determining if a patient suffered a TBI who is in the extremes of age may be challenging as symptoms may be indolent. Children without visible physical injury may present with a delayed onset effects of TBI including poor academic performance and difficulty with social relationships. ^, Older adults with past TBI may have their symptoms misattributed to the normal process of aging. As a result, providers should maintain a high clinical suspicion for TBI, especially given the recent epidemiologic shift toward falls being the leading cause of TBI, which are common in the elderly. Additionally, compared with females, males contribute to the majority (59%) of TBI-related medical visits, ^, which may be due to males participating in more high-risk activities.

Other patient characteristics associated with elevated risk for TBI include lower socioeconomic status, minority races, and living in rural geographical regions, which are factors that may be interrelated. Comparing insurance status as a surrogate for socioeconomic status, patients who were uninsured were nearly twice as likely to have a TBI compared with those with private insurance. Individuals who are from Black, Hispanic, or American Indian/Alaska Native backgrounds within the United States have greater risk of TBI compared with white individuals. Additionally, those living in rural regions also have increased risk of suffering from a TBI compared with those living in urban settings. Several studies suggest that these populations, in addition to experiencing TBI more frequently than the general population, may also have poorer outcomes. Differences in clinical outcomes may be due to several factors including reduced access to care, delayed presentation, ^, and lower likelihood to participate in follow-up care. Future studies are needed to understand how improved resource distribution may reduce rates of TBI in these populations and improve patient outcomes.

Incidence and epidemiology of lateral skull base trauma in the United States

In addition to TBI, lateral skull base trauma is a growing public health concern, but recognition of the lateral skull base as a distinct anatomical area has been fairly recent over the past three decades. The lateral skull base is defined by a combination of two subregions. The first region is the area that extends from the orbit’s posterior wall to the petrous temporal bone and formed by the pterygopalatine and infratemporal fossae with the overlying part of the middle cranial fossa, which contains vasculature structures such as the internal carotid artery, and cranial nerves (maxillary and mandibulary divisions of the trigeminal nerve, facial, and vestibulocochlear nerves). The second region is primarily composed of the posterior cranial fossa and the posterior segment of the middle cranial fossa, which contains vasculature structures such as the internal jugular vein and cranial nerves (glossopharyngeal, vagus, spinal accessory, and hypoglossal nerves). The following section, however, will focus on primarily temporal bone fractures (TBFs) as robust epidemiologic studies of other areas of the lateral skull base are limited.

Following head injury, the high energy impact may lead to fractures of the skull base and temporal bone. It is estimated that 4%–30% of head injuries lead to skull base fractures and 18%–40% of these result in TBFs where the majority of TBFs are unilateral and bilateral TBF occurs in only 4.4%–20% of patients. Given the amount of force required to cause a TBF, it is common for trauma to occur to other structures such as the facial nerve or tympanic membrane ^, or result in cerebrospinal fluid (CSF) leaks. TBF occurs through three primary mechanisms: motor vehicle accidents (MVAs) (12%–47%), falls (16%–40%), and assaults (10%–37%), ^{, ,} where MVA is currently the most common mechanism of injury, but recent studies suggest that falls are becoming increasingly common. The increased use of automotive safety features such as airbags and seat belts may contribute to the decline in MVA. Risk factors for sustaining a TBF include patient characteristics such as younger age (second to fourth decades) and male gender, which is similar to the risk factors in TBI, and may be due to males participating in risky behavior. Consistent with the severity of injury resulting in TBF, mortality rates following TBF range are high and estimated to be 7.9%–12%. ^{, , ,}

Historically, TBFs have been classified by the orientation of the fracture line relative to the long axis of the petrous temporal bone as either transverse (perpendicular) or longitudinal (parallel) fractures. Prior studies suggest that using this classification scheme, 70%–90% of TBFs are transverse and 10%–30% of TBFs are longitudinal. ^{, , , , ,} Growing evidence, however, suggests that a significant amount of TBF cannot be discretely organized in these two categories, where most TBFs have a mixed fracture pattern. ^, Given the inability for this earlier TBF scheme to prognosticate important clinical information, such as neurotologic deficits, a newer scheme describing involvement of the otic capsule, which is a bony structure that contains the cochlea, vestibule, and semicircular canals, has been increasingly used. ^{, , ,} TBFs using this scheme are categorized as otic capsule-violating (OCV) or otic capsule-sparing (OCS); compared with OCS TBF, OCV TBFs are associated with significantly higher rates of facial nerve paralysis, sensorineural hearing loss, CSF leak, and intracranial complications. ^{, , ,} Since the more recent adoption of the otic capsule classification scheme, the prevalence of OCV appears to occur in 2%–8% of TBF. ^{, , ,} The mechanism of injury that results in OCV TBF is often due to impact of the occipital area toward the foramen magnum, petrous pyramid, and otic capsule. Future studies are needed to assess individuals at risk for experiencing OCV TBF to help improve the diagnosis and management of these injuries.

Healthcare resource utilization due to traumatic brain injury and lateral skull base injury

In addition to being a leading cause of mortality in the United States, TBI and its associated sequelae are associated with significant morbidity. The comorbidities from TBI can greatly affect quality of life by limiting physical function and disturbing cognitive function (e.g., memory, attention) and mood. ^{, ,} The domains that TBI and lateral skull base injury are extensive and can impact both social relationships and the ability to work of those directly injured and for caregivers. ^,

In the United States, it is estimated that TBI results in 2.5 million ED visits, inpatient stays, and deaths, and between 3.2 and 5.3 million people have a TBI-related disability. Managing TBI acutely and its sequelae places a large financial burden on the healthcare system; the annual expenditure for TBI-related care in the United States is approximately 60 billion dollars. Healthcare-related costs for TBI are composed of several domains: direct medical (acute medical treatment and follow-up), societal (lost productivity due to disability), and rehabilitation (cost due to use of rehabilitation centers). In a study analyzing patients with severe TBI, the majority of expenditures were societal costs followed by direct medical and rehabilitation costs, suggesting that the main cost is opportunity cost due to lost productivity. As a result, areas for reduced healthcare resource utilization related to TBI care should be focused on education, prevention, and targeted treatment protocols. Over the past 40 years, the Brain Trauma Foundation, which is an organization created by the CDC provided evidence-based guidelines for the treatment and monitoring of TBI. Authors who performed a cost–benefit analysis utilizing the Brain Trauma Foundation guidelines noted that if widely adopted, the national cost of TBI-related care could be reduced by 4 billion dollars while decreasing mortality rates. Future studies are needed to identify additional patient-related factors to further lower this societal cost.

Conclusion

TBI and lateral skull base injuries are major public health issues in the United States. Individuals who suffer from these injuries may experience reduced functional status that may affect them socially and cognitively. Economically, TBI and lateral skull base injuries also place a significant burden on the healthcare system. Increased awareness and adoption of evidence-based protocols may help improve clinical outcomes and reduce healthcare resource utilization.