Definitions

Classification of Traumatic Brain Injury

Different approaches to classification of TBI exist. From a mechanistic perspective, closed, penetrating, crush, and blast injuries are distinguished. Blast injuries have recently been identified as a separate entity and are frequently caused by improvised explosive devices used during armed conflicts and terrorist activities.

Epidemiologic studies on TBI are more or less based exclusively on the administrative classification of the ICD 9 or ICD 10 codes. In ICD 9, different codes are not mutually exclusive, which results in problems and variability in coding, and the coding in no way reflects the actual clinical severity of injury.⁹ Similar criticism is applicable to the ICD 10 codes. High agreement (96.5%) between the ICD 9 and ICD 10 codes in identifying TBI has been reported.¹⁰

In clinical medicine, scoring systems are frequently used to classify the severity of injury (see Table 323-1). The clinical severity of intracranial injuries is commonly assessed according to the degree of depression of the level of consciousness as assessed by the GCS.¹¹ The GCS consists of the sum score (range, 3 to 15) of three components (eye, motor, and verbal scales), each assessing different aspects of reactivity. The motor component provides more discrimination in patients with severe injuries, whereas the eye and verbal scales are more discriminative in patients with moderate and mild injuries. For assessment of severity in individual patients, the three components should be reported separately. For purposes of classification, however, calculation of the sum score is useful. Severe TBI is defined as a GCS score of 3 to 8, moderate TBI as a GCS score of 9 to 13, and mild TBI as a GCS score of 14 to 15. A limitation of classifying clinical severity with the GCS is that accurate assessment may be confounded by the prehospital use of sedation and paralysis.^12,13 The severity of extracranial injuries is commonly scored according to the Abbreviated Injury Score (AIS)¹⁴ or the Injury Severity Score (ISS).¹⁵ TBI is associated with extracranial injuries (limb fractures, thoracic or abdominal injuries) in about 35% of patients.¹⁶ Extracranial injuries increase the risk for secondary damage as a result of hypoxia, hypotension, pyrexia, and coagulopathy. In the assessment of overall injury severity, therefore, recording of the severity of extracranial injuries is highly relevant.

Assessment of the extent of structural damage is commonly performed according to the Marshall CT classification. This classification was proposed by Marshall and colleagues in 1991 as a descriptive system that focused on the presence or absence of a mass lesion.¹⁷ The scale further differentiates diffuse injuries by signs of increased intracranial pressure (e.g., compression of the basal cisterns, midline shift). This classification has limitations, however, such as broad differentiation between diffuse injuries and mass lesions and lack of specification. For purposes of prognosis, better discrimination can be obtained by combining information available from individual CT characteristics into a prognostic model. A score chart for applying such a score has been proposed by Maas and associates.¹⁸ A different approach to classifying patients is by prognostic risk. Recently, well-validated models developed from large patient samples have become available to facilitate this approach.^19,20 Prognostic classification can serve various purposes, including comparison of different TBI series, quality assessment for the delivery of health care, and support of the analysis of clinical trials. All these approaches to classification are characterized by some form of scoring of severity.

The Impact of Traumatic Brain Injury from A Global Perspective

TBI is a major health and socioeconomic problem that affects all societies around the world. Globally, in excess of 10 million people suffer TBI serious enough to result in death or hospitalization each year.²¹ In 2003, in the United States alone there were an estimated 1,565,000 TBIs resulting in 1,224,000 emergency department visits, 290,000 hospital admissions, and 51,000 deaths.²² The prevalence of TBI in the United States has been estimated at approximately 5.3 million. In the European Union with 330 million inhabitants, approximately 7,775,000 new TBI cases occur each year. Worldwide, TBI will surpass many diseases as the major cause of death and disability by the year 2020.⁴ It has been estimated that TBI accounts for 9% of global mortality and is a threat to health in every country in the world. For every death there are dozens of hospitalizations, hundreds of emergency department visits, and thousands of doctor appointments. A large proportion of people surviving their injuries incur temporary or permanent disability. Brain trauma accounts for approximately a third of all injury-related deaths and the majority of permanent disability. Despite the success of preventive measures, injuries, including unintentional injuries, homicide, and suicide, are the leading cause of death in the United States and Europe in individuals younger than 45 years. In low- and middle-income countries, the incidence of TBI is rising sharply because of increasing motorization. Most patients with TBI have milder injuries, but residual deficits are common.²³ TBI occurs more frequently in young adults, particularly males, and has a high cost to society because of life years lost as a result of death and disability. The financial burden of TBI has been estimated to be greater than $60 billion per year in the United States alone.²⁴ The true cost is even higher in that this figure does not address the indirect effects on families or other caregivers. These numbers stand in stark contrast to the amount of funding for TBI research, which has one of the highest unmet needs within the already severely underfunded field of brain research.