Introduction to Traumatic Brain Injury

Published on 26/03/2015 by admin

Filed under Neurosurgery

Last modified 22/04/2025

Print this page

This article have been viewed 1238 times

CHAPTER 322 Introduction to Traumatic Brain Injury

M. Ross Bullock, David A. Hovda

Traumatic brain injury (TBI) remains the leading cause of death and long-term disability in people younger than 40 years worldwide. Although the incidence of closed TBI in “developed regions” such as Europe, North America, Japan, and Australia continues to fall, its incidence is rising at epidemic proportions in regions with rapidly increasing motorization because of industrialized development. This incidence varies from 67 to 317 per 100,000 individuals, and mortality rates range from around 4% to 8% for moderate injury to approximately 50% with severe head injury. In some rapidly developing countries such as China, Brazil, Colombia, and India, the availability of neurosurgical expertise is a major limiting factor that contributes to poor outcome in patients sustaining neurotrauma; however, this is changing rapidly, and there are now almost as many neurosurgeons practicing in Brazil as there are in the United States, and more are practicing in China than in any other country. Thus, for many of the world’s neurosurgeons, neurotrauma remains the most common major disorder that they are called on to treat.

Recently, neurosurgeons in developed countries have seen dramatic changes in their practice patterns, with increasing numbers of patients being managed with nonoperative interventions, such as endovascular treatment of intracranial aneurysms and radiosurgical treatment of an increasing range of intracranial tumors. However, the need for neurosurgeons to be involved in the management of moderate and severe TBI is greater than ever with the emergence of decompressive craniotomy and multimodality monitoring techniques together with modern neurological intensive care, which have combined to produce dramatic reductions in mortality rates from around 80% for severe TBI in the 1950s to about 20% for severe TBI reported by many of the specialized centers in the last 5 years. About 80,000 craniotomies for removal of intracranial hematomas are preformed in the United States each year, and the figure is slightly higher in Pakistan, as an example. Population-based studies have shown that the single most cost-effective surgical operation is removal of an acute epidural hematoma, given the severe consequences of that hematoma in terms of death or vegetative survival.

It is also well known that at the levels of trauma care systems and organizations, the impact that neurosurgeons can have on the populations that they serve may be large and disproportionate to the small size of the specialty. Examples include working with trauma surgeons to improve prehospital care, improving the quality of trauma systems and emergency departments for trauma victims in general, and optimizing neurocritical care. The dramatic reductions seen in mortality rates for patients with neurotrauma are directly attributable to systems-based collaborations such as this; yet in a majority of cities in rapidly developing countries, such systems are nonexistent or inadequate. Therefore, the need to mentor and foster such interdisciplinary, collaborative trauma care systems among neurosurgeons and other health care providers in these developing countries is clear. It is through these efforts that evidence-based guidelines for the prehospital, surgical, medical, and pediatric management of severe TBI have emerged (Table 322-1).

TABLE 322-1 Evidence-Based Guidelines for Brain Trauma and Internet/Journal Sources

TITLE OF GUIDELINE DOCUMENT	YEAR PUBLISHED	WEBSITE JOURNAL
Management of Severe Head Injury	1996	www.braintrauma.org J Neurotrauma 1996;13:641-734
Management and Prognosis of Severe TBI, 2nd edition	2000	www.braintrauma.org J Neurotrauma 2000
Management of Severe TBI, 3rd edition	2007	www.braintrauma.org J Neurotrauma 2007;24:S71-S76
Prehospital Management of TBI	2000	www.braintrauma.org
Surgical Management of TBI	2006	www.braintrauma.org Neurosurgery 2006;58(3 Suppl 2):1-62
Pediatric Severe TBI Guidelines	2003	www.braintrauma.org Pediatr Crit Care Med 2003;4(3):S1-S75
Field Management of Combat-Related Head Trauma	2005	www.braintrauma.org
Penetrating Brain Injury	2001	J Trauma 2001;51(2):S3-S43

TBI, traumatic brain injury.

Neurotrauma Research

In excess of 700 researchers and clinicians are engaged in full-time research on TBI worldwide. Although there has been a massive increase in our understanding of the pathologic mechanisms of TBI over the last 25 years, pharmacologic treatments, such as for occlusive stroke and many other acute central nervous system disorders, have remained elusive. Within the last few years, funding levels for neurotrauma research by both the National Institutes of Health and the Department of Defense have increased in the United States. This increase in support by the Department of Defense has been particularly substantial. Recently, the military spent more than $200 million (U.S. dollars) in 2008 on neurotrauma research projects, which when compared with the approximately $100,000 spent annually on federally funded TBI research in previous years, reveals a substantial increase in support. This influx of funds has increased the scope of both preclinical and clinical research studies in TBI. It is hoped that the benefits of these investments in TBI research will be felt incrementally over the next 5 years.

The emergence of trial consortia for TBI is one tangible example of such benefits that can already be seen. Currently, with at least six major TBI clinical trial consortia in Europe and North America, the power of more than 200 hospitals has been harnessed to standardize treatment of severe TBI for the purpose of conducting clinical trials. This in turn has led to renewed interest in the field by the pharmaceutical industry and has resulted in at least four major new phase II and phase III drug evaluation trials for severe TBI in 2010.

However, all who seek to improve outcomes after TBI are now well aware that the “single-drug magic bullet” concept, or the restriction in focus solely on neuroprotection that drove clinical trials in the 1980s and 1990s, is naïve. The pathophysiology of TBI is extremely complex. Some cellular responses once thought to be pathologic are normal neurobiologic responses to injury that activate endogenous processes for both cell survival and recovery of function.

Of course, the most effective approach to the general health problem of TBI is prevention. The incidence of severe TBI in “developed countries” has fallen in recent years primarily because of better automobile design, seat belt and air bag use and deployment, highway safety, reduced alcohol consumption, better police work, and better promotion of safety techniques in the workplace. This enhanced prevention/protection has been particularly evident in the effort to protect military personnel in developed countries. The rapid evolution in the design of military helmets and body armor with the use of “Kevlar sandwich” designs has led to survival being commonplace after full cranial impact with high-velocity rifle bullets, truly a modern miracle that culminated from the work of Horsley, Cairns, Carey, and other neurosurgeons influential in this field. Supporting all these efforts at prevention has been the rapid dissemination of information by the Internet, telemetry, and computerized design systems.

Once TBI has occurred, it is clear that the reduction in mortality rates reported since the 1960s is due primarily to the synergistic effects of better prehospital care, more rapid detection and evacuation of intracranial hematomas, and prevention of secondary brain damage through intensive care techniques such as respiratory and cardiac support, decompressive craniotomy, intracranial pressure monitoring, osmotherapy, and prevention of hyperthermia and infective complications. All these aspects emphasize the importance of the regional and temporal means by which the human brain responds to trauma.

These regional and temporal characteristics of TBI have continued to present a challenge to the development of therapeutic treatments. However, over the last decade, the field and technology of neuroscience have rapidly advanced and allowed investigators to overcome some of the limitations associated with the complexity and heterogeneity of TBI. Examples of these advancements in technology include high-throughput screening, immunohistochemistry, enzyme-linked immunosorbent assays, mass spectroscopy, and new brain imaging parameters, all of which have brought forth major discoveries. These combined advances can now be translated to the clinic in periods as short as 3 to 5 years. Not only has this resulted in a new approach to pharmacology for neuroprotection, but it has also launched a renewed effort to develop treatments that enhance neuroplasticity. The importance of this enhancement of translational research cannot be understated. The previous challenges in moving treatments from the basic science laboratory to the clinic underscore the necessity of having direct linkage via biomarkers or imaging (or both) to allow confirmation of a purported treatment effect in the injured human brain.

In addition to the advancements in technology, the confirmation that new neurons are born within the injured nervous system after TBI, ischemia, seizures, and other acute central nervous system insults is only one of many new discoveries that have changed the approach of investigators interested in finding a cure for TBI. This particular discovery has opened the possibility of repair of the adult nervous system with techniques such as stem and precursor cell transplantation, trophic factor augmentation, and genetic manipulation of the host environment. In addition, there is compelling new information that is forcing investigators to revisit previously accepted dogma. For example, discoveries such as the effects of TBI on the developing brain, the process of traumatic axonal injury, the postinjury changes in fuel demands, the potential benefit of stimulation of “excitotoxic” receptors, and the influence of diet and exercise on recovery will all have a major impact on not only how the brain responds during the first few hours after injury but, more importantly, on how it will recover its function over the weeks and months of rehabilitation.

The field of neurotrauma is truly being transformed. What was once regarded as a small and arcane field of study in which a few enthusiasts were trying to improve the outcome of patients whose outcome was thought by an older generation of neurosurgeons to be determined at the moment of impact with the potential for severe disabilities, cognitive impairment, and vegetative survival or death has now radically changed. The pathologic mechanisms leading to neuronal death and dysfunction after TBI are now well understood, and much insight has been gained into the nonpathologic responses of the brain to injury, as clearly outlined in Chapters 324 and 326 in this book. Advances in understanding the neurobiology of TBI have shown that most of the secondary damage, as well as even diffuse axonal injury, which was long thought to be fully established at the moment of impact, is actually an evolving process that may be halted, reversed, or repaired by therapies. In addition, better understanding of the management of mild and moderate injuries, sports concussions, and the interface between posttraumatic stress disorder and mild post-TBI psychometric impairment has led to better ways of fully integrating TBI victims back into athletics and society in general, as outlined in Chapter 328.

We are hopeful that this volume will constitute a single contemporary knowledge resource for neurosurgeons, neuroscientists, or other health care providers seeking to increase their understanding of the etiology, epidemiology, pathologic mechanisms, neurobiology, and management of neurotrauma patients. The reader is also referred to the sets of guidelines, many recently updated, that are listed in Table 322-1. Finally, we hope that neurosurgeons entering the field of neurotrauma will be inspired not only to provide the best possible care for their patients based on the information available but also to take the challenge of improving their local trauma infrastructure and management systems to enhance prehospital care, emergency department management, and intensive care of their neurotrauma patients. Only in this manner can the best possible outcome be achieved for the maximum number of patients.

Related

Youmans Neurological Surgery