alterations (Jeremitsky et al. 2003; Saatman et al. 2008). These early, acute events are highly relevant to long-term outcomes, as they can critically affect an individual’s degree of disability and need for rehabilitation. The following chapter does not contain exhaustive descriptions of the many factors related to TBI. The reader may refer to Gulf War and Health, Volume 7: Long-Term Consequences of Traumatic Brain Injury (IOM 2009) for more in-depth discussion of TBI biology.

The response to injury and subsequent treatment varies by multiple factors unique to the affected individual, such as age, gender, genetics, cognitive reserve, polytrauma, multiple concussions from the same impact, and history of prior brain injury (Colantonio et al. 2008; Loane and Faden 2010; Perel et al. 2008). Such variability influences long-term functional outcomes, including cognitive processes. The ultimate degree of recovery likely reflects individual variability with regard to neuroplasticity, or the ability of undamaged brain regions or pathways to take over irreparably damaged cells or brain regions (Cramer et al. 2011). Although most mild injuries appear to recover completely within weeks to months after trauma, a small but not insignificant subset of mild TBIs cause longer-term symptoms, and these also may be associated with sustained or progressive neuroimaging abnormalities (Vannorsdall et al. 2010). Secondary injury processes may continue for months or years, particularly with moderate or severe injuries, which may lead to progressive long-term tissue loss (Greve and Zink 2009; Werner and Engelhard 2007). Thus, characteristics of the injury and the individual contribute to the heterogeneity of TBI, which has implications for treatment options.

CLASSIFICATION SCHEMES

Head injuries have historically been classified using various clinical indexes that include pathoanatomical features, severity of injury, or the physical mechanisms of the injury (i.e., causative forces). Different classification systems may be used for clinical research, clinical care and management, or prevention. Additional classification schemes include those that address secondary injury. The classification systems most relevant to rehabilitation help determine pace of recovery or expected degree of impairment. These systems include the Glasgow Coma Scale (GCS), posttraumatic amnesia (PTA), duration of loss of consciousness (LOC), and degree of altered consciousness.

Pathoanatomical Classification

Sometimes known as the “where and what” of TBI classification, pathoanatomical classification describes the location and the pathological



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