features (i.e., pathoanatomy) of tissue damage induced by the injury. Pathoanatomical features influence outcomes for individuals with brain injuries (Saatman et al. 2008) and indicate the likelihood of developing certain secondary problems (e.g., cerebral edema) (Saatman et al. 2008). Pathoanatomical classification may aid with prognosis (Saatman et al. 2008), which helps determine the appropriate timing and type of rehabilitation. The injury is classified based on the presence or absence of a mass lesion, which is found using diagnostic tools such as computed tomography (CT) and magnetic resonance imaging (MRI) (Olson-Madden et al. 2010). Imaging helps with location of injury, which can be useful in understanding localization of deficits (e.g., frontal lobe injuries are associated with problems with attention, initiating activity) (Kringelbach and Rolls 2004).

Severity Scales

Severity of TBI is generally graded from mild to moderate or severe. Severity can be classified in multiple ways, and each measure has different predictive utility, including determining morbidity, mortality, or long-term functional outcomes. Patients with more severe head injuries demonstrate lower cognitive functioning and have more gradual cognitive improvements following the initial injury (Novack et al. 2000). Degree of severity is often based on the acute effects of the injury, such as an individual’s level of arousal or duration of amnesia, and these are measured by the GCS, PTA, duration of LOC (Ptak et al. 1998) and degree of altered consciousness.

The majority of TBIs are mild, consisting of a brief change in mental status or unconsciousness. Mild TBI is also referred to as a concussion. While most people fully recover from mild TBI, individuals may experience both short- and long-term effects. Moderate-severe TBI is characterized by extended periods of unconsciousness or amnesia, among other effects. The distinction between moderate and severe injuries is not always clear; as such, individuals with moderate and severe injuries are often grouped for research purposes. Throughout the remainder of this report, the committee refers to more severe injuries as moderate-severe TBI. Chapter 1 provides epidemiological statistics on TBI by severity.

These classification systems not only determine the severity of TBI, but also may be indicative of the degree of long-term disability. The more severe the injury, the more severe and persistent the cognitive deficits—though clinical measurements do not always concur. Severity measures graded during the acute phase sometimes reflect variance due to medications used during resuscitation, substance use, and communication issues. However, the relationship between clinical severity measures (e.g., GCS, LOC, and PTA) and various types of outcome measures (e.g., neuropsychological, functional disability, levels of handicap) has been well established (Cifu et



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