<unk>  is defined as damage to the<unk>  resulting from external mechanical force, such as rapid acceleration or deceleration, impact, blast waves, or penetration by a projectile.<unk>  function is temporarily or permanently impaired and structural damage may or may not be detectable with current technology.<unk>  is one of two subsets of acquired<unk>  injury<unk>  damage that occur after birth); the other subset is non-traumatic<unk>  injury, which does not involve external mechanical force (examples include stroke and infection). All<unk> es are head injuries, but the latter term may also refer to injury to other parts of the head. However, the terms head injury and<unk>  injury are often used interchangeably. Similarly,<unk>  injuries fall under the classification of central nervous system injuries and neurotrauma. In neuropsychology research literature, in general the term<unk> " is used to refer to non-penetrating<unk> es.<unk>  is usually classified based on severity, anatomical features of the injury, and the mechanism (the causative forces). Mechanism-related classification divides<unk>  into closed and penetrating head injury. A closed (also called nonpenetrating, or blunt) injury occurs when the<unk>  is not exposed. A penetrating, or open, head injury occurs when an object pierces the skull and breaches the dura mater, the outermost membrane surrounding the<unk> . Severity + Severity of<unk>  GCS PTA LOC Mild 13–15 day 0–30 minutes Moderate 9–12 >1 to days >30 min to 7 days >24 hours<unk>  injuries can be classified into mild, moderate, and severe categories. The Glasgow Coma Scale (GCS), the most commonly used system for classifying<unk>  severity, grades a person's level of consciousness on a scale of 3–15 based on verbal, motor, and eye-opening reactions to stimuli. In general, it is agreed that a<unk>  with a GCS of 13 or above is mild, 9–12 is moderate, and 8 or below is severe. Similar systems exist for young children. However, the GCS grading system has limited ability to predict outcomes. Because of this, other classification systems such as the one shown in the table are also used to help determine severity. A current model developed by the Department of Defense and Department of Veterans Affairs uses all three criteria of GCS after resuscitation, duration of post-traumatic amnesia (PTA), and loss of consciousness (LOC). It also has been proposed to use changes that are visible on neuroimaging, such as swelling, focal lesions, or diffuse injury as method of classification. Grading scales also exist to classify the severity of mild<unk> , commonly called concussion; these use duration of LOC, PTA, and other concussion symptoms. Pathological features CT scan Spread of the subdural hematoma (single arrows), midline shift (double arrows) Systems also exist to classify<unk>  by its pathological features. Lesions can be extra-axial, (occurring within the skull but outside of the<unk>  or intra-axial (occurring within the<unk>  tissue). Damage from<unk>  can be focal or diffuse, confined to specific areas or distributed in a more general manner, respectively. However, it is common for both types of injury to exist in a given case. Diffuse injury manifests with little apparent damage in neuroimaging studies, but lesions can be seen with microscopy techniques post-mortem, and in the early 2000s, researchers discovered that diffusion tensor imaging (DTI), a way of processing MRI images that shows white matter tracts, was an effective tool for displaying the extent of diffuse axonal injury. Types of injuries considered diffuse include edema (swelling), concussion and diffuse axonal injury, which is widespread damage to axons including white matter tracts and projections to the cortex. Focal injuries often produce symptoms related to the functions of the damaged area. Research shows that the most common areas to have focal lesions in non-penetrating<unk>  are the orbitofrontal cortex (the lower surface of the frontal lobes) and the anterior temporal lobes, areas that are involved in social behavior, emotion regulation, olfaction, and decision-making, hence the common social/emotional and judgment deficits following moderate-severe<unk> . Symptoms such as hemiparesis or aphasia can also occur when less commonly affected areas such as motor or language areas are, respectively, damaged. One type of focal injury, cerebral laceration, occurs when the tissue is cut or torn. Such tearing is common in orbitofrontal cortex in particular, because of bony protrusions on the interior skull ridge above the eyes. In a similar injury, cerebral contusion (bruising of<unk>  tissue), blood is mixed among tissue. In contrast, intracranial hemorrhage involves bleeding that is not mixed with tissue. Hematomas, also focal lesions, are collections of blood in or around the<unk>  that can result from hemorrhage. Intracerebral hemorrhage, with bleeding in the<unk>  tissue itself, is an intra-axial lesion. Extra-axial lesions include epidural hematoma, subdural hematoma, subarachnoid hemorrhage, and intraventricular hemorrhage. Epidural hematoma involves bleeding into the area between the skull and the dura mater, the outermost of the three membranes surrounding the<unk> . In subdural hematoma, bleeding occurs between the dura and the arachnoid mater. Subarachnoid hemorrhage involves bleeding into the space between the arachnoid membrane and the pia mater. Intraventricular hemorrhage occurs when there is bleeding in the ventricles.
Traumatic brain injury
Alcohol intoxication
Pediatric concussion
Epidural hematoma
Acquired brain injury
Abnormal posturing  Abnormal posturing  1
Penetrating head injury
Cerebral edema  Cerebral edema  1