Traumatic brain injury classification

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]

Overview

Traumatic brain injury may be classified into several subtypes including focal or diffuse, open or close, and mild, moderate or severe.

Classification

Focal vs. Diffuse

• The damage from TBI can be focal, confined to one area of the brain, or diffuse, involving more than one area.
• Diffuse trauma to the brain is frequently associated with concussion (a shaking of the brain in response to sudden motion of the head), diffuse axonal injury, or coma.
• Localized injuries may be associated with neurobehavioral manifestations, hemiparesis or other focal neurologic deficits.
• Types of focal brain injury include bruising of brain tissue called a contusion and intracranial hemorrhage or hematoma, heavy bleeding in the skull. Hemorrhage, due to rupture of a blood vessel in the head, can be extra-axial, meaning it occurs within the skull but outside of the brain, or intra-axial, occurring within the brain. Extra-axial hemorrhages can be further divided into subdural hematoma, epidural hematoma, and subarachnoid hemorrhage. An epidural hematoma involves bleeding into the area between the skull and the dura. With a subdural hematoma, bleeding is confined to the area between the dura and the arachnoid membrane. A subarachnoid hemorrhage involves bleeding into the space between the surface of the brain and the arachnoid membrane that lies just above the surface of the brain, usually resulting from a tear in a blood vessel on the surface of the brain. Bleeding within the brain itself is called an intracerebral hematoma. Intra-axial bleeds are further divided into intraparenchymal hemorrhage which occurs within the brain tissue itself and intraventricular hemorrhage which occurs into the ventricular system.

Open vs. Closed

TBI can result from a closed or penetrating head injury. A closed injury occurs when the skull is not breached, while a penetrating injury occurs when an object pierces the skull and enters brain tissue.

As the first line of defense, the skull is particularly vulnerable to injury. Skull fractures occur when a bone in the skull cracks or breaks. A depressed skull fracture occurs when pieces of the broken skull press into the tissue of the brain. A penetrating skull fracture occurs when something pierces the skull, such as a bullet, leaving a distinct and localized traumatic injury to brain tissue. Skull fractures can cause cerebral contusion.

Severity

Levels of TBI severity

	GCS	PTA	LOC
Mild	13 to 15	<1 hour	<30 minutes
Moderate	9 to 12	30 minutes to 24 hours	1 to 24 hours
Severe	<8	>1 day	>24 hours

Head injuries can be subdivided into mild, moderate, and severe TBI to help predict outcome. One common classification system determines severity based on the Glasgow Coma Scale (GCS) and duration of post-traumatic amnesia (PTA) and loss of consciousness (LOC) according to the table at right. Other classification systems use GCS alone or PTA or LOC alone or together. Prognosis worsens with the severity of injury, but mild TBI is more poorly defined and prognosis is not as clear with it.

Mild TBI is also commonly called concussion. Though prognosis for concussion is usually very good, a portion of people may suffer lasting problems associated with the injury, such as post-concussion syndrome. A patient who receives a second concussion before symptoms from another one have healed is at risk for developing a very rare but deadly condition called second-impact syndrome, in which the brain swells catastrophically after even a mild blow.