Traumatic Brain Injury – An Overview
Traumatic brain injury occurs when an external mechanical force causes brain dysfunction temporarily or permanently that may or may not be detectable with current diagnostic technologies.
Traumatic brain injury usually occurs as a result of a sudden and violent blow or jolt to the head or body. An object penetrating the skull, such as a bullet or shattered piece of skull, also can cause traumatic brain injury.
Mild traumatic brain injury (MTBI) may result in temporary dysfunction of brain cells (neurons). More serious traumatic brain injury could result in bruising, torn tissues, bleeding and other physical damage to the brain that can result in worse outcomes, long-term complications or death.
Severity of traumatic brain injury (TBI) is typically defined by the initial Glasgow Coma Scale (GCS) score. The GCS score is a widely used assessment of neurological function that has been validated in many studies since it was first introduced in 19761 .
Severity of TBI as determined by initial GCS score is as follows:
- Mild (GCS score 13 to 15)
- Moderate (GCS score 9 to 12)
- Severe (GCS score <9)
TBI is usually classified based on severity, anatomical features of the injury, and the mechanism (the causative forces). Mechanismrelated classification divides TBI into closed and penetrating head injury. A closed (also called non-penetrating, or blunt) injury occurs when the brain 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 brain.
Brain injuries can be classified into mild, moderate, and severe categories on the basis of Glasgow coma scale. The Glasgow Coma Scale (GCS), the most commonly used system for classifying TBI severity, grades a person’s level of consciousness on a scale of 3–15 based on and eye-opening reactions to stimuli, verbal and motor. It is generally agreed that a TBI 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 TBI, commonly called concussion; these use duration of LOC, PTA, and other concussion symptoms.
Mild traumatic brain injury (TBI) occurs with head injury due to contact and/or acceleration/deceleration forces. It is typically defined as mild by a Glasgow Coma Scale (GCS) score of 13 to 15, measured at approximately 30 minutes after the injury (table 1). Some recommend classifying patients with a GCS score of 13 as moderate head injury (GCS score of 9 to 12) because they seem more similar with regard to prognosis and incidence of intracranial abnormalities.
The term concussion is often used in the medical literature as a synonym for mild TBI, but it probably describes a subset of milder brain injury. The Quality Standards Subcommittee of the American Academy of Neurology defines concussion as a trauma-induced alteration in mental status that may or may not involve loss of consciousness.
- Concussion may be caused by a direct blow to the head, face, neck, or elsewhere on the body with an ‘impulsive’ force transmitted to the head.
- Concussion typically results in the rapid onset of short-lived impairment of neurologic function that resolves spontaneously. However, in some cases, symptoms and signs may evolve over a number of minutes to hours.
- Concussion may result in neuropathological changes, but the acute clinical symptoms largely reflect a functional disturbance rather than structural injury, and as such, no abnormality is seen on standard structural neuroimaging studies.
- Concussion results in a graded set of clinical syndromes that may or may not involve loss of consciousness. Resolution of the clinical and cognitive symptoms typically follows a sequential course. However, it is important to note that in some cases, symptoms may be prolonged.
Acute symptoms and signs – The hallmark symptoms of concussion are confusion and amnesia, sometimes with, but often without, preceding loss of consciousness. These symptoms may be apparent immediately after the head injury or may appear several minutes later. It is important to emphasize that the alteration in mental status characteristic of concussion can occur without loss of consciousness. In fact, the majority of concussions in sports occur without loss of consciousness and are often unrecognized.
The amnesia almost always involves loss of memory for the traumatic event but frequently includes loss of recall for events immediately before (retrograde amnesia) and after (anterograde amnesia) the head trauma. An athlete with amnesia may be unable to recall details about recent plays in the game or details of well known current events in the news. Amnesia also may be evidenced by the patient repeatedly asking a question that has already been answered. Details regarding the presence and the duration of loss of consciousness, confusion, and amnesia are considered potentially important to understanding the severity of the injury and the risk of subsequent complications.
Other signs and symptoms of a concussion may immediately follow the head trauma or evolve gradually over several minutes to hours. Early symptoms of concussion (within minutes to hours) include headache, dizziness (vertigo or imbalance), lack of awareness of surroundings, and nausea and vomiting. Over the next hours and days, patients may also complain of mood and cognitive disturbances, sensitivity to light and noise, and sleep disturbances. Many concussions occur without observed findings. Signs observed in someone with a concussion may include the following:
- Vacant stare (befuddled facial expression)
- Delayed verbal expression (slower to answer questions or follow instructions)
- Inability to focus attention (easily distracted and unable to follow through with normal activities)
- Disorientation (walking in the wrong direction, unaware of time, date, place)
- Slurred or incoherent speech (making disjointed or incomprehensible statements)
- Gross observable incoordination (stumbling, inability to walk tandem/straight line)
- Emotionality out of proportion to circumstances (appearing distraught, crying for no apparent reason)
- Memory deficits (exhibited by patient repeatedly asking the same question that has already been answered or inability to memorize and return three of three words and three of three objects for five minutes)
- Any period of loss of consciousness (coma, unresponsiveness to stimuli)
Seizures — Early post-traumatic seizures are those that occur within the first week after head injury. These seizures are considered to be acute symptomatic events and not epilepsy. Post-traumatic seizures occur in fewer than 5 percent of mild or moderate traumatic brain injury (TBI), and they are more common with more severe TBI, especially if complicated by intracranial hematoma . About half occur within the first 24 hours of the injury; one quarter occurs within the first hour. The earlier a seizure begins, the more likely it will be generalized in onset; after the first hour more than half are either simple partial (pure motor) seizures or focal with secondary generalization. Complex partial seizures are rare in this setting. Early seizures increase the risk of post-traumatic epilepsy by fourfold, to more than 25 percent. While anticonvulsants may be used in the treatment of early seizures, they are not helpful in the prevention of post-traumatic epilepsy
Complicated concussion — With uncomplicated, mild TBI, limited structural axonal injury may be present but not evident on diagnostic computed tomographic (CT) scanning or magnetic resonance imaging (MRI). However, mild TBI can be complicated by coexistent cortical contusions and the development of intracranial hemorrhage.
Neurologic deterioration after mild TBI is highly suggestive of an evolving intracranial hematoma, which may be intracerebral, or subor epidural andusually occurs secondary to a tear in an intracranial artery or vein.
Traumatic brain injury can have wide-ranging physical and psychological effects. Some signs or symptoms may appear immediately after the traumatic event, while others may appear days or weeks later.