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Mild traumatic brain injury mTBI

Mild traumatic brain injury (mTBI), often referred to as concussion.

Glasgow Coma Scale between 13-15


Alteration of consciousness without structural damage as a result of non penetrating traumatic brain injury (TBI).

The alteration should be “brief”, but there is no consensus on the length of time considered to be brief.

There are no gross or microscopic parenchymal abnormalities.

CT is normal or significant only for mild swelling which may represent hyperemia.

MRI will demonstrate abnormalities in up to 25% of cases where CT is normal.


Mild traumatic brain injury (TBI) or concussion is estimated to occur in 3.8 million each year in the US.

The peak ages for these injuries are in adolescence and young adulthood, and sport-related concussions are particularly common among young persons 1).

It accounts for 80% of all craniocerebral injuries 2).

The incidence worldwide is approximately 600/100,000 pop. per year, with the incidence requiring hospitalization in the range of 100 to 300/100,000 pop. per year.

It occurs in men twice as often as in the female population, with the age group at highest risk being those aged 15-24 years.

The main causes of MBI are traffic accidents and falls 3).


Neurometabolic cascade


The initial ionic flux and glutamate release result in significant energy demands and a period of metabolic crisis for the injured brain. These physiological perturbations can now be linked to clinical characteristics of concussion, including migrainous symptoms, vulnerability to repeat injury, and cognitive impairment. Furthermore, advanced neuroimaging now allows a research window to monitor postconcussion pathophysiology in humans noninvasively. There is also increasing concern about the risk for chronic or even progressive neurobehavioral impairment after concussion/mild traumatic brain injury. Critical studies are underway to better link the acute pathobiology of concussion with potential mechanisms of chronic cell death, dysfunction, and neurodegeneration 4).

Glutamate release and ionic disequilibrium

As a result of mechanical trauma, neuronal cell membranes and axons undergo disruptive stretching, leading to temporary ionic disequilibrium 5).

As a result, levels of extracellular potassium increase drastically, and indiscriminate glutamate release occurs 6).

Glutamate release activates N-methyl-D-aspartate receptors, which leads to accumulation of intracellular calcium 7) 8) 9) , causing mitochondrial respiration dysfunction, protease activation, and often initiating apoptosis 10) 11). Elevated glutamate levels were also found to be significantly correlated with derangements in lactate, potassium, brain tissue pH, and brain tissue CO2 levels in human studies 12). Additionally, sodium channel upregulation, fueled by ATPase proteins depending on glucose for energy, is observed following axonal stretch injuries 13).

Energy crisis and mitochondrial dysfunction

In combination, the cellular response to the above-mentioned ionic shifts and the downstream effects of the neurotransmitter release lead to an acute energy crisis. This occurs when, to restore ionic equilibrium, adenosine-triphosphate (ATP) -dependent sodium-potassium ion transporter pump activity increases, which augments local cerebral glucose demand 14).

Further metabolic demand is incurred by ATP-dependent sodium channel upregulation. This occurs in the face of mitochondrial dysfunction, leading cells to primarily utilize glycolytic pathways instead of aerobic metabolism for energy, and causing extracellular lactate accumulation as a byproduct 15). This acidosis, caused by hyperglycolysis, has been shown to worsen membrane permeability, ionic disequilibrium, and cerebral edema 16).

Some evidence shows that the lactate produced by this process may eventually be utilized as a source of energy by the neurons once mitochondrial oxidative respiration normalizes; in fact, one study showed that in moderate to severe TBI the incidence of abnormally high levels of lactate uptake were seen in 28% of subjects 17). The same study showed that patients exhibiting a higher rate of brain lactate uptake relative to arterial lactate levels tended to have more favorable outcomes compared to others with lower relative lactate uptake.

Alterations in cerebral blood flow

Some studies have shown that cerebral blood flow decreases immediately following the insult, and the amount of time it remains lowered seems to depend on the severity of the injury 18) 19).

Other studies, however, show no significant differences in CBF following mild TBI in subjects over 30 years of age 20). In pediatric studies, CBF has been seen to increase during the first day following mild TBI, followed by decreased CBF for many days after 21) 22). Data comparing cerebral blood flow in pediatric TBI patients has shown impaired autoregulation in 42% of moderate and severe and 17% of mild injuries 23).

Histopathologic changes

The underlying histopathologic changes that occur are relatively unknown. In order to improve understanding of acute injury mechanisms, appropriately designed pre-clinical models must be utilized.

The clinical relevance of compression wave injury models revolves around the ability to produce consistent histopathologic deficits. Mild traumatic brain injuries activate similar neuroinflammatory cascades, cell death markers and increases in amyloid precursor protein in both humans and rodents. Humans, however, infrequently succumb to mild traumatic brain injuries and, therefore, the intensity and magnitude of impacts must be inferred. Understanding compression wave properties and mechanical loading could help link the histopathologic deficits seen in rodents to what might be happening in human brains following concussions 24).

Clinical Features

Posttraumatic headache is one of the most common symptoms following mild traumatic brain injury in children.

From the available evidence, slowed reaction time, impaired verbal learning and memory, impaired balance, and disorientation or confusion were found to be significantly prevalent in early samples of exposed individuals. There is insufficient evidence to assess the relationships among these measures.At a minimum, future studies should include comparison groups; take measures at fixed and relevant time points; report distinct signs, symptoms, and deficits in terms of frequencies and correlations; and follow standards for minimizing bias and confound 25).

Symptoms are typically short-lived, and may correlate to physiologic changes in the acute period after injury. There are many available tools that can be utilized on the sideline as well as in the clinical setting for assessment and diagnosis of concussion. It is important to use validated tests in conjunction with a thorough history and physical examination. Neurocognitive testing may be helpful in the subacute period.

Possible findings

vacant stare or befuddled expression

delayed verbal & motor responses: slow to answer questions or follow instructions

easy distractibility, difficult focusing attention, inability to perform normal activities

disorientation: walking in the wrong direction, unaware of date, time or place.

speech alterations: slurred or incoherent, disjoined or incomprehensible statements

incoordination: stumbling, inability to tandam walk

exaggerated emotionality: inappropriate crying, distraught appearance

memory deficits: repeatedly asking same question that has been answered cannot name 3 out of 3 objects after 5 minutes

any period of LOC: paralytic coma, unresponsiveness to stimuli.


May be evident immediately following the blow, or may take several minutes to develop.

Loss of consciousness (LOC)

Loss of consciousness is not a requirement.

Patients themselves may be unaware whether or not they experienced LOC.

When there is LOC, the fact that it is often virtually instantaneous (there may be a latency of a few seconds), and the usually rapid return of function with no evidence of microscopic changes suggests that the LOC is due to a transient disturbance in neuronal function. Levels of glutamate (an excitatory neurotransmitter) rise after concussion and the brain enters a hyperglycolytic and hypermetabolic state which may persist up to 7-10 days after the injury.

During this period the brain may be more susceptible to a second impact syndrome.


Concussion grading

The Glasgow coma scale is too insensitive for use.

Many concussion grading systems have been proposed, the two most widely used are those of Cantu, and that of the American Academy of Neurology (AAN)

LOC by itself may not be a significant discriminant (e.g. confusion > 30 minutes may be worse than LOC for a few seconds). Most systems consider a concussion to be mild if there is a change in sen- sorium without loss of consciousness, however they differ mostly in the definotion of “change in sensorium”.

There is no scientific basis to recommend one system over another.

Recommendation: select one system and use it consistently. Do not place undue emphasis on grading.


Previous studies have indicated that there is no consensus about management of mild traumatic brain injury (mTBI) at the emergency department (ED) and during hospital admission 26).

Management should begin with removal from risk if a concussion is suspected, and once diagnosis is made, education and reassurance should be provided. Once symptoms have resolved, a graded return-to-play protocol can be implemented with close supervision and observation for return of symptoms. Management should be tailored to the individual, and if symptoms are prolonged, further diagnostic evaluation may be necessary 27).

Implementation of a selective neurosurgical consultation policy reduced neurosurgical consultations without any impact on patient outcomes, suggesting that trauma surgeons can effectively manage these patients 28) 29).

Patients with the constellation of traumatic subarachnoid hemorrhage and/or intraparenchymal hemorrhage IPH and mTBI do not require neurosurgical consultation, and these findings should not be used as the sole criteria to justify transfer to tertiary centers 30).

Since 2000, center's standard practice has been to obtain a repeat head computed tomography (CT) at least 6 hours after initial imaging. Patients are eligible for discharge if clinical and CT findings are stable. Whether this practice is safe is unknown.

Discharge after a repeat head CT and brief period of observation in the ED allowed early discharge of a cohort of mild TBI patients with traumatic ICH without delayed adverse outcomes. Whether this justifies the cost and radiation exposure involved with this pattern of practice requires further study 31).

Management in Europe

Foks et al. aimed to study variability between management policies for TBI patients at the ED and hospital ward across Europe. Centers participating in the Collaborative European NeuroTrauma Effectiveness Research in Traumatic Brain Injury (CENTER-TBI) study received questionnaires about different phases of TBI care. These questionnaires included 71 questions about TBI management at the ED and at the hospital ward. We found differences in how centers defined mTBI. For example, 40 centers (59%) defined mTBI as a Glasgow Coma Scale (GCS) score between 13-15 and 26 (38%) as a GCS score between 14-15. At the ED various guidelines for the use of head CT in mTBI patients were used; 32 centers (49%) used national guidelines, 10 centers (15%) local guidelines and 14 centers (21%) used no guidelines at all. Also differences in indication for admission between centers were found. After ED discharge, 7 centers (10%) scheduled a routine follow-up appointment, while 38 (54%) did so only after ward admission. In conclusion, large between-center variation exists in policies for diagnostics, admission and discharge decisions in patients with mTBI at the ED and in hospital. Guidelines are not always operational in centers, and reported policies systematically diverge from what is recommended in those guidelines. The results of this study may be useful in the understanding of mTBI care in Europe and show the need for further studies on the effectiveness of different policies on outcome 32).


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mild_traumatic_brain_injury.txt · Last modified: 2017/07/20 13:48 by administrador