32 Mild Traumatic Brain Injury

Gustavo G. Domeniconi ¹, Cesar M. Costilla ², Walter Videtta ²

¹ Sanatorio de la Trinidad, San Isidro, Buenos Aires, Argentina

² Hospital Nacional Prof. A. Posadas, El Palomar, Buenos Aires, Argentina

32.1 Introduction

Traumatic brain injury (TBI) is a major health problem and a leading cause of death or disability in persons aged under 45 years. TBI has social and economic implications with a direct impact on healthcare resource utilization. Despite decisive changes in the diagnosis and management of head-injured patients in the last 25 years, prevention remains the most effective treatment. In reference to a disease, the term “mild” implies “not severe or dangerous; benign” (Webster’s Third New International Dictionary). But within the context of TBI this definition falls short of describing the totality of cases, since the initial condition may worsen in some and will require further diagnostic procedures and therapeutics. Over the medium and long term, the adjective “mild” loses relevance in such cases, given that physical and neurocognitive sequelae after an acute “mild” traumatic event have been variously reported.

We find often ourselves attending head-injured patients, either intoxicated or with a previous pathology, in whom the initial management must be appropriate. Although very few will need therapeutic manoeuvres and still fewer will require surgery, an error in the initial diagnosis can lead to lengthy – and worst of all, unnecessary – hospitalization, as well as dilatory interventions that can be fatal in the prognosis of the disease.

Various different strategies for the management of mild traumatic brain injury (MTBI) are based on the availability and/or accessibility of resources for its diagnosis and treatment. Any approach adopted, however, requires a working algorithm adapted to the complexity and diversity of the local or regional healthcare system. The objective in case management thus consists in identifying those brain injuries involving greater risk and then selecting the appropriate therapy or intervention. the focus of this chapter is the management of mild traumatic brain injury.

32.2 Epidemiology

The incidence of TBI varies between 229 and 2000 cases per 100,000 inhabitants per year in Europe, constituting the primary cause of death in persons aged under 45, with the highest occurrence in the 15-to-25-year age group. About 95% are MTBI, 6.3 to 21% of which can exhibit abnormalities on computed tomography (CT), while injuries possibly needing surgery account for between 0.2 and 3.1% of cases.

In the United States, the incidence of MTBI is 128 cases per 100,000 inhabitants per year, with similar age-group distributions, CT findings, and frequency of surgical interventions as reported for Europe.

In Argentina, Marchio et al. (2006) reported, based on a series of 1540 patients hospitalised in a trauma hospital in Buenos Aires, an incidence of 300 cases of MTBI per 100,000 inhabitants, with a trimodal distribution according to age group from 20 to 24, 40 to 44, and more than 75 years. Of a total of 108 CT scan, only 3 (2.7%) showed hemorrhagic lesions that required surgical drainage.

32.3 Classification

32.3.1 Risk categorization

The risk for neurologic deterioration or the presence of potentially surgical intracranial lesions is predicted on the basis of the Glasgow Coma Scale (GCS) score after the patient has been resuscitated, the presence of neurologic symptoms and risk factors, together with neuroimaging evaluation for deciding a possible hospitalization.

Glasgow Coma Scale

The GCS, devised by Teasdale and Jennet in 1974, is a physiological scale that evaluates the level of consciousness according to three components: motor, ocular, and verbal. While easy and quick to use, interobserver variability and difficulties in recording certain of the scale’s components have documented, e.g., the ocular in facial injury, the motor in injury of the extremities, discrepancies between pre-hospital services and in-hospital emergency departments in recording GCS components.

GCS upon hospital admission after TBI has great prognostic value for outcome. But since the time elapsed between the moment of injury and arrival at hospital can influence categorization, various authors have established that the measurements are valid for 24 hours after the injury. Alterations in the state of consciousness exponentially increase the possibility of encountering lesions on CT. For example, patients with 14 points on the GCS have double the risk of developing intracranial hemorrhage than those with 15 points, while those with 13 points are at four times the risk of having CT abnormalities.

Continuous evaluation of the state of consciousness is of utmost importance for noting clinical improvement in cases with favourable evolution or clinical deterioration which requires more aggressive therapeutic interventions. This approach is necessary above all in a medical centre where the diagnostic resources (e.g., neuroimaging services) or treatment facilities (e.g., emergency neurosurgery and/or a critical care unit) are limited.

Neurologic Alarm Symptoms

Loss of consciousness. In a patient who has suffered a TBI, it be must established whether or not loss of consciousness (LOC) has occurred, and if so, its duration. The occurrence of LOC represents a ten-fold increase in the risk of cranial fracture and brain lesions, although the absolute risk of the latter still remains low.

Establishing the duration of LOC is difficult if no witness of the event is available for questioning. Although different time limits can be cited for determining the relevance of LOC, the clearest interval applies to pediatric patients in whom LOC longer than 15 minutes necessitates CT in order to discard the possibility of an intracranial lesion. In adults, a LOC for 15 to 30 minutes is believed valid by some authors, while others hold that the occurrence of LOC is sufficient for ordering a CT scan.

Posttraumatic amnesia. Posttraumatic amnesia (PTA) is defined as the difficulty in acquiring and/or recalling new |sensory or cognitive information after the moment of injury, i.e., a lack of remembering daily activities. PTA is a functional expression of focal anatomical damage in the frontal and/or temporal lobe secondary to diffuse axonal injury or contusions. PTA may be associated with spatiotemporal disorientation – especially in persons with attention disorder, retrograde amnesia, confabulation, agitation and uninhibited behaviour – depending on the extent of injury. The duration of PTA is one of the most useful prognostic factors for the eventual recovery of cognitive functions in TBI patients. According to the American Academy of Neurology guidelines, a lesion is considered mild when PTA lasts for less than 30 minutes.

Risk Factors

Risk factors include predictive variables independent of the presence of an intracranial hemorrhagic lesion such as age over 60 years, coagulopathy or antithrombotic treatment, very recent use of illicit drugs or alcohol, previous neurochemical treatment, history of epilepsy, a high-energy trauma mechanism, or evidence of injury above the clavicle. Depending on the literature consulted, the principal causes of traumatic injury are vehicle collisions, falls, and physical aggression. Stiell (2001) reported that the most frequent situations involved a pedestrian run over by a car, a driver or a passenger thrown out of a moving vehicle or off a motorcycle, and a fall from a height of 1 meter or 5 steps.

32.3.2 Definitions

The World Health Organization (WHO) classification distinguishes three categories of brain trauma: mild, moderate, and severe, according to the severity of the alteration. In accordance with this scheme, we can clearly determine what we consider to be MTBI.

In 1981 Rimel applied the term light to designate head-injured patients with a score between 13 and 15 on the GCS. In 1996 Culotta published a paper illustrating a pronounced difference between patients with a GCS score of 13 and those with score of 14 or 15 with respect to CT findings, cranial fractures, and the need of |neurosurgery. On the basis of these observations, along with the differences in the extent of brain damage and the risk of death, a distinct differentiation among patients with MTBI must be made.

Certain authors define concussion as being that form of cranial trauma where the victim exhibits LOC or amnesia, but the skull is not fractured and no lesions are radiolographically demonstrable. This definition, however, we regard as rather broad and risks blurring the initial categorization.

In accordance with the Neurotraumatology Committee of the World Federation of Neurosurgical Societies classification, we prefer to define MTBI as the presentation of a patient with a GCS score of 14 to 15. Within this classification and according to the incidence of hemorrhagic lesions, we would define three risk levels.

• Low risk: GCS of 15 with no history of LOC, amnesia, vomiting or diffuse headaches; the risk of presenting with a hematoma requiring neurosurgery is <0.1%.
• Moderate risk: GCS of 15 with one or more of the above-mentioned symptoms, including recovery from concussion; the risk of presenting with a hematoma requiring neurosurgery is between 1 and 3%.
• High risk: GCS of 14 or 15 along with cranial fracture or a neurologic deficit; the risk of a finding that requires neurosurgery is from 6 to 10%.

To finalize this classification we must determine whether or not the patient presentation includes the associated risk factors cited above. These risk factors include elements from the patient’s medical history that increase the incidence of lesions potentially requiring surgery. The inclusion of any one of these risk factors would place the patient in the high-risk group with respect to the occurrence of surgically relevant findings.

32.3.3 Initial Management

All patients with a traumatic injury to the brain or the cranium must be admitted to the emergency service for evaluation. According to the severity of the injury, the symptoms, and the associated lesions, a decision is made following a treatment algorithm.

The first step in the treatment plan is to document the means of trauma, the nature of the presenting symptoms, the risk factors involved, and the extensiveness of the objective data. Finally, the evaluation on the basis of the norms for all trauma patients – in addition to an assessment of the state of consciousness, pupil diameter, and neurologic foci – will assist in making an initial categorization of the patient’s condition, including a definition of that victim’s risk situation.

Table 32.1 illustrates our proposed systematic approach to decision-making in patients with MTBI. This table is based on 1996 Italian guidelines and on the 2001 Neurotraumatology Committee classification.

Table 32.1. Algorithm for the management of mild traumatic brain injury. Risk factors: coagulopathy or antithrombotic or anticoagulant treatment, alcoholism, drug addiction, epilepsy, previous neurosurgical treatments, age >60 or risk factor, advanced age with some degree of disability.

32.3.4 Special Situations

MTBI in Patients Under the Effect of Depressants or Toxicants

Alcohol intoxication is involved in 35-50% of head-injured patients. The effect of alcohol is dose-dependent, with a minimal effect at blood concentrations <80 mg/dl, but causing coma at concentrations >200 mg/dl. The authors of a recent study were unable to find a linear relationship between the level of alcohol intoxication and the initial GCS score (unintoxicated, 10.1±4.8 vs. intoxicated, 10.3±4.7; p=0.5). This would imply| that a lower GCS should not be attributed to alcohol intoxication alone and that the attending physician should not wait until a patient has metabolized the ethanol load before making a diagnostic decision.

MTBI in Patients With Coagulopathy

Since TBI patients are part of the general population, a certain proportion may be under medication with warfarin or acenocumarol or may harbour hepatic lesions or hematologic alterations. Accordingly, this patient subset will constitute a group at higher risk for bleeding and with larger and more rapidly growing hematomas.

Cohen et al. found that in patients with a GCS <8 the International Normalized Ratio (INR) in more than 50% was >5.0 and that the mortality rate was 91.5%. In this group the most frequent brain CT finding was subdural hematoma, and progression was furthermore documented by CT for up to 18 hours after the first scan. The combination of coagulopathy, age >65 years, and TBI should be regarded as a potentially lethal circumstance.

Working with this patient group requires caution in admitting a patient; CT studies in accordance with established criteria; and if surgical treatment has been elected, the provision of vitamin K, freshly obtained frozen plasma, and concentrated coagulation factors in order to ensure proper homeostasis during the intervention.

MTBI in Sports

The incidence of MTBI during a sports event – and especially contact sports such as boxing, rugby or American football – is an interesting subject for discussion. Athletes presenting after a high-contact sports accident should be examined with the same criteria in mind as for MTBI under any other circumstance regardless of the trauma’s having occurred during competitive event. The pressure to “get back into the game” should in no way jeopardize the patient’s health by influencing the decision-making process; and the persistence of symptoms should be carefully evaluated, if necessary, advising the athlete against returning to competition or practice in the days to weeks after the accident. Another point to stress is that although more than twenty sets of guidelines have been issued on this subject in recent decades, the level of available evidence for definitive recommendations for the timing of resumption of physical activity is low.

The U.S. Academy of Neurology defines sports-related concussion as an alteration in mental state following an injury that may or may not be accompanied by a change in the level of consciousness and further emphasizes that the state of confusion that characterizes this circumstance can appear either immediately or some minutes afterwards. The Academy classifies concussion into three grades: grade 1, where symptoms persist for <15 minutes; grade 2, where the symptoms persist for >15 minutes; and grade 3, where LOC occurs. In the initial evaluation (at the place of competition), the state of consciousness (orientation, concentration, and memory); response to external stimuli; and degree of| motor ability, acuteness of sensation, and pupillary reflexes are all assessed.

Individuals presenting with grade 1 are fit to return to competition if no further symptoms persist after 15 minutes. Those with grade 2 are recommended to discontinue the sport for at least 24 hours, provided that the symptoms (headache or others) resolve; but if the latter continue or worsen during the first 7 days, neuroimaging evaluation and neurologist consultation are recommended. In LOC (grade 3) the patient should be taken immediately to the emergency department of the nearest hospital for appropriate evaluation and a brain CT with a bone window to rule out possible spinal cord injury. The patient must refrain from participation in sport for 7 to 14 days, during which he/she will undergo sequential monitoring by a specialized neurologic team.

32.4 Radiological Diagnosis

32.4.1 Skull Radiography

Between 3 and 18% of radiographed MTBI patients exhibit a cranial fracture with an ample margin owing to the heterogeneity of the indication. The risk of harbouring a lesion requiring surgical drainage after skull fracture is 4%; and if accompanied by a deterioration in consciousness, it increases to 25%. Conversely, some 95% of patients with epidural hematoma will also be found to have an associated skull fracture. Skull radiography, however, is not sufficiently sensitive or specific to warrant its recommendation as a routine procedure, especially since the reading of radiograms is difficult and on occasion incorrect.

Nevertheless, the technique can play a role in centres lacking brain CT services. The recommendation is that skull radiography be reserved for the moderate-risk group. The absence of fractures on skull radiography will still require clinical observation of the patient for 24 hours, while the presence of skull fractures will necessitate a CT in order to discard the possibility of lesions requiring surgical drainage.

32.4.2 Brain CT Without Contrast Material

Neither the clinical history nor the neurological findings – and not even the GCS – can predict with certainty the presence of lesions within the cranial cavity. A CT with normal findings can indeed ensure that a discharged patient has no dangerous lesions; but the volume of patients with MTBI makes this generalization difficult to apply to the general population, especially in countries without optimal resources.

Not all tomographic findings require neurosurgery; nevertheless, the physician must not rule out the possibility that skull fracture on an early initial CT will not necessarily eliminate the possibility of the later development of epidural hematoma [Poons, 1992; Riesgo, 1997; Matsuda, 2008].

On the basis of the proposed algorithm, CT would be appropriate in patients with a GCS score of 14, a GCS of 15 with a skull fracture, or a GCS of 15 with a high-risk factor.

Whether or not the availability of a resource or device should influence management guidelines is a subject of debate. The norm should perhaps be to improve the use of the technical resource through the application of algorithms or clinical guidelines before using the technology either in a defensive manner or excessively. More specifically, the question is whether or not to carry out a series of CT studies in such patients. The literature proposes as a good option the assessment of the severity of the initial CT and clinical findings as a criterion for deciding upon the necessity for ordering a second image.

A routine second CT in patients whose primary lesions are considered to have no risk of progression is not recommended. Nevertheless, in patients with associated risk factors such as coagulopathy or coagulant use, clinically observed neurologic deterioration, or hemodynamic alterations, a second image would aid in ruling outing the possibility of late lesions that would compromise the evolution.

32.4.3 New Radiologic Modalities

The evaluation of the brain structures by magnetic resonance imaging (MRI) in the acute stage of MTBI has disadvantages compared to CT. For example, MRI is less useful for identifying bone lesions, needs patient cooperation in order to minimize movement-associated artifacts, requires lengthy time periods for image acquisition (less so with last generation machines), involves the cost of the imaging study, and is hampered by the irregular availability of MRI machines and trained personnel for correct image interpretation. This would relegate the use of MRI to situations where CT services are unavailable and the degree of patient risk be such that the potential presence of surgically operable lesions or the need for hospitalization be discarded. The imaging sequences of spin-spin relaxation time (T2) and fast-fluid inversion-attenuated recovery (FLAIR) have greater sensitivity than CT for the detection of contusions, diffuse axonal lesions or edema and also enable differentiation between acute hemorrhagic and other types of subacute or chronic lesions. The technique termed susceptibility-weighted imaging (SWI) shows higher sensitivity in detecting hemosiderin deposition in the acute stage of TBI; but although this modality is highly promising, the technique is not widely available for use.

In the post-concussion syndrome, MRI during the follow-up period exhibits a good correlation with neuropsychological-testing results – for which reason we consider the technique as a support modality in such patients – and is able to detect minimal frontal and temporal lobe lesions at up to 3 months after injury.

Very recent studies have shown ever-increasing accuracy between image findings and clinical findings, as, for example in MRI and the modality called diffusion-tensor technique or tractography. The latter is an extension of the sequence employed by diffusion and allows reconstruction of the white matter tracts; in so doing, it constitutes an assessment of axonal integrity. In acute TBI, tractography can identify small alterations in the white matter that are consistent with a diffuse axonal lesion of the corpus callosum and the internal capsule not evident on CT. In chronic lesions, generally those associated with high-contact sports such as boxing, the degree of alteration in the diffusion of water within the white matter is related to motor sequelae and long-term neurocognitive alterations.

In a 2008 paper published by a group from Baylor University, abnormalities in the tractography of patients with mood changes or the post-concussion syndrome indicating cytotoxic edema were readily visualized. These findings can now serve to redefine the long-term management of this patient group in order to select different, more appropriate modalities of therapy and neuropsychological support.

Single-photon-emission computed tomography (SPECT) employs a tracer to indicate by indirect means changes in cerebral metabolism by measuring blood flow through the brain. In MTBI or moderate TBI, the authors found alterations in 40-70% of patients followed for up to 3 months after the injury – the affected zones being areas local of hyperperfusion within the frontal and temporal lobes and the gray basal nuclei. The persistence of these findings was correlated with the duration of the post-concussion syndrome. An initial SPECT study is a reliable indicator of good functioning at the end of 3 months. Despite these characteristics, SPECT application remains limited because of its low resolution, high radiation dosage, and difficulties in obtaining quantitative data, in addition to its higher cost.

Perfusion CT enables the quantification of cerebral blood volume, the transit time for the clearance of a contrast marker, and the cerebral blood flow rate, though only within a limited area of the brain. Nevertheless, perfusion CT reveals hemodynamic alterations within the regions near a hemorrhagic lesion which, because undetectable by CT without the use of contrast material, would constitute a potential target for treatment.

32.5 Timing of Hospital Discharge

Patients with a normal neurologic examination and without associated symptoms can be discharged if accompanied by another person and given an instructions sheet informing them about warning symptoms which, if they occur, the patient must return to the hospital immediately. An analysis by Servadei and colleagues indicated that, among 1480 patients discharged in this way to home care, no new lesions were detected. On the basis of this evidence, a hospital discharge policy under such criteria can be considered safe. Table 32.2 illustrates a hospital discharge instructions sheet for the caregiver or the patient. These instructions would be adequate for any healthcare facility or institution utilizing them.

By contrast, if a patient does present symptoms, the following patterns of timing must be borne in mind. Clinical deterioration associated with an epidural hematoma occurs within the first 6 hours, while a delayed hematoma may have its onset up to 24 hours after the injury. Therefore, in the moderate-risk group if only a fracture without hematoma is demonstrated on skull radiography or CT or some risk factor is determined, in-hospital observation should continue for at least 24 hours.

In high-risk patients, i.e., with a GCS score of 14 or 15 and neurologic findings, the timing of discharge should be determined by resolution of the symptoms.

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