Clinical policy: Neuroimaging and decisionmaking in adult mild traumatic brain injury in the acute setting☆☆☆

Article Outline

• Abstract
• Introduction
  • Definitions
• Methodology
• Critical questions
  • I. Is there a role for plain film radiographs in the assessment of acute MTBI in the ED?
  • Recommendation
    • Recommendation B
  • II. Which patients with acute MTBI should have a noncontrast head CT scan in the ED?
  • Recommendation
    • Recommendation A
  • III. Can a patient with MTBI be safely discharged from the ED if a noncontrast head CT scan shows no evidence of acute injury?
  • Recommendation
    • Recommendation C
• Future directions
• Acknowledgements
• Evidentiary Table
• References
• Copyright

Abstract 

[Jagoda AS, Cantrill SV, Wears RL, Valadka A, Gallagher EJ, Gottesfeld SH, Pietrzak MP, Bolden J, Bruns JJ Jr, Zimmerman R. Clinical policy: neuroimaging and decisionmaking in adult mild traumatic brain injury in the acute setting. Ann Emerg Med. August 2002;40:231-249.]

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Introduction 

There are approximately 1 million emergency department visits annually for traumatic brain injury (TBI) in the United States.¹ The vast majority of these visits are for “mild” injuries that are primarily the result of motor vehicle crashes and falls.¹ The highest incidence of mild TBI (MTBI) is seen in men between the ages of 15 and 24 years and in men and women 75 years of age and older. Three percent to 13% of those patients evaluated in the ED with a Glasgow Coma Scale (GCS) score of 15 will have an acute lesion on head computed tomography (CT).², ³, ⁴, ⁵, ⁶, ⁷ Less than 1% of these patients will have a lesion requiring a neurosurgical intervention.⁵, ⁶, ⁸ Depending on how disability is defined, up to 15% of patients with MTBI will have compromised function 1 year after their injury.⁹, ¹⁰ These statistics establish the clinical importance of MTBI to the acute care provider. However, inconsistencies in definitions, inclusion and exclusion criteria, and outcome measures have fueled an ongoing controversy on how best to evaluate and manage the patient with an MTBI.

The question of how best to define an MTBI is of great importance and has been a source of confusion.¹¹ A small subset of these patients will harbor a life-threatening injury, whereas many will suffer with neurocognitive sequelae for days to months after the injury. In fact, it is difficult to convince a patient disabled from the postconcussive syndrome that their injury was “mild.” Unfortunately, there exists no consensus regarding classification. Terms used have included: “mild,” “minor,” “minimal,” “grade I,” “class I,” and “low risk.”³ Even the terms “head” and “brain” have been used interchangeably. Head injury and TBI are 2 distinct entities that are often, but not necessarily, related. A “head injury” is best defined as an injury that is clinically evident on physical examination and is recognized by the presence of ecchymoses, lacerations, deformities, or cerebrospinal fluid (CSF) leakage. A “traumatic brain injury” refers specifically to an injury to the brain itself and is not always clinically evident; if unrecognized, it may result in an adverse outcome.

The American Congress of Rehabilitation Medicine delineated inclusion criteria for a diagnosis of MTBI of which at least 1 of the following must be met: (1) any period of loss of consciousness (LOC) of less than 30 minutes and GCS score of 13 to 15 after this period of LOC; (2) any loss of memory of the event immediately before or after the accident, with posttraumatic amnesia of less than 24 hours; (3) any alteration in mental state at the time of the accident (eg, feeling dazed, disoriented, or confused). This definition is extremely broad and contributes to the difficulty of interpreting the MTBI literature.

Historically, the system most often used for grading severity of brain injury is the GCS score. The phrase “MTBI” is usually applied to patients with a score of 13 or greater. Some authors have suggested that patients with a GCS score of 13 be excluded from the “mild” category and placed into the “moderate” risk group because of their high incidence of lesions requiring neurosurgical intervention.¹² Lesions requiring neurosurgical intervention may not be the only injuries that require identification. In a prospective study, patients with a GCS score of 13 or greater were grouped according to the presence or absence of head abnormalities.¹³ Despite having the same GCS score, those patients with intraparenchymal lesions performed on neuropsychological testing similar to those patients categorized as having moderate TBI by GCS criteria.

Created by Teasdale and Jennett¹⁴ in 1974, the GCS was developed as a standardized clinical scale to facilitate reliable interobserver neurologic assessments of comatose patients with head injury. The original studies applying the GCS score as a tool for assessing outcome required that coma be present for at least 6 hours.¹⁴, ¹⁵, ¹⁶ The scale was not designed to diagnose patients with mild or even moderate TBI nor was it intended to supplant a neurologic examination. Instead, the GCS was designed to provide an easy-to-use assessment tool for serial evaluations by relatively inexperienced care providers and to facilitate communication between care providers on rotating shifts.¹⁴ This need was especially great because CT scanning was not yet available. Since its introduction, however, the GCS has become quite useful for diagnosing severe and moderate TBI and for prioritizing interventions in these patients. Nevertheless, for MTBI, a single GCS score is of limited prognostic value and is insufficient to determine the degree of parenchymal injury after trauma.¹⁴ On the other hand, serial GCS scores are quite valuable in patients with MTBI. A low GCS score that remains low or a high GCS that decreases predicts a poorer outcome than a high GCS score that remains high or a low GCS score that progressively improves.³, ¹⁶, ¹⁷ To illustrate this, in their original paper, Teasdale and Jennett¹⁴ presented a patient who was admitted to the neurosurgical intensive care unit (NICU) with a GCS score of 14. The NICU chart reflected hourly scores of 14 for 3 hours, followed by a decline to 13 and then to 4, at which point the patient was taken to the operating room for evacuation of a subdural hematoma.

From an out-of-hospital and ED perspective, the key to using the GCS in patients with MTBI is in serial determinations. When head CT is not available, serial GCS scores clearly are the best insurance against missing a patient who needs a neurosurgical procedure. The GCS score continues to play this role and to provide important prognostic information. However, the previous discussion should make it clear that the use of a single GCS determination cannot be used solely in diagnosing MTBI. In one of the original multicenter studies validating the scale in the pre-CT era, approximately 13% of patients who became comatose had an initial GCS score of 15.¹⁶

The challenge for the acute care provider lies in identifying the apparently well, neurologically intact patient with a potentially lethal intracranial injury that requires immediate neurosurgical intervention. These patients are the focus of this clinical policy. A second challenge is to identify those patients at risk for postconcussive syndrome to ensure proper discharge planning. These patients are the focus of a separate clinical policy under development by the International Brain Injury Association.

Definitions 

The vast majority of patients classified as having MTBI have a GCS score of 15 when they are in the ED.¹, ¹⁸, ¹⁹, ²⁰ Consequently, the Task Force members of this clinical policy chose to focus specifically on this group. Large studies demonstrate that the absence of LOC or amnesia in patients with blunt head injury are negative predictors of the need for acute intervention after brain injury. After a review of these studies, the Task Force agreed to use LOC or amnesia as a criterion for this clinical policy.¹⁹, ²¹ Focal neurologic deficits have been associated with an increased incidence of intracranial lesions and thus were used as an inclusion/exclusion criterion by the Task Force.¹⁷, ²² Because MTBI management in the pediatric population has been recently presented in a clinical policy developed by the American Academy of Pediatrics and the American Academy of Family Physicians, this clinical policy specifically addresses MTBI in patients older than 15 years of age.²³

Inclusion criteria for application of this clinical policy's recommendations are:

Exclusion criteria for application of this clinical policy's recommendations include:

Evidence-based practice guidelines require that a focused question be asked and that a clear outcome measure be identified. There are many questions to be asked about MTBI management. The task force identified the 3 questions that it thought most important to clinical practice:

The task force considered several outcome measures in developing this clinical policy, including presence of an acute abnormality on noncontrast CT scan, clinical deterioration, need for neurosurgical intervention, and development of postconcussive syndrome.

The limitations of this outcome measure were discussed. There is a paucity of literature that discusses the natural course of acute traumatic intracranial lesions in patients who initially appear intact. The Canadian CT Head Rule suggests that there are inconsequential traumatic lesions, such as smear subdurals less than 4 mm thick, for which detection is not necessary²⁰; however, this is based on survey data and not on prospective studies. Therefore, the Task Force agreed that, although an acute lesion may not predict clinical outcome or development of the postconcussive syndrome, it is the best currently available marker of injury in the acute setting, pending further research.

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Methodology 

A MEDLINE search of English-language publications was conducted for the period from January 1980 through June 2001 using the medical subject heading (MeSH) search terms mild or minor traumatic brain injury, mild or minor head trauma, acute diagnosis or management, skull radiography, head CT, neuroimaging, and neuroradiography. These terms were searched in all fields of publication (eg, title, abstract, key word).

Age was not used in the search because many articles included both adults and children (age 14 and under) in the study populations. Articles that included children were noted during the critical review by the committee.

The search identified 1,438 articles. Nonsystematic review articles, surveys, editorials, and expert opinion–based articles were excluded. A total of 58 articles were pooled and critically reviewed by the committee. All articles were reviewed by at least 4 committee members, and a composite evidentiary table was constructed.

The group reviewed the methodology of each paper and graded the design using the classification schema used by the American College of Emergency Physicians. This scheme uses the design and purpose of the study to assign initial design strength as shown in Table 1.

Table 1. Literature classification schema.

Studies were downgraded 1 or more levels, depending on limitations in the control of bias, assessment of outcome, external validity, and other factors. Essentially, no study's strength could be higher than its design class, but it could be lower based on the number, severity, and relevance of its limitations. Table 2 illustrates how this combination of design and execution ratings was used to develop a final strength of evidence assessment for an individual study.

Table 2. Approach to downgrading strength of evidence.

An Evidentiary Table was constructed to summarize study design, outcome measure, findings, and limitations. The final “Class of Evidence” assigned to each study was based on the limitations of the study's methodology and the relevance of end points. Those studies that had sufficient bias to affect validity or end points different from the single target end point chosen by the Task Force were either downgraded to a lower category or discarded if rated as X. Some studies were downgraded to X but left in the evidentiary table because of historical importance or because they contained important background information.

Evidence was combined to support recommendations as follows:

A recommendation —Sufficient Class I evidence in substantial agreement.

B recommendation —Class II evidence in substantial agreement, or Class I studies not in good agreement on size or direction of effect.

C recommendation —Class III evidence, or higher evidence classes not in good agreement.

In general, the strength of a recommendation was not allowed to exceed the strength of the individual pieces of evidence on which it depended. One theoretically possible exception, which is not without some controversy, would be to allow a Class A recommendation to be based on a number of small but well-executed randomized controlled trials (or equivalent Design/Class 1 studies) that had been downrated primarily because of small sample size. In such a case, some might argue for a Class A recommendation, as if there had been a good meta-analysis of those studies.

It should be noted that this evaluation scheme does not consider many of the factors that are important in implementing recommendations. Factors such as cost, practicability, and distributive justice are variables that must be independently weighed by individual health care systems.

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Critical questions 

I. Is there a role for plain film radiographs in the assessment of acute MTBI in the ED? 

Skull plain film radiographs continue to be used as the first step in assessing MTBI in many health care facilities, particularly those where head CT scanning is not readily available.¹⁹, ²⁰ Arienta et al¹⁹ reported on 7,991 patients; all had plain film radiographs, and 9% demonstrated a fracture. They reported that no patient with a negative radiographic finding developed complications; however, only 592 of the patients had a CT scan, and follow-up was not clearly defined.

Cooper and Ho²⁴ retrospectively studied 207 patients with intracranial lesions on CT scanning who also had plain films, 63% of which were normal. Although this study included only admitted patients, plain films appeared to be neither sensitive nor specific for brain injury. In 1980, Masters²⁵ performed a retrospective study on 1,845 patients; 26 (79%) of 33 patients with significant intracranial sequelae had normal skull films. This study was followed 8 years later by a prospective study involving 7,035 patients. Although methodologically flawed, the authors reported that, in the group most similar to the focus of this clinical policy (moderate risk), 3 (6.4%) of 47 patients with a skull fracture had an intracranial lesion, 44 (93.6%) of 47 patients with a fracture had no intracranial lesion, and 7 (70%) of 10 patients with an intracranial lesion had no fracture (95% confidence interval [CI] 35% to 93%). It was concluded that skull film radiographs are rarely helpful in managing MTBI and should not be used to select patients for additional testing.

A meta-analysis published in 2000 examined the association between skull fracture and brain injury.⁴ The authors recognized the difficulty of comparing studies with varying design, and after retrieving 200 studies for review, they identified 20 that fulfilled their inclusion criteria. Their analysis found that the sensitivity of skull fracture in detecting patients with an intracranial lesion ranged from 0.13 to 0.75, with a specificity of 0.91 to 0.995. The authors discussed their concern about both selection bias and verification bias contributing to the high specificity reported by the studies (ie, patients were more likely to receive a CT scan if their GCS score was less than 15 or if they had a positive plain film). Using the combined results for sensitivity, specificity, and prevalence, the authors reported the positive predictive value of a skull fracture for the diagnosis of an intracranial lesion as 0.41 and the negative predictive value as 0.94. These findings suggest that the presence of a skull fracture increases the probability of an intracranial lesion fivefold. However, the meta-analysis concluded that, although a fracture demonstrated on plain film increased the likelihood of an intracranial lesion, its low sensitivity precluded its use to rule out the diagnosis of an intracranial hemorrhage and thus is of limited clinical value in risk stratification for brain injury.

Recommendation 

Skull film radiographs are not recommended in the evaluation of MTBI. Although the presence of a skull fracture increases the likelihood of an intracranial lesion, its sensitivity is not sufficient to be a useful screening test. Indeed, negative findings on skull films may mislead the clinician.

II. Which patients with acute MTBI should have a noncontrast head CT scan in the ED? 

Many of the studies on MTBI have focused on identifying lesions in need of neurosurgical intervention.²⁰, ²⁶ The literature does not clearly state which patients with intracranial lesions deteriorate, nor is it clear about the predictive value of intracranial lesions in predicting the development of postconcussive syndrome. Therefore, the Task Force chose “presence of an acute intracranial lesion” on noncontrast head CT scan as its outcome measure on patients with MTBI.

Livingston et al²⁷ evaluated 91 patients who had a GCS score of 15 and reported that 9 (10%) of those had abnormal CT scan findings (95% CI 4.6% to 18%). They were unable to identify any combination of findings that predicted all patients with pathology. Jeret et al⁸ conducted a prospective study on 712 consecutive patients with head trauma who had a GCS score of 15 and a period of LOC or amnesia. There were 67 patients (9.4%; 95% CI 7.3% to 11.8 %) with acute traumatic brain lesions; only 2 patients (0.3%) required urgent neurosurgical intervention. They were unable to create a statistical model that could be used to classify 95% of patients into a CT-normal or CT-abnormal group.

Miller et al²⁸ prospectively studied 2,143 patients in an attempt to identify risk factors for a neurosurgical lesion. There were 6.4% (95% CI 5.4% to 7.6%) of the patients with positive CT scan findings, and 0.2% needed neurosurgery. Nausea, vomiting, severe headache, or depressed skull fracture had a positive predictive value of 100% for those patients requiring neurosurgical intervention. No patient without a risk factor deteriorated even if CT scan findings were positive.

Borczuk²⁹ retrospectively reviewed 1,211 patients with a GCS score of 15 and reported that 75 (5.9%) had an abnormality on CT scan, and 1 patient (0.08%) required neurosurgery. Cranial soft tissue injury, focal neurologic deficits, or signs of trauma above the clavicle were found to be predictive of an intracranial lesion.

Dunham et al¹⁸ retrospectively analyzed a prospectively collected trauma center database and reported on 1,481 patients with a GCS score of 15; 45 (3.0%) patients had positive CT scan findings, and 2 (0.13%) required neurosurgical intervention. Positive CT scan findings were correlated with evidence of trauma above the clavicle and age greater than 60 years.

Lee et al³⁰ followed up 1,812 patients discharged from the ED after an MTBI and reported that 28 (1.5%) deteriorated from their injury in the succeeding 2 months. Unfortunately, the majority of the patients in this study did not have an initial CT scan. However, in congruence with the previously cited studies, Lee et al reported that predictors of deterioration included headache, focal neurologic deficit, vomiting, and age greater than 60 years.

Vilke et al³¹ specifically studied the value of a detailed neurologic examination, including a careful mental status assessment, in predicting the presence of an acute intracranial lesion on CT scan. The study's well-defined methodology was undermined by its small sample size of only 58 patients. Three (5%) patients were found to have positive CT scan findings, 2 of whom had a normal neurologic examination of whom 1 required a craniotomy. The authors concluded that a decision for CT cannot be based solely on the neurologic examination.

Working with the predictors identified in the aforementioned studies, 2 recent papers have attempted to define criteria for CT scanning in patients with MTBI.⁵, ²⁰ Stiell et al²⁰ performed a derivation study by prospectively evaluating 3,121 patients, 2,489 of whom had a GCS score of 15, using a structured assessment tool. Only 2,078 (67%) of the 3,121 patients had a CT scan; telephone follow-up and a neuropsychiatric test were used as equivalent to negative CT scan findings. Patients had a follow-up interview at 14 days to assess outcome. The primary outcome measure was the need for neurosurgical intervention, and the secondary outcome was a “clinically important brain injury” defined by a survey consensus. “Clinically unimportant lesions” included solitary contusions less than 5 mm in diameter, smear subdurals less than 4 mm thick, isolated pneumocephalus, and closed depressed skull fractures not through the inner table. Because the study sites were the primary neurosurgical centers for the respective cities, the authors concluded that no patient with “clinically unimportant” CT scan findings deteriorated after discharge. The authors concluded that CT in MTBI is indicated only in those patients with 1 of 5 high-risk factors: failure to reach a GCS score of 15 within 2 hours of injury, suspected open skull fracture, sign of basal skull fracture, vomiting more than once, or age greater than 64 years.

In a Class I study, Haydel et al⁵ prospectively assessed 1,429 patients with MTBI. The study consisted of an initial phase with 520 patients in whom predictors for intracranial lesions were identified, followed by a validation phase that included 909 patients. The authors reported that 93 (6.5%) of their patients had an intracranial lesion and that 6 (0.4%) required neurosurgical intervention. Seven predictors of abnormal CT scan findings were identified: headache (any head pain), vomiting, age greater than 60 years, intoxication, deficit in short-term memory (persistent anterograde amnesia), physical evidence of trauma above the clavicle, and seizure. Absence of all 7 findings had a negative predictive value of 100% (95% CI 99% to 100%).

Recommendation 

A head CT scan is not indicated in those patients with MTBI who do not have headache, vomiting, age greater than 60 years, drug or alcohol intoxication, deficits in short-term memory, physical evidence of trauma above the clavicle, or seizure.

III. Can a patient with MTBI be safely discharged from the ED if a noncontrast head CT scan shows no evidence of acute injury? 

During the past decade there has been a decline in the hospitalization rate of patients with TBI.³² This decrease has been attributed to increased reliance on CT scanning to identify patients at risk for life-threatening injuries. The literature does not reflect an increase in morbidity or mortality from this practice; however, up to this point in time, no guidelines exist to help the clinician decide who can be safely sent home. Two issues relevant to this question emerge from the literature. The first issue is that patients who are admitted to the hospital for observation often do not receive the observation for which they were admitted. In 1 study, only 50% of admitted patients had documented serial neurologic examinations ranging in frequency from 1 to 8 hours.²⁷ In another study, 30% of patients admitted for TBI did not have documented serial neurologic examinations.¹⁷ The second issue is that, although discharge instructions are routinely given to patients with MTBI, they are rarely remembered.³³ Levitt et al³⁴ found that 23% of patients discharged from the ED with MTBI could not remember any of their discharge instructions. These 2 issues combined suggest that expectant observation might not be the best strategy for managing patients with TBI.

There is literature that clearly identifies a subset of patients with MTBI who deteriorate. The focus of research must be to identify this group. In addition to case reports and small case series,³⁵, ³⁶, ³⁷ several larger cohort studies exist. Lee et al³⁰ prospectively followed up 1,812 patients who were discharged from the hospital with a GCS score of 15 at 3, 7, 30, and 60 days. Twenty-eight (1.5%) of these patients deteriorated, 16 (57%) of the 28 within the first 24 hours; 23 (82%) of the 28 who deteriorated required a neurosurgical intervention. Unfortunately, most of the patients did not have initial CT scans. In a Class III retrospective study that is difficult to interpret, Shackford et al¹⁷ reported on 933 patients with normal neurologic examinations and normal head CT findings who were admitted to the hospital for observation. They reported that 11 (1.2%) patients in this group required intubation (ie, deteriorated), although none required neurosurgical intervention. Unfortunately, the authors do not provide the timing of the deterioration or other specific information related to the cases.

Nagy et al² prospectively studied 1,170 trauma center patients, all of whom had a CT scan and were admitted for 24 hours of observation. Similar to the studies already described, 39 (3.3%) of the patients had positive CT scan findings, and 4 (0.3 %) required neurosurgery. Despite the study design's spectrum bias favoring sicker patients, no patient deteriorated, thus supporting the authors' recommendation to discharge patients who have negative CT scan findings home from the ED.

In the study by Stein and Ross³ already cited, none of 1,117 patients admitted with a diagnosis of MTBI deteriorated, although the length of observation was not defined. Livingston et al²⁷ followed up 79 patients with a GCS score of 15 and negative CT scan findings who were discharged from the ED. Although only 57 patients were reached in follow-up at 48 hours, none had deteriorated.

Dunham et al¹⁸ analyzed data from 2,587 trauma center patients; 45 (3.0%) of the 1,481 patients with a GCS score of 15 had positive CT scan findings. No patient with negative CT scan findings deteriorated, and all patients who did deteriorate did so within 4 hours of arrival at the trauma center.

Jeret et al⁸ prospectively studied 712 patients, 67 (9.4%) of whom had positive CT scan findings. One patient who initially had normal examination results deteriorated within “several hours” of arriving in the ED, at which point a CT scan disclosed a left temporal contusion; by 6 hours after arrival in the ED, he was lethargic and had a craniotomy.

A recent prospective study by Livingston et al³⁸ attempted to answer the question of which patients with MTBI could be safely discharged from the ED. Unfortunately, the study's design flaws prevented the formulation of any conclusions regarding those patients addressed in this policy.

Recommendation 

Patients with MTBI who present 6 hours after sustaining the injury, have a normal clinical examination, and who have a head CT scan that does not demonstrate acute injury can be safely discharged from the ED. Patients can be discharged after a shorter period of observation if they are under the care of a responsible third party.

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Future directions 

The small number of well-designed studies limits the strength of recommendations that can be made regarding the management of patients with MTBI. Inconsistent definitions and outcome measures contribute to the ongoing controversy of how best to manage these patients. Future research must begin with a collaborative effort in the neuroscience community on how to define MTBI and how to measure its related outcomes.

The true incidence of MTBI is unknown. Epidemiologic studies have focused on those patients managed in trauma centers and admitted; they therefore suffer from selection bias. The vast majority of MTBI epidemiologic studies focus on preexisting data sets that were not originally intended for research purposes, such as International Classification of Diseases, 9th Revision (ICD-9 ) codes. Many patients sustain MTBI but do not seek medical care and are thus not included in estimates, thereby underestimating the true incidence of MTBI. More thorough and accurate epidemiologic evaluation of MTBI is needed to define the enormity of the problem and to direct both public education and preventative strategies.

An improved elucidation of the pathophysiologic characteristics of MTBI is critical for the research and development of therapeutic measures. Pharmacologic therapy used to prevent or reduce neuronal injury after MTBI remains a formidable yet crucial goal. More conclusive evidence is needed to help identify in a timely manner the small but important number of patients who develop intracranial hematomas despite initially normal CT scan findings and normal neurologic examination results. Only a multicenter, prospective study with long-term patient follow-up, implementing the specific guidelines as outlined in this document, will identify the subset of patients at risk and validate the recommendations presented in this document.

Patients with a GCS score of 15 and normal head CT scan findings are at risk for the development of cognitive, psychosocial, and neurobehavioral abnormalities related to MTBI.⁹, ¹⁰, ³⁹ This postconcussive syndrome may adversely affect the patient's personal, financial, and social life. Thus, future research must address mechanisms for identifying patients at risk and interventions that may minimize or prevent disability.

It is possible that the resolution of head CT scanning limits the diagnosis of clinically significant neuronal lesions that may be responsible for the postconcussive syndrome.⁴⁰, ⁴¹ The role of magnetic resonance imaging and other neuroimaging modalities in the acute evaluation of MTBI is yet to be determined.⁴², ⁴³ The implication on the management and follow-up of the nonoperative lesions found on CT scanning or other neuroimaging studies is also an area in need of elucidation.

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Acknowledgements 

The developers thank Rhonda Whitson, RHIA, for her assistance in preparing the document for publication.

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Evidentiary Table 

Table. Evidentiary Table.

PTA, Posttraumatic amnesia; NA, not applicable; PCS, postconcussive syndrome; ETOH, ethanol; SAH, subarachnoid hemorrhage.

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