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

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.]

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.

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:

• Blunt trauma to the head within 24 hours of presentation to the ED

• Any period of posttraumatic LOC or of posttraumatic amnesia

• A GCS score of 15 on initial evaluation in the ED

• Age older than 15 years

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

• Presence of a bleeding disorder

• Penetrating trauma

• Patients with multisystem trauma

• Focal neurologic findings

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:

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

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

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

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.

• Presence of an acute intracranial abnormality on noncontrast head CT scan was chosen as the outcome measure for all 3 questions.

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.