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Mild Traumatic Brain Injury; CT vs. MRI for Evaluating Hyperacute Stroke

Lovato, Luis M. MD

doi: 10.1097/01.EEM.0000324843.19922.d8
Living with the LLSA: Articles from the 2006 LLSA Reading List

Author Credentials and Financial Disclosure: Dr. Lovato is an Assistant Clinical Professor of Medicine at the David Geffen School of Medicine at the University of California at Los Angeles, the Director of Critical Care for the Department of Emergency Medicine at Olive View-UCLA Medical Center, and the LLSA Workshop Co-Director for the Olive View-UCLA National Conference on Advances in Emergency Medicine.

All faculty and staff in a position to control the content of this CME activity have disclosed that they have no financial relationships with, or financial interests in, any commercial companies pertaining to this educational activity.

Learning Objectives: After reading this article, the physician should be able to:

  1. Summarize the American College of Emergency Physicians' definition of mild traumatic brain injury and identify clinical criteria used to rule out intracranial lesions in these patients.
  2. Identify the advantages of CT over MRI for the evaluation of hyperacute stroke.
  3. Describe the limitations of CT for evaluating hyperacute stroke and chronic intracerebral hemorrhage.

Release Date: June 2008

Clinical Policy: Neuro-imaging and Decision-making in Adult Mild Traumatic Brain Injury in the Acute Setting

Jagoda AS, et al Ann Emerg Med 2002;40(2):231

Emergency physicians evaluate patients with head trauma on just about every shift. Although patients with moderate and severe head trauma are often very ill, present dramatically, and provide us with more vivid memories, decision-making is often straightforward in these patients, especially when determining the need for imaging and disposition.

Mild head trauma, however, is another beast. If you remember one of these patients, it is often because they looked so well before deteriorating. Evaluating these patients presents us with the challenge of appropriately limiting the cost and risk of diagnostic imaging without missing a mild brain injury patient destined to decompensate.

This clinical policy written by a special task force and adopted by the American College of Emergency Physicians offers recommendations on three questions regarding managing patients with acute mild traumatic brain injury (MTBI). For this policy, MTBI was defined as patients over 15 with blunt head trauma presenting to the emergency department within 24 hours, with posttraumatic loss of consciousness (LOC) or amnesia, and an initial Glasgow Coma Scale of 15. Patients with bleeding disorders, penetrating trauma, multisystem trauma, or focal neurologic findings were excluded.

It is critical to note that this policy does not apply to the large group of patients with mild head trauma without loss of consciousness or amnesia and clinical presentations of no concern in which we can continue to make safe clinical decisions without the need for diagnostic imaging.

For this project, a list of 1438 potential articles was compiled via a Medline search, and after the inclusion criteria were applied, 58 articles were pooled for extensive review by the task force. Reviewers assigned the articles one of four grades (I, II, III, or X), and used them to answer three specific clinical questions with a particular strength of recommendation (A, B, or C).

Is there a role for plain film radiographs in assessing acute MTBI in the ED? Skull film radiographs are not recommended in the evaluation of MTBI. (Level B recommendation.) In one Class III retrospective study (Am J Roentgenol 1980;135[3]:539), 27 percent of patients had fractures on plain films but negative CT findings, while 32 percent had negative plain films with positive CT findings. Plain films can indeed be misleading.

Which patients with acute MTBI should have a noncontrast head CT scan in the ED? A head CT scan is not indicated in those patients with MTBI who do not have headache, vomiting, drug or alcohol intoxication, deficits in short-term memory, physical evidence of trauma above the clavicle, or seizure or are over 60. (Level A recommendation.) In one Class I study of 1429 patients presenting with a GCS of 15 and LOC or amnesia, the absence of all seven of these criteria had a 100% negative predictive value for intracranial lesions. (N Engl J Med 2000;343[2]:100.)

Can a patient with MTBI be safely discharged from the ED if a noncontrast head CT scan shows no evidence of acute injury? Patients with MTBI who present six hours after sustaining the injury, have a normal clinical examination, and who have had a head CT scan that does not demonstrate acute injury can be safely discharged from the emergency department. (Level C recommendation.) In one Class III study of 2587 patients, no patients with negative CT findings deteriorated, and all those with positive CT findings deteriorated within four hours of arrival. (J Trauma 1996;41[4]:679.)

As always, clinical policies should not replace clinical judgment and experience, especially if the recommendations come from relatively weak levels of evidence. Follow these recommendations with discretion, and document your medical reasoning in those instances when the most sensible decision is to disregard them.

Comparison of MRI and CT for Detection of Acute Intracerebral Hemorrhage

Kidwell CS, et al JAMA 2004;292(15):1823

Acute nonhemorrhagic stroke has become a hotbed of activity for medical malpractice lawyers. With vocal disagreement in some academic circles regarding the National Institute of Neurological Disorders and Stroke (NINDS) guidelines and the extremely small clinical window available for medical decision-making, thrombolytics for hyperacute stroke has become the emergency physician's quintessential trap between a rock and a hard place. We must now consider which imaging study to obtain, potentially adding complexity to initial stroke management.

The quick answer is that noncontrast CT is still the initial brain imaging study of choice for the emergency patient presenting with acute symptoms of stroke. CT is still regarded as the gold standard for ruling out hyperacute intracerebral bleeding, an important criterium for determining eligibility for acute thrombolytic therapy.

Given its limited sensitivity in identifying early cerebral ischemia, CT has significant disadvantages compared with stroke protocol MRI studies. Most centers rely on a combination of imaging techniques to determine the full extent of neurological injury in patients with acute stroke symptoms, a strategy that is not only time-consuming but expensive.

In this prospective, multicenter study, MRI with gradient recalled echo (GRE) pulse sequences was compared with gold standard CT to establish equal sensitivity in identifying acute hemorrhage in stroke patients. Patients were included if they presented within six hours of acute stroke symptom onset. Significant exclusion criteria were coma, a contraindication to MRI, inability to obtain MRI within six hours of symptom onset, initiation of thrombolytic therapy, or cardiorespiratory instability.

The initial protocol called for MRI followed by CT, both done between 90 minutes of presentation, with no more than 30 minutes between each study. An independent panel of radiologists and neurologists reviewed all of the studies, with several methods of blinding and randomization used to reduce possible bias. The study was stopped early, after 200 patients, when an unplanned interim analysis suggested that MRI was catching acute bleeding not visible on CT, suggesting a flaw in the initial study design that presumed CT was superior.

When the results were finally analyzed, the panel found acute hemorrhage in 25 patients on both CT and MRI. In four additional patients, hemorrhage was read as present on the MRI but not on the corresponding CT. These were all interpreted as cases of hemorrhagic transformation of an ischemic infarction. In four other patients, the reverse was true with acute hemorrhage read on CT but not on the corresponding MRI. In three of these instances, the MRI was incorrectly interpreted as showing chronic rather than acute bleeding, and in one case, a subarachnoid hemorrhage accompanying an acute stroke was missed.

Although not part of the objectives of this study, chronic hemorrhage was identified in 52 patients on MRI and in none of the patients on CT, validating prior evidence that MRI is clearly superior for evaluating chronic intracerebral hemorrhage.

So how does this information translate to the bedside management of hyperacute stroke? With the universal availability of CT, the relatively quick speed at which it can be obtained and the fact that CT was the diagnostic study of choice in the NINDS trial, CT will remain the initial imaging study of choice for the hyperacute stroke patient for a long time to come. Stroke protocol MRI may be the initial study of choice in specialized stroke centers with dedicated resources and expert personnel, but not for the vast majority of community hospitals or even most academic centers.

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About the LLSA

As part of its continuous certification program, the American Board of Emergency Medicine has developed the Lifelong Learning and Self-Assessment (LLSA) program to promote continuous education of diplomates. Each year, beginning in 2004, 16 to 20 articles are chosen based on the Emergency Medicine Model. A list of these articles can be found on the ABEM web site,

ABEM is not authorized to confer CME credit for the successful completion of the LLSA test, but it has no objection to physicians participating in such activities. EMN's CME activity, Living with the LLSA, is not affiliated with ABEM's LLSA program, and reading this article and completing the quiz does not count toward ABEM certification. Rather, participants may earn 1 CME credit from the Lippincott Continuing Medical Education Institute, Inc., for each completed EMN quiz.

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Seven Predictors of Abnormal CT Scan in Patients with Mild Traumatic Brain Injury

  • ▪ Headache (any pain)
  • ▪ Vomiting
  • ▪ Over age 60
  • ▪ Intoxication
  • ▪ Deficit in short-term memory (persistent anterograde amnesia)
  • ▪ Trauma above the clavicle
  • ▪ Seizure

Note: Absence of all seven findings in patients with MTBI had a negative predictive value of 100%.

© 2008 Lippincott Williams & Wilkins, Inc.