Altered Mental Status in the Emergency Department

Austin T. Smith, MD; Jin H. Han, MD, MSc

Disclosures

Semin Neurol. 2019;39(1):5-19. 

In This Article

Imaging

Radiography

Imaging should be guided by history, physical exam, and laboratory analysis. In patients who are unable to provide history, a broader approach may be necessary. A chest X-ray should be considered in undifferentiated patients with AMS to evaluate for an infectious infiltrate. It may also identify a pneumothorax, neoplasm, pulmonary edema, or a pleural effusion. In patients with abdominal pain, careful attention should be paid to the hemidiaphragms evaluating for free air which can suggest a perforated viscous. An abdominal X-ray should also be considered in patients with abdominal pain, though they are much less sensitive than abdominal CT. Plain abdominal films should be evaluated for free air, an obstructive bowel gas pattern, presence of a volvulus, and pneumointestinalis.

Further imaging should be performed based on history, physical exam, and laboratory analysis, though clinicians should have a low threshold for advanced imaging in patients who are unable to provide history.

Neurologic Imaging

Noncontrast Head Computed Tomography. The most common neuroimaging test ordered in the ED is a noncontrast head CT due to its speed and availability. It can rapidly evaluate for hemorrhage, infarction, cerebral edema, and bony injury.[135] If the clinician is concerned about any of those, a head CT is indicated.

Controversy exists regarding the use of noncontrast head CT in patients with undifferentiated AMS. In general, older patients, those with seizures, those with signs/symptoms concerning for stroke or trauma, or those with sudden onset of impaired consciousness should undergo a noncontrast head CT.[37,136,137]

Computed Tomography Angiography. If concern for stroke, carotid artery dissection, or subarachnoid hemorrhage exists, CT angiography of the head and neck should be considered. CT angiography is highly sensitive for detecting stenosis of vessels, aneurysms, and dissections. Additionally, angiography can be used to estimate perfusion of the brain parenchyma and may detect large vessel occlusions, including of the vertebral and basilar arteries.[135] Venous phase angiography can detect dural venous thromboses.

Magnetic Resonance Imaging. Magnetic resonance imaging (MRI) is not available in all centers and is more time consuming, but is superior at detecting ischemic change,[138] visualizing the posterior fossa,[139] and visualizing intracranial masses. An MRI can be considered if no other etiologies for the patient's AMS are found, and is usually done as an inpatient. If an MRI is unavailable or a contraindication to such exists, a contrast-enhanced CT may be indicated.

It is important to note that several diseases are largely clinical diagnoses. For example, initial imaging in locked-in syndrome such as CT can be poorly sensitive,[140] although CTA should be utilized to assess for this when suspicion exists. MRI has a higher sensitivity for brainstem strokes, but can still result in false negatives within the first 24 hours.[141] Similarly, MRI findings for central pontine myelinolysis are often not present for 2 or more weeks after the initial neurologic symptoms.[55] A normal MRI does not indicate absence of disease.

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