Test your skills: Which imaging studies would you order for these neurologic complaints?

When patients present with neurologic complaints in outpatient primary care practice, 2 key questions often arise: Should brain imaging be ordered, and if so, which study? Careful history-taking and physical exam findings can suggest differential diagnoses and help determine whether imaging studies could identify potential underlying causes. Further considerations in making a decision are the type of information each modality offers, the possible need for contrast media, benefits vs radiation exposure risks, potential contraindications, and cost and local availability. In this article, we present 3 common outpatient scenarios, and in each case we describe the evidence to support clinical decision-making about imaging.

The American College of Radiology (ACR) Appropriateness Criteria Web site (http://www.acr.org/Quality-Safety/Appropriateness-Criteria) provides radiation exposure information, numerical ratings of imaging studies for individual clinical scenarios, evidence tables, and reference tables for each of its recommendations.¹ ACR’s recommendations were developed by expert panels of diagnostic radiologists, interventional radiologists, and radiation oncologists, and designed to help physicians order the most appropriate imaging studies based on patients’ clinical conditions.² We used these criteria to develop an evaluation strategy for each of our clinical scenarios.

CASE 1 › Carrie D is a 45-year-old woman with a history of migraine without aura generally controlled with Excedrin (acetaminophen, aspirin, and caffeine). She arrives at your office with a 2-day history of severe headache over the top of her head and associated tingling sensation over the left side of her face, but with no vision changes, weakness, or slurred speech. She denies any prior history of numbness or tinging with past headaches. She is a business executive and reports that in the last few weeks, her company has been involved in a high-profile merger. On physical exam, her vital signs are within normal limits. She does not appear acutely ill, but on exam she reports diminished sensation to light touch over the left side of her face, left arm, and left leg compared with the right side.

›› What imaging options might you consider?

A prospective review of physicians in an ambulatory family practice setting found that neurologic imaging was typically ordered for patients with headache who were suspected of having a brain tumor or subarachnoid hemorrhage.³ For our patient, who has a history of migraines without aura and whose current severe headache is accompanied by an abnormal sensation on one side of the face, the following questions are relevant: Is this presentation part of her primary headache syndrome or could there be a different cause? If there is a different cause, is it likely to be detected with brain imaging such as computed tomography (CT) or magnetic resonance imaging (MRI)?

Patients with isolated headache and an absence of neurologic symptoms or abnormalities on neurologic exam are unlikely to have a clinically significant intracranial abnormality.^4-10 Imaging of the brain is typically not indicated for these patients.² However, given that this patient does have a positive focal neurologic finding, a CT or MRI is indicated, as findings are more likely to influence management decisions.

The decision to order CT or MRI should be based on how acutely ill the patient is. CT without contrast is an excellent tool to rule out suspected emergent intracranial abnormalities such as an intracranial hemorrhage, hydrocephalus, or a mass.¹¹ In patients presenting with symptoms suggesting acute illness such as carotid or vertebral artery dissection, the most appropriate test would be CT angiography of the head and neck.²

However, the list of less dire causes of headache is vast. Included in this list would be trauma, other vascular disorders such as arteriovenous malformation or temporal arteritis, infection, abnormal intracranial pressure (mass, pseudotumor cerebri, intracranial hypotension), and disorders of the head/face/spine (eg, temporomandibular joint disorder).¹²

In the non-acute setting where a patient has stable vital signs and is not in acute distress, an MRI with contrast would be the most appropriate test to identify such causes. Avoid contrast only if there is a firm contraindication, such as pregnancy, severely impaired renal function, or known allergy to gadolinium. If history and physical exam findings suggest possible stroke, arrange for MRI and MR angiography with contrast, even if the result of a head CT scan is negative. The ALGORITHM¹³ offers guidance for choosing imaging studies for headache based on history, physical exam, and laboratory findings.