When does an adult with headaches need central nervous system imaging?
GUIDELINES AND CHOOSING WISELY
High-quality reviews have found no benefit in performing imaging for primary headache disorders.1–3 This is due, in large part, to the rarity of secondary headache disorders in the primary care setting. In fact, most patients—90% in one study6—presenting to their primary care physicians with headaches meet the diagnostic criteria for migraine.
Significant abnormalities on imaging in patients with migraine headaches are also very rare. In patients with migraine headaches who undergo imaging, the rate of worrisome abnormalities that could lead to a change in management (0.2%) is less than that in the general population at the time of autopsy (0.8%).7
As part of the Choosing Wisely campaign, the American College of Radiology and the American Headache Society recommend against imaging for patients at low risk with migraine headaches. Because of the potential for harm from radiation exposure, the American Headache Society also recommends against computed tomography (CT) for evaluating headaches when magnetic resonance imaging (MRI) is available, except in emergencies.
Lists of tests and treatments that physicians and patients should question and discuss together to make wise decisions are available at www.choosingwisely.org.
HARMS ASSOCIATED WITH CNS IMAGING
Medical tests can be associated with significant harm. Potential harms of head imaging include radiation exposure from CT and false-positive findings. These false-positives, such as the finding of lesions that eventually prove to be benign, may require further testing and cause significant anxiety to the patient.
The effective radiation dose from a CT scan of the head is 2.0 mSv, equivalent to 250 days of background radiation exposure or 100 chest radiographs. Radiation exposure has been linked to increased risk of fatal cancer, and the risks increase with subsequent radiation doses.8
Incidental findings are common on head imaging and often lead to additional medical procedures and workup, without improvements in patient well-being. While the harms of false-positive testing and the finding of benign lesions are difficult to quantify, it is clear that downstream costs can accumulate and that these results cause significant undue worry to the patient.
CLINICAL BOTTOM LINE
Patients with migraine headache who do not have red-flag signs or symptoms are unlikely to benefit from CNS imaging and may experience harm. The rate of abnormalities in this population is not significantly different from that in the general population. A thorough history and physical examination should be done to find the proper diagnosis and to uncover any red-flag symptoms. For migraine headaches that are worsened by identified triggers, those triggers should be addressed before further evaluation is performed. When imaging is needed, physicians should consider minimizing radiation risk by ordering MRI instead of CT.
