Neuroimaging
Neuroimaging is the technique of imaging, or taking pictures of, the structure and function of the brain and spinal column. Neuroimaging tools include CT scans, which use a series of X-rays compiled by computers to create pictures of cross-sections of the body; and MRI, which uses powerful magnets and radiofrequency waves to create detailed images of almost any region of the body.
Most patients with suspected migraine will not require neuroimaging studies such as CT scan or MRI, but in some cases, these tests may be appropriate. The American Academy of Neurology (AAN) and the U.S. Headache Consortium have developed physician guidelines for ordering neurological imaging studies in headache patients. These guidelines suggest that neuroimaging should be ordered in the following circumstances:
When a patient has an abnormal finding on a neurological examination (described above).
When a patient's chronic headache does not neatly fit the diagnostic criteria for a primary headache disorder such as migraine, cluster headache, or tension-type headache.
When the patient is at a higher risk of a pathological, or disease-based, neurological cause of secondary headache due to family or medical history.
When clinical “red flags” are present, including a headache that awakens the patient from sleep, abrupt onset of severe headache, abnormal vital signs (e.g., fever, high blood pressure), headache following head trauma, new onset headache in patients under five or over fifty, or headaches triggered by exertion.
In the end, a physician will use his clinical judgment in ordering any neuroimaging studies. Some doctors may order neuroimaging if a patient is extremely fearful or anxious that there may be a pathological, or disease-based cause of their head pain (e.g., brain tumor or cancer) and this fear and anxiety is causing significant distress or disability.
Are PET scans useful for migraine diagnosis?
Positron emission tomography (PET) is a nuclear medicine scan that can be used to evaluate metabolic functioning of the brain. It is not useful for migraine diagnosis, but PET scans are used frequently in migraine research and have shown that migraine is associated with specific changes in certain brain regions, especially the brainstem.
Magnetic Resonance Imaging
An MRI can't diagnose migraine, but it can rule out brain tumor, infection, stroke, and other causes of secondary headache. An MRI may be very helpful if you have any risk factors or red flags of a nonmigrainous condition.
MRI is also extremely useful in clinical research on headache and migraine. Studies have shown that migraineurs are more likely to show white matter abnormalities on MRI. Researchers have also used functional magnetic resonance imaging techniques to establish that the aura of migraine is caused by a phenomenon called cortical spreading depression (a unique depression of the metabolic function that seems to migrate over the cortex of the brain).
Alert
If you are allergic to iodine or shellfish; have kidney disease, asthma, heart disease, or multiple myeloma; or take the type 2 diabetes drug metformin (or a combination drug containing metformin), inform your doctor before undergoing any neuroimaging test involving contrast medium.
Computerized Axial Tomography Scans
A CT scan may be ordered if your provider believes that your headaches may be associated with sinus problems, or if bleeding, swelling, or infection of the brain is suspected.
CT scans are also frequently used in patients who show up in urgent care or emergency rooms with sudden severe “thunderclap” headaches because they are more sensitive than MRI in detecting brain hemorrhage. Contrast medium, an iodine-based dye that is injected into the bloodstream to enhance CT images, may be used in a scan.
