What is required before ordering a Magnetic Resonance Imaging (MRI) scan for a patient with prolonged migraines?

When to Order MRI for Prolonged Migraines

MRI is not routinely needed for prolonged migraines if the neurological examination is completely normal and there are no red flag features. 1, 2

Key Decision Point: The Neurological Examination

The single most important factor determining whether neuroimaging is warranted is the neurological examination. 3, 1

• Normal neurological exam + typical migraine features = No MRI needed (Grade A recommendation). The prevalence of significant intracranial abnormalities in this scenario is only 0.2%, equivalent to the general asymptomatic population. 1, 2, 4

• Abnormal neurological exam = MRI indicated (Grade B recommendation). Any unexplained abnormal finding on neurological examination significantly increases the likelihood of intracranial pathology such as brain tumors, arteriovenous malformations, and hydrocephalus. 3, 1, 2

Red Flags That Mandate Neuroimaging

Even with a normal neurological exam, MRI should be strongly considered if any of these features are present:

Primary Red Flags (Strong Indications)

• Thunderclap headache or "worst headache of life" suggesting subarachnoid hemorrhage 1
• New-onset headache in patients over age 50, raising suspicion for temporal arteritis or other secondary causes 3, 1, 4
• Progressive headache that worsens over time, potentially indicating a space-occupying lesion 3, 1
• Marked change in previously stable headache pattern 3, 1
• Headache awakening patient from sleep, possibly indicating increased intracranial pressure 3, 1, 4
• Headache aggravated by Valsalva maneuver, suggesting increased intracranial pressure 3, 1, 2
• Rapidly increasing frequency of headaches 3, 1
• Focal neurological symptoms or signs accompanying the headache 3, 1
• Persistent headache following head trauma 3, 1

Secondary Red Flags

• Unexplained fever (possible meningitis) 1
• Neck stiffness (possible meningitis or subarachnoid hemorrhage) 1
• Weight loss (possible malignancy) 1
• Impaired memory, altered consciousness, or personality changes 1
• Uncoordination (possible cerebellar pathology) 3, 1

Special Migraine Subtypes Requiring Imaging

Certain migraine presentations warrant neuroimaging regardless of examination findings (Grade C, consensus-based):

• Hemiplegic migraine (motor manifestations) 4
• Migraine with brainstem aura 4
• Prolonged or persistent aura (unusual duration) 4
• Aura without headache 4
• Side-locked headache (always same side) 4
• Migraine with confusion 4

What Is NOT Required Before Ordering MRI

Contrary to common assumptions, you do not need:

• Electroencephalography (EEG) - Not useful in routine migraine evaluation unless seizure disorder is suspected 3
• Trial of migraine medications first - If red flags are present, imaging should not be delayed 1
• Referral to neurology - Primary care physicians can appropriately order neuroimaging when indicated 3

MRI vs. CT: Which to Order

MRI brain without contrast is the preferred initial study for elective/outpatient migraine evaluation. 2

• MRI advantages: Higher resolution, no radiation exposure, superior for detecting structural lesions and tumors 1, 2
• CT is preferred only when: Acute subarachnoid hemorrhage is suspected (CT has 98% sensitivity for acute blood) or in emergency settings requiring rapid evaluation 2
• Add contrast when: Focal neurological deficits are present, as contrast is critical for detecting enhancing lesions, meningeal infiltration, and isodense tumors 5

There is insufficient evidence to definitively state MRI is more sensitive than CT for clinically significant pathology, though MRI may detect more clinically insignificant abnormalities. 1, 2

Common Pitfalls to Avoid

• Over-ordering imaging in patients with typical migraine features and completely normal neurological examinations - this leads to false positive findings and unnecessary anxiety 1, 6
• Under-ordering imaging when red flags are present, missing serious pathology 1
• Misdiagnosing "sinus headache" - this is frequently migraine and does not warrant neuroimaging 2
• Ordering MRI without contrast when focal neurological findings are present - this may miss enhancing lesions 5
• Assuming prolonged symptoms alone mandate imaging - the neurological examination and presence of red flags are more important than duration alone 1, 4

Clinical Context: What "Prolonged" Means

The term "prolonged migraines" requires clarification. If this means:

• Prolonged individual attacks (lasting days) with normal exam between attacks = Consider imaging if attacks are atypical or increasing in frequency 4
• Chronic daily headache with typical migraine features and normal exam = No routine imaging needed 1, 2
• Prolonged aura (lasting >1 hour) = Imaging warranted to exclude stroke or structural lesion 4

The American Headache Society found that clinically significant neuroimaging abnormalities requiring intervention were relatively rare in migraine patients without red flags, occurring at rates no higher than the general population. 4