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Headache is a very common condition that affects up to 60% of the world’s population.

In general, headache can be classified into two main categories: primary and secondary headaches. Headaches have many possible causes, and proper management requires accurate diagnosis.

A primary headache is related to increased sensitivities, but not structural alterations of brain tissues. Common primary headaches are migraine with and without aura, tension-type headache, and trigeminal autonomic cephalalgias (headaches, such as cluster headache, which also involve facial pain and autonomic symptoms such as tear production and nasal congestion).

Secondary headaches have various underlying causes, including structural vascular disorders, tumor, trauma, seizure, substance use, infection, metabolic problems or autoimmune diseases.

Primary headaches are typically managed with some combination of preventive and symptom-relieving medications. Secondary headaches may be treated by addressing the underlying cause.

When to see a doctor

Seeing a medical provider is strongly recommended if headaches become more frequent, last longer, change patterns, or increase in intensity.

For a new headache visit, healthcare providers typically perform physical and neurological examinations to determine the cause of the headache.

A primary care provider (PCP) would be the first contact for mild headache symptoms that have been worsening. Your PCP would likely refer you to a neurologist if your headaches did not respond to medications, or if he or she suspected a secondary headache.

Sudden onset of severe headache should prompt a visit to the emergency department.

What tests help with diagnosis?

Many providers would consider ordering brain imaging studies, such as CT scans and MRIs, to help them diagnose worsening headache.

CT scan, an X-ray-based imaging study, is an excellent initial imaging test for detecting bleeding, skull fractures, and space-occupying lesions such as tumors. However, since CT scans expose patients to a low dose of radiation, their use should be limited because the effects of radiation exposures add up over time and could reach a harmful level.

In contrast, MRI uses a magnetic field to generate imaging without radiation. It produces more detailed images than CT scans, especially of the brain, the meninges (the membranes that enclose the brain and spinal cord), nerves and blood vessels.

In certain conditions that involve bleeding, blood clots or abnormal vascular structures, tests known as arteriograms and venograms may be necessary for detailed structural analysis of blood vessels.

Red flags to look for

It is understandable that people with increasingly severe headaches would want to have brain imaging to determine the underlying causes. But most headaches that are categorized as primary (based on a person’s headache history and physical and neurological evaluation) do not require brain imaging studies. Brain scans are much more effective for identifying underlying causes of secondary headaches.

Several evidence-based guidelines, including guidelines published in the Journal of the American College of Radiology in November 2019, can help providers decide which imaging studies are appropriate and when.

These guidelines describe certain red flags that warrant the use of brain imaging during the initial headache evaluation. They are summarized into five main categories:

• Primary headache with abnormal findings on clinical examinations. Abnormal findings may include abnormal vital signs (blood pressure, pulse, body temperature, oxygen saturation), changes in mental alertness or memory loss, and neurological deficits such as visual, coordination, sensory or motor impairments
• Sudden severe (thunderclap) headache, often described as “the worst headache of a person’s life” that doesn’t respond to drug treatment
• New headache with swelling of the optic disc, an area on the retina where it meets the optic nerve
• New or progressive headaches 1) in people with a history of recent head injury, cancer, immunosuppression, pregnancy or age older than 50, and 2) in patients with headaches that are worsened after exertion and when they change position, and whose headaches are accompanied by a whooshing or pulsating sound
• New suspected trigeminal autonomic headaches

If a headache falls into these categories, having brain imaging studies would help early diagnosis and enable timely intervention of a secondary headache, in order to reduce the possibility of severe complications or death.

Hsinlin Thomas Cheng, M.D., Ph.D., is a contributor to Harvard Health Publications.

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