Updated February 05, 2015.

Written or reviewed by a board-certified physician. See About.com's Medical Review Board.

When a patient has a dangerous headache, doctors will order imaging of the brain. This imaging will reveal whether there is a serious condition going on around the brain, like a bleed. But, what type of imaging is warranted? A CT scan or an MRI? Or a magnetic resonance angiography (MRA) of the brain, which is essentially an MRI of the brain's blood vessels.

In 2000, the American College of Radiology made specific recommendations to help determine the optimal type of brain imaging needed for an acute headache.

Headache in immunocompromised patients: MRI of the head with and without contrast media.

• Immunocompromised means that a patient has an impaired immune system, weakening their ability to defend themselves against infection. Their impaired immune system could be secondary to a number of factors like disease (e.g. diabetes, HIV) or drugs (e.g. steroids, chemotherapy).

Headache in patients older than 60 with suspected temporal arteritis—also known as giant cell arteritis: MRI of the head with and without contrast media.

• Giant cell arteritis is a type of vasculitis (inflammation of blood vessels) that typically causes a headache in the temple area and may be accompanied by a number of other symptoms including fatigue, jaw pain, and body aches. The most worrisome feature of GCA is vision loss.

Headache with suspected meningitis: CT or MRI of the head without contrast media.

• Meningitis is an infection of the membranes that surround the brain and spinal cord. It is most commonly caused by a bacteria or virus, and rarely a fungus. After brain imaging is completed, the diagnosis is made by a lumbar puncture.

Severe headache in pregnancy: CT or MRI of the head without contrast media.

• While most headaches are benign in pregnancy, a severe headache is concerning. Read more about signs to look out for in Headaches During Pregnancy.

Severe unilateral headache caused by possible dissection of the carotid or arterial arteries: MRI of the head with and without contrast media, MRA of the head and neck, or CTA of the head and neck.

• Dissection refers to tearing of the inside wall of the blood vessels that supply the brain. Dissection of the carotid and vertebral arteries usually causes pain of the head and/or neck and is a life-threatening condition—as it can lead to stroke.

Sudden onset or severe headache: CT of the head without contrast media; CTA of the head with contrast media, MRA of the head with or without contrast media, or MRI of the head without contrast media.

• A headache that is severe and/or begins suddenly is particularly worrisome for a bleed in the brain (i.e. subarachnoid hemorrhage) and warrants emergent brain imaging.

Take Home Message

If you see your doctor or go to the emergency room with a potentially dangerous headache, imaging of the brain will be ordered. While you do not necessarily need to know what to order—that's why we have doctors—it's always a good idea to know the reasoning behind what is being ordered.

<sub>Sources

Gonzalez-Gay MA, Barros S, Lopez-Diaz MJ, Garcia-Porrua C, Sanchez-Andrade A, Llorca J. Giant cell arteritis: disease patterns of clinical presentation in a series of 240 patients. Medicine (Baltimore). 2005 Sep;84(5):269-76.

Hainer BL & Matheson EM. Approach to Acute Headache in Adults. Am Fam Physician. 2013 May 15;87(10):682-87.

Hunder GG, Bloch DA, Michael BA, Stevens MB, Arend WP, Calabrese LH et al. The American College of Rheumatology 1990 criteria for the classification of giant cell arteritis. Arthritis Rheum 1990;33(8):1122.

http://www.cdc.gov/meningococcal/. Accessed Jan 28th 2015.

Silbert PL, Mokri B, Schievink WI. Headache and neck pain in spontaneous internal carotid and vertebral artery dissections. Neurology. 1995 Aug;45(8):1517-22.
Strain JD, Strife JL, Kushner DC, et al. Headache. American College of Radiology. ACR appropriateness criteria. Radiology. 2000;215(suppl):855–860.</sub>
 

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