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A cranial computed tomography (CT) scan is an imaging method that uses x-rays to create cross-sectional pictures of the head, including the skull, brain, eye sockets, and sinuses.

See: Computed tomography

You will be asked to lie on a narrow table that slides into the center of the CT scanner. Depending on the study being done, you may need to lie on your stomach, back, or side.

A cranial CT scan produces images from your upper neck to the top of your head.

You must be still during the exam, because movement causes blurred images. If you can't stay still, pillows or cushions may be placed around your head to hold it in place.

Once inside the scanner, the machine's x-ray beam rotates around you. (Modern "spiral" scanners can perform the exam in one continuous motion.) You may be told to hold your breath for short periods of time.

Small detectors inside the scanner measure the amount of x-rays that make it through the part of the body being studied. A computer takes this information and uses it to create several individual images, called slices. These images can be stored, viewed on a monitor, or printed on film. Three-dimensional models of your head can be created by stacking the individual slices together.

Special dye, called contrast, may be used to help highlight blood vessels and look for a mass (tumor). If this is needed, the health care provider will inject the dye into a vein.

Generally, complete scans take only a few minutes. The newest multidetector scanners can image your entire body, head to toe, in less than 30 seconds.

Usually, no preparation is needed. However, if contrast is needed, you may be asked not to eat or drink anything for 4-6 hours before the test.

Tell your health care provider if you are allergic to IV contrast.

Since x-rays have difficulty passing through metal, you will be asked to remove jewelry and wear a hospital gown during the study.

The x-rays produced by the CT scan are painless. Some people may have discomfort from lying on the hard table.

Contrast give through a vein may cause a slight burning sensation, a metallic taste in the mouth, and a warm flushing of the body. These sensations are normal and usually go away within a few seconds.

A cranial CT scan is recommended to help diagnose or monitor the following conditions:

• Abnormal development of the head or neck
• Bleeding in the brain
• Brain infection
• Brain tumor

A cranial CT may also be done to:

• Determine the cause of a headache
• Determine the cause of vision problems, muscle weakness, numbness and tingling, hearing loss, speaking difficulties, or swallowing problems
• Diagnose a new stroke
• Evaluate changes in thinking or behavior
• Evaluate injury to the head and face

Abnormal results may be due to:

• Abnormal blood vessels (arteriovenous malformation)
• Abnormal sinus drainage
• Aneurysm
• Bleeding (for example, chronic subdural hematoma or intracranial hemorrhage)
• Bone infection
• Brain abscess or infection
• Brain damage due to injury
• Brain tissue swelling or injury
• Brain tumor or mass
• Cerebral atrophy (loss of brain tissue)
• Hydrocephalus (fluid collecting in the skull)
• Problems with the hearing nerve
• Stroke or transient ischemic attack (TIA)

Iodine is the usual contrast dye. Some patients are allergic to iodine and may experience a reaction that may include hives, itching, nausea, breathing difficulty, or other symptoms.

As with any x-ray examination, radiation is potentially harmful. Consult your health care provider about the risks if multiple CT scans are needed over a period of time.

A CT scan can decrease or eliminate the need for invasive procedures to diagnose problems in the skull. This is one of the safest means of studying the head and neck.

Alternative tests that may be performed in place of Cranial CT scan include:

• MRI of the head
• Positron emission tomography (PET) scan of the head
• Skull x-ray

Brain CT; Head CT; CT scan - skull; CT scan - head; CT scan - orbits; CT scan - sinuses

Shaw AS, Dixon AK. Multidetector computed tomography. In: Grainger RC, Allison D, Adam, Dixon AK, eds. Diagnostic Radiology: A Textbook of Medical Imaging. 5th ed. New York, NY: Churchill Livingstone; 2008:chap 4.

Saunders D, Jäger HR, Murray AD, Stevens JM. Skull and brain: methods of examination and anatomy. In: Grainger RC, Allison D, Adam, Dixon AK, eds. Diagnostic Radiology: A Textbook of Medical Imaging. 5th ed. New York, NY: Churchill Livingstone; 2008:chap 55.

Updated by: David C. Dugdale, III, MD, Professor of Medicine, Division of General Medicine, Department of Medicine, University of Washington School of Medicine; and Daniel B. Hoch, PhD, MD, Assistant Professor of Neurology, Harvard Medical School, Department of Neurology, Massachusetts General Hospital. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc.