Cranial CT scan

Definition

A cranial computed tomography (CT) scan uses many x-rays to create pictures of the head, including the skull, brain, eye sockets, and sinuses.

See: Computed tomography

Alternative Names

Brain CT; Head CT; CT scan - skull; CT scan - head; CT scan - orbits; CT scan - sinuses; Computed tomography - cranial

How the test is performed

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 you are inside the scanner, the machine's x-ray beam rotates around you. (Modern "spiral" scanners can perform the exam in one 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 viewed on a monitor or printed on film. Three-dimensional models of your head can be created by stacking the slices together.

Special dye, called contrast, may be used to help highlight blood vessels and look for a growth (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.

How to prepare for the test

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.

How the test will feel

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

Contrast given 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.

Why the test is performed

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

• Birth (congenital) defect of the head or brain
• Brain infection
• Brain tumor
• Buildup of fluid inside the skull (hydrocephalus)
• Craniosynostosis
• Injury (trauma) to the head and face
• Stroke or bleeding in the brain

A cranial CT may also be done to look for the cause of:

• Changes in thinking or behavior
• Fainting
• Headache, when certain other signs or symptoms are present
• Hearing loss (in some patients)
• Symptoms of damage to part of the brain, such as vision problems, muscle weakness, numbness and tingling, hearing loss, speaking difficulties, or swallowing problems

Normal Values

What abnormal results mean

Abnormal results may be due to:

• Abnormal blood vessels (arteriovenous malformation)
• Aneurysm in the brain
• 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 other growth (mass)
• Cerebral atrophy (loss of brain tissue)
• Hydrocephalus (fluid collecting in the skull)
• Problems with the hearing nerve
• Stroke or transient ischemic attack (TIA)

What the risks are

Iodine is the usual contrast dye. Some patients are allergic to iodine and may experience a reaction that may include:

• Breathing difficulty
• Hives
• Itching
• Nausea
• Other symptoms

As with any x-ray examination, radiation may be harmful. Talk to your health care provider about the risks if you need many CT scans over a period of time.

Special considerations

A CT scan can reduce or avoid the need for invasive procedures to diagnose problems in the skull. This is one of the safest ways to study the head and neck.

Other tests that may be done instead of Cranial CT scan include:

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

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References

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.