You will be asked to lie on a narrow table that slides into the center of the CT scanner.

Once you are inside the scanner, the machine's x-ray beam rotates around you. (Modern "spiral" scanners can perform the exam without stopping.)

A computer creates separate images of the shoulder area. These are called slices. These images can be stored, viewed on a monitor, or printed on film. Three-dimensional models of the shoulder area can be created by adding the slices together.

You must be still during the exam, because movement causes blurred images. You may be told to hold your breath for short periods of time.

The scan should take only 10 to 15 minutes.

Certain exams require a special dye, called contrast, to be delivered into the body before the test starts. Contrast helps certain areas show up better on the x-rays.

• Contrast can be given through a vein (IV). If contrast is used, you may also be asked not to eat or drink anything for 4 to 6 hours before the test.
• Let your health care provider know if you have ever had a reaction to contrast. You may need to take medicines before the test in order to safely receive this substance.
• Before receiving the contrast, tell your provider if you take the diabetes medicine metformin (Glucophage) because you may need to take extra precautions.

If you weigh more than 300 pounds (135 kilograms), find out if the CT machine has a weight limit. Too much weight can cause damage to the scanner's working parts.

You will be asked to remove jewelry and wear a hospital gown during the study as metal can affect the CT images.

Some people may have discomfort from lying on the hard table.

Contrast given through an IV may cause a slight burning sensation, a metallic taste in the mouth, and a warm flushing of the body. These sensations are normal and most often go away within a few seconds.

CT rapidly creates detailed pictures of the shoulder. The test may help diagnose or detect:

• A dislocation, fracture, or other shoulder injury
• Soft tissue problems such as damage to the rotator cuff tendons
• Abscess or infection
• The cause of pain or other problems in the shoulder joint when MRI cannot be done
• Masses and tumors, including cancer
• Healing problems or scar tissue following surgery
• Help planning for your surgical treatment

This test may also help a surgeon perform a biopsy or plan surgical treatment to the shoulder.

Results are considered normal if the shoulder being examined is normal in appearance.

Abnormal results may be due to:

• Abscess (collection of pus)
• Bone tumors or cancer
• Dislocated shoulder
• Shoulder fracture
• Rotator cuff tears
• Failure to heal or development of scar tissue after surgery

Risks of CT scans include:

• Being exposed to radiation
• Allergic reaction to contrast dye
• Birth defect if done during pregnancy

CT scans do expose you to more radiation than regular x-rays. Having many x-rays or CT scans over time may increase your risk for cancer. However, the risk from any one scan is small. You and your provider should weigh this risk against the benefits of getting a correct diagnosis for a medical problem.

Some people have allergies to contrast dye. Let your provider know if you have ever had an allergic reaction to injected contrast dye.

• The most common type of contrast given into a vein contains iodine. If a person with an iodine allergy is given this type of contrast, nausea or vomiting, sneezing, itching, or hives may occur.
• If you absolutely must be given such contrast, you may need to get antihistamines (such as Benadryl) or steroids before the test.
• The kidneys help remove iodine out of the body. Those with kidney disease or diabetes may need to receive extra fluids after the test to help flush the iodine out of the body.

Rarely, the dye may cause a life-threatening allergic response called anaphylaxis. If you have any trouble breathing during the test, you should notify the scanner operator immediately. Scanners come with an intercom and speakers, so the operator can hear you at all times.

CAT scan - shoulder; Computed axial tomography scan - shoulder; Computed tomography scan - shoulder; CT scan - shoulder

Kapoor G, Toms AP. Current status of imaging of the musculoskeletal system. In: Adam A, Dixon AK, Gillard JH, Schaefer-Prokop CM, eds. Grainger & Allison's Diagnostic Radiology. 7th ed. Philadelphia, PA: Elsevier; 2021:chap 38.

Perez EA. Fractures of the shoulder, arm, and forearm. In: Azar FM, Beaty JH, eds. Campbell's Operative Orthopaedics. 14th ed. Philadelphia, PA: Elsevier; 2021:chap 57.

Sheah K, Bredella MA. Shoulder. In: Haaga JR, Boll DT, eds. CT and MRI of the Whole Body. 6th ed. Philadelphia, PA: Elsevier; 2017:chap 61.

Updated by: C. Benjamin Ma, MD, Professor, Chief, Sports Medicine and Shoulder Service, UCSF Department of Orthopaedic Surgery, San Francisco, CA. Also reviewed by David C. Dugdale, MD, Medical Director, Brenda Conaway, Editorial Director, and the A.D.A.M. Editorial team.