DefinitionA computed tomography (CT) scan of the shoulder is an imaging method that uses x-rays to create cross-sectional pictures of the shoulder.Alternative NamesCAT scan – shoulder; Computed axial tomography scan – shoulder; Computed tomography scan – shoulder; CT scan – shoulderHow the test is performedYou 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 machines x-ray beam rotates around you. (Modern “spiral” scanners can perform the exam without stopping.)A computer creates separate images of the shoulder area, 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 10-15 minutes.How to prepare for the testCertain 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) in your hand or forearm. If contrast is used, you may also be asked not to eat or drink anything for 4-6 hours before the test.Let your doctor know if you have ever had a reaction to contrast. You may need to take medications before the test in order to safely receive this substance.Before receiving the contrast, tell your health care provider if you take the diabetes medication metformin (Glucophage) because you may need to take extra precautions.If you weigh more than 300 pounds, find out if the CT machine has a weight limit. Too much weight can cause damage to the scanners working parts.advertisementYou will be asked to remove jewelry and wear a hospital gown during the study.How the test will feelSome 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 usually go away within a few seconds.Why the test is performedCT rapidly creates detailed pictures of the shoulder. The test may help diagnose or detect:A dislocation, fracture, or other shoulder injuryEvaluate the soft tissue such as rotator cuff tendonsAbscess or infectionThe cause of pain or other problems in the shoulder joint when MRI cannot be doneMasses and tumors, including cancerThis test may also help guide a surgeon to the right area during a biopsy in the shoulder area.Normal ValuesResults are considered normal if the shoulder being examined is normal in appearance.What abnormal results meanAbnormal results may be due to:Abscess (collection of pus)Bone tumors or cancerDislocated shoulderShoulder fractureWhat the risks areRisks of CT scans include:Being exposed to radiationAllergic reaction to contrast dyeCT 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 doctor 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 doctor 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, your doctor may give you 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.ReferencesDeLee JC, Drez D Jr, Miller MD, eds. DeLee and Drez?s Orthopaedic Sports Medicine. 3rd ed. Philadelphia, Pa: Saunders Elsevier; 2009:chap 17.Perez EA. Fractures of the Shoulder, Arm, and Forearm. In: Canale ST, Beaty JH. Campbells Operative Orthopaedics. 12th ed. Philadelphia, Pa:Mosby Elsevier;2012:chap 57. advertisementGrainger RG, Thomsen HS, Morcos SK, Koh DM, Roditi G. Intravascular contrast media for radiology, CT, and MRI. In: Adam A, Dixon AK, eds. Grainger & Allisons Diagnostic Radiology: A Textbook of Medical Imaging. 5th ed. New York, NY: Churchill Livingstone; 2008:chap 2.Shaw AS, Dixon AK. Multidetector computed tomography. In: Adam A, Dixon AK, eds. Grainger & Allisons Diagnostic Radiology: A Textbook of Medical Imaging. 5th ed. New York, NY: Churchill Livingstone; 2008:chap 4.Review Date:1/17/2013Reviewed By:C. Benjamin Ma, MD, Assistant Professor, Chief, Sports Medicine and Shoulder Service, UCSF Department of Orthopaedic Surgery. Also reviewed by A.D.A.M. Health Solutions, Ebix, Inc., Editorial Team: David Zieve, MD, MHA, David R. Eltz, Bethanne Black, Stephanie Slon, and Nissi Wang.