DefinitionA computed tomography (CT) scan of the lumbar spine makes cross-sectional pictures of the lower back (lumbar spine). It uses x-rays to create the images.Alternative NamesCAT scan – lumbar spine; Computed axial tomography scan – lumbar spine; Computed tomography scan – lumbar spine; CT – lower backHow 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 spine area, called slices. These images can be stored, viewed on a monitor, or printed on film. Three-dimensional models of the spine area can be created by adding the slices together.You must be still during the exam. Movement can cause 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 Test Some exams use a special dye, called contrast, that is put into your body before the test starts. Contrast helps certain areas show up better on the x-rays.Contrast can be given in different ways.It may be given through a vein (IV) in your hand or forearm.It may be given as an injection into the space around the spinal cord.If contrast is used, you may also be asked not to eat or drink anything for 4-6 hours before the test.advertisementLet your doctor know if you have ever had a reaction to contrast. You may need to take medicines before the test in order to avoid this problem.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.You 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 feeling, a metal taste in the mouth, and a warm flushing of the body. These feelings are normal and go away in a few seconds.Why the Test is PerformedCT rapidly makes detailed pictures of the lower back. The test may be used to look for:Birth defects of the spine in childrenInjury in the lower spineSpine problems when MRI cannot be usedThis test can also be used during or after an x-ray of the spinal cord and spinal nerve roots (myelography) or an x-ray of the disk (discography).Normal ResultsResults are considered normal if no problems are seen in the lumbar region in the images.What Abnormal Results MeanAbnormal results may be due to:Birth defects of the spineBone problemsFractureLumbar disk herniationLumbar spinal stenosisSpondylolisthesisRisksRisks of CT scans include:Being exposed to radiationAllergic reaction to contrast dyeCT scans 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. Talk to your doctor about this risk and how it weighs against the benefits of the test for your 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 must have this type of contrast, your doctor may give you antihistamines (such as Benadryl) or steroids before the test.The kidneys help remove iodine out of the body. People 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 tell the scanner operator right away. Scanners come with an intercom and speakers, so the operator can hear you at all times.ConsiderationsThe lumbar CT scan is good for evaluating large herniated disks, but it can miss smaller ones. This test can be combined with a myelogram to get a better image of the nerve roots and pick up smaller injuries.ReferencesGardocki RJ, Camillo FX. Other disorders of the spine. In: Canale ST, Beaty JH, eds. Campbells Operative Orthopaedics. 12th ed. Philadelphia, Pa: Mosby Elsevier; 2012:chap 44.advertisementDillin W, Eismont FJ, Kitchel S. Thoracolumbar injuries. In: DeLee JC, Drez D Jr, Miller MD, eds. DeLee and Drezs Orthopaedic Sports Medicine. 3rd ed. Philadelphia, Pa: Saunders Elsevier; 2009:section B. Grainger 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, Bethanne Black, Stephanie Slon, and Nissi Wang.