Pelvic CT scan

Definition

A computed tomography (CT) scan of the pelvis is an imaging method that uses x-rays to create cross-sectional pictures of the organs inside and near the pelvis (liver, kidneys, gallbladder, pancreas, and bladder, prostate, lymph nodes, and pelvic bones).

Alternative Names

CAT scan - pelvis; Computed axial tomography scan - pelvis; Computed tomography scan - pelvis

How the test is performed

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

Once you are inside the scanner, the machine's x-ray beam rotates around you. (Modern "spiral" scanners can perform the exam in one continuous motion.)

Small detectors inside the scanner measure the amount of x-rays that make it through the pelvis. 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 the organs inside the pelvis can be created by stacking the individual 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. Straps and pillows may be used to hold you still during the exam.

The scan should take about 30 minutes.

How to prepare for the test

Certain exams require a special dye, called contrast, to be delivered into the body before the test starts. Contrast can highlight specific areas inside the body, which creates a clearer image.

Some people have allergies to IV contrast and may need to take medications before their test in order to safely receive this substance.

Contrast can be given several ways, and depends on the type of CT being performed.

• It may be delivered through a vein (IV) in your hand or forearm.
• You might drink the contrast before your scan. When you actually drink the contrast depends on the type of exam being done. The contrast liquid may taste chalky, although some are flavored to make it taste a little better. The contrast eventually passes out of your body through your stools.

If contrast is used, you may also be asked not to eat or drink anything for 4 - 6 hours before the test.

If you weigh more than 300 pounds, have your doctor contact the scanner operator before the exam. CT scanners have a weight limit. Too much weight can cause damage to the scanner's working parts.

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

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 usually go away within a few seconds.

Why the test is performed

CT rapidly creates detailed pictures of the body, including the pelvis and areas near the pelvis. The test may be used to:

• Diagnose and monitor cancer
• Diagnose the cause of pelvic pain
• Evaluate after trauma to the pelvis
• Evaluate a pelvic mass found during a physical exam
• Guide a surgeon to the right area during a biopsy or other procedures
• Help the health care provider plan for and evaluate the results of surgery
• Plan and deliver radiation treatment for cancer

Normal Values

Results are considered normal if the organs of the pelvis that are being examined are normal in appearance.

What abnormal results mean

Abnormal results may be due to:

• Bladder stones
• Cancers of the bladder, rectum, prostate, cervix, vagina
• Diverticulitis
• Fracture of the pelvis
• Pelvic abscess

What the risks are

CT scans and other x-rays are strictly monitored and controlled to make sure they use the least amount of radiation. CT scans do create low levels of ionizing radiation, which has the potential to cause cancer and other defects. However, the risk associated with any individual scan is small. The risk increases as numerous additional studies are performed.

In some cases, a CT scan may still be done if the benefits greatly outweigh the risks. For example, it can be more risky not to have the exam, especially if your health care provider thinks you might have cancer.

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. Let your doctor know if you have ever had an allergic reaction to injected contrast dye.

If you absolutely must be given such contrast, your doctor may choose to treat you with antihistamines (such as Benadryl) or steroids before the test.

The kidneys help filter the iodine out of the body. Therefore, those with kidney disease or diabetes should receive plenty of fluids after the test, and be closely monitored for kidney problems. If you have diabetes or are on kidney dialysis, talk to your health care provider before the test about your risks.

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.

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.

Special considerations

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References

Fox JC, Irwin Z. Emergency and critical care imaging. Emerg Med Clin North Am.2008; 26: 787-812, ix-x.