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Virtual colonoscopyPublished by Bupa's health information team, healthinfo@bupa.com, June 2007. This factsheet is for people who are planning to have virtual colonoscopy, or who would like information about it. Virtual colonoscopy is also called a computerised tomography (CT) colonography. It allows doctors to examine the large bowel for polyps and signs of cancer. The scanner uses X-rays to produce two-dimensional and three-dimensional images of the colon and rectum. Your care will be adapted to meet your individual needs and may differ from what is described here. So it's important that you follow your doctor's advice.
About the large bowelThe large bowel, also called the colon, is the lower part of your intestines. It absorbs water and nutrients from digested food that passes through it. Your colon has three sections - the ascending, transverse and descending colon - see the illustration below. The rectum, at the end of your colon, is where faeces collect before they go out through your anus as a bowel movement.
PolypsA polyp is a small ball of tissue that can grow on the inside of the bowel wall. It's formed by an overgrowth of cells from the bowel wall, known as an adenoma. A polyp is harmless but can sometimes turn into cancer. To be safe, the polyp is usually removed and tested for cancer. What are the alternatives?There are several other tests that can detect cancers and polyps.
Your choice of test depends on several factors. A virtual colonoscopy, for example, may be particularly suitable for frail or elderly people as it's easier to tolerate than conventional colonoscopy. Your doctor will explain your options to you. Preparing for your scanYour doctor will explain how to prepare for your scan. You may need follow a special diet for a few days before the procedure and take a laxative to empty your bowel. Alternatively, you may need to swallow an iodine-based fluid called a contrast agent (a type of dye), with meals around two days before the scan. This helps to show the bowel more clearly on the scans. Virtual colonoscopy is routinely done in the out-patients department of the hospital. The scan is performed by a radiologist (a doctor trained in radiology). The radiologist is usually assisted by a skilled technician, called a radiographer. You must tell your doctor about any medicines you are taking and if you have any allergies. If you are a woman of childbearing age, you will be asked if you are pregnant. The scan is not recommended for pregnant women, unless there is an urgent medical reason. Please tell your doctor if you could be pregnant. Your doctor will usually ask you to sign a consent form. This confirms that you understand the risks, benefits and possible alternatives to the procedure and have given your permission for it to go ahead. About the scan
The scan usually takes 10 to 20 minutes. In a private cubicle, you will be asked to remove your clothing and put on a hospital gown. You will be taken to the scanning room. The scanner is a large machine with a hole in the centre (like a ring). Only the part of your body inside the ring can be scanned. You will need to lie on a table attached to the scanner. This can slide in and out of the ring. You may be given an injection of a muscle relaxant to help relax the muscles of the bowel wall. You may also be given an injection of contrast dye at the same time. A thin tube is placed into your rectum. Carbon dioxide or air is passed into your colon to make the bowel wall easier to see. When this happens, you may briefly feel pains similar to trapped wind and the urge to go to the toilet, but as the colon is empty, this will not be possible. You may pass wind, but try not to feel embarrassed, as the radiographer expects this to happen. The scanner is operated from behind a window. Your doctor and radiographer will be able to see, hear, and speak to you throughout the procedure. The table will move into the ring so that the middle part of your body is lying in the centre of the scanner. The X-ray unit will rotate around you to help produce images from every direction. You will have some scans taken with you lying on your back and a few more with you lying on your stomach. It can take several minutes for each image to form and it's important to lie very still during the process. At certain points during the scan you may be asked to hold your breath for a couple of seconds. What to expect afterwardsYou will be able to go home when you feel ready. If you have muscle relaxants or a contrast injection you should wait an hour before driving. It is best to arrange for someone to drive you home after the scan. Try to drink water regularly for the next 24 hours to help flush the contrast dye out of your body. If you are breastfeeding, it is recommended that you wait 24 hours after having a contrast injection before you breastfeed. You may need to express and discard your milk for 24 hours. Please ask your doctor or radiographer for specific advice. ResultsYour results are usually sent in a report to the doctor who requested your scan. The report can take a few days to reach your doctor. If you haven't been told the results of your scan within two weeks, you should contact the doctor who requested your scan for advice. What happens if the scan identifies polyps or cancer?Virtual colonoscopy is a diagnostic not therapeutic technique. If the virtual colonoscopy finds that you have polyps, you will need to have either conventional colonoscopy or a sigmoidoscopy to remove them. Large polyps or cancer usually need surgery to remove them. What are the risks?Virtual colonoscopy is commonly performed and generally safe. However, in order to make an informed decision and give your consent, you need to be aware of the possible side-effects and the risk of complications of this procedure. You will be exposed to some X-ray radiation. The level of exposure is about the same as you would receive naturally from the environment over 20 months. Pregnant women are advised not to have CT scans as there's a risk the radiation may cause some damage to the unborn child. If you could be pregnant, please tell your doctor. Side-effectsThese are the unwanted but mostly temporary effects of a successful procedure.
It may also make you feel constipated for a few days. Mild laxatives can help with this. ComplicationsThis is when problems occur during or after the procedure. Complications from virtual colonoscopy are uncommon. It's possible, although very rare, to have an allergic reaction to the contrast injection. If you experience any itching or difficulty in breathing tell your doctor or radiographer immediately. Medicines are available to treat any allergic reaction. There is a small risk your colon may be damaged or perforated when the carbon dioxide is being pumped into your bowel. This can lead to bleeding and infection, which may require treatment with medicines or surgery. Most people don't mind having part of their body in a CT scanner but if you feel at all worried, please tell your doctor. You may be offered a sedative to help you relax. The exact risks are specific to you and differ for every person, so we have not included statistics here. Ask your doctor to explain how these risks apply to you. Further information
Sources
Related topicsThis information was published by Bupa's health information team and is based on reputable sources of medical evidence. It has been peer reviewed by Bupa doctors. The content is intended for general information only and does not replace the need for personal advice from a qualified health professional. Publication date: June 2007. Expected review date: June 2009.
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