There are other procedures that can be used to look at your bowel. The main ones are listed below.
- Conventional colonoscopy. With conventional colonoscopy, your doctor looks inside your large bowel using a long, flexible, illuminated, telescopic camera. This camera, called a colonoscope, is inserted through your anus.
- Flexible sigmoidoscopy. This is a similar procedure to colonoscopy, but uses a shorter telescopic camera called a sigmoidoscope. It looks inside your rectum and the lower part of your bowel only (because most bowel cancers develop in this area).
- Rigid sigmoidoscopy. This procedure uses an instrument shorter than the camera used in flexible sigmoidoscopy and looks at your rectum only.
- Barium enema. This test involves placing a fluid containing barium (a substance which shows up on X-rays) into your bowel via your anus. X-ray images of your abdomen (tummy) then show the inside of your bowel more clearly.
Conventional colonoscopy and barium enema are used more often than virtual colonoscopy. However, virtual colonoscopy is less invasive than conventional colonoscopy. Have a chat with your doctor about the options available to you.
Virtual colonoscopy is usually carried out in the CT scanning department of the hospital. At least a few days beforehand, you’ll be given information about how to prepare for your visit.
Usually, your bowel needs to be empty during the test so that the CT scanner can produce clear pictures of your bowel. You may need to follow a special diet for up to three days before your test. This is likely to involve cutting down on solid food and drinking enough clear liquids. You’ll also be asked to take a laxative the day before the procedure to completely empty your bowel.
Alternatively, your doctor may ask you to take an iodine-based fluid for a couple of days before your test. This is taken with meals for about two days before your test. The fluid helps to show your bowel more clearly on the scan. If you have asthma or an allergy to iodine, you must let your doctor know beforehand.
It’s important that you tell your doctor about any medicines you're taking and if you are, or could be, pregnant. Virtual colonoscopy, like all X-ray tests, isn’t recommended for pregnant women, unless there’s an urgent medical reason.
Your doctor will discuss with you what will happen before, during and after your procedure, and any pain you might have. This is your opportunity to understand what will happen. You can help yourself by preparing questions to ask about the risks, benefits and any alternatives to the procedure. This will help you to be informed, so you can give your consent for the procedure to go ahead. You may be asked to give your consent by signing a consent form.
If you have any last minute questions about how to prepare for the procedure, contact the clinic where you’ll have your test.
Virtual colonoscopy is usually carried out in the CT scanning department of the hospital. You’ll have the test and go home on the same day. The procedure usually takes about 10 to 15 minutes.
A radiologist (a doctor who specialises in using imaging methods to diagnose medical conditions) will carry out the test.
You’ll be asked to change into a hospital gown and lie on the scanning table. Your doctor may give you an injection of a medicine that will help to relax the muscles of your bowel wall. You may also have an injection of a dye (contrast medium) at the same time. This helps to show up your bowel more clearly on the X-rays. You’ll be given this through a drip placed into a vein in the back of your hand.
Your doctor will gently pass a thin tube a few centimetres into your rectum. They will then pump a small amount of carbon dioxide or air into your bowel. This will inflate your bowel so that it can be seen more easily on the X-ray. You may feel some slight discomfort when this happens, but few people experience a lot of pain.
The table will move into the tunnel of the CT scanner so that the middle part of your body is lying in the centre. You’ll have scans taken when you’re lying on your back and others taken when you’re lying on your front or side. At certain points during the scan you may be asked to hold your breath for a few seconds. It can take several minutes for each image to form so it’s important that you lie very still during the scan.
After your virtual colonoscopy, you’ll be able to go home when you feel ready.
If you’ve had an injection of contrast medium, you’ll need to wait for an hour before you can drive as it can blur your vision. Your results are usually sent in a report to the doctor who requested your scan. This may take a few days.
Virtual colonoscopy is used to help diagnose your condition rather than to treat it. If the test shows that you have polyps, you’ll need to have another procedure, for example a conventional colonoscopy, to remove them. See our FAQs for more information.
If you’re found to have large polyps or cancer, you may need to have surgery. You may also need to have another procedure if the virtual colonoscopy wasn’t able to find the cause of your symptoms.
After your virtual colonoscopy, you’ll be able to return to your usual activities straight away. This is because you don’t usually need painkillers or sedation for a virtual colonoscopy.
It’s possible that you’ll feel bloated and as though you have trapped wind for a short time. This is due to the air that was pumped into your bowel. You may pass gas. You may also have some abdominal pain but this is rare and doesn’t usually last long. You can go back to eating a normal diet after the procedure unless advised otherwise.
As with every procedure, there are some risks associated with virtual colonoscopy. We haven’t included the chance of these happening as they are specific to you and differ for every person. Ask your doctor to explain how these risks apply to you.
CT scanners use X-rays to produce images, so you will be exposed to some radiation. This is about the same amount as the natural radiation that you get from the atmosphere over about three years.
If you are, or think you could be, pregnant, you shouldn't have a CT scan as there is a risk that the radiation may harm your unborn baby.
Side-effects are the unwanted but mostly temporary effects you may get after having the procedure. The main side-effects of virtual colonoscopy are:
- pain or discomfort when the air or carbon dioxide is put into your bowel
- a feeling of warmth when you have an injection of contrast medium
- blurred vision from the medicine used to relax your bowel
Complications are when problems occur during or after the procedure. Complications from virtual colonoscopy are uncommon.
Very rarely, it's possible to have an allergic reaction to the contrast medium. Tell your doctor if you’ve had a reaction to contrast medium in the past. If you feel unwell or have problems breathing during the test, tell your doctor straight away.
There is a very small chance that your bowel may be damaged or torn when air or carbon dioxide is put in during the procedure. This is very rare and happens to fewer than one in 10,000 people who have a virtual colonoscopy. If your bowel is damaged, it can lead to bleeding and infection and you may need surgery to repair it.
What will happen if a polyp is found during my virtual colonoscopy?
Polyps are small growths that can develop inside your bowel. They’re quite common and don’t usually cause any problems. However, in some people polyps can grow into cancer over time. So, if the results of your virtual colonoscopy show you have polyps, your doctor will discuss with you whether they need to be removed.
Polyps are growths that can occur inside your bowel. They are small, fleshy lumps, usually less than 1cm in size, but they can grow to be bigger. Polyps are common. About one in four people will have a polyp at some time in their lives, most often after the age of 60.
Some polyps are attached to the side of your bowel on a stalk and look a bit like a mushroom. Others are flatter and have no stalk. You may have just one polyp or several.
Most polyps don’t cause any problems. There’s a small chance that over a long period of time a certain type of polyp called an adenoma will grow into a cancer. An adenoma that’s over 1cm in size has almost a one in 10 risk of containing cancer cells.
If your virtual colonoscopy shows that you have a polyp, your doctor may suggest that you have it removed. This is usually done during a conventional colonoscopy.
After your polyp is removed it will be sent to a laboratory. This is to find out exactly what type it is and whether any of the cells show signs of cancer or might have developed into cancer in the future. Depending on the results, you may need to go back to hospital for more treatment or further tests.
Some people are at higher risk of getting polyps. If you develop polyps a number of times, your doctor may advise you to have check-ups with conventional colonoscopy every few years.
What’s the difference between a virtual colonoscopy and a conventional colonoscopy?
Conventional colonoscopy and virtual colonoscopy are both procedures that enable your doctor to look at your large bowel (your colon and rectum). One important difference is that during a conventional colonoscopy your doctor can remove any polyps found, or take a biopsy.
There are a number of differences between conventional and virtual colonoscopy.
During a conventional colonoscopy your doctor looks at the inside of your bowel using a narrow, flexible, tube-like, telescopic camera called a colonoscope. You’ll usually have a sedative during the procedure to relieve any anxiety and help you to relax.
In contrast, virtual colonoscopy takes images from outside your body, using a CT scanner, and you won’t usually need a sedative. It’s less invasive because less of the procedure involves instruments being used internally. Virtual colonoscopy can be quicker compared to conventional colonoscopy. You may find virtual colonoscopy more comfortable, but this can vary from person to person.
If you have a conventional colonoscopy, your doctor can pass thin instruments through the colonoscope to remove polyps or to take biopsies if needed. This isn't possible during a virtual colonoscopy. If your doctor finds any polyps or possible tumours with a virtual colonoscopy, you may need a conventional colonoscopy afterwards to have them removed.
With conventional colonoscopy, there’s slightly more risk of your bowel being damaged during the procedure.
Sometimes, it isn’t always possible to see all of your bowel with a conventional colonoscopy (for example if the camera cannot pass through the whole bowel). This isn’t a problem with virtual colonoscopy. Another advantage of virtual colonoscopy is that it may be safer if:
- you’re elderly or frail
- your bowel is blocked
- you’re taking a medicine to thin your blood, such as warfarin
Some patients find virtual colonoscopy more convenient and prefer this procedure.
It’s important to remember that virtual colonoscopy is carried out using a CT scanner. This uses X-rays to produce images, so you’ll be exposed to some radiation. This doesn’t happen during a conventional colonoscopy.
The investigation that’s best for you will depend on your general health, your symptoms and what your doctor thinks may be causing them. Your doctor will discuss with you the different types of tests available.
How accurate is a virtual colonoscopy compared with other investigations?
Virtual colonoscopy is a relatively new procedure so there’s less information available about how accurate it is than for some other procedures. However, based on studies, experts believe virtual colonoscopy is safe and works well.
The research shows that a virtual colonoscopy may not detect all small or flat polpys, but this is true of other procedures too. For example, a study found that virtual colonoscopy found large polyps (bigger than 1cm) in nine out of 10 patients who had them. However, it found small polyps (smaller than half a centimetre) in only six or seven out of every 10 patients who had them. This accuracy was similar to that with conventional colonoscopy.
Overall, experts agree that virtual colonoscopy is safe and works well.
If you need to have repeat check-ups for polyps, usually this will be done with conventional colonoscopy.
All of the investigations for bowel cancer and polyps have benefits and risks. Your doctor will discuss these so that you can find out which one is most suitable for you.
- Computed tomographic colonography (virtual colonoscopy). National Institute for Health and Clinical Excellence (NICE), 2005. www.nice.org.uk
- Bowel cancer. Cancer Research UK. www.cancerresearchuk.org, published August 2013
- Map of Medicine. Colorectal cancer. International View. London: Map of Medicine; 2014 (Issue 4)
- Colonic polyps. Medscape. www.emedicine.medscape.com, published October 2014
- Virtual colonoscopy. National Digestive Diseases Information Clearinghouse (NDDIC). www.digestive.niddk.nih.gov, published September 2013
- Computed tomographic colonography (virtual colonoscopy): Understanding NICE guidance – information for people considering the procedure, and for the public. National Institute for Health and Clinical Excellence (NICE), 2005. www.nice.org.uk
- Bowel cancer. Macmillan Cancer Support. www.macmillan.org.uk, published January 2013
- Pox CP, Schmiegel W. Role of CT colonography in colorectal cancer screening: risks and benefits. Gut 2010;59(5):692−700. doi: 10.1136/gut.2009.183046
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