Virtual colonoscopy

A virtual colonoscopy is a procedure that uses CT scans to look inside your large bowel. It’s also known as CT colonography or CT colonoscopy. A virtual colonoscopy can check your large bowel for growths or signs of cancer, and investigate bowel symptoms.

About virtual colonoscopy

A virtual colonoscopy is an alternative procedure to a traditional colonoscopy – the usual test to examine your large bowel. In a traditional colonoscopy, a doctor will insert a camera into your bottom to look at your large bowel. Virtual colonoscopy is as good at picking up bowel cancer as traditional colonoscopy. It’s also less invasive and tends to be more comfortable.

Reasons to have a bowel procedure

Reasons for needing to look inside your large bowel include the following.

• As part of the national bowel cancer screening programme in England, if initial tests have found blood in your poo.
• Investigating symptoms that suggest bowel cancer. These might include bleeding from your bottom, abnormal blood tests that could indicate blood loss (anaemia), or a change in bowel habit. This might be needing to poo more often, diarrhoea or constipation.
• You have a strong family history of bowel cancer. This could be if two or more first-degree relatives have had bowel cancer or one relative under the age of 45 has had it.
• To monitor you for any changes. If you’ve had polyps or bowel cancer before, your doctor may check your bowel every so often to make sure you haven’t developed any new polyps.

Who can have a virtual colonoscopy?

There are various reasons why you might be offered a virtual colonoscopy instead of a traditional colonoscopy. These include if you have health issues or mobility needs that might make a traditional colonoscopy difficult or unsafe. You may also be offered a virtual colonoscopy if you previously had a colonoscopy, but it failed to see all of your large bowel. You may also have virtual colonoscopy as part of a private bowel cancer screening test.

Who can’t have a virtual colonoscopy?

Not everyone can have a virtual colonoscopy. Your doctor may not recommend it if you:

• have an active flare-up of inflammatory bowel disease, such as Crohn’s disease or ulcerative colitis
• have diverticulitis
• have recently had surgery on your bowel or rectum
• are a child or young adult

Check if your hospital offers a virtual colonoscopy, as not all do.

Your doctor will be able to tell you why they recommend a virtual colonoscopy. They’ll explain exactly what to expect when you have the procedure and may give you some information to take away. Be sure to ask your doctor any questions you have. It's important that you feel fully informed because you’ll need to give your consent to go ahead with the procedure.

Preparation for virtual colonoscopy

You’ll have a virtual colonoscopy in the CT scanning department at a hospital as an outpatient. This means you have the test and go home the same day. A radiographer (a health professional trained in CT scans) or a doctor called a radiologist may carry out your procedure.

Your hospital will give you detailed information about how to prepare for your test. This may include the following.

Clearing your bowel

Your bowel usually needs to be empty for a virtual colonoscopy. This is so the pictures produced are as clear as possible. The hospital may ask you to take one of the following to help clear your bowel.

• A strong medicine called a laxative that you’ll usually need to take the day or evening before your virtual colonoscopy.
• A liquid dye that you’ll need to drink over the day or two before your test. This mixes with your poo but also acts as a laxative. It helps to show up any abnormalities in your large bowel.

Laxatives clear your bowel by making you need to poo. They can quickly give you diarrhoea, so make sure you stay close to a toilet after you take them.

What to eat and drink

Your hospital will also give you some instructions about what you can eat or drink before the procedure. This might include only eating low-fibre foods for a day or two beforehand, and only drinking clear fluids like water, squash or black tea or coffee, or clear soup.

Medicines to stop

You may need to stop taking certain medicines before you have a virtual colonoscopy. These may include iron supplements and other medicines that can cause constipation. Let your doctor know if you’re taking anything like this before your virtual colonoscopy. They’ll advise if you need to stop taking them, and for how long.

Virtual colonoscopy procedure

A virtual colonoscopy may take up to 30 minutes, but you’ll be in the department for longer – usually an hour or so. When you’re ready, you’ll be given a hospital gown to change into. You’ll meet with the doctor or radiographer performing the procedure. They’ll check that you’re happy to give your consent to go ahead.

You won’t need an anaesthetic or sedative for a virtual colonoscopy. Your radiographer will ask you to lie on your side on the scanning table. They’ll place a fine tube (a cannula) into a vein in your arm. Your doctor may give you a medicine to relax your bowel. Sometimes, you may also have an injection of dye (contrast) to show up your bowel and surrounding organs. This might make you feel hot for a few minutes and give you a strange, metallic taste in your mouth. But it should pass quickly.

Your radiographer will gently pass a small tube into your bottom. They’ll use this to pump gas into your bowel to inflate it so it can be seen more clearly on the scan. You may feel some slight discomfort when this happens, but a virtual colonoscopy isn’t usually painful.

Your radiographer will then move the scanning table into the tunnel of the CT scanner. They’ll then leave the room while the scan is done but will be able to see you through the scanner room window. And if you need to talk to them, there’s an intercom system. Your radiographer will take scans while you’re lying on your back and then ask you to lie on your front or side and take some more. They might also ask you to hold your breath for a few seconds at certain points during the scan. It’s important to try to lie very still.

Your results

Your scans will be analysed by a specialist doctor called a radiologist. They’ll send the results to whoever referred you for the virtual colonoscopy. This can take up to a week or two. There are several possibilities of what your virtual colonoscopy may show.

• Polyps. These are growths that can develop in the lining of your bowel. There’s a small chance that, over time, they may grow into a cancer. Your doctor may recommend a standard colonoscopy to take a closer look and remove them.
• Signs of bowel cancer. If this happens, you’re likely to need further tests to confirm a diagnosis. Sometimes, you may be offered further scans on the same day as your virtual colonoscopy.
• Diverticulosis. These are small pouches in the lining of your bowel that can become inflamed and infected.
• Problems within the organs outside of your large bowel. You may need to have further tests.
• The test may not find a cause for your symptoms. Your doctor may sometimes recommend further tests, such as a traditional colonoscopy, to have a closer look at your bowel.

Complications of virtual colonoscopy

Complications are when problems occur during or after the procedure. Complications from virtual colonoscopy are uncommon but may include the following.

• Feeling faint. A combination of filling your large bowel with air and the medicine used to relax your bowel can sometimes cause you to feel faint. This doesn’t usually last long.
• Allergic reaction to the contrast medium. This is very rare. But if you feel unwell or find it difficult to breathe during the test, tell the radiographer or doctor doing your test straight away.
• Damage to your bowel. There’s a very small risk of your bowel being damaged or torn during the procedure. It’s estimated that this happens in around 1 in 2,500 people who have a virtual colonoscopy. If it does happen, you may need an operation to repair the tear.

CT scanners use X-rays to produce images, so you’ll be exposed to a small amount of radiation. If you’re pregnant or think you could be, let your doctor know because they may recommend an alternative test, such as a traditional colonoscopy.

Alternatives to virtual colonoscopy

If you’re unable to have a virtual colonoscopy, your doctor may recommend you have a standard CT scan of your abdomen and pelvis.

At some hospitals, you may be offered a capsule endoscopy if you have symptoms of bowel cancer. This involves swallowing a capsule that contains a small disposable camera. The camera takes pictures as it travels along the length of your bowel. These are transmitted wirelessly to a data recorder, which your doctor will then review. You’ll need to take laxatives and restrict what you eat and drink the day before you take the capsule. If the test identifies any problems, you may still need to have a colonoscopy.

Capsule endoscopy isn’t available in all hospitals. Which test you are offered will depend on your circumstances, and what’s available at your local hospital. Your doctor will talk to you about the options available and which is best for you.