CT Pneumocolon and CT Colon


A computed tomography (CT) scan is a means of visualising the inside of your bowel to detect tumours or polyps. It may be used if conventional colonoscopy cannot be carried out. Multiple X-rays taken at different angles allow a computer to piece together an accurate image of your bowel.

There are two types of CT scan that our consultants may refer you for:

  • CT pneumocolon, also known as ‘virtual colonoscopy’, ‘CT colonography’ or ‘CT colonoscopy’: This is as effective at detecting abnormalities as conventional colonoscopy. It is sometimes used if conventional colonoscopy has failed or is incomplete.
  • CT colon: This gives less detailed results, but does not require you to restrict your diet, take laxative or large doses of Gastrografin. It is a more gentle examination suited to people who are less fit.

Both can be effective tests, but, unlike colonoscopy, they are purely diagnostic and do not allow the operator to remove polyps or biopsies.

Both of these tests are carried out in the Department of Radiology.


Both of these tests involve exposure to X-rays, which could very slightly increase your lifetime risk of cancer. This is difficult to quantify as it is dependent on several factors, including your body size. The link below gives guideline information about what this risk might be:

GOV.UK: patient dose information.

Please talk to your radiologist or radiographer if you have concerns about this.

CT scans are not usually recommended for pregnant women because of risk to the baby from X-rays.

CT pneumocolon carries a small risk of bowel perforation when the bowel is inflated with carbon dioxide, though this is much lower than in conventional colonoscopy.

Your doctor would not recommend these tests unless he or she thought that the benefits greatly outweighed the risks.


You will be provided with a colourless liquid (Gastrografin) to drink at home either 2 or 3 days before your test. This shows up on the CT picture and optimizes the view of the bowel. If you are having a CT pneumocolon you will also be asked to restrict your diet.

The Department of Radiology will give detailed instructions and will advise on whether to continue taking regular medication. If you suffer from any allergies please inform the radiographer before the scan. If you are diabetic please inform the Department of Radiology in advance.

If possible, come to hospital wearing loose, comfortable clothing with no metal parts (zips, underwires or hooks) as this will allow you to have the scan without getting changed.


CT colon:
You will be asked to lie on the CT table and you may have a small needle or cannula placed into a vein on your arm. This allows ‘x-ray contrast’, if necessary, to be injected in order to improve the quality of the scan.

CT Pneumocolon:
You will be asked to lie on the CT table and you will have a small needle or cannula placed into a vein on your arm. You will have an injection of ‘X-ray contrast’ which improves the quality of the scan. You may also be given an injection of Buscopan to relax your bowel. A small tube will be inserted into the back passage and carbon dioxide will be passed through the tube into the colon. This will make you feel very bloated.


The scanner is shaped like a large doughnut. You will like on the scan table and this will move you through the scanner as the images are taken. Several passes will be needed in order to obtain a full set of images.


You can go home immediately after the test and you should be able to continue your normal activities straight away as long as you feel well.

Results are normally be sent to your referring consultant within a week of the test. You should make an appointment for a consultation to discuss your results.


Please note that these tests are carried out by our colleagues in the Department of Radiology. The above information is for guidance only, and should never supersede any information or guidance that they give to you.