CT Colonography

CT colonography (virtual colonoscopy) is a specialised imaging test which involves using a CT scanner to look for polyps or signs of bowel cancer. Also known as virtual colonoscopy, it is a less invasive, but equally accurate alternative to conventional colonoscopy.

A recent large multi centre randomised control trial (The Siggar data) published in the Lancet has confirmed that CT colonoscopy is as good as conventional colonoscopy at detecting large polyps and cancers.

Colorectal (bowel) cancer is the second most common cancer in the UK in women and the third most common cancer in men. Early diagnosis is vital as the treatments are very good, over 90% of people with early disease now survive more than 5 years.

Most (over 75%) of colorectal cancers develop from polyps which are nodular fleshy growths of the lining of the colon. Polyps grow slowly and can gradually become cancerous, usually over an approximately 10-20 year period. CT colonoscopy can accurately detect small polyps (6mm in size) and larger cancers. Unlike conventional colonoscopy, CT colonoscopy is also able to detect other abnormalities within the abdominal organs outside the bowel.

Who would be referred for this test?

A CT colonoscope may be requested by your family doctor or specialist to find out what is causing symptoms such as abdominal pain, weight loss, a change in usual bowel habit or blood in faeces. You may have had a positive faecal occult blood test. Alternatively patients may have a family history of polyps or colorectal cancer or be undergoing health screening.

Advantages of CT Colonography compared to a conventional colonoscopy

Disadvantages of CT colonography compared to a conventional colonoscopy

  • Less invasive and uncomfortable
  • Equally accurate to a colonoscopy
  • More likely to be diagnostic in women
  • Preferred by patients
  • Reduced risk of bowel perforation
  • No sedation necessary
  • Patients can drive home afterwards
  • Assesses other organs in the abdomen outside the bowel
  • If CT colonography finds an abnormality patients will have to undergo a colonoscopy
  • Small radiation dose

CT colonography or Conventional Colonoscopy??

CT colonography has a lower risk of perforation, which is rare, than conventional colonoscopy.

CT colonography can see outside the colon at the other abdominal structures (such as the liver, kidneys, aorta), whereas conventional colonoscopy just examines the inside of the colon.

Most conventional colonscopies require sedation, whereas CT colonography is quick and no sedation is required. You will be able to resume normal activities immediately after the test.

Both tests distend the bowel to aid good visualisation. Air is used to distend the colon in conventional colonoscopy. CT colonography uses carbon dioxide which is usually more comfortable as the body absorbs it faster.

Both tests examine the large bowel and both require that the bowel is lining is cleaned prior to the test using laxatives so visualization is good.

Any abnormality identified on a CT colonography examination may require a conventional colonoscope to investigate it further and potentially remove a polyp or take a tissue sample (biopsy). Conventional colonoscopy has the advantage that these procedures can be carried out during the initial scope. The likelihood of finding an abnormality however is small.

Undergoing CT colonography requires receiving a small dose of radiation and there is a link between developing cancer and excessive exposure to radiation. We keep the radiation dose to an absolute minimum and the dose you are exposed to during a CTC is approximately the equivalent to three years natural background radiation (i.e. the amount of natural radiation you would receive from living in the UK for 3 years).

Further information

If you would like to discuss undergoing CT colonography please call Berkshire Imaging.

Alternatively, please click here for a detailed patient information sheet.

To read the 'Siggar data' Lancet paper comparing CT colonoscopy with conventional colonoscopy click on the following link: http://www.thelancet.com/journals/lancet/article/PIIS0140-6736(12)62186-2/abstract

Further information can be found at:

Patient information sheet

Berkshire Imaging LLP . The Forbury Clinic . 23 Craven Road . Reading . Berkshire . RG1 5LE . Telephone: 0118 921 3177
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