Interventional procedures consultation document - Computed tomographic colonography (virtual colonoscopy)


Interventional Procedure Consultation Document

Computed tomographic colonography (virtual colonoscopy)

The National Institute for Clinical Excellence is examining computed tomographic colonography (virtual colonoscopy) and will publish guidance on its safety and efficacy to the NHS in England, Wales and Scotland. The Institute's Interventional Procedures Advisory Committee has considered the available evidence and the views of Specialist Advisors, who are consultants with knowledge of the procedure. The Advisory Committee has made provisional recommendations about computed tomographic colonography.

This document summarises the procedure and sets out the provisional recommendations made by the Advisory Committee. It has been prepared for public consultation. The Advisory Committee particularly welcomes:

  • comments on the preliminary recommendation
  • the identification of factual inaccuracies
  • additional relevant evidence.

Note that this document is not the Institute's formal guidance on this procedure. The recommendations are provisional and may change after consultation.

The process that the Institute will follow after the consultation period ends is as follows:

  • The Advisory Committee will meet again to consider the original evidence and its provisional recommendations in the light of the comments received during consultation.
  • The Advisory Committee will then prepare draft guidance which will be the basis for the Institute's guidance on the use of the procedure in the NHS in England, Wales and Scotland.

For further details, see the Interventional Procedures Programme manual, which is available from the Institute's website (
Closing date for comments: 21 December 2004
Target date for publication of guidance: 23 March 2005

Note that this document is not the Institute's guidance on this procedure. The recommendations are provisional and may change after consultation.

1 Provisional recommendations

Current evidence on the safety and efficacy of computed tomographic colonoscopy (virtual colonoscopy) appears adequate to support the use of this procedure provided that the normal arrangements are in place for consent, audit and clinical governance.

2 The procedure
2.1 Indications

Computed tomographic (CT) colonography is used to examine the colon and rectum, and to detect abnormalities such as polyps and cancer. Polyps may be adenomatous (precancerous) or benign.

2.1.2 Colorectal cancer is the third most common cancer in men, and the second most common cancer in women in the UK. Symptoms include blood in the stool, change in bowel habit, abdominal pain and unexplained weight loss. In addition to its use as a diagnostic test in symptomatic patients, CT colonography may be used in asymptomatic patients with a high risk of developing colorectal cancer.

Conventional colonoscopy and double-contrast barium enema are the main methods currently used for examining the colon.

2.2 Outline of the procedure

CT colonography involves using a CT scanner to produce two- and three-dimensional images of the entire colon and rectum. CT colonography is less invasive than conventional colonoscopy.

2.2.2 The patient should have an empty colon for CT colonography. Sedation is not usually required. The colon is distended by insufflation with air or carbon dioxide via a small rectal tube. Antispasmodic agents and/or contrast agents may be administered intravenously before the scan. The images are manipulated and interpreted by a radiologist.
2.3 Efficacy

A meta-analysis of data from 14 studies with a total of 1324 patients reported the sensitivity and specificity of CT colonography for the detection of polyps, using conventional colonoscopy as the reference standard. The pooled per-patient sensitivity for polyps 10 mm or larger was 88% (95% confidence interval [CI], 84-93%), for polyps 6-9 mm it was 84% (95% CI, 80-89%), and for polyps 5 mm or smaller it was 65% (95% CI, 57-73%). The pooled per-polyp sensitivity for polyps 10 mm or larger was 81% (95% CI, 76-85%), for polyps 6-9 mm it was 62% (95% CI, 58-67%) and for polyps 5 mm or smaller it was 43% (95% CI, 39-47%). The overall specificity for the detection of polyps 10 mm or larger was 95% (95% CI, 94-97%). For more details, refer to the sources of evidence (see Appendix).

2.3.2 A recent study involving 1233 asymptomatic adults reported that the per-patient sensitivity of CT colonography for polyps 10 mm or larger was 94% (95% CI, 83-99%) for CT colonography and 88% (95% CI, 75-95%) for conventional colonoscopy. The per-patient sensitivity for polyps 6 mm or larger was 89% (95% CI, 83-93%) for CT colonography compared with 92% (95% CI, 87-96%) for conventional colonoscopy. A study of 703 asymptomatic patients reported per-patient sensitivities of 64% (95% CI, 48-77%) for polyps 10 mm or larger, and 65% (95% CI, 53-76%) for polyps 5-9 mm. For more details, refer to the sources of evidence (see Appendix).

The Specialist Advisors noted that the procedure may fail to detect small or flat lesions, but commented that this was also the case with other diagnostic techniques.

2.4 Safety

No significant complications were reported in the studies. Two studies reported on the level of discomfort felt by patients during the procedure. One study reported that 1% (9/696) of patients experienced 'extreme' or 'severe' discomfort during CT colonography, compared with 4% (25/696) for colonoscopy. In the same study, less than 1% (4/617) of patients had 'severe' or 'extreme' discomfort during CT colonography compared with 29% (181/617) during a barium enema (p < 0.001). A second study reported that 54% (546/1005) of patients found CT colonography to be more uncomfortable than conventional colonoscopy, but this may have been affected by the fact that patients were sedated for the conventional colonoscopy and not for the CT colonography. In the same study, CT colonography was reported to be more acceptable in terms of convenience than conventional colonoscopy in 68% (686/1005) of patients. For more details, refer to the sources of evidence (see Appendix).

2.4.2 In one study, 72% (357/494) of patients were reported to prefer CT colonography to conventional colonoscopy, and 97% (518/534) preferred CT colonography to double-contrast barium enema. For more details, refer to the sources of evidence (see Appendix).

The Specialist Advisors noted that the potential complications are similar to those associated with other techniques, and include bowel perforation and reaction to the contrast medium.

Bruce Campbell
Chairman, Interventional Procedures Advisory Committee
December 2004

Appendix: Sources of evidence

The following document, which summarises the evidence, was considered by the Interventional Procedures Advisory Committee when making its provisional recommendations.

Interventional procedure overview of computed tomographic colonography (virtual colonoscopy), August 2004

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This page was last updated: 04 February 2011