CT Colonography (Virtual Colonoscopy)

Findings by SBU Alert

Version: 1

Technology and target group

Computed tomographic (CT) colonography is a new application for computed tomography that has been enabled by advancements in rapid spiral computed tomography and computerized work stations for image processing. This technology makes it possible to detect pathological changes, mainly tumors and polyps, without inserting medical devices into the intestine. The term "virtual colonoscopy" refers to the capacity to produce images from a perspective within the intestine that corresponds to the view obtained from usual fiber-optic investigation of the colon (conventional colonoscopy). Currently, CT colonography is used only to a limited extent in Sweden, mainly to complement incomplete colonoscopy and as an alternative to double-contrast barium enema of the colon and colonoscopy in patients with impaired mobility due to old age or disability. One issue in this context is the extent to which CT colonography can replace double-contrast barium enema, and the extent to which the method can complement or replace conventional colonoscopy. In Sweden approximately 5 400 individuals annually are diagnosed with cancer in the colon or rectum. Potential target groups for CT colonography consist mainly of patients suspected of having malignant tumors as well as asymptomatic individuals at greater than average risk for developing colon cancer in whom the treatable early stages of cancer can be detected.

Patient benefit

CT colonography has been assessed in a relatively large number of clinical studies, mainly addressing patients with disease symptoms or patients with a genetic predisposition to be at higher risk for colon disease. The extent to which CT colonography can complement or replace colonoscopy in diagnosing polyps and tumors depends on the detection level (polyp size) considered as clinically relevant. Most studies have shown that CT colonography offers high diagnostic reliability for malignant tumors and polyps 10 mm or larger, inconsistent diagnostic reliability for changes of 5 to 9 mm, and insufficient diagnostic reliability for changes smaller than 5 mm. Some studies, however, have shown unacceptable diagnostic reliability even for malignant tumors and polyps larger than 10 mm. The extent to which CT colonography can replace double-contrast barium enema in patients with disease symptoms has not been completely studied since CT colonography almost exclusively has been compared to colonoscopy. However, the diagnostic reliability of CT colonography compared to colonoscopy appears to be at least equal to the diagnostic reliability of double contrast barium enema compared to colonoscopy. In findings of colon tumors, CT colonography can, in the same examination, also provide information on changes in adjacent tissues and metastases in the lymph nodes and liver. Patients usually experience less discomfort and pain with CT colonography than with conventional colonoscopy and double-contrast barium enema. Generally, however, it is not the examination per se that causes the most discomfort for the patient, but the pre-examination procedure, ie, the use of laxatives, that is similar in all of the methods.

Ethical aspects

Ethical and practical ways need to be established to address the secondary and incidental findings that may be detected by CT colonography in organs other than the colon.

Economic aspects

Cost estimates for routine CT colonography are not available since, in Sweden, the method has been used mainly in research projects. Substantial costs have been required for effective imaging work stations and specialized software as well as for the time needed for image reconstruction, evaluation, and training. Since it is likely that the software for CT colonography will be included as a standard feature in new CT installations, the total cost for CT colonography will probably be reduced. Currently, the cost of a CT colonography examination is estimated at SEK 3 000-3 500, which is equal to the cost of a double-contrast barium enema, but somewhat lower than the cost of colonoscopy.

Scientific evidence

Scientific evidence on the diagnostic reliability of CT colonography is not fully conclusive. The differences in results from different studies can be due to differences in equipment, procedures, and experience. Scientific evidence for assessing the cost effectiveness of the method is lacking. Studies should be conducted on expected effects and costs under ordinary conditions before applying the method more generally in routine health services.

This summary is based on a report prepared at SBU in collaboration with Prof. Mikael Hellström, Sahlgrenska University Hospital, Göteborg. It has been reviewed by Prof. Stefan Lindgren, Malmö University Hospital, Malmö.

The complete report is available only in Swedish.

SBU Alert is a service provided by SBU in collaboration with the Medical Products Agency, the National Board of Health and Welfare, and the Federation of Swedish County Councils.

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