FAQs - Fast Facts (Virtual Colonoscopy)
Question: Is virtual colonoscopy an accepted alternative to standard colonoscopy?
Answer:Conventional colonoscopy remains the preferred screening standard in average-risk adults aged 50 years and older. However, the application of computed tomographic (CT) colonography (also known as virtual colonoscopy) is currently under investigation.1 Although this procedure is significantly less invasive (ie, it does not require rectal insertion of a colonoscope), reduces time expenditure, and does not require sedation, it does require bowel preparation and does not permit the physician to take tissue samples or remove polyps, thus necessitating a second conventional colonoscopy should abnormalities be identified. Also, conflicting reports on accuracy have delayed its inclusion in colorectal screening standards of care.1 As clinicians gain experience and technology continues to advance, it is likely that a clear role for virtual colonoscopy will be defined.
Virtual colonoscopy is a radiologic technique that uses a helical CT scanner to obtain a sequence of 2-D slices of the abdomen and computer software to convert those scans into 3-D images of the colon and rectum. Patients need to take laxatives and to fast for 24 hours before the test to ensure that the bowel is free of fecal material that could obscure abnormalities and make analysis difficult. A rectal tube is used to distend the colon with air for the entire procedure, which takes about 10 minutes.
The use of virtual colonoscopy has been under investigation for the past 10 years; conflicting recent findings have delayed its inclusion as a standard of care. In a 2003 study of 1,233 asymptomatic individuals, Pickhardt and colleagues reported high sensitivity for virtual colonoscopy in locating adenomatous polyps (ie, 93.8% for polyps 10 mm in diameter, 93.9% for 8-mm polyps, and 88.7% for 6-mm polyps), as well as high specificity that compared favorably with that of optical colonoscopy. The investigators concluded that virtual colonoscopy is an accurate screening method for detecting colorectal abnormalities in average-risk adults.2 However, in a later trial, Cotton and coworkers found that standard colonoscopy detected 99% of 6-mm polyps versus a 39% detection rate using the virtual technique, raising questions about the influence of clinician experience and the quality of equipment used.3 A meta-analysis of 33 studies with a total of 6,393 patients describes variable results. The investigators included only studies using state-of-the-art technology. They conclude that virtual colonoscopy is highly specific but has variable sensitivity. This issue must be resolved before virtual colonoscopy can be considered the standard of care.4
References
- National Comprehensive Cancer Network (NCCN). Clinical practice guidelines in oncology: colorectal cancer screening, version 1, 2006. Available at: http://www.nccn.org/professionals/physician_gls/default.asp.
- Pickhardt PJ, Choi JR, Hwang I, et al. Computed tomographic virtual colonoscopy to screen for colorectal neoplasia in asymptomatic adults. N Engl J Med. 2003;349:2191-2200. [ Pub Med ]
- Cotton PB, Durkalski VL, Pineau BC, et al. Computed tomographic colonography (virtual colonoscopy): a multicenter comparison with standard colonoscopy for detection of colorectal neoplasia. JAMA. 2004;291:1713-1719.
- Mulhall B, Veerappan GR, Jackson JL. Meta-analysis: computed tomographic colonography. Ann Intern Med. 2005;142:635-650.
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