CT Colonography: Is It a Good Option?
Abstract & Commentary
By Eileen C. West, MD, Director of Primary Care Women's Health, Clinical Associate Professor of Internal Medicine, University of Oklahoma School of Medicine, Oklahoma City. Dr. West serves on the speakers bureau for Novartis.
Synopsis: CT colonography is a screening tool that appears to be reasonably good at identifying colorectal cancer in asymptomatic patients at increased risk for colorectal cancer when compared to colonoscopy. Increased risk is defined as those with a family history of advanced neoplasia in first-degree relatives, personal history of colorectal adenomas, or positive results from fecal occult blood tests (FOBTs).
Source: Regge D, et al. Diagnostic accuracy of computed tomographic colonography for the detection of advanced neoplasia in individuals at increased risk of colorectal cancer. JAMA 2009:301:2453-2461.
Colorectal cancer (CRC) accounts for about 210,000 deaths each year in Europe, where this multicenter study took place. More than 50,000 die yearly from the disease in the United States. Most CRCs arise within adenomatous polyps and polypectomy is associated with a reduction in CRC incidence and mortality.1 Computed tomographic (CT) colonography has been shown to be sufficiently accurate in detecting colorectal cancer,2 and is now considered by some to be a valid alternative for CRC screening in the general population.3 The objective of this study was to assess the accuracy of CT colonography in detecting advanced colorectal neoplasia in asymptomatic individuals at increased risk of CRC using unblinded colonoscopy as the reference standard. Each subject underwent CT colonography followed the same day by colonoscopy advanced to the cecum. The endoscopist was initially blind to the CT colonography results. At the end of each bowel segment evaluation, results for that segment were disclosed.
The final analysis included 937 patients: 373 in the family history group, 343 with a personal history of adenomas, and 221 with positive FOBTs. Colonography identified 151 of 177 patients with advanced neoplasia 6 mm or larger (sensitivity, 85.3%; 95% confidence interval [CI], 79.0%-90.0%) and correctly identified negative results for 667 of 760 patients without polyps (specificity 87.8%; 95% CI, 85.2%-90.0%). Positive and negative predictive values were 61.9% and 96.3%, respectively. The FOBT-positive group had a significantly lower negative predictive value of 84.9%, meaning that a healthy colon was deemed negative only 85% of the time.
Commentary
So, what new information have we obtained from this study, and how can we use it in our practices? The analysis supports the use of CT colonography in screening patients with a first-degree relative with advanced CRC, and those with a personal history of adenomas. The data aren't quite as strong for FOBT-positive patients. In an editorial in the same issue, Emily Finlayson, MD, eloquently points out that because up to 50% of patients with positive FOBT results have underlying colorectal pathology that would require colonoscopy for biopsy and polyp removal, CT colonography would be poorly cost-effective in these patients. Also, CT colonography is a poor test for detecting flat lesions, and for this reason patients with a history of flat neoplasia or increased risk for flat neoplasia, such as is seen with inflammatory bowel disease, should not rely on this procedure.
Colonoscopy remains the gold standard for colorectal cancer screening. However, understanding that a majority of patients who qualify for colorectal cancer screening and surveillance are not compliant with screening recommendations, there may be room for CT colonography in high-risk patients despite a slightly lower degree of accuracy. It has the advantage of not requiring sedation, which significantly improves risk. Also, perforation is a serious complication of colonoscopy, with frequently poor outcomes. Risk of perforation is greatly reduced, though insufflation of the bowel still occurs. On the negative side, bowel prep, felt by many patients to be the worst aspect of colonoscopy, is still required. Also, there is the risk of increased radiation with serial studies, though intravenous contrast is not used. Finally, the guidelines for proceeding to colonoscopy are poorly defined at this time. Stay tuned there will no doubt be many debates and discussions in the months to come about this emerging technology.
References
1. Winawer SJ, Zauber AG. The advanced adenoma as the primary target of screening. Gastrointest Endosc Clin North Am 2002;12:1-9.
2. Johnson CD, et al. Accuracy of CT colonography for detection of large adenomas and cancers. N Engl J Med 2008;359;1207-1217.
3. Levin B, et al; American Cancer Society Colorectal Cancer Advisory Group; U.S. Multi-Society Task Force; American College of Radiology Colon Cancer Committee. Screening and surveillance for the early detection of colorectal cancer and adenomatous polyps, 2008: A joint guideline from the American Cancer Society, the U.S. Multi-Society Task Force on Colorectal Cancer, and the American College of Radiology. Gastroenterology 2008;134:1570-1595.
CT colonography is a screening tool that appears to be reasonably good at identifying colorectal cancer in asymptomatic patients at increased risk for colorectal cancer when compared to colonoscopy. Increased risk is defined as those with a family history of advanced neoplasia in first-degree relatives, personal history of colorectal adenomas, or positive results from fecal occult blood tests (FOBTs).You have reached your article limit for the month. Subscribe now to access this article plus other member-only content.
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