Computed tomographic colonography

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In medicine, computed tomographic colonography, also called CT colonography and virtual colonoscopy, is a "non-invasive imaging method that uses computed tomographic data combined with specialized imaging software to examine the colon."^[1]

Accuracy[edit]

According to the US Preventive Services Task Force (USPSTF), the accuracy of CT colonography is:^[2] For adenomas at least 10 mm in size

• sensitivity = 92%
• specificity is uncertain and ranges from 88 to 96%

For adenomas at smaller than 10 mm in size

• sensitivity is uncertain and ranges from 65^[3] to 89%
• specificity is uncertain and ranges from 80 to 88%

The positive predictive value of seeing a colonic polyp greater than 10 mm in size with CT colonoscopy and actually having such a polyp by colonoscopy is about 25%.^[3]

Role in colorectal cancer prevention[edit]

A clinical practice guideline by the U.S. Preventive Services Task Force (USPSTF) gave a grade I recommendation for CT colongraphy in screening for colorectal cancer stating "the evidence is insufficient to assess the benefits and harms of computed tomographic colonography."^[2][4] The most recent study used by the systematic review for this clinical practice guideline was in 2008.^[3]

A joint clinical practice guideline by the American Cancer Society, the US Multi-Society Task Force on Colorectal Cancer, and the American College of Radiology states that CT colonography is an acceptable option for colorectal cancer screening.^[5]

A recent study proposed that any patient with a colonic polyp 5 mm or more size seen by CT colonography, should be referred for colonoscopy.^[3] However, even polyps less than 5 mm may have villus histology or high-grade dysplasia.^[6]

Adecision analysis study^[7] and a cost-benefit analysis^[8] study have addressed management of diminutive (< or = 5 mm), small (6-9 mm), and large (> or = 10 mm) polyps. These studies suggest that patients with polyps larger than 10 mm undergo immediate colonoscopy while those with polyps 6-9 mm in size have repeat computed tomographic colonography in 3 years. However, these studies optimistically assumed that the sensitivity was 89% and specificity was 89% for colonography in detecting polyps 6-9 mm in size.

Adverse effects[edit]

Repeated CT colonography over a patient's lifetime may create risk of causing cancer. The risk associated with a CT scan (the increased risk of cancer associated with the radiation doses) is extremely low for any one person. However, given the increasing number of CT scans being obtained, the increasing exposure to radiation in the population may be a public health issue in the future. ^[9]

References[edit]