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

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

For adenomas at smaller than 10 mm in size

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

A clinical practice guideline by the US 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

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

  1. Anonymous (2015), Computed tomographic colonography (English). Medical Subject Headings. U.S. National Library of Medicine.
  2. 2.0 2.1 U.S. Preventive Services Task Force (October 2008). "Screening for Colorectal Cancer: U.S. Preventive Services Task Force Recommendation Statement". Annals of internal medicine. PMID 18838716[e]
  3. 3.0 3.1 3.2 3.3 Johnson CD, Chen MH, Toledano AY, et al (September 2008). "Accuracy of CT colonography for detection of large adenomas and cancers". The New England journal of medicine 359 (12): 1207–17. DOI:10.1056/NEJMoa0800996. PMID 18799557. Research Blogging.
  4. Whitlock EP, Lin JS, Liles E, Beil TL, Fu R (October 2008). "Screening for Colorectal Cancer: A Targeted, Updated Systematic Review for the U.S. Preventive Services Task Force". Annals of internal medicine. PMID 18838718[e]
  5. Levin B, Lieberman DA, McFarland B, et al (May 2008). "Screening and surveillance for the early detection of colorectal cancer and adenomatous polyps, 2008: a joint guideline from the American Cancer Society, the US Multi-Society Task Force on Colorectal Cancer, and the American College of Radiology". Gastroenterology 134 (5): 1570–95. DOI:10.1053/j.gastro.2008.02.002. PMID 18384785. Research Blogging.
  6. Butterly LF, Chase MP, Pohl H, Fiarman GS (March 2006). "Prevalence of clinically important histology in small adenomas". Clinical gastroenterology and hepatology : the official clinical practice journal of the American Gastroenterological Association 4 (3): 343–8. DOI:10.1016/j.cgh.2005.12.021. PMID 16527698. Research Blogging.
  7. Pickhardt PJ, Hassan C, Laghi A, et al (January 2008). "Small and diminutive polyps detected at screening CT colonography: a decision analysis for referral to colonoscopy". AJR Am J Roentgenol 190 (1): 136–44. DOI:10.2214/AJR.07.2646. PMID 18094303. Research Blogging.
  8. Pickhardt PJ, Hassan C, Laghi A, et al (November 2008). "Clinical management of small (6- to 9-mm) polyps detected at screening CT colonography: a cost-effectiveness analysis". AJR Am J Roentgenol 191 (5): 1509–16. DOI:10.2214/AJR.08.1010. PMID 18941093. Research Blogging.
  9. Brenner DJ, Hall EJ (2007). "Computed tomography--an increasing source of radiation exposure". N Engl J Med 357: 2277–84. DOI:10.1056/NEJMra072149. PMID 18046031. Research Blogging.