Gastroenterology Book


Virtual Colonoscopy

Aka: Virtual Colonoscopy, Computed Tomographic Colonography, Computed Tomographic Colonoscopy, CT Colonography
  1. See Also
    1. Virtual Endoscopy
    2. Colon Cancer Screening
  2. Epidemiology
    1. Adjusted protocol has recently improved efficacy
      1. Same Bowel Preparation as Colonoscopy
      2. CT programmed to remove artifact
        1. Barium solution (500 cc) tags solid stool
        2. Opacifying solution (120 ml) tags fluid
    2. Adjusted protocol efficacy equivalent to Colonoscopy
      1. Polyps >6 mm
        1. Test Sensitivity: 88.7%
        2. Test Specificity: 79.6%
      2. Polyps >10 mm
        1. Test Sensitivity: 93.8%
        2. Test specificty: 96%
      3. Study showed lower predictive value of CTC
        1. Positive Predictive Value if >6 mm: 46.6%
        2. Positive Predictive Value if >6 mm: 50%
        3. Cotton (2004) JAMA 291:1713-9 [PubMed]
    3. Proposed Indication
      1. Pre-screening for colonscopy in average risk patients
      2. Positive screening would result in Colonoscopy
      3. Colonoscopy would only be needed in a third of cases
    4. Causes of False Positives
      1. Residual stool
    5. Causes of False Negatives
      1. Flat lesions
      2. Polyps smaller than 10 mm
      3. Inadequate insufflation
    6. References
      1. Pickhardt (2003) N Engl J Med 349:2191-200 [PubMed]
  3. Advantages: Compared over Colonoscopy
    1. Well tolerated
    2. Minimally invasive without risk of bowel perforation
    3. No sedation required
    4. Fast procedure that images entire colon
  4. Disadvantages: Compared with Colonoscopy
    1. May not be covered by insurance
    2. Incidental findings in up to 70% of cases (but only 3% require management)
    3. Guidelines for significant polyp size not established
    4. Lesion biopsy requires another procedure (yet still requires all the Bowel Preparation)
    5. Radiation Exposure (equal to 70 plain Chest XRay films)
    6. Recommended every 5 years (instead of 10 years for Colonoscopy)
  5. References
    1. Fenlon (1999) N Engl J Med 341:1496-503 [PubMed]
    2. Wood (2002) Am Fam Physician 66(1):107-12 [PubMed]

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