Gastroenterology Book

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Virtual ColonoscopyAka: Computed Tomographic Colonography, Computed Tomographic Colonoscopy, CT Colonography

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  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. Recent 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
    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
  3. Advantages 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. Currently only experimental (not reimbursed)
    2. Guidelines for significant polyp size not established
    3. Lesion biopsy requires another procedure
    4. Radiation Exposure (equal to 2 plain abdominal films)
  5. References
    1. Fenlon (1999) N Engl J Med 341:1496
    2. Wood (2002) Am Fam Physician 66(1):107

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