CT colonography (protocol)

Last revised by Andrew Murphy on 23 Mar 2023

Computed tomographic (CT) colonography, also called CTC, virtual colonoscopy (VC) or CT pneumocolon, is a powerful minimally invasive technique for colorectal cancer screening. 

  • screening test for colorectal carcinoma
  • colon evaluation after incomplete or unsuccessful optical (conventional) colonoscopy
  • assessment of strictures
  • to better evaluate the colon proximal to obstructing neoplasms detected by conventional colonoscopy
  • patients with contraindications to or refusing conventional colonoscopy
  • patient preparation
    • for optimal image quality, the colon should be clean and completely distended
    • residual stool and fluid may lead to a false negative or false positive diagnosis
    • residual stool may be "tagged" using oral contrast agents such as Gastrografin
  • bowel distension
    • optimal colonic distention is critical to technical success for proper intraluminal evaluation of the large bowel
    • distension can be achieved via a pressure-regulated device with carbon dioxide (preferred) or room air
  • intravenous contrast
    • not necessary for colonic interpretation although it is used in some centers for better assessment of the remaining abdominal organs
    • if used, the time difference between scanning in supine and prone positions means the first acquisition may be portal venous, but the second acquisition will be a more excretory (urographic) phase
  • antispasmodic agent
    • IV/IM hyoscine-N-butylbromide (Buscopan), an antimuscarinic drug reduces colonic motion, leading to higher quality images and reduced patient discomfort
    • IV glucagon is used in some countries/institutions as a first or second-line antiperistaltic agent: its efficacy is contentious
  • CT scanning is ideally performed on a multidetector computed tomography (MDCT) scanner in both supine and prone positions with a thin collimation
  • image review with the use of two-dimensional (2D) and three-dimensional (3D) displays is strongly advised for optimal evaluation
  • CTC more difficult to perform if a colostomy is present as there is no natural sphincter mechanism to retain the gas
  • general CT contraindications e.g. pregnancy, claustrophobia, etc.
  • history of severe allergy/anaphylaxis to iodinated contrast media
  • patients at high risk for a gastrointestinal tumor (e.g. Lynch syndrome) may not be good candidates for CTC screening 7

Virtual colonoscopy has several advantages over optical colonoscopy:

  • less invasive procedure, therefore complication rate lower
  • takes less time
  • can visualize colon beyond the obstruction or narrowing
  • detects extracolonic pathology
  • residual fecal material can give rise to wrong interpretation
  • biopsy specimen cannot be taken at the time of the procedure
  • exposure to ionizing radiation

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Cases and figures

  • Case 1: normal virtual colonoscopy
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  • Case 1: 3D transparency view
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  • Case 1: 3D endoluminal (fly through)
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  • Case 2: apple-core in colon cancer
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  • Case 3: colonic diverticulosis 3D VC
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  • Case 3: colonic diverticulosis 3D endoluminal view
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  • Case 4: ulcerative colitis
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  • Case 5: polyp (pneumocystis coli)
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  • Case 6: sigmoid volvulus
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  • Case 7: hyperplastic colonic polyp
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  • Case 8: 2D CTC, mild diverticulosis
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