Computed tomographic (CT) colonography

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 conventional colonoscopy
  • assessment of strictures
  • to better evaluate the colon proximal to obstructing neoplasms detected by conventional colonoscopy
  • patients with contraindications 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 although it is used in some centres
  • anti-spasmodic agent
    • IV/IM hyoscine butylbromide (Buscopan), an anti-muscarinic drug reduces colonic motion, leading to higher quality images and reduced patient discomfort
  • CT scanning is ideally performed on a multi-detector 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
  • acute inflammatory conditions such as acute diverticulitis, active stage of ulcerative colitis or Crohn disease
  • recent abdominal or pelvic surgery
  • CTC cannot be performed if a colostomy is present as there is no natural sphincter mechanism to retain the tube
  • general CT contraindications e.g. pregnancy, claustrophobia, etc
  • history of severe allergy/anaphylaxis to iodinated contrast media

Virtual colonoscopy has several advantages over conventional colonoscopy:

  • minimally invasive procedure, therefore complication rate lower
  • takes less time
  • can visualise colon beyond the obstruction or narrowing
  • detects extracolonic pathology
  • residual faecal material can give rise to wrong interpretation
  • biopsy specimen cannot be taken at the time of the procedure
  • it is a screening procedure, if there is any positive finding with virtual colonoscopy, conventional colonoscopy is required for confirmation of diagnosis
  • exposure to ionising radiation
CT examinations
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Article information

rID: 29924
Sections: Physics, Approach
Synonyms or Alternate Spellings:
  • CT colonography
  • CT pneumocolon
  • Computed tomographic colonography
  • Virtual colonoscopy (VC)
  • Virtual colonoscopy
  • CTC
  • CT colonogram

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Cases and figures

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    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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    CT colonography, ...
    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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