VIRTUAL COLONOSCOPY
Virtual colonoscopy: provides a computer-simulated image of the air-filled distended colon.
The technique uses conventional CT scan or magnetic resonance images (MRI) acquired as
an uninterrupted volume of data, and employs sophisticated post processing software to
generate images which allow the operator to fly-through and navigate a cleansed colon in any
chosen direction

The exact clinical utility and role of virtual colonoscopy and associated CT colographic
techniques is still being determined. It may be a reasonable option in certain clinical settings
including those in whom a colonoscopy cannot be performed due to  technical difficulty,
obstructing Colo-rectal cancer, or other risk factors for the procedure (including cardiac and
pulmonary disorders (making them poor candidates for sedation).

However, there remain a number of issues regarding its role in Colo-rectal cancer
screening. Conventional endoscopic colonoscopy is currently the gold standard for
detecting colon polyps and cancer. AGA and ACG recommend conventional
colonoscopy over virtual colonoscopy for colo-rectal cancer screening. However
with new information available, the recommendations may change in the future.

Disadvantages of Virtual colonoscopy as a routine test:

  • Local expertise in performing and interpreting virtual colonoscopy may be important.
    Sensitivity has been variable in different reports.
  • The methods of performing and interpreting virtual colonoscopy have not been
    standardized.
  • Effectiveness as a screening tool has not yet been demonstrated.
  • The size of a polyp found on virtual colonoscopy that should prompt an optical
    colonoscopy is unclear.
  • Furthermore, systems to allow patients to go directly from virtual colonoscopy to optical
    colonoscopy (if needed) may be difficult to coordinate.
  • Thus, a significant proportion of patients who have a positive virtual colonoscopy may
    have to undergo two bowel preparations and two procedures.
  • Even worse, some patients found to have a polyp on virtual colonoscopy may not follow-
    up with their standard colonoscopy.
  • Virtual colonoscopy has the potential to uncover unexpected findings outside of the
    colon (because it also gives complete image of CT abdomen) potentially leading to
    serendipitous discovery of important diseases or unnecessary evaluation of incidental
    findings. The net effect is unclear.
  • Virtual colonoscopy exposes patients to radiation. Repeated examination might lead to
    substantial cumulative radiation exposure with associated risk of excess cancer
    mortality.
  • Furthermore, the sensitivity and specificity of optical colonoscopy (currently considered
    the gold standard) is not remaining static. Newer imaging techniques (such as
    magnification colonoscopy and chromo-endoscopy) continue to evolve suggesting that
    optical colonoscopy will likely remain superior for detecting neoplastic lesions.
  • On the other hand, virtual colonoscopy offers the possibility of increasing Colo-rectal
    cancer screening (and possibly reducing its costs) suggesting that it holds promise for
    reducing the incidence of Colo-rectal cancer.
  • Virtual colonoscopy is definitely useful in select population who have co-morbid cardio-
    pulmonary disorders with sedation difficulties, incomplete colonoscopy due to technical
    difficulties, obstructing colonic cancer etc.