Virtual Colonoscopy is a promising new method for detecting colorectal polyps and cancers. Air is insufflated into a cleansed colon, and high resolution, thinly-collimated spiral CT slices are acquired. The two dimensional slices, as well as the post-processed "fly-through" virtual colonoscopic images, are examined for polyps and tumors. Research performed at Boston University and elsewhere has shown that Virtual Colonoscopy is better able to see polyps than Barium Enema and is nearly as accurate as Conventional Colonoscopy. In addition, most patients report that the Virtual Colonoscopy technique is more comfortable than either Barium Enema or Conventional Colonoscopy.

Studies suggest a very high sensitivity and specificity (96%) for the detection of polyps 1 cm or greater. Such polyps have significant malignant potential. Sensitivity for polyps less than 10 mm is significantly less. Although controversy exists as to the definition of a "significant" polyp with regard to size, polyps < 1 cm in size have a low probability of malignancy and the likelihood of any single lesion progressing to cancer is also small. Many leading authorities have suggested that a policy aimed at identifying and removing only polyps above a threshold size, as opposed to universal polypectomy, could result in a similar benefit in terms of mortality reduction, but at a lower risk and cost.

Data suggests that the Virtual Colonoscopic Exam is significantly more sensitive and less operator-dependent than the Barium Enema. In the only direct comparison to date, Virtual Colonoscopy proved more sensitive than Single Contrast Barium Enema for polyp detection. Our data at Boston Medical Center also suggests that Virtual Colonoscopy is likely to be superior to Double Contrast Barium Enema, which has a reported sensitivity in the range of 65% to 75% for detecting polyps > 7 mm.

Virtual Colonoscopy is minimally invasive, and does not carry the low but real (1 in 1500) risk of perforation associated with Conventional Colonoscopy. It is well tolerated by patients and does not require sedation. It is capable of evaluating the colon upstream from obstructing lesions that prevent passage of an endoscope. Virtual Colonoscopy is significantly less expensive than Conventional Colonoscopy.

The dose of ionizing radiation is less than that of a conventional abdominal CT, and is comparable to obtaining a supine and upright plain film exam of the abdomen. Virtual Colonoscopy by CT does not provide the same information as Conventional Colonoscopy. Mucosal detail and color is not visible which limits the characterization of lesions.

In addition, the detection of small polyps is inferior. As with any procedure, including Conventional Colonoscopy, there are no guarantees that all clinically significant growths will be detected. It should be remembered than between 10 and 20% of all polyps, and up to 5% of colon cancers are missed, even on Conventional Colonoscopy. Virtual Colonoscopy (like the Barium Enema) is a diagnostic not therapeutic technique. All patients in whom polyps are identified would need to undergo Conventional Colonoscopy for removal.

The prep consists of a 48 hour liquid diet, two 8 oz doses of magnesium citrate, and Fleet Prep 3, an "over-the-counter" kit containing bisacodyl and phosphasoda.

Virtual Colonoscopy may become a screening tool for detecting colorectal neoplasia, potentially supplanting Conventional Colonoscopy as a tool for detecting lesions. Increased screening, with increased detection, should decrease the incidence of colorectal cancer, as premalignant growths can be found at an earlier stage. Conventional Colonoscopy could then be reserved as a tool for polyp removal.