Indications for Virtual Colonoscopy

Indications for virtual colonoscopy include screening for polyps, incomplete or failed colonoscopy and preoperative assessment of the colon proximal to an occlusive cancer (defined as a tumor that cannot be traversed endoscopically).

Virtual colonoscopy excels in the evaluation of the ascending colon, particularly the cecum due to the degree of distension achievable and the typical lack of spasm or muscular hypertrophy which is seen in the sigmoid colon. It is therefore a useful complement to an incomplete colonoscopy.

Polyp detection
Preliminary results indicate that the accuracy of CT virtual colonoscopy for polyp detection approaches conventional colonoscopy. Recent published studies from Boston Medical Center (BMC) the Mayo clinic and the University of California in San Francisco reported results on relatively large patient populations.

Occlusive cancer
Another application of virtual colonoscopy, is the preoperative assessment of the colon proximal to an occlusive cancer (defined as a tumor that cannot be traversed endoscopically) was recently reported by Fenlon et al from Boston Medical Center. In 29 patients with occlusive carcinomas, virtual colonoscopy identified all 29 occlusive cancers and demonstrated two cancers and 24 polyps in the proximal colon. Both of the synchronous cancers were confirmed intraoperatively and resected. Virtual colonoscopy successfully demonstrated the proximal colon in 26 of 29 patients studied compared with preoperative barium enema which failed to adequately demonstrate the proximal colon in any patient studied.

Incomplete colonoscopy
Colonoscopy fails to visualize the cecum in a significant number of patients, the completion rate may be 80-90% or less. Thiis-Evensen et al. (Gut. 1999 Dec;45(6):834-9.) published their findings in a total of 241 men and women randomly selected from the population register who were offered a colonoscopic screening examination to detect and remove polyps. The cecum was intubated in only 193(80%) of patients. In such patients Virtual Colonoscopy is ideally performed on the same day as the colon is already cleansed and usually partially distended with air. Transferral to the CT suite immediately after sedation wears off is now a standard procedure at Boston Medical Center and many othe academic institutions in the United States.

Frail, Elderly Patients
Aged, infirmed patients who require examination of colon are more easily examined by Virtual Colonoscopy than by conventional colonoscopy or barium enema with high diagnostic accuracy for pathology that would be relevant in this age group.

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