CT colonography provides a computer-simulated endoluminal perspective of the air-filled distended colon. The technique uses conventional spiral or helical CT scan images acquired as an uninterrupted volume of data and employs sophisticated post-processing software to generate images that allow the operator to evaluate a cleansed colon in any chosen direction. 

CT colonography is an option for colorectal cancer (CRC) screening in asymptomatic average-risk individuals over the age of 50 years. Other indications for CT colonography include the evaluation of the proximal colon in patients with an obstructing CRC or evaluation of signs or symptoms of CRC in whom a colonoscopy cannot be performed due to intolerance, technical difficulty, or in whom a colonoscopy is contraindicated. (See ‘Indications’ above.)

Relative contraindications to CT colonography include the following:

•Active colonic inflammation (eg, acute diarrhea, active inflammatory bowel disease)

•Symptomatic colon-containing abdominal wall hernia

•Recent acute diverticulitis

•Recent colorectal surgery

•Recent deep endoscopic biopsy/polypectomy/mucosectomy

•Known or suspected colonic perforation

•Symptomatic or high-grade small bowel obstruction

Patient preparation consists of dietary restriction with a low-residue diet and clear liquids for 24 hours or more and bowel preparation with a laxative.

The available data suggest that CT colonography provides a similarly sensitive, less invasive alternative to colonoscopy in patients presenting with symptoms suggestive of CRC. CT colonography may be particularly valuable in patients with an obstructing CRC with the ability to tolerate a bowel preparation. In one study, performing a CT colonography led to a change in the surgical plan because of the presence of synchronous tumors in 1.4 percent of cases [59]. However, given that colonoscopy permits removal/biopsy of the lesion and any synchronous cancers or polyps that are seen during the same procedure, in our view, colonoscopy remains the gold standard for investigation of symptoms suggestive of CRC. CT colonography is preferred over barium enema where access to colonoscopy is limited.

(ref. UpToDate)