**3.5 Computed tomographic Colonography (CTC)**

CTC uses multiple thin slice computed tomographic data to construct images of the bowel mucosa in two or three dimensions in detecting polyps. It requires bowel preparation similar to conventional colonoscopy and during the procedure, air or carbon dioxide is introduced into the rectum via a rubber catheter. No sedation is required and patient is usually able to return to work post procedure.

Estimated sensitivities for patients with polyps or adenomas ≥6 mm were 75.9% (95% CI 62.3–85.8) and 82.9% (95% CI 73.6–89.4), with corresponding specificities 94.6% (95% CI 90.4–97.0) and 91.4% (95% CI 84.1–95.5) respectively. On the other hand, estimated sensitivities for patients with polyps or adenomas ≥10 mm were 83.3% (95% CI 76.8–89.0) and 87.9% (95% CI 82.1–92.0), with corresponding specificities 98.7% (95% CI 97.6–99.3) and 97.6% (95% CI 95.0–98.9) respectively [19].

The major drawbacks of CTC are that it is non-therapeutic, with the need for colonoscopy after the identification of polyps for excision and tissue diagnosis. Other reasons include argument for radiation exposure, presence of flat adenomas that are more likely to be missed by CTC than colonoscopy, and issues of incidental extra-colonic pathological findings that may arise [19, 20].
