Colonoscopy, Sigmoidoscopy, and Other Techniques Used to Visualize the Colon. If a digital rectal examination or occult blood tests show signs of trouble, several methods to visualize the colon are available, including sigmoidoscopy, colonoscopy, or a double-contrast barium enema. Sigmoidoscopy can only view the rectum and the left side of the colon, while colonoscopy and barium enemas allow a view of the entire large intestine. Both flexible sigmoidoscopy and colonoscopy involve snaking a fiberoptic tube through regions of the rectum and colon to view the walls of the intestine. During either procedure, the physician is able to remove polyps or other abnormalities revealed by these procedures.
Sigmoidoscopy involves the rectum and the lower two feet of the colon.
It lasts about 10 minutes and may be mildly uncomfortable, but it is not painful. Either colonoscopy or a barium enema allows a view of the rectum and the entire colon. In colonoscopy, air may be introduced to widen the intestine and allow the tube to navigate curves. The procedure requires a sedative, although it is still performed on an outpatient bases. A colonoscopy also avoids the risk of radiation, although it should be noted that even a colonoscopy does not detect all cancers.