Before having a sigmoidoscopy the colon must be clear of stool so that the doctor has good visibility. The patient must undergo a preparation that may include a liquid diet, enema, and laxatives to clear stool from the colon. The technique for bowel preparation may differ by health facility. A colonoscopy is an examination of the rectum and the entire colon. It is performed with a lighted, flexible, hollow tube, which is slightly larger in diameter than an enema tube.
Colonoscopy permits the doctor to see much farther into the bowel than sigmoidoscopy.
The colonoscope allows the doctor to see whether polyps or cancer are present. A biopsy forceps may be inserted through a channel in the colonoscope to remove a small sample of tissue for microscopic examination. Sometimes it is necessary for the doctor to introduce air into the colon to improve visibility. Before having a colonoscopy the colon must be clear of stool so that the doctor has good visibility. The patient must undergo a preparation that may include a liquid diet, enema, and laxatives to clear stool from the colon.