Physicians may use the procedure to find the cause of diarrhea, abdominal pain, or constipation. They also use it to look for early signs of cancer in the descending colon and rectum. With flexible sigmoidoscopy, the physician can see bleeding, inflammation, abnormal growths, and ulcers in the descending colon and rectum. Flexible sigmoidoscopy is not sufficient to detect polyps or cancer in the ascending or transverse colon (the first two-thirds of the colon).
For the procedure, you will lie on your left side on the examining table. The physician will insert a short, flexible, lighted tube into your rectum and slowly guide it into your colon. The tube is called a sigmoidoscope (sig-MOY-duh-skope). The scope transmits an image of the inside of the rectum and colon, so the physician can carefully examine the lining of these organs. The scope also blows air into these organs, which inflates them and helps the physician see well.
If anything unusual is in your rectum or colon, like a polyp or inflamed tissue, the physician can remove a piece of it using instruments inserted into the scope. The physician will send that piece of tissue (biopsy) to the lab for testing.
Bleeding and puncture of the colon are possible complications of sigmoidoscopy. However, such complications are uncommon.
Flexible sigmoidoscopy takes 10 to 20 minutes. During the procedure, you might feel pressure and slight cramping in your lower abdomen. You will feel better afterward when the air leaves your colon.
The colon and rectum must be completely empty for flexible sigmoidoscopy to be thorough and safe, so the physician will probably tell you to drink only clear liquids for 12 to 24 hours beforehand. The night before or right before the procedure, you may also be given an enema, which is a liquid solution that washes out the intestines. Your physician may give you other special instructions.