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Sigmoidoscopy is also called a proctosigmoidoscopy or rectosigmoidoscopy. It is a procedure that lets the doctor look at the lining of the sigmoid colon (the last part of the colon) and the rectum. It is done using a sigmoidoscope, which is a type of endoscope (a thin, tube-like instrument with a light and lens).
The sigmoidoscope can be flexible, which means that it bends. It can also be rigid, which means that it is straight and stiff. A flexible sigmoidoscope is used more often than a rigid sigmoidoscope.
Why sigmoidoscopy is done
A sigmoidoscopy may be done to:
- screen for colorectal cancer in people who have a high risk of developing the disease
- find out what is causing changes in bowel habits, bleeding from the rectum, blood in the stool or pain in the abdomen
- look closely at polyps or other growths found during another test (such as a barium enema)
- help diagnose colorectal cancer
- measure how far a rectal tumour is from the anus (for accurate staging)
- find out if cancer has spread to the rectum or anus
- follow up after treatment for rectal cancer
How sigmoidoscopy is done
A sigmoidoscopy is usually done in a doctor’s office. It takes about 20 minutes. Medicines for sedation are not usually needed for a sigmoidoscopy.
The sigmoid colon and rectum need to be clean and empty before the test. You will be given special instructions on how to flush out the colon using laxatives, an enema or both. You may also be told to have only clear fluids before the test. Some people need to stop taking certain medicines before a sigmoidoscopy.
You will need to take off your clothes and may be given a gown to wear during the test. You will probably be asked to lie on your left side and bend your knees.
Before the sigmoidoscopy, the doctor checks if anything is blocking the rectum by inserting a gloved finger with lubricant into the anus and rectum (called a digital rectal exam, or DRE).
After the DRE, the doctor puts the sigmoidoscope into the anus and slowly passes it through the rectum and sigmoid colon. Air is pumped into the colon to stretch the lining so the doctor can see the entire surface. Having air pumped into the colon can make you feel some discomfort and pressure. It is normal to feel like you need to pass gas.
The doctor may pass small tools through the sigmoidoscope to collect a biopsy sample, remove polyps (called polypectomy) and stop bleeding. Biopsy samples and polyps are sent to a lab for more testing.
Once the doctor has seen the entire sigmoid colon and rectum, the sigmoidoscope is slowly removed. Most people can go home right after the test and resume their normal diet and activities.
The side effects of a sigmoidoscopy are temporary. They include:
- discomfort in the lower abdomen
- bloating or cramping
- bleeding from the rectum
In rare cases, a sigmoidoscopy can make a hole or tear in the colon (called bowel perforation). This is a more serious side effect of the test. If it happens, you may need surgery to repair it.
What the results mean
Any biopsy samples taken and polyps removed are sent to a lab to check for cancer. An abnormal result may mean:
- non-cancerous polyps, hemorrhoids, diverticulosis or diverticulitis
- an inflammatory bowel disease (IBD) such as ulcerative colitis
- a precancerous condition such as adenomas or dysplasia
- colorectal cancer
- cancer that has spread to the rectum from another part of the body such as the vagina or prostate
What happens if a change or abnormality is found
Your doctor will decide if you need more tests, procedures or treatment or other follow-up care.
If polyps are found, you may be sent for a colonoscopy to check if there are more polyps in the rest of the colon. Find out more about colonoscopy.
Special considerations for children
Preparing children before a test or procedure can lower anxiety, increase cooperation and help them develop coping skills. Preparation includes explaining what will happen during the test, including what they will see, feel and hear.
The preparation for a sigmoidoscopy depends on the age and experience of the child. Find out more about helping children cope with tests and treatment.