Colonoscopy, Virtual Colonoscopy and Flexible Sigmoidoscopy: Preparing and What Happens

Three ways to look inside the large intestine

A colonoscopy and a flexible sigmoidoscopy let a doctor see the inside of the rectum and colon (the large intestine) with a scope: a long, thin tube carrying a light and a tiny camera. They show problems such as inflamed tissue, ulcers, polyps and cancer.

Who needs one

These tests help find the cause of unexplained symptoms:

• bleeding from the anus (the opening at the end of the rectum)
• changes in bowel habits, such as diarrhea
• pain in the belly
• weight loss with no clear reason

They are also used for screening — testing people with no symptoms — for colon polyps and cancer, when disease is easier to treat. For people not at higher risk of colorectal cancer, screening usually starts at age 45; those at higher risk may need to begin earlier. Stool tests are another screening option. Ask your provider which test suits you, and when and how often to have it.

Getting ready

• Go over your health and medicines. Tell your doctor about every health problem, medicine and supplement; some may need to be stopped beforehand.
• Do the bowel prep your doctor gives you. It empties the colon so the doctor can see it:
• • a clear liquid diet, usually for about a day before — skipping red or purple drinks and gelatin, whose dye can look like blood in the colon;
  • most likely nothing to eat or drink from the night before;
  • laxatives — pills, a powder mixed into liquid, an enema, or a combination. They cause diarrhea, so stay near a bathroom.
• For a virtual colonoscopy, you also drink a contrast medium the night before: a dye or other substance that shows on x-rays and helps tell stool apart from polyps.

What happens during each test

Colonoscopy

• Done at a hospital or outpatient center; usually 30 to 60 minutes.
• You get sedatives or anesthesia through an IV, usually with pain medicine, so you are not awake and feel no pain.
• Lying on a table, you have the colonoscope passed through the anus into the rectum and colon. It fills the large intestine with air for a clearer view, and its camera sends video to a monitor.
• Once the scope reaches the opening to the small intestine, the doctor slowly withdraws it, examining the colon a second time on the way out.
• Polyps can be removed and sent to a lab. Most are not cancer, but taking them out can keep them from becoming cancer later. Abnormal tissue may be biopsied.
• The sedation takes time to wear off: expect to stay 1 to 2 hours afterward, and have someone drive you home.

Virtual colonoscopy

• Done at a hospital or outpatient center; usually about 10 to 15 minutes, with no anesthesia.
• A specially trained x-ray technician passes a thin tube through the anus into the rectum and fills the large intestine with air.
• The table slides into a tunnel-shaped scanner for the images; you turn onto your side or stomach for more.

Flexible sigmoidoscopy

• Done at a hospital, medical office or outpatient center; usually about 20 minutes, with no anesthesia.
• The doctor passes a thin scope through the anus into the rectum, fills the bowel with air, and watches the lower colon on a monitor.
• On reaching the top of the lower colon, the doctor slowly withdraws the scope, examining it again. Polyps can be removed and abnormal tissue biopsied, as in a colonoscopy.

Afterward

• Cramping or bloating is common during the first hour after any of the three tests.
• If polyps were removed or a biopsy taken, light bleeding from the anus is normal.
• After a virtual colonoscopy or sigmoidoscopy, you can return to your usual activities and diet right away. After a colonoscopy, expect a full recovery and your normal diet by the next day.
• Your doctor will give you the results; biopsy results can take a few days.

Sources

Based on "Colonoscopy," MedlinePlus, National Library of Medicine, drawing on the National Institute of Diabetes and Digestive and Kidney Diseases; a work of the United States government in the public domain.