Test Overview

Anoscopy, proctoscopy, and sigmoidoscopy tests allow your doctor to look at the inner lining of your anus, rectum, and the lower part of the large intestine (colon). These tests are used to look for abnormal growths (such as tumors or polyps), inflammation, bleeding, hemorrhoids, and other conditions (such as diverticulosis).

These tests use different scopes look at different sections of the colon.

• Anoscopy. During an anoscopy, a short, rigid, hollow tube (anoscope) that may contain a light source is used to look at the last 2 in. (5 cm) of the colon (anal canal). Anoscopy can usually be done at any time because it does not require any special preparation (enemas or laxatives) to empty the colon.
• Proctoscopy. During a proctoscopy, a slightly longer instrument than the anoscope is used to view the inside of the rectum. You will usually have to use enemas or laxatives to empty the colon before the test is done.
• Sigmoidoscopy. During a sigmoidoscopy, a lighted tube that may be either rigid or flexible is inserted through the anus. Your doctor can remove small growths and collect tissue samples (biopsy) through a sigmoidoscope. You will have to use enemas or laxatives (or both) to empty the colon before the test is done.
  • The flexible sigmoidoscope is about 2.3 ft (70 cm) long and 0.5 in. (1 cm) wide with a lighted lens system. This instrument allows your doctor to see around bends in the colon. A flexible sigmoidoscope allows a more complete view of the lower colon than a rigid scope and usually makes the examination more comfortable. The flexible sigmoidoscope generally has replaced the rigid sigmoidoscope.
  • The rigid sigmoidoscope is used less often. It is about 10 in. (25 cm) to 12 in. (32 cm) long and 1 in. (2.5 cm) wide. It allows your doctor to look into the rectum and the bottom part of the colon, but it does not reach as far into the colon as the flexible sigmoidoscope.

Flexible sigmoidoscopy is one of many tests that may be used to screen for colon cancer. Which screening test you choose depends on your risk, your preference, and your doctor. Talk to your doctor about what puts you at risk and what test is best for you.

For more information on screening tests for colon cancer, see:

Colon Cancer: Which Screening Test Should I Have?