An examination of the large intestine (see Diagram — Anatomy of the Gastrointestinal System). A tube is inserted through the anus and threaded all the way up the bowel to the cecum. Pictures can be taken of abnormalities, biopsies can be obtained, and polyps removed (see below).
The exam takes about 20 minutes, and is usually done under I.V. sedation with pain control (not general anesthesia) (and patients can forgo the pain control if they’d prefer). The hardest part is the day before, when you have to not eat, only drink clear liquids, and take some sort of medication to provoke diarrhea & clean the bowel (every gastroenterologist has their own favorite). This is really important, or it will be hard to see what needs to be seen.
The main reasons for performing a colonoscopy include:
- Screening for colon cancer in people over 50, or those with certain diseases or family history of early colon cancer.
- Diagnosing and treating rectal bleeding
- Diagnosing chronic diarrhea, abdominal pain, weight loss, or certain other symptoms
As with everything medical, there are certain risks. For colonoscopy, the most serious ones are bleeding or bowel perforation. They occur in about 1 in 400 exams, usually during polyp removal. Risk of death is about 1 in 10,000, which is the same as for a woman dying in pregnancy in the U.S. (this is a degree of risk that we all assume without thinking twice). All risks are higher in older and sicker people than in younger, healthier ones.
Routine screening colonoscopies do more than just look for cancer, they actually prevent it. The large majority of cancers begin in certain common types of polyps. So if these are removed, nothing can happen. Of course, as with all tests, there’s also a risk of missing polyps or even cancer. Nothing’s perfect.
A sigmoidoscopy is a quicker, easier test, but only examines a third to one half of the bowel. The day-before preparation is the same. It’s not as uncomfortable, so sedation isn’t used to avoid that cost and small risk, which makes it more uncomfortable. There’s also a “Virtual Colonoscopy,” done by special CT Scan, but it requires the same bowel prep. And if it’s abnormal, a regular colonoscopy is needed afterwards. The “Virtual” test never made much sense to me.
Screening for colon cancer is perhaps the most important routine preventive exam that we do. Blood tests for prostate cancer & even mammograms for breast cancer are controversial. But since colon cancer grows slowly, screening for it certainly saves lives.