16 MARCH 2018

Colonoscopy: Common Questions about Colonoscopic Screening


Why a scope?

Colorectal cancer is one of the most preventable cancers. Dr Dennis Koh, Medical Director and Colorectal Surgeon at the Colorectal Practice, answers some common questions about colonoscopic screening.

What is a colonoscopy?

Colonoscopy is a procedure to examine the colon and rectum. A thin, flexible tube with a camera – called an endoscope – is inserted through the anus and through the rectum and colon. This allows doctors to check these parts of the body for any polyp that may develop into cancer. Polyps can be removed on the spot and checked to see if they are malignant.

Why is it so important?

A colonoscopy is the key to detecting colorectal cancer as early as possible, and even preventing it. Studies have shown that regular colonoscopy can prevent colon cancer by as much as 90 per cent.

How does a colonoscopy prevent cancer?

Most cases of colon cancer (95 per cent) grow from adenocarcinoma or polyps, which are growths on the inner surface of the colon. Polyps are usually benign (non-cancerous), but some can develop into cancer. This generally takes 5 to 10 years. Thus, removing polyps does not give them a chance to grow into cancer. If colon cancer has already developed, then a colonoscopy allows it to be diagnosed and treated at an earlier stage, giving a better chance of recovery.

Why and how do polyps form? Are there symptoms?

No one really knows how or why polyps form. They usually result from changes in the cells of the colon. This could be due to chemical interactions, perhaps from the food we eat. Today, we eat more processed food. But unless you grow your own plants and rear your own animals, it is very hard to avoid. Polyps in the colon usually show no symptoms as they grow.

How often should I go for a colonoscopy? When should I start?

It depends on individuals and their risks. If you have no symptoms of colon cancer, you should start colonoscopic screening at the age of 50, and do one every five years. If you have a higher risk, such as a history of family members with colorectal cancer, or detect any symptoms (see box), you should start earlier and get screening more frequently. Consult your doctor to see when you should start and how often you should get a colonoscopy.

If a polyp is found, does it mean I have cancer?

Most of the time, no. A polyp indicates cell changes in your colon, but it is not necessarily malignant. This is sometimes referred to as Stage 0. Most of the time, polyps are not found to be cancerous. In the rare case that a polyp is found to be malignant, doctors will remove part of the colon. Nowadays, this is generally done through a keyhole operation, if possible. This allows for faster recovery, as the wound is smaller.

What if the polyp is very big? Will I need to undergo surgery?

I have removed polyps as big as 4-5 cm through colonoscopy. They were still benign. If I am treated for colon cancer, what are the chances of it recurring? This depends on the stage at which the cancer was detected and treated. The earlier it is detected, the higher the chance of a full recovery.

Stage 1: Chances of a full recovery: 90 to 95 per cent

Stage 2: 80 per cent

Stage 3: 40 to 60 per cent. With surgery and chemotherapy, 80 per cent

Stage 4: Very low, less than 5 per cent You can avoid reaching a later stage of cancer through regular screening.

What does colonoscopy involve?

Before you go for a colonoscopy, your bowels need to be cleansed of stools and waste material so that they will not affect visual examination of the colon. Three days before the procedure, you will usually be advised not to take any fibre (fruits and vegetables). If the colonoscopy is being done in the morning, you will be given a special cleansing solution or laxatives the night before. If it is being done in the afternoon, you will take the laxatives in the morning. The procedure itself is done under sedation.

Will it hurt?

Not at all. The entire procedure is done under sedation: You will be given an intravenous injection to sleep throughout the procedure, and wake up after it is completed. The only discomfort you may feel is the night before, when you take the laxatives. But some patients actually like this part! They have told me that it makes them feel very clean, like a detox.

How about after?

You will usually not feel any discomfort after a colonoscopy. Some patients may feel some bloatedness in their abdomen because of residual air in the intestines, but this usually clears with the passage of flatus. You will be discharged after the procedure, but it might be a good idea to have someone accompany you home because of the sedation.

When will I know the results?

You will usually get the results and findings of the colonoscopic evaluation on the same day. If a polyp is found, it will be removed immediately and sent for histological testing. A biopsy may also be done to obtain tissue for testing. The results of such testing will come later.

Are there any risks?

Any procedure involves risks, but the risks in colonoscopy are very low. One of the two main risks is post-polypectomy bleeding, which can take place 7 to 10 days later. The incidence is very low (0.1 to 0.6 per cent) and it can be easily treated. The other risk is perforation during colonoscopy. This is also very rare (less than 0.1 per cent), but will require surgery if it happens. The risks are much lower when colonoscopy is done by experienced and skilled endoscopists.

If I really do not want to do a colonoscopy, are there alternatives?

Yes. You can do a barium enema or Computer Tomography (CT) colonography. They are considered less invasive, but they also carry a risk of perforation. There are some disadvantages – you will be exposed to X-rays, and any polyps found cannot be removed on the spot. There is also a greater risk of missing polyps. The gold standard test is still the colonoscopy.

Colon cancer: What to look out for

  • Bleeding in the rectum
  • Change in bowel habits
  • Long, thin stools
  • Unexplained weight loss
  • Unexplained low red blood cell count
  • Pain in abdomen
  • Feeling of bloatedness in abdomen
  • Persistent tiredness

  Written by Kok Bee Eng

POSTED IN Cancer Prevention
TAGS cancerous polyps, colonoscopy, prevent cancer
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