A colonoscopy is a screening test that allows doctors to examine the inside of the colon and rectum. During a colonoscopy, a long, flexible tube called a colonoscope is inserted into the rectum. A tiny video camera at the tip of the tube allows the doctor to view the inside of the entire colon.
Colonoscopies are commonly used to screen for colorectal cancer, which is cancer of the colon or rectum. Colorectal cancer usually develops from growths called polyps that form in the colon and rectum. During a colonoscopy, doctors can find and remove polyps before they become cancerous. Removing polyps early is one of the best ways to prevent colorectal cancer.
Colorectal Cancer
Colorectal cancer begins in either the colon or the rectum. These two parts together make up the large intestine, which plays an important role in the body’s ability to process waste.
The colon makes up the largest portion of the large intestine. It is a muscular tube about 5 feet long. The colon absorbs water and nutrients from food matter and serves as a storage place for waste matter.
The rectum is the final 6 inches of the digestive system. It serves as a holding area for waste matter before it passes out of the body through the anus.
Colorectal cancer usually develops slowly over a period of several years. Most often, it starts as a growth called a polyp inside the colon or rectum. A polyp is a mass of cells that forms on the lining of the colon or rectum. Most polyps are harmless. However, some can turn cancerous over time.
Screening tests like colonoscopies can find polyps so they can be removed before becoming cancerous. If colorectal cancer does develop, it can often be treated more easily if caught at an early stage through screening.
Risk Factors
Several factors can increase a person’s risk of developing colorectal cancer:
- Age – Risk increases after age 50
- Family history of colorectal cancer or polyps
- Personal history of colorectal cancer or polyps
- Inflammatory bowel diseases like Crohn’s disease or ulcerative colitis
- Lifestyle factors like smoking, heavy alcohol use, lack of exercise, obesity, and red meat consumption
- Type 2 diabetes
Symptoms
Early stage colorectal cancer often has no symptoms. This highlights the importance of screening tests. By the time symptoms develop, the cancer may be more advanced.
Possible signs and symptoms of colorectal cancer include:
- Changes in bowel habits, such as constipation or diarrhea
- Stools that are narrower than usual
- Bright red or dark blood in the stool
- Persistent abdominal discomfort like cramps, gas, or pain
- A feeling that the bowel doesn’t empty completely
- Weakness or fatigue
- Unexplained weight loss
These symptoms can also be caused by conditions other than cancer. Still, it’s important to let your doctor know if you have any persistent changes in bowel habits, blood in your stool, or abdominal pain.
How a Colonoscopy Detects Colorectal Cancer
Doctors recommend regular screening for colorectal cancer starting around age 50 for people at average risk. Screening can detect colon polyps or colorectal cancer at an early stage when treatment is most effective.
A colonoscopy is one of several screening tests available. It is considered the “gold standard” because of its ability to view the entire colon and to remove polyps during the same procedure.
Preparing for a Colonoscopy
Proper cleansing of the colon is necessary for doctors to get a clear view during a colonoscopy. Your doctor will provide preparation instructions to follow at home, which will likely include:
- Avoiding certain foods and drinks beforehand
- Taking laxatives or enemas the day before
- Drinking only clear liquids leading up to the procedure
- Fasting after midnight before the colonoscopy
You will also need to arrange for a ride home after the procedure since anesthesia is used to sedate you.
What to Expect During the Procedure
During the colonoscopy, you will lie on your side on an exam table. Sedation is given through an IV to make you relaxed and comfortable:
- You will likely fall asleep and not remember the procedure
- Medications also relax the muscles in the colon to allow for an easier examination
- The doctor carefully inserts a lubricated colonoscope into the rectum and slowly guides it through the colon
- Air is pumped through the scope to inflate the colon for better viewing
- The scope transmits images to a video screen so the doctor can closely examine the intestinal lining
- You may feel mild cramping from the air or movement of the scope
- The procedure itself usually takes 15-30 minutes
Removing Polyps to Prevent Cancer
If the doctor sees any polyps during the colonoscopy, specialized instruments can be passed through the scope to painlessly remove them. The samples are sent to a lab for testing. Colon polyps can be:
- Hyperplastic polyps – Typically harmless with little risk of becoming cancer
- Adenomatous polyps – Can become cancerous over time; removing prevents progression
- Sessile serrated polyps – Slow growing but with high cancer risk if allowed to remain
Removing polyps interrupts the process that could lead to cancer down the road. You won’t feel it when a polyp is removed since the colon lacks pain-sensing nerves.
Taking Biopsy Samples
During the colonoscopy, the doctor may also take biopsy samples:
- Small samples of tissue can be collected through the colonoscope
- If any abnormalities are seen, a biopsy determines if cancer is present
- Biopsies don’t hurt and don’t cause bleeding
- Removed tissue gets examined under a microscope
Biopsies confirming cancer help determine appropriate treatment. Catching cancer early leads to better outcomes.
Other Cancers Besides Colorectal Cancer
While checking for colorectal cancer is the main purpose of a colonoscopy, it may also detect cancers originating elsewhere that spread to the colon and rectum. This includes cancers that started in the:
- Stomach
- Pancreas
- Uterus
- Ovaries
- Prostate
For example, ovarian cancer sometimes spreads to the surface of the colon or rectum. A colonoscopy and biopsy could make the initial diagnosis.
Also, the colonoscope can be inserted a short distance into the lower end of the small intestine. This allows the doctor to examine that area and potentially detect cancers like small bowel cancer.
Conclusion
Colonoscopies allow doctors to find colorectal cancer at its earliest and most treatable stage. They are the most effective screening method because of the ability to view the entire colon and to remove precancerous polyps during the procedure.
Regular colon cancer screening beginning at age 50 saves lives. Colonoscopies every 10 years are the recommended screening method for most people at average risk.
Talk to your doctor about what colorectal cancer screening tests make sense for your individual health profile and family history.