They generally begin with the formation of a single polyp. Since polyps come in different varieties, some may be precursors to cancer. However, polyps can be easily detected and removed during a screening called a colonoscopy.
A colonoscopy is an outpatient procedure that either a gastroenterologist or colorectal surgeon performs to evaluate the colon for polyps or cancer. Colonoscopies can also be used to evaluate blood in the stool, anemia, abdominal pain, diarrhea or other changes in bowel habits. A colonoscopy begins with sedating the patient and making him or her as comfortable as possible. A long, flexible tube with a fiberoptic camera at its tip is inserted into the rectum so the entire colon can be viewed. The scope bends as it is gently pushed through the colon to the point where it meets the small intestine. The camera transmits an image to a computer screen allowing the doctor to closely examine the intestinal lining. If polyps are found, they are removed through the scope and sent to the laboratory for diagnosis. The doctor may also remove tissue for a biopsy if any other abnormalities are discovered. The procedure usually lasts 30 minutes and is rarely painful.
In order for the doctor to view the colon without obstruction, the colon needs to be emptied. A patient prepares for the screening by drinking a special liquid preparation and only clear liquids the day before. Pre-colonoscopy preparations may vary but your doctor will give you full instructions before the procedure. It is important to follow all instructions carefully.
Most doctors who treat colorectal cancer recommend that patients who are at average risk for colon cancer should have a screening colonoscopy beginning around age 50. Some people may need screenings earlier if they have risk factors such as family history of colorectal cancer or inflammatory bowel disease. The screening colonoscopy should be repeated every five to 10 years. It may need to be repeated sooner if polyps or cancer are found.
Patients who undergo a colonoscopy need to take the day off from work and will need a ride home since they are sedated for the procedure. Before discharge, your physician or nurse will give you the necessary post-test instructions.
The screening colonoscopy is usually covered by insurance.
Virtual colonoscopy is a relatively new procedure that may be very useful in the future. It requires the same bowel preparaton the day before as a traditional colonoscopy, but no sedation is used during the procedure. Air is blown into the colon through a small tube placed in the rectum. CT scan-like pictures are then taken. Polyps can be seen but cannot be removed during virtual colonoscopy. A traditional colonoscopy is still required for polyp removal. Another drawback of virtual colonoscopy is that it's diffult to determine if the polyps can be safely watched or need to be removed.
The virtual colonoscopy readily available today is two-dimensional and not as sensitive as traditional colonoscopy. The new three-dimensional scans are not yet widely available. At present, two-dimensional virtual colonoscopy is not covered by insurance, and traditional colonoscopy is still recommended.
In the future, virtual colonoscopy that employs three-dimensional imaging and other advanced features may be comparable to traditional colonoscopy.