Exams and Preps > CT Scan > CT Virtual Colonoscopy

This is a non-invasive method of screening for colonrectal cancer. It is available at the Silverdale location.

Colonoscopy vs. CT Colonography
(aka Virtual Colonoscopy)
By Dr. Johnny B. Green, MD, FACS
Dr. Mike Cook, MD

Colorectal cancer is now the second leading cause of cancer deaths in both men and women in America. Over 90 percent of colon cancers start as polyps. Finding and removing colon polyps stops the development of colon cancer. Recent studies have shown that colorectal cancer screening with colonoscopy reduces the rate of developing colorectal cancer and the risk of dying from colorectal cancer.

While colonoscopy is effective in screening for colorectal cancer it is expensive and inconvenient. Depending on the patient group studied, up to 70 percent of patients have a normal colon and could have been screened by a less invasive method. One promising new non-invasive method of identifying polyps is computed (CT) colonography, also called virtual colonoscopy. While colonoscopy is a direct examination of the lining of the colon with a video camera at the end of the colonoscope, CT colonography is a high-resolution x-ray picture of the lining of the colon. The picture is presented in high definition gray scale on the computer monitor for viewing by the radiologist. It would probably be best to consider this test like a faster and easier barium enema.

Both studies require a bowel preparation to remove stool from the colon. In both studies air is inserted into the colon. For colonography the air is important since the density difference between the air and the bowel lining forms the x-ray picture. For colonoscopy air is needed to allow careful viewing of the bowel wall. Patients are usually sedated for colonoscopy. This usually makes the procedure easy on the patient, but requires a day off work, with limited activity the remainder of the day. Colonography is performed without sedation, is quite brief, and allows immediate return to normal activity except for the passage of residual bowel air.

Both studies are very accurate in finding polyps greater than 1 cm in size. Colonoscopy is better at finding smaller polyps, though this is not clearly an advantage since very few (well under 1 percent) of these smaller polyps will harbor even a microscopic area of cancer. Polyps can be removed during colonoscopy, while patients polyps found at colonography will need a colonoscopy to remove the polyp(s). In the series performed so far up to 50 percent of patients have gone on to colonoscopy, depending on the make up of the patient group.

Colonoscopy is an invasive procedure and has some serious, though rarely occurring risks. The colon can be perforated during colonoscopy, either with the colonoscope itself, or with cautery of a polyp. This occurs in well under 1 percent of patients but can lead to hospitalization or urgent surgery. Bleeding can also occur after removal of a colonic polyp. Colonography is a non-invasive test with no such risks, though, again, polyps cannot be removed, only identified.

Colonoscopy is expensive for a screening test, ranging up to $2000 total cost in some scenarios. Colonography cost is not yet clear, though it will need to be in the range of $300-$400 to be considered cost effective. Most payers, including Medicare, have started covering colonoscopy for colorectal cancer screening, and all will cover colonoscopy for rectal bleeding, blood found on stool testing and family history or personal history of colorectal cancers or polyps. Colonography is new enough that many payers have not formed a policy on it yet, or may consider it "investigational." The optimal interval for colonography is also still uncertain, but should be similar to barium enema, which is approved for every 5-10 years. A secondary advantage of the CT colonography is the "free" look at the other organs surrounding the colon.

Since the colonoscope is inside the colon no direct information is gained about other organs. In about 11 percent of patients an abnormality in another organ will be found.

The new CT scanner at Advanced Medical Imaging in the Harrison-Silverdale complex is able to perform CT colonography and several such procedures have recently been done. Currently we are requiring patients to be referred by their doctor for this exam, and some doctors are requiring that you have a colonoscopy exam the same day to give us more local experience with this alternative.

Colorectal cancer screening is important to reduce the rate of colorectal cancer. Screening should be done with colonoscopy in patients who must have a biopsy, such as those with colitis. In other patients with a high risk of polyps, such as frequent previous polyps or a very positive family history colonoscopy may still be the best first test, since polyps can be removed when found. For truly screening patients with no rectal bleeding, no family history, or those with difficult previous colonoscopy, CT colonography may be a very feasible alternative.

This is a reprint of an article published in the Kitsap Business journal
http://www.wetapple.com/report/articles/2002-01-04-RPT-04.html

You will need the following supplies with are available at any pharmacy: 10 oz Magnesium Citrate, 4 Dulcolax tablets (5 mgs each) and 1 Dulcolax suppository or pick up a kit at either Bremerton or Silverdale AMI offices.

Adults: On the day before your exam:

1. Lunch: Light meal but avoid dairy products, vegetables and fruit.
2. 1 PM: Drink one glass of water.
3. 2 PM: Drink the 10 oz. Magnesium Citrate.
4. 3 PM: Drink one glass of water.
5. 5 PM: Take the 4 Dulcolax tablets with one glass of water.
6. 6 PM: Clear liquid supper: Broth, plain jello, coffee, tea or non carbonated beverages. No milk products, fruit of vegetables.
7. Drink plenty of clear liquids the rest of the evening.

On the morning of your exam:

1. Nothing to eat or drink. Do not chew gum. Do not smoke.
2. Use the Dulcolax suppository (place in rectum) at least two hours prior to exam time. Try to retain suppository in rectum for at least 20 minutes.

Children up to 6 years: No preparation necessary.

Children 6-12 years: Same instructions as adults, except give only 5 oz. Magnesium Citrate and 2 Dulcolax tablets.