Virtual Colonoscopy

We have discussed many options for colon cancer screening including the FIT (Fecal Immunochemical Test), Stool DNA test (Cologuard by trade name) and colonoscopy, which is considered the gold standard for detecting colon cancer. There is another option for colon cancer screening called a CT colonography. Another name for CT colonography is “virtual colonoscopy.” Let’s find out more about this virtual colonoscopy and whether this test is right for you.

A virtual colonoscopy is another option for colon cancer screening and involves taking pictures of the colon by way of a CT scan to find polyps, adenomas, pre-cancerous and cancerous masses. When the results of a virtual colonoscopy are normal, this test can be performed every 5 years. You would still need to undergo a “bowel preparation” by drinking a laxative based solution to cleanse your bowels. Yet, unlike an actual colonoscopy, there is no large tubing with a camera that is inserted into your rectum and passed throughout your colon. Instead, a small flexible catheter is inserted into your rectum and used to inflate air into your colon. (1) This will allow for better pictures to be taken. With a virtual colonoscopy, it is difficult to take pictures of polys that line the inside of your colon when the colon is decompressed and flat. This is why your colon needs to be filled with air during this procedure.

A virtual colonoscopy has many advantages. First, there is no need to hold medications, such as blood thinners. Also, typically sedation is not required and you can drive yourself home after the procedure if you are feeling up to it. Other the other hand, much like the FIT and DNA stool test, if a poly is found on virtual colonoscopy, an actual colonoscopy will be required. Pictures taken of a polyp during virtual colonoscopy give information about the size and shape, not whether this polyp is harmless or cancerous. This is why a colonoscopy, which can obtain samples of tissues, is needed. Complications tend to be lower for virtual colonoscopy as well since samples of tissues, or biopsies, are not taken. Therefore, you should not expect bleeding. The risk of having a small hole or puncture your bowel, as known as a bowel perforation, is also lower than an actual colonoscopy; with the understanding that the risk of bowel perforation for an actual colonoscopy is already very low. Otherwise, a virtual colonoscopy has the risk of radiation exposure. Having many CT scans over a lifetime can increase the risk of cancers due to radiation, but it is thought that more lives are saved by performing virtual colonoscopy than lost with cancers due to radiation. (2) A major disadvantage of virtual colonoscopy is its inability to find polys and adenomas less than 1 cm in size. Small pre-cancerous polyps and adenomas detected and removed by an actual colonoscopy, can be missed by a virtual colonoscopy about half of the time. (3)

While a virtual colonoscopy may sound exciting, it’s uses is limited to a small group of individuals. Virtual colonoscopy should only be used in those who have an average risk for colon cancer and no symptoms. Also, those who have failed or had an incomplete colonoscopy may consider a virtual colonoscopy as well. Other the hand, there are many groups that should not have a virtual colonoscopy.  If you are at high risk for colon cancer or have known adenomas on a prior colonoscopy, a virtual colonoscopy is not right for you. If you have Ulcerative colitis, Crohn’s disease or a recent history or diverticulitis colon surgery, a virtual colonoscopy is not right for you. If you are having diarrhea or signs of a bowel blockage, a virtual colonoscopy is also not right for you. (1) Remember to discuss all you screening options for colon cancer with your doctor before making a decision.

Here’s the bottom line: A virtual colonoscopy does not replace an actual colonoscopy as the gold standard for colon cancer screening.  Again, there may be some convenience with a virtual colonoscopy, including not needing to hold certain medications. Despite this, a virtual colonoscopy still requires a full bowel preparation, just like an actual colonoscopy. Small polys and masses can be missed on virtual colonoscopy. Therefore, a negative virtual colonoscopy does not mean you do not have a poly or adenoma, it means you do not have a mass large enough to be found on CT scan. Also, if a poly or adenoma is found on virtual colonoscopy, more information about its risk and genetics is need. As a result, an actual colonoscopy, where biopsies can be performed, will be needed anyway. This means another bowel preparation and procedure. Which begs the question: Should I start with a colonoscopy? As with an actual colonoscopy, we always prefer a test that can both detect disease and potentially treat it at the same time without the need for another procedure. While a virtual colonoscopy may be a reasonable option for a select group of individuals, the virtual colonoscopy does not replace an actual colonoscopy as the gold standard in colon cancer screening.

REFERENCES
1. Doubeni C. Tests fir Screening for Colorectal Cancer. In: UpToDate, Elmore JG AD & Lamon TJ. (Eds), UpToDate, Waltham, MA. (Accessed on August 29, 2021)
2. Berrington de González A, Kim KP, Knudsen AB, Lansdorp-Vogelaar I, Rutter CM, Smith-Bindman R, Yee J, Kuntz KM, van Ballegooijen M, Zauber AG, Berg CD. Radiation-related cancer risks from CT colonography screening: a risk-benefit analysis. AJR Am J Roentgenol. 2011 Apr;196(4):816-23.
3. Lin JS, Piper MA, Perdue LA, Rutter CM, Webber EM, O’Connor E, Smith N, Whitlock EP. Screening for Colorectal Cancer: Updated Evidence Report and Systematic Review for the US Preventive Services Task Force. JAMA. 2016 Jun 21;315(23):2576-94.