Virtual Colonoscopy

Doctors at NewYork-Presbyterian routinely screen patients for colon cancer. One of the newer screening techniques they employ is virtual colonoscopy, also called computed tomographic (CT) colonoscopy. Virtual colonoscopy allows doctors to take 2-dimensional X-ray pictures and 3-dimensional "fly-through" images of the colon, helping them to detect polyps or cancerous cells.

Suggested Patients

Compared to traditional colonoscopy, virtual colonoscopy is less invasive, does not require sedation, takes less time, and may identify abnormalities outside of the colon. It may be especially appropriate for patients who cannot tolerate sedation because of other medical conditions. It is deemed as effective as traditional colonoscopy at finding advanced cancer and large polyps, but may miss some of the smaller abnormalities (less than 10mm in diameter). Because virtual colonoscopy does not allow for biopsy or removal of polyps at the time of the exam, patients must schedule a follow-up appointment for a conventional colonoscopy if an abnormality is detected.

The Prep

Similarly to traditional colonoscopy, patients begin the procedure at home by sticking to a clear liquid diet and drinking large quantities of a liquid bowel preparation designed to empty the colon. With virtual colonoscopy, a laxative is also required the night before the procedure. The CT colonoscopy is usually performed in the radiology department of a hospital or medical center and takes about 10 minutes. Before the procedure begins, patients may be asked to drink a contrast media liquid to help doctors identify abnormal tissues.

The Procedure

During the procedure, patients lie on a special table with a CT scanner. A doctor will insert a small, flexible tube into the rectum and air is pumped through the tube to expand the colon for better images. The table moves slowly through the CT machine, capturing hundreds of images to create an animated 3-dimensional view of the colon. A radiologist examines the CT test results for abnormal lesions.

Side Effects

There are few side effects from virtual colonoscopy. Similar to other types of CT tests, the procedure exposes patients to radiation but the levels are not considered harmful. Patients may feel bloated from the air pumped into the colon, but it will subside once the air passes from the body. An unanticipated consequence of virtual colonoscopy is that it may identify abnormalities in other areas of the body – outside of the colon. This can be seen as advantageous if it uncovers a life threatening medical condition such as kidney cancer, but it can also be cause for increased patient anxiety and unnecessary further testing if the CT test results are inaccurate.

Not Gold Standard, But Convenient

Although traditional colonoscopy has long been considered the "gold standard" of colon cancer screening, proponents of the less invasive and less time-consuming virtual colonoscopy are promoting it as the test of choice. Because it is a newer technology it may not be as widely available and may not be covered by all insurance carriers.


Digestive and Liver Diseases


Center for Advanced Digestive Care
NewYork-Presbyterian/Weill Cornell