Image Bank: Virtual Colonoscopy

Virtual colonoscopy is a new examination performed by radiologists to look for polyps and tumors in the large intestine (colon). It combines information from a detailed computed tomographic (CT) scan of the abdomen and pelvis with advanced computer applications to produce pictures of the colon that look like what the gastroenterologist sees when he or she performs colonoscopy. Similar to colonoscopy, patients must cleanse their intestines to prepare for the examination.

View of colon polyp using virtual colonoscopy.	View of cancerous colon using virtual colonoscopy, with three views of same colon using CT scan.

Although the test is considered investigational for certain purposes (it has been used at Memorial Sloan Kettering since 1999), because of its particular advantages and its lack of untoward effects, virtual colonoscopy has been well received and accepted for use in specific clinical situations. Patients who have had an incomplete colonoscopy and those who cannot undergo colonoscopy because of the associated risks of sedation and/or biopsy of the colon are some of those who have had the procedure.

The procedure is rapid (requiring 10 to 20 minutes) and is generally well tolerated. Because the colon is inflated with air by means of a rectal tube, some discomfort and cramping are to be expected. Since no sedation is required, most patients can resume their normal activities immediately after the test.

Patients whose virtual colonoscopy shows normal results may be able to avoid having a conventional colonoscopy; however, patients with abnormal results may need confirmation and subsequent biopsy using conventional colonoscopy in the detection of polyps that are 1 centimeter or larger.

The cost of virtual colonoscopy is comparable to the cost of an abdominal and pelvic CT scan. The dose of radiation to the patient will depend on indication for the study, and will either equal or exceed that of a routine abdominal and pelvic CT scan. The hope is that virtual colonoscopy may one day provide an alternative to colonoscopy as a safer and more cost-effective strategy to screen for colon cancer.

In ongoing research, Memorial Sloan Kettering investigators are comparing polyp detection using virtual and conventional colonoscopies in patients with a history of polyps and colon cancer.