Colonoscopy versus virtual colonoscopy

Apr 2 2009

Today, patients have a wide selection of colorectal cancer screening exams from which to choose, unlike with other types of cancers.

Experts at The University of Texas M. D. Anderson Cancer Center provide insight on the two most talked about tests, colonoscopy and virtual colonoscopy.

"The most widely used screening exam is colonoscopy, which is an accepted, standard screening test." said George J. Chang, M.D., M.S., assistant professor in M. D. Anderson's Department of Surgical Oncology.

However, many people have concerns about colonoscopy-related complications, such as bleeding and/or tearing of the colon. A newer option, virtual colonoscopy, sounds less invasive and may appeal to the public as a more desirable alternate screening tool.

Chang and David J. Vining, M.D., inventor of the virtual colonoscopy procedure and professor in M. D. Anderson's Department of Diagnostic Radiology, list advantages and disadvantages of both exams.

Colonoscopy (every 10 years unless polyps are found) - A doctor uses a colonoscope, a lighted tube, to examine the rectum and colon.

Advantages:

• Most colorectal cancers begin as a polyp (a small, non-cancerous growth on the colon wall that can grow larger and become cancerous over time). During a colonoscopy, doctors can detect and immediately remove these polyps. Polyp removal is considered the most effective way to prevent the development of colorectal cancer.

Disadvantages:

• This test may not detect all small polyps, nonpolypoid lesions (flat and depressed abnormal pieces of tissue), or cancers, but it is one of the most sensitive tests currently available.
• Thorough cleansing of the colon is necessary before this test. Patients may take laxatives 24 hours before the test. They also will not be able to eat or drink anything after midnight the night before the test.
• Some form of sedation is used in most cases. If sedation is used, someone will need to drive the patient home.
• Although uncommon, sedation or instrument-related complications, such as bleeding and/or tearing of the colon, can occur.

"Getting accurate colonoscopy test results depends greatly on the skill of the examiner and the amount of time he or she spends viewing the colon," Chang said. "The same can be said about virtual colonoscopy test results."

Virtual colonoscopy (every 5 years) - A health care provider uses specialized CT scan techniques to produce images of the abdomen and pelvis. A computer then assembles these images into detailed three-dimensional pictures of the colon and rectum that can show polyps and other abnormalities.

Advantages:

• It is less invasive than standard colonoscopy.
• Virtual colonoscopy may be as sensitive as standard colonoscopy if performed in experienced centers.
• Because sedation is not needed, virtual colonoscopy does not have sedation-related risks and does not require someone to accompany the patient to the examination.
• Risk of instrument-related complications, such as bleeding or tearing of the colon, may be lower than with standard colonoscopy.

Disadvantages:

• Like standard colonoscopy, this test may not detect all small polyps, nonpolypoid lesions and cancers.
• Thorough cleansing of the colon is necessary before this test, similar to what is done to prepare for a colonoscopy.
• If an abnormality, such as a polyp, is detected, the patient will need to undergo a standard colonoscopy after the virtual procedure to remove the polyp or lesion, or to perform a biopsy.
• Because sedation is not used, patients may experience some discomfort during virtual colonoscopy when air is pumped into the colon.
• Not all insurance providers currently cover the costs of this exam.
• Virtual colonoscopy exposes the patient to a low dose of radiation (more than a chest x-ray but less than a conventional CT scan).

"A frequent argument is that if virtual colonoscopy finds a polyp, then colonoscopy is needed for polyp removal," Vining said. "However, about 90 percent of patients do not have a significant polyp that needs removal, eliminating the need for a follow-up colonoscopy in the majority of patients."

Get Screened!

"The take-home message here is that both exams are viable options for testing for the disease, and it's better to get screened for colorectal cancer than not," says Chang. "Also, the detection rate for these exams improves if you follow the appropriate recommendations for test preparation as well as the suggested screening schedule."

"The five-year survival for early-stage colon cancer is 90 percent but for later stages, when it spreads to distant organs like the liver, it's only 10 percent," Vining said. "So, getting screened for colorectal cancer means that you're improving your odds of finding the cancer early, when it's easiest to treat, or better yet, you can prevent the disease altogether by detecting and removing precancerous polyps."

In addition to colonoscopy and virtual colonoscopy, M. D. Anderson also supports the fecal occult blood test (FOBT), fecal immunochemical test (FIT), double contrast barium enema and sigmoidoscopy as effective options to screen for colorectal cancer.

Your Doctor Can Help You Make the Decision

People between the ages of 50 and 75 should speak with their health care provider about colonoscopy and virtual colonoscopy, as well as other colorectal cancer screening exams. Below are additional issues to discuss with a health care provider:

• People with a family history of colorectal cancer or a personal history of inflammatory bowel disease may need to start colorectal cancer screening before age 50.
• * People over age 75 and in good health may still need to continue colorectal cancer screening.

Colorectal cancer is the third most common cancer in this country, and affects men and women equally. Almost 150,000 people in the U.S. were expected to be diagnosed with colorectal cancer during 2008, according to the American Cancer Society. Colorectal cancer also is the second leading cause of cancer death among Americans, with about 50,000 deaths expected in 2008. With wider use of cancer screening exams, colorectal cancer can be considered a highly preventable disease.

For additional information, visit www.mdanderson.org/focused .

M. D. Anderson experts available for interview:

George J. Chang, M.D., Assistant Professor, Department of Surgical Oncology
Chang is a colon and rectal cancer surgeon whose interests include treating patients with colon and rectal cancer with minimally invasive approaches, and clinical epidemiologic and quality of life research. He is the principal investigator and collaborator on a number of clinical trials and research projects, including laparoscopic and robotic surgery for rectal cancer as well as decision models for optimizing treatment strategies for rectal cancer.

G. S. Raju, M.D., Professor, Department of Gastroenterology, Hepatology and Nutrition
Raju's interests include colon cancer screening and therapeutic endoscopy of all aspects of colorectal pathology. In the laboratory, he has worked extensively in the development of endoscopic closure of colon perforations and full-thickness endoscopic resections. Raju tries to come up with novel endoscopic treatment options to help patients with complex gastrointestinal problems not amenable for surgical correction. He works very closely with the DAVE Project to develop Web-based endoscopic education and also serves as an associate editor of Gastrointestinal Endoscopy.  

David J. Vining, M.D., Professor, Department of Radiology
Vining is credited with having invented virtual colonoscopy as well as several other imaging-related technologies. He specializes in body imaging (CT, MRI, ultrasound, fluoroscopy of the chest and abdomen), especially as it relates to cancer detection. Vining is actively involved in research to advance imaging methods in this field. He also is working with the Division of Cancer Prevention and Population Sciences at M. D. Anderson to build a comprehensive colorectal cancer screening program in the Houston metropolitan area.