Virtual colonoscopy creates 3-D images of the colon, unlike a traditional colonoscopy.
One in 20 men and women in the United States are diagnosed with colorectal cancer, a leading cause of cancer deaths, according to the National Cancer Institute. While regular screening programs can detect cancer early, existing techniques are imperfect or potentially harmful. Virtual colonoscopy, or CT colonography, an emerging, less-invasive screening option, is showing positive results. However, patients should consider the risks before deciding on the screening method right for them.
Radiation
Virtual colonoscopy uses a medical imaging test known as a computerized tomography (CT) scan in combination with computer software to produce 3D, cross-sectional images of the inside of the colon. While the procedure provides doctors with better images to detect pre-cancerous polyps or tissue growths in the lining of the colon, the CT scan uses X-ray equipment that emits radiation.
Patients are exposed to about 10 millisieverts of radiation during the procedure, equal to the amount of radiation released from natural sources over three years, RadiologyInfo says. According to an Oct. 19, 2007 issue of "Digestion," Arye Blachar and Jacob Sosna conclude the risk of fatal cancer from exposure to radiation from virtual colonoscopy is 0.02 percent in people 50 and older. For younger patients, the risk may be higher because of the need for repeat tests over time as part of regular screening. The test may also pose a significant risk for pregnant women. Depending on the stage of pregnancy, the risk of a serious illness or complication to the developing fetus varyies. In general, a CT scan is not recommended for pregnant women.
Colon Injury
During a virtual colonoscopy, doctors inflate the colon by pumping air through a small tube inserted into the rectum. The air can injure or perforate the colon. In an Oct. 19, 2007 issue of "Digestion," Arye Blachar and Jacob Sosna found the reported risk of injury is between 0.06 to 0.08 percent. Those who suffered a perforated colon were older and had underlying medical conditions. These results were validated by authors Atalia MA and colleagues in a June 2010 issue of the "Journal of Medical Screening," that reports two cases of perforation among nearly 3,500 virtual colonoscopies or a risk of 0.06 percent. Overall, the risk of colonic perforation remains lower than that from a traditional colonoscopy.
Medication Side Effects
Prior to a virtual colonoscopy, a contrasting agent, usually barium tablets or iodinated liquids, is administered to patients. The agent helps doctors identify stool from polyps. However, an adverse reaction to these agents is possible. According to The National Institutes of Health, nausea, vomiting, bloating and rectal irritation are possible side effects.
Missed Polyps
While virtual colonoscopy provides doctors with clearer images of the colon and provides patients with a less invasive screening option, the technique is not as sensitive in detection of polyps as the traditional colonoscopy. Virtual colonoscopy is deemed just as effective as colonoscopy in detection of polyps at least 10 millimetres in diameter. However, virtual colonoscopy may miss polyps under 10 millimetres and flat lesions. What's more, a Nov. 4, 2008 article in the "Annals of Internal Medicine" by Dr. Evelyn Whitlock and colleagues cited differences in a radiologist's training and experience as "a major factor" in the discrepancy of virtual colonoscopy test results.
Tags: traditional colonoscopy, virtual colonoscopy, 2007 issue, 2007 issue Digestion, Arye Blachar, Arye Blachar Jacob, Blachar Jacob
