Colorectal cancer is the second-leading cause of cancer death in the United States, and the third most common cancer. Despite its prevalence and morbidity, most people forego colonoscopies because the procedure is uncomfortable and invasive. A virtual colonoscopy may increase the number of screenings as a more favorable alternative, however it is not painless.
Accuracy of a Virtual Colonoscopy
A September 2008 study published in the New England Journal of Medicine (NEJM) found virtual colonoscopies to be as accurate as traditional colonoscopies. The study included 2600 asymptomatic adults (meaning no family history of colorectal cancer). The CT colonography screenings found 90% of people who had cancer or benign tumors of 10mm or larger. However, polyps that are 5mm to 9mm are less likely to be detected. It is not known if polyps of that size are dangerous.
The study says “These findings augment published data on the role of CT colonography in screening patients with an average risk of colorectal cancer.”
Dr. David Kim, from the University of Wisconsin School of Medicine and Public Health, said “Indeed, this study provides another push for noninvasive/minimally invasive screening by CT colonography” (AMA). Dr. Kim was not involved with the study, but is an assistant professor of abdominal imaging.
A second study published in the Journal of the American Medical Association in 2009 also found CT colonography to be accurate. Unlike the previous study, this one focused on people at an increased risk of colorectal cancer “due to either family history of advanced neoplasia in first-degree relatives, personal history of colorectal adenomas, or positive results from fecal occult blood tests” (JAMA). This study also compared CT colonoscopies to traditional ones.
In this study, CT colonography found advanced neoplasia 6 mm 85.3% of the time, and 10 mm or larger 90.8% of the time. When compared with traditional colonoscopy, CT colonography “resulted in a negative predictive value of 96.3% and a positive value of 61.9% overall.” They concluded that CT colonography can be an “alternative to colonoscopy for screening individuals with family history of advanced colorectal neoplasia.”
Virtual Colonoscopy Procedure
In addition to being accurate, virtual colonoscopies are more comfortable than traditional ones. Advantages include “rapid imaging of the entire colorectum; a relatively noninvasive technique, with no need for sedation; and a low risk of procedure-related complications.”
Traditional colonoscopy “is the only test that can both detect cancer at an early curable stage and prevent cancer by removing precancerous polyps,” according to the American Gastroenterological Association. This means that people who undergo Virtual CT colonography that detects polyps will have to have a traditional colonoscopy as well to have them removed.
Although virtual colonoscopy is minimally invasive, it is not painless. Patients must still undergo the bowel cleaning, and the abdomen must be insufflated with air. Also, patients are not sedated (as they are for traditional colonoscopies.)
A second study also published in September 2008 in the NEJM tested the window in which colonoscopies should be performed. Traditional medical advice says that the average person should get one colonoscopy every ten years. The study found that a second colonoscopy five years after the first negative resulted in a cancerous polyp very rarely. It supports the rescreening interval “of 5 years or longer after a normal colonoscopic examination.”
Only 61% of people over 50 get colonoscopies. Additionally, many colorectal cancer survivors do not get the recommended follow-up screenings (AMA).
Medicare began coverage of colonoscopies for people at high risk of colorectal cancer in 1997. However virtual colonoscopies are not currently covered by insurance. In February 2009, the Centers for Medicare and Medicaid Services proposed that Medicare not pay for virtual colonoscopies (AMA). CMS said it found inadequate evidence that virtual (CT) colonography was an accurate screening tool, despite the evidence to the contrary in the New England Journal of Medicine and the backing of CT colonoscopies by the American Cancer Society.
This technique is performed at the University of Wisconsin, some military hospitals, and various Radiology departments across the United States. It began to more widely used in April 2009.