CT scan nearly as good as regular colonoscopy

Undergoing a virtual colonoscopy might be just the ticket for people at high risk of colorectal cancer who need screening every few years, a new study finds. By spotting 85 percent of polyps, computed tomography scans offer a way to detect the precancerous growths in a way that is less invasive than a conventional colonoscopy, a European team of researchers reports in the June 17 Journal of the American Medical Association.

A slew of tests over the past decade have shown that CT scanning can be useful in detecting polyps (SN: 12/6/03, p. 355). The scans aren’t quite as thorough as a conventional colonoscopy, widely considered the gold standard for colorectal cancer screening. In the conventional procedure, a doctor uses a flexible tube fitted with a tiny scope to inspect the colon. The flexible device can also snip off any polyps found during the procedure, making colorectal cancer highly preventable (SN: 11/11/00, p. 312).

But flexible-scope colonoscopy carries a risk of colon perforation, requires some degree of sedation and causes discomfort. For these reasons, many people delay or avoid getting the procedure. About half of the people in the United States due for a colonoscopy or other colon screening test haven’t gotten one, says radiologist Daniele Regge of the Institute for Cancer Research and Treatment in Turin, Italy.

Regge and his colleagues identified 937 people in Italy and Belgium who were at high risk for colorectal cancer. Of these, 373 had a family history of the disease, 343 others had a personal history of polyps and the remaining 221 had stool samples that contained traces of blood. From December 2004 to May 2007, each volunteer underwent a CT scan for colorectal polyps and later on the same day had a routine flexible-scope colonoscopy.

The scope colonoscopies revealed polyps in 177 people, whereas the CT scan detected them in 151, for an 85 percent accuracy rate. The CT scan caught polyps one centimeter in length or larger 91 percent of the time.

Though this study looked only at people with high risk, virtual colonoscopy might also be useful to the broad population. With so many people skipping flexible-scope colonoscopies, “an imperfect test that has a lower risk profile and greater acceptance among patients seems to be an appealing solution,” says surgeon Emily Finlayson of the University of Michigan in Ann Arbor, in an editorial in the same JAMA issue.

People who have had a polyp removed are at highest risk and should get screened every three years thereafter, Regge says. The new findings suggest that the adoption of CT scans could make the regimen of frequent screenings less onerous, he says.

People without any known risk factors should get a colonoscopy or other screening every 10 years starting at age 50, according to the American College of Gastroenterology. These other screenings include stool sample testing, virtual colonoscopy or a partial colonoscopy, called a sigmoidoscopy.