March is Colorectal Cancer Awareness Month in the U.S., and with "Today Show" host Katie Couric leading the charge, several news reports have focused on a disease that killed 56,000 Americans last year. The media attention may convince more patients to seek routine diagnostic exams, but is radiology ready to meet the demand?
Radiology's diagnostic options didn't garner as much attention as others, particularly given that Couric took a video crew along for her conventional colonoscopy exam. But imaging's alternatives have gotten some press this month as well.
A debate over the potential of virtual colonoscopy erupted in the letters section of the March 9 issue of the New England Journal of Medicine, as correspondents responded to a November 1999 NEJM article that found the CT exam as effective as conventional colonoscopy in detecting larger polyps.
One correspondent criticized the study's authors for giving short shrift to radiology's other exams, noting that the American College of Radiology "will soon implement an accreditation program for the performance of double-contrast barium enema, which is likely to improve the accuracy of the procedure."
But the ACR says it will include a double-contrast barium enema exam only as part of its radiography/fluoroscopy accreditation program to debut in late 2000 or early 2001. The college already has a quality control manual on its Web site covering the use of barium enemas.
ACR spokesperson Marie Zinninger said the ACR had no plans to implement a colorectal cancer imaging accreditation program per se, though she hoped the college might someday offer accreditation in virtual colonoscopy. Zinninger said the main problem facing screening right now is not the techniques' effectiveness in finding polyps and cancer, but rather the lack of patient acceptance for uncomfortable procedures such as colonoscopy and barium enemas. "They tend to just try to ignore (the symptoms)," she said. "If an exam could be developed that was more acceptable to patients, it certainly would be beneficial."
Three-dimensional helical CT colography, or virtual colonoscopy (VC), is a new technique that can eliminate some of the discomfort that must be endured in other screening methods, although bowel prep is still required, and the colon must be insufflated with as much gas as the patient can tolerate before imaging can begin.
Still, VC has some advantages in that it can be performed without sedation, with little risk of complications, and in less time than conventional colonoscopy. And unlike colonoscopy, images resulting from VC can be displayed in many different ways and scrutinized carefully after the procedure. There are few published studies comparing VC to other procedures, but VC's results so far have been promising, and interest in the technique is growing faster than you can say proctosigmoidoscopy.
The latest such study, published in the November 1999 New England Journal of Medicine (NEJM, Vol. 341, No. 20) generated several lively letters to the editor in the March 9 edition, in addition to the comments on barium enemas mentioned earlier.
In the study, authors Helen M. Fenlon, David P. Nunes, Paul C. Schroy III et al examined 100 patients (60 men, 40 women, mean age 62 years) at high risk for colorectal neoplasia, performing VC immediately before conventional colonoscopy. Glucagon (1 mg) was administered intravenously before the procedure to minimize smooth-muscle spasm and peristalsis and reduce discomfort.
Conventional colonoscopy results for 89 patients who underwent the procedure were as follows: Findings were normal in 51, and the researchers identified 115 polyps and 3 carcinomas in the other 49 patients.
Virtual colonoscopy performed in 87 patients found all three cancers. It found 20 of 22 (91%) of polyps that were 10 mm or more in diameter, 33 of 40 (82%) of polyps ranging from 6-9 mm, and 29 of 53 (55%) that were 5 mm or smaller. There were 19 false-positive findings of polyps, and no false-positive findings of cancer, the authors wrote, and VC correctly identified 46 of 51 (90%) adenomatous polyps that were 5 mm or smaller. The authors noted that no patients specifically requested that the procedure be stopped due to discomfort, and concluded that "In patients at high risk for colorectal neoplasia, virtual and conventional colonoscopy have similar efficacy for the detection of polyps 6 mm or more in diameter."
In an editorial accompanying the November article, NEJM's editors said that VC "has come a long way in a short time, and its future appears bright." However, they cautioned that to be economically feasible, the cost needs "to drop below that of conventional colonoscopy, since virtual colonoscopy is only a diagnostic test," and many patients would presumably need subsequent colonoscopy to evaluate abnormalities and resect polyps. The editors concluded that several technical advances would also be needed before VC was ready for prime-time -- including faster, higher-resolution scanners to detect small and flat polyps better, specialized software to enable automated reading of images, and techniques that obviate the need for bowel cleansing and that enable doctors to distend the bowel more comfortably.
In a letter to the NEJM editors, Dr. Scott Mackenzie et al from the University of Glasgow, U.K., said their study to assess VC's sensitivity, specificity, and accuracy in 25 patients with large-bowel symptoms showed much poorer results than the Fenlon study, despite using similar techniques. Out of 5 patients with a polyp or cancer larger than 10 mm, only 1 was revealed by VC, Mackenzie et al wrote, and there were also 4 false-positive findings of polyps with VC. The authors hypothesized that differences in patient selection may have been a crucial factor causing the disparate results, since patients with recent sigmoidoscopic evidence of polyps were excluded from the Mackenzie study, and 52% of them also had substantial diverticular disease.
"This condition may adversely affect the results of virtual colonoscopy because of narrowing of the colonic lumen, thickening of the bowel wall, and the presence of solid fecal matter adhering to the bowel wall at the site of diverticula," they wrote.
Dr. Seth Glick of MCP Hahnemann University in Philadelphia questioned the Fenlon study's assertion that VC is superior to the double-contrast barium enema. Glick cited published articles reporting the sensitivity of the barium enema at 81% and 98%, respectively, for polyps larger than 10 mm -- in contrast to the 65%-75% sensitivity cited in the Fenlon study. Glick also said that since most important neoplasms that are missed with a barium enema are visible when the results are reexamined, "concentration and perception are the keys to enhancing proficiency," of that technique, especially considering that VC studies have been produced in "highly dedicated centers, where 20-30 minutes are devoted to the interpretation of each examination."
Dr. Martina Morrin et al from the Beth Israel Deaconess Medical Center in Boston wrote that while arguments will continue about the relative diagnostic accuracy of conventional and virtual colonoscopy, if VC's advantages can increase patient compliance by just 10%-20%, then the technique will find its place as an effective examination. "Therapeutic colonoscopy in patients with positive results on VC should be performed the same day...thus sparing the patient a second bowel preparation," they wrote.
However, Dr. Carl Silverman of Madison, WI, remained unconvinced of VC's advantages in the realm of patient acceptance.
"I can tell you that from the patient's point of view, VC will not be perceived as a major advance unless or until it can be preceded by a virtual bowel preparation, in which virtual GoLytely is used," Silverman wrote. "Then and only then would I embrace the world of virtual reality with genuine enthusiasm."
By Eric BarnesAuntMinnie.com staff writer
March 21, 2000
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