Positive results strengthen case for CT colonography screening

This fall brought good news for advocates of CT colonography. A study in the November issue of Radiology presented the latest results from the University of Wisconsin, and they were very good: in a population of 1110 patients, CT colonography demonstrated a positive predictive value of 93.8% for polyps 6 mm and larger, up from 58.5% in an earlier trial conducted at the same institution (Radiology 2006;241:417-425).

These results were not unexpected. The lead author, Dr. Perry Pickhardt, an associate professor of radiology at the University of Wisconsin, previewed the study at the 2005 RSNA meeting. In addition, many who have followed the evolution of CT colonography have long believed its accuracy would someday prove competitive with the optical colon exam.

But the Pickhardt study is significant in another way as well. The results are presented in the context of a unique screening program at the University of Wisconsin that combines CT colonography with the ready availability of optical/therapeutic procedures that can spot and remove potentially cancerous lesions while the bowel is still cleansed for the virtual exam.

One of the long-standing objections to virtual colonoscopy has been that much of the discomfort associated with it is the bowel cleansing process. Naysayers argue that if you are going to suffer that discomfort, why not go directly to an optical exam where suspicious polyps can be removed at the same time?

Pickhardt and his team provide the answer. Among patients sent on to optical colonoscopy, 86% underwent the procedure the same day, thereby avoiding the need for repeat bowel preparation. For polyps 10 mm or larger, immediate optical colonoscopy was recommended. For polyps 6 to 9 mm, patients were offered immediate optical colonoscopy for polypectomy or CT colonography surveillance.

Obviously, this approach is probably easier to execute in a university setting than in a small private practice. But it is one that, with a little careful thought and planning, could be duplicated in a variety of settings. Dr. Abraham H. Dachman, a professor of radiology at the University of Chicago Hospitals and an expert in CT colonography, observes that a radiology practice could screen in the morning and ask a nearby gastroenterology practice to hold space in its schedule for one potential polypectomy early in the afternoon. If no actionable polyps are found in the virtual scans, the gastroenterology practice could receive an early notice and perhaps schedule another procedure. The system is easily scalable and offers an elegant solution to the problem of avoiding double bowel prep regimes. It also offers the potential to reduce unnecessary optical colonoscopies, a more invasive and complex procedure than CT colonography, and permits better use of medical resources.

Indeed, some researchers have questioned whether gastroenterologists alone can handle the screening needs of our steadily growing 50-plus population. A study published in 2004 estimated that there are 41.8 million average-risk people aged 50 or older who have not been screened for colorectal cancer. That study posited the use of fecal occult blood testing followed by optical colonoscopy for positive tests. Depending on the proportion of available capacity used for colorectal cancer screening, it could take up to 10 years to screen the unscreened population using flexible sigmoidoscopy or colonoscopy, according to the study (Gastroenterology 2004;127:166-1677).

Put another way, most gastroenterologists already have full schedules. If we are to make a dent in the relatively low rate of colon cancer screening in the U. S., options other than optical colonoscopy must exist. CT colonography, as the Pickhardt study proves, offers an attractive alternative and is probably the best route to improving colon cancer screening rates and reducing preventable deaths from colon cancer.

What are your thoughts on this topic? Please e-mail me at jhayes@cmp.com.