More on virtual colonoscopy

I blogged on this story last week. This article adds important information to the discussion. I was at a birthday party over the weekend (for a 50 year old), and had several people ask me about virtual colonoscopy. I suspect most physicians are getting these questions. Not quite in a comfort zone

Patient excitement at the prospect of a more convenient and comfortable exam would be understandable but, doctors say, premature until the findings can be corroborated. There are other reasons too.

For starters, the preparation for both types of screenings is the same. As those who have had the conventional exam can attest, fasting and cleansing the intestines the night before is by far the worst part of the screening. That process is still required with a CT scan.

The virtual exam also comes with its own discomfort, because the intestine must be inflated with either air or carbon dioxide for an accurate and precise picture of the intestinal lining.

Furthermore, if a patient is found to have polyps, a conventional procedure must then be scheduled to have them removed.

All things considered, patients who need to be screened should have a conventional exam because it’s still the gold standard, with a three-decade track record, and allows polyps to be removed at the same time, most doctors say. For now.

This assessment seems quite similar to my interpretation last week.

Very few medical centers or radiologists now offer the optimal techniques used in the new study. (Although virtual colonoscopy surpassed standard colonoscopy in picking up polyps greater than 10 millimeters in size ? 98.3% versus 87.5%, it was not nearly as good in detecting those smaller than 5 millimeters, which are generally considered insignificant but could enlarge over many years.)

“All virtual colonoscopies are not created equal,” said lead study author Dr. Perry J. Pickhardt, an associate professor of radiology at the University of Wisconsin in Madison. He led the trial of more than 1,200 asymptomatic patients who underwent both procedures. “Most free-standing centers doing whole-body scans offer something called virtual colonoscopy, but in reality, what they offer is clearly inferior to our technique.”

Most radiologists who interpret virtual colonoscopy first scroll through cross-sectional images of the colon before studying the 3-D images produced from the scans. But Pickhardt’s study, published in last week’s New England Journal of Medicine and presented to the Radiological Society of North America, used computer software that allowed radiologists to do a 3-D virtual fly-through of the patient’s colon, then use the conventional, 2-D images to confirm any suspected abnormalities. That approach nearly doubled the detection rate.

Pickhardt’s study also used state-of-the-art CT scanners, plus computer filtering to electronically cleanse the images of any fecal particles that might be mistaken for polyps.

Radiologists who do virtual colonoscopies and gastroenterologists who probe colons with small, lighted cameras agree that the virtual examination is best suited to patients at average to low risk, whose colons are unlikely to have polyps. Those with symptoms such as rectal bleeding, anemia or unexpected weight loss, which can be symptoms of colon cancer, are “better suited to undergo conventional colonoscopy as the initial test,” Pickhardt said.

So as I said last week, we have promising results, but not definitive results. I would not “settle” for virtual colonoscopy yet. I will follow the literature for further developments.