Not quite in a comfort zone
Colorectal screenings are not pleasant exams, and many people have longed for an easier way to have their large intestine checked for cancerous or precancerous polyps. Last week, they may have thought they had a solution.
Radiologists reported that a virtual colonoscopy -- using a CT scan -- could be just as effective as the conventional type of exam, in which a thin, flexible lighted tube with a camera attached is threaded through the rectum into the large intestine, usually while the patient is sedated. Because a CT scan takes pictures from outside the body, no invasive probing is necessary.
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.
“In the long run, this is going to be perfected and will become the standard in the future,” said Dr. Bennett E. Roth, chief of clinical gastroenterology at UCLA, of the new procedure.
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.
Although only about 2 in 1,000 polyps found during colonoscopy become malignant, detecting and removing them has been shown to vastly reduce rates of potentially deadly colon cancer. One of the unanswered issues with virtual colonoscopy involves what to do about smaller polyps, which doctors agree have a minute chance of becoming cancerous over time.
The virtual procedure has its benefits of course. Because it’s not invasive, there’s no risk of perforating the colon and having to undergo emergency surgical repair. In addition, it doesn’t require anesthesia or sedation, so patients can resume regular activities. Unlike the conventional procedure, which takes 30 to 60 minutes, the virtual procedure lasts fewer than 15 minutes.
Medicare and most insurance companies pay for routine screening with conventional colonoscopy, which can run $600 to $1,000, as recommended beginning at age 50. They don’t cover the virtual procedure, which costs $500 to $2,000, except when a patient has cancer obstructing the colon, or had an incomplete colonoscopy.
Patients set on having virtual colonoscopy now should be prepared to pay for it themselves, find a facility that offers advanced scanning equipment and 3-D software and make sure the radiologist is experienced in virtual colonoscopy, he advised.
