SAN DIEGOVirtual colonoscopy is an accurate screening tool for
colorectal cancer in lesions greater than 10 mm with good patient
tolerance, Richard J. Farrell, MD, said at the American
Gastroenterological Association meeting held during the Digestive
Disease Week conference.
Dr. Farrell, of Beth Israel Deaconess Hospital, Boston, said that
virtual colonoscopy (CT colonoscopy) employs thin-section, helical CT
to generate high-resolution 2D axial images and 3D endoluminal
images. The 2D image is used first, and, if a questionable lesion or
polyp is observed, the image can be switched over to 3D.
In collaboration with Dr. Martina Morrin of the hospitals
radiology department, he recruited 100 patients at high risk for
colorectal cancer and polyps, all around the age of 60. All underwent
CT colonoscopy immediately prior to elective complete colonoscopy.
The patient requires no sedation with CT, unlike
conventional colonoscopy, which requires conscious sedation,
Dr. Farrell said.
Using conventional colonoscopy, 45 patients had normal findings. In
the other 55 patients, researchers found 88 polyps and 13 masses,
including 9 carcinomas, he said.
CT colonoscopy identified 12 (90%) of the 13 masses, all of which
were greater than 20 mm in diameter; 28 (92%) of 31 polyps that were
greater than 10 mm in diameter; 15 (65%) of 23 that were 6 to 9 mm;
and 12 (35%) of 34 that were 5 mm or smaller. There were 11
false-positive findings of polyps and three false-positive findings
of masses, resulting in a specificity of 90%. The majority of
false-positive tests occurred in either poorly prepped or
At 0 and 24 hours, patients reported similar scores for pain and
discomfort. Patient tolerance was an important component of
this study, Dr. Farrell said. There was no significant
difference in pain, embarrassment, or discomfort, but more patients
preferred the conventional colonoscopy because they preferred to be sedated.
For CT colonoscopy to be as cost-effective as conventional
colonoscopy, he said, it would need to be less than half the price of
the conventional technique or need to attract considerably more
patients for screening than colonoscopy.
CT colonoscopy showed excellent sensitivity and specificity for the
detection of lesions 10 mm or larger in diameter, but missed one
third of polyps 6 to 9 mm in diameter, he concluded. The best test,
the gold standard, he said, remains conventional
colonoscopy. CT is a good diagnostic tool, but you cant
remove tissue, so patients with polyps prefer conventional
colonoscopy. He added that large prospective trials comparing
CT with conventional colonoscopy in a screening population are