GASTROENTEROLOGY LITERATURE ALERT!
LANDMARK ARTICLE - Required reading
| Fenlon HM, Nunes DP, Schroy PC, Barish MA, Clarke PD, Ferrucci JT. A
Comparison of Virtual and Conventional Colonoscopy for the Detection of Colorectal Polyps.
N Engl J Med 1999;341:1496-1503. Bond JH. Virtual Colonoscopy: Promising, but Not Ready for Widespread Use. N Engl J Med 1999;341:1540-1542 (editorial) |
First study to look at the accuracy of virtual colonoscopy compared to standard endoscopic colonoscopy in a fair-sized sample group
Helical CT is used to generate high resolution, two-dimensional axial images. Three-dimensional images of the colon, similar to those seen during conventional colonoscopy, are reconstructed off-line.
100 patients at high risk for colorectal neoplasia (age >50, and history of polyps, FOBT positive results, colorectal cancer in 1 or more 1st degree relatives) were examined using both methods.
Preparation was similar to that for conventional colonoscopy. All virtual studies were done before the conventional colonoscopy.
Rectal tube was inserted and the colon insufflated with air. Glucagon IV was used. No sedation. Images were obtained during one breath-holding session only when at all possible. Images were obtained with the patient supine, then prone. Virtual colonoscopy was followed by conventional colonoscopy.
71% of polyps seen on conventional colonoscopy were detected by virtual colonoscopy. Sensitivity of virtual colonoscopy for polyps <5mm was 55%, for polyps 6-9mm was 82% and for polyps >10mm was 91%
Small adenomatous polyps were more likely to be detected by virtual exam (67%) than hyperplastic (48%)
The entire colon was visualized on virtual colonoscopy in 87%, compared with 89% with conventional colonoscopy
FACTS TO REMEMBER FOR BOARDS
Advantages of virtual colonoscopy: 1) no sedation, 2) less time to perform than conventional colonoscopy, 3) involves little risk, 4) both sides of bowel folds can be examined.
Disadvantages of virtual colonoscopy: 1) bowel cleansing and infusion of gas, 2) expensive hardware, difficult interpretation of images, 3) retained stool or fluid or contracted segments of bowel interfere with detection of lesions, 4) inability to do therapeutic interventions
Polyps > 10mm which are flat and located in the right colon, are easily missed by virtual colonoscopy
Learning curve for assembling and reading images is steep.
Barium enema usually misses polyps and should not be used as a screening tool for colorectal cancer
Clinical Application
This technique is not yet ready for widespread use, but expect patients to ask you about it, as it is receiving widespread press
Keep an eye on developments in this area, eventually; virtual colonoscopy could impair your ability to put bread on your table!