When Distinguishing Colorectal Polyps, Narrow-Band Imaging Is Comparable to White Light Colonoscopy

Researchers recently compared narrow-band imaging (NBI) without high magnification to conventional white light colonoscopy in differentiating colorectal polyps during real-time colonoscopy and found that NBI was no more accurate than white light colonoscopy. The study found, however, a significant learning curve for these experienced endoscopists using NBI as a new diagnostic tool. Once this learning curve was achieved, NBI performed significantly better.

The study, preformed by investigators from Yale University School of Medicine (New Haven, CT, USA), appears in the December 2008 issue of Gastrointestinal Endoscopy (GIE), the scientific journal of the American Society for Gastrointestinal Endoscopy (ASGE).

Endoscopy is a procedure that uses an endoscope--a thin, flexible tube with a light and a lens on the end to examine the esophagus, stomach, duodenum, small intestine, colon, or rectum, in order to diagnose or treat a condition. The many types of endoscopy include colonoscopy, sigmoidoscopy, gastroscopy, enteroscopy, and esophogogastroduodenoscopy (EGD). Colonoscopy is frequently used to screen for colorectal cancer, which most typically develops from polyps. The two main polyp types are adenomatous, which are precancerous and hence require removal, and nonadenomatous, which do not have a high likelihood of developing into cancer.

Narrow-band imaging is a new optical technology that modifies white light by using only specific wavelengths to enhance the image. The technology provides more visual detail of the lining of the colon (including polyps) and of the small blood vessels near the surface of the polyps. At present, there is no widely adopted, easily applied method for distinguishing between adenomatous (potentially pre-cancerous polyps) and nonadenomatous polyps during real-time colonoscopy. From a practical standpoint, the ability to distinguish the two would allow the endoscopist to remove only those polyps with precancerous potential.

"In this prospective trial, we aimed to compare standard broadband white light colonoscopy with narrow-band imaging for the differentiation of colorectal polyps during real-time colonoscopy by using a modified Kudo pit pattern classification and vascular color intensity grading,” said study lead author Jason Rogart, M.D., from Yale University School of Medicine. "Overall, NBI accuracy was 80%, compared with 77% for white light alone. We also demonstrated that improved performance could be achieved over time. NBI was most useful in correctly identifying adenomas, polyps that have the most risk of developing into cancer, especially those that are small.” The investigators additionally reported that this is, to their knowledge, the largest study to date that addresses the question of whether NBI outperforms ordinary white light in predicting the histopathologic diagnosis of polyps during real-time colonoscopy.

Three hundred and two patients were enrolled from August 2006 to July 2007 at Yale University; 265 polyps were found in 131 patients resulting in an adenoma detection rate of 30%. Of the polyps, 49% were adenomas or carcinomas, whereas 51% were nonadenomatous; 74% of adenomas were 5 mm or smaller and 42% were 3 mm or smaller.

Overall, NBI accuracy was 80% compared with 77% for white light alone. NBI performed significantly better than white light in diagnosing adenomas (sensitivity 80% vs. 69%), particularly for 5-mm adenomas (75% vs. 60%). There was no difference between NBI and white light for nonadenomatous polyps. Diagnostic accuracies were better for larger polyps (mean size of correct prediction 4.7 mm vs. 3.9 mm) and nonsignificant for polypoid shape (87% vs. 79% for polyps with sessile shape). Compared with white light, however, NBI did not significantly improve accuracy in any size or shape category, nor for any segment of the colon.

An equal number of polyps were analyzed in each of the two study periods (133 and 132, respectively). NBI accuracies significantly improved from 74-87% between the two study periods whereas, white light accuracies were unchanged (78% first half and 79% second half). In the second half of the study (i.e., after the learning curve was reached), therefore, NBI was significantly more accurate than white light.

Researchers reported that the study demonstrated that there is a learning curve with regard to NBI assessment of colorectal polyps, and that NBI outperforms ordinary broadband white light once this "learning” is achieved. They concluded that their findings also highlight the variable NBI appearance of both adenomatous and nonadenomatous polyps. At present, current NBI accuracy rates of 80% are inadequate to defer polypectomy (polyp removal) and, therefore, limit the utility of NBI in evaluating colorectal polyps during routine clinical practice. Accuracy rates that approach 100% would be required for endoscopists to use this assessment to determine the need for polyp removal with confidence. Additional study into superficial mucosal patterns of polyps and the optimal method of viewing them with NBI is needed, according to the researchers.

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Yale University School of Medicine