Gastroenterology
Volume 136, Issue 4 , Pages 1149-1151, April 2009

Confidence With Narrow Band Imaging: Will It Change Our Practice of Polyp Resection?

  • Heiko Pohl

      Affiliations

    • Corresponding Author InformationReprint requests Address requests for reprints to: Heiko Pohl, MD, Assistant Professor of Medicine, Dartmouth Medical School, Section of Gastroenterology, VA Medical Center, White River Junction, VT 05009. fax: 802 296 6476
    • ,
  • Douglas J. Robertson

Section of Gastroenterology, VA Medical Center, Whiter River Junction, Vermont

published online 25 February 2009.

Article Outline

 

See “Narrow-band imaging without optical magnification for histologic analysis of colorectal polyps,” by Rex, et al, on page 1174.

Unarguably, colorectal cancer (CRC) is a significant public health threat. In the United States, the lifetime risk of CRC is 5%–6%.1 However, the truth is, about 94% of those undergoing CRC screening will not benefit because they were never destined to develop cancer. This simple calculation highlights the fact that improvements in colonoscopy practice should not only focus on increasing adenoma detection, but also decreasing the risks associated with colonoscopy performance.

With regard to screening colonoscopy, much of the benefit is not from the detection of early cancers, but rather from detection and removal of a well-accepted cancer precursor—the adenomatous polyp. To date, practicing endoscopists have uniformly removed all raised mucosal lesions from the colon irrespective of size or appearance. However, there are reasons to believe that perhaps this paradigm should change. Of all polyps, 34% are nonadenomatous.2 Most of these are small (≤5 mm) and do not harbor a malignant potential. In other words, at least one third of polyps are removed unnecessarily if the goal of colonoscopy is cancer prevention.

Removing all polypoid lesions from the bowel has potential downsides to both the patient and society. From the patient's perspective, biopsy or polypectomy measurably increases procedural risk. The risk of bleeding during a colonoscopy increases about 10-fold with polyp resection.3 From the societal perspective, removal of all lesions increases both the time and cost of colonoscopy. For example, each individual polyp resection requires additional time for the endoscopy team both removing and retrieving samples for histologic review. Pathologic evaluation takes time, too, for slide preparation and interpretation. Finally, this extra work has a real associated cost for the patient and society. Therefore, if polyp resection could be minimized without sacrificing adenoma detection, a safer examination can be completed at a reduced societal cost.

In this issue of Gastroenterology, Rex et al4 report their results on using narrow band imaging (NBI) with high-definition endoscopy for real-time interpretation of polyps. Several previous publications on this subject suggest a high diagnostic yield for the distinction of adenomatous from hyperplastic polyps using either the Lucera system (primarily used in Asia)5, 6, 7, 8, 9, 10, 11 or the Exera system (primarily used in the United States and Europe; Table 1).12, 13, 14, 15

Table 1. Studies Evaluating Yield of Narrow Band Imaging Endoscopy With the Exera System With or Without High-Definition (HD) Endoscopy or Zoom Magnification to Predict Adenomatous Polyps
StudyImagingNo. of polypsSizeSensitivity (%)Specificity (%)
Tischendorf et al14Zoom, no HD20075% <10 mm9089
Rastogi et al12HD12384% ≤5 mm9686
Sikka et al13HD80100% <10 mm9590
Rogart et al15HD26574% ≤5 mm8069
Rex et al4HD45188% ≤5 mm9287
HD, high confidence36885% ≤5 mm9692

However, the study by Rex et al is novel in various aspects. Aside from being the largest study on the subject to date, it also employed predefined criteria to distinguish hyperplastic from adenomatous polyps. The criteria were developed from an NBI image library of 320 polyps and then prospectively applied to 136 patients undergoing colonoscopy. Also, the focus of this paper specifically targets NBI's performance in distinguishing neoplastic from nonneoplastic, small polyps. Statistically, this is the most likely area where endoscopic polypectomy practice could be changed without having a deleterious effect on cancer incidence.

Another interesting feature of the assessment of NBI performance is the integration of a “confidence level” into the clinical interpretation of polyps. Using the prespecified criteria, the examiner made the diagnosis (ie, either hyperplastic or adenomatous) with “high confidence” in about 80% of polyps, and in these instances 92% of polyps were diagnosed accurately when compared with histology. In fact, a few other studies have evaluated a level of confidence when making an in vivo diagnosis of polyps,5, 12, 14 and 1 recent publication reported an increased accuracy when the diagnosis was made with “high confidence.”15 However, the current study extends prior work by assessing NBI performance in directing surveillance recommendation when relying on high-confidence, in vivo diagnosis in combination with conventional polypectomy for large and “low-confidence” polyps. When considering this practical end point, the approach worked well. Fewer then 3% of patients would have been scheduled for a colonoscopy at a later surveillance interval when applying current guidelines.16 These changes in management are small and seem acceptable when considering the variability in adenoma detection17 and in defining the surveillance interval in clinical practice.18 The authors conclude that if most small polyps can be diagnosed in vivo with high confidence, retrieval and further evaluation of small polyps can be avoided.

The potential implications of this study on clinical practice may be sizable. For example, it may become common place to leave a significant number of “high-confidence” hyperplastic lesions in place while discarding (without pathologic interpretation) small, “high-confidence” adenomatous lesions that would be deemed unlikely to harbor malignancy. Rarely misclassification will occur and small adenomas will be left in place. However, the risk of leaving small adenomas behind (false negatives) is probably low, because very few adenomas of this size harbor an immediate malignant risk.19 If such practice were adopted, this would decrease procedural risk and cost for the patient. Although the per-procedure gains in efficiency might be relatively small, the societal benefit could be substantial. It was recently estimated that 1.27 million colonoscopies are performed by gastroenterologists annually for CRC screening-related indications alone and so this paradigm shift clearly could have substantial ramifications.20

However, before we can consider changes in clinical practice, several concerns need to be addressed. First, we need to determine that others can readily learn (and more importantly apply) the criteria proposed by Rex et al. Whether NBI in vivo diagnosis will work outside the expert hands (and eyes!) of a colonoscopist who has dedicated much of his academic career studying polyps, needs further assessment. At its core, NBI-assisted interpretation of polyps involves pattern recognition. It is clear from the computerized tomography colonoscopy (CTC) literature that pattern recognition may vary even among well-trained specialists. For example, in the National CT Colonography Trial,18 all participating radiologists had experience reading CTC and completed a training program to improve reading before study inception. Although only the highest performing radiologists were included, there remained substantial variation in polyp detection among the 15 radiologists in the study.

Although it is reasonable to assume that their will be some similar variation from endoscopist to endoscopist using NBI in vivo diagnosis, there are emerging data that training can improve performance. Interestingly, in a study on in vivo prediction of polyp histology 4 endoscopists improved their accuracy from 74% during the first half of the study to 87% during the last half of the study.15 The level of performance achieved at the end of this study is remarkably similar to the 89% accuracy achieved by Dr Rex in the current report. Of course, the generalizability of the approach taken by Rex et al can only be definitively assessed when a similar study using the same criteria is completed utilizing a much larger cross-section of endoscopists.

Aside from an assessment of generalizability, a number of issues also need to be addressed before more widespread application can become a reality. For instance, the performance of NBI in correctly identifying serrated adenomas, which may be erroneously diagnosed as hyperplastic polyps needs further study. For this purpose, in vivo microscopic imaging techniques such as confocal laser microscopy may offer additional value.18

From a more practical standpoint, it is not clear how much additional time will be needed to make an in vivo diagnosis. Clearly, the longer it takes (relative to the time to just simply remove the polyp), the less benefit in procedural efficiency will be gained. One might wonder whether NBI is even better than a simple assessment with white light, high-definition endoscopy (a comparison not done in the Rex paper). One study does suggest that NBI is superior,15 but further work may be needed. The impact of this technology on our current metrics to assess quality will also need to be better understood. For example, is an adenoma detected by NBI given the same weight as an adenoma diagnosed by pathology? Further, if endoscopists erroneously adjudicate an extra small polyp or 2 as a “high-confidence” adenoma, this could have substantial negative effects on surveillance interval recommendations moving patients from 5 years to 3 years without any pathologic proof. Quality control programs for endoscopists may need to be developed where some fraction of “high-confidence” lesions are regularly submitted for microscopic confirmation.

Certainly, in vivo diagnostic technology, like NBI, offers the opportunity to improve colonoscopy performance. The ability to assess polypoid lesions without biopsy and determine surveillance intervals without histology can improve the safety and efficiency of endoscopic practice. Of course, these endoscopic technologies are not the only technological advancements driving a reassessment of the currently accepted practice of removing all mucosal polypoid lesions. CTC is the primary technology that is generating a national discussion of the importance of small- and even medium-sized colorectal polyps. In fact, guidelines for the application of CTC favor the nonreport of small lesions.16 The recommendation reflects partly the accuracy of the technology for detecting small polyps, but also the view that such lesions have little neoplastic potential. The paradigm regarding the importance of small polyps and the need to remove all small lesions is unarguably shifting. The practice of gastroenterology may have to adapt accordingly. The application of NBI light to target polyps most at risk for neoplasia could provide an important tool in our endoscopic armamentarium as we move forward.

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References 

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 Conflicts of interest The authors disclose no conflicts.

PII: S0016-5085(09)00205-4

doi:10.1053/j.gastro.2009.02.025

Refers to article:

  • Editorial Accompanies Article Narrow-Band Imaging Without Optical Magnification for Histologic Analysis of Colorectal Polyps , 11 December 2008

    Douglas K. Rex
    Gastroenterology April 2009 (Vol. 136, Issue 4, Pages 1174-1181)

Gastroenterology
Volume 136, Issue 4 , Pages 1149-1151, April 2009

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