Prevalence of flat lesions in a large screening population and their role in colonoscopy quality improvement

We read with great interest the article by Reinhart et al. [1], who evaluated the prevalence and significance of flat lesions in a nationwide screening program in Austria. Indeed, the monitoring of colonoscopy findings and its quality at a national level is vital for developing strategies to improve the effectiveness of a screening service. In a retrospective analysis of 52 521 participants who underwent colonoscopy between 2007 and 2011, the authors found that polyp size rather than polyp shape was the strongest predictor for advanced histology, thus discouraging the inclusion of flat polyp detection rates as a quality indicator of screening colonoscopy.

There are several important issues that need to be addressed regarding this study. First, we question the validity of the morphological description because the study did not specify the precise definitions used for flat lesions, nor did it provide details about the formal training of the endoscopists to ensure uniformity in classification of flat lesions. Second, the study lacked detail about subcategories of flat lesions, in particular the lateral spreading tumors of nongranular type (LST-NG) and the depressed lesions (0-IIc, 0-IIa + IIc, 0-IIc + IIa, etc.). Evidence from Asian [2] [3] and Western [4] [5] [6] studies indicates that, although uncommon, such lesions have a greater risk of containing advanced histology than their polypoid counterparts. Furthermore, a recent meta-analysis [7] found that LST-NG and depressed lesions have distinct biologic features, leading to a more rapid progression to cancer. Third, not unexpectedly, a large proportion of the flat lesions in this study were diminutive (65.94 % were < 5 mm) and hyperplastic (48.59 %) polyps, which might have diluted the effect of the biologically relevant, yet less common, subtypes. In addition, diminutive flat (0-IIa) lesions might be also more difficult to distinguish from the diminutive sessile (0-Is) ones, further increasing the likelihood of misclassification. Fourth, the authors found that 54.39 % of the flat lesions in this study were located in the rectum and sigmoid colon, which contradicts previous findings of a preferential proximal location of flat adenomas [2] [4], and for which no clear explanation was provided. Last, but not least, the ability to detect and to classify the nonpolypoid colorectal neoplasms requires training [8] – the participants of the study were not trained to detect flat lesions.

The incorporation of the nonpolypoid colorectal neoplasm or its subcategories as a quality indicator in screening colonoscopy needs further prospective investigation. Although we agree with the authors that polyp size is a predictor for advanced histology, we caution their conclusion on polyp shape due to the significant study limitations.

• References

• 1 Reinhart K, Bannert C, Dunkler D et al. Prevalence of flat lesions in a large screening population and their role in colonoscopy quality improvement. Endoscopy 2013; 45: 350-356
• 2 Chiu HM, Lin JT, Chen CC et al. Prevalence and characteristics of nonpolypoid colorectal neoplasm in an asymptomatic and average-risk Chinese population. Clin Gastroenterol Hepatol 2009; 7: 463-470
• 3 Kudo SE, Lambert R, Allen JI et al. Nonpolypoid neoplastic lesions of the colorectal mucosa. Gastrointest Endosc 2008; 68: 3-S47
• 4 Soetikno RM, Kaltenbach T, Rouse RV et al. Prevalence of nonpolypoid (flat and depressed) colorectal neoplasms in asymptomatic and symptomatic adults. JAMA 2008; 299: 1027-1035
• 5 Bianco MA, Cipolletta L, Rotondano G et al. Prevalence of nonpolypoid colorectal neoplasia: an Italian multicenter observational study. Flat Lesions Italian Network (FLIN). Endoscopy 2010; 42: 279-285
• 6 Moss A, Bourke MJ, Williams SJ et al. Endoscopic mucosal resection outcomes and prediction of submucosal cancer from advanced colonic mucosal neoplasia. Gastroenterology 2011; 140: 1909-1918
• 7 Voorham QJ, Rondagh EJ, Knol DL et al. Tracking the molecular features of nonpolypoid colorectal neoplasms: a systematic review and meta-analysis. Am J Gastroenterol 2013; 108: 1042-1056
• 8 Sanduleanu S, Rondagh EJ, Masclee AA. Development of expertise in the detection and classification of non-polypoid colorectal neoplasia: experience-based data at an academic GI unit. Gastrointest Endosc Clin N Am 2010; 20: 449-460