Serrated Polyps of the Large Intestine: A Morphologic and Molecular Review of an Evolving Concept

Abstract

Serrated polyps of the large intestine, including traditional hyperplastic polyps, traditional serrated adenomas, and more recently described sessile serrated adenomas, have gained increased recognition in recent years because of growing evidence that one of these lesions, the sessile serrated adenoma, might be the precursor lesion for some cases of microsatellite unstable colorectal carcinoma. Nevertheless, there has been some reluctance to embrace the concept of sessile serrated adenoma, and numerous diagnostic challenges exist. This article, which grew out of the Roger C. Haggitt Gastrointestinal Pathology Society Forum presented in Vancouver, Canada, March 6, 2004 as part of the annual meeting of the United States-Canadian Academy of Pathology, reviews the morphologic and molecular evidence for the concept of various polyps in the general category of serrated polyps of the large intestine, in particular the lesion known as the sessile serrated adenoma, and provides a conceptual framework for diagnosis of these lesions.

Selective expression of gastric mucin MUC6 in colonic sessile serrated adenoma but not in hyperplastic polyp aids in morphological diagnosis of serrated polyps

“…Although not a consecutive sample of all serrated polyps, the patient's demographic characteristics (Table 3) were similar to those previously seen in the literature. 4,7 Thus, most sessile serrated adenomas in our series were found in the right colon of older women, whereas the majority of hyperplastic polyps came from the left colon with no gender preference. Given the finding of only one right-sided hyperplastic polyp, our data also support the concept that hyperplastic polyps rarely arise, or at least are rarely sampled, in the right colon.…”

“…For the polyps without cytological dysplasia, a diagnosis of sessile serrated adenoma or hyperplastic polyp was made based on previously published morphological criteria. 4 Briefly, the polyps were assessed for the presence of morphological features of abnormal proliferation including basal crypt dilation, branching, serration and horizontal orientation, in combination with abundant goblet cell or gastric-type mucin production in the basal crypts (ie, the 'proliferation zone' of normal mucosa and hyperplastic polyp) (Figure 1a-c).…”

“…Sessile serrated adenoma is one recently described entity that, although lacking in conventional adenomatous cytological dysplasia, is thought to be related to colorectal adenocarcinoma by the so-called 'serrated pathway' of colorectal neoplasia. [1][2][3][4][5] This pathway results in invasive adenocarcinomas that are frequently microsatellite unstable (MSI-high). 3,6 Sessile serrated adenomas occur most commonly on the right side of the colon, but can be found throughout.…”

“…3,6 Sessile serrated adenomas occur most commonly on the right side of the colon, but can be found throughout. 4,7 The increasing acceptance of sessile serrated adenoma as a diagnostic entity has undermined the traditional notion that colonic polyps could be broadly divided into traditional adenomatous polyps, exhibiting characteristic cytological dysplasia and imparting a higher risk of progression to invasive adenocarcinoma, and 'hyperplastic polyps', lacking cytological dysplasia and thought to be of essentially no risk for development of carcinoma. Whether such a 'safe' category actually exists-especially in the right colon-is a matter of current debate and study.…”

“…Whether such a 'safe' category actually exists-especially in the right colon-is a matter of current debate and study. 8 According to Snover et al 4 , sessile serrated adenomas are those serrated polyps with evidence of abnormal proliferation, including basal crypt branching, dilation, serration and horizontal basal crypt orientation, creating T-or L-shaped crypts. 4 These features have been termed architectural dysplasia in the literature, and are evaluated in combination with an assessment of traditional cytological dysplasia, which is absent in sessile serrated adenomas.…”