Serrated lesions of the colorectum: review and recommendations from an expert panel

Abstract

Serrated lesions of the colorectum are the precursors of perhaps one-third of colorectal cancers (CRCs). Cancers arising in serrated lesions are usually in the proximal colon, and account for a disproportionate fraction of cancer identified after colonoscopy. We sought to provide guidance for the clinical management of serrated colorectal lesions based on current evidence and expert opinion regarding definitions, classification, and significance of serrated lesions. A consensus conference was held over 2 days reviewing the topic of serrated lesions from the perspectives of histology, molecular biology, epidemiology, clinical aspects, and serrated polyposis. Serrated lesions should be classified pathologically according to the World Health Organization criteria as hyperplastic polyp, sessile serrated adenoma/polyp (SSA/P) with or without cytological dysplasia, or traditional serrated adenoma (TSA). SSA/P and TSA are premalignant lesions, but SSA/P is the principal serrated precursor of CRCs. Serrated lesions have a distinct endoscopic appearance, and several lines of evidence suggest that on average they are more difficult to detect than conventional adenomatous polyps. Effective colonoscopy requires an endoscopist trained in the endoscopic appearance of serrated lesions. We recommend that all serrated lesions proximal to the sigmoid colon and all serrated lesions in the rectosigmoid > 5 mm in size, be completely removed. Recommendations are made for post-polypectomy surveillance of serrated lesions and for surveillance of serrated polyposis patients and their relatives.

Figures

Figure 1

Photomicrographs of hyperplastic polyps. (a) Microvesicular hyperplastic polyp (MVHP). The crypts and surface epithelium show a luminal serrated or saw-toothed contour more prominent in the upper levels of the crypts than at the base. The epithelial layer is composed of cells with goblet cell differentiation and others with microvesicular cytoplasmic mucin. (b) Goblet cell hyperplastic polyp. In contrast to MVHP, this polyp shows a much less pronounced serrated or saw-toothed luminal epithelial growth pattern and shows a preponderance of goblet cells and an absence of cells with microvesicular mucin. The crypts are straight, linear, and without architectural distortion. (c) Mucin poor hyperplastic polyp. The overall configuration of this polyp is similar to the microvesicular hyperplastic polyp but the cells are mucin depleted. The nuclei also are more hyperchromatic than the MVHP.

Figure 1

Photomicrographs of hyperplastic polyps. (a) Microvesicular hyperplastic polyp (MVHP). The crypts and surface epithelium show a luminal serrated or saw-toothed contour more prominent in the upper levels of the crypts than at the base. The epithelial layer is composed of cells with goblet cell differentiation and others with microvesicular cytoplasmic mucin. (b) Goblet cell hyperplastic polyp. In contrast to MVHP, this polyp shows a much less pronounced serrated or saw-toothed luminal epithelial growth pattern and shows a preponderance of goblet cells and an absence of cells with microvesicular mucin. The crypts are straight, linear, and without architectural distortion. (c) Mucin poor hyperplastic polyp. The overall configuration of this polyp is similar to the microvesicular hyperplastic polyp but the cells are mucin depleted. The nuclei also are more hyperchromatic than the MVHP.

Figure 1

Photomicrographs of hyperplastic polyps. (a) Microvesicular hyperplastic polyp (MVHP). The crypts and surface epithelium show a luminal serrated or saw-toothed contour more prominent in the upper levels of the crypts than at the base. The epithelial layer is composed of cells with goblet cell differentiation and others with microvesicular cytoplasmic mucin. (b) Goblet cell hyperplastic polyp. In contrast to MVHP, this polyp shows a much less pronounced serrated or saw-toothed luminal epithelial growth pattern and shows a preponderance of goblet cells and an absence of cells with microvesicular mucin. The crypts are straight, linear, and without architectural distortion. (c) Mucin poor hyperplastic polyp. The overall configuration of this polyp is similar to the microvesicular hyperplastic polyp but the cells are mucin depleted. The nuclei also are more hyperchromatic than the MVHP.

Figure 2

Photomicrograph of sessile serrated adenoma/polyps. (a) A sessile serrated adenoma/polyp showing a hyperserrated luminal epithelial growth pattern more pronounced that in microvesicular hyperplastic polyps. In addition, the crypts show luminal dilation towards the bases of the crypts, some crypts show horizontal growth along the long axis of the muscularis mucosa (arrow). Goblet cells are present at all levels of the crypts, some of which are dystrophic. Mitotic figures are easily recognized, and located predominantly in the basal aspects of the crypts. (b) Sessile serrated adenoma/polyp with cytological dysplasia. The portion of the polyp without cytological dysplasia on the left shows cells with uniform nuclei without pseudostratification. The cytologically dysplastic portion on the right (arrows) show hyperchromatic pseudostratified nuclei with numerous mitoses.

Figure 2

Photomicrograph of sessile serrated adenoma/polyps. (a) A sessile serrated adenoma/polyp showing a hyperserrated luminal epithelial growth pattern more pronounced that in microvesicular hyperplastic polyps. In addition, the crypts show luminal dilation towards the bases of the crypts, some crypts show horizontal growth along the long axis of the muscularis mucosa (arrow). Goblet cells are present at all levels of the crypts, some of which are dystrophic. Mitotic figures are easily recognized, and located predominantly in the basal aspects of the crypts. (b) Sessile serrated adenoma/polyp with cytological dysplasia. The portion of the polyp without cytological dysplasia on the left shows cells with uniform nuclei without pseudostratification. The cytologically dysplastic portion on the right (arrows) show hyperchromatic pseudostratified nuclei with numerous mitoses.

Figure 3

Traditional serrated adenoma. This polyp is composed of villiform projections of hypereosinophilic cells with small oval-shaped nuclei oriented basally along the basement membrane. The cells are growing in a hyperserrated luminal contour. Multiple ectopic crypts are present. These are composed of crypts oriented perpendicular to the long axis of the villi. Overall, goblet cells are decreased in number.

Figure 4

A schematic representation of the putative development of CIMP-high CRCs with microsatellite instability through a serrated pathway via methylation of the MLH1 gene.

Figure 5

Both sessile serrated adenoma/polyps and hyperplastic polyps in the proximal colon may demonstrate a “mucus cap,” which may be yellow, green or rust-colored in white light (a) and red in narrow-band imaging (b).

Figure 5

Both sessile serrated adenoma/polyps and hyperplastic polyps in the proximal colon may demonstrate a “mucus cap,” which may be yellow, green or rust-colored in white light (a) and red in narrow-band imaging (b).

Figure 6

Typical serrated lesions in the proximal colon. a–d. A sessile serrated adenoma/polyp in the cecum. Note the adherent mucus in white light (a) and with narrow-band imaging (b). After removal of the cap by washing the characteristics surface features are seen in white light (c) and narrow-band imaging (d), including indistinct edges, color similar to the surrounding normal mucosa, and a paucity of blood vessels. e–h. A flat sessile serrated adenoma/polyp in the transverse colon, with the mucus cap in white light (e) and narrow-band imaging (f) and with the cap washed off in white light (g) and blue light (h). Note the subtlety of the lesion after the cap is washed off.

Figure 6

Typical serrated lesions in the proximal colon. a–d. A sessile serrated adenoma/polyp in the cecum. Note the adherent mucus in white light (a) and with narrow-band imaging (b). After removal of the cap by washing the characteristics surface features are seen in white light (c) and narrow-band imaging (d), including indistinct edges, color similar to the surrounding normal mucosa, and a paucity of blood vessels. e–h. A flat sessile serrated adenoma/polyp in the transverse colon, with the mucus cap in white light (e) and narrow-band imaging (f) and with the cap washed off in white light (g) and blue light (h). Note the subtlety of the lesion after the cap is washed off.

Figure 6

Typical serrated lesions in the proximal colon. a–d. A sessile serrated adenoma/polyp in the cecum. Note the adherent mucus in white light (a) and with narrow-band imaging (b). After removal of the cap by washing the characteristics surface features are seen in white light (c) and narrow-band imaging (d), including indistinct edges, color similar to the surrounding normal mucosa, and a paucity of blood vessels. e–h. A flat sessile serrated adenoma/polyp in the transverse colon, with the mucus cap in white light (e) and narrow-band imaging (f) and with the cap washed off in white light (g) and blue light (h). Note the subtlety of the lesion after the cap is washed off.

Figure 6

Typical serrated lesions in the proximal colon. a–d. A sessile serrated adenoma/polyp in the cecum. Note the adherent mucus in white light (a) and with narrow-band imaging (b). After removal of the cap by washing the characteristics surface features are seen in white light (c) and narrow-band imaging (d), including indistinct edges, color similar to the surrounding normal mucosa, and a paucity of blood vessels. e–h. A flat sessile serrated adenoma/polyp in the transverse colon, with the mucus cap in white light (e) and narrow-band imaging (f) and with the cap washed off in white light (g) and blue light (h). Note the subtlety of the lesion after the cap is washed off.

Figure 6

Typical serrated lesions in the proximal colon. a–d. A sessile serrated adenoma/polyp in the cecum. Note the adherent mucus in white light (a) and with narrow-band imaging (b). After removal of the cap by washing the characteristics surface features are seen in white light (c) and narrow-band imaging (d), including indistinct edges, color similar to the surrounding normal mucosa, and a paucity of blood vessels. e–h. A flat sessile serrated adenoma/polyp in the transverse colon, with the mucus cap in white light (e) and narrow-band imaging (f) and with the cap washed off in white light (g) and blue light (h). Note the subtlety of the lesion after the cap is washed off.

Figure 6

Typical serrated lesions in the proximal colon. a–d. A sessile serrated adenoma/polyp in the cecum. Note the adherent mucus in white light (a) and with narrow-band imaging (b). After removal of the cap by washing the characteristics surface features are seen in white light (c) and narrow-band imaging (d), including indistinct edges, color similar to the surrounding normal mucosa, and a paucity of blood vessels. e–h. A flat sessile serrated adenoma/polyp in the transverse colon, with the mucus cap in white light (e) and narrow-band imaging (f) and with the cap washed off in white light (g) and blue light (h). Note the subtlety of the lesion after the cap is washed off.

Figure 6

Typical serrated lesions in the proximal colon. a–d. A sessile serrated adenoma/polyp in the cecum. Note the adherent mucus in white light (a) and with narrow-band imaging (b). After removal of the cap by washing the characteristics surface features are seen in white light (c) and narrow-band imaging (d), including indistinct edges, color similar to the surrounding normal mucosa, and a paucity of blood vessels. e–h. A flat sessile serrated adenoma/polyp in the transverse colon, with the mucus cap in white light (e) and narrow-band imaging (f) and with the cap washed off in white light (g) and blue light (h). Note the subtlety of the lesion after the cap is washed off.

Figure 6

Typical serrated lesions in the proximal colon. a–d. A sessile serrated adenoma/polyp in the cecum. Note the adherent mucus in white light (a) and with narrow-band imaging (b). After removal of the cap by washing the characteristics surface features are seen in white light (c) and narrow-band imaging (d), including indistinct edges, color similar to the surrounding normal mucosa, and a paucity of blood vessels. e–h. A flat sessile serrated adenoma/polyp in the transverse colon, with the mucus cap in white light (e) and narrow-band imaging (f) and with the cap washed off in white light (g) and blue light (h). Note the subtlety of the lesion after the cap is washed off.

Figure 7

The risk of developing colorectal cancers through the serrated pathway parallels the number, size, type, and anatomic distribution of the serrated polyps.