Serrated neoplasia of the colorectum

Figure 1 Sessile serrated adenoma (lower arrow). These polyps tend to be large, sessile and situated on the crest of the mucosal folds. This appearance contrasts with that of a typical adenomatous polyp (upper arrow).

Figure 2 Low power appearance of a sessile serrated adenoma. Serration is seen to the base of the crypts, which are dilated and may show growth parallel to the muscularis mucosae (HE, x 20).

Figure 3 The crypts of a sessile serrated adenoma may herniate through the muscularis mucosae, producing an appearance which may be confused with invasive tumour (HE, x 20).

Figure 4 An example of hyperplastic polyposis, demonstrating numerous sessile serrated adenomas (arrows).

Figure 5 Immunohistochemical staining for the mismatch repair protein MLH1, demonstrating “clonal” loss of expression in a sessile serrated adenoma (x 20).

Figure 6 Virtual colonoscopic image demonstrating a sessile serrated adenoma (arrow).