Case: AP115
Contributor's Comment: Serrated adenoma is an adenoma with serrated crypts that resembles hyperplastic polyps(1,2). On casual low-power examination, one may miss the dysplastic epithelium lining the serrated crypts which is characterized by eosinophilic columnar cells with nuclear pseudostratification, elongated and often vesicular nuclei, and large nucleoli. The N/C ratios are greater in serrated adenomas than in hyperplastic polyps, but slightly less than those in traditional adenomas. Kang et al. found that the immunohistochemical features of "serrated adenoma" with regard to cell proliferation and bcl-2 expression were intermediate between those of tubular adenomas and hyperplastic polyps, suggesting the distinct nature of "serrated adenoma" as a colorectal epithelial neoplasm(3). Beside solitary lesions, serrated adenomatous polyposis has been reported(4)

This case is a serrated adenoma with low-grade dysplasia. Marks are deducted from those who failed to recognise the dysplastic epithelium (the main lesson of this case). Mixed hyperplastic adenomatous polyp is an acceptable diagnosis, although, strictly speaking, it should contain areas of hyperplastic polyp and traditional adenomatous area in the form of tubules/villi in contrast to the dysplastic serrated crypts seen in serrated adenomas. (YF Lo / MS Tsui)

Ref.
1. Gastrointestinal Pathology, an atlas and text, 2nd edition. Cecilia M. Fenoglio-Preiser P.948 ?P.952
2. Longacre TA, Fenoglio-Preiser CM. Mixed hyperplastic adenomatous polyps / serrated adenomas. A distinct form of colorectal neoplasia. Am J Surg Pathol 1990;14:524-37
3. Kang M. Mitomi H. Sada M, et al. Ki-67, p53 and Bcl-2 expression of serrated adenomas of the colon. Am J Surg Pathol 1997;21:417-23.
4. Torlakovic E, Snover DC. Serrated adenomatous polyposis in humans. Gastroenterology 1996;110:748-55.