Incidental morphological findings in colorectal adenomas

Abstract

Owing to a sharp increase in the frequency of diagnosis of colorectal adenomas in the current era of population screening, distinctive morphological features are increasingly being observed. These may present diagnostic challenges and cause clinical management issues. Paneth cell metaplasia is a more common occurrence, but the incidence rates of squamous metaplasia, clear cell metaplasia, osseous metaplasia, neuroendocrine differentiation and signet-ring cell-like lesion are low, and they can be seen in <1% of colorectal adenomas. Their histomorphological characteristics are quite unique; ancillary studies are not very helpful and often not needed. In this review, we give an overview and describe the potential clinical consequences of such incidental and special morphological findings in colorectal adenomas.

Keywords: Paneth cell metaplasia; clear cell metaplasia; colorectal adenomas; neuroendocrine differentiation; osseous metaplasia; population screening; signet-ring cell-like; squamous metaplasia.

Figure 1

A–D, Paneth cell metaplasia (A,B, haematoxylin and eosin), with nuclear β‐catenin expression (C) and absence of Congo red staining (D).E,F, Clear cell metaplasia adjacent to dysplastic glands.G,H, Osseous metaplasia in a tubular adenoma.I,J, Signet‐ring cell‐like lesions, mainly luminal, situated in dysplastic glands.K,L, Prominent goblet cells in dysplastic glands.

Figure 2

Squamous metaplasia in adenomas.A,B, Transition of dysplastic glandular structures into squamous metaplasia (haematoxylin and eosin).C, Absence of p63 expression.D, Strong cyclin D1 expression.E, Patchy cytokeratin 5/6 expression.F, Nuclear and cytoplasmic β‐catenin expression.

Figure 3

Neuroendocrine differentiation in an adenoma. There are small groups of neuroendocrine cells between and beneath the dysplastic glands (A,C, haematoxylin and eosin) with strong synaptophysin expression (B,D).

Figure 4

The incorporation of special features in the adenoma–carcinoma sequence: a hypothetical explanation of morphology, based on the molecular characteristics of a small series of adenomas with special features.